Cellular HIV-1 reservoirs that persist despite antiretroviral treatment are incompletely defined. We show that during suppressive antiretroviral therapy, CD4+ T memory stem cells (TSCM) harbor high per-cell levels of HIV-1 DNA, and make increasing contributions to the total viral CD4+ T cell reservoir over time. Moreover, phylogenetic studies suggested long-term persistence of viral quasispecies in CD4+ TSCM cells. Thus, HIV-1 may exploit stem cell characteristics of cellular immune memory to promote long-term viral persistence.

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Initiation of antiretroviral therapy during the earliest stages of HIV-1 infection may limit the seeding of a long-lasting viral reservoir, but long-term effects of early antiretroviral treatment initiation remain unknown. Here, we analyzed immunological and virological characteristics of nine patients who started antiretroviral therapy at primary HIV-1 infection and remained on suppressive treatment for >10 years; patients with similar treatment duration but initiation of suppressive therapy during chronic HIV-1 infection served as controls. We observed that independently of the timing of treatment initiation, HIV-1 DNA in CD4 T cells decayed primarily during the initial 3 to 4 years of treatment. However, in patients who started antiretroviral therapy in early infection, this decay occurred faster and was more pronounced, leading to substantially lower levels of cell-associated HIV-1 DNA after long-term treatment. Despite this smaller size, the viral CD4 T cell reservoir in persons with early treatment initiation consisted more dominantly of the long-lasting central-memory and T memory stem cells. HIV-1-specific T cell responses remained continuously detectable during antiretroviral therapy, independently of the timing of treatment initiation. Together, these data suggest that early HIV-1 treatment initiation, even when continued for >10 years, is unlikely to lead to viral eradication, but the presence of low viral reservoirs and durable HIV-1 T cell responses may make such patients good candidates for future interventional studies aiming at HIV-1 eradication and cure. IMPORTANCEAntiretroviral therapy can effectively suppress HIV-1 replication to undetectable levels; however, HIV-1 can persist despite treatment, and viral replication rapidly rebounds when treatment is discontinued. This is mainly due to the presence of latently infected CD4 T cells, which are not susceptible to antiretroviral drugs. Starting treatment in the earliest stages of HIV-1 infection can limit the number of these latently infected cells, raising the possibility that these viral reservoirs are naturally eliminated if suppressive antiretroviral treatment is continued for extremely long periods of time. Here, we analyzed nine patients who started on antiretroviral therapy within the earliest weeks of the disease and continued treatment for more than 10 years. Our data show that early treatment accelerated the decay of infected CD4 T cells and led to very low residual levels of detectable HIV-1 after long-term therapy, levels that were otherwise detectable in patients who are able to maintain a spontaneous, drug-free control of HIV-1 replication. Thus, long-term antiretroviral treatment started during early infection cannot eliminate HIV-1, but the reduced reservoirs of HIV-1 infected cells in such patients may increase their chances to respond to clinical interventions aiming at inducing a drug-free remission of HIV-1 infection.

Background COVID-19 patients can develop a cytokine release syndrome that eventually leads to acute respiratory distress syndrome (ARDS) requiring invasive mechanical ventilation (IMV). Since interleukin-6 (IL-6) is a relevant cytokine in ARDS, the blockade of its receptor with Tocilizumab (TCZ) could reduce mortality and/or morbidity in severe COVID-19. Objective To determine whether baseline IL-6 serum levels can predict the need for IMV and the response to TCZ. Methods Retrospective observational study performed in hospitalized patients diagnosed of COVID-19. Clinical information and laboratory findings, including IL-6 levels, were collected approximately 3 and 9 days after admission to be matched with pre- and post-administration of TCZ. Multivariable logistic and linear regressions, and survival analysis were performed depending on outcomes: need for IMV, evolution of arterial oxygen tension/fraction of inspired oxygen ratio (PaO 2 /FiO 2 ) or mortality. Results One hundred and forty-six patients were studied, predominantly male (66%); median age was 63 years. Forty-four patients (30%) required IMV, and 58 patients (40%) received treatment with TCZ. IL-6 levels>30 pg/ml was the best predictor for IMV (OR:7.1; p<0.001). Early administration of TCZ was associated with improvement of oxygenation (PaO 2 /FiO 2 ) in patients with high IL-6 (p=0.048). Patients with high IL-6 not treated with TCZ showed high mortality (HR: 4.6; p=0.003), as well as those with low IL-6 treated with TCZ (HR: 3.6; p=0.016). No relevant serious adverse events were observed in TCZ-treated patients. Conclusion Baseline IL-6>30 pg/ml predicts IMV requirement in patients with COVID-19 and contributes to establish an adequate indication for TCZ administration.

The generation of natural regulatory T cells (nTregs) is crucial for the establishment of immunologic self-tolerance and the prevention of autoimmunity. Still, the origin of nTregs and the mechanisms governing their differentiation within the thymus are poorly understood, particularly in humans. It was recently shown that conventional dendritic cells (cDCs) in human thymus were capable of inducing nTreg differentiation. However, the function of plasmacytoid DCs (pDCs), the other major subset of thymic DCs, remains unknown. Here we report that pDCs resident in the human thymus, when activated with CD40 ligand (CD40L) plus interleukin-3, efficiently promoted the generation of CD4 ؉ CD25 ؉ Foxp3 ؉ nTregs from autologous thymocytes. The progenitors of these nTregs were selectively found within CD4 ؉ CD8 ؉ thymocytes that had accomplished positive selection, as judged by their CD69 hi TCR hi phenotype. Supporting the involvement of the CD40-CD40L pathway in pDC-induced nTreg generation, we show that positively selected CD4 ؉ CD8 ؉ progenitors specifically transcribed CD40L in vivo and upregulated CD40L expression on T-cell receptor engagement, thereby promoting the activation of pDCs. Finally, evidence is provided that nTregs primed by pDCs displayed reciprocal interleukin-10/transforming growth factor-␤ cytokine expression profiles compared with nTregs primed by cDCs. This functional diversity further supports a nonredundant tolerogenic role for thymic pDCs in the human thymus. (Blood. 2010;115(26):5366-5375) IntroductionDendritic cells (DCs) are highly specialized antigen-presenting cells (APCs) that are crucial in the regulation of innate and adaptive immunity. DCs respond to danger signals by antigen uptake, maturation, and induction of antigen-specific immune responses in secondary lymphoid organs. 1,2 In addition, tissue DCs are able to present antigen in a tolerogenic fashion, leading to anergy or deletion of potentially self-reactive T cells, or inducing the generation of regulatory T cells (Tregs). [3][4][5][6] Tregs play a key role in the control of immune homeostasis and immunologic tolerance and are crucial to protect against fatal autoimmunity throughout life. Tregs also regulate or suppress other classes of immune responses, such as allograft rejection, allergy, tumor immunity, and responses to microbes. 7,8 Thus, there is great interest in understanding how do Tregs develop.During thymopoiesis, nearly all positively selected CD4 ϩ CD8 ϩ double-positive (DP) thymocytes carrying high-affinity T-cell receptors (TCRs) for self-peptide-major histocompatibility complexes are eliminated by a mechanism of clonal deletion that ensures central tolerance. 6 Self-reactive thymocytes that escape clonal deletion undergo an alternative process of nondeletional tolerance that involves their positive selection and further differentiation into immunosuppressive CD4 ϩ T cells, termed natural Tregs (nTregs). [8][9][10][11] In addition, Tregs can be induced in the periphery (iTregs) from CD4 ϩ T lymphocytes. 4 Generation o...