Genevieve E. Martin

Aging is associated with chronic innate immune activation and dysregulation of monocyte phenotype and function

Chronic inflammation in older individuals is thought to contribute to inflammatory, age‐related diseases. Human monocytes are comprised of three subsets (classical, intermediate and nonclassical subsets), and despite being critical regulators of inflammation, the effect of age on the functionality of monocyte subsets remains to be fully defined. In a cross‐sectional study involving 91 healthy male (aged 20–84 years, median 52.4) and 55 female (aged 20–82 years, median 48.3) individuals, we found age was associated with an increased proportion of intermediate and nonclassical monocytes (P = 0.002 and 0.04, respectively) and altered phenotype of specific monocyte subsets (e.g. increased expression of CD11b and decreased expression of CD38, CD62L and CD115). Plasma levels of the innate immune activation markers CXCL10, neopterin (P < 0.001 for both) and sCD163 (P = 0.003) were significantly increased with age. Whilst similar age‐related changes were observed in both sexes, monocytes from women were phenotypically different to men [e.g. lower proportion of nonclassical monocytes (P = 0.002) and higher CD115 and CD62L but lower CD38 expression] and women exhibited higher levels of CXCL10 (P = 0.012) and sCD163 (P < 0.001) but lower sCD14 levels (P < 0.001). Monocytes from older individuals exhibit impaired phagocytosis (P < 0.05) but contain shortened telomeres (P < 0.001) and significantly higher intracellular levels of TNF both at baseline and following TLR4 stimulation (P < 0.05 for both), suggesting a dysregulation of monocyte function in the aged. These data show that aging is associated with chronic innate immune activation and significant changes in monocyte function, which may have implications for the development of age‐related diseases.

Age-associated changes in monocyte and innate immune activation markers occur more rapidly in HIV infected women

Background Aging is associated with immune dysfunction and the related development of conditions with an inflammatory pathogenesis. Some of these immune changes are also observed in HIV infection, but the interaction between immune changes with aging and HIV infection are unknown. Whilst sex differences in innate immunity are recognized, little research into innate immune aging has been performed on women. Methods This cross-sectional study of HIV positive and negative women used whole blood flow cytometric analysis to characterize monocyte and CD8+ T cell subsets. Plasma markers of innate immune activation were measured using standard ELISA-based assays. Results HIV positive women exhibited elevated plasma levels of the innate immune activation markers CXCL10 (p<0.001), soluble CD163 (sCD163, p = 0.001), sCD14 (p = 0.022), neopterin (p = 0.029) and an increased proportion of CD16+ monocytes (p = 0.009) compared to uninfected controls. Levels of the innate immune aging biomarkers sCD163 and the proportion of CD16+ monocytes were equivalent to those observed in HIV negative women aged 14.5 and 10.6 years older, respectively. CXCL10 increased with age at an accelerated rate in HIV positive women (p = 0.002) suggesting a synergistic effect between HIV and aging on innate immune activation. Multivariable modeling indicated that age-related increases in innate immune biomarkers CXCL10 and sCD163 are independent of senescent changes in CD8+ T lymphocytes. Conclusions Quantifying the impact of HIV on immune aging reveals that HIV infection in women confers the equivalent of a 10–14 year increase in the levels of innate immune aging markers. These changes may contribute to the increased risk of inflammatory age-related diseases in HIV positive women.

The importance of monocytes and macrophages in HIV pathogenesis, treatment, and cure.

Monocytes and macrophages play critical roles in HIV transmission, viral spread early in infection, and as a reservoir of virus throughout infection. There has been a recent resurgence of interest in the biology of monocyte subsets and macrophages and their role in HIV pathogenesis, partly fuelled by efforts to understand difficulties in achieving HIV eradication. This article examines the importance of monocyte subsets and tissue macrophages in HIV pathogenesis. Additionally, we will review the role of monocytes and macrophages in the development of serious non-AIDS events including cardiovascular disease and neurocognitive impairment, their significance in viral persistence, and how these cells represent an important obstacle to achieving HIV eradication.

