Alcides Chaux, Magda Zanelli, Antonio De Leo, Maria Paola Bonasoni, Sofia Canete-Portillo, Alessandra Bisagni, Valerio Copelli, Jatin Gandhi, Eleonora Zanetti, Luigi Cormio, Dario de Biase, Maurizio Zizzo, Stefania Croci, Beatrice Melli, Martina Bonacini, Francesca Sanguedolce, Alessandra Soriano, Moira Ragazzi, Andrea Palicelli, Stefano Ascani, Matteo Landriscina, Giuseppe Carrieri, Daniel M. Berney, Giacomo Santandrea, Guido Giordano, Giuditta Bernardelli, Carolina Castro Ruiz, Palicelli A., Croci S., Bisagni A., Zanetti E., De Biase D., Melli B., Sanguedolce F., Ragazzi M., Zanelli M., Chaux A., Canete-Portillo S., Bonasoni M.P., Soriano A., Ascani S., Zizzo M., Ruiz C.C., De Leo A., Giordano G., Landriscina M., Carrieri G., Cormio L., Berney D.M., Gandhi J., Copelli V., Bernardelli G., Santandrea G., and Bonacini M.
The tumor microenvironment (TME) includes immune (T, B, NK, dendritic), stromal, mesenchymal, endothelial, adipocytic cells, extracellular matrix, and cytokines/chemokines/soluble factors regulating various intracellular signaling pathways (ISP) in tumor cells. TME influences the survival/progression of prostate cancer (PC), enabling tumor cell immune-evasion also through the activation of the PD-1/PD-L1 axis. We have performed a systematic literature review according to the PRISMA guidelines, to investigate how the PD-1/PD-L1 pathway is influenced by TME and ISPs. Tumor immune-escape mechanisms include suppression/exhaustion of tumor infiltrating cytotoxic T lymphocytes, inhibition of tumor suppressive NK cells, increase in immune-suppressive immune cells (regulatory T, M2 macrophagic, myeloid-derived suppressor, dendritic, stromal, and adipocytic cells). IFN-γ (the most investigated factor), TGF-β, TNF-α, IL-6, IL-17, IL-15, IL-27, complement factor C5a, and other soluble molecules secreted by TME components (and sometimes increased in patients’ serum), as well as and hypoxia, influenced the regulation of PD-L1. Experimental studies using human and mouse PC cell lines (derived from either androgen-sensitive or androgen-resistant tumors) revealed that the intracellular ERK/MEK, Akt-mTOR, NF-kB, WNT and JAK/STAT pathways were involved in PD-L1 upregulation in PC. Blocking the PD-1/PD-L1 signaling by using immunotherapy drugs can prevent tumor immune-escape, increasing the anti-tumor activity of immune cells.