Impaired immunity in AIDS. The mechanisms responsible and their potential reversal by antiviral therapy

Single-cell analysis of immune cell transcriptome during HIV-1 infection and therapy

BACKGROUND

Cellular immune responses are phenotypically and functionally perturbed during HIV-1 infection, with the majority of function restored upon antiretroviral therapy (ART). Despite ART, residual inflammation remains that can lead to HIV-related co-morbidities and mortality, indicating that ART does not fully restore normal immune cell function. Thus, understanding the dynamics of the immune cell landscape during HIV-1 infection and ART is critical to defining cellular dysfunction that occurs during HIV-1 infection and imprints during therapy.

RESULTS

Here, we have applied single-cell transcriptome sequencing of peripheral blood immune cells from chronic untreated HIV-1 individuals, HIV-1-infected individuals receiving ART and HIV-1 negative individuals. We also applied single-cell transcriptome sequencing to a primary cell model of early HIV-1 infection using CD4+ T cells from healthy donors. We described changes in the transcriptome at high resolution that occurred during HIV-1 infection, and perturbations that remained during ART. We also determined transcriptional differences among T cells expressing HIV-1 transcripts that identified key regulators of HIV-1 infection that may serve as targets for future therapies to block HIV-1 infection.

CONCLUSIONS

This work identified key molecular pathways that are altered in immune cells during chronic HIV-1 infection that could remain despite therapy. We also identified key genes that are upregulated during early HIV-1 infection that provide insights on the mechanism of HIV-1 infection and could be targets for future therapy.

Simian Immunodeficiency Virus Infection of Rhesus Macaques Results in Delayed Zika Virus Clearance

Flaviviruses are controlled by adaptive immune responses but are exquisitely sensitive to interferon-stimulated genes (ISGs). How coinfections, particularly simian immunodeficiency viruses (SIVs), that induce robust ISG signatures influence flavivirus clearance and pathogenesis is unclear. Here, we studied how Zika virus (ZIKV) infection is modulated in SIV-infected nonhuman primates. We measured ZIKV replication, cellular ZIKV RNA levels, and immune responses in non-SIV-infected and SIV-infected rhesus macaques (RMs), which we infected with ZIKV. Coinfected animals had a 1- to 2-day delay in peak ZIKV viremia, which was 30% of that in non-SIV-infected animals. However, ZIKV viremia was significantly prolonged in SIV-positive (SIV⁺) RMs. ISG levels at the time of ZIKV infection were predictive for lower ZIKV viremia in the SIV⁺ RMs, while prolonged ZIKV viremia was associated with muted and delayed adaptive responses in SIV⁺ RMs.IMPORTANCE Immunocompromised individuals often become symptomatic with infections which are normally fairly asymptomatic in healthy individuals. The particular mechanisms that underlie susceptibility to coinfections in human immunodeficiency virus (HIV)-infected individuals are multifaceted. ZIKV and other flaviviruses are sensitive to neutralizing antibodies, whose production can be limited in HIV-infected individuals but are also sensitive to type I interferons, which are expressed at high levels in HIV-infected individuals. Data in this study highlight how individual components of the innate and adaptive immune responses which become perturbed in HIV-infected individuals influence ZIKV infection.

Ten years of antiretroviral therapy: Incidences, patterns and risk factors of opportunistic infections in an urban Ugandan cohort

BACKGROUND

Despite increased antiretroviral therapy (ART) coverage and the raised CD4 threshold for starting ART, opportunistic infections (OIs) are still one of the leading causes of death in sub-Saharan Africa. There are few studies from resource-limited settings on long-term reporting of OIs other than tuberculosis.

METHODS

Patients starting ART between April 2004 and April 2005 were enrolled and followed-up for 10 years in Kampala, Uganda. We report incidences, patterns and risk factors using Cox proportional hazards models of OIs among all patients and among patients with CD4 cell counts >200 cells/μL.

RESULTS

Of the 559 patients starting ART, 164 patients developed a total of 241 OIs during 10 years of follow-up. The overall incidence was highest for oral candidiasis (25.4, 95% confidence interval (CI): 20.5-31.6 per 1000 person-years of follow-up), followed by tuberculosis (15.3, 95% CI: 11.7-20.1), herpes zoster (12.3, 95% CI: 9.1-16.6) and cryptococcal meningitis (3.0, 95% CI: 1.7-5.5). Incidence rates for all OIs were highest in the first year after ART initiation and decreased with the increase of the current CD4 cell count. Factors independently associated with development of OIs were baseline nevirapine-based regimens, time-varying higher viral load, time-varying lower CD4 cell count and time-varying lower hemoglobin. In patients developing OIs at a current CD4 cell count >200 cells/μL, factors independently associated with OI development were time-varying increase in viral load and time-varying decrease in hemoglobin, whereas a baseline CD4 cell count <50 cells/μL was protective.

