Human CD4+ T cells express P-glycoprotein (P-gp), the ATP binding cassette efflux transporter encoded by MDR1. A common MDR1 single-nucleotide polymorphism in exon 26 (C3435T), which is linked to an exon 21 polymorphism (G2677T/A) and reportedly alters expression, has been associated with greater CD4+ T-cell increases during antiretroviral therapy. P-gp overexpression prevents apoptosis and inhibits HIV-1 replication in model systems, suggesting a potential effect on T-cell turnover. This study explored relationships between MDR1 polymorphisms and phase 1 viral decay among 31 HIV-infected individuals initiating antiretroviral therapy. Position 3435 genotypes were CC in 7 (23%), CT in 14 (45%), and TT in 10 (32%). Position 2677 genotypes were GG in 8 (26%), GT in 18 (58%), and TT in 5 (16%). There was no significant relationship between allelic variants in either exon 26 or 21 and phase 1 or phase 2 viral decay, changes in lymphocyte subsets over time, or plasma trough ritonavir concentrations. It is concluded with 95% confidence that phase 1 viral decay differences between exon 26 TT and CC groups are unlikely to exceed 18%.
Therapeutic interventions to eradicate latent HIV in ART-treated infection have yet to show efficacy. We used a systems biology approach to identify a subset of ART-treated individuals with immune-dysfunction that had the highest frequencies of cells with inducible HIV. Contrary to the prevailing notion that immune activation drives HIV persistence, blood from these individuals was enriched in senescence-inducing genes (high FOXO3, SMAD2 and IRF3), Treg frequencies and TGF-β signaling expression. In these "Senescent-INRs", high Firmicute phylum plasma nucleotides and butyrate/bile acids (like a-ketobutyrate) correlated with Treg frequencies and inducible HIV levels. Stimulation of naive CD4 T-cells with a-ketobutyrate led to TGF-β producing Treg differentiation, and PD-1 up-regulation on less differentiated cells. A dose dependent increase in latent HIV-infected memory CD4 T-cells was observed after TGF-β stimulation. Senescence cascades identified here can be targeted by PD-1/TGF-β specific interventions that have shown safety/efficacy in cancer, and can be crucial for HIV eradication.
Background: HIV-infected patients who fail to normalize CD4 T cells despite suppressive antiretroviral therapy have impaired immune homeostasis: diminished naive T-cell numbers, elevated T-cell turnover, senescence, and inflammation. Methods: Blood samples from immune failures (n = 60), immune successes (n = 20), and healthy controls (n = 20) were examined for plasma interleukin (IL)-7 levels, for cellular expression of the IL-7Rα chain (CD127), for the exhaustion and senescence markers programed death 1 (PD-1) and CD57, and for the survival factor Bcl2. Because both inflammatory and homeostatic cytokines can induce T-cell cycling, we also examined the effects of these mediators on exhaustion and senescence markers. Results: Plasma levels of IL-7 were elevated and both CD4 and CD8 T-cell CD127 expression was decreased in immune failure. Plasma levels of IL-7 correlated directly with naive CD4 T-cell counts in immune success and inversely with T-cell cycling (Ki67) in healthy controls and immune success, but not in immune failure. CD4 T-cell density of PD-1 was increased and Bcl2+ CD4 T cells were decreased in immune failure but not in immune success, whereas the proportion of T cells expressing CD57 was increased in immune failure. PD-1 and CD57 were induced on CD4 but not CD8 T cells by stimulation in vitro with inflammatory IL-1β or homeostatic (IL-7) cytokines. Conclusions: Perturbation of the IL-7/IL-7 receptor axis, increased T-cell turnover, and increased senescence may reflect dysregulated responses to both homeostatic and inflammatory cytokines in immune failure patients.
