Self-adjuvant Astragalus polysaccharide-based nanovaccines for enhanced tumor immunotherapy:a novel delivery system candidate for tumor vaccines

The study of tumor nanovaccines(NVs)has gained interest because they specifically recognize and eliminate tumor cells.However,the poor recognition and internalization by dendritic cells(DCs)and insufficient immunogenicity restricted the vaccine efficacy.Herein,we extracted two molecular-weight Astragalus polysaccharides(APS,12.19 k D;APSHMw,135.67 k D)from Radix Astragali and made them self-assemble with OVA257–264directly forming OVA/APS integrated nanocomplexes through the microfluidic method.The nanocomplexes were wrapped with a sheddable calcium phosphate layer to improve stability.APS in the formed nanocomplexes served as drug carriers and immune adjuvants for potent tumor immunotherapy.The optimal APS-NVs were approximately 160 nm with uniform size distribution and could remain stable in physiological saline solution.The FITC-OVA in APS-NVs could be effectively taken up by DCs,and APS-NVs could stimulate the maturation of DCs,improving the antigen cross-presentation efficiency in vitro.The possible mechanism was that APS can induce DC activation via multiple receptors such as dectin-1 and Toll-like receptors 2 and 4.Enhanced accumulation of APS-NVs both in draining and distal lymph nodes were observed following s.c.injection.Smaller APS-NVs could easily access the lymph nodes.Furthermore,APS-NVs could markedly promote antigen delivery efficiency to DCs and activate cytotoxic T cells.In addition,APS-NVs achieve a better antitumor effect in established B16-OVA melanoma tumors compared with the OVA+Alum treatment group.The antitumor mechanism correlated with the increase in cytotoxic T cells in the tumor region.Subsequently,the poor tumor inhibitory effect of APS-NVs on the nude mouse model of melanoma also confirmed the participation of antitumor adaptive immune response induced by NVs.Therefore,this study developed a promising APS-based tumor NV that is an efficient tumor immunotherapy without systemic side effects.