Lentiviral Gene Therapy for Artemis-Deficient SCID

Abstract

Background: The DNA-repair enzyme Artemis is essential for rearrangement of T- and B-cell receptors. Mutations in DCLRE1C, which encodes Artemis, cause Artemis-deficient severe combined immunodeficiency (ART-SCID), which is poorly responsive to allogeneic hematopoietic-cell transplantation.

Methods: We carried out a phase 1-2 clinical study of the transfusion of autologous CD34+ cells, transfected with a lentiviral vector containing DCLRE1C, in 10 infants with newly diagnosed ART-SCID. We followed them for a median of 31.2 months.

Results: Marrow harvest, busulfan conditioning, and lentiviral-transduced CD34+ cell infusion produced the expected grade 3 or 4 adverse events. All the procedures met prespecified criteria for feasibility at 42 days after infusion. Gene-marked T cells were detected at 6 to 16 weeks after infusion in all the patients. Five of 6 patients who were followed for at least 24 months had T-cell immune reconstitution at a median of 12 months. The diversity of T-cell receptor β chains normalized by 6 to 12 months. Four patients who were followed for at least 24 months had sufficient B-cell numbers, IgM concentration, or IgM isohemagglutinin titers to permit discontinuation of IgG infusions. Three of these 4 patients had normal immunization responses, and the fourth has started immunizations. Vector insertion sites showed no evidence of clonal expansion. One patient who presented with cytomegalovirus infection received a second infusion of gene-corrected cells to achieve T-cell immunity sufficient for viral clearance. Autoimmune hemolytic anemia developed in 4 patients 4 to 11 months after infusion; this condition resolved after reconstitution of T-cell immunity. All 10 patients were healthy at the time of this report.

Conclusions: Infusion of lentiviral gene-corrected autologous CD34+ cells, preceded by pharmacologically targeted low-exposure busulfan, in infants with newly diagnosed ART-SCID resulted in genetically corrected and functional T and B cells. (Funded by the California Institute for Regenerative Medicine and the National Institute of Allergy and Infectious Diseases; ClinicalTrials.gov number, NCT03538899.).

Figure 1.. Lymphocytes and Lymphocyte Subsets after Infusion of Autologous Lentiviral-Transduced CD34+ Cells.

Shown are cells per cubic millimeter of peripheral blood. The values that were used to define T-cell immune reconstitution (dashed lines) are as follows: CD3 T cells, more than 1000 per cubic millimeter; CD4 T cells, more than 500 per cubic millimeter; CD8 T cells, more than 300 per cubic millimeter; and naive CD4 T cells, more than 200 per cubic millimeter.^, The mean number of regulatory T cells for children 10 to 48 months of age is 60 per cubic millimeter (range, not available).

Figure 2.. Diversity of T-Cell Receptor β-Chain Variable Sequences at Baseline and after Infusion of CD34+ Gene-Corrected Cells.

Panel A shows hierarchical tree maps of sequence diversity in Patients ART007 and ART009 from baseline to 36 months after infusion. Panel B shows serial measurements of scores on the Shannon index (the range includes all numbers >0), scores on the equitability index (range, 0 to 1), and scores for information density (range, 0 to 1); for all three scales, higher values indicate greater diversity. Scores on all three scales increased during the first 6 to 12 months after infusion, and these increases were then sustained. Details are provided in Figure S5 in the Supplementary Appendix.

Figure 3.. Gene Marking in Peripheral Blood Cells after Infusion of Autologous Lentiviral-Transduced CD34+ Cells.

Subpopulations of peripheral-blood mononuclear cells were sorted after staining for the following cell-surface markers: T cells, CD3+; B cells, CD19+; myeloid cells, CD14+/CD15+; and natural killer cells, CD3−/CD19−/CD56+.