CXCR5 and infection: Sorting and transferring PD-1lo/hi subsets into infection-matched hosts based upon CXCR5 positivity validated that PD-1loTim-3−CXCR5+CD8+ Tex marked a self-renewing population that gave rise to PD-1hiTim-3+CXCR5−CD8+ Tex (47).