Effects of Imatinib on Normal Hematopoiesis and Immune Activation
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《干细胞学杂志》
a Department of Hematology, Oncology and Immunology, University Medical Center, Tübingen, Germany;
b Department of Oncology and Hematology, University Hospital Hamburg-Eppendorf, Hamburg, Germany
Key Words. Bcr-Abl ? Imatinib ? T cells ? Dendritic cells ? Hematopoiesis
Correspondence: Peter Brossart, M.D., Department of Hematology, Oncology and Immunology, University of Tübingen, Otfried-Müller Str. 10, D-72076 Tübingen, Germany. Telephone: 49-7071-2982726; Fax: 49-7071-295709; e-mail: peter.brossart@med.uni-tuebingen.de
ABSTRACT
Imatinib (Glivec, formerly STI571; Novartis International, Basel, Switzerland, http://www.glivec.com/content/home.jsp) is a 2-phenylaminopyrimidine derivate designed as a specific inhibitor of the Abl protein tyrosine kinases (v-Abl, Bcr-Abl, and c-Abl) . It is also active against the platelet-derived growth factor receptor (PDGF-R), c-Kit (CD117), Abl-related gene, macrophage colony stimulating factor receptor (c-fms), and their fusion proteins, whereas other kinases are probably not affected . Imatinib binds selectively to the ATP-binding site of these kinases, thereby blocking their activity. Pharmacokinetic studies revealed that imatinib has a half-life of 18.2 hours given at a daily oral dose of 400 mg .
In recent clinical trials of imatinib in the treatment of chronic myeloid leukemia (CML) in chronic phase, it was shown that the drug is well tolerated with only few adverse effects. In many patients, complete hematological and cytogenetic responses could be induced . Imatinib is also active in accelerated phase orblast crises CML and in patients with primary, relapsed, or refractory Philadelphia chromosome–positive (Ph+) acute lymphoid leukemias . Furthermore, imatinib treatment has shown promising results in patients with gastrointestinal stroma tumors (GISTs) caused by c-Kit mutations and myeloproliferative disorders with mutations in the gene encoding PDGF-R beta .
In the following review, we will discuss recent data suggesting an inhibitory, antiproliferative effect of imatinib on different compartments of the normal hematopoietic hierarchy excluding the immature hematopoietic stem cell compartment. The results of these studies are relevant both considering long-term toxicity and also concerning novel yet only partly explored applications of the drug, such as a potential immunomodulatory agent or for the treatment of Bcr-Abl–negative myeloproliferative (lymphoproliferative) disorders.
Effect of Imatinib on Dendritic Cells
Dendritic cells (DCs) are recognized as the most potent antigen-presenting cells capable of initiating and maintaining primary immune responses. They originate from bone marrow–derived progenitor cells, spread via the blood stream, and can be found in almost every organ as the sentinels of the immune system. DCs can be generated in vitro from CD34+ progenitor cells or from peripheral blood monocytes by culturing these cells with different cytokine cocktails .
Recently, it was shown that the differentiation of mobilized human CD34+ peripheral blood progenitor cells (PBPCs) into DCs is impaired by imatinib . When CD34+ PBPCs were incubated in vitro with GM-CSF, tumor necrosis factor-, interleukin (IL)-4, and Flt3 ligand in the presence of imatinib from the beginning of the culture, the morphology of the generated cells resembled that of DCs but the phenotype was different. The generated cells were characterized by low expression of DC-associated cell-surface molecules like CD1a and CD83 as major histocompatibility complex class II and costimulatory molecules like CD80 and CD40 in a concentration-dependent manner . Blocking antibodies against c-Kit and stem cell factor (SCF) had no phenotypic effects, suggesting that the inhibitory effects of imatinib are not mediated by inhibition of c-Kit receptor signaling and that other mechanisms might be involved. Beside these phenotypical alterations, the cells were unable to respond to a maturation stimulus. Moreover, they were unable to elicit primary T-cell responses as well as T-cell responses against a recall antigen. Importantly, the observed inhibitory effects on DC development and function were not mediated by induction of apoptosis. Because a broad variety of genes during immune responses are regulated by members of the nuclear factor (NF)-B transcription factor family , their nuclear expression was studied to analyze the signaling pathways involved in the inhibitory effects of imatinib on CD34+-derived DCs. Nuclear-localized RelB protein was down-regulated in DCs treated with imatinib and could not be induced upon maturation with CD40L and interferon (IFN)-, suggesting that inhibition of RelB signaling is at least in part mediating the effects of imatinib (Fig. 1).
Figure 1. Inhibitory effects of imatinib treatment on DC development and T-cell stimulatory capacity. Abbreviations: DC, dendritic cell; IL, interleukin; MHC, major histocompatibility complex; PBPC, peripheral blood progenitor cell; TCR, T-cell receptor.
Taieb et al. confirmed these in vitro–generated results by analyzing the effects of imatinib in an animal model. Daily feeding of mice with imatinib twice from day 5 to 10 resulted in the inhibition of Flt3 ligand–induced expansion of DC in vivo and impaired the induction of a protective antitumor immunity in these animals. In line with these results, Boissel et al. showed that treatment of CML patients with imatinib does not normalize blood DC rates and Th1/Th2 balance in these patients despite normalization of vascular endothelial growth factor levels, suggesting that imatinib inhibits normal development of DCs in vivo.
Moreover, analyses of human monocyte-derived DC (MDC) revealed that addition of imatinib from day one of culturing the cells resulted in the reduced expression of cell-surface molecules known to be upregulated or induced during the differentiation of monocytes into DCs . In analogy to DCs generated from CD34+ PBPCs, imatinib did not induce apoptosis of these cells. Functionally, secretion of cytokines and chemokines shown to be important for T-cell activation was reduced, and these cells were unable to initiate primary T-cell responses. Immature MDCs incubated with imatinib had a reduced endocytic activity, as analyzed by their capacity to internalize fluorescein isothiocyanate–dextran. Imatinib treatment of DC resulted in decreased activation-induced upregulation of nuclear localized RelB, RelA, c-Rel, and NF-B p50, suggesting that imatinib mediates its effects in part via the NF-B pathway, as postulated for CD34+-derived DCs. In concordance, the presence of imatinib during MDC generation reduced phosphorylation of Akt, which is a kinase upstream of NF-B . Furthermore, Dewar et al. showed that the function of cultured human monocytes is impaired by imatinib treatment, characterized by decreased cytokine production after stimulation with lipopolysaccharide as well as reduced phagocytic capacity after M-CSF and GM-CSF stimulation, indicating that imatinib inhibits monocyte/macrophage development (Fig. 1).
A novel aspect of antitumor activity of imatinib was recently presented by Zitvogel and colleagues in an interesting study demonstrating that imatinib-treated DCs can activate natural killer (NK) cell functions and promote antitumor-directed immune responses. They reported that imatinib treatment resulted in DC-mediated NK cell activation in vitro and in vivo.
In contrast to these findings, Sato et al. showed that antigen presentation of Bcr-Abl+ DC from CML patients might be improved by imatinib treatment. However, DCs of CML patients are functionally defective and differ from normal DCs. Inline with this observation, a study by Mohty et al. demonstrated that plasmacytoid DC function is restored in CML patients under imatinib treatment, indicating distinct effects of imatinib in Ph+malignant and Ph– nonmalignant cells . Wang et al. reported that imatinib enhances antigen-presenting cell function in a transgenic mouse model analyzed by IL-2 and IFN- production and may overcome tumor-induced CD4+ T-cell tolerance. However, in this study, imatinib was administered for only 24 hours to already matured bone marrow–derived DCs, which might explain the different findings mentioned above.
