Using genome-wide CRISPR screening in CD8+ T cells, Zhao et al. showed that ~2600 and ~1500 genes, respectively, were required for optimal expansion of CD8+ T cells transferred into wild-type mice or stimulated by IL-2 in vitro. The absence of only a few genes strongly boosted CD8+ T cell expansion. Roquin, an RNA-binding protein that promotes RNA decay and regulates inflammation, was the most potent repressor, targeting IRF4, which was upregulated in Roquin-deficient CD8+ T cells. Ablating Roquin or overexpressing IRF4 in adoptively transferred CD8+ T cells enhanced their proliferation and antitumor activity in lymphoreplete mice.
Contributed by Paula Hochman
ABSTRACT: Robust expansion of adoptively transferred T cells is a prerequisite for effective cancer immunotherapy, but how many genes in the genome modulate T cell expansion remains unknown. Here, we perform in vivo and in vitro CRISPR screens to systematically identify genes influencing CD8 T cell expansion. In the mouse genome, ∼2,600 and ∼1,500 genes are required for optimal CD8 T cell expansion in vivo and in vitro, respectively. In vivo-specific CD8 T cell essential genes are enriched in metabolic pathways, including mitochondrial metabolism. The strongest repressor of CD8 T cell expansion is Roquin, the ablation of which drastically boosts T cell proliferation by enhancing cell-cycle progression and upregulation of IRF4. Roquin deficiency or IRF4 overexpression potently enhances anti-tumor immunity. These data provide a functional catalog of CD8 T cell fitness genes and suggest that targeting the Roquin-IRF4 axis is an effective strategy to enhance efficacy of adoptive transfer therapy for cancer.