Inducible T-cell costimulator (ICOS, CD278) is a costimulatory receptor primarily expressed by activated T cells. It binds to ICOS ligand (ICOSL, CD275), which is expressed by various immune and non-immune cell types, particularly in inflamed tissues. ICOSL can also bind to osteopontin (OPN), a protein that functions both as a component of the extracellular matrix and as a soluble pro-inflammatory cytokine. Previous studies, including ours, have shown that ICOS and ICOSL play a role in skin wound healing, as mice deficient in either ICOS or ICOSL exhibit delayed healing. The aim of this study was to investigate the involvement of the ICOS/ICOSL/OPN network in skin wound healing by analyzing mice that are single knockouts for ICOS, ICOSL, or OPN, or double knockouts for ICOS/OPN or ICOSL/OPN. Our results showed that wound healing is impaired in all single knockout strains, but not in the two double knockout strains. Cellular and molecular analyses of the wound healing sites revealed that the healing defect in the single knockout strains is associated with reduced neutrophil infiltration and decreased expression of α-SMA (a marker of myofibroblasts), IL-6, TNFα, and VEGF. In contrast, the normalization of wound closure observed in the double knockout strains was primarily linked to increased vessel formation. A local treatment with recombinant ICOS-Fc improved healing in all mouse strains expressing ICOSL, but not in those lacking ICOSL, and led to a local increase in vessel formation and macrophage recruitment, predominantly of the M2 type.

Background: Paclitaxel (PTX) is an anti-neoplastic drug that inhibits not only melanoma cell proliferation but also migration and angiogenesis. ICOS-Fc is a recombinant molecule that triggers ICOS ligand (ICOSL) on tumor cells and cells of the tumor microenvironment and inhibits tumor growth, angiogenesis, and metastasis. This study investigated the effects of chitosan nanobubbles loaded with low doses of PTX and surface decorated with ICOS-Fc (ICOS-Fc-NB-PTX) in inhibiting in vitro and in vivo melanoma cell growth and invasiveness. Methods: Preparation and characterization of nanoformulations, as well as in vitro drug release studies, were carried out. Nanoformulations were studied both in vitro and in vivo. In melanoma cells, viability, migration, and invasion assays were analyzed. For the in vivo experiments, C57BL/6 Wild-type (WT) male mice were injected subcutaneously with D4M-3A cells, a murine melanoma cell line engineered to carry the BRAF^V600E mutation. After treatments, in vivo tumor growth, proliferation, and angiogenesis markers were studied. Results: In vitro tests showed the great ability of ICOS-Fc-NB-PTX to inhibit cell viability, migration, and invasion. These results were confirmed in vivo, where the tumors of mice treated with ICOS-Fc-NB-PTX displayed decreased growth accompanied by downregulation of the proliferation marker Ki-67 and reduced development of CD31⁺ blood vessels. Conclusions: In conclusion, the ICOS-Fc-NB-PTX formulation deserves to be further analyzed as a highly effective combination for melanoma, exerting multifaceted anti-tumor activities.