TAG HIV Basic Science, Vaccines, and Cure Project Blog

Study Uncovers Sex Differences in Immune Activation

There is a large body of evidence showing that innate and adaptive immune responses can differ in women and men, but the reasons for these differences are only partly understood (as reviewed recently in Nature Reviews Immunology). In HIV infection, it has been reported that average viral loads in early infection are lower in women than men, but women face a 1.6-fold higher risk of developing AIDS compared to men with the same viral load. Marc Hellerstein’s group has also presented data demonstrating that women have significantly higher T cell turnover compared to men with similar CD4 T cell counts. The mechanistic basis for these differences has been unclear.

A paper in Nature Medicine now offers a possible explanation for the observed sex differences in HIV pathogenesis. Angela Meier and colleagues from Marcus Altfeld’s group at the Ragon Institute of Massachusetts General Hospital have previously shown that HIV stimulates an innate immune receptor called toll-like receptor-7 (TLR7). In the new study, they report that a key immune cell called a plasmacytoid dendritic cell (pDC) responds differently to TLR7 stimulation depending on the sex of the donor. Specifically, significantly more pDC from women produced interferon-alpha compared to pDC from men. The study authors note that this finding has also been reported with a different TLR7 stimulus, a drug called imiquimod.

The researchers went on to evaluate the role of sex hormones, finding that the percentage of pDC producing interferon-alpha after TLR7 stimulation was significantly correlated with plasma progesterone concentrations. There was also a trend toward lower percentages of pDC producing interferon-alpha in postmenopausal women compared to premenopausual women.

Because interferon-alpha induces the expression of the immune activation marker CD38 on CD8 T cells in vitro, the researchers decided to explore whether women might show higher levels of immune activation than men despite comparable viral loads. In a comparison of 109 women and 514 men participating in the ACTG 384 trial (all treatment naive), women were found to have significantly higher levels of CD8 T cell activation than men after adjustment for viral load. On average, women had 4.6% more activated CD8 T cells. As immune activation levels are the strongest predictor of disease progression in HIV infection, the study results offer a compelling explanation for why women have a higher risk of developing AIDS compared to men with the same viral load.

The authors conclude: “Modulation of the TLR7 pathways in pDCs could…represent a unique approach to reduce HIV-1–associated pathogenesis and might have implications that go beyond HIV-1 infection, as differential susceptibility to several RNA viruses have been described for men and women, and autoimmune diseases that show sex differences in their incidence, such as systemic lupus erythematosus, have also been shown to involve the TLR7 and TLR8 pathway.”

Nature Medicine

Published online: 13 July 2009 | doi:10.1038/nm.2004

Letter

Sex differences in the Toll-like receptor–mediated response of plasmacytoid dendritic cells to HIV-1

Angela Meier1,8, J Judy Chang1,8, Ellen S Chan2, Richard B Pollard3, Harlyn K Sidhu1, Smita Kulkarni4, Tom Fang Wen1, Robert J Lindsay1, Liliana Orellana2, Donna Mildvan5, Suzane Bazner1,6, Hendrik Streeck1, Galit Alter1, Jeffrey D Lifson7, Mary Carrington4, Ronald J Bosch2, Gregory K Robbins6 & Marcus Altfeld1,6

Manifestations of viral infections can differ between women and men1, and marked sex differences have been described in the course of HIV-1 disease. HIV-1–infected women tend to have lower viral loads early in HIV-1 infection but progress faster to AIDS for a given viral load than men2, 3, 4, 5, 6, 7. Here we show substantial sex differences in the response of plasmacytoid dendritic cells (pDCs) to HIV-1. pDCs derived from women produce markedly more interferon- (IFN-) in response to HIV-1–encoded Toll-like receptor 7 (TLR7) ligands than pDCs derived from men, resulting in stronger secondary activation of CD8+ T cells. In line with these in vitro studies, treatment-naive women chronically infected with HIV-1 had considerably higher levels of CD8+ T cell activation than men after adjusting for viral load. These data show that sex differences in TLR-mediated activation of pDCs may account for higher immune activation in women compared to men at a given HIV-1 viral load and provide a mechanism by which the same level of viral replication might result in faster HIV-1 disease progression in women compared to men. Modulation of the TLR7 pathway in pDCs may therefore represent a new approach to reduce HIV-1–associated pathology.

1. Ragon Institute of Massachusetts General Hospital, Massachusetts Institute of Technology and Harvard University, Boston, Massachusetts, USA.

