Abstract P104: Therapeutic targeting of TREM1 with PY159 promotes myeloid cell reprogramming and unleashes anti-tumor immunity
Authors: Mayes Erin , Juric Vladi , Binnewies Mikhail , Canaday Pamela , Lee Tian , Dash Subhadra , Pollack Joshua L. , Rudolph Joshua , Huang Vicky , Du Xiaoyan , Jahchan Nadine , Ramoth Asa J. , Mankikar Shilpa , Norng Manith , Santamaria Carlos , Baker Kevin P. , Liang Linda 
Published: December 2021

Abstract
Myeloid cells present in the tumor microenvironment can exist in immunosuppressive states that impede productive anti-tumor immunity. One strategy for targeting these immunosuppressive mechanisms is reprogramming of myeloid cells from immunosuppressive to immunostimulatory, resulting in the removal of the immune inhibition and unleashing of anti-tumor immunity. Triggering receptor expressed on myeloid cells-1 (TREM1) is an immunoglobulin superfamily cell surface receptor expressed primarily on neutrophils and subsets of monocytes and tissue macrophages. TREM1 signals through the association with DAP12 adaptor protein and mediates proinflammatory signaling, amplifies the host immune response to microbial pathogens, and has been implicated in the development of acute and chronic inflammatory diseases. TREM1 is also enriched in tumors, specifically on tumor-associated myeloid cells. To investigate the potential of TREM1 modulation as an anti-cancer therapeutic strategy, we developed PY159, an afucosylated humanized anti-TREM1 monoclonal antibody. We found that PY159 does not deplete TREM1-expressing cells, but rather acts as a TREM1 agonist. In vitro human blood assays showed that PY159 treatment upregulated activation markers on monocytes and stimulated neutrophil chemotaxis, as assayed by flow cytometry, transcriptional analysis, and in vitro migration assays. Furthermore, PY159 induced a selective set of proinflammatory cytokines and chemokines, which was dependent on PY159 afucosylation. We validated TREM1 expression in human tumors by single-cell RNAseq, immunohistochemistry, and flow cytometry, and found that it is expressed on myeloid populations, including tumor-associated neutrophils (TAN), tumor-associated macrophages (TAM), and monocytic myeloid-derived suppressive cells (mMDSC). We showed that PY159 can also induce proinflammatory cytokines and chemokines in dissociated human tumors in vitro, demonstrating that PY159 can reprogram tumor-associated myeloid cells. Finally, in vivo treatment of mice with a surrogate anti-mouse TREM1 antibody, PY159m, promoted anti-tumor efficacy in several syngeneic mouse tumor models, both as single-agent and in combination with checkpoint inhibitors, such as anti-PD-1 antibody. Together, these results demonstrate that therapeutic targeting of TREM1 with a TREM1 agonist antibody, PY159, promotes myeloid cell reprogramming and anti-tumor immunity. PY159 safety and tolerability have been demonstrated in non-human primates, and safety and efficacy of PY159 are currently being evaluated in first-in-human clinical trial (NCT04682431) including solid tumors that are resistant and refractory to standard of care therapies.
Citation Format: Erin Mayes, Vladi Juric, Mikhail Binnewies, Pamela Canaday, Tian Lee, Subhadra Dash, Joshua L. Pollack, Joshua Rudolph, Vicky Huang, Xiaoyan Du, Nadine Jahchan, Asa J. Ramoth, Shilpa Mankikar, Manith Norng, Carlos Santamaria, Kevin P. Baker, Linda Liang. Therapeutic targeting of TREM1 with PY159 promotes myeloid cell reprogramming and unleashes anti-tumor immunity [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P104.