As expected, we found that human PD-L1 fusion protein could activate PD-1/PD-Ls pathway to upregulate BATF mRNA expression in the presence of PPD stimulation, which is consistent with the study of HIV infection showing a two- to three-fold increase of BATF mRNA level in primary human T cells after culture with PD-L1, anti-CD3 and anti-CD28 (11). Here, CD28 is linked to HIV infectious disease.