Effects of Imatinib on T Cells
In addition to the inhibitory effects of imatinib on CD34+ PBPCs as well as monocyte-derived DCs and monocytes, imatinib was shown to inhibit T-cell proliferation by arresting the cells in G0/G1 without affecting the viability of the cells . Furthermore, a reduction of NF-B and phosphorylation of LCK and ERK1/2 were observed in phytohemagglutinin-stimulated T cells treated with imatinib. This impaired T-cell function was confirmed in a murine model of delayed-type hypersensitivity, indicating that imatinib might have immunosuppressive effects by inhibiting antigen presentation and T-cell effector functions . Recently, these findings were extended by Seggewiss et al. , who reported that imatinib affects T-cell receptor (TCR) signal transduction by inhibition of LCK . In their study, proliferation of T cells as well as expression of CD25 and CD69 was drastically reduced in human T cells that were activated via TCR and treated with imatinib. Moreover, CD8+ T-cell expansion in response to immunodominant cytomegalovirus and Epstein-Barr virus peptides was reduced. Analysis of the TCR-induced signaling cascade revealed that these effects were due to inhibition of LCK.
Effects of Imatinib on Normal Hematopoietic Stem and Progenitor Cells
Normal nonhematological side effects of imatinib given at a daily dose of 400 mg are mostly moderate. Hematologic side effects of imatinib are dose-dependent, are reversible, and affect all hematopoietic lineages, although to a variable degree . Grade 3 or 4 neutropenia is among the most common dose-limiting toxicities, occurring in 14% of the patients, followed by thrombocytopenia (8%) and anemia (3%) . However, when imatinib was given at a higher dose, that is, 800 mg daily, incidence of grade 3 or higher toxicities increased substantially to 38%, 17%, and 5%, respectively, even when imatinib was administered in early chronic phase . The impact of imatinib pretreatment on the outcome of allogeneic stem cell transplantation is still controversial. In a recent report, it has been shown that pretreatment with imatinib resulted in a higher transplant-related mortality in patients with Ph+ leukemias . However, other studies did not confirm these findings . Considering the known inhibitory effects of the drug on other (apart from Bcr-Abl) relevant tyrosine kinases, however, one could suspect potential hematotoxic side effects, particularly after long-term exposure to imatinib. c-Kit represents the receptor for human SCF, a cytokine that, together with Flt3 ligand and thrombopoietin, is assumed to be critical for the expansion of immature human hematopoietic stem/progenitor cells, at least in vitro . More recently, PDGF has been shown to be effective for the exvivo expansion of normal early stem and progenitor cells . It has been speculated that myelosuppression under imatinib treatment depends on the fact that after reduction of Ph+ hematopoiesis in response to treatment, normal hematopoietic stem and progenitor cells have to recover from pre-existing suppression by the malignant clone and to re-expand in the bone marrow. This interpretation is supported by the observation that the incidence of grade 3 or 4 hematotoxicities is most predominant at the initiation of treatment and decreases substantially to 3.8% (neutropenia), 2.1% (thrombocytopenia), and 1.9% (anemia), respectively, after 18 months of first-line treatment . Moreover, a prospective study of CML patients on higher-dose imatinib over 1 year revealed highly significant changes in serum immunoglobulin G and immunoglobulin M levels .
In the light of these observations, data from imatinib-treated patients with GIST were of particular interest because these patients can be expected to have a normal bone marrow function. Interestingly, even in patients with GIST treated with imatinib for a median follow-up of 9 months, 7% developed neutropenias (5% of which were grade 3 or 4) and 9% developed anemia (2% of which were grade 3 or 4) , supporting the assumption that hematological side effects of the drug are at least partly explained by a direct inhibition of normal hematopoiesis.
To analyze the effect of imatinib on normal human CD34+ stem/ progenitor cells in vitro, we applied a bulk culture system including serum-free medium supplemented with cytokines . The degree of expansion decreased in a significant and dose-dependent fashion in treated compared with untreated cells . The exact mechanism by which imatinib induces its antiproliferative effect on normal CD34+ cells has yet to be clarified. An increased population of apoptotic cells has been described in Bcr-Abl+ cells . However, in vitro exposure to imatinib up to a concentration of 10 μM for 48 hours led neither to a significant induction of apoptosis nor to a significant G1 arrest in normal cytokine-stimulated CD34+ cells . Thus, the apoptosis-inducing effects of imatinib seen in Ph+ cells appear unlikely to be responsible for its growth-inhibitory effect on normal hematopoiesis, at least at the concentrations usually achieved in patients (Fig. 2).
Figure 2. Cellular compartment of the normal hematopoietic hierarchy affected by imatinib treatment. Modified from , with permission. Abbreviations: CLP, common lymphoid progenitor; CMP, common myeloid progenitor; DC, dendritic cell; LT-HSC, long-term hematopoietic stem cell; MPP, multipotent progenitor; NF, nuclear factor; NK, natural killer; ST-HSC, short-term hematopoietic stem cell.
The observation of an antiproliferative effect of imatinib on Bcr-Abl– hematopoietic cells is supported clinically by recent reports of patients with Ph– myeloproliferative disorders that have been treated successfully with imatinib . Nevertheless, reconstitution of murine cells after allogeneic transplantation in a syngeneic mouse transplantation model argues against a stem cell toxic effect of the drug . Furthermore, no effect of imatinib was observed in the experimental human-mouse transplantation model . These data suggest that imatinib acts primarily on the more actively cycling, as opposed to the quiescent, components of the stem/progenitor cell compartment, as has been shown in the Ph+ compartment in patients with CML . Consistent with these findings, we and others reported a dose-dependent decrease in colony-forming unit formation with imatinib treatment , whereas no significant effect on the in vitro stem cell activity (e.g., cobblestone area–forming cells) capacity of normal CD34+ cells was observed, similar to findings by others . Dewar et al. have shown that imatinib significantly inhibited monocyte/macrophage development from normal bone marrow progenitors in vitro, whereas neutrophil and eosinophil development was less affected. Altogether, these results are in support of a selective inhibitory effect of imatinib on the progenitor cell level, whereas the immature stem cell compartment seems to be spared.
Beside these inhibitory effects on the proliferation of progenitor cells, the studies from Hui et al. indicate that imatinib treatment of CML patients affected the mobilization of CD34+ cells. The median CD34+ cell yield per apheresis was significantly higher when imatinib was temporarily withheld . More recently, imatinib has been shown to severely affect marrow stromal cells (MSCs) in vitro. This effect was also at least partly independent of PDGF-R and c-Kit signaling and seemed to be related to the proliferative status of the cells . These data might be of potential relevance for the administration of imatinib in situations with increased MSC turnover such as regeneration after intensive chemotherapy/radiotherapy.
In summary, it now appears that imatinib has a significant and dose-dependent inhibitory effect on the proliferation of normal CD34+ progenitor cells and MSCs (but not stem cells) that is largely independent of c-Kit signaling and seems to be linked to cell-cycle activity of the cells.
CONCLUSION
S.A. and S.B. contributed equally to this work.
REFERENCES
Druker BJ, Lydon NB. Lessons learned from the development of an abl tyrosine kinase inhibitor for chronic myelogenous leukemia. J Clin Invest 2000;105:3–7.
Druker BJ, Talpaz M, Resta DJ et al. Efficacy and safety of a specific inhibitor of the BCR-ABL tyrosine kinase in chronic myeloid leukemia. N Engl J Med 2001;344:1031–1037.
Druker BJ, Tamura S, Buchdunger E et al. Effects of a selective inhibitor of the Abl tyrosine kinase on the growth of Bcr-Abl positive cells. Nat Med 1996;2:561–566.
Deininger MW, Goldman JM, Lydon N et al. The tyrosine kinase inhibitor CGP57148B selectively inhibits the growth of BCR-ABL-positive cells. Blood 1997;90:3691–3698.
Gambacorti-Passerini C, le Coutre P, Mologni L et al. Inhibition of the ABL kinase activity blocks the proliferation of BCR/ABL+ leukemic cells and induces apoptosis. Blood Cells Mol Dis 1997;23:380–394.
Buchdunger E, Cioffi CL, Law N et al. Abl protein-tyrosine kinase inhibitor STI571 inhibits in vitro signal transduction mediated by c-kit and platelet-derived growth factor receptors. J Pharmacol Exp Ther 2000;295:139–145.
Heinrich MC, Griffith DJ, Druker BJ et al. Inhibition of c-kit receptor tyrosine kinase activity by STI 571, a selective tyrosine kinase inhibitor. Blood 2000;96:925–932.
