LMO2 and Gene Therapy for Severe Combined Immunodeficiency
http://www.100md.com
《新英格兰医药杂志》
To the Editor: McCormack and Rabbitts (Feb. 26 issue)1 discuss the role of activation of the T-cell oncogene LMO2 in inducing clonal T-cell proliferation in two patients after gene therapy for X-linked severe combined immunodeficiency (SCID), a condition caused by mutation of the c cytokine-receptor subunit gene. The authors point to a role of c as a cofactor of clonal proliferation. However, there are no data to suggest that, as proposed, the expression of a CD25–c interleukin-2–receptor complex by T-cell precursors will make these cells hypersensitive to interleukin-2, since signal transduction without the R subunit of interleukin-2 is highly questionable.2 It is more likely that LMO2 and c exert a synergistic effect in mediating T-cell growth. The mechanisms by which LMO2 triggers cell proliferation are also not necessarily homogeneous. Aberrant LMO2 expression in mice blocks T-cell differentiation at an immature, double-negative stage,1 whereas transgenic LMO2+ clones exhibit a mature phenotype,3 suggestive of a post-thymic role.
The authors mention the unpublished finding of another integration site in the LMO2 locus in a third patient. This finding should not be overemphasized, since this integration site was detected once and not in two more samples. In addition, it did not result in detectable LMO2 expression.
Age at the time of treatment is another cofactor associated with these serious adverse events.3 The likelihood that serious adverse events occurred by chance in the 2 youngest of the 13 successfully treated patients3 (and Gaspar et al.: unpublished data) is 1.2 percent ([2÷13]x[1÷12]). The characteristics of hematopoiesis in newborns4 could lead to a higher risk of insertion of the retrovirus in the LMO2 locus. Although this hypothesis requires testing, it may have an effect on the continuation of clinically successful trials of gene therapy for X-linked SCID. To select for gene therapy those patients with X-linked SCID who are older than a specified age limit is likely to be a strategy that combines efficacy and increased safety.
Alain Fischer, M.D., Ph.D.
Salima Hacein-Bey Abina, Pharm.D., Ph.D.
INSERM Unité 429
75015 Paris, France
fischer@necker.fr
Adrian Thrasher, M.D., Ph.D.
Institute of Child Health
London WC1N 1EH, United Kingdom
Christof von Kalle, M.D., Ph.D.
Children's Hospital Research Foundation
Cincinnati, OH 45229
Marina Cavazzana-Calvo, M.D., Ph.D.
INSERM Unité 429
75015 Paris, France
References
McCormack MP, Rabbitts TH. Activation of the T-cell oncogene LMO2 after gene therapy for X-linked severe combined immunodeficiency. N Engl J Med 2004;350:913-922.
Sugamura K, Asao H, Kondo M, et al. The interleukin-2 receptor gamma chain: its role in the multiple cytokine receptor complexes and T cell development in XSCID. Annu Rev Immunol 1996;14:179-205.
Hacein-Bey-Abina S, Von Kalle C, Schmidt M, et al. LMO2-associated clonal T cell proliferation in two patients after gene therapy for SCID-X1. Science 2003;302:415-419.
Hirose J, Kouro T, Igarashi H, Yokota T, Sakaguchi N, Kincade PW. A developing picture of lymphopoiesis in bone marrow. Immunol Rev 2002;189:28-40.
To the Editor: With regard to the excellent review article on gene therapy for X-linked SCID, I would like to clarify a point about lymphocyte phenotypes in SCID. The authors state, both in the text and in Figure 1B, that affected patients are deficient in T cells, B cells, and natural killer cells. Actually, patients with X-linked SCID are T-cell–negative and natural-killer-cell–negative but B-cell–positive (T–NK–B+).1
The common subunit, which is genetically defective in these patients, is essential for the normal function of the receptors for interleukins-2, 4, 7, 9, 15, and 21 on T cells and natural killer cells. The interleukin-7 receptor is crucial for the normal development of T cells, whereas the interleukin-15 receptor is necessary for the normal development of natural killer cells. Patients with X-linked SCID generally have normal numbers of B cells that function poorly because of the lack of T-cell help.
Adenosine deaminase deficiency is the cause of SCID that would result in the T–B–NK– phenotype. Patients with adenosine deaminase deficiency are not candidates for this type of gene therapy.
Bryan D. Stone, M.D.
Dartmouth–Hitchcock Medical Center
Keene, NH 03431
References
Buckley RH. Primary immunodeficiency disease due to defects in lymphocytes. N Engl J Med 2000;343:1313-1324.
