The importance of CDC42, and of Rho GTPases more broadly, in T cells is underscored by the plethora of inherited genetic variants that impact immune function (known as human inborn errors of immunity), involving autoinflammation and/or recurrent infections, caused by mutations in genes encoding CDC42, Rac1, RhoA, CDC42 effectors and CDC42 regulators (Bucciol et al., 2020; Burns et al., 2017; Comrie and Lenardo, 2018; Lam et al., 2019; Martinelli et al., 2018; van Wijck et al., 2023). Here, CDC42 is linked to infection.