Although CD31 expression on human thymocytes has been reported, a detailed analysis of CD31 expression at various stages of T cell development in the human thymus is missing. Herein, we provide a global picture of the evolution of CD31 expression from the CD34+ hematopoietic precursor to the CD45RA+ mature CD4+ and CD8+ single positive T cells. Using 9-color flow cytometry, we show that CD31 is highly expressed on CD34+ progenitors and stays high until the early double positive stage (CD3− CD4+ CD8α+β −). After β-selection, CD31 expression levels become low to undetectable. CD31 expression then increases and peaks on CD3high CD4+CD8+ double positive thymocytes. However, following positive selection, CD31 expression differs dramatically between CD4+ and CD8+ lineages: homogeneously high on CD8 SP but lower or negative on CD4 SP cells, including a subset of CD45RA+ CD31− mature CD4+ thymocytes. CD31 expression on TCRγδ thymocytes is very similar to that of CD4 SP cells. Remarkably, there is a substantial subset of semi-mature (CD45RA−) CD4 SP thymocytes that lack CD31 expression. Moreover, FOXP3+ and ICOS+ cells are over-represented in this CD31− subpopulation. Despite this CD31− CD45RA− subpopulation, the majority of egress-capable mature CD45RA+ CD4 SP thymocytes expresses CD31. The variations in CD31 expression appear to coincide with three major selection processes occurring during thymopoiesis: β-selection, positive selecion and negative selection. Considering the ability of CD31 to modulate the TCR’s activation threshold via the recruitment of tyrosine phosphatases, our results suggest a significant role for CD31 during T cell development.

Mature human thymocytes rely on S1P-R1 to migrate toward S1P. Taken in the context of murine work demonstrating that S1P is required for thymocyte egress to the periphery, our data highlight a new key chemokine for human thymocyte egress.

“Shock and kill” therapeutic strategies toward HIV eradication are based on the transcriptional activation of latent HIV with a latency-reversing agent (LRA) and the consequent killing of the reactivated cell by either the cytopathic effect of HIV or an arm of the immune system. We have recently found several benzotriazole and benzotriazine analogues that have the ability to reactivate latent HIV by inhibiting signal transducer and activator of transcription 5 (STAT5) SUMOylation and promoting STAT5 binding to the HIV long terminal repeat and increasing its transcriptional activity. To understand the essential structural groups required for biological activity of these molecules, we performed a systematic analysis of >40 analogues. First, we characterized the essential motifs within these molecules that are required for their biological activity. Second, we identified three benzotriazine analogues with similar activity. We demonstrated that these three compounds are able to increase STAT5 phosphorylation and transcriptional activity. All active analogues reactivate latent HIV in a primary cell model of latency and enhance the ability of interleukin-15 to reactivate latent HIV in cells isolated from aviremic participants. Third, this family of compounds also promote immune effector functions in vitro in the absence of toxicity or global immune activation. Finally, initial studies in mice suggest lack of acute toxicity in vivo. A better understanding of the biological activity of these compounds will help in the design of improved LRAs that work via inhibition of STAT5 SUMOylation.

Primary cell models of human immunodeficiency virus (HIV) latency have become tools to both understand the mechanisms involved in establishment of latency and test preclinical strategies toward HIV-1 cure. These models rely on infection of CD4 T cells from healthy donors. As such, these models provide an opportunity to explore the role of biological sex, age, and HIV status on establishment and reactivation of latent HIV in vitro. We have used an established primary cell model of latency based on the generation of latently infected central memory CD4 T cells with the CXCR4 strain HIV-1 to address whether these variables influence (i) HIV-1 replication, (ii) establishment of latency, and (iii) latency reversal in CD4 T cells. Our results indicate that replication of HIV-1, but not establishment of latency, is influenced by the age of female, but not male, donors. Moreover, the frequency of latently infected cells in this model is directly correlated with levels of productive infection in both male and female donors independent of age. We did not find differences in the ability of five different latency-reversing agents to reactivate latent HIV-1. Finally, we have found that this model can be generated using cells from aviremic participants. In conclusion, we have further characterized the central memory T cell model of latency regarding biological sex and age and demonstrated that this model is suitable for use with cells isolated from aviremic participants, opening the opportunity to use this primary cell model to address cure approaches, including shock and kill, in HIV-infected individuals.