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Immune Activation, Inflammation and Complications of HIV
19th IAC 2012:
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David H. Shepp, MD
Associate Professor of Medicine
Hofstra North Shore-LIJ School of Medicine
North Shore University Hospital - Manhasset, NY
"Non-AIDS-defining cancers (NADC), liver disease and CVD are the leading non-AIDS-related causes of mortality and the proportion of deaths due to NADC is rising"
"Multiple co-morbid diagnoses are more common in HIV-infected compared to age matched HIV-uninfected individuals. Immune activation and inflammation are present in untreated HIV, persist in many cases after otherwise effective ART and contribute to the increased risk of non-AIDS medical illnesses."
"Intervention against inflammation: initiation of ART very early in HIV infection, by Markowitz et al......Normalization of CD8+ T-cell activation (CD38+/HLA-DR+) to levels seen in healthy controls was achieved at 48 and 96 weeks"
"5 weekly injections of IL-21 reversed the progressive depletion of Th17+ T-cells in intestinal mucosal tissues"
"markers are needed that correlate with risk of clinical events, including non-AIDS medical illnesses, in patients already receiving ART"
"Low level ongoing HIV replication & immunological non-response to HAART may cause activation & inflammation"
"HCV antibody positivity and lower current CD4 were all independently associated with higher levels of CD8+ immune activation"
"higher BMI category was significantly associated with higher levels of the inflammatory markers"
Untreated HIV infection causes a state of immune activation and inflammation that drives the progressive loss of CD4+ T-cells and the development of immune dysfunction. Along with traditional risk factors such as aging, smoking, obesity, dyslipidemia, drug and alcohol abuse, chronic inflammation is an important contributor to the pathogenesis of many disease states, including cardiovascular/cerebrovascular disease (CVD), cancer, diabetes, liver disease, osteoporosis and neurocognitive dysfunction. Combination antiretroviral therapy (ART) reduces but does not necessarily normalize chronic inflammation due to HIV. Therefore, chronic immune activation that exists before and persists after otherwise successful ART leaves patients at increased risk for non-AIDS medical illnesses. Updated information on mortality trends in HIV was presented at the XX International AIDS Conference (IAC), held in Washington DC, July 22-27. Data from the large D:A:D cohort showed overall mortality and deaths due to AIDS-related causes declined from 1999 to 2010 (Smith CJ. THAB0304). Non-AIDS-related illnesses now cause about 3/4 of deaths in HIV-infected individuals. Non-AIDS-defining cancers (NADC), liver disease and CVD are the leading non-AIDS-related causes of mortality and the proportion of deaths due to NADC is rising. Another cohort study of HIV-infected and HIV-negative individuals in Amsterdam demonstrated that in every age bracket, HIV-infected individuals are diagnosed with multiple comorbid illnesses more often than their HIV-negative counterparts. A multivariable analysis controlling for other know risk factors confirmed that being HIV-infected was independently associated with a doubling (OR 2.1) of risk for multiple comorbidities (Schouten J. THAB0205)
Causes of Inflammation. The pathogenesis of persistent immune activation in HIV-infected patients on ART is complex. Multiple causes have been identified. Microbial translocation due to persistent immunologic injury in gut-associated lymphoid tissue, chronic co-infections such as CMV and HCV, low-level HIV infection, metabolic derangements, effects of antiretrovirals (ARV), and incomplete or dysfunctional immune reconstitution may all play a role. Abstracts from the XX IAC presented new insights into some of these potential causes.
Low level HIV replication. Successful ART durably suppresses plasma HIV RNA, but a variable level of residual virus may remain. Some patients are intermittently detectable by standard clinical assays, while others are detectable only when more sensitive research techniques are used. When lymphoid tissue is sampled, most patients have residual HIV RNA. This ongoing, low-level HIV production may provide the antigenic stimulation to drive immune activation. Zheng et al. (MOPE012) studied 832 patients who were on ART in ACTG trials for at least 96 week and had HIV RNA <200 copies/mL. CD8+ T-cell activation (CD38+/HLA-DR+) was significantly reduced from pre-ART levels, but remained higher in those with HIV RNA between 51-200 copies/mL compared to those <50 copies. In those with HIV RNA <50 copies, older age, race/ethnicity, HCV antibody positivity and lower current CD4 were all independently associated with higher levels of CD8+ immune activation. A second study used a more sensitive assay to examine 871 Italian patients virologically suppressed below 50 copies/mL on long-term ART. Patients with plasma HIV RNA <3 copies/mL had significantly lower levels of CD8+ T-cell activation (CD38+/HLA-DR+) than did patients who experienced viral load blips above 50 copies/mL, but had similar activation levels to those with HIV RNA detectable between 3-50 (Bernardini C. MOPE008). Patients on NNRTI-based ART were found to have lower activation levels than those on either boosted or unboosted PI-based ART. This study also found age and HCV antibody positivity were independently associated with higher levels of CD8+ activation.
