Design And Screening Of Polypeptide Inhibitors Blocking Immune Checkpoint Proteins BTLA And HVEM Interactions

Cancer are the first human cause of death,its treatments and pathogenesis have attracted extensive attention from researchers all over the world.Immunotherapy has been emerged as a novel cancer treatment method in recent years,among which immune checkpoint inhibitors have been widely used in clinical practice.Immune checkpoint proteins are a set of immune system-signaling molecules that can stimulate or suppress immune response.After the immune checkpoint protein interacts with its ligand,it can regulate the immune system by releasing stimulatory or inhibitory signals.B and T lymphocyte attenuator(BTLA)is a specific lymphocyte surface receptor on T cells,while its ligand,the herpes virus entry mediator(HVEM),is often overexpressed on tumor cells.Physiologically,binding of HVEM with BTLA triggers inhibitory signals that attenuate the immune response and prevent the depletion of immune cells.However,cancer cells can escape from the immune system by inducing T cells to continuously express BTLA or by overexpressing HVEM themselves.Therefore,BTLA/HVEM,a pair of proteins,can be a new target for cancer immunotherapy,and the study of inhibitors that block their interaction is of great significance for the development of new anticancer drugs.The crystal structure of the BTLA/HVEM complex has been solved,and HVEM(26-38)is the core region of the BTLA/HVEM interaction interface.Peptides containing this region have been shown to block BTLA/HVEM binding.Based on this segment,we used computer simulation to carry out saturated mutation and screen out sequences with stronger binding ability.Based on the results of virtual screening,nine mutant peptides were synthesized,and the inhibitory ability of the mutant peptides on BTLA/HVEM binding was examined by competitive ELISA.With the most potent sequence as the core,the extended peptide inhibitors were further designed and the binding ability was evaluated.Finally,molecular docking computer simulation was used to explore the binding mechanism of the new peptide inhibitor with BTLA.In sum,we have successfully obtained a peptide inhibitor with high affinity to BTLA and unraveled its binding mechanism,which provides new insights for the development of immune checkpoint drugs targeting BTLA/HVEM.