2. Harvard School of Public Health, Boston, Massachusetts, USA.

3. University of California–Davis Medical Center, Sacramento, California, USA.

4. Cancer and Inflammation Program, Laboratory of Experimental Immunology and Science Applications International Corporation–Frederick, National Cancer Institute, Frederick, Maryland, USA.

5. Beth Israel Medical Center, New York, New York, USA.

6. Division of Infectious Diseases, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA.

7. AIDS and Cancer Virus Program, Science Applications International Corporation–Frederick, National Cancer Institute, Frederick, Maryland, USA.

8. These authors contributed equally to this work.

Lymphatic Tissue Gene Expression During HIV Infection

The new issue of the Journal of Immunology features a paper from Ashley Haase’s group looking at lymphoid tissue gene expression in HIV infection. The study, led by Qingsheng Li, uses microarray technology to investigate gene expression changes during the acute, asymptomatic and late (AIDS) stages of disease compared to healthy uninfected individuals. The analyses reveal that the expression of 46 genes is significantly altered (in most cases upregulated) at all stages of infection; half of these genes have known functions in immunity, particularly immune activation. Examples include CD38 (the well-known immune activation marker that predicts the pace of disease progression in HIV infection), CCR5, pro-apoptotic genes and nine different interferon-related genes.

Acute infection is associated with altered expression of another 358 unique genes, more than any other stage of infection. Again, in most cases (81%) these genes are upregulated and a large proportion are related to immune activation (e.g. proinflammatory cytokines, signal transduction molecules, activators of cell proliferation, mediators of cell cycle progression and the pro-apoptotic Fas-Fas pathway). However, there are also increases in the expression of genes associated with dampening the immune response such as IDO, an enzyme with powerful immune-suppressing properties. A suite of additional genes involved in innate immunity are also upregulated during acute infection, including the toll-like receptors TLR7 and TLR8 and numerous components of the interferon pathway.

The asymptomatic stage of infection is associated with a dramatic shift in gene expression, with levels returning to baseline in most cases. In addition to the 46 genes with altered expression at all stages of infection, only 18 genes are uniquely altered in asymptomatic individuals. The majority relate to immune activation and lymphoid tissue remodeling and repair.

In people with AIDS, 183 genes are uniquely altered and - in contrast to the other stages of infection - most of these genes (84%) are downregulated. Examples include genes involved in immune activation, apoptosis, and tissue remodeling and repair. A substantial proportion of the genes belong to the CD28 T cell co-stimulatory pathway, consistent with the accumulation of dysfunctional CD28-negative T cells that occurs over the course of HIV infection. The researchers also note that at this stage of disease “decreased expression could be due to loss of cells expressing these genes, decreased expression in a particular cell type, or both.”

In the discussion section of the paper, the authors conclude: “the major finding of this study is that there are stage-specific transcriptional signatures in lymphoid tissues during HIV-1 infection.” The results set the stage for additional investigations into the consequences of the documented changes in gene expression using a comprehensive systems biology approach. The ultimate aim is “not only to better understand viral pathogenesis during the various stages of HIV-1 disease but also to identify adjunctive approaches to improving treatment and immune reconstitution.”

FIGURE 2. In human LT of HIV-1-infected subjects, the general functional categories of genes with altered expression (1.7 times the level at baseline, p < 0.05). A, Common to all stages (C1); B, unique to the acute stage (S1); C, unique to the asymptomatic stage (S2); and D, unique to the AIDS stage (S3). Green and red letters indicate, respectively, decreased and increased expression. The size of each sector in a pie diagram is proportional to the number of genes in its category (in parentheses). All genes and their names derived from abbreviations can be found in supplemental Table I.

CREDIT: The Journal of Immunology, 2009, doi:10.4049/jimmunol.0803222

The Journal of Immunology, 2009, doi:10.4049/jimmunol.0803222

Published online July 13, 2009

Microarray Analysis of Lymphatic Tissue Reveals Stage-Specific, Gene Expression Signatures in HIV-1 Infection

Qingsheng Li2,*, Anthony J. Smith2,*, Timothy W. Schacker, John V. Carlis, Lijie Duan*, Cavan S. Reilly and Ashley T. Haase3,*

*Department of Microbiology  Division of Infectious Diseases, Department of Medicine, Medical School  Department of Computer Science and Engineering, Institute of Technology, and  Division of Biostatistics, School of Public Health, University of Minnesota, Minneapolis, MN 55455

