TAG HIV Basic Science, Vaccines, and Cure Project Blog

HIV Replication in CCR5-Expressing T Cells

A new study from the laboratory of Elizabeth Connick at the University of Colorado takes a detailed look at HIV replication in activated T cells. The study demonstrates that the chemokine receptor CCR5 is highly expressed by CD4 T cells displaying dual activation markers, HLA-DR and CD38, and that these cells are the major source of virus in lymph node samples from infected individuals. Importantly, there were differences observed between viral replication studied in lab culture conditions (in vitro) compared to the lymph node samples: the bulk of the CD4 cells replicating HIV in vitro were CD38+ but lacked HLA-DR and did not preferentially express CCR5.

The researchers also extend the findings of prior studies suggesting that CD4 downregulation is common among activated, HIV-infected cells. The DR+CD38+ T cells could be sorted into the following subsets:

• CD4-CD8- T cells (contributing a median of 48% of the total HIV RNA copies detected)
• CD4+CD8- T cells (median HIV RNA copies, 15%)
• CD4+CD8+ T cells (median HIV RNA copies, 29%)
• CD4-CD8+ T cells (HIV RNA copies, 8%)

Thus the bulk of HIV RNA in the lymph node samples was coming from cells that had downregulated their CD4 receptors, similar to the previously reported results obtained from the blood of untreated HIV-positive individuals. CD4 cells co-expressing CD8 are an unusual subset and the authors note they need further study; whether the observed CD8 expression is stable or a transient activation-related phenomena is unclear. The amount of HIV RNA produced by each of the DR+CD38+ T cell subsets correlated with the amount of CCR5 they expressed. 

The importance of CCR5 expression in facilitating viral replication is also underscored by a recent Nature Medicine paper from Miko Paiardini and colleagues. The researchers document that non-pathogenic SIV infection of sooty mangabeys is associated with greatly reduced CCR5 expression on long-lived central memory CD4 T cells. A consequence of the reduced CCR5 expression is that the amount of SIV found in central memory CD4 T cells in sooty mangabeys is a log lower than in rhesus macaques, whereas there is no significant difference when SIV infection of short-lived effector memory CD4 T cells is compared. The authors argue that this sparing of central memory CD4 T cell allows sooty mangabeys to co-exist peacefully with SIV, because the short-lived effector memory CD4 T cells the virus does infect are relatively dispensable.

JVI Accepts, published online ahead of print on 3 August 2011

J. Virol. doi:10.1128/JVI.02529-10

HLA-DR+CD38+CD4+ T Lymphocytes Have Elevated CCR5 Expression and Produce the Majority of R5-tropic HIV-1 RNA in Vivo

Amie L. Meditz1, Michelle K. Haas1, Joy M. Folkvord1, Kelsey Melander1, Russ Young1, Martin McCarter3, Samantha MaWhinney4, Thomas B. Campbell1, Yolanda Lie5, Eoin Coakley5, David N. Levy7, and Elizabeth Connick1

