Abstract 3918: Targeting MARCO in combination with anti-CTLA4 leads to enhanced melanoma regression and immune cell infiltration via macrophage reprogramming
Authors: Takahashi Hidenori , Perez-Villarroel Patricio , Falahat Rana , Mulé James J. 
Published: March 2024

Tumor-associated macrophages (TAM) are known to suppress responses to conventional therapeutics and the presence of TAM is generally related to poor prognosis in various cancers. Therefore, depletion of TAM has been one of the main strategies to break the ceiling of efficacy in cancer treatment. However, to date, TAM depletion strategies have not been successful in clinical trials1. Here, we introduce an approach to target TAM by employing Macrophage Receptor with Collagenous Structure (MARCO), a class A scavenger receptor, as a novel immune checkpoint. Previously, we showed MARCO to be the most upregulated mRNA in murine and human dendritic cells following their uptake of dead tumor cells (TP-DC)2. We also showed ex vivo treatment of TP-DC with anti-MARCO mAb (ED31) led to enhanced anti-tumor responses in vivo3,4. The aim of this current study was to explore whether targeting MARCO using ED31 could improve the efficacy of an immune checkpoint inhibitor in murine models of melanoma. In C57BL/6 mice with B16F10 tumors, adding ED31 to anti-CTLA4 mAb (αCTLA4) resulted in enhanced tumor regression and longer survival (p=0.001, p&lt;0.05 vs αCTLA4 monotherapy; p&lt;0.05, p&lt;0.01 vs ED31 monotherapy, respectively). To explore the immune mechanism of ED31 with αCTLA4, we focused on the tumor microenvironment (TME) by flow cytometry. TME immune-profiling consistently revealed that one time treatment with this combination resulted in a rapid increase in the number of tumor infiltrating lymphocytes (TIL) including CD8+T (2.8-fold) and CD4+T cells (2.9-fold), NK cells (2.5-fold), activated CD11c+DC (2.2-fold) and F4/80+Mφ (2.5-fold), compared to αCTLA4 monotherapy (all with p&lt;0.0001; vs αCTLA4 monotherapy, vs ED31 monotherapy, vs control, respectively). As measured by chemokine production using murine bone marrow-derived, in vitro M-CSF induced Mφ phenotypes (M1: polarized by IFNγ and LPS, M2: polarized by IL4, TAM-like Mφ: polarized by a supernatant from B16F10 cell line culture), ED31 exposure switched the pattern of chemokine productions from M2 and TAM-like Mφ into an M1 pattern. In vivo depletion of each immune cell type had a diminishing effect on the treatment efficacy (p&lt;0.001 for CD8 depletion, p=0.01 for CD4 depletion, p&lt;0.01 for NK1.1 depletion). However, Mφ depletion had a more profound impact by completely abrogating the anti-tumor efficacy and the associated survival benefit, in addition to completely reversing the increase in TIL infiltration and canceling the increase of M1 chemokines in vivo (all with p&lt;0.05 vs Mφ depletion). These preclinical data support the proof-of-concept that a combination strategy of targeting MARCO along with αCTLA4 can lead to enhanced anti-tumor responses through utilizing TAMs rather than their depletion. 1 Immunity 2023;56:2188. 2 J Immunol 2003;171:2879. 3 Cancer Immunol Immunother 2010;59:875. 4 PLoS One 2013;8:e67795.

Citation Format: Hidenori Takahashi, Patricio Perez-Villarroel, Rana Falahat, James J. Mulé. Targeting MARCO in combination with anti-CTLA4 leads to enhanced melanoma regression and immune cell infiltration via macrophage reprogramming [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3918.