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. Overall design: We evaluated TIE-2+ M-MDSC by flow cytometry and ANGPT2 levels  by ELISA in peripheral blood collected at baseline in 40 patients with advanced melanoma treated with anti-PD-1 therapy (ITHER cohort NCT02840058). Three main groups were distinguished according to the median rate of TIE-2+ M-MDSC (5%) and median level of ANGPT2 (1000 pg/mL) at baseline:  group 1 with ANGPT2high/ TIE-2high M-MDSC (n= 8), group 2 with ANGPT2low/ TIE-2low M-MDSC  (n=8) and third composite group (group 3) with ANGPT2high /TIE-2Low M-MDSC (n=14) and ANGPT2Low /TIE-2high M-MDSC (n=7). Antitumor T cell responses against melanoma antigens were also evaluated at baseline by IFN-y ELISpot in patients from group 1 and 2. Next, preliminary transcriptomic analysis was performed using bulk RNA sequencing of TIE-2+ and TIE-2- M-MDSC cells isolated from patients in group 1 (ANGPT2high/ TIE-2high M-MDSC) based on CD14+ HLA-DR-/low and TIE2 expression. PBMC from three patients were pooled and TIE-2+ and TIE-2- M-MDSC were sorted to form two paired samples