1 Division of Infectious Diseases, Department of Medicine, University of Colorado Denver, Aurora, CO

3 Department of Surgery, University of Colorado Denver, Aurora, CO

4 Department of Biostatistics and Informatics, University of Colorado Denver, Aurora, CO

5 Monogram Biosciences, South San Francisco, CA

7 New York University, College of Dentistry, New York City, NY

ABSTRACT

Percentages of activated T-cells correlate with HIV-1 disease progression, but underlying mechanisms are not fully understood. We hypothesized that HLA-DR+CD38+ (DR+38+) CD4+ T-cells produce the majority of HIV-1 due to elevated expression of CCR5 and CXCR4. In PHA-stimulated CD8-depleted PBMC infected with HIV-1 GFP reporter viruses, DR-38+ T-cells constituted the majority of R5-tropic (median, 62%) and X4-tropic HIV-1-producing cells (median, 61%), although cell surface CCR5 and CXCR4 were not elevated on this subset. In lymph nodes from untreated individuals infected with R5-tropic HIV-1, percentages of CCR5+ cells were elevated in DR+38+CD4+ T-cells (median, 36.4%) compared to other CD4+ T-cell subsets (median, DR-38- 5.7%; DR+38- 19.4%; DR-38+ 7.6%; n=18; p<0.001). In sorted CD8- lymph node T-cells, median HIV-1 RNA copies/105 cells was higher for DR+38+ (1.8x106) compared to DR-38- (0.007x106), DR-38+ (0.064x106), and DR+38- (0.18x106) subsets (n=8; p<0.001 for all). After adjusting for percentages of subsets, a median of 87% of viral RNA was harbored by DR+38+ cells. Percentages of CCR5+ CD4+ T-cells and concentrations of CCR5 molecules among subsets predicted HIV-1 RNA levels among CD8- DR/38 subsets (p<0.001 for both). Median HIV-1 DNA copies/105 cells was higher in DR+38+ (5, 360) compared to DR-38- (906), DR-38+ (814), and DR+38- (1, 984) subsets (n=7, p<=0.031). Thus, DR+38+CD4+ T-cells in lymph nodes have elevated CCR5 expression, are highly susceptible to infection with R5-tropic virus, and produce the majority of R5-tropic HIV-1. PBMC assays failed to recapitulate in vivo findings, suggesting limited utility. Strategies to reduce numbers of DR+38+CD4+ T-cells may substantially inhibit HIV-1 replication.

Nat Med. 2011 Jun 26;17(7):830-6. doi: 10.1038/nm.2395.

Low levels of SIV infection in sooty mangabey central memory CD4(+) T cells are associated with limited CCR5 expression.

Paiardini M, Cervasi B, Reyes-Aviles E, Micci L, Ortiz AM, Chahroudi A, Vinton C, Gordon SN, Bosinger SE, Francella N, Hallberg PL, Cramer E, Schlub T, Chan ML, Riddick NE, Collman RG, Apetrei C, Pandrea I, Else J, Munch J, Kirchhoff F, Davenport MP, Brenchley JM, Silvestri G.

Abstract

Naturally simian immunodeficiency virus (SIV)-infected sooty mangabeys do not progress to AIDS despite high-level virus replication. We previously showed that the fraction of CD4(+)CCR5(+) T cells is lower in sooty mangabeys compared to humans and macaques. Here we found that, after in vitro stimulation, sooty mangabey CD4(+) T cells fail to upregulate CCR5 and that this phenomenon is more pronounced in CD4(+) central memory T cells (T(CM) cells). CD4(+) T cell activation was similarly uncoupled from CCR5 expression in sooty mangabeys in vivo during acute SIV infection and the homeostatic proliferation that follows antibody-mediated CD4(+) T cell depletion. Sooty mangabey CD4(+) T(CM) cells that express low amounts of CCR5 showed reduced susceptibility to SIV infection both in vivo and in vitro when compared to CD4(+) T(CM) cells of rhesus macaques. These data suggest that low CCR5 expression on sooty mangabey CD4(+) T cells favors the preservation of CD4(+) T cell homeostasis and promotes an AIDS-free status by protecting CD4(+) T(CM) cells from direct virus infection.

Exercise as Immune-Based Therapy

Many studies have reported that regular exercise confers health benefits and that, conversely, a sedentary lifestyle is a major risk factor for morbidity and mortality (particularly from cardiovascular disease). In recent years, researchers have begun to look more specifically at the immunological effects of exercise. The scientist Richard Simpson, formerly at Napier University in Edinburgh and now based at the University of Houston in Texas, has pioneered the exploration of the intersection between exercise and immune senescence. This research is potentially relevant to HIV infection because, as reported in some prior blog posts (see the immunosenescence category), senescent immune cells—particularly CD8 T cells—accumulate over time and may persist despite antiretroviral therapy. Simpson’s recent work suggests that exercise mobilizes senescent immune system cells from the tissues into the blood and increases their death by apoptosis; if confirmed this may offer both a more practical approach to addressing senescence than the idea of physically removing cells, and could also explain some of the positive contributions of exercise to healthy aging that have been described in the literature.

Exercise may also have a beneficial impact on inflammation, another problem common to both aging and HIV infection. In Nature Reviews Immunology, Mike Gleeson and colleagues from Loughborough University in the UK review the mechanisms by which exercise may reduce inflammation, and highlight some of the questions that remain to be answered about which mechanisms are most important in producing beneficial health outcomes.

Finally, in a paper in press at the Journal of the Association of Nurses in AIDS Care, Anella Yahiaoui and colleagues review the literature in an attempt to offer evidence-based exercise recommendations for older individuals with HIV. They conclude that:

“Combined moderate to vigorous aerobic and resistance exercise for 20-40 minutes, 3 times per week, is safe and effective in older adults and has many benefits to decrease symptom burden, decrease disease progression, and increase quality of life.”

