BACKGROUND In recent years,the T-cell therapy and immune checkpoint inhibitors toward CTLA-4 and PD-1/PD-L1 axis antibody therapy have acquired encouraging success. However,most of patients were still not benefited with lots of troubles,such as low penetration of tissues/cells,strong immunogenicity and cytokine release syndrome,and long manufacturing process and expensive costs. By contrast,the immune-modulating small molecules possessed natural advantages to overcome these obstacles and might achieve greater success. PURPOSE Exploring the potent immune-modulating natural small molecules and revealing what kinds of molecules or structures with the immunomodulatory activity against cancers. METHODS A novel non-cytotoxic T-cell immunomodulating screening model was used to identify the cytotoxic/selective/immunomodulatory bioactivity for 148 natural steroidal saponins. The structure-activity relationships (SARs) research was used to reveal the key groups for immunomodulation/cytotoxicity/selectivity. The negative selection was used to isolate and purify the T-cell. The cell viability assay was used to measure the anti-cancer effect in vitro. The ELISA assay was used to detect the cytokines for IL-1$\beta$,IL-6,TNF-$\alpha$,IFN-$\gamma$,IL-12,perforin and granzyme B (GZMB). The western blotting assay was used to research the immunomodulatory mechanism. The siRNA knockdown was used to generate the IFN-$\gamma$ resistant melanoma cells. The NOG immune-deficient mice were used to evaluate the anti-tumor efficacy in vivo. The peripheral blood samples from 10 cancer patients were used to detect the broad population anti-tumor efficacy. RESULTS It was reported that the correlation among structures and immunomodulation/ cytotoxicity/selectivity,in which opening ring-F with 26-O-glucopyranosyl,disaccharide and trisaccharide chains at C-3,steric hindrance and polarity of C-22 were key immunomodulatory groups. Moreover,taccaoside A was identified as the most potent candidate against cancer cells,including non-small cell lung cancer,triple negative breast cancer,and the IFN-$\gamma$ resistant melanoma,partly through enhancing T lymphocyte mTORC1-Blimp-1 signal to secrete GZMB. Besides,10 patients derived T-cell also would be modulated against cancer cells in vitro. Moreover,the overall survival was great extended (>140 days vs 93 days) with nearly 100% tumor burden disappearance (0 mm3vs 1006 ± 79.5 mm3) in mice. CONCLUSION This work demonstrated one possibility for this concerned purpose,and identified a potent immune-modulating natural molecule taccaoside A,which might contribute to cancer immunotherapy in future.
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