Okuda K, Weisberg E, Gilliland DG et al. ARG tyrosine kinase activity is inhibited by STI571. Blood 2001;97:2440–2448.
Carroll M, Ohno-Jones S, Tamura S et al. CGP 57148, a tyrosine kinase inhibitor, inhibits the growth of cells expressing BCR-ABL, TEL-ABL, and TEL-PDGFR fusion proteins. Blood 1997;90:4947–4952.
Dewar AL, Cambareri AC, Zannettino AC et al. Macrophage colony stimulating factor receptor, c-fms, is a novel target of imatinib. Blood 2005;105:3127–3132.
Fabian MA, Biggs WH, Treiber DK et al. A small molecule-kinase interaction map for clinical kinase inhibitors. Nat Biotechnol 2005;23:329–336.
Deininger M, Buchdunger E, Druker BJ. The development of imatinib as a therapeutic agent for chronic myeloid leukemia. Blood 2005;105:2640–2653.
le Coutre P, Kreuzer KA, Pursche S et al. Pharmacokinetics and cellular uptake of imatinib and its main metabolite CGP74588. Cancer Chemother Pharmacol 2004;53:313–323.
Kantarjian H, Sawyers C, Hochhaus A et al. Hematologic and cytogenetic responses to imatinib mesylate in chronic myelogenous leukemia. N Engl J Med 2002;346:645–652.
Sawyers CL, Hochhaus A, Feldman E et al. Imatinib induces hematologic and cytogenetic responses in patients with chronic myelogenous leukemia in myeloid blast crisis: results of a phase II study. Blood 2002;99:3530–3539.
Talpaz M, Silver RT, Druker BJ et al. Imatinib induces durable hematologic and cytogenetic responses in patients with accelerated phase chronic myeloid leukemia: results of a phase 2 study. Blood 2002;99:1928–1937.
Druker BJ, Sawyers CL, Kantarjian H et al. Activity of a specific inhibitor of the BCR-ABL tyrosine kinase in the blast crisis of chronic myeloid leukemia and acute lymphoblastic leukemia with the Philadelphia chromosome. N Engl J Med 2001;344:1038–1042.
Ottmann OG, Druker BJ, Sawyers CL et al. A phase 2 study of imatinib in patients with relapsed or refractory Philadelphia chromosome-positive acute lymphoid leukemias. Blood 2002;100:1965–1971.
Apperley JF, Gardembas M, Melo JV et al. Response to imatinib mesylate in patients with chronic myeloproliferative diseases with rearrangements of the platelet-derived growth factor receptor beta. N Engl J Med 2002;347:481–487.
Heinrich MC, Blanke CD, Druker BJ et al. Inhibition of KIT tyrosine kinase activity: a novel molecular approach to the treatment of KIT-positive malignancies. J Clin Oncol 2002;20:1692–1703.
Caux C, Dezutter-Dambuyant C, Schmitt D et al. GM-CSF and TNF-alpha cooperate in the generation of dendritic Langerhans cells. Nature 1992;360:258–261.
Brossart P, Wirths S, Brugger W et al. Dendritic cells in cancer vaccines. Exp Hematol 2001;29:1247–1255.
Cella M, Sallusto F, Lanzavecchia A. Origin, maturation and antigen presenting function of dendritic cells. Curr Opin Immunol 1997;9:10–16.
Maraskovsky E, Brasel K, Teepe M et al. Dramatic increase in the numbers of functionally mature dendritic cells in Flt3 ligand-treated mice: multiple dendritic cell subpopulations identified. J Exp Med 1996;184:1953–1962.
Sallusto F, Lanzavecchia A. Efficient presentation of soluble antigen by cultured human dendritic cells is maintained by granulocyte/macrophage colony-stimulating factor plus interleukin 4 and downregulated by tumor necrosis factor alpha. J Exp Med 1994;179:1109–1118.
Siena S, Di Nicola M, Bregni M et al. Massive ex vivo generation of functional dendritic cells from mobilized CD34+ blood progenitors for anti-cancer therapy. Exp Hematol 1995;23:1463–1471.
Young JW, Szabolcs P, Moore MA. Identification of dendritic cell colony-forming units among normal human CD34+ bone marrow progenitors that are expanded by c-kit-ligand and yield pure dendritic cell colonies in the presence of granulocyte/macrophage colony-stimulating factor and tumor necrosis factor alpha. J Exp Med 1995;182:1111–1119.
Zhou LJ, Tedder TF. CD14+ blood monocytes can differentiate into functionally mature CD83+ dendritic cells. Proc Natl Acad Sci U S A 1996;93:2588–2592.
Appel S, Boehmler AM, Grunebach F et al. Imatinib mesylate affects the development and function of dendritic cells generated from CD34+ peripheral blood progenitor cells. Blood 2004;103:538–544.
Ghosh S, May MJ, Kopp EB. NF-kappa B and Rel proteins: evolutionarily conserved mediators of immune responses. Annu Rev Immunol 1998;16:225–260.
Rescigno M, Martino M, Sutherland CL et al. Dendritic cell survival and maturation are regulated by different signaling pathways. J Exp Med 1998;188:2175–2180.
Neumann M, Fries H, Scheicher C et al. Differential expression of Rel/ NF-kappaB and octamer factors is a hallmark of the generation and maturation of dendritic cells. Blood 2000;95:277–285.
Weih F, Carrasco D, Durham SK et al. Multiorgan inflammation and hematopoietic abnormalities in mice with a targeted disruption of RelB, a member of the NF-kappa B/Rel family. Cell 1995;80:331–340.
Oyama T, Ran S, Ishida T et al. Vascular endothelial growth factor affects dendritic cell maturation through the inhibition of nuclear factor-kappa B activation in hemopoietic progenitor cells. J Immunol 1998;160:1224–1232.
Ammon C, Mondal K, Andreesen R et al. Differential expression of the transcription factor NF-kappaB during human mononuclear phagocyte differentiation to macrophages and dendritic cells. Biochem Biophys Res Commun 2000;268:99–105.
Wu L, D’Amico A, Winkel KD et al. RelB is essential for the development of myeloid-related CD8alpha– dendritic cells but not of lymphoid-related CD8alpha+ dendritic cells. Immunity 1998;9:839–847.
Pettit AR, Quinn C, MacDonald KP et al. Nuclear localization of RelB is associated with effective antigen-presenting cell function. J Immunol 1997;159:3681–3691.
Burkly L, Hession C, Ogata L et al. Expression of relB is required for the development of thymic medulla and dendritic cells. Nature 1995;373:531–536.
Ouaaz F, Arron J, Zheng Y et al. Dendritic cell development and survival require distinct NF-kappaB subunits. Immunity 2002;16:257–270.
Taieb J, Maruyama K, Borg C et al. Imatinib mesylate impairs Flt3L-mediated dendritic cell expansion and antitumor effects in vivo. Blood 2004;103:1966–1967.
Boissel N, Rousselot P, Raffoux E et al. Defective blood dendritic cells in chronic myeloid leukemia correlate with high plasmatic VEGF and are not normalized by imatinib mesylate. Leukemia 2004;18:1656–1661.
Appel S, Rupf A, Weck M M et al. Effects of imatinib on monocyte-derived dendritic cells are mediated by inhibition of nuclear factor-{kappa}B and Akt signaling pathways. Clin Cancer Res 2005;11:1928–1940.
Bhattacharyya S, Sen P, Wallet M et al. Immunoregulation of dendritic cells by IL-10 is mediated through suppression of the PI3K/Akt pathway and I B kinase activity. Blood 2004;104:1100–1109.
Gustin JA, Ozes ON, Akca H et al. Cell type-specific expression of the IkappaB kinases determines the significance of phosphatidylinositol 3-kinase/Akt signaling to NF-kappa B activation. J Biol Chem 2004;279:1615–1620.
Ozes ON, Mayo LD, Gustin JA et al. NF-kappaB activation by tumour necrosis factor requires the Akt serine-threonine kinase. Nature 1999;401:82–85.