Additional specifics are included in the paper. The authors also recommend the basic "Exercise Tips for Older Americans" offered on the website of the American Heart Association.

Brain Behav Immun. 2011 Jul 19. [Epub ahead of print]

Aerobic fitness is associated with lower proportions of senescent blood T-cells in man.

Spielmann G, McFarlin BK, O'Connor DP, Smith PJ, Pircher H, Simpson RJ.

Laboratory of Integrated Physiology, Department of Health and Human Performance, University of Houston, 3855 Holman Street, Houston, TX 77204, USA; Biomedicine and Sports Science Research Group, School of Life Sciences, Edinburgh Napier University, 10 Colinton Road, Edinburgh, EH10 5DT, UK.

Abstract

Senescent T-cells accumulate with age, lowering the naïve T-cell repertoire and increasing host infection risk. As this response is likely to be influenced by certain lifestyle factors, we examined the association between aerobic fitness (V˙O(2max)) and the age-related accumulation of senescent T-cells. Blood lymphocytes from 102 healthy males (18-61yr) were analyzed for KLRG1, CD57, CD28, CD45RA, CD45RO surface expression on CD4+ and CD8+ T-cells by 4-color flow cytometry. Advancing age (yr) was positively associated with the proportion (%) of senescent (KLRG1+/CD57+; KLRG1+/CD28-) CD4+ (B=1.00; 1.02) and CD8+ (B=0.429; 1.02) T-cells and inversely associated with naïve (KLRG1-/CD28+) CD4+ (B=-1.000) and CD8+ (B=-0.993) T-cells. V˙O(2max) was inversely associated with senescent CD4+ (B=-0.97) and CD8+ (B=-0.240). Strikingly, age was no longer associated with the proportions of senescent or naïve T-cells after adjusting for V˙O(2max), while the association between V˙O(2max) and these T-cell subsets withstood adjustment for age, BMI and percentage body fat. Ranking participants by age-adjusted V˙O(2max) revealed that the highest tertile had 17% more naïve CD8+ T-cells and 57% and 37% less senescent CD4+ and CD8+ T-cells, respectively, compared to the lowest tertile. V˙O(2max) was not associated with latent cytomegalovirus (CMV), Epstein-Barr virus (EBV) or herpes simplex virus-1 (HSV-1) infection, indicating that the moderating associations of V˙O(2max) were not confounded by persistent viral infections. This is the first study to show that aerobic fitness is associated with a lower age-related accumulation of senescent T-cells, highlighting the beneficial effects of maintaining a physically active lifestyle on the aging immune system.

Exerc Sport Sci Rev. 2011 Jan;39(1):23-33.

Aging, persistent viral infections, and immunosenescence: can exercise "make space"?

Simpson RJ.

Laboratory of Integrated Physiology, Department of Health and Human Performance, University of Houston, Houston, TX 77204, USA.

Abstract

Overcrowding the immune space with excess clones of viral-specific T cells causes the naïve T-cell repertoire to shrink, which increases infection susceptibility to novel pathogens. Physical exercise preferentially mobilizes senescent T cells from the peripheral tissues into the blood, which might facilitate their subsequent apoptosis and create "vacant space" for newly functional T cells to occupy and expand the naïve T-cell repertoire.

Exerc Immunol Rev. 2010;16:40-55.

Senescent phenotypes and telomere lengths of peripheral blood T-cells mobilized by acute exercise in humans.

Simpson RJ, Cosgrove C, Chee MM, McFarlin BK, Bartlett DB, Spielmann G, O'Connor DP, Pircher H, Shiels PG.

Laboratory of Integrated Physiology, Department of Health and Human Performance, University of Houston, 3855 Holman Street, Houston, Texas 77204, USA.

