gamma c Gene Transfer in the Presence of Stem Cell Factor, FLT-3L, Interleukin-7 (IL-7), IL-1alpha , 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-Xl) is a rare humaninherited disorder in which early T and natural killer (NK) lymphocyte development is blocked. The genetic disorder results from mutations in the common c chain that participates in several cytokine receptors including the interleukin-2 (IL-2), IL-4, IL-7, IL-9, and IL-15 receptors. We have shown in a previous report that cgene transfer into SCID-Xl bone marrow (BM) cells restores efficient NKcell differentiation. In this study, we have focused on theintroduction of the c gene into SCID-Xl hematopoietic stem cellswith the goal of obtaining differentiation into mature T cells. Forthis purpose, we used the in vitro hybrid fetal thymic organ culture(FTOC) system in which a combination of cytokines consisting of stemcell factor (SCF), Flt-3L, IL-7, IL-1, and IL-15 is addedconcomitantly. In this culture system, CD34⁺ marrow cellsfrom two SCID-Xl patients were able to mature into double positiveCD4⁺ CD8⁺ cells and to a lesser degree intoCD4⁺ TCR⁺ single positive cells afterretroviral-mediated c gene transfer. In addition, examination of theoutput cell population at the TCR DJ1 locus exhibited multiplerearrangements. These results indicate that restoration of thec/JAK/STAT signaling pathway during the early developmental stagesof thymocytes can correct the T-cell differentiation block in SCID-Xlhematopoietic progenitor cells and therefore establishes a basis forfurther clinical c gene transfer studies.