CONCLUSION

We report high early incidences of OIs, decreasing with increasing CD4 cell count and time spent on ART. Ongoing HIV replication and anemia were strong predictors for OI development independent of the CD4 cell count. Our findings support the recommendation for early initiation of ART and suggest close monitoring for OIs among patients recently started on ART, with low CD4 cell count, high viral load and anemia.

How histopathology can contribute to an understanding of defense mechanisms against cryptococci

Invasive fungal infections, particularly those considered opportunistic, have become a common and significant complication of procedures performed in advanced contemporary medicine. Among such infections, cryptococcosis, which is usually caused by infection with Cryptococcus neoformans and Cryptococcus gattii, is particularly problematic because this fungal infection occurs in immunocompromised and apparently immunocompetent individuals. It has been largely accepted that Cryptococcus species are recognized by cellular receptors and that Th1-type immune responses play an important role in defense mechanisms against the yeast. However, the interaction between the yeast and host tissue varies depending on the characteristics of the yeast and the immune status of the host. To gain a better understanding of the pathophysiology of cryptococcosis, we wish to emphasize the usefulness of histopathological examinations, because it allowed more detailed information of an extremely complex interaction between the causative yeasts and tissue response. In the present review, we describe the pathophysiology of cryptococcosis as largely revealed in our previous histopathological investigations of the experimental infection.

Engagement of the CD4 receptor affects the redistribution of Lck to the immunological synapse in primary T cells: implications for T-cell activation during human immunodeficiency virus type 1 infection

Understanding the molecular mechanisms underlying dysregulated immune responses in human immunodeficiency virus type 1 (HIV-1) infection is crucial for the control of HIV/AIDS. Despite the postulate that HIV envelope glycoprotein gp120-CD4 interactions lead to impaired T-cell responses, the precise mechanisms underlying such association are not clear. To address this, we analyzed Lck and F-actin redistribution into the immunological synapse in stimulated human primary CD4(+) T cells from HIV-1-infected donors. Similar experiments were performed with CD4(+) T cells from HIV-uninfected donors, which were exposed to anti-CD4 domain 1 antibodies, as an in vitro model of gp120-CD4 interactions, or aldithriol-inactivated HIV-1 virions before stimulation. CD4(+) T cells from HIV-infected patients exhibited a two- to threefold inhibition of both Lck and F-actin recruitment into the synapse, compared to cells from uninfected donors. Interestingly, defective recruitment of Lck was ameliorated following suppressive highly active antiretroviral therapy. Engagement of the CD4 receptor on T cells from HIV-uninfected donors before anti-CD3/CD28 stimulation led to similar defects. Furthermore, the redistribution of Lck into lipid rafts was abrogated by CD4 preengagement. Our results suggest that the engagement of CD4 by HIV gp120 prior to T-cell receptor stimulation leads to dysregulation of early signaling events and could consequently play an important role in impaired CD4(+) T-cell function.

Association of CD80 and CD86 expression levels with disease status of Visna/Maedi virus infected sheep

In small ruminant lentivirus infections, cellular immune responses are diminished in clinically affected animals. The underlying mechanisms for this are unknown. In this study, we tested the hypothesis that alterations in expression of the co-stimulatory molecules B7-1 and B7-2 are involved in infections with Visna/Maedi virus (VMV), the prototype lentivirus of sheep. We studied B7 expression levels ex vivo in peripheral blood mononuclear cells (PBMCs), determining B7 RNA levels by real time reverse transcriptase polymerase chain reaction in asymptomatic as well as clinically affected VMV-seropositive sheep. The levels of both B7 molecules were increased in VMV-seropositive asymptomatic sheep. However, in VMV clinically affected sheep, the level of CD80 (but not CD86) was low compared with the level in uninfected sheep (p < 0.05). CD80 and CD86 RNA levels were associated with the ability of PBMCs to respond to VMV gag antigens (p14, p17, and p25) by proliferation, with most seropositive asymptomatic sheep showing positive proliferative responses but clinically affected sheep showing no response. The response to p25 in clinically affected animals was increased by the addition of interleukin-2 to the cultures. Decreased recall responses to unrelated antigens (assessed by production of interferon-gamma) were also found in clinically affected sheep. Thus, among seropositive sheep, decreased B7-1 (CD80) RNA levels and diminished antigen-specific cellular immune responses in PBMCs point to a VMV disease status, whereas increased CD80 and CD86 levels and augmented cellular responses are linked to asymptomatic infection.