The authors reply: Stone points out that patients with X-linked SCID in fact have the T–NK–B+ phenotype but that adenosine deaminase–deficient patients with SCID lack B cells as well. Although it is true that B cells are usually present in patients with X-linked SCID, these cells are intrinsically defective1 (even in the presence of normal T cells), so that adequate function can usually be obtained only by engraftment with normal B cells. The portrayal of B-cell engraftment in Figure 1 of our article indicates the introduction of functional B cells into the patients. We also point out that adenosine deaminase deficiency is treatable by a regimen similar to that used in the X-linked SCID trial but by means of adenosine deaminase replacement.
Fischer and colleagues raise three issues that require further comment. Regarding the possible hypersensitivity of developing T cells to mitogenic signaling after overexpression of the common c subunit of the interleukin-2 receptor (IL2Rc), we note that human pro–T cells do respond to interleukin-2 in vitro, implying the presence of functional receptors. Moreover, the receptors for other IL2Rc-containing receptors, including interleukin-7, are present in these cells,2 suggesting hypersensitivity to growth-factor signaling as a mechanism of synergy between IL2Rc and LMO2 in oncogenesis.
Concerning the biology of LMO2-associated leukemia, we sought to correlate knowledge from mouse models of Lmo2-dependent leukemia with possible forced expression by way of retroviral insertion, as a stimulus for further experimentation. In the mouse models, Lmo2 expression is necessary but not sufficient for T-cell leukemia.3 Although the tumors can progress to the mature phenotype, this is not always the case, and more important, a post-thymic role is not necessary since leukemogenesis is identical in mice with or without RAG recombinase, meaning that T-cell leukemias can arise from immature cells without T-cell receptors.3
Finally, the information about the third patient with X-linked SCID with retroviral insertion into LMO2 is in fact in the public domain,4 quoted by one of Fischer's cosignatories. We do not imply that leukemia exists in this patient, but, rather, ask "whether the LMO2 gene is a preferred . . . target." The observation by Dave and colleagues of a retrovirally induced T-cell leukemia in mice with insertions into both the LMO2 and IL2Rc genes5 gives verisimilitude to this notion.
Terence H. Rabbitts, Ph.D.
Medical Research Council Laboratory of Molecular Biology
Cambridge CB2 2QH, United Kingdom
Matthew P. McCormack, Ph.D.
Rotary Bone Marrow Research Laboratory
Melbourne, Victoria 3050, Australia
References
White H, Thrasher A, Veys P, Kinnon C, Gaspar HB. Intrinsic defects of B cell function in X-linked severe combined immunodeficiency. Eur J Immunol 2000;30:732-737.
Fry TJ, Mackall CL. Interleukin-7: from bench to clinic. Blood 2002;99:3892-3904.
Rabbitts TH. Chromosomal translocation master genes, mouse models and experimental therapeutics. Oncogene 2001;20:5763-5777.
Check E. Cancer fears cast doubts on future of gene therapy. Nature 2003;421:678-678.
Dave UP, Jenkins NA, Copeland NG. Gene therapy insertional mutagenesis insights. Science 2004;303:333-333.
The authors mention the unpublished finding of another integration site in the LMO2 locus in a third patient. This finding should not be overemphasized, since this integration site was detected once and not in two more samples. In addition, it did not result in detectable LMO2 expression.
Age at the time of treatment is another cofactor associated with these serious adverse events.3 The likelihood that serious adverse events occurred by chance in the 2 youngest of the 13 successfully treated patients3 (and Gaspar et al.: unpublished data) is 1.2 percent ([2÷13]x[1÷12]). The characteristics of hematopoiesis in newborns4 could lead to a higher risk of insertion of the retrovirus in the LMO2 locus. Although this hypothesis requires testing, it may have an effect on the continuation of clinically successful trials of gene therapy for X-linked SCID. To select for gene therapy those patients with X-linked SCID who are older than a specified age limit is likely to be a strategy that combines efficacy and increased safety.
Alain Fischer, M.D., Ph.D.
Salima Hacein-Bey Abina, Pharm.D., Ph.D.
INSERM Unité 429
75015 Paris, France
fischer@necker.fr
Adrian Thrasher, M.D., Ph.D.
Institute of Child Health
London WC1N 1EH, United Kingdom
Christof von Kalle, M.D., Ph.D.
Children's Hospital Research Foundation
Cincinnati, OH 45229
Marina Cavazzana-Calvo, M.D., Ph.D.
INSERM Unité 429
75015 Paris, France
References
McCormack MP, Rabbitts TH. Activation of the T-cell oncogene LMO2 after gene therapy for X-linked severe combined immunodeficiency. N Engl J Med 2004;350:913-922.
Sugamura K, Asao H, Kondo M, et al. The interleukin-2 receptor gamma chain: its role in the multiple cytokine receptor complexes and T cell development in XSCID. Annu Rev Immunol 1996;14:179-205.