Manna SK, Aggarwal BB. Wortmannin inhibits activation of nuclear transcription factors NF-kappaB and activated protein-1 induced by lipo-polysaccharide and phorbol ester. FEBS Lett 2000;473:113–118.
Xie P, Browning DD, Hay N et al. Activation of NF-kappa B by bradykinin through a Galpha(q)- and Gbeta gamma-dependent pathway that involves phosphoinositide 3-kinase and Akt. J Biol Chem 2000;275:24907–24914.
Dewar AL, Doherty KV, Hughes TP et al. Imatinib inhibits the functional capacity of cultured human monocytes. Immunol Cell Biol 2005;83:48–56.
Borg C, Terme M, Taieb J et al. Novel mode of action of c-kit tyrosine kinase inhibitors leading to NK cell-dependent antitumor effects. J Clin Invest 2004;114:379–388.
Sato N, Narita M, Takahashi M et al. The effects of STI571 on antigen presentation of dendritic cells generated from patients with chronic myelogenous leukemia. Hematol Oncol 2003;21:67–75.
Mohty M, Jourdan E, Mami NB et al. Imatinib and plasmacytoid dendritic cell function in patients with chronic myeloid leukemia. Blood 2004;103:4666–4668.
Wang H, Cheng F, Cuenca A et al. Imatinib mesylate (STI-571) enhances antigen-presenting cell function and overcomes tumor-induced CD4+ T-cell tolerance. Blood 2005;105:1135–1143.
Dietz AB, Souan L, Knutson GJ et al. Imatinib mesylate inhibits T-cell proliferation in vitro and delayed-type hypersensitivity in vivo. Blood 2004;104:1094–1099.
Seggewiss R, Lore K, Greiner E et al. Imatinib inhibits T-cell receptor-mediated T-cell proliferation and activation in a dose-dependent manner. Blood 2005;105:2473–2479.
Druker BJ. Imatinib alone and in combination for chronic myeloid leukemia. Semin Hematol 2003;40:50–58.
O’Brien SG, Guilhot F, Larson RA et al. Imatinib compared with interferon and low-dose cytarabine for newly diagnosed chronic-phase chronic myeloid leukemia. N Engl J Med 2003;348:994–1004.
Demetri GD, von Mehren M, Blanke CD et al. Efficacy and safety of imatinib mesylate in advanced gastrointestinal stromal tumors. N Engl J Med 2002;347:472–480.
Cortes JE, Talpaz M, O’Brien S et al. High rates of major cytogenetic response in patients with newly diagnosed chronic myeloid leukemia (CML) in early chronic phase treated with imatinib at 400 mg or 800 mg daily. Blood 2002;100a.
Zander A, Zabelina T, Renges H et al. Pre-treatment with glivec increases transplant-related mortality after allogeneic transplant. Bone Marrow Transplant 2004;33a.
Tiribelli M, Marin L, Calistri E et al. Imatinib mesylate (Glivec) pre-treatment does not have a negative effect on outcome of allogenic hematopoietic stem cell transplantation in Philadelphia-positive leukemias. Bone Marrow Transplant 2004;34:827–828.
Shimoni A, Kroger N, Zander AR et al. Imatinib mesylate (STI571) in preparation for allogeneic hematopoietic stem cell transplantation and donor lymphocyte infusions in patients with Philadelphia-positive acute leukemias. Leukemia 2003;17:290–297.
Petzer AL, Eaves CJ, Barnett MJ et al. Selective expansion of primitive normal hematopoietic cells in cytokine-supplemented cultures of purified cells from patients with chronic myeloid leukemia. Blood 1997;90:64–69.
Brummendorf TH, Dragowska W, Zijlmans JMJM et al. Asymmetric cell divisions sustain long-term hematopoiesis from single-sorted human fetal liver cells. J Exp Med 1998;188:1117–1124.
Glimm H, Eaves CJ. Direct evidence for multiple self-renewal divisions of human in vivo repopulating hematopoietic cells in short-term culture. Blood 1999;94:2161–2168.
Su RJ, Zhang XB, Li K et al. Platelet-derived growth factor promotes ex vivo expansion of CD34+ cells from human cord blood and enhances long-term culture-initiating cells, non-obese diabetic/severe combined immunodeficient repopulating cells and formation of adherent cells. Br J Haematol 2002;117:735–746.
Guilhot F. Sustained durability of responses plus high rates of cytogenetic responses result in long-term benefit for newly diagnosed chronic-phase chronic myeloid leukemia (CML-CP) treated with imatinib (IM) therapy: update from the IRIS study. Blood 2004;104a.
Seymour JF, Grigg A, Reynolds A et al. Imatinib’s potential effects on fertility, immunity and pulmonary function: a prospective study in patients with previously untreated CML. Blood. 2005;104a.
Bartolovic K, Balabanov S, Hartmann U et al. Inhibitory effect of imatinib on normal progenitor cells in vitro. Blood 2004;103:523–529.
Fang G, Kim CN, Perkins CL et al. CGP57148B (STI-571) induces differentiation and apoptosis and sensitizes Bcr-Abl-positive human leukemia cells to apoptosis due to antileukemic drugs. Blood 2000;96:2246–2253.
Holtz MS, Slovak ML, Zhang F et al. Imatinib mesylate (STI571) inhibits growth of primitive malignant progenitors in chronic myelogenous leukemia through reversal of abnormally increased proliferation. Blood 2002;99:3792–3800.
Horita M, Andreu EJ, Benito A et al. Blockade of the Bcr-Abl kinase activity induces apoptosis of chronic myelogenous leukemia cells by suppressing signal transducer and activator of transcription 5-dependent expression of Bcl-xL. J Exp Med 2000;191:977–984.
Silver RT. Imatinib mesylate (Gleevec (TM)) reduces phlebo to my requirements in polycythemia vera. Leukemia 2003;17:1186–1187.
Jones CM, Dickinson TM. Polycythemia vera responds to imatinib mesylate. Am J Med Sci 2003;325:149–152.
Oehler L, Jaeger E, Eser A et al. Imatinib mesylate inhibits autonomous erythropoiesis in patients with polycythemia vera in vitro. Blood 2003;102:2240–2242.
Hoepfl J, Miething C, Grundler R et al. Effects of imatinib on bone marrow engraftment in syngeneic mice. Leukemia 2002;16:1584–1588.
Pirson L, Baron F, Giet O et al. Despite inhibition of hematopoietic progenitor cell growth in vitro, the tyrosine kinase inhibitor STI571 does not impair engraftment of human CD34+ cells into NOD/SCIDb2mnull mice. Blood 2002;100a.
Graham SM, Jorgensen HG, Allan E et al. Primitive, quiescent, Philadelphia-positive stem cells from patients with chronic myeloid leukemia are insensitive to STI571 in vitro. Blood 2002;99:319–325.
Bhatia R, Holtz M, Niu N et al. Persistence of malignant hematopoietic progenitors in chronic myelogenous leukemia patients in complete cytogenetic remission following imatinib mesylate treatment. Blood 2003;101:4701–4707.
Marley SB, Deininger MW, Davidson RJ et al. The tyrosine kinase inhibitor STI571, like interferon-alpha, preferentially reduces the capacity for amplification of granulocyte-macrophage progenitors from patients with chronic myeloid leukemia. Exp Hematol 2000;28:551–557.
Dewar AL, Domaschenz RM, Doherty KV et al. Imatinib inhibits the in vitro development of the monocyte/macrophage lineage from normal human bone marrow progenitors. Leukemia 2003;17:1713–1721.
Hui CH, Goh KY, White D et al. Successful peripheral blood stem cell mobilisation with filgrastim in patients with chronic myeloid leukaemia achieving complete cytogenetic response with imatinib, without increasing disease burden as measured by quantitative real-time PCR. Leukemia 2003;17:821–828.
Melzer D, Neumann U, Ebell W et al. Imatinib mesylate (STI571) considerably affects normal human bone marrow stromal cell growth in vitro. Blood 2004;104a.
