Comparison of five retrovirus vectors containing the human IL-2 receptor gamma chain gene for their ability to restore T and B lymphocytes in the X-linked severe combined immunodeficiency mouse model

X-linked severe combined immunodeficiency (XSCID) is caused by mutations in the IL-2 receptor gamma chain (IL2RC) gene, resulting in absent T lymphocy tes and nonfunctional B lymphocytes. Recently T lymphocyte production and B lymphocyte function were restored in XSCID patients infused with autologou s stem cells transduced with a retrovirus containing the human IL2RC cDNA. To optimize the expression of human IL2RC for future clinical trials, we co mpared five retroviral vectors expressing human IL2RC from different LTR en hancer-promoter elements in a mouse model. Northern and Southern blot analy sis of hematopoietic tissues from repopulated mice revealed that the retrov iral vector with the highest expression per copy number was MFG-S-hIL2RC, f ollowed by MND-hlL2RG, All five vectors were capable of restoring lymphopoi esis in irradiated XSCID mice transplanted with transduced IL2RG-deficient hematopoietic stem cells. Transduction of IL2RG-deficient hematopoietic ste m cells with all five vectors restored T lymphopoiesis in transplanted stem cell-deficient W/W-v mouse recipients. However, only XSCID stem cells tran sduced with the MFG-S-hIL2RG vector generated B lymphocytes in W/W-v mice. We conclude that the MFG-S-hIL2RG vector provides the best opportunity for in vivo selection and development of B and T lymphocytes for human XSCID ge ne therapy.