Untreated HIV-1 infection progresses through acute and asymptomatic stages to AIDS. Although each of the three stages has well-known clinical, virologic, and immunologic characteristics, much less is known of the molecular mechanisms underlying each stage. In this study, we report lymphatic tissue microarray analyses, revealing for the first time stage-specific patterns of gene expression during HIV-1 infection. We show that although there is a common set of key genes with altered expression throughout all stages, each stage has a unique gene expression signature. The acute stage is most notably characterized by increased expression of hundreds of genes involved in immune activation, innate immune defenses (e.g., RIG-1, MDA-5, TLR7 and TLR8, PKR, APOBEC3B, 3F, 3G), adaptive immunity, and in the proapoptotic Fas-Fas ligand pathway. Yet, quite strikingly, the expression of nearly all acute stage genes return to baseline levels in the asymptomatic stage, accompanying partial control of infection. This transition from acute to asymptomatic stage is tied to increased expression of a diverse array of immunosuppressive genes (e.g., CLEC12B, ILT4, galectin-3, CD160, BCMA, FGL2, LAG3, GPNMB). In the AIDS stage, decreased expression of numerous genes involved in T cell signaling identifies genes contributing to T cell dysfunction. These common and stage-specific gene expression signatures identify potential molecular mechanisms underlying the host response and the slow, natural course of HIV-1 infection.

The Role of Ad5-Specific CD4 T cells in Enhancing Risk of HIV Acquisition in the Merck Vaccine Trial: New Papers Offer Absolution, But Questions Remain

In September 2007 it was announced that immunizations were being halted in the STEP study, a phase IIb efficacy trial of Merck’s HIV vaccine candidate. A review of the interim results by the Data Safety Monitoring Board found that there was no possibility of the vaccine showing efficacy for preventing HIV infection, or reducing post-infection viral load levels in vaccine recipients who became infected. These events and the subsequent fallout were covered in grisly detail on this blog.

The most surprising and disturbing finding from STEP was that receipt of the vaccine was associated with a significantly increased risk of HIV acquisition in a subset of trial participants: uncircumcised men with pre-existing antibodies against adenovirus serotype 5 (Ad5). The Merck vaccine construct used an attenuated Ad5 virus vector as a delivery vehicle for the HIV antigens Gag, Pol & Nef. In its natural form, Ad5 causes severe colds and many people are exposed during childhood and hence have anti-Ad5 immune responses.

When the data from STEP showing enhanced risk of acquisition became known, there was understandably much discussion of what the potential mechanism might be. One hypothesis posited that the presence of anti-Ad5 antibodies at baseline was a marker for the presence of Ad5-specific CD4 T cell responses, and immunization with the Ad5 vector activated Ad5-specific CD4 T cell responses, thereby increasing the number of potential target cells for HIV infection in vaccine recipients. This hypothesis was explored to limited extent in one of the papers presenting the STEP results that was published in The Lancet last year by Juliana McElrath and colleagues; in that paper, analyses of Ad5-specific CD4 T cells showed that responses tended to be lower in vaccine recipients who became HIV infected, at least in peripheral blood.

Two new studies just published online in Nature Medicine now offer a more detailed absolution of Ad5-specific CD4 T cells. The results show that baseline antibody titers did not correlate with the magnitude of the Ad5-specific CD4 T cell response as measured by production of IL-2, interferon gamma, TNF-alpha, MIP-1beta and perforin (production of Th2-type cytokines by Ad5-specific CD4 T cells has not yet been evaluated). Furthermore, most individuals who lacked anti-Ad5 antibodies nevertheless displayed Ad5-specific CD4 T cell responses. The studies also demonstrate that receipt of the vaccine rapidly induced both Ad5-specific CD4 T cells and antibodies in people who lacked them at baseline, suggesting that if these responses enhanced the risk of HIV infection then the enhancement should have been seen in all vaccine recipients after the initial immunizations, not just the subset with detectable anti-Ad5 antibodies at baseline.

