Expression of TAM-R in Human Immune Cells and Unique Regulatory Function of MerTK in IL-10 Production by Tolerogenic DC.

Tumor-infiltrating myeloid cells are a key component of the immune infiltrate often correlated with a poor prognosis due to their capacities to sustain an immunosuppressive environment. Among membrane receptors implicated in myeloid cell functions, Tyro3, Axl, and MerTK, which are a family of tyrosine kinase receptors (TAM-R), have been described in the regulation of innate cell functions. Here, we have identified MerTK among TAM-R as the major marker of both human M2 macrophages and tolerogenic dendritic cells (DC). In situ, MerTK expression was found within the immune infiltrate in multiple solid tumors, highlighting its potential role in cancer immunity. TAM-R ligands Gas6 and PROS1 were found to be constitutively produced by myeloid cells in vitro. Importantly, we describe a novel function of MerTK/PROS1 axis in the regulation of IL-10 production by tolerogenic DC. Finally, the analysis of TAM-R expression within the lymphoid compartment following activation revealed that MerTK, but not Axl or Tyro3, is expressed on activated B lymphocytes and regulatory T cells, as well as CD4+ and CD8+ T cells. Thus, our findings deepen the implication of MerTK in the regulation of myeloid cell-mediated immunosuppression and identified new cellular targets expressing MerTK that could participate in the antitumor immune response.

Anti-CD160, Alone or in Combination With Bevacizumab, Is a Potent Inhibitor of Ocular Neovascularization in Rabbit and Monkey Models.

Purpose: To assess the efficacy of the murine first-in-class CL1-R2 monoclonal antibody (mAb) targeting human CD160 (alone or in combination with bevacizumab) by using the rabbit corneal neovascularization (CNV) model, and determine the safety and efficacy of ELB01101, a novel CL1-R2-derived humanized IgG4 mAb, in a monkey model of choroidal neovascularization (ChNV). Methods: Comparison of effect of CL1-R2, bevacizumab, or aflibercept or IgG1 (control) injections in early and late treatment schemes on evolution of VEGF- or FGF2-induced rabbit CNV was performed. In the combination setting, bevacizumab was coinjected with different doses of CL1-R2. ELB01101 or vehicle was administered intravitreally in monkeys after laser-induced ChNV. Individual laser-induced lesions were semiquantitatively graduated by using fluorescein angiography to determine leakage. Results: In the rabbit model, early and late treatments with CL1-R2 significantly decreased both area and length of CNV neovessels. The effect was as potent as produced with anti-VEGF comparators. When combined with bevacizumab, an additive effect of CL1-R2 was measured at all doses tested. In the ChNV model, on day 29, eyes treated with ELB01101 showed a statistically significant reduction in clinically relevant lesions compared to vehicle-treated eyes (∼50%; χ2 test, P = 0.032001). Conclusions: The additive effects of anti-CD160 and bevacizumab in the CNV model suggest that these compounds could act via different pathways, opening new therapeutic pathways for cotargeted or combination therapies. In the ChNV model, ELB01101 was well tolerated and prevented approximately 50% of clinically relevant lesions, validating CD160 targeting as a safe approach for treatment of retinal diseases in the most relevant animal model of wet AMD.

A unique anti-CD115 monoclonal antibody which inhibits osteolysis and skews human monocyte differentiation from M2-polarized macrophages toward dendritic cells.

Cancer progression has been associated with the presence of tumor-associated M2-macrophages (M2-TAMs) able to inhibit anti-tumor immune responses. It is also often associated with metastasis-induced bone destruction mediated by osteoclasts. Both cell types are controlled by the CD115 (CSF-1R)/colony-stimulating factor-1 (CSF-1, M-CSF) pathway, making CD115 a promising target for cancer therapy. Anti-human CD115 monoclonal antibodies (mAbs) that inhibit the receptor function have been generated in a number of laboratories. These mAbs compete with CSF-1 binding to CD115, dramatically affecting monocyte survival and preventing osteoclast and macrophage differentiation, but they also block CD115/CSF-1 internalization and degradation, which could lead to potent rebound CSF-1 effects in patients after mAb treatment has ended. We thus generated and selected a non-ligand competitive anti-CD115 mAb that exerts only partial inhibitory effects on CD115 signaling without blocking the internalization or the degradation of the CD115/CSF-1 complex. This mAb, H27K15, affects monocyte survival only minimally, but downregulates osteoclast differentiation and activity. Importantly, it inhibits monocyte differentiation to CD163(+)CD64(+) M2-polarized suppressor macrophages, skewing their differentiation toward CD14(-)CD1a(+) dendritic cells (DCs). In line with this observation, H27K15 also drastically inhibits monocyte chemotactic protein-1 secretion and reduces interleukin-6 production; these two molecules are known to be involved in M2-macrophage recruitment. Thus, the non-depleting mAb H27K15 is a promising anti-tumor candidate, able to inhibit osteoclast differentiation, likely decreasing metastasis-induced osteolysis, and able to prevent M2 polarization of TAMs while inducing DCs, hence contributing to the creation of more efficient anti-tumor immune responses.