In this issue of AIDS, Robbins et al. (pp. 1121–1126) report that vaccination with an envelope (gp120)-depleted inactivated HIV vaccine in incomplete Freund's adjuvant was able to induce CD4 T cell proliferative responses in five out of five immunized HIV-infected individuals. These findings demonstrate that HIV-specific T helper responses can be generated by vaccination in HIV-infected patients who failed to develop or restore them once viral replication was controlled by combination antiviral therapies. The immunogenicity of this vaccine preparation is not surprising because good CD4 T cell responses had been described in earlier studies [1]. What is novel and important in this short communication is that neither the breadth nor the magnitude of CD8 T cell responses to HIV peptides were enhanced by this approach. Why is this result important? A key question regarding immune pathogenesis in HIV infection has been why host immune defences fail to control HIV replication. Although immune responses appear to limit HIV replication, continued viral replication and progressive immune destruction are the rule in all but a small minority of infected individuals. This occurs despite the presence of CD8 T cells that recognize HIV peptides. These cells are demonstrable in most infected individuals, yet neither their frequency nor the breadth of peptides they recognize reliably predict the degree to which viral replication is controlled. Indeed, studies that show no correlation or a positive correlation between viral load and HIV-specific CD8 T cells [2–5] simply suggest that these cells respond to the virus, but provide no assurance that the responses as measured determine the control of HIV replication. A number of explanations for this cytotoxic T lymphocyte (CTL) failure have been proposed, including mutational escape from CTL recognition, a failure of T cell receptor signalling, diminished expression of the cytolytic molecule perforin, inability to access sites of HIV replication in lymphoid tissue [6], inappropriate maturation [7] and inability to proliferate [8]. In animal models of chronic infection, the depletion of CD4 cells renders CD8 CTL responses short-lived and ineffective [9]. This situation is somewhat, although not completely, analogous to the situation in HIV disease, in which although HIV-specific CD4 T cells may be detectable at most stages of disease [2,10], they may be specifically targeted by HIV replication [11,12] and their function as measured by proliferation capacity is clearly impaired [13,14]. A key question then, was whether the induction of HIV-specific CD4 helper cell proliferation would permit restoration of HIV-specific CTL responses. The answer in this admittedly small but careful study appears to be no. Why is this the case? As the authors point out, the administration of an inactivated subunit vaccine like this ‘should’ not directly induce the CD8 T cell responses to viral peptides processed through the endogenous pathway and presented by class I MHC antigens. Although this is quite true, there is increasing evidence that cross-talk between the endogenous and exogenous antigen presentation pathways can occur in vitro and in vivo [15–18], and this may not be rate-limiting when using different vaccine strategies and newer adjuvants in the future [19,20]. In this regard, in these patients with well-controlled HIV replication, there may have been insufficient exposure to viral peptides presented by class I MHC antigens to have permitted the expansion of CD8 T cells recognizing these peptides. On the other hand, if the impairment in function of HIV-specific CD8 T cells already present in these individuals is directly related to a failure of HIV-specific T cell help, some improvement in cytolytic activity against HIV targets might be anticipated after immunization. Whereas assays of IFN-γ gamma expression as performed in these studies may predict cytolytic function [21], the results of functional assays were not reported here. Are we entirely confident that the peptides utilized to evaluate CTL responses were each relevant to the sequences expressed by each patient's viruses? In chronically infected individuals, the escape from selection pressure of the cytotoxic T cells is expected [22,23], and although the authors’ selection of predicted immunodominant peptides is reasonable, it is hard to know with certainty how many of these peptides reflect the sequences actually present within each individual's viral isolates. The complexities of making these precise determinations for each patient in a study like this make such an experiment logistically challenging to say the least. In a related way, is it possible that the helper response generated by the vaccine preparation was irrelevant? Although the selection pressure exerted by cytolytic T cells is more proximate than the potential selection pressure exerted by CD4 T helper cells, escape from CD4 cell help has been reported [24] but the frequency with which this occurs in HIV infection is unknown. Ultimately, the test of activity of therapeutic vaccines will require evidence of attenuated HIV replication, such as may be seen during an ‘analytic’ treatment interruption. Although it may be argued that treatment interruption may not be warranted in the absence of a demonstrable effect on CTL activity, it is not known whether pre-existent T cell help will facilitate the expansion of functional effector CTL once endogenous HIV replication and the attendant exposure to relevant HIV peptides resumes. Although these investigators report results on an admittedly small set of patients, the studies were intensive and credible. Moreover, another group is reporting similar findings using the same vaccine preparation in another small group of patients [25]. The results of these studies thus suggest that in chronic HIV infection effectively treated with antiretroviral therapies, the provision of help through the administration of a subunit vaccine does not result in the expansion of CD8 cells reactive to HIV peptides. This said, it is not yet clear that the expansion of HIV-specific CD8 T cells in chronic infection will necessarily result in a more favorable disease course. Does this mean that help may not be enough to permit immune control of HIV replication? Indeed, a fundamental question remains whether impaired functional immunity in HIV infection determines the progressive nature of this disease. It is clear that the immune system does mount a valiant response to the virus, easily on a par with responses to other persistent viruses such as cytomegalovirus and Epstein–Barr virus (EBV). In fact, the ‘skewed’ maturation phenotypes of HIV-specific CD8 T cells [7] are often the dominant subset at particular stages of protective immune responses against cytomegalovirus and EBV [26]. However, as these infections enter their chronic phase, whereas cytomegalovirus and EBV disease progression is controlled by specific immune responses, HIV disease is not. If, as the data of Robbins and colleagues (pp. 1121–1126) suggest, help alone is not enough, it is clear that sometimes, like this time, more work needs to be done. Hopefully, the correlates of immunity that we try to establish will not evade us in the same way that the virus evades the immune response against it.
HIV-1-infected patients have an increased risk for atherothrombosis and cardiovascular disease, but the mechanism behind these risks is poorly understood. We have previously reported that expression of tissue factor (TF) on circulating monocytes is increased in persons with HIV infection and that TF expression is related to immune activation, to levels of HIV in plasma, and to indices of microbial translocation. In this study, we explore the activation state of platelets in HIV disease.Here, using flow cytometry-based assays, we measured platelet and platelet microparticle (PMP) activation in samples from HIV-1-infected donors and controls.Platelets and PMPs from HIV-1-infected patients are activated (as reflected by expression of CD62 P-selectin) and also more frequently expressed the procoagulant TF than did platelets and PMPs obtained from controls. Expression of these proteins was directly related to expression of TF on monocytes, to markers of T-cell activation (CD38 and HLA-DR), and to plasma levels of soluble CD14, the coreceptor for bacterial lipopolysaccharride. Platelet and microparticle expression of TF was not related to plasma levels of HIV but expression of P-selectin was related to plasma levels of HIV; neither TF nor P-selectin expression was related to CD4 T-cell count.Platelets and microparticles are activated in HIV infection, and this activated phenotype may contribute to the increased risk for cardiovascular and thrombotic events in this population although a role for other confounding cardiovascular risks cannot be completely excluded.
We examined changes in soluble inflammatory cytokines and T-cell activation after antiretroviral therapy (ART) initiation in an AIDS Clinical Trials Group (ACTG) nested case-control study. Cases were 143 human immunodeficiency virus (HIV)–infected adults who developed a non-AIDS event; 315 controls remained event-free. Specimens were tested pre-ART, year 1 post-ART, and at the visit preceding the event. Conditional logistic regression evaluated the associations of biomarker changes with non-AIDS events. Inflammatory and most activation biomarkers declined from pre-ART to year 1 for cases and controls. Subsequently, inflammatory biomarkers remained mostly stable in controls but not cases. Cellular activation markers generally declined for both cases and controls between year 1 and the pre-event sampling. Controls with greater pre-ART RNA levels or lower CD4+ levels had higher biomarker levels while also experiencing greater biomarker declines in the first year of ART. Changes in biomarkers to year 1 showed no significant associations with non-AIDS events. Cases, however, had significantly greater increases in all plasma biomarkers (but not cellular activation) from year 1 to the visit preceding the event. Inflammation increases prior to non-AIDS events in treated HIV-infected adults. These biomarker changes may reflect subclinical disease processes or other alterations in the inflammatory environment that causally contribute to disease. NCT00001137.
