Global transcriptome-wide analysis of CIK cells identify distinct roles of IL-2 and IL-15 in acquisition of cytotoxic capacity against tumor

BACKGROUND: Cytokine-induced killer (CIK) cells are an emerging approach of cancer treatment. Our previous study have shown that CIK cells stimulated with combination of IL-2 and IL-15 displayed improved proliferation capacity and tumor cytotoxicity. However, the mechanisms of CIK cell proliferation and acquisition of cytolytic function against tumor induced by IL-2 and IL-15 have not been well elucidated yet. METHODS: CIK(IL-2) and CIK(IL-15) were generated from peripheral blood mononuclear cells primed with IFN-γ, and stimulated with IL-2 and IL-15 in combination with OKT3 respectively. RNA-seq was performed to identify differentially expressed genes, and gene ontology and pathways based analysis were used to identify the distinct roles of IL-2 and IL-15 in CIK preparation. RESULTS: The results indicated that CIK(IL-15) showed improved cell proliferation capacity compared to CIK(IL-2). However, CIK(IL-2) has exhibited greater tumor cytotoxic effect than CIK(IL-15). Employing deep sequencing, we sequenced mRNA transcripts in CIK(IL-2) and CIK(IL-15). A total of 374 differentially expressed genes (DEGs) were identified including 175 up-regulated genes in CIK(IL-15) and 199 up-regulated genes in CIK(IL-2). Among DEGs in CIK(IL-15), Wnt signaling and cell adhesion were significant GO terms and pathways which related with their functions. In CIK(IL-2), type I interferon signaling and cytokine-cytokine receptor interaction were significant GO terms and pathways. We found that the up-regulation of Wnt 4 and PDGFD may contribute to enhanced cell proliferation capacity of CIK(IL-15), while inhibitory signal from interaction between CTLA4 and CD80 may be responsible for the weak proliferation capacity of CIK(IL-2). Moreover, up-regulated expressions of CD40LG and IRF7 may make for improved tumor cytolytic function of CIK(IL-2) through type I interferon signaling. CONCLUSIONS: Through our findings, we have preliminarily elucidated the cells proliferation and acquisition of tumor cytotoxicity mechanism of CIK(IL-15) and CIK(IL-2). Better understanding of these mechanisms will help to generate novel CIK cells with greater proliferation potential and improved tumor cytolytic function.