Metabolic Reprogramming of Myeloid Cells to Enhance Cancer Immunotherapy - PROJECT ABSTRACT/SUMMARY Immunotherapy has revolutionized how oncologists treat cancer patients. One type of immunotherapy includes immune checkpoint inhibitors (ICIs), such as those that engage programmed cell death protein 1 (PD-1) on cytotoxic CD8+ T cells to bolster their effector functions. However, in several cancer types, single-agent therapy is moderately effective, but when combined with anti-leukocyte immunoglobulin-like receptor subfamily B member 4 (LILRB4), the combination regimen improves overall response rates (ORR). Therapeutic efficacy may be hampered by numerous barriers, including the immune suppressive tumor microenvironment (TME). Two major cellular components of the TME include myeloid-derived suppressor cells (MDSCs) and M2-like tumor associated macrophages (TAMs), which correlate with poorer survival outcomes and suppress antitumor activity of CD8+ T cells in response to these ICIs. To overcome these obstacles of immune suppression, we developed separate approaches to target MDSC ‘biogenesis’ in the bone marrow (BM) and M2-like macrophages in the TME to mitigate their production and function, and boost ICI activity in mouse models of triple-negative breast cancer (TNBC) and melanoma. Strategies that target myeloid cells are likely to improve ORRs to diverse systemic oncologic treatments, including combination therapy with anti-LILRB4; however, such strategies have yet to be fully realized in the clinical setting. Additionally, previous research identified a unique approach to target MDSCs in the BM. Specifically, the inhibition of a metabolic target, known as dihydroorotate dehydrogenase (DHODH), differentiated MDSCs and significantly enhanced anti-PD-1 monoclonal antibody (mAb) therapy in mouse models of TNBC using the pharmacologic inhibitor brequinar (BRQ); however, solid tumors persisted and retained regenerative progression. We also observed anti-LILRB4 and DHODH inhibition independently improves CD8+ T cell activity. First, it remains unclear how therapeutic efficacy can be further augmented and, secondly, it remains unclear how immunotherapy alters hematopoietic stem cell response. In Aim 1, we will focus on optimizing a tetra-therapy regimen combining BRQ and anti-LILRB4 with an ICI-based platform. We propose to build our understanding of how single and combination therapy affects cell fate lineage in the BM. Due to the complex, multi-systemic nature of solid tumors, computational, in vitro, and invertebrate models lack the required physiological complexity to accurately mimic the immune response. Therefore, animal models will help accurately elucidate our proposed research. In Aim 2, we will determine whether our therapeutic regimens affect myeloid and lymphoid lineages. Therefore, we hypothesize that adding ICI immunotherapy to a BRQ/anti-LILRB4 mAb regimen potentiates CD8+ T cell activity and achieves durable antitumor immunity. We further hypothesize, that DHODH inhibition, anti-LILRB4, anti-PD-1, and anti-cytotoxic T-lymphocyte associated protein 4 (anti-CTLA-4) separately and in combination have an impact on the BM landscape driving cell fate differentiation toward antitumor myeloid and lymphoid cell lineages.