Passegue E, Jamieson CH, Ailles LE et al. Normal and leukemic hematopoiesis: are leukemias a stem cell disorder or a reacquisition of stem cell characteristics? Proc Natl Acad Sci U S A 2003;100(suppl 1):11842–11849.(Silke Appela, Stefan Bala)
b Department of Oncology and Hematology, University Hospital Hamburg-Eppendorf, Hamburg, Germany
Key Words. Bcr-Abl ? Imatinib ? T cells ? Dendritic cells ? Hematopoiesis
Correspondence: Peter Brossart, M.D., Department of Hematology, Oncology and Immunology, University of Tübingen, Otfried-Müller Str. 10, D-72076 Tübingen, Germany. Telephone: 49-7071-2982726; Fax: 49-7071-295709; e-mail: peter.brossart@med.uni-tuebingen.de
ABSTRACT
Imatinib (Glivec, formerly STI571; Novartis International, Basel, Switzerland, http://www.glivec.com/content/home.jsp) is a 2-phenylaminopyrimidine derivate designed as a specific inhibitor of the Abl protein tyrosine kinases (v-Abl, Bcr-Abl, and c-Abl) . It is also active against the platelet-derived growth factor receptor (PDGF-R), c-Kit (CD117), Abl-related gene, macrophage colony stimulating factor receptor (c-fms), and their fusion proteins, whereas other kinases are probably not affected . Imatinib binds selectively to the ATP-binding site of these kinases, thereby blocking their activity. Pharmacokinetic studies revealed that imatinib has a half-life of 18.2 hours given at a daily oral dose of 400 mg .
In recent clinical trials of imatinib in the treatment of chronic myeloid leukemia (CML) in chronic phase, it was shown that the drug is well tolerated with only few adverse effects. In many patients, complete hematological and cytogenetic responses could be induced . Imatinib is also active in accelerated phase orblast crises CML and in patients with primary, relapsed, or refractory Philadelphia chromosome–positive (Ph+) acute lymphoid leukemias . Furthermore, imatinib treatment has shown promising results in patients with gastrointestinal stroma tumors (GISTs) caused by c-Kit mutations and myeloproliferative disorders with mutations in the gene encoding PDGF-R beta .
In the following review, we will discuss recent data suggesting an inhibitory, antiproliferative effect of imatinib on different compartments of the normal hematopoietic hierarchy excluding the immature hematopoietic stem cell compartment. The results of these studies are relevant both considering long-term toxicity and also concerning novel yet only partly explored applications of the drug, such as a potential immunomodulatory agent or for the treatment of Bcr-Abl–negative myeloproliferative (lymphoproliferative) disorders.
Effect of Imatinib on Dendritic Cells
Dendritic cells (DCs) are recognized as the most potent antigen-presenting cells capable of initiating and maintaining primary immune responses. They originate from bone marrow–derived progenitor cells, spread via the blood stream, and can be found in almost every organ as the sentinels of the immune system. DCs can be generated in vitro from CD34+ progenitor cells or from peripheral blood monocytes by culturing these cells with different cytokine cocktails .
Recently, it was shown that the differentiation of mobilized human CD34+ peripheral blood progenitor cells (PBPCs) into DCs is impaired by imatinib . When CD34+ PBPCs were incubated in vitro with GM-CSF, tumor necrosis factor-, interleukin (IL)-4, and Flt3 ligand in the presence of imatinib from the beginning of the culture, the morphology of the generated cells resembled that of DCs but the phenotype was different. The generated cells were characterized by low expression of DC-associated cell-surface molecules like CD1a and CD83 as major histocompatibility complex class II and costimulatory molecules like CD80 and CD40 in a concentration-dependent manner . Blocking antibodies against c-Kit and stem cell factor (SCF) had no phenotypic effects, suggesting that the inhibitory effects of imatinib are not mediated by inhibition of c-Kit receptor signaling and that other mechanisms might be involved. Beside these phenotypical alterations, the cells were unable to respond to a maturation stimulus. Moreover, they were unable to elicit primary T-cell responses as well as T-cell responses against a recall antigen. Importantly, the observed inhibitory effects on DC development and function were not mediated by induction of apoptosis. Because a broad variety of genes during immune responses are regulated by members of the nuclear factor (NF)-B transcription factor family , their nuclear expression was studied to analyze the signaling pathways involved in the inhibitory effects of imatinib on CD34+-derived DCs. Nuclear-localized RelB protein was down-regulated in DCs treated with imatinib and could not be induced upon maturation with CD40L and interferon (IFN)-, suggesting that inhibition of RelB signaling is at least in part mediating the effects of imatinib (Fig. 1).
Figure 1. Inhibitory effects of imatinib treatment on DC development and T-cell stimulatory capacity. Abbreviations: DC, dendritic cell; IL, interleukin; MHC, major histocompatibility complex; PBPC, peripheral blood progenitor cell; TCR, T-cell receptor.
Taieb et al. confirmed these in vitro–generated results by analyzing the effects of imatinib in an animal model. Daily feeding of mice with imatinib twice from day 5 to 10 resulted in the inhibition of Flt3 ligand–induced expansion of DC in vivo and impaired the induction of a protective antitumor immunity in these animals. In line with these results, Boissel et al. showed that treatment of CML patients with imatinib does not normalize blood DC rates and Th1/Th2 balance in these patients despite normalization of vascular endothelial growth factor levels, suggesting that imatinib inhibits normal development of DCs in vivo.
Moreover, analyses of human monocyte-derived DC (MDC) revealed that addition of imatinib from day one of culturing the cells resulted in the reduced expression of cell-surface molecules known to be upregulated or induced during the differentiation of monocytes into DCs . In analogy to DCs generated from CD34+ PBPCs, imatinib did not induce apoptosis of these cells. Functionally, secretion of cytokines and chemokines shown to be important for T-cell activation was reduced, and these cells were unable to initiate primary T-cell responses. Immature MDCs incubated with imatinib had a reduced endocytic activity, as analyzed by their capacity to internalize fluorescein isothiocyanate–dextran. Imatinib treatment of DC resulted in decreased activation-induced upregulation of nuclear localized RelB, RelA, c-Rel, and NF-B p50, suggesting that imatinib mediates its effects in part via the NF-B pathway, as postulated for CD34+-derived DCs. In concordance, the presence of imatinib during MDC generation reduced phosphorylation of Akt, which is a kinase upstream of NF-B . Furthermore, Dewar et al. showed that the function of cultured human monocytes is impaired by imatinib treatment, characterized by decreased cytokine production after stimulation with lipopolysaccharide as well as reduced phagocytic capacity after M-CSF and GM-CSF stimulation, indicating that imatinib inhibits monocyte/macrophage development (Fig. 1).
A novel aspect of antitumor activity of imatinib was recently presented by Zitvogel and colleagues in an interesting study demonstrating that imatinib-treated DCs can activate natural killer (NK) cell functions and promote antitumor-directed immune responses. They reported that imatinib treatment resulted in DC-mediated NK cell activation in vitro and in vivo.
In contrast to these findings, Sato et al. showed that antigen presentation of Bcr-Abl+ DC from CML patients might be improved by imatinib treatment. However, DCs of CML patients are functionally defective and differ from normal DCs. Inline with this observation, a study by Mohty et al. demonstrated that plasmacytoid DC function is restored in CML patients under imatinib treatment, indicating distinct effects of imatinib in Ph+malignant and Ph– nonmalignant cells . Wang et al. reported that imatinib enhances antigen-presenting cell function in a transgenic mouse model analyzed by IL-2 and IFN- production and may overcome tumor-induced CD4+ T-cell tolerance. However, in this study, imatinib was administered for only 24 hours to already matured bone marrow–derived DCs, which might explain the different findings mentioned above.
