CD19-CAR-T Cells Bearing a KIR/PD-1-Based Inhibitory CAR Eradicate CD19+HLA-C1- Malignant B Cells While Sparing CD19+HLA-C1+ Healthy B Cells

Simple Summary CD19-targeted chimeric antigen receptor (CAR) T (CD19-CAR-T) cell therapy usually causes B cell aplasia because of on-target off-tumor toxicity. The aim of the study was to assess the concept that the introduction of an inhibitory CAR (iCAR) into CAR-T cells could alleviate the side effect of CD19-CAR-T cell therapy. The results showed that CD19-CAR-T cells with a novel KIR (killer inhibitory receptor) /PD-1 (programmed death receptor-1)-based inhibitory CAR (iKP-19-CAR-T) exhibited more naive, less exhausted phenotypes and preserved a higher proportion of central memory T cells (T-CM). Furthermore, iKP-19-CAR-T cells exerted the similar level of cytotoxicity on CD19(+)HLA-C1(-) Burkitt's lymphoma cells compared to CD19-CAR-T cells while sparing CD19(+)HLA-C1(+) healthy human B cells both in vitro and in the xenograft model. Our data demonstrates that the KIR/PD-1-based inhibitory CAR can be a promising strategy to avoid B cell aplasia caused by CD19-CAR-T cell therapy. B cell aplasia caused by on-target off-tumor toxicity is one of the clinical side effects during CD19-targeted chimeric antigen receptor (CAR) T (CD19-CAR-T) cells treatment for B cell malignancies. Persistent B cell aplasia was observed in all patients with sustained remission, which increased the patients' risk of infection. Some patients even died due to infection. To overcome this challenge, the concept of incorporating an inhibitory CAR (iCAR) into CAR-T cells was introduced to constrain the T cells response once an on-target off-tumor event occurred. In this study, we engineered a novel KIR/PD-1-based inhibitory CAR (iKP CAR) by fusing the extracellular domain of killer cell immunoglobulin-like receptors (KIR) 2DL2 (KIR2DL2) and the intracellular domain of PD-1. We also confirmed that iKP CAR could inhibit the CD19 CAR activation signal via the PD-1 domain and CD19-CAR-T cells bearing an iKP CAR (iKP-19-CAR-T) exerted robust cytotoxicity in vitro and antitumor activity in the xenograft model of CD19(+)HLA-C1(-) Burkitt's lymphoma parallel to CD19-CAR-T cells, whilst sparing CD19(+)HLA-C1(+) healthy human B cells both in vitro and in the xenograft model. Meanwhile, iKP-19-CAR-T cells exhibited more naive, less exhausted phenotypes and preserved a higher proportion of central memory T cells (T-CM). Our data demonstrates that the KIR/PD-1-based inhibitory CAR can be a promising strategy for preventing B cell aplasia induced by CD19-CAR-T cell therapy.