SAP Mediated Antigen-specific CD8~+ T Cell Response To Viral Infection And Tumor

Viral infection and tumor are serious challenges for health of human beings,while CD8⁺T cells is essential for preventing and treatment of those diseases.An in-depth understanding of immune responses and its regulation in CD8⁺T cells would pave a way to improve immune therapies against viral infection and tumor.An adaptor protein SAP,which encoded by Sh2d1a,functions widely on mediating NKT cells development,CD4⁺T cells differentiation as well as NK cells and CD8⁺T cells cytotoxicity.Study around intrinsic role of SAP in CD8⁺T cells toward viral infection and tumor remains paucity.In present study,we utilized a variety of acute/chronic infection and tumor modes,as well as PBMC samples from COVID-19 patients with different disease severity to uncover the role of SAP in CD8⁺T cells in distinct immune condition.1.SAP modulates the proliferation and differentiation of virus-specific CD8⁺T cellsWe found virus specific Sh2d1a^-/-CD8⁺T cells had a less proliferation and a deviation from effector cells to memory precursor cells comparing with WT CD8⁺T cells counterpart in response to LCMV Armstrong,despite the expression of cytotoxic molecules remain comparable.In consistent,Sh2d1a^-/-CD8⁺T cells less proliferated and effector differentiated but had a higher level of TCF1^hi population in draining lymph node when H1N1 locally infection in lung.To our surprise that the memory biased Sh2d1a^-/-CD8⁺T cells more potently protected mouse from H1N1-induced lethal infection than WT CD8⁺T cells.By virtue of stimulating or capturing cells with SARS-CoV-2 specific RBD protein or peptide,we further assessed adaptive immune response including T and B cells from COVID-19 patients with a variety of disease severities.The CD4⁺T_H1 and cytotoxic CD8⁺T cells differentiation and responses substantially biased to in asymptomatic and mild patients,while CD4⁺T_FH and B cells responses as well as SARS-CoV-2 specific Ig production and maintenance dominated in moderate and server patients.Interestingly,SAP expression level in SARS-CoV-2 specific CD8⁺T cells was positively correlation with disease severities among COVID-19 patients.This result corresponds well to previous report that memory bias of CD8⁺T cells related to less severe symptoms in COVID-19 patients.However,LCMV Cl13 chronic infection drove Sh2d1a^-/-CD8⁺T cells enriching in progenitor exhausted phenotype despite a proliferation defect in early infection phase,which was much recovered during chronic infection phase.2.SAP modulates the proliferation,differentiation,and infiltration of tumor-specific CD8⁺T cellsIt remains unknown the role of SAP in tumor-specific CD8⁺T cells.Our results suggested that SAP deficient mouse restrained multiple tumor cells growth in vivo due to CD8⁺T cells but not CD4⁺T cells or NK cells.Co-transferring assay supported an exclusive accumulation of Sh2d1a^-/-CD8⁺T cells into tumor microenvironment comparing with in tumor draining lymph nodes,blood,or spleen.This is ascribed to the critical role of tumor draining lymph nodes,where tumor specific Sh2d1a^-/-CD8⁺T cells exhibited more profoundly proliferation,effector-like differentiation and achieved a stronger tumor infiltrating ability comparing to WT CD8⁺T cells.More importantly,Sh2d1a^-/-CD8⁺T cells produced higher levels of cytotoxic molecules in tumor microenvironment though the distribution of subpopulation among exhausted CD8⁺T cells was comparable to WT CD8⁺T cells.Sh2d1a^-/-CD8⁺T cells remain responsiveness toαPD1/L1 therapy and knockout SAP in CAR-T cells markedly improved its efficacy on control of solid tumor.Mechanistically,TCR stimulation induced a higher Ca²⁺influx,which unexpectedly upregulation of NFATc1/A nucleus localization and subsequently programmed the proliferation and effector function in Sh2d1a^-/-CD8⁺T cells but not in WT CD8⁺T cells.These data demonstrated SAP-mediated CD8⁺T cells responses probably with a context-dependent manner.SAP and its associated signal molecules could be potential targets for treatment of viral infection and cancer in the future.