eLife assessment
This study provides a useful description of two evolutionary conserved motifs in CD4 that contribute to the CD4-mediated enhancement of T cell receptor (TCR) signaling, which are notably acting independently of the CD4-LCK interaction. The supporting evidence is solid and supported using a T cell hybridoma in vitro system, but remains incomplete without experiments with primary T cells or the use of in vivo models to assess the importance of the CD4 motifs in T-cell biology.