Enhanced antitumor immune response in melanoma-bearing mice via attenuated Salmonella carrying an IL-21-shRNA-CCR2 co-expression plasmid.

Interleukin-21 (IL-21), a pivotal immune molecule, exerts an antitumor effect by regulating immune responses in vivo. Nevertheless, the short half-life of IL-21 protein and the difficulty of intratumoral injection of recombinant proteins for the majority of patients present obstacles. We have engineered an IL-21 gene expression vector and confirmed its ability to stably express IL-21 in tumor tissue, exhibiting a certain anti-melanoma effect. Meanwhile, the chemokine CCL2 (chemokine(C-C motif) ligand 2) promotes tumor progression in various cancers by binding to its receptor CCR2 (C-C Chemokine Receptor Type 2), potentially serving as an important target for tumor therapy. However, whether it can synergistically function with IL-21 in antitumor activity remains uncertain. This comprehensive study employed diverse methodologies to validate the anti-melanoma efficacy of an IL-21 and shRNA-CCR2 co-expression plasmid, administered via attenuated Salmonella. By inhibiting CCR2 and augmenting IL-21 levels, this innovative therapy markedly inhibited tumor growth and extended survival in vivo. Mechanistically, it suppressed melanoma cell proliferation, downregulated migration-associated proteins like MMP2 (Matrix Metallopeptidase 2), c-Myc (cellular myelocytomatosis viral oncogene homolog), and CyclinD1 (Cyclin - dependent kinase 4 regulatory subunit 1), and induced apoptosis. Furthermore, it triggered apoptosis in tumor cells while enhancing the presence and infiltration of CD4+, CD8+ T cells, and NK cells (Natural Killer Cells) within the spleen and the tumor microenvironment. This groundbreaking research introduces a novel combinatorial treatment strategy for melanoma, which is expected to transform clinical management.