Selective HLA knockdown and PD-L1 expression prevent allogeneic CAR-NK cell rejection and enhance safety and anti-tumor responses in xenograft mice

Allogeneic cellular immunotherapy exhibits promising efficacy for cancer treatment, but donor cell rejection remains a major barrier. Here, we systematically evaluate human leukocyte antigens (HLA) and immune checkpoints PD-L1, HLA-E, and CD47 in the rejection of allogeneic NK cells and identify CD8+ T cells as the dominant cell type mediating allorejection. We demonstrate that a single gene construct that combines an shRNA that selectively interferes with HLA class I but not HLA-E expression, a chimeric antigen receptor (CAR), and PD-L1 or single-chain HLA-E (SCE) enables the one-step construction of allogeneic CAR-NK cells that evade host-mediated rejection both in vitro and in a xenograft mouse model. Furthermore, CAR-NK cells overexpressing PD-L1 or SCE effectively kill tumor cells through the upregulation of cytotoxic genes and reduced exhaustion and exhibit a favorable safety profile due to the decreased production of inflammatory cytokines involved in cytokine release syndrome. Thus, our approach represents a promising strategy in enabling "off-the-shelf" allogeneic cellular immunotherapies. The use of donor-derived CAR-NK cells is limited by CD8 T cell-mediated allorejection. Here, the authors describe a one-step approach, based on selective HLA knockdown and overexpression of PD-L1, that allows allogeneic modified CAR-NK cells to escape rejection by the host immune system while exhibiting enhanced anti-tumor activity and safety in preclinical mouse models.