The HIV-Tat protein favors the activation of T lymphocytes. Implications for new therapeutic strategies against HIV and other viral infections

The HIV-Tat protein favors the activation of T lymphocytes. Implications for new therapeutic strategies against HIV and other viral infections Background. The human immunodeficiency virus (HIV) is one of the major plagues in the world for number of people infected and deaths per year. The most devastating damages caused by HIV infection are observed at level of cellular immunity and include the depletion of CD4+ T cells and important dysfunctions of both CD8+ and CD4+ T cells as impairment of functionality, exhaustion, increased T cell proliferation, susceptibility to apoptosis and expansion of memory T cells. Several studies have reported that the regulatory HIV-Tat protein, produced very early after HIV infection and necessary for viral gene expression, cell-to-cell virus transmission and disease progression, can be released extracellularly and, upon release, enters uninfected T cells affecting their functionality. However, how Tat can modulate the CD8+ and CD4+ T cells responses is not completely clear. In our studies we propose a contribution of Tat to T cells dysfunctions described during HIV infection and a possible use of this protein in new therapeutic strategy against HIV and other viral infections. Methods. In vitro: To characterize the role of Tat on CD8+ and CD4+ T cells, PBLs from healthy donors resting and stimulated with anti-CD3/CD28, were treated with the Tat protein. Before and after treatment, T lymphocytes subtypes were sorted through separation by negative selection with magnetic beads. Purified CD8+ and CD4+ T cells populations were analyzed by Western Blotting, Flow Cytometry, qPCR, Elispot and Cr51 release assay. In vivo: Mice were vaccinated with recombinant herpes simplex viruses expressing the Tat protein or a control gene. Tat mediated modulation of anti-HSV1 specific cellular immunity was followed by Flow Cytometry. Results. In vitro: Dysfunctionality of T lymphocytes in HIV-positive patients has been linked with the deep modification of their transcriptional profile and cytokine release. In our studies we demonstrate that Tat enhances IL-2 and IFNγ production in activated CD8+ and CD4+ T cells, modifies T cells fate but does not affect their proliferation and phenotype. Furthermore, memory CD8+ T cells stimulated by antigenic peptides in the presence of Tat show an increase of their effector functions. Moreover, CTL cultures generated in the presence of Tat exhibited higher numbers of both IFNγ and granzime B secreting CTLs against dominant and subdominant antigenic peptides, suggesting that Tat favors the expansion of epitope-specific and actively secreting CD8+ T cells. The same effect was observed on naïve CD8+ T cells primed with CD8 peptide antigens. As Tat enhances the activation and functionality of stimulated CD8+ and CD4+ T cells, we sought to determine whether this effect might be due to a modulation of some transcriptional factors important for activation and effector functions of T cells. The data demonstrate that Tat favors the activation of CD8+ and CD4+ T cells affecting the expression of transcriptional factors crucial for T cell programming and functionality like T-bet, Eomes and Blimp-1. In vivo: The presence of Tat within a HSV vector favored the expansion of HSV specific CD8+ T cells and accumulation of CD8 T cells with an effector memory phenotype. Conclusion. These results suggest that the Tat protein of HIV enhances the stimulation of CD8+ and CD4+ T cells thus contributing to immune activation and T cells dysfunctionality as observed during the course of HIV infection. Thus, our data provide new insights regarding the causes of immune activation and underscore the importance of addressing anti-Tat immunity in future preventive and therapeutic approaches aimed at HIV control and cure. Furthermore, the Tat protein, in addition to being a safe and relevant HIV vaccine antigen, possesses several immunomodulatory features which make it an attractive molecule to be exploited for vaccination strategies and therapeutic interventions aimed at modulating antigen-specific immune responses in different types of human diseases.