Effects of Imatinib on T Cells
In addition to the inhibitory effects of imatinib on CD34+ PBPCs as well as monocyte-derived DCs and monocytes, imatinib was shown to inhibit T-cell proliferation by arresting the cells in G0/G1 without affecting the viability of the cells . Furthermore, a reduction of NF-B and phosphorylation of LCK and ERK1/2 were observed in phytohemagglutinin-stimulated T cells treated with imatinib. This impaired T-cell function was confirmed in a murine model of delayed-type hypersensitivity, indicating that imatinib might have immunosuppressive effects by inhibiting antigen presentation and T-cell effector functions . Recently, these findings were extended by Seggewiss et al. , who reported that imatinib affects T-cell receptor (TCR) signal transduction by inhibition of LCK . In their study, proliferation of T cells as well as expression of CD25 and CD69 was drastically reduced in human T cells that were activated via TCR and treated with imatinib. Moreover, CD8+ T-cell expansion in response to immunodominant cytomegalovirus and Epstein-Barr virus peptides was reduced. Analysis of the TCR-induced signaling cascade revealed that these effects were due to inhibition of LCK.
Effects of Imatinib on Normal Hematopoietic Stem and Progenitor Cells
Normal nonhematological side effects of imatinib given at a daily dose of 400 mg are mostly moderate. Hematologic side effects of imatinib are dose-dependent, are reversible, and affect all hematopoietic lineages, although to a variable degree . Grade 3 or 4 neutropenia is among the most common dose-limiting toxicities, occurring in 14% of the patients, followed by thrombocytopenia (8%) and anemia (3%) . However, when imatinib was given at a higher dose, that is, 800 mg daily, incidence of grade 3 or higher toxicities increased substantially to 38%, 17%, and 5%, respectively, even when imatinib was administered in early chronic phase . The impact of imatinib pretreatment on the outcome of allogeneic stem cell transplantation is still controversial. In a recent report, it has been shown that pretreatment with imatinib resulted in a higher transplant-related mortality in patients with Ph+ leukemias . However, other studies did not confirm these findings . Considering the known inhibitory effects of the drug on other (apart from Bcr-Abl) relevant tyrosine kinases, however, one could suspect potential hematotoxic side effects, particularly after long-term exposure to imatinib. c-Kit represents the receptor for human SCF, a cytokine that, together with Flt3 ligand and thrombopoietin, is assumed to be critical for the expansion of immature human hematopoietic stem/progenitor cells, at least in vitro . More recently, PDGF has been shown to be effective for the exvivo expansion of normal early stem and progenitor cells . It has been speculated that myelosuppression under imatinib treatment depends on the fact that after reduction of Ph+ hematopoiesis in response to treatment, normal hematopoietic stem and progenitor cells have to recover from pre-existing suppression by the malignant clone and to re-expand in the bone marrow. This interpretation is supported by the observation that the incidence of grade 3 or 4 hematotoxicities is most predominant at the initiation of treatment and decreases substantially to 3.8% (neutropenia), 2.1% (thrombocytopenia), and 1.9% (anemia), respectively, after 18 months of first-line treatment . Moreover, a prospective study of CML patients on higher-dose imatinib over 1 year revealed highly significant changes in serum immunoglobulin G and immunoglobulin M levels .
In the light of these observations, data from imatinib-treated patients with GIST were of particular interest because these patients can be expected to have a normal bone marrow function. Interestingly, even in patients with GIST treated with imatinib for a median follow-up of 9 months, 7% developed neutropenias (5% of which were grade 3 or 4) and 9% developed anemia (2% of which were grade 3 or 4) , supporting the assumption that hematological side effects of the drug are at least partly explained by a direct inhibition of normal hematopoiesis.
To analyze the effect of imatinib on normal human CD34+ stem/ progenitor cells in vitro, we applied a bulk culture system including serum-free medium supplemented with cytokines . The degree of expansion decreased in a significant and dose-dependent fashion in treated compared with untreated cells . The exact mechanism by which imatinib induces its antiproliferative effect on normal CD34+ cells has yet to be clarified. An increased population of apoptotic cells has been described in Bcr-Abl+ cells . However, in vitro exposure to imatinib up to a concentration of 10 μM for 48 hours led neither to a significant induction of apoptosis nor to a significant G1 arrest in normal cytokine-stimulated CD34+ cells . Thus, the apoptosis-inducing effects of imatinib seen in Ph+ cells appear unlikely to be responsible for its growth-inhibitory effect on normal hematopoiesis, at least at the concentrations usually achieved in patients (Fig. 2).
Figure 2. Cellular compartment of the normal hematopoietic hierarchy affected by imatinib treatment. Modified from , with permission. Abbreviations: CLP, common lymphoid progenitor; CMP, common myeloid progenitor; DC, dendritic cell; LT-HSC, long-term hematopoietic stem cell; MPP, multipotent progenitor; NF, nuclear factor; NK, natural killer; ST-HSC, short-term hematopoietic stem cell.
The observation of an antiproliferative effect of imatinib on Bcr-Abl– hematopoietic cells is supported clinically by recent reports of patients with Ph– myeloproliferative disorders that have been treated successfully with imatinib . Nevertheless, reconstitution of murine cells after allogeneic transplantation in a syngeneic mouse transplantation model argues against a stem cell toxic effect of the drug . Furthermore, no effect of imatinib was observed in the experimental human-mouse transplantation model . These data suggest that imatinib acts primarily on the more actively cycling, as opposed to the quiescent, components of the stem/progenitor cell compartment, as has been shown in the Ph+ compartment in patients with CML . Consistent with these findings, we and others reported a dose-dependent decrease in colony-forming unit formation with imatinib treatment , whereas no significant effect on the in vitro stem cell activity (e.g., cobblestone area–forming cells) capacity of normal CD34+ cells was observed, similar to findings by others . Dewar et al. have shown that imatinib significantly inhibited monocyte/macrophage development from normal bone marrow progenitors in vitro, whereas neutrophil and eosinophil development was less affected. Altogether, these results are in support of a selective inhibitory effect of imatinib on the progenitor cell level, whereas the immature stem cell compartment seems to be spared.
Beside these inhibitory effects on the proliferation of progenitor cells, the studies from Hui et al. indicate that imatinib treatment of CML patients affected the mobilization of CD34+ cells. The median CD34+ cell yield per apheresis was significantly higher when imatinib was temporarily withheld . More recently, imatinib has been shown to severely affect marrow stromal cells (MSCs) in vitro. This effect was also at least partly independent of PDGF-R and c-Kit signaling and seemed to be related to the proliferative status of the cells . These data might be of potential relevance for the administration of imatinib in situations with increased MSC turnover such as regeneration after intensive chemotherapy/radiotherapy.
In summary, it now appears that imatinib has a significant and dose-dependent inhibitory effect on the proliferation of normal CD34+ progenitor cells and MSCs (but not stem cells) that is largely independent of c-Kit signaling and seems to be linked to cell-cycle activity of the cells.
CONCLUSION
S.A. and S.B. contributed equally to this work.
REFERENCES
Druker BJ, Lydon NB. Lessons learned from the development of an abl tyrosine kinase inhibitor for chronic myelogenous leukemia. J Clin Invest 2000;105:3–7.
Druker BJ, Talpaz M, Resta DJ et al. Efficacy and safety of a specific inhibitor of the BCR-ABL tyrosine kinase in chronic myeloid leukemia. N Engl J Med 2001;344:1031–1037.
Druker BJ, Tamura S, Buchdunger E et al. Effects of a selective inhibitor of the Abl tyrosine kinase on the growth of Bcr-Abl positive cells. Nat Med 1996;2:561–566.
Deininger MW, Goldman JM, Lydon N et al. The tyrosine kinase inhibitor CGP57148B selectively inhibits the growth of BCR-ABL-positive cells. Blood 1997;90:3691–3698.
Gambacorti-Passerini C, le Coutre P, Mologni L et al. Inhibition of the ABL kinase activity blocks the proliferation of BCR/ABL+ leukemic cells and induces apoptosis. Blood Cells Mol Dis 1997;23:380–394.
Buchdunger E, Cioffi CL, Law N et al. Abl protein-tyrosine kinase inhibitor STI571 inhibits in vitro signal transduction mediated by c-kit and platelet-derived growth factor receptors. J Pharmacol Exp Ther 2000;295:139–145.
Heinrich MC, Griffith DJ, Druker BJ et al. Inhibition of c-kit receptor tyrosine kinase activity by STI 571, a selective tyrosine kinase inhibitor. Blood 2000;96:925–932.
Okuda K, Weisberg E, Gilliland DG et al. ARG tyrosine kinase activity is inhibited by STI571. Blood 2001;97:2440–2448.