CD4+ T cells from simian immunodeficiency virus disease-resistant sooty mangabeys produce more IL-2 than cells from disease-susceptible species: involvement of p300 and CREB at the proximal IL-2 promoter in IL-2 up-regulation

IL-2 is an important cytokine required for the physiological function of CD4(+) T cells. Immunological unresponsiveness-anergy- of CD4(+) T cells is characterized by the inability of these cells to synthesize IL-2. Both progressive HIV infection leading to AIDS in humans and SIV infection in rhesus macaques (RM) are associated with dysregulation of IL-2 synthesis. In certain nonhuman primate species, such as sooty mangabeys (SM), SIV infection does not lead to AIDS. We have shown that this is associated with the resistance of the CD4(+) T cells from SM to undergo anergy in vitro. In this study, we show that CD4(+) T cells from SM spontaneously synthesize 2- to 3-fold higher levels of IL-2 than corresponding cells from RM. Proximal IL-2 promoter constructs derived from SM show significantly higher activity than the RM-derived constructs in primary CD4(+) T cells, which is associated with an element at approximately nt -200. Activity of both constructs was up-regulated by p300 and down-regulated by CREB to a similar degree. Chromatin immunoprecipitation analysis showed significantly higher binding of p300 and lower binding of CREB to the SM promoter in vivo. Two single nucleotide substitutions present in the SM sequence around position -200 and -180 seem to increase the affinity of these sites for the binding of transcription factors, one of which was identified as Oct-1. These unique characteristics of the proximal IL-2 promoter in SM therefore can represent one of the mechanisms contributing to the resistance of these cells to undergo anergy.

Central memory CD4 T cells are the predominant cell subset resistant to anergy in SIV disease resistant sooty mangabeys

OBJECTIVE

HIV infection in humans and experimental SIV infection in rhesus macaques leads to the loss of recall antigen responses, immunological anergy in CD4 T cells and AIDS. In contrast, natural infection in sooty mangabeys with SIV does not lead to disease despite high viral loads accompanied by resistance of their CD4 T cells to undergo immunological anergy. The objective of the study was to further elucidate the mechanisms that contribute to anergy resistance in CD4 T cells from sooty mangabeys and identify whether the anergy resistance is a function of a specific subset or the entire cell population.

MATERIALS AND METHODS

Susceptibility or resistance to anergy was analyzed in antigen specific and defined CD4 T cell subsets from peripheral blood of sooty mangabeys and rhesus macaques by using an in vitro anergy inducing protocol; expression of the anergy associated gene GRAIL was measured.

RESULTS

Antigen specific CD4 T cells from SIV disease resistant sooty mangabey are relatively resistant to the development of anergy. This resistance is associated with a lack of an upregulation of GRAIL. Conversely, rhesus macaque CD4 T cells are sensitive to anergy induction associated with upregulation of GRAIL. Furthermore the anergy resistant phenotype of sooty mangabey CD4 T cells predominantly resides in central memory cells defined either as CD4+CD45RA-CD62L+ or CD4+CD28+CD95+CCR7+.

CONCLUSIONS

The maintenance of recall responses in sooty mangabeys is associated with the resistance of central memory CD4 T cells to the induction of anergy which may represent an important mechanism underlying SIV disease resistance in this species.

Relative resistance in the development of T cell anergy in CD4+ T cells from simian immunodeficiency virus disease-resistant sooty mangabeys

Despite high viral loads, T cells from sooty mangabey (SM) monkeys that are naturally infected with SIV but remain clinically asymptomatic, proliferate and demonstrate normal Ag-specific memory recall CD4(+) T cell responses. In contrast, CD4(+) T cells from rhesus macaques (RM) experimentally infected with SIV lose Ag-specific memory recall responses and develop immunological anergy. To elucidate the mechanisms for these distinct outcomes of lentiviral infection, highly enriched alloreactive CD4(+) T cells from humans, RM, and SM were anergized by TCR-only stimulation (signal 1 alone) and subsequently challenged with anti-CD3/anti-CD28 Abs (signals 1 + 2). Whereas alloreactive CD4(+)T cells from humans and RM became anergized, surprisingly, CD4(+) T cells from SM showed marked proliferation and IL-2 synthesis after restimulation. This resistance to undergo anergy was not secondary to a global deficiency in anergy induction of CD4(+) T cells from SM since incubation of CD4(+) T cells with anti-CD3 alone in the presence of rapamycin readily induced anergy in these cells. The resistance to undergo anergy was reasoned to be due to the ability of CD4(+) T cells from SM to synthesize IL-2 when incubated with anti-CD3 alone. Analysis of phosphorylated kinases involved in T cell activation showed that the activation of CD4(+) T cells by signal 1 in SM elicited a pattern of response that required both signals 1 + 2 in humans and RM. This function of CD4(+) T cells from SM may contribute to the resistance of this species to SIV-induced disease.

