GAMMA-C GENE-TRANSFER IN THE PRESENCE OF STEM-CELL FACTOR, FLT-3L, INTERLEUKIN-7 (IL-7), IL-1-ALPHA, AND IL-15 CYTOKINES RESTORES T-CELL DIFFERENTIATION FROM GAMMA-C(-) X-LINKED SEVERE COMBINED IMMUNODEFICIENCY HEMATOPOIETIC PROGENITOR CELLS IN MURINE FETAL THYMIC ORGAN-CULTURES

X-linked severe combined immunodeficiency (SCID-XI) is a rare human in herited disorder in which early T and natural killer (NK) lymphocyte d evelopment is blocked. The genetic disorder results from mutations in the common gamma c chain that participates in several cytokine recepto rs including the interleukin-2 (IL-2), IL-4, IL-7, IL-9, and IL-15 rec eptors. We have shown in a previous report that gamma c gene transfer into SCID-XI bone marrow (BM) cells restores efficient NK cell differe ntiation. In this study, we have focused on the introduction of the ga mma c gene into SCID-XI hematopoietic stem cells with the goal of obta ining differentiation into mature T cells. For this purpose, we used t he in vitro hybrid fetal thymic organ culture (FTOC) system in which a combination of cytokines consisting of stem cell factor (SCF), Flt-3L , IL-7, IL-1 alpha, and IL-15 is added concomitantly. In this culture system, CD34(+) marrow cells from two SCID-XI patients were able to ma ture into double positive CD4(+) CD8(+) cells and to a lesser degree i nto CD4(+) TCR alpha beta(+) single positive cells after retroviral-me diated gamma c gene transfer. In addition, examination of the output c ell population at the TCR DJ beta 1 locus exhibited multiple rearrange ments. These results indicate that restoration of the gamma c/JAK/STAT signaling pathway during the early developmental stages of thymocytes can correct the T-cell differentiation block in SCID-XI hematopoietic progenitor cells and therefore establishes a basis for further clinic al gamma c gene transfer studies. (C) 1998 by The American Society of Hematology.