Genetic deletion or kinase inactivation of TAOK3 resulted in a profound, cell-intrinsic loss of naive CD8⁺ T cells. Despite enhanced sensitivity to TCR ligation and enhanced downstream signalling, proliferating CD8⁺ T cells did not survive in vitro and anti-viral CD8⁺ T cell immunity was compromised in vivo in the absence of TAOK3. To delineate the molecular pathways governed by TAOK3, we performed an unbiased phosphoproteomic analysis of Taok3-deficient cells.