Genome-wide screens identify FBOX11-CCNC axis as a suppressor of CD155 mediated cancer immune evasion

The CD155/TIGIT axis plays a crucial role in the suppression of anti-tumor responses. The clinical benefit for patients with diverse types of advanced cancers that has been observed upon blockade of the interaction between CD155 and TIGIT has highlighted the need to study the mechanisms by which CD155 is regulated. Here we identify Cyclin C (CCNC) as a novel modulator of CD155 by using a genome-wide CRISPR-Cas9 screen. Notably, CCNC depletion increases the CD155 expression at the transcriptional level in a broad range of cancer cells. We further found that CCNC suppresses the CD155 expression by inhibiting the transcriptional activity of FOSL2. We further found that the stability of CCNC is negatively regulated by the E3 ubiquitin ligase complex component FBXO11. Functionally, CCNC depletion significantly suppresses the anti-tumor activity of natural killer (NK) and T cells both in vitro and in vivo. Clinically, the expression level of CCNC is negatively correlated with CD155 in cancer patient tissues. Together, our findings provide insights into the biology of CD155 regulation, identify a previously unrecognized master regulator of this critical immune checkpoint and highlight a combination immunotherapy (TIGIT/PD-1 co-blockade) as a promising anti-cancer therapeutic strategy to overcome immune evasion by CCNC-deficient tumor cells. We generated CCNC knockout T24 cells and performed total mRNA sequencing to determine how the gene expression is altered in both parental and CCNC-KO cells.