Critical Variables Affecting Clinical-Grade Production of the Self-Inactivating Gamma-Retroviral Vector for the Treatment of X-linked Severe Combined Immunodeficiency

In two earlier trials, patients with X-linked Severe Combined Immune Deficiency (SCID-X1) were successfully cured following gene therapy with a gamma-retroviral vector (gRV) expressing the common gamma chain of the interleukin-2 receptor (IL2RG). We have previously demonstrated that GMP-grade SIN gRV can be produced at high titers using transient transfection in bioreactors (van der Loo et al, Gene Ther 2011). Herein we report on the large-scale production of a clinical-grade SIN IL2RG gRV pseudotyped with the Gibbon Ape Leukemia Virus envelope for a new gene therapy trial for SCID-X1, and highlight variables that were found to be critical for transfection-based large-scale SIN gRV production. The vector was certified and released for treatment of SCID-X1 in a multi-center international phase I/II trial which is currently recruiting patients in Paris, London, Los Angeles, Boston and Cincinnati.