Co-infections. Despite good control of HIV replication by ART, immune activation in HIV may be driven by persistent or recurrent co-infections. Two abstract mentioned above (MOPE008, MOPE012) found HCV-infection was independently associated with higher CD8+ activation in patients responding to ART. A third small study focusing on elite controllers found a trend toward higher levels of activation markers (CD38+/HLA-DR+) in CD8+ but not CD4+ T-cells when HCV RNA was detected compared to elite controllers who were HCV antibody positive but RNA negative. In contrast, another small study (n=59) examining multiple markers of inflammation and immune activation found no difference in CD8+ activation markers among individuals with HIV mono-infection, HCV mono-infection, HIV/HCV co-infection with chronic HCV, and co-infection with cleared HCV (Howdowanec A. MOPE011). The HIV-infected patients were described as well controlled on ART. However, CD4+HLA-DR+ cells were elevated in the 3 HCV-infected groups while CD4+CD38+ cells were higher in the 3 HIV-infected groups, suggesting different activation markers may be selectively affected by these two infections. Among 9 cytokines assessed, only IL-10, an anti-inflammatory cytokine that down-regulates certain Th1 responses was found to be significantly higher in HIV/HCV co-infection compared to HIV mono-infection.
Metabolic Disturbances. A combination of genetics, diet and physical inactivity conspire to create a syndrome of visceral abdominal adiposity, dyslipidemia, insulin resistance and hypertension that is increasingly prevalent in the general population worldwide. This metabolic syndrome is associated with high CVD risk. Obesity, insulin resistance and dyslipidemia are also risk factors for cancer and liver disease. Markers of chronic inflammation are often present in such individuals, although which is "chicken" and which is "egg" is controversial. Weight gain is common in HIV-infected patients responding to ART. Some weight gain corresponds to a return to pre-HIV health status, but overweight and obesity are increasingly common problems. A multi-center longitudinal cohort study of 494 HIV-infected adults (95% using ART) studied the problem of obesity (Conley L. WEPE096). As defined by BMI, about 60% were overweight or obese. In univariate analysis, higher BMI category was significantly associated with higher levels of the inflammatory markers hsCRP, IL-6, TNF-alpha and d-dimer as well as higher total cholesterol, ApoE, insulin, leptin HOMA-IR and carotid intima-media thickness. The independent importance of each of these parameter was unclear as multivariate analysis was not presented.
Incomplete Immune Recovery on ART. Despite years of complete virologic suppression, many patients on ART fail to normalize CD4+ T-cell counts. Older age, lower nadir CD4+ counts and HCV co-infection are often cited associations with incomplete immune recovery, but these may be surrogates for higher levels of persistent immune activation. Previous studies have found higher levels of peripheral blood T-cell activation markers in immunologic non-responders (INR). Dunham et al. (MOPE023) compared INRs and immunologic responders (IR), defined as having CD4+ T-cell counts <350 and >500, respectively, after > 1 year of effective ART. CD4+ T-cell activation and proliferation markers were higher in the peripheral blood INRs, as was expression of MX1, an interferon-stimulated gene. Plasmacytoid dendritic cells and activated macrophages were more common in rectosigmoid mucosal biopsies of INRs compared to IRs. These findings are consistent with the hypothesis that INRs have greater residual intestinal mucosal dysfunction, causing microbial translocation and systemic inflammation.
Prognosis. Markers of T-cell activation have been shown to be as powerful or perhaps even more powerful than HIV viral load and CD4+ T-cell counts in predicting disease progression and death in untreated HIV infection. Pre-ART inflammatory markers, including TNF-alpha and its receptors, hsCRP, IL-6, sCD14 and d-dimer all have shown correlation with disease progression and mortality in patients initiating ART. However, markers are needed that correlate with risk of clinical events, including non-AIDS medical illnesses, in patients already receiving ART. ACTG 320 was a randomized comparison of indinavir vs. placebo, both combined with zidovudine and lamivudine, that was published 15 years ago. The trial demonstrated the benefits of triple ART using the clinical endpoint of AIDS progression or death. Using stored serum, Spritzler et al. (MOPE007) designed a case-cohort analysis that examined the ability of soluble TNF-alpha receptor-II (sTNFR-II) and a panel of 94 other biomarkers to predict AIDS-related disease progression or death after adjustment for HIV RNA, CD4+ count, treatment randomization and other variables. sTNFR-II levels after 8 weeks of treatment independently correlated with the risk of AIDS progression/death. Numerous other markers were found to correlate with viral suppression but did not add to prediction of AIDS events/death. Three less well-studied markers (von Willebrand factor, brain-derived neurotrophic factor and IL-18) appeared to add prognostic value but require confirmation. In this study, non-AIDS events were not assessed. An analysis of a more contemporary study that included non-AIDS events also supported the value of sTNFR-II as a predictive marker. ACTG 5224s was a substudy of the larger ACTG 5202 which randomized treatment-naive patients to abacavir/lamivudine or tenofovir/emtricitabine with either efavirenz or ritonavir-boosted atazanavir. Multiple inflammatory biomarkers were measured at baseline and at weeks 24, 48 and 96 of study, and correlations with both AIDS and non-AIDS events were made. In analyses adjusting for other risk factors, time-updated levels of sTNFR-I and sTNFR-II had the strongest correlation with the combined endpoint of AIDS-related or non-AIDS events (McComsey G. THLBB06). When only baseline values were considered, hsCRP and IL-6 were also correlated with all events. AIDS and non-AIDS-related events were also analyzed separately with somewhat varying results, but these analyses were limited by the small numbers of endpoints.
