CD28 and viral infectious disease: By contrast, we also identify a separate, Vγ9− Vδ2+ T-cell subset that typically has a CD27hiCCR7+CD28+IL-7Rα+ naive-like phenotype and a diverse TCR repertoire, however in response to viral infection, undergoes clonal expansion and differentiation to a CD27loCD45RA+CX3CR1+granzymeA/B+ effector phenotype.