Carroll M, Ohno-Jones S, Tamura S et al. CGP 57148, a tyrosine kinase inhibitor, inhibits the growth of cells expressing BCR-ABL, TEL-ABL, and TEL-PDGFR fusion proteins. Blood 1997;90:4947–4952.
Dewar AL, Cambareri AC, Zannettino AC et al. Macrophage colony stimulating factor receptor, c-fms, is a novel target of imatinib. Blood 2005;105:3127–3132.
Fabian MA, Biggs WH, Treiber DK et al. A small molecule-kinase interaction map for clinical kinase inhibitors. Nat Biotechnol 2005;23:329–336.
Deininger M, Buchdunger E, Druker BJ. The development of imatinib as a therapeutic agent for chronic myeloid leukemia. Blood 2005;105:2640–2653.
le Coutre P, Kreuzer KA, Pursche S et al. Pharmacokinetics and cellular uptake of imatinib and its main metabolite CGP74588. Cancer Chemother Pharmacol 2004;53:313–323.
Kantarjian H, Sawyers C, Hochhaus A et al. Hematologic and cytogenetic responses to imatinib mesylate in chronic myelogenous leukemia. N Engl J Med 2002;346:645–652.
Sawyers CL, Hochhaus A, Feldman E et al. Imatinib induces hematologic and cytogenetic responses in patients with chronic myelogenous leukemia in myeloid blast crisis: results of a phase II study. Blood 2002;99:3530–3539.
Talpaz M, Silver RT, Druker BJ et al. Imatinib induces durable hematologic and cytogenetic responses in patients with accelerated phase chronic myeloid leukemia: results of a phase 2 study. Blood 2002;99:1928–1937.
Druker BJ, Sawyers CL, Kantarjian H et al. Activity of a specific inhibitor of the BCR-ABL tyrosine kinase in the blast crisis of chronic myeloid leukemia and acute lymphoblastic leukemia with the Philadelphia chromosome. N Engl J Med 2001;344:1038–1042.
Ottmann OG, Druker BJ, Sawyers CL et al. A phase 2 study of imatinib in patients with relapsed or refractory Philadelphia chromosome-positive acute lymphoid leukemias. Blood 2002;100:1965–1971.
Apperley JF, Gardembas M, Melo JV et al. Response to imatinib mesylate in patients with chronic myeloproliferative diseases with rearrangements of the platelet-derived growth factor receptor beta. N Engl J Med 2002;347:481–487.
Heinrich MC, Blanke CD, Druker BJ et al. Inhibition of KIT tyrosine kinase activity: a novel molecular approach to the treatment of KIT-positive malignancies. J Clin Oncol 2002;20:1692–1703.
Caux C, Dezutter-Dambuyant C, Schmitt D et al. GM-CSF and TNF-alpha cooperate in the generation of dendritic Langerhans cells. Nature 1992;360:258–261.
Brossart P, Wirths S, Brugger W et al. Dendritic cells in cancer vaccines. Exp Hematol 2001;29:1247–1255.
Cella M, Sallusto F, Lanzavecchia A. Origin, maturation and antigen presenting function of dendritic cells. Curr Opin Immunol 1997;9:10–16.
Maraskovsky E, Brasel K, Teepe M et al. Dramatic increase in the numbers of functionally mature dendritic cells in Flt3 ligand-treated mice: multiple dendritic cell subpopulations identified. J Exp Med 1996;184:1953–1962.
Sallusto F, Lanzavecchia A. Efficient presentation of soluble antigen by cultured human dendritic cells is maintained by granulocyte/macrophage colony-stimulating factor plus interleukin 4 and downregulated by tumor necrosis factor alpha. J Exp Med 1994;179:1109–1118.
Siena S, Di Nicola M, Bregni M et al. Massive ex vivo generation of functional dendritic cells from mobilized CD34+ blood progenitors for anti-cancer therapy. Exp Hematol 1995;23:1463–1471.
Young JW, Szabolcs P, Moore MA. Identification of dendritic cell colony-forming units among normal human CD34+ bone marrow progenitors that are expanded by c-kit-ligand and yield pure dendritic cell colonies in the presence of granulocyte/macrophage colony-stimulating factor and tumor necrosis factor alpha. J Exp Med 1995;182:1111–1119.
Zhou LJ, Tedder TF. CD14+ blood monocytes can differentiate into functionally mature CD83+ dendritic cells. Proc Natl Acad Sci U S A 1996;93:2588–2592.
Appel S, Boehmler AM, Grunebach F et al. Imatinib mesylate affects the development and function of dendritic cells generated from CD34+ peripheral blood progenitor cells. Blood 2004;103:538–544.
Ghosh S, May MJ, Kopp EB. NF-kappa B and Rel proteins: evolutionarily conserved mediators of immune responses. Annu Rev Immunol 1998;16:225–260.
Rescigno M, Martino M, Sutherland CL et al. Dendritic cell survival and maturation are regulated by different signaling pathways. J Exp Med 1998;188:2175–2180.
Neumann M, Fries H, Scheicher C et al. Differential expression of Rel/ NF-kappaB and octamer factors is a hallmark of the generation and maturation of dendritic cells. Blood 2000;95:277–285.
Weih F, Carrasco D, Durham SK et al. Multiorgan inflammation and hematopoietic abnormalities in mice with a targeted disruption of RelB, a member of the NF-kappa B/Rel family. Cell 1995;80:331–340.
Oyama T, Ran S, Ishida T et al. Vascular endothelial growth factor affects dendritic cell maturation through the inhibition of nuclear factor-kappa B activation in hemopoietic progenitor cells. J Immunol 1998;160:1224–1232.
Ammon C, Mondal K, Andreesen R et al. Differential expression of the transcription factor NF-kappaB during human mononuclear phagocyte differentiation to macrophages and dendritic cells. Biochem Biophys Res Commun 2000;268:99–105.
Wu L, D’Amico A, Winkel KD et al. RelB is essential for the development of myeloid-related CD8alpha– dendritic cells but not of lymphoid-related CD8alpha+ dendritic cells. Immunity 1998;9:839–847.
Pettit AR, Quinn C, MacDonald KP et al. Nuclear localization of RelB is associated with effective antigen-presenting cell function. J Immunol 1997;159:3681–3691.
Burkly L, Hession C, Ogata L et al. Expression of relB is required for the development of thymic medulla and dendritic cells. Nature 1995;373:531–536.
Ouaaz F, Arron J, Zheng Y et al. Dendritic cell development and survival require distinct NF-kappaB subunits. Immunity 2002;16:257–270.
Taieb J, Maruyama K, Borg C et al. Imatinib mesylate impairs Flt3L-mediated dendritic cell expansion and antitumor effects in vivo. Blood 2004;103:1966–1967.
Boissel N, Rousselot P, Raffoux E et al. Defective blood dendritic cells in chronic myeloid leukemia correlate with high plasmatic VEGF and are not normalized by imatinib mesylate. Leukemia 2004;18:1656–1661.
Appel S, Rupf A, Weck M M et al. Effects of imatinib on monocyte-derived dendritic cells are mediated by inhibition of nuclear factor-{kappa}B and Akt signaling pathways. Clin Cancer Res 2005;11:1928–1940.
Bhattacharyya S, Sen P, Wallet M et al. Immunoregulation of dendritic cells by IL-10 is mediated through suppression of the PI3K/Akt pathway and I B kinase activity. Blood 2004;104:1100–1109.
Gustin JA, Ozes ON, Akca H et al. Cell type-specific expression of the IkappaB kinases determines the significance of phosphatidylinositol 3-kinase/Akt signaling to NF-kappa B activation. J Biol Chem 2004;279:1615–1620.
Ozes ON, Mayo LD, Gustin JA et al. NF-kappaB activation by tumour necrosis factor requires the Akt serine-threonine kinase. Nature 1999;401:82–85.
Manna SK, Aggarwal BB. Wortmannin inhibits activation of nuclear transcription factors NF-kappaB and activated protein-1 induced by lipo-polysaccharide and phorbol ester. FEBS Lett 2000;473:113–118.
