Structural Basis Of Tumor Neoantigen Recognition In Tumor Immunotherapy

Cancer is a common disease that threatens the human health.DNA damage and mutations may be the major risk factors to driver cancer progression.Based on the World Health Organization(World Health Organization,WHO)estimates,about 22 million new cancer cases occur in 2020 worldwide.Hence,cancer therapy and prevention are vital to human health.In the past decades,surgical resection,radiation therapy and chemotherapy are the commonly used cancer therapy methods.Cancer immunotherapy is one of the most promising ways to treat tumor by stimulating body’s own immune system,which is the fourth therapy mode in cancer.Our research aimed at the T cell adoptive immunotherapy for colorectal cancer,a common malignant tumor,combining the advanced technologies of structural biology,molecular biology and immunology to explore the structural basis of tumor neoantigen recognition in cancer immunotherapy.In T cell adoptive immunotherapy,the antigen presentation by major histocompatibility complex(MHC)is the basis of T cell to exert immune function.In2016,the team of Steven Rosenberg launched a research of T cell adoptive immunotherapy for a patient with metastatic colorectal cancer.Fortunately,the patient’s lung metastasis of tumor was completely regressed and had a good prognosis after 9months’ treatment.This is the first clinical case of adoptive immunotherapy to treat colorectal cancer successfully.In this study,researchers found the tumor neoantigen KRAS G12 D in tumor,a very common pathogenic mutation occurs as frequently as 30-40% in gastrointestinal cancers through whole exome sequencing and transcriptome sequencing.In addition,the cell experiments in vitro further confirmed that the deletion of the HLA-C*0802 encoding gene was the only reason for tumorigenesis.Thus,the elements to achieve a successful T cell adoptive immunotherapy including HLAC*0802,tumor neoantigen KRAS G12 D and specific TCRs.In the study,we obtained two homogenous and biologically active binary complexes of HLA-C*0802 with neoantigen mutants of KRAS G12 D by molecular cloning,E.coli prokaryotic expression system,inclusion body refolding and protein purification,which had high purity up to 90%.Then,we gained two p-HLA-C*0802 crystals,named HLA-C*0802-KG12D9 m and HLA-C*0802-KG12D10 m,after high-throughput screening and optimization of crystallization conditions.The X-ray diffraction data was collected and processed by Shanghai Synchrotron Radiation facility(SSRF),and finally showed structural details of these two binary complexes.The structure of HLA-C*0802-KG12D9 m and HLA-C*0802-KG12D10 m reveal that MHC I can present tumor neoantigens to T cells in a non-classical binding mode.Neoantigens anchor at antigen binding cleft of HLA-C*0802 by amino acids of P3 and PΩ,which adapt to neoantigens with the same mutation site of different lengths by changing the spatial position of the amino acids in antigen binding cleft.These results not only help us to understand the presentation patterns of tumor neoantigens,but also reasonably explain why tumor neoantigens containing the same site are recognized by different TCRs.It provides an objective theoretical guidance for us to study the molecular mechanism of recognition of tumor neoantigens by TCRs.Thus,our followup experiments will focus on studying the recognition mechanism of specific TCR molecules for tumor neoantigens,exploring the pattern of it to activate the autoimmune response to achieve tumor immunotherapy,which will lay a certain theoretical foundation for clinical application of this method in the future.