Point mutation in CD19 facilitates immune escape of B cell lymphoma from CAR-T cell therapy

BACKGROUND: Tumor relapse due to mutation in CD19 can hinder the efficacy of chimeric antigen receptor (CAR)-T cell therapy. Herein, we focused on lymphoma patients whose B cells exhibited a point mutation in CD19 of B cells after CAR-T cell infusion. METHODS: The CAR-T and CD19(+) B cells from peripheral blood or bone marrow were assessed using flow cytometry. Genome sequencing was conducted to identify the molecular characteristics of CAR-T and CD19(+) B cells from pre-relapse and postrelapse samples. CD19 in CARs comprising single chain fragments variable (scFV) antibody with FMC63 or 21D4 was constructed. The cytotoxic efficacy of CAR-T cells was also evaluated via in vitro and in vivo experiments. RESULTS: A patient with high-grade B cell lymphoma exhibited complete response, but the lymphoma relapsed in her left breast at 6 months after CD19 CAR (FMC63)-T cell infusion. A mutation was found in exon 3 of CD19 (p.163. R-L) in malignant B cells of the patient. In two lymphoma patients who exhibited resistance to CAR-T cell therapy, a mutation was detected in exon 3 of CD19 (p.174. L-V). Functional analysis revealed that FMC63 CAR-T cells exhibited antitumor ability against wild-type CD19(+) cells but were unable to eradicate these two types of mutated CD19(+) cells. Interestingly, 21D4 CAR-T cells were potentially capable of eradicating these mutated CD19(+) cells and exhibiting high antitumor capacity against CD19(+) cells with loss of exon 1, 2, or 3. CONCLUSIONS: These findings suggest that point mutation can facilitate immune escape from CAR-T cell therapy and that alternative CAR-T cells can effectively eradicate the mutated B cells, providing an individualized therapeutic approach for lymphoma patients showing relapse.