Targeting PD-L1 in solid cancer with myeloid cells expressing a CAR-like immune receptor.

Introduction: Solid cancers Myeloid cells are prevalent in solid cancers, but they frequently exhibit an anti-inflammatory pro-tumor phenotype that contribute to the immunosuppressive tumor microenvironment (TME), which hinders the effectiveness of cancer immunotherapies. Myeloid cells' natural ability of tumor trafficking makes engineered myeloid cell therapy an intriguing approach to tackle the challenges posed by solid cancers, including tumor infiltration, tumor cell heterogenicity and the immunosuppressive TME. One such engineering approach is to target the checkpoint molecule PD-L1, which is often upregulated by solid cancers to evade immune responses. Method: Here we devised an adoptive cell therapy strategy based on myeloid cells expressing a Chimeric Antigen Receptor (CAR)-like immune receptor (CARIR). The extracellular domain of CARIR is derived from the natural inhibitory receptor PD-1, while the intracellular domain(s) are derived from CD40 and/or CD3ζ. To assess the efficacy of CARIR-engineered myeloid cells, we conducted proof-of-principle experiments using co-culture and flow cytometry-based phagocytosis assays in vitro. Additionally, we employed a fully immune-competent syngeneic tumor mouse model to evaluate the strategy's effectiveness in vivo. Result: Co-culturing CARIR-expressing human monocytic THP-1 cells with PD-L1 expressing target cells lead to upregulation of the costimulatory molecule CD86 along with expression of proinflammatory cytokines TNF-1α and IL-1ß. Moreover, CARIR expression significantly enhanced phagocytosis of multiple PD-L1 expressing cancer cell lines in vitro. Similar outcomes were observed with CARIR-expressing human primary macrophages. In experiments conducted in syngeneic BALB/c mice bearing 4T1 mammary tumors, infusing murine myeloid cells that express a murine version of CARIR significantly slowed tumor growth and prolonged survival. Conclusion: Taken together, these results demonstrate that adoptive transfer of PD-1 CARIR-engineered myeloid cells represents a promising strategy for treating PD-L1 positive solid cancers.

Targeting MerTK decreases efferocytosis and increases anti-tumor immune infiltrate in prostate cancer.

The prostate cancer tumor microenvironment (TME) is comprised of many cell types that can contribute to and influence tumor progression. Some of the most abundant prostate cancer TME cells are macrophages, which can be modeled on a continuous spectrum of M1-like (anti-tumor macrophages) to M2-like (pro-tumor macrophages). A function of M2-like macrophages is efferocytosis, the phagocytosis of apoptotic cells. Based on literature from other models and contexts, efferocytosis further supports the M2-like macrophage phenotype. MerTK is a receptor tyrosine kinase that mediates efferocytosis by binding phosphatidylserine on apoptotic cells. We hypothesize efferocytosis in the prostate cancer TME is a tumor-promoting function of macrophages and that targeting MerTK-mediated efferocytosis will slow prostate cancer growth and promote an anti-tumor immune infiltrate. The aims of this study are to measure efferocytosis of prostate cancer cells by in vitro human M1/M2 macrophage models and assess changes in the M2-like, pro-tumor macrophage phenotype following prostate cancer efferocytosis. Additionally, this study aims to demonstrate that targeting MerTK decreases prostate cancer efferocytosis and promotes an anti-tumor immune infiltrate. We have developed methodology using flow cytometry to quantify efferocytosis of human prostate cancer cells using the LNCaP cell line. We observed that M2 macrophages efferocytose the LNCaP cell line more than M1 macrophages. Following efferocytosis of LNCaP cells by M2 human monocyte-derived macrophages (HMDMs), we observed an increase in the M2-like, pro-tumor phenotype by flow cytometry cell surface marker analysis. By qRT-PCR, flow cytometry, and Western blot, we detected greater MerTK expression in M2 than M1 macrophages. Targeting MerTK with antibody Mer590 decreased LNCaP efferocytosis by M2 HMDMs, establishing the role of MerTK in prostate cancer efferocytosis. In the prostate cancer mouse model hi-myc, Mertk KO increased anti-tumor immune infiltrate including CD8 T cells. These findings support targeting MerTK-mediated efferocytosis as a novel therapy for prostate cancer.