The Proliferative Role of Immune Checkpoints in Tumors: Double Regulation

Simple Summary Cancer remains a serious health problem owing to its high morbidity and mortality. Immunotherapy, represented by anti-programmed death-1D1/anti-PD-Ligand 1 treatments, has become one of the most important methods for cancer treatment. However, there are still some challenges in this method such as low response rate, limited therapeutic targets, and unclear underlying molecular mechanisms of immune checkpoints. Thus, in this review, we aim to focus on the proliferative role of fifteen immune checkpoints that occur in various tumors. This has provided more clarity on the functions and mechanisms of immune checkpoints in tumors, especially on their proliferation role. This may provide better insights in developing more therapeutic targets and strategies in tumor immunotherapy. Cancer remains a serious social health problem, and immunotherapy has become the major treatments in tumor treatment. Additionally, improving the efficiency and safety of treatment is necessary. Further, more therapy targets are warranted for future tumor treatments. In this review, in addition to examining the currently recognized role of immune regulation, we focus on the proliferative role of 15 immune checkpoints in various tumors, including PD1, PD-L1, FGL1, CD155, CD47, SIRP alpha, CD276, IDO1, SIGLEC-15, TIM3, Galectin-9, CD70, CD27, 4-1BBL, and HVEM. We managed to conclude that various immune checkpoints such as PD1/PD-L1, FGL1, CD155, CD47/SIRP alpha, CD276, and SIGLEC-15 all regulate the cell cycle, and specifically through Cyclin D1 regulation. Furthermore, a variety of signal pathways engage in proliferation regulation, such as P13K, AKT, mTOR, and NK-kappa B, which are also the most common pathways involved in the regulation of immune checkpoint proliferation. Currently, only PD1/PD-L1, CD47/SIRP alpha, TIM3/Galectin-9, and CD70/CD27 checkpoints have been shown to interact with each other to regulate tumor proliferation in pairs. However, for other immune checkpoints, the role of their receptors or ligands in tumor proliferation regulation is still unknown, and we consider the enormous potential in this area. An increasing number of studies have validated the various role of immune checkpoints in tumors, and based on this literature review, we found that most of the immune checkpoints play a dual regulatory role in immunity and proliferation. Therefore, the related pathways in proliferation regulation can served the role of therapy targets in tumor therapy. Further, great potential is displayed by IDO1, SIGLEC-15, 4-1BBL, and HVEM in tumor proliferation regulation, which may become novel therapy targets in tumor treatment.