CD4 and viral infectious disease: Importantly, cell-intrinsic factors, such as TCR signal strength, TCR affinity for cognate peptide, and TCR chain usage have all recently been implicated in contributing to shaping CD4+ T cell fate decision during viral infection (Tubo et al., 2013; Tubo et al., 2016; Cho et al., 2017; Künzli et al., 2020; Khatun et al., 2021).