While these papers make an important contribution to the analyses of what occurred in STEP, there are some caveats.  Most critically - and contrary to what has been written in one media story on The Scientist website - the new results do not absolve the Merck HIV vaccine of significantly enhancing the risk of HIV acquisition among uncircumcised men with pre-existing antibodies against Ad5. It is disheartening to read quotes from Alan Bernstein, Executive Director of the Global HIV/AIDS Vaccine Enterprise, erroneously stating otherwise. Also in The Scientist article, Nelson Michael is quoted as saying that including circumcision status as a variable in the multivariate analyses of STEP “washes out” the enhancing effect of vaccination. Based on Susan Buchbinder’s talk at Keystone earlier this year, this is simply not true; what the circumcision data show is that the enhancement effect was most significant in the uncircumcised subgroup with anti-Ad5 antibodies. Additionally, Buchbinder noted that continued follow-up of STEP participants indicates the enhancement effect has waned over time, which adds to the evidence that receipt of the Ad5 vector was responsible.

Another more speculative caveat is that the new data may not entirely rule out a role for Ad5-specific CD4 T cell responses in the trial outcome. One possibility that remains to be studied is whether the presence of persistent Ad5 infection alters the behavior of Ad5-specific CD4 T cell responses after immunization (i.e. if natural Ad5 antigens are being expressed somewhere in the body, Ad5-specific CD4 T cells would be expected to traffic to those sites). Recent research from Linda Gooding’s group at Emory (abstracts and links appended at the end of the post) has employed PCR to confirm that Ad5 infection can persist in humans. The main cell type infected by Ad5 in these studies was T cells, and activation of infected T cells stimulated Ad5 replication. In the context of the STEP results, these data suggest several questions:

• Can persistent Ad5 infection be detected in the foreskin?
• Is there any correlation between Ad5 serostatus and detection of persistent Ad5 infection?
• Does immunization with an Ad5 vector lead to any detectable changes in the interactions between Ad5-specific CD4 T cells and Ad5-infected cells?

Juliana McElrath’s Lancet paper cites the need to consider events in the mucosa, stating that Ad5-specific CD4 T cells “could have trafficked to mucosal sites—a process known to occur in natural infection—and thus increased the number of susceptible CD4+ T-cell targets for HIV… To address this possibility, studies are planned to examine lower gastrointestinal tissue and foreskin after immunization for enhanced T-cell activation.” This idea is not unprecedented, as studies from Larry Corey’s laboratory have strongly implicated the persistent presence of activated HSV-2-specific CD4 T cells interacting with HSV-2-infected cells in the mucosa as the explanation for the association between HSV-2 infection and increased susceptibility to HIV acquisition. At the Keystone conference earlier this year, Corey showed that these interactions continue to be detectable even when HSV-2-infected individuals are on chronic suppressive therapy with acyclovir, offering a reason for the failure of the drug to reduce the risk of HIV infection in several large trials.

There is one other slightly uncomfortable caveat to the Nature Medicine papers: both groups of researchers include people working on vaccines using alternative adenovirus serotypes. If evidence did suggest that Ad5-specific CD4 T cells played a role in enhancing risk of HIV acquisition in STEP, this could potentially impact their work because Ad5-specific T cell responses have been shown to cross-react with multiple adenovirus serotypes. Because the alternative adenovirus-based vaccines are being developed for neglected diseases that do not represent profitable vaccine markets, it’s not a case of suspecting significant financial conflicts-of-interest, but the issue should perhaps have been acknowledged in the papers.

Nature Medicine

Published online: 20 July 2009 | doi:10.1038/nm.1989

Brief Communication abstract

Baseline Ad5 serostatus does not predict Ad5 HIV vaccine–induced expansion of adenovirus-specific CD4+ T cells

Natalie A Hutnick1, Diane G Carnathan1, Sheri A Dubey2, Kara S Cox2, Lisa Kierstead2, Sarah J Ratcliffe3, Michael N Robertson2, Danilo R Casimiro2, Hildegund C J Ertl4 & Michael R Betts1

The mechanisms underlying possible increased HIV-1 acquisition in adenovirus 5 (Ad5)-seropositive subjects vaccinated with Ad5–HIV-1 vectors in the Merck STEP trial remain unclear. We find that Ad5 serostatus does not predict Ad5-specific CD4+ T cell frequency, and we did not observe durable significant differences in Ad5-specific CD4+ T cells between Ad5-seropositive and Ad5-seronegative subjects after vaccination. These findings indicate no causative role for Ad5-specific CD4+ T cells in increasing HIV-1 susceptibility in the STEP trial.

1. Department of Microbiology and Center for AIDS Research, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA.

2. Merck Research Laboratories, West Point, Pennsylvania, USA.

3. Department of Biostatistics and Epidemiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA.

4. The Wistar