Identifying and characterizing a stimulatory immune checkpoint in macrophage immunosurveillance

/Abstract This proposal seeks to identify and characterize critical regulators of macrophage-mediated Programmed Cell Removal (PrCR), a vital process in tumor surveillance and elimination. While immunotherapy has achieved significant breakthroughs, substantial challenges persist, including insufficient immune cell infiltration into tumors and compromised immune responses caused by the immunosuppressive tumor microenvironment (TME). Tumor-associated macrophages (TAMs), which are among the most abundant immune cell populations within the TME, represent a promising target for immunotherapy. PrCR, a process of macrophage-mediated cancer immunosurveillance, involves the recognition and phagocytosis of target cells, playing a critical role in tumor control. However, in contrast to the well-established field of T cell immune checkpoint therapies, the identification and characterization of innate immune checkpoints regulating PrCR remain limited, highlighting a significant knowledge gap. A better understanding of these innate immune regulatory mechanisms is essential to advance the development of effective PrCR-based immunotherapies. Using a high-throughput CRISPR-based screening approach, we identified a novel stimulatory innate immune checkpoint that interacts with the lymphocyte function- associated antigen 1 (LFA-1) receptor on macrophages to induce PrCR. Suppression of the stimulatory phagocytosis checkpoint in preclinical models significantly reduced PrCR and promoted tumor growth, whereas its overexpression enhanced macrophage phagocytosis and inhibited tumor development. These findings provide a compelling rationale for further investigation into the underlying mechanisms by which stimulatory phagocytosis checkpoints mediate cancer-immune interaction and regulate PrCR. In Aim 1, we will evaluate the role of such stimulatory phagocytosis checkpoint in regulating PrCR and its impact on tumor development and the efficacy of immunotherapy using preclinical models of triple-negative breast cancer (TNBC) and microsatellite-stable colorectal cancer (MSS CRC). Aim 2 will focus on elucidating the molecular mechanisms by which the stimulatory checkpoint interacts with and activates LFA-1 in macrophages. This will involve resolving high-resolution structures of the phagocytosis checkpoint complex using cryo-electron microscopy, coupled with molecular dynamics simulations, to uncover the mechanism underlying their activation and signaling. Aim 3 will investigate how activation of the LFA-1 receptor drives phagocytic machinery and reprograms macrophages for sustained PrCR. Together, this research aims to establish a previously unrecognized stimulatory phagocytosis checkpoint and elucidate the underlying mechanisms for its activation and function in PrCR. These findings will significantly enhance our understanding of macrophage-mediated cancer immunosurveillance and create new opportunities to develop innovative cancer immunotherapies that harness the tumoricidal potential of macrophages. Project Number: 1R01CA307311-01 | Fiscal Year: 2026 | NIH Institute/Center: National Cancer Institute (NCI) | Principal Investigator: Mingye Feng (+1 co-PI) | Institution: BECKMAN RESEARCH INSTITUTE/CITY OF HOPE, DUARTE, CA | Award Amount: $733,864 | Activity Code: R01 | Study Section: Basic Cancer Immunobiology Study Section[BCIB] View on NIH RePORTER: https://reporter.nih.gov/project-details/11269816