Sarcoidosis after antiretroviral therapy in a patient with acquired immunodeficiency syndrome

A 53-year-old man with acquired immunodeficiency syndrome (AIDS) developed clinical and radiological features compatible with sarcoidosis 14 months after starting highly active antiretroviral therapy (HAART). The CD4 lymphocyte count had increased from 5 cells/mm(3) to 235 cells/mm(3) with HAART. Transbronchial lung biopsy showed nonnecrotizing granulomas. All studies for an infectious etiology were negative. His condition improved after treatment with corticosteroids. To our knowledge, this is the fifth case report of sarcoidosis occurring after initiation of antiretroviral therapy for AIDS.

Calmodulin-binding function of LLP segments from the HIV type 1 transmembrane protein is conserved among natural sequence variants

LLP1 is a peptide, derived from the cytoplasmic tail of HIV-1 TM glycoprotein, that binds and inhibits calmodulin; this region is generally conserved among isolates, but amino acid variation does exist both within clade B and among different clades, as well as SIV. In light of previous studies showing that selected single amino acid changes can have a qualitatively significant effect on the calmodulin-binding properties of this peptide, we sought to examine the properties of naturally occurring variant LLP1 sequences. Using a quantitative fluorescence-based method to measure dissociation constants of calmodulin-LLP1 complexes, a remarkable conservation of calmodulin-binding function among natural variants was revealed. In contrast, engineered nonconservative single amino acid changes altered the affinity of the peptide for calmodulin. The results show that the calmodulin-binding function is well preserved despite the sequence variation observed in nature, suggesting that this region of the TM protein is important to viral replication.

TGF beta and HIV infection

TGF beta is a cytokine which is involved with the regulation of different aspects of host defense responses to injury. Overexpression of TGF beta can lead to the conversion of its protective functions to pathogenetic manifestations. TGF beta is a potent factor in promoting anabolic aspects in connective tissue metabolism, and uncontrolled production of TGF beta has been associated with the development of fibrosis. With respect to its effects on immune and inflammatory responses, TGF beta is an important endogenous immunosuppressive factor which physiologically may protect the organism from tissue damage caused by chronic activation of leukocytes. As a result of overproduction in HIV infection, this function of TGF beta can contribute to noncytopathic mechanisms of immunodeficiency. TGF beta is involved with several aspects of HIV disease and promotes virus replication and spreading through multiple distinct mechanisms. It directly stimulates virus replication in infected monocytes and peripheral blood mononuclear cells under certain in vitro conditions. It may stimulate the production of other cytokines that enhance virus replication and it may be the mediator of other HIV-stimulating agents such as cocaine. It enhances recruitment of mononuclear phagocytes as cells susceptible to virus infection. Through its profound and broad inhibitory effects on different antiviral defense mechanisms, it facilitates more rapid progression of virus infection and increases susceptibility to opportunistic infections and malignancies. Although these findings are largely based on in vitro systems, the demonstration of TGF beta overexpression in HIV-infected patients supports the notion that this cytokine is an important pathogenetic mediator in HIV infection and its associated diseases. Therapeutic strategies to interfere with these functions of TGF beta are the development of TGF beta-neutralizing antibodies and soluble TGF beta-binding proteins and receptors as well as approaches directed at reducing TGF beta gene expression.

Histopathologic and immunohistochemical findings associated with inflammatory dermatoses in human immunodeficiency virus type 1 disease and their correlation with Walter Reed stage. Military Medical Consortium for Applied Retroviral Research

BACKGROUND

Cutaneous lesions are common in patients with human immunodeficiency virus type 1 (HIV-1) infection. In many cases they are nonspecific inflammatory dermatoses.

OBJECTIVE

Our goal was to determine whether features of these inflammatory dermatoses were characteristic of HIV-1 infection and whether the changes correlated with the stage of disease.

METHODS

Biopsy specimens of inflammatory dermatoses from 176 HIV-1-infected patients in all Walter Reed stages were reviewed and the changes were compared with each WR stage.

RESULTS

The changes found were nonspecific but were suggestive of features described in graft-versus-host disease and became more prominent in late-stage disease.

CONCLUSION

A correlation was found between the changes and the stage of disease, and the findings add support to prior reports that at least some of the changes in HIV-1 infection may be autoimmune in origin.