Restoration of B Cell Development after Lentiviral Transduction of CD34+ Hematopoietic Cells from RAG-1 Deficient Patient.

Patients lacking expression of either RAG-1 or RAG-2 suffer from a Severe Combined Immuno-Deficiency (SCID) disease characterized by an early block in T and B lymphocytes differentiation leading to the absence of both mature lymphocyte subsets. This disease accounts for about 20% of SCID and the only curative treatment is hematopoietic stem cell transplantation, usually successful when an HLA-genoidentical donor is available. In the absence of such a donor, the success rate decreases along with the degree of HLA disparity between donor and recipient. Ex-vivo gene therapy of hematopoietic stem cells can be considered as an alternative treatment as a selective advantage of transgene-expressing cells is expected. Moreover, constitutive expression of only one of the two RAG proteins should not be harmful as concomitant expression of both genes is required for the recombination activity.

We used a lentivecteur containing the RAG-1 cDNA transgene as a therapeutic vector to transduce bone marrow CD34+ cells obtained from RAG-1 deficient patients. The transduced cells were injected into N0D-SCID mice previously irradiated (3Gy) and treated with an anti-TMb1 antibody. Ten weeks after transplantation, in all treated mice, 35±15% of the bone-marrow cells express the human CD45 marker. In this population, 24±2% co-express CD19 and IgM demonstrating that B cell differentiation capacity has been restored. We also detected some CD33+ cells attesting the presence of human myeloid progenitors cells. Altogether, these results suggest that both lymphoid and myeloid precursors have been transduced and demonstrate that gene transfer into hematopoietic cells can reconstitute B cell development in vivo.

Our data support the hypothesis that gene therapy could represent a possible alternative to bone marrow transplantation in RAG-1 deficient SCID disease.