Inflammatory Co-morbidities in HIV+ Individuals: Learning Lessons from Healthy Ageing

Increased life expectancy due to improved efficacy of cART has uncovered an increased risk of age-related morbidities in HIV+ individuals and catalyzed significant research into mechanisms driving these diseases. HIV infection increases the risk of non-communicable diseases common in the aged, including cardiovascular disease, neurocognitive decline, non-AIDS malignancies, osteoporosis, and frailty. These observations suggest that HIV accelerates immunological ageing, and there are many immunological similarities with the aged, including shortened telomeres, accumulation of senescent T cells and altered monocyte phenotype/function. However, the most critical similarity between HIV+ individuals and the elderly, which most likely underpins the heightened risk of non-communicable diseases, is chronic inflammation and associated immune activation. Here, we review the similarities between HIV+ individuals and the aged regarding the pathogenesis of inflammatory diseases, the current evidence for mechanisms driving these processes and discuss current and potential therapeutic strategies for addressing inflammatory co-morbidity in HIV+ infection.

Exhaustion of Activated CD8 T Cells Predicts Disease Progression in Primary HIV-1 Infection.

The rate at which HIV-1 infected individuals progress to AIDS is highly variable and impacted by T cell immunity. CD8 T cell inhibitory molecules are up-regulated in HIV-1 infection and associate with immune dysfunction. We evaluated participants (n = 122) recruited to the SPARTAC randomised clinical trial to determine whether CD8 T cell exhaustion markers PD-1, Lag-3 and Tim-3 were associated with immune activation and disease progression. Expression of PD-1, Tim-3, Lag-3 and CD38 on CD8 T cells from the closest pre-therapy time-point to seroconversion was measured by flow cytometry, and correlated with surrogate markers of HIV-1 disease (HIV-1 plasma viral load (pVL) and CD4 T cell count) and the trial endpoint (time to CD4 count <350 cells/μl or initiation of antiretroviral therapy). To explore the functional significance of these markers, co-expression of Eomes, T-bet and CD39 was assessed. Expression of PD-1 on CD8 and CD38 CD8 T cells correlated with pVL and CD4 count at baseline, and predicted time to the trial endpoint. Lag-3 expression was associated with pVL but not CD4 count. For all exhaustion markers, expression of CD38 on CD8 T cells increased the strength of associations. In Cox models, progression to the trial endpoint was most marked for PD-1/CD38 co-expressing cells, with evidence for a stronger effect within 12 weeks from confirmed diagnosis of PHI. The effect of PD-1 and Lag-3 expression on CD8 T cells retained statistical significance in Cox proportional hazards models including antiretroviral therapy and CD4 count, but not pVL as co-variants. Expression of ‘exhaustion’ or ‘immune checkpoint’ markers in early HIV-1 infection is associated with clinical progression and is impacted by immune activation and the duration of infection. New markers to identify exhausted T cells and novel interventions to reverse exhaustion may inform the development of novel immunotherapeutic approaches.

Viremic and Virologically Suppressed HIV Infection Increases Age-Related Changes to Monocyte Activation Equivalent to 12 and 4 Years of Aging, Respectively.

Background:Chronic inflammation and immune activation occur in both HIV infection and normal aging and are associated with inflammatory disease. However, the degree to which HIV influences age-related innate immune changes, and the biomarkers which best reflect them, remains unclear. Methods and Results:We measured established innate immune aging biomarkers in 309 individuals including 88 virologically suppressed (VS) and 52 viremic (viral load ⩽ and >50 copies per milliliter, respectively) HIV-positive individuals. Levels of soluble (ie, CXCL10, soluble CD163, neopterin) and cellular (ie, proportions of inflammatory CD16+ monocytes) biomarkers of monocyte activation were increased in HIV-positive individuals and were only partially ameliorated by viral suppression. Viremic and VS HIV-positive individuals show levels of age-related monocyte activation biomarkers that are similar to uninfected controls aged 12 and 4 years older, respectively. Viremic HIV infection was associated with an accelerated rate of change of some monocyte activation markers (eg, neopterin) with age, whereas in VS individuals, subsequent age-related changes occurred at a similar rate as in controls, albeit at a higher absolute level. We further identified CXCL10 as a robust soluble biomarker of monocyte activation, highlighting the potential utility of this chemokine as a prognostic marker. Implications:These findings may partially explain the increased prevalence of inflammatory age-related diseases in HIV-positive individuals and potentially indicate the pathological mechanisms underlying these diseases, which persist despite viral suppression.