Abstract

Acute bouts of aerobic exercise are known to mobilize antigen-experienced CD8+ T-cells expressing the cell surface marker of senescence, KLRG1, into the blood. It is not known; however if this is due to a selective mobilization of terminally differentiated T-cells (i.e., KLRG1 +/CD28-/CD57+) or a population of effector memory T-cells (i.e., KLRG1+/CD28+/CD57-) that have not reached terminal differentiation. The aim of this study was to further characterize KLRG1 + T-cells mobilized by acute exercise by assessing the co-expression of KLRG1 with CD28 or CD57 and to determine telomere lengths in the CD4+ and CD8+ T-cell subsets. Nine moderately trained male subjects completed an exhaustive treadmill running protocol at 80%. Blood lymphocytes isolated before, immediately after and 1h after exercise were labelled with antibodies against KLRG1, CD28 or CD57, CD4 or CD8 and CD3 for 4-color flow cytometry analysis. Telomere lengths in CD3+, CD4+ and CD8+ T-cells were determined using Q-PCR. The relative proportion of KLRG1 + cells among the CD8+ T-cells increased by 40% immediately after exercise, returning to baseline 1h later. This was due to a mobilization of KLRG1+/CD28- (61% increase), KLRG1+/CD57+ (56% increase) and to a lesser extent, KLRG1+/CD57- cells (24% increase). Telomeres in CD8+ T-cells displayed an increased relative length immediately after exercise, whereas no change occurred for CD4+ or the overall CD3+ T-cells. In conclusion, the increased frequency of KLRG1 +/CD8+ T-cells in blood after acute exercise is predominantly due to a selective mobilization of terminally differentiated T-cells. The increased relative telomere length in CD8+ T-cells after exercise might indicate that KLRG1+ cells mobilized by exercise are under stress or aberrant signaling-induced senescence (STASIS). We postulate that a frequent mobilization of these cells by acute exercise might eventually allow naïve T-cells to occupy the "vacant" immune space and increase the naïve T-cell repertoire.

Nat Rev Immunol. 2011 Aug 5. doi: 10.1038/nri3041. [Epub ahead of print]

The anti-inflammatory effects of exercise: mechanisms and implications for the prevention and treatment of disease.

Gleeson M, Bishop NC, Stensel DJ, Lindley MR, Mastana SS, Nimmo MA.

Inflammation, Exercise and Metabolism Research Group, School of Sport, Exercise and Health Sciences, Loughborough University, Ashby Road, Loughborough, Leicestershire LE11 3TU, UK.

Abstract

Regular exercise reduces the risk of chronic metabolic and cardiorespiratory diseases, in part because exercise exerts anti-inflammatory effects. However, these effects are also likely to be responsible for the suppressed immunity that makes elite athletes more susceptible to infections. The anti-inflammatory effects of regular exercise may be mediated via both a reduction in visceral fat mass (with a subsequent decreased release of adipokines) and the induction of an anti-inflammatory environment with each bout of exercise. In this Review, we focus on the known mechanisms by which exercise - both acute and chronic - exerts its anti-inflammatory effects, and we discuss the implications of these effects for the prevention and treatment of disease.

J Assoc Nurses AIDS Care. 2011 Jul 29. [Epub ahead of print]

Development of Evidence-Based Exercise Recommendations for Older HIV-Infected Patients.

Yahiaoui A, McGough EL, Voss JG.

Abstract

Advances in antiretroviral therapy (ART) have decreased HIV-related morbidity and mortality and contributed to rapidly increasing numbers of older people living with HIV. Successful management of ART-related side effects (metabolic syndrome) and age-related comorbidities (frailty) are major challenges for patients and providers. Exercise has proven beneficial for younger HIV-infected patients, but we know little about which exercise regimens to recommend to the elderly. Our goal was to develop age-appropriate, evidence-based exercise recommendations for older HIV-infected adults (age > 50). We reviewed randomized controlled trials on the effects of physical exercise for: (a) HIV-infected young adults, (b) frail older adults, and (c) elderly individuals with metabolic syndrome. We recommend a combination of endurance and resistance exercises 3 times per week for at least 6 weeks to improve cardiovascular, metabolic, and muscle function. Further research is warranted to study the benefits and risks of physical exercise in older HIV-infected patients.

Mapping the Long Genetic Road to Broadly Neutralizing Antibodies

Over the past couple of years, several new antibodies capable of neutralizing a broad array of HIV isolates have been discovered. As mentioned in prior posts about these discoveries, one common feature of these antibodies is that the B cells that produce them have undergone an unusual degree of somatic hypermutation—a process in which the cell’s antibody-producing genetic code is progressively revised in order to increase the affinity of the antibody for its target. The genetic code that the B cell starts out with is called the germline sequence, and it is typically altered by around 5-15% to produce antibodies against common infections, whereas this figure ranges from 19-46% for the broadly neutralizing antibodies against HIV that have been identified. Antibodies targeting the part of the HIV envelope that binds to the CD4 receptor, such as the recently discovered VRC01, are at the extreme end of this scale (showing sequence alterations of 40-46%).

