Aiming to render the solid tumor microenvironment more permissive to CAR T therapy, Xie et al. engineered CAR T cells to secrete VHH “nanobodies” – single-domain antibody fragments. Secreted anti-CD47 (”don’t eat me” signal) VHH enhanced melanoma control mediated by PD-L1-targeted CAR T cells plus anti-TRP1 antibody. CAR T cells producing anti-PD-L1 or anti-CTLA-4 VHH reduced exhaustion marker expression in vitro and improved persistence and expansion in vivo. CAR T cells secreting an anti-CD47 nanobody-Fc fusion, to also drive phagocytosis, reduced systemic toxicities compared to free nanobody-Fc, and increased tumor immune infiltration.
Contributed by Alex Najibi
Chimeric antigen receptor (CAR) T cell therapy is effective in the treatment of cancers of hematopoietic origin. In the immunosuppressive solid tumor environment, CAR T cells encounter obstacles that compromise their efficacy. We developed a strategy to address these barriers by having CAR T cells secrete single-domain antibody fragments (VHHs or nanobodies) that can modify the intratumoral immune landscape and thus support CAR T cell function in immunocompetent animals. VHHs are small in size and able to avoid domain swapping when multiple nanobodies are expressed simultaneously, features that can endow CAR T cells with desirable properties. The secretion of an anti-CD47 VHH by CAR T cells improves engagement of the innate immune system, enables epitope spreading, and can enhance the anti-tumor response. CAR T cells that secrete anti-PD-L1 or anti-CTLA-4 nanobodies show improved persistence and demonstrate the versatility of this approach. Furthermore, local delivery of secreted anti-CD47 VHH-Fc fusions by CAR T cells at the tumor site limits their systemic toxicity. CAR T cells can further be engineered to simultaneously secrete multiple modalities, allowing for even greater tailoring of the anti-tumor immune response.
Author Info: (1) Massachusetts Institute of Technology. (2) Division of Gastroenterology, Department of Medicine, Massachusetts General Hospital. (3) Department of Cancer Immunology and Virolog
Author Info: (1) Massachusetts Institute of Technology. (2) Division of Gastroenterology, Department of Medicine, Massachusetts General Hospital. (3) Department of Cancer Immunology and Virology, Dana-Farber Cancer Institute. (4) Program in Cellular and Molecular Medicine, Children's Hospital Boston. (5) Boston Children's Hospital. (6) Biological Engineering, Massachusetts Institute of Technology. (7) Program in Cellular and Molecular Medicine, Boston Children's Hospital hidde.ploegh@childrens.harvard.edu.
