Genetic Mutation and Epigenetic Silencing Drive Antigen-Negative Relapse in CD7 CAR T-Treated T-cell Lymphoid Malignancies.
UNLABELLED: CD7 is a promising target for chimeric antigen receptor (CAR) T-cell therapy in T-cell lymphoid malignancies; however, antigen loss-mediated relapse has emerged as a major challenge. In this study, we systematically analyzed the genetic and epigenetic alterations of paired specimens (pretreatment and relapsed) from 10 patients with T-cell lymphoma/leukemia receiving CD7 CAR T cells. Overall, we identified three distinct mechanisms underlying CD7 loss: first, frameshift insertion (patient 4; c.164dupG:p.R55fs) or deletion (patient 7; c.122delG:p.G41Efs*19) resulting in truncation of the CD7 transmembrane domain in two of 10 patients; second, hypermethylation of the CD7 promoter in seven of 10 patients without CD7 mutation; third, simultaneous occurrence of promoter region hypermethylation and multiple in-frame mutations with predicted functional interference in one of 10 patients (patient 2). Collectively, these findings demonstrate that both clonal heterogeneity and epigenetic plasticity drive antigen-negative relapse in T-cell lymphoid malignancies under the selective pressure of CD7 CAR T-cell therapy. SIGNIFICANCE: Understanding mechanisms of antigen-negative relapse is critical for developing effective CD7-targeting CAR-T therapies against T-cell lymphoid malignancies. Our study identifies both genetic truncation mutations and epigenetic silencing as contributors to CD7-negative relapse. Monitoring and preventing these events is warranted to improve treatment outcomes.