Human IL15 mRNA

Immunogene therapy is a new approach for the treatment of colorectal cancer. The cytokine IL-15 has shown potential for anticancer therapy due to its immunostimulatory properties. However, conventional IL-15-based cancer gene therapy studies usually use plasmid DNA, which has potential drawbacks such as low delivery efficiency and backbone effects. Here, researchers describe a study using in vitro transcribed mRNA for IL-15 immunogene therapy of colon cancer. A protamine/liposome system (CLPP) was developed to provide efficient concentration and delivery capabilities for mRNA transport in vivo. The results showed that the prepared CLPP system was able to efficiently deliver IL-15-encoding mRNA to C26 cells. The IL-15 cytokine secreted and expressed by C26 cells successfully produced lymphocyte stimulation in vitro and produced anticancer cell toxicity against cancer cells. Local or systemic administration of the CLPP/mIL-15 complex showed significant inhibitory effects on a variety of C26 mouse colon cancer models, with inhibition rates as high as 70% in the C26 abdominal metastasis model, 55% in the subcutaneous metastasis model, and 69% in the lung metastasis model, showing high efficacy and safety. This result successfully demonstrated the great therapeutic potential of the CLPP/mIL-15 complex in colorectal cancer immunogene therapy.

Since the activity of expressed IL-15 depends on the tumor microenvironment, attempts were made to mimic its therapeutic process in vitro (Figure 1A). To evaluate the anticancer ability of the CLPP/mIL-15 complex, the researchers first investigated whether high levels of IL-15 mRNA accumulation were achieved in C26 cells after delivery. Therefore, intracellular mRNA levels were analyzed. As shown in Figure 1B, IL-15 mRNA levels in C26 cells increased rapidly to nearly 1500-fold 24 hours after transfection compared with the untreated group. High concentrations of IL-15 mRNA lay a solid foundation for further therapeutic activation. In addition, since IL-15 is a secreted cytokine, it was analyzed whether the level of IL-15 protein in the C26 supernatant was also increased. As shown in Figure 4B, high levels of mouse IL-15 protein were detected using ELISA in the CLPP/mIL-15 complex-treated group 72 hours after transfection. In addition, IL-15 expression was still detectable 7 days after transfection, indicating that its expression behavior was persistent (Figure 1C). Therefore, these results indicate that with the help of the CLPP system, IL-15 mRNA has been successfully delivered to C26 cells and expressed, providing effective support for further anticancer activity.

Figure 1. (A) A schematic view of the experimental design. (B) IL-15 mRNA and cytokine levels after transfection. (C) Concentration of the IL-15 cytokine in the C26 cell culture supernatant on each day. (Lei S, et al., 2020)