Yesterday in Science Express, researchers from the Vaccine Research Center (VRC), the Center for HIV/AIDS Vaccine Immunology (CHAVI) and the International AIDS Vaccine Initiative (IAVI) published the latest results from their collaborative effort to better understand how these antibodies are generated. The work involves analyses of mind-boggling numbers of B cell genetic sequences, and identifies several new broadly neutralizing antibodies from infected individuals that target HIV’s CD4 binding site. Of potential importance for vaccine design, the B cell sequences that give rise to the antibodies are not uncommon, and although a similarly extensive degree of somatic hypermutation is involved in their generation, it appears that the mutations do not have to be exactly the same to produce structurally similar antibodies. The researchers are hopeful that these data can be used as a map for guiding the development of broadly neutralizing antibodies using vaccines.

NIAID Press Release: NIH-Led Team Maps Route for Eliciting HIV Neutralizing Antibodies

Published Online 11 August 2011

Science DOI: 10.1126/science.1207532

RESEARCH ARTICLE

Focused Evolution of HIV-1 Neutralizing Antibodies Revealed by Structures and Deep Sequencing

Xueling Wu1,*, Tongqing Zhou1,*, Jiang Zhu1,*, Baoshan Zhang1, Ivelin Georgiev1, Charlene Wang1, Xuejun Chen1, Nancy S. Longo1, Mark Louder1, Krisha McKee1, Sijy O’Dell1, Stephen Perfetto1, Stephen D. Schmidt1, Wei Shi1, Lan Wu1, Yongping Yang1, Zhi-Yong Yang1, Zhongjia Yang1, Zhenhai Zhang1,2, Mattia Bonsignori3, John A. Crump4,5, Saidi H. Kapiga6, Noel E. Sam5,6, Barton F. Haynes3, Melissa Simek7, Dennis R. Burton8, Wayne C. Koff7, Nicole Doria-Rose9, Mark Connors9, NISC Comparative Sequencing Program10, James C. Mullikin10, Gary J. Nabel1, Mario Roederer1, Lawrence Shapiro1,2, Peter D. Kwong1,†, John R. Mascola1

Author Affiliations

1 Vaccine Research Center, National Institutes of Health, Bethesda, MD 20892, USA.

2 Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA.

3 The Duke Human Vaccine Institute, Duke University School of Medicine, and Duke University Medical Center, Durham, NC 27710, USA.

4 Division of Infectious Diseases and International Health, Department of Medicine, and Department of Pathology, Duke University Medical Center, Durham, NC 27710, USA.

5 Christian Medical Center and Kilimanjaro Christian Medical College, Tumaini University, Moshi, Tanzania.

6 Kilimanjaro Reproductive Health Programme, Moshi, Tanzania.

7 International AIDS Vaccine Initiative (IAVI), New York, NY 10038, USA.

8 Department of Immunology and Microbial Science and IAVI Neutralizing Antibody Center, The Scripps Research Institute, La Jolla, CA 92037, and Ragon Institute of MGH, MIT, and Harvard, Cambridge, MA 02129, USA.

9 Laboratory of Immunoregulation, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA.

10 NIH Intramural Sequencing Center (NISC), National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA. 

* These authors contributed equally to this work.

ABSTRACT

Antibody VRC01 is a human immunoglobulin that neutralizes ~90% of HIV-1 isolates. To understand how such broadly neutralizing antibodies develop, we used x-ray crystallography and 454 pyrosequencing to characterize additional VRC01-like antibodies from HIV-1–infected individuals. Crystal structures revealed a convergent mode of binding for diverse antibodies to the same CD4-binding-site epitope. A functional genomics analysis of expressed heavy and light chains revealed common pathways of antibody–heavy chain maturation, confined to the IGHV1-2*02 lineage, involving dozens of somatic changes, and capable of pairing with different light chains. Broadly neutralizing HIV-1 immunity associated with VRC01-like antibodies thus involves the evolution of antibodies to a highly affinity-matured state required to recognize an invariant viral structure, with lineages defined from thousands of sequences providing genetic roadmaps of their development.