SELL and infection: Moreover, we observed that KLF2, an anti-proliferative transcription factor [16,17,18] that is also necessary for the regulation of T cell egress from the thymus [19] and has been shown to regulate the expression of S1PR1 as well as other receptors such as CD62L, CCR3, and CCR5 [20], was also upregulated in the HIV-infected thymus at both 5 and 9 weeks post-infection.