FOS and neoplasm: In line with this, a group of genes that were highly increased by RARα‐KO CTLs were transcription factors, such as Irf4, Jun, Egr1, Prdm1, Fos, and Eomes (Figure 6A), which are important for CTL differentiation.[1, 23] The differential expression of IRF4 was verified at protein level in tumor‐infiltrating CTLs of mice bearing MC38 or B16 tumors (Figure S12B, Supporting Information).