CD19 loss by CAR T cell mediated trogoctyosis is regulated by CAR affinity

Abstract

Abstract CD19 CAR T cell therapy has entered the spotlight for the treatment of B cell lymphoma, however, relapse with CD19 negative disease is common in many subtypes of lymphoma. CD19 CAR T cells were recently shown to strip CD19 from the surface of B cell lymphoma cell lines in a process called “trogocytosis,” however, the clinical relevance of this phenomenon remains poorly defined. The purpose of this study was to determine the impact of CD19 trogocytosis on CAR T cell escape in B cell lymphoma and the importance of CAR T cell affinity to trogocytosis mediated tumor escape. We cocultured CD19 CAR T cells with primary CLL, ALL, mantle cell lymphoma and diffuse large B cell lymphoma patient material and identified rapid loss of CD19 from the surface of the malignant cells in all subtypes. CD19 was also observed to be transferred from the lymphoma cell to CD19 CAR T cells, resulting in CAR T cell autoreactivity termed “fratricide.” We then utilized a recently developed low affinity CD19 CAR to assess the importance of CAR affinity in CD19 loss by trogocytosis. Coculture of low affinity CD19 CAR T cells revealed significantly reduced loss of CD19 by trogocytosis from several ALL cell lines and primary samples when compared to high affinity CD19 CAR T cells. Finally, in vivo analysis of CAR affinity revealed increased CAR T cell efficacy and persistence by low affinity CD19 CAR T cells when compared to high affinity CD19 CAR T cells in an established ALL mouse model. Taken together, these data demonstrate that loss of CD19 by CAR T cell mediated trogocytosis occurs in many B cell malignancies and can be ameliorated by modulation of CAR affinity, providing a possible avenue for more effective CAR T cell therapies in the clinic.