Xie P, Browning DD, Hay N et al. Activation of NF-kappa B by bradykinin through a Galpha(q)- and Gbeta gamma-dependent pathway that involves phosphoinositide 3-kinase and Akt. J Biol Chem 2000;275:24907–24914.
Dewar AL, Doherty KV, Hughes TP et al. Imatinib inhibits the functional capacity of cultured human monocytes. Immunol Cell Biol 2005;83:48–56.
Borg C, Terme M, Taieb J et al. Novel mode of action of c-kit tyrosine kinase inhibitors leading to NK cell-dependent antitumor effects. J Clin Invest 2004;114:379–388.
Sato N, Narita M, Takahashi M et al. The effects of STI571 on antigen presentation of dendritic cells generated from patients with chronic myelogenous leukemia. Hematol Oncol 2003;21:67–75.
Mohty M, Jourdan E, Mami NB et al. Imatinib and plasmacytoid dendritic cell function in patients with chronic myeloid leukemia. Blood 2004;103:4666–4668.
Wang H, Cheng F, Cuenca A et al. Imatinib mesylate (STI-571) enhances antigen-presenting cell function and overcomes tumor-induced CD4+ T-cell tolerance. Blood 2005;105:1135–1143.
Dietz AB, Souan L, Knutson GJ et al. Imatinib mesylate inhibits T-cell proliferation in vitro and delayed-type hypersensitivity in vivo. Blood 2004;104:1094–1099.
Seggewiss R, Lore K, Greiner E et al. Imatinib inhibits T-cell receptor-mediated T-cell proliferation and activation in a dose-dependent manner. Blood 2005;105:2473–2479.
Druker BJ. Imatinib alone and in combination for chronic myeloid leukemia. Semin Hematol 2003;40:50–58.
O’Brien SG, Guilhot F, Larson RA et al. Imatinib compared with interferon and low-dose cytarabine for newly diagnosed chronic-phase chronic myeloid leukemia. N Engl J Med 2003;348:994–1004.
Demetri GD, von Mehren M, Blanke CD et al. Efficacy and safety of imatinib mesylate in advanced gastrointestinal stromal tumors. N Engl J Med 2002;347:472–480.
Cortes JE, Talpaz M, O’Brien S et al. High rates of major cytogenetic response in patients with newly diagnosed chronic myeloid leukemia (CML) in early chronic phase treated with imatinib at 400 mg or 800 mg daily. Blood 2002;100a.
Zander A, Zabelina T, Renges H et al. Pre-treatment with glivec increases transplant-related mortality after allogeneic transplant. Bone Marrow Transplant 2004;33a.
Tiribelli M, Marin L, Calistri E et al. Imatinib mesylate (Glivec) pre-treatment does not have a negative effect on outcome of allogenic hematopoietic stem cell transplantation in Philadelphia-positive leukemias. Bone Marrow Transplant 2004;34:827–828.
Shimoni A, Kroger N, Zander AR et al. Imatinib mesylate (STI571) in preparation for allogeneic hematopoietic stem cell transplantation and donor lymphocyte infusions in patients with Philadelphia-positive acute leukemias. Leukemia 2003;17:290–297.
Petzer AL, Eaves CJ, Barnett MJ et al. Selective expansion of primitive normal hematopoietic cells in cytokine-supplemented cultures of purified cells from patients with chronic myeloid leukemia. Blood 1997;90:64–69.
Brummendorf TH, Dragowska W, Zijlmans JMJM et al. Asymmetric cell divisions sustain long-term hematopoiesis from single-sorted human fetal liver cells. J Exp Med 1998;188:1117–1124.
Glimm H, Eaves CJ. Direct evidence for multiple self-renewal divisions of human in vivo repopulating hematopoietic cells in short-term culture. Blood 1999;94:2161–2168.
Su RJ, Zhang XB, Li K et al. Platelet-derived growth factor promotes ex vivo expansion of CD34+ cells from human cord blood and enhances long-term culture-initiating cells, non-obese diabetic/severe combined immunodeficient repopulating cells and formation of adherent cells. Br J Haematol 2002;117:735–746.
Guilhot F. Sustained durability of responses plus high rates of cytogenetic responses result in long-term benefit for newly diagnosed chronic-phase chronic myeloid leukemia (CML-CP) treated with imatinib (IM) therapy: update from the IRIS study. Blood 2004;104a.
Seymour JF, Grigg A, Reynolds A et al. Imatinib’s potential effects on fertility, immunity and pulmonary function: a prospective study in patients with previously untreated CML. Blood. 2005;104a.
Bartolovic K, Balabanov S, Hartmann U et al. Inhibitory effect of imatinib on normal progenitor cells in vitro. Blood 2004;103:523–529.
Fang G, Kim CN, Perkins CL et al. CGP57148B (STI-571) induces differentiation and apoptosis and sensitizes Bcr-Abl-positive human leukemia cells to apoptosis due to antileukemic drugs. Blood 2000;96:2246–2253.
Holtz MS, Slovak ML, Zhang F et al. Imatinib mesylate (STI571) inhibits growth of primitive malignant progenitors in chronic myelogenous leukemia through reversal of abnormally increased proliferation. Blood 2002;99:3792–3800.
Horita M, Andreu EJ, Benito A et al. Blockade of the Bcr-Abl kinase activity induces apoptosis of chronic myelogenous leukemia cells by suppressing signal transducer and activator of transcription 5-dependent expression of Bcl-xL. J Exp Med 2000;191:977–984.
Silver RT. Imatinib mesylate (Gleevec (TM)) reduces phlebo to my requirements in polycythemia vera. Leukemia 2003;17:1186–1187.
Jones CM, Dickinson TM. Polycythemia vera responds to imatinib mesylate. Am J Med Sci 2003;325:149–152.
Oehler L, Jaeger E, Eser A et al. Imatinib mesylate inhibits autonomous erythropoiesis in patients with polycythemia vera in vitro. Blood 2003;102:2240–2242.
Hoepfl J, Miething C, Grundler R et al. Effects of imatinib on bone marrow engraftment in syngeneic mice. Leukemia 2002;16:1584–1588.
Pirson L, Baron F, Giet O et al. Despite inhibition of hematopoietic progenitor cell growth in vitro, the tyrosine kinase inhibitor STI571 does not impair engraftment of human CD34+ cells into NOD/SCIDb2mnull mice. Blood 2002;100a.
Graham SM, Jorgensen HG, Allan E et al. Primitive, quiescent, Philadelphia-positive stem cells from patients with chronic myeloid leukemia are insensitive to STI571 in vitro. Blood 2002;99:319–325.
Bhatia R, Holtz M, Niu N et al. Persistence of malignant hematopoietic progenitors in chronic myelogenous leukemia patients in complete cytogenetic remission following imatinib mesylate treatment. Blood 2003;101:4701–4707.
Marley SB, Deininger MW, Davidson RJ et al. The tyrosine kinase inhibitor STI571, like interferon-alpha, preferentially reduces the capacity for amplification of granulocyte-macrophage progenitors from patients with chronic myeloid leukemia. Exp Hematol 2000;28:551–557.
Dewar AL, Domaschenz RM, Doherty KV et al. Imatinib inhibits the in vitro development of the monocyte/macrophage lineage from normal human bone marrow progenitors. Leukemia 2003;17:1713–1721.
Hui CH, Goh KY, White D et al. Successful peripheral blood stem cell mobilisation with filgrastim in patients with chronic myeloid leukaemia achieving complete cytogenetic response with imatinib, without increasing disease burden as measured by quantitative real-time PCR. Leukemia 2003;17:821–828.
Melzer D, Neumann U, Ebell W et al. Imatinib mesylate (STI571) considerably affects normal human bone marrow stromal cell growth in vitro. Blood 2004;104a.
Passegue E, Jamieson CH, Ailles LE et al. Normal and leukemic hematopoiesis: are leukemias a stem cell disorder or a reacquisition of stem cell characteristics? Proc Natl Acad Sci U S A 2003;100(suppl 1):11842–11849.(Silke Appela, Stefan Bala)