Timothy Davis

Introduction.  Non-Hodgkin Lymphoma (NHL) is a cancer of lymphocytes that has 60-70% survival rate and a poor prognosis in patients with relapsed or refractory disease.^1,2 Therefore, new therapeutic approaches are urgently needed.^1,2 The vast majority, 85-90%, of NHLs have B-cell origin^1,2 and express the antigens CD19 or CD20.^1,3  Chimeric Antigen Receptor (CAR) T-cell Therapy is an antigen specific form of adoptive cell therapy.^4,5,6  The CAR protein consists of a single chain variable fragment (ScFv) derived from the variable portions of an IgG, a hinge and transmembrane domain, and an intracellular signaling domain.^4,5,6  On recognition of the antigen, the CAR protein activates the T-cells leading to lysis of the target cell.^4,5,6  Antigen escape is a major mechanism of relapse post CAR-T therapy in which the selective pressure of the CARs against the target antigen leads to the survival and growth of antigen negative lymphoma.⁷  Bispecific CARs are designed to overcome antigen escape by having two different ScFv portions each targeting a separate antigen.^4,5  Methods.  Bispecific CAR constructs targeting both CD19 and CD20 were transduced into T-cells and cocultured overnight with various lymphoma cell lines to assess antigen specific cytotoxicity via flow cytometry.⁴  Next, both bispecific and monospecific CARs were cocultured with B lymphoblast Raji cells at a low effector to target cell ratio to compare antigen escape via flow cytometry.⁴  CAR T-cells were then injected into immunodeficient NSG mice previously injected with Luciferase expressing Raji cells to assess therapeutic efficacy in vivo.⁴  In a phase 1 clinical trial 22 patients with lymphoma refractory to chemotherapy were selected to receive bispecific CAR treatments.⁸  PET/CT scans were used to assess therapeutic responses and lymphomas were analyzed by flow cytometry to asses presence or absence of target antigen.⁸  Results.  Bispecific CAR constructs demonstrated cytotoxic efficacy against lymphoma cell lines expressing either CD19, CD20, or both (p<0.0001).⁴  Significantly less antigen loss was observed in Raji cells cultured with bispecific CARs compared with monospecific CARs (p<0.05), suggesting bispecific CARs avoid antigen escape.⁴  Bispecific CARs showed cytotoxic efficacy in Raji tumor xenograft mouse models (p<0.001).⁴  In patients, overall response rate was 82% (n=18), with 64% (n=14) in complete remission.⁸  Bispecific treatment was effective  in patients with lymphomas expressing either CD19, CD20, or both.⁸  Conclusion.  Preclinical and clinical studies have demonstrated improved efficacy of bispecific CAR T-cell therapy for treating lymphomas expressing either or both target antigens.^4,8  Studies have also demonstrated that bispecific CARs avoid antigen escape by avoiding a selective pressure against a single antigen.^4,8 Overall the evidence suggests that bi-specific CAR-T therapy can effectively reduce the risk of antigen escape relapse in lymphoma patients.^4,8

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8. Shah NN, Johnson BD, Schneider D, et al. Bispecific anti-CD20, anti-CD19 CAR T cells for relapsed B cell malignancies: a phase 1 dose escalation and expansion trial. Nat Med. 2020;26(10):1569-1575. doi:10.1038/s41591-020-1081-3