A natural hypothesis given these findings Apoptosis inhibitor is that the diminished exhaustion seen in LTNPs could be dependent on lower expression of Blimp-1. This is the possibility addressed in the paper published in this issue of the European Journal of Immunology, in which Seddiki et al. [18] present experiments measuring Blimp-1 levels in the CD4+ T cells from HIV+ LTNPs, individuals with CHI and healthy controls. These experiments showed that, at both the protein and mRNA levels, Blimp-1 expression is higher in individuals with CHI than in LTNPs. Supporting this was the finding

that the downstream effects of elevated Blimp-1 expression in chronic infection, namely elevated PD-1 and diminished IL-2 expression, were also more pronounced in individuals with CHI relative to levels in LTNPs. This prompted Seddiki et al. [18] AUY-922 to consider the mechanism by which Blimp-1 expression is regulated in T lymphocytes.

One manner in which gene expression is regulated in cells is via microRNA (miR). These are small noncoding sequences of RNA that bind to untranslated regions of target mRNA and either suppress their translation or accelerate their degradation. The authors assessed the ability of different miRs to suppress Blimp-1 expression. In results consistent with those of other researchers [19], Seddiki et al. [18] found that transfection of miR-9 decreased Blimp-1, while increasing IL-2, expression in CD4+ T cells. The authors also demonstrated that, in CD4+ T cells, TCR stimulation leads to expression of miR-9. Finally, to support the hypothesis that diminished Blimp-1 levels in LTNPs is due to miR-9 expression, the authors measured CD4+ T cell miR-9 levels and found them to be elevated in LTNPs relative to levels

in individuals Sucrase with CHI. This study [18] provides strong evidence that differences in the CD4+ T-cell expression of Blimp-1 can explain the improved anti-viral profile of the CD4+ T cells from LTNPs versus those from individuals with CHI. It supports data gained from the murine system and proposes, together with another recent publication [19], a novel mechanism for Blimp-1 regulation. The therapeutic possibility raised by this work is that a reduction of Blimp-1 levels in individuals with CHI could improve viral control and provide the proof that the improved viral control seen in LTNPs is Blimp-1 dependent. That this is an important consideration in T-cell directed therapies for HIV is underlined by the failure of IL-2 therapy in HIV to produce a clinical benefit despite improving the CD4+ T-cell count [20]. Blimp-1 was initially described as being dependent on IL-2 signalling and the failure of IL-2 therapy may therefore be attributable to the IL-2-induced Blimp-1 expression and the exhausted phenotype that it promotes.