Engineering VHH-based chimeric antigen receptor (CAR) T cell therapy for solid tumor treatment

Abstract

Chimeric antigen receptor (CAR) T cells are a promising cancer therapeutic, as they can specifically redirect the cytotoxic function of a T cell to a chosen target of interest. CAR T cells have been successful in clinical trials against hematological cancers, but have experienced low efficacy against solid tumors for a number of reasons, including a paucity of tumor-specific antigens to target and a highly immunosuppressive solid tumor microenvironment. In chapter 2 of this thesis, we develop a strategy to target multiple solid tumor types through markers in their microenvironment. The use of single domain antibody (VHH)-based CAR T cells that recognize these markers circumvents the need for tumor-specific targets. Chapter 3 will describe methods to overcome the immunosuppressive microenvironment of solid tumors. Here, we have developed VHH-secreting CAR T cells that can modulate additional aspects of the tumor microenvironment, including the engagement of the innate immune system through secretion of a VHH against an inhibitor of phagocytosis. We show that this strategy of VHH-secretion by CAR T cells can lead to significant benefits in outcome. We also demonstrate that delivery of therapeutics by CAR T cells can improve the safety profile of the therapeutic. Chapter 4 of this thesis explores strategies to increase the targeting capacity of CAR T cells by building logic-gated CARs. Finally, chapter 5 will describe work in imaging CAR T cells specifically, longitudinally, and non-invasively through PET imaging. Our results demonstrate the flexibility of VHHs in CAR T cell engineering and the potential of VHH-based CAR T cells to target the tumor microenvironment, modulate the tumor microenvironment, and treat solid tumors.