Treatment. Recently reported trials of ART in treatment-naive patients have achieved viral suppression rates near 90%. While small improvements in ART are still possible, further advances in HIV care will more likely come from improved understanding and management of non-AIDS medical illnesses. Managing chronic inflammation will play an important role. Several presentations at this IAC suggested a few promising new approaches to reducing inflammation.
Aspirin (ASA) has both anti-thrombotic and anti-inflammatory effects, is inexpensive, has a well established adverse effect profile and is widely used for long-term CVD prevention. O'Brien et al. (THAB0202) reported a pilot study examining the effects of daily low dose (81 mg) daily ASA in both HIV-infected patients on ART and healthy volunteers. After one week, ASA significantly reduced the abnormal levels of platelet aggregation, soluble p-selectin (a marker of activated platelets an endothelial cells), CD4+ and CD8+ T-cell activation (CD38+/HLA-DR+) and sCD14 (a marker of monocyte activation) found in HIV-infected subjects. Leukocyte responsiveness to TLR-4 agonists, an important component of the innate immune response to microbial translocation was also improved.
Numerous previous studies have attempted to reduce low-level residual viral production by intensifying standard ART, with largely negative results. However, certain ARVs have immunomodulatory properties. Maraviroc (MVC) is an ARV that blocks CCR5, which is both a co-receptor for HIV cell entry and a receptor for beta-chemokines. Previous studies of the effects of MVC intensification on immune activation have shown conflicting results but have not examined the impact on immune function. Westrop et al. (WEPE095) evaluated immune function in a 24 week, randomized placebo-controlled study of MVC intensification that included 47 patients already virologically suppressed on standard ART. MVC enhanced antibody response to intramuscular meningococcal but not oral cholera vaccine. Recall antibody response to tetanus toxoid was similar in both study arms. In vitro T-cell gamma interferon production in response to stimulation with HIV antigen and tetanus toxoid also appeared to improve with MVC.
Despite improvement or normalization of CD4+ T-cells counts in peripheral blood with ART, T-cell populations in lymphatic tissues remain abnormal. Immunologic abnormalities in gut-associated lymphoid tissues are thought to be a major cause of microbial translocation and resulting chronic immune activation in HIV-infected patients on ART. The status of two cytokines under investigation to improve immune reconstitution was reviewed in symposia at this year's IAC. IL-7 is cytokine that plays a vital role in T-cell growth and regulation. It is produced within the fibroreticular cell network in the parafollicular zones of lymph nodes. HIV infection and associated inflammation causes fibrosis of these structures, impairing proper T-cell repopulation and function (Shacker T. MOSYS0603). Therapeutic administration of IL-7 offers the promise of correcting this abnormality. In a pilot study, IL-7 was shown to increase both peripheral CD4+ and CD8+ T-cells and had different, possibly more favorable effects on subsets of T-cells compared to IL-2, which was not clinically effective for treatment of HIV (Levy Y. MOSY0604). Increased CD4+ T-cells in the gut were seen in a small number of subjects who underwent biopsy, while circulating LPS and sCD14 decreased.
Th17 cells are a specific subset of T-cell that play an important role in the immune response to microbial infection and maintenance of mucosal integrity. Th17 depletion is seen in mucosal sites in both animal models of AIDS and human HIV infection. Loss of Th17 correlates with microbial translocation and systemic immune activation. IL-21 is a growth and differentiation factor for Th17 cells. In rhesus macaques, 5 weekly injections of IL-21 beginning 2 weeks after infection with pathogenic SIV did not affect SIV RNA or CD4+ T-cells in peripheral blood but reversed the progressive depletion of Th17+ T-cells in intestinal mucosal tissues that was seen in control animals at weeks 4 and 6 (Paiardini M. TUAA0305). Total CD4+ T-cell depletion in intestinal mucosa also was reversed and sustained after discontinuation of IL-21 such that by week 23, levels reached 46% of pre-infection values with IL-21 vs. only 12% in controls. Markers of T-cell proliferation were also reduced. Plasma levels of LPS and sCD14 were lower at week 23 in IL-21 treated animals, suggesting microbial translocation was controlled.
Another approach to reducing the effects of microbial translocation is treating gut microbes directly. Asmuth et al. described results of a single arm trial of oral serum bovine immunoglobulin (SBI) taken orally twice daily in 8 men with a diagnosis of HIV enteropathy (TUAA304). All subjects were on stable ART but had persistent GI symptoms. On treatment, these symptoms improved dramatically, a result that is hard to interpret in the absence of a control group. There was no effect on T-cells counts, activations markers, a panel of soluble markers of inflammation and microbial translocation, or measures of intestinal permeability and absorption. CD4+ T-cell percentages in duodenal biopsies improved when assessed by immunohistochemical staining, but not by flow cytometry. More encouraging results were obtained in a study of the non-absorbable antibiotic rifaxamin plus sulfasalazine, an anti-inflammatory agent used clinically for inflammatory bowel disease. The combination was given for 3 months to pigtail macaques who were simultaneously infected with pathogenic SIV. Compared to infected control animals, CD4+ and CD8+ T-cell activations markers (CD38+/HLA-DR+) were decreased, as were various plasma markers of inflammation including d-dimer, sCD14, TNF-alpha, IL-1 beta and INF-gamma. No improvement in peripheral CD4+ T-cells was observed but less CD4+ T-cell depletion in the intestinal mucosa was seen. The same investigators are also using this model to evaluate sevelamer, a phosphate binder used in management of chronic kidney disease which can also bind LPS.
A conceptually simple approach to limiting injury to host mucosal defenses and subsequent microbial translocation is initiation of ART very early in HIV infection, before irreversible damage to gut-associated lymphoid tissues occurs. Markowitz et al. (TUPD0204) reported on a cohort of 31patients treated with ART during acute or early HIV infection. Normalization of CD8+ T-cell activation (CD38+/HLA-DR+) to levels seen in healthy controls was achieved at 48 and 96 weeks. The median estimated duration of infection at ART initiation was 52 days with a range of 19-155 days. The study used both a standard 3 drug and an intensified 5 drug regimen, but the number of ARVs did not appear to affect the normalization of immune activation.
Summary. With improvements in the efficacy of and access to ART, deaths due to AIDS-related illnesses are declining while non-AIDS medical illnesses are increasing. Multiple co-morbid diagnoses are more common in HIV-infected compared to age matched HIV-uninfected individuals. Immune activation and inflammation are present in untreated HIV, persist in many cases after otherwise effective ART and contribute to the increased risk of non-AIDS medical illnesses. New studies from the XX IAC enhance our understanding of the causes of chronic inflammation and point to potential applications in prognosis and treatment. In patients responding to ART, residual HIV replication detectable above 50 copies but not below increases T-cell activation in peripheral blood, as does HCV co-infection. Obesity is common in contemporary ART treated patients and is associated with higher levels of inflammatory markers, although a causal relationship is not established. Immunologic dysfunction in gut-associated lymphoid tissue leading to microbial translocation may account for peripheral T-cell activation and impaired immune recovery in some patients responding virologically to ART. Two important studies suggest measuring soluble TNF-alpha receptors has potential predictive value to assess risk of AIDS-related and non-AIDS-related events in patients treated with ART, but further work is needed to understand how these measurements can affect clinical practice.
Various approaches to modulating immune activation and inflammation are being explored in animal models of AIDS and pilot clinical trials. Low dose ASA demonstrated many potentially beneficial effects on inflammation and coagulation in a short-term trial. Larger, longer-term studies are warranted to assess the persistence and magnitude of these effects and to assess unique safety issues that present in an HIV-infected population on ART. Adding the immunomodulatory ARV MVC to standard ART appears to improve some aspects of immune function and deserves further study. IL-21 and rifaxamin/sulfasalazine have favorable effects on systemic inflammation and mucosal immunity when used in animal models of acute SIV infection, before immunologic damage to gut-associated lymphoid tissue is severe. They will need to be studied in chronic infection to see if similar effects can be achieved. IL-7 therapy could correct a key immunologic defect that impairs reconstitution of T-cells in lymph nodes and has shown potential benefits in early human trials. SBI may improve symptoms of HIV enteropathy but does not appear promising as a treatment for chronic immune activation associated with GI tract immunologic dysfunction. Initiation of ART in early HIV may normalize immune activation without any other adjunctive therapy. Future studies should establish how late in HIV infection ART can be started and still achieve normalization, the durability of the response, the effect on other biomarkers of inflammation, and assess if restoration of intestinal immune function is adequate.
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