Lactiplantibacillus plantarum K4-9 strain stimulates antitumor immune responses through the activation of dendritic cells and CD8+ T cells.

Activated dendritic cells (DCs) present tumor antigens to T cells, while CD8+ T cells induce apoptosis in cancer cells through the production of interferon (IFN)-γ and Granzyme B. Immune cells expressing chemokine receptors migrate to tumor sites in response to chemokines secreted by cancer cells. In our previous study, we demonstrated that Lactiplantibacillus plantarum K4-9 (K4-9), isolated from nozawana pickles, strongly promotes IFN-γ production. However, the detailed mechanisms underlying its antitumor effects remain unclear. This study aimed to elucidate the antitumor mechanisms of K4-9, particularly its involvement with DCs and CD8+ T cells. Oral administration of K4-9 increased the proportion of DCs in mouse spleen cells and upregulated the expression of activation markers CD40 and CD86 on DCs. Additionally, CD8+ T cells derived from the spleen cells of K4-9-administered mice exhibited increased mRNA expression levels of IFN-γ and Granzyme B. Administration of K4-9 also enhanced cytotoxic activity against B16F10 melanoma cells. Analysis of chemokine receptor expression revealed elevated CCR7 expression in DCs and increased CXCR3 expression in CD8+ T cells. Oral administration of K4-9 suppressed metastatic tumor formation in a mouse liver metastasis model using B16F10 cells. These results suggest that K4-9 exerts antitumor effects by promoting DC activation and enhancing CD8+ T cell responses. K4-9 holds promise as a functional food ingredient with potential antitumor properties.