CD4 and neoplasm: In contrast, the activated SMARTA cells couldn’t suppress solid tumor progression, which might be caused by their less infiltration into the tumor tissue and more severe exhaustion state within the solid tumor microenvironments, and a better understanding of the regulatory networks of antigen-specific CD4+ T cells between metastatic and solid tumor will be of great value in providing new insight for CD4+ T cell-based immunotherapies, which still need further investigation.