Post-treatment control or treated controllers? Viral remission in treated and untreated primary HIV infection

Objective(s):An HIV cure will impose aviraemia that is sustained following the withdrawal of antiretroviral therapy (ART). Understanding the efficacy of novel interventions aimed at curing HIV requires characterization of both natural viral control and the effect of ART on viral control after treatment interruption. Design:Analysis of transient viral control in recent seroconverters in the Short Pulse AntiRetroviral Therapy at Acute Seroconversion trial. Methods:We compared untreated and treated HIV seroconverters (n = 292) and identified periods of control (plasma HIV RNA < 400 copies/ml for ≥16 weeks off therapy) in 7.9% of ART-naive participants, and in 12.0% overall. HIV DNA was measured by qPCR, and HIV-specific CD8+ responses were measured by enzyme-linked immunosorbent spot assay (ELISpot). T-cell activation and exhaustion were measured by flow cytometry. Results:At baseline, future controllers had lower HIV DNA, lower plasma HIV RNA, higher CD4+ : CD8+ ratios (all P < 0.001) and higher CD4+ cell counts (P < 0.05) than noncontrollers. Among controllers, the only difference between the untreated and those who received ART was higher baseline HIV RNA in the latter (P = 0.003), supporting an added ART effect. Conclusion:Consideration of spontaneous remission in untreated individuals will be critical to avoid overestimating the effect size of new interventions used in HIV cure studies.

CD32-Expressing CD4 T Cells Are Phenotypically Diverse and Can Contain Proviral HIV DNA

Efforts to both characterize and eradicate the HIV reservoir have been limited by the rarity of latently infected cells and the absence of a specific denoting biomarker. CD32a (FcγRIIa) has been proposed to be a marker for an enriched CD4 T cell HIV reservoir, but this finding remains controversial. Here, we explore the expression of CD32 on CD3+CD4+ cells in participants from two primary HIV infection studies and identify at least three distinct phenotypes (CD32low, CD32+CD14+, and CD32high). Of note, CD4 negative enrichment kits remove the majority of CD4+CD32+ T cells, potentially skewing subsequent analyses if used. CD32high CD4 T cells had higher levels of HLA-DR and HIV co-receptor expression than other subsets, compatible with their being more susceptible to infection. Surprisingly, they also expressed high levels of CD20, TCRαβ, IgD, and IgM (but not IgG), markers for both T cells and naïve B cells. Compared with other populations, CD32low cells had a more differentiated memory phenotype and high levels of immune checkpoint receptors, programmed death receptor-1 (PD-1), Tim-3, and TIGIT. Within all three CD3+CD4+CD32+ phenotypes, cells could be identified in infected participants, which contained HIV DNA. CD32 expression on CD4 T cells did not correlate with HIV DNA or cell-associated HIV RNA (both surrogate measures of overall reservoir size) or predict time to rebound viremia following treatment interruption, suggesting that it is not a dominant biomarker for HIV persistence. Our data suggest that while CD32+ T cells can be infected with HIV, CD32 is not a specific marker of the reservoir although it might identify a population of HIV enriched cells in certain situations.

Enrichment of the HIV reservoir in CD32+ CD4 T cells occurs early in blood and tissue

The Fc receptor CD32 has been proposed as a marker for CD4 T cells latently infected with HIV. We demonstrate that enrichment for HIV DNA in CD32+ CD4 T cells can be found early in infection in both tissue and blood. However, we find no evidence for a correlation between CD32 expression on CD4 T cells and either HIV DNA levels or time to rebound viraemia following treatment interruption. CD32+ CD4 T cells have a more differentiated memory phenotype, and high levels of expression of immune checkpoint receptors PD-1, Tim-3 and TIGIT as well as the activation marker, HLA DR. There was no difference in the phenotype or frequency of CD32 expressing cells prior to or after the initiation of antiretroviral therapy, or compared with healthy controls, suggesting that preferential infection or survival, rather than up-regulation, may be responsible for the observed enrichment of proviral HIV DNA in CD32+ CD4 T cells.