Hacein-Bey-Abina S, Von Kalle C, Schmidt M, et al. LMO2-associated clonal T cell proliferation in two patients after gene therapy for SCID-X1. Science 2003;302:415-419.
Hirose J, Kouro T, Igarashi H, Yokota T, Sakaguchi N, Kincade PW. A developing picture of lymphopoiesis in bone marrow. Immunol Rev 2002;189:28-40.
To the Editor: With regard to the excellent review article on gene therapy for X-linked SCID, I would like to clarify a point about lymphocyte phenotypes in SCID. The authors state, both in the text and in Figure 1B, that affected patients are deficient in T cells, B cells, and natural killer cells. Actually, patients with X-linked SCID are T-cell–negative and natural-killer-cell–negative but B-cell–positive (T–NK–B+).1
The common subunit, which is genetically defective in these patients, is essential for the normal function of the receptors for interleukins-2, 4, 7, 9, 15, and 21 on T cells and natural killer cells. The interleukin-7 receptor is crucial for the normal development of T cells, whereas the interleukin-15 receptor is necessary for the normal development of natural killer cells. Patients with X-linked SCID generally have normal numbers of B cells that function poorly because of the lack of T-cell help.
Adenosine deaminase deficiency is the cause of SCID that would result in the T–B–NK– phenotype. Patients with adenosine deaminase deficiency are not candidates for this type of gene therapy.
Bryan D. Stone, M.D.
Dartmouth–Hitchcock Medical Center
Keene, NH 03431
References
Buckley RH. Primary immunodeficiency disease due to defects in lymphocytes. N Engl J Med 2000;343:1313-1324.
The authors reply: Stone points out that patients with X-linked SCID in fact have the T–NK–B+ phenotype but that adenosine deaminase–deficient patients with SCID lack B cells as well. Although it is true that B cells are usually present in patients with X-linked SCID, these cells are intrinsically defective1 (even in the presence of normal T cells), so that adequate function can usually be obtained only by engraftment with normal B cells. The portrayal of B-cell engraftment in Figure 1 of our article indicates the introduction of functional B cells into the patients. We also point out that adenosine deaminase deficiency is treatable by a regimen similar to that used in the X-linked SCID trial but by means of adenosine deaminase replacement.
Fischer and colleagues raise three issues that require further comment. Regarding the possible hypersensitivity of developing T cells to mitogenic signaling after overexpression of the common c subunit of the interleukin-2 receptor (IL2Rc), we note that human pro–T cells do respond to interleukin-2 in vitro, implying the presence of functional receptors. Moreover, the receptors for other IL2Rc-containing receptors, including interleukin-7, are present in these cells,2 suggesting hypersensitivity to growth-factor signaling as a mechanism of synergy between IL2Rc and LMO2 in oncogenesis.
Concerning the biology of LMO2-associated leukemia, we sought to correlate knowledge from mouse models of Lmo2-dependent leukemia with possible forced expression by way of retroviral insertion, as a stimulus for further experimentation. In the mouse models, Lmo2 expression is necessary but not sufficient for T-cell leukemia.3 Although the tumors can progress to the mature phenotype, this is not always the case, and more important, a post-thymic role is not necessary since leukemogenesis is identical in mice with or without RAG recombinase, meaning that T-cell leukemias can arise from immature cells without T-cell receptors.3
Finally, the information about the third patient with X-linked SCID with retroviral insertion into LMO2 is in fact in the public domain,4 quoted by one of Fischer's cosignatories. We do not imply that leukemia exists in this patient, but, rather, ask "whether the LMO2 gene is a preferred . . . target." The observation by Dave and colleagues of a retrovirally induced T-cell leukemia in mice with insertions into both the LMO2 and IL2Rc genes5 gives verisimilitude to this notion.
Terence H. Rabbitts, Ph.D.
Medical Research Council Laboratory of Molecular Biology
Cambridge CB2 2QH, United Kingdom
Matthew P. McCormack, Ph.D.
Rotary Bone Marrow Research Laboratory
Melbourne, Victoria 3050, Australia
References
White H, Thrasher A, Veys P, Kinnon C, Gaspar HB. Intrinsic defects of B cell function in X-linked severe combined immunodeficiency. Eur J Immunol 2000;30:732-737.
Fry TJ, Mackall CL. Interleukin-7: from bench to clinic. Blood 2002;99:3892-3904.
Rabbitts TH. Chromosomal translocation master genes, mouse models and experimental therapeutics. Oncogene 2001;20:5763-5777.
Check E. Cancer fears cast doubts on future of gene therapy. Nature 2003;421:678-678.
Dave UP, Jenkins NA, Copeland NG. Gene therapy insertional mutagenesis insights. Science 2004;303:333-333.