Mycobacterium smegmatis enhances shikonin-induced immunogenic cell death-an efficient in situ tumor vaccine strategy.

Abstract

Tumor vaccines are a promising avenue in cancer immunotherapy. Despite the progress in targeting specific immune epitopes, tumor cells lacking them can evade treatment. Here, we aimed to construct an efficient in situ tumor vaccine Vac-SM, utilizing shikonin (SKN) to induce immunogenic cell death (ICD) and Mycobacterium smegmatis ( M. smegmatis) as an immune adjuvant to enhance in situ tumor vaccine efficacy. SKN demonstrated a dose-dependent and time-dependent cytotoxic effect on the tumor cell line as seen using the CCK-8 assay and induced ICD in tumor cells by detecting the expression of relevant indicators respectively. Compared to that in the control groups, in situ Vac-SM injection in mouse subcutaneous metastatic tumors significantly inhibited tumor growth and distant tumor growth and improved survival rates. M. smegmatis effectively induced bone marrow-derived dendritic cells (DC) maturation and activation and in vivo tumor-draining lymph nodes showed increased maturation of DC and a higher proportion of effector memory T-cell subsets with Vac-SM treatment, based on flow cytometry analysis results.Collectively, Vac-SM vaccine effectively induces ICD, improves antigen presentation by DC, activates a specific systemic antitumor T-cell immune response, exhibits favorable safety profile, and holds promise for clinical translation for local tumor immunotherapy.