TIE-2 expressing monocytic myeloid-derived suppressor cells are involved in resistance to anti-PD-1 mediates by angiopoietin 2 in melanoma patients

Immunotherapy using immune checkpoint inhibitors (ICI) has revolutionized the management of melanoma. Although the anti-PD-1 antibodies induce a 40% objective response rate (ORR) in advanced melanoma patients, the majority of patients have a primary resistance or develop a secondary resistance (Robert et al. 2015). Many resistance mechanisms have been described including the loss of the expression of class I MHC, the alteration of antigen presentation, JAK/STAT pathway mutation, or the overexpression of another inhibitory molecule (LAG-3, TIM-3, …). It was also known that immunosuppressive cells such as myeloid-derived Suppressor Cells (MDSC) can negatively impact the efficacy of anti-PD-1 therapy (Limagne et al. 2019). MDSCs are a group of immunosuppressive heterogenous cells found in many cancers that inhibit antitumor T cell functions by several mechanisms. We previously described in lung cancer a novel subpopulation of monocytic MDSC (M-MDSC) overexpressing TIE-2 that mediate inhibition of antitumor T cell responses after angiopoietin-2 (ANGPT2) exposure. Furthermore, we found, that a high level of circulating TIE-2+ M-MDSC and ANGPT2 in melanoma patients is associated with a poor prognosis by inhibiting anti-melanoma T-cell responses (Marguier et al. 2022).TIE-2 is a tyrosine kinase with immunoglobulin and EGF homology domains. This receptor was mainly expressed by endothelial cells but can be expressed by tumor cells and some immune cells such as monocytes. TIE-2 binds to the pro-angiogenic factor ANGPT2 which is involved in tumor neo-angiogenesis. Recent findings in melanoma also showed the implication of ANGPT2 in resistance to anti-PD-1 therapy by promoting the exclusion of T cells (Park et al. 2023). Thus, we assumed that TIE-2+ M-MDSC would be involved in this negative impact of ANGPT2 on anti-PD-1 therapy.