A trio of recent papers delve into the gut as an important site of HIV pathogenesis. Two are from the research group of Joseph Wong at UCSF, and they involve the same small cohort individuals analyzed before (in the JID paper) and after (in the journal AIDS) they started a clinical trial involving intensification of their antiretroviral therapy. The third paper, led by Shari Gordon from Guido Silvestri’s laboratory, studies a larger group of 28 people with HIV (15 untreated and 13 on antiretroviral therapy) and 11 healthy controls.
One unifying theme of the results is that not all gut sites are equal; both the levels of HIV infection and the proportions of CD4 vs. CD8 T cells vary when samples from the duodenum, terminal ileum, right colon and rectum are compared in Steven Yukl’s JID paper. HIV DNA levels show a trend toward a stepwise increase as the sample sites descend, with the lowest levels in the terminal ileum and highest in the rectum. Conversely, unspliced HIV RNA – a potential indicator of active viral replication - shows the opposite trend, with levels highest in the terminal ileum. Shari Gordon’s study samples a slightly different array of gut sites – terminal ileum, right colon, left colon, and sigmoid colon – but also finds variation in representation of CD4 T cell subsets; naïve CD4 T cell levels are highest in the terminal ileum but decrease progressively as the sample sites get lower down the GI tract.
The Yukl paper also reports some major differences between blood and gut samples. HIV DNA levels are consistently higher in all gut sites compared to peripheral blood mononuclear cells (PBMC) and the differences are highly statistically significant with the exception of the duodenum. And while there is a positive correlation between HIV DNA levels and markers of immune activation in PBMC, there is an inverse correlation in the gut, a novel finding that the researchers suggest may be due to infected cells in the gut being tolerant or anergic (the gut is known to be a site where T cell tolerance against commensal bacteria and food antigens is induced and maintained).
Shari Gordon’s study identifies several parallels between blood and gut. The levels of CD4 T cell depletion in blood correlate directly with the level of depletion measured in all gut sites. Levels of memory CD4 T cell proliferation (measured the Ki67 marker) also directly correlate in both compartments. Gordon finds that the magnitude of CD4 and CD8 T cell proliferation in the blood correlates with the severity of CD4 T cell depletion in the gut. This latter finding indicates that the loss of gut CD4 T cells impacts the normal balance (or “homeostasis”) of the immune system in a way that contributes to systemic immune activation. Encouragingly, the study reveals substantial repopulation of gut CCR5-expressing CD4 T cells in the cohort of individuals on ART and notes that: “in our hands the extent of depletion of intestinal CD4+CCR5+ T cells appeared to be less severe than what has been reported by others during HIV infection.”
The Steven Yukl paper in AIDS describes the impact of intensifying ART (with either raltegravir alone or raltegravir plus efavirenz or darunavir) for 12 weeks in seven of the eight individuals whose baseline values are reported in JID (one dropped out shortly after starting the trial for personal reasons). CD4 T cell counts and HIV DNA levels remained unchanged, but a significant drop in levels of unspliced HIV RNA was seen in the terminal ileum of 5/7 participants. There was also a slight decline in levels of activated CD4 and CD8 T cells in blood and gut, with the greatest change seen in the terminal ileum. The researchers conclude that the findings may be suggestive of some ongoing viral replication occurring in the terminal ileum that was impacted by ART intensification, but they stress that this interpretation needs to be confirmed by larger studies.
These papers add to the evidence that the gut plays an important role in the pathogenesis of HIV infection, but also highlight the need to better understand gut immunology in health as well as disease (an area of research that remains relatively obscure and under-supported). The suggestion that HIV may be establishing latency in tolerant CD4 T cells also has implications for cure research, because targeting this population may require different strategies than those being considered for other HIV reservoirs.
Published online October 12, 2010
The Journal of Infectious Diseases 2010;202:000–000
Steven A. Yukl,1,2 Sara Gianella,6,a Elizabeth Sinclair,3,2 Lorrie Epling,3,2 Qingsheng Li,5,a Lijie Duan,5 Alex L. M. Choi,1,2 Valerie Girling,3,2 Terence Ho,3,2 Peilin Li,1,2 Katsuya Fujimoto,1,2 Harry Lampiris,1,2 C. Bradley Hare,3,2 Mark Pandori,4 Ashley T. Haase,5 Huldrych F. Günthard,6 Marek Fischer,6 Amandeep K. Shergill,1,2 Kenneth McQuaid,1,2 Diane V. Havlir,3,2 and Joseph K. Wong1,2
1San Francisco Veterans Affairs Medical Center, 2University of California, San Francisco, 3San Francisco General Hospital, and 4Department of Public Health, San Francisco, California; 5University of Minnesota, Minneapolis; 6Division of Infectious Diseases and Hospital Epidemiology, University Hospital Zurich, University of Zurich, Zurich, Switzerland
Background. The gut is a major reservoir for human immunodeficiency virus (HIV) in patients receiving antiretroviral therapy (ART). We hypothesized that distinct immune environments within the gut may support varying levels of HIV.
Methods. In 8 HIV‐1‐positive adults who were receiving ART and had CD4+ T cell counts of >200 cells/μL and plasma viral loads of <40 copies/mL, levels of HIV and T cell activation were measured in blood samples and endoscopic biopsy specimens from the duodenum, ileum, ascending colon, and rectum.
Results. HIV DNA and RNA levels per CD4+ T cell were higher in all 4 gut sites compared with those in the blood. HIV DNA levels increased from the duodenum to the rectum, whereas the median HIV RNA level peaked in the ileum. HIV DNA levels correlated positively with T cell activation markers in peripheral blood mononuclear cells (PBMCs) but negatively with T cell activation markers in the gut. Multiply spliced RNA was infrequently detected in gut, and ratios of unspliced RNA to DNA were lower in the colon and rectum than in PBMCs, which reflects paradoxically low HIV transcription, given the higher level of T cell activation in the gut.
Conclusions. HIV DNA and RNA are both concentrated in the gut, but the inverse relationship between HIV DNA levels and T cell activation in the gut and the paradoxically low levels of HIV expression in the large bowel suggest that different processes drive HIV persistence in the blood and gut.
AIDS. 2010 Oct 23;24(16):2451-60.
Yukl SA, Shergill AK, McQuaid K, Gianella S, Lampiris H, Hare CB, Pandori M, Sinclair E, Günthard HF, Fischer M, Wong JK, Havlir DV.
a San Francisco VA Medical Center (SFVAMC) and University of California, San Francisco (UCSF), San Francisco, California, USA b University Hospital Zurich, Division of Infectious Diseases and Hospital Epidemiology, University of Zurich, Zurich, Switzerland c San Francisco General Hospital and University of California, San Francisco (UCSF), USA d Department of Public Health, San Francisco, California, USA.
OBJECTIVE: To determine whether raltegravir-containing antiretroviral therapy (ART) intensification reduces HIV levels in the gut.
DESIGN: Open-label study in HIV-positive adults on ART with plasma HIV RNA below 40 copies/ml.
METHODS: Seven HIV-positive adults received 12 weeks of ART intensification with raltegravir alone or in combination with efavirenz or darunavir. Gut cells were obtained by upper and lower endoscopy with biopsies from duodenum, ileum, colon, and rectum at baseline and 12 weeks. Study outcomes included plasma HIV RNA, HIV DNA and RNA from peripheral blood mononuclear cells (PBMC) and four gut sites, T-cell subsets, and activation markers.
RESULTS: Intensification produced no consistent decrease in HIV RNA in the plasma, PBMC, duodenum, colon, or rectum. However, five of seven participants had a decrease in unspliced HIV RNA per 10 CD4 T cells in the ileum. There was a trend towards decreased T-cell activation in all sites, which was greatest for CD8 T cells in the ileum and PBMC, and a trend towards increased CD4 T cells in the ileum.
CONCLUSION: Most HIV RNA and DNA in the blood and gut is not the result of ongoing replication that can be impacted by short-term intensification with raltegravir. However, the ileum may support ongoing productive infection in some patients on ART, even if the contribution to plasma RNA is not discernible.
Published online October 1, 2010
The Journal of Immunology, 2010, doi:10.4049/jimmunol.1001801
Shari N. Gordon, Barbara Cervasi, Pamela Odorizzi, Randee Silverman, Faten Aberra, Gregory Ginsberg, Jacob D. Estes, Mirko Paiardini, Ian Frank, and Guido Silvestri
Department of Pathology and Laboratory Medicine and Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA 19104; Animal Models and Vaccine Section and AIDS Vaccine Section, SAIC–Frederick, National Cancer Institute, National Institutes of Health, Frederick, MD, 20892; and Yerkes National Primate Research Center, Emory University, Atlanta, GA 30329
HIV infection is associated with depletion of intestinal CD4+ T cells, resulting in mucosal immune dysfunction, microbial translocation, chronic immune activation, and progressive immunodeficiency. In this study, we examined HIV-infected individuals with active virus replication (n = 15), treated with antiretroviral therapy (n = 13), and healthy controls (n = 11) and conducted a comparative analysis of T cells derived from blood and four gastrointestinal (GI) sites (terminal ileum, right colon, left colon, and sigmoid colon). As expected, we found that HIV infection is associated with depletion of total CD4+ T cells as well as CD4+CCR5+ T cells in all GI sites, with higher levels of these cells found in ART-treated individuals than in those with active virus replication. While the levels of both CD4+ and CD8+ T cell proliferation were higher in the blood of untreated HIV-infected individuals, only CD4+ T cell proliferation was significantly increased in the gut of the same patients. We also noted that the levels of CD4+ T cells and the percentages of CD4+Ki67+ proliferating T cells are inversely correlated in both blood and intestinal tissues, thus suggesting that CD4+ T cell homeostasis is similarly affected by HIV infection in these distinct anatomic compartments. Importantly, the level of intestinal CD4+ T cells (both total and Th17 cells) was inversely correlated with the percentage of circulating CD4+Ki67+ T cells. Collectively, these data confirm that the GI tract is a key player in the immunopathogenesis of HIV infection, and they reveal a strong association between the destruction of intestinal CD4+ T cell homeostasis in the gut and the level of systemic CD4+ T cell activation.