Project Summary/Abstract
Recent breakthroughs in tumor immunology led to the development of cancer immunotherapies which have been
successfully applied to a range of human cancers. Among the immune cellularity in the tumor microenvironment,
tumor-associated macrophages (TAMs) are often the most abundant immune cells and play critical roles in tumor
immunosurveillance. Recent progress demonstrates that cancer cells upregulate anti-phagocytic “don’t eat me”
signals as self-protective mechanisms against macrophage surveillance. When these signals are blocked,
macrophages are capable of eliminating various malignant hematopoietic and solid tumor cells through cellular
phagocytosis. Inducing cancer cell phagocytosis demonstrates significant anticancer effects and therapeutic
potential in preclinical models and recent clinical trials. Tyrosine phosphorylation and dephosphorylation,
mediated by protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs), is an essential
mechanism underlying signal transduction involved in multiple critical biological functions including the regulation
of immune responses. PTPs such as SHP1/SHP2 have been shown to be involved in the inhibitory signaling in
macrophages and T cells for deactivating immune activities. Despite its importance, however, the underlying
molecular mechanisms of macrophage-mediated cancer cell phagocytosis are still unclear, and the critical
components mediating this process in addition to cell surface receptors have mainly remained unidentified. In
this proposal, we are focusing on the functions and roles of PTPs in macrophage immunosurveillance. Through
a CRISPR-based loss-of-function screening in macrophages, we have identified non-receptor PTP candidates
that negatively regulate phagocytosis. When their expression is suppressed, the phagocytic ability of
macrophages toward cancer cells is significantly enhanced. Our central hypothesis is that such PTPs function
as inhibitory regulators of macrophage-mediated cancer cell phagocytosis, and thus their inhibition can promote
the efficacy of macrophage phagocytosis-based cancer immunotherapy. In this proposal, we will first investigate
to what extent the deficiency of inhibitory PTPs in macrophages promotes the efficacy of cancer cell phagocytosis
with multiple preclinical models. Second, we will dissect the molecular mechanism of how deficiency of PTPs in
macrophages augments cancer cell phagocytosis. Finally, we will examine the anticancer efficacy of suppressing
PTPs in macrophages with in vivo cancer models. The completion of this study will identify and establish the
roles of new regulators of cancer cell phagocytosis and inspire the development of new therapeutic strategies to
enhance the efficacy of macrophage-based cancer immunotherapy.