Engineering T Cells to Stimulate Endogenous Antitumor Immunity

Adoptive cell therapy (ACT) is an immunotherapy that employs living immune cells to target and destroy cancer cells. However, the inhibitory tumor microenvironment features several obstacles to antitumor immunity, including hypoxia, inhibitory ligands, and altered immune cell programming, supporting conversion of anti- to pro-tumorigenic cell types. We developed T cell engineering strategies to address multiple inhibitory mechanisms and enhance ACT efficacy. In the first approach, we developed Fas switch receptors that convert a death signal to a costimulatory signal for T cells. Here we show that this approach can “supercharge” T cells to overcome hypoxia barriers and significantly improve survival in murine models of cancer. Another obstacle to ACT efficacy is the induction of pro-tumor macrophages that promote resistance to therapy and exhibit reduced phagocytosis. Pro-tumor macrophages show significant plasticity and can be polarized to antitumor programming with costimulatory signals, increasing phagocytosis of tumor cells and recruitment of other antitumor immune cells. One such costimulatory signal, CD40, has been explored to induce antitumor myeloid immunity and agonist CD40 antibodies have been tested in clinical trials. However, enthusiasm for agonist antibody therapies has been dampened by dose-limiting toxicities, inadequate pharmacokinetics and tissue penetration, and the non-tumor targeted delivery of the antibody modality. We sought to develop a T cell engineering strategy to deliver CD40 costimulatory signals to the AML-BM and reprogram inhibitory macrophages. We engineered membrane-bound fusion proteins, CD40L Dual Costimulatory Receptors (DCR), that pair the CD40L ectodomain costimulatory endodomains. We advanced leading CD40L DCRs to proof-of-concept in vivo testing in murine tumor models and found that CD40L DCR-T cell therapy significantly enhanced therapeutic outcomes. We also observed a significant increase in antitumor macrophages as compared to control T cells, suggesting that CD40L DCR expression indeed induced macrophage conversion. Our long-term objective is to develop strategies and define mechanisms to employ both innate and adaptive immunity to provide a diverse and durable antitumor immune response against cancer, and support clinical translation.

Learning Objectives:

1. Summarize assays to evaluate T cell antitumor function.

2. Describe tumor microenvironment inhibitory mechanisms.

3. Explain how CD40 signaling alters immune cell programming.