Scientific Update: Modulating Alternative Splicing to Unleash Anti-tumor Immunity - A Novel Therapeutic Approach

Researchers have found around 100,000 proteins in the human body, but only 20,000 to 25,000 protein-coding genes. How is the number of proteins four to five times larger than the number of genes?

Making proteins from genes isn’t a 1:1 process, as alternative splicing allows the synthesis of multiple distinct proteins from a single gene. Genes are transcribed into mRNA, which is then translated into protein. However, significant processing occurs at the mRNA stage: non-coding introns are removed, and protein-coding exons can be skipped by alternative splicing to generate modified mRNAs encoding structurally and functionally distinct proteins.

Alternative splicing modulators are an active area of research for cancer therapy, and a recent study examined whether alternative splicing of PD-1 could be therapeutically regulated and have anti-tumor effects. The study induced PD-1 exon 3 skipping by SRPK1 knockdown and SPHINX31 treatment, both of which inhibit SRSF1 phosphorylation. The resulting PD-1 protein (∆Ex3PD1) lacked the transmembrane domain needed to attach to the T cell surface, leading to a soluble/secreted form of PD-1.

Shifting PD-1 splicing towards the soluble ∆Ex3PD1 form may slow cholangiocarcinoma growth through two mechanisms. First, less PD-1 on T cell surfaces may prevent the PD-1/PD-L1 interaction, thereby unlashing T cells to kill tumor cells. The secreted PD-1 could also competitively inhibit PD-1/PD-L1 interactions to promote anti-tumor T cell activity. Accordingly, ∆Ex3PD1 expression increased T cell-mediated killing of cholangiocarcinoma cells in lab-based co-culture models. Treatment with SPHINX31 also increased IL-2, which facilitates anti-tumor T cell activity. The effect of SPHINX31 on IL-2 levels was comparable to pembrolizumab, an existing antibody-based immunotherapy targeting PD-1/PD-L1. Emerging therapeutics that increase alternative splicing of PD-1 thus merit further investigation as novel immunotherapy options for cholangiocarcinoma and other cancer types.

Reference: https://link.springer.com/article/10.1007/s00262-023-03534-z

Kelly Butler
Yale School of Medicine, MD program student