γc Gene transfer into SCID X1 patients' B-cell lines restores normal high-affinity interleukin-2 receptor expression and function

Abstract

SCID X1 is characterized by faulty T-cell and natural killer cell differentiation caused by mutation of the γc chain gene encoding a number of multiple cytokine receptors (interleukin-2 [IL-2], IL-4, IL-7, IL-9, and IL- 15 receptors). To assess the feasibility of inducing long-term expression and function of the γc chain, Epstein-Barr virus (EBV)-transformed B-cell lines from two patients with SCID X1 were transduced with a Moloney-derived retroviral vector containing the γc chain cDNA. The viral LTR was used as the promoter. Immediately after two cycles of coculture with the Ψcrip clone producing the MEG(B2)-γc cDNA vector, γc expression, assessed by detection of the mRNA and membrane protein expression, was found in 15% to 20% of cells. The degree of membrane expression was similar to that in control EBV- B cells. Expression increased steadily over 6 months, becoming detectable in 100% of cells, and remained stable thereafter for a total of 9 months, reflecting positive selection of transduced cells. A study of provirus integration sites showed multiple integration. The expressed γc was functional, because it restored high-affinity IL-2 receptor binding, IL-2 endocytosis, and IL-2-triggered phosphorylation of JAK-3 tyrosine kinase. Similar results were obtained with the two B-cell lines. These results show that efficient γc gene transfer into B-cells lacking functional γc is feasible and results in strong and stable expression of a functional γc chain, apparently conferring a selective growth advantage in culture. Further in vitro studies of γc gene transfer into γc- hematopoietic progenitors are being conducted to assess the feasibility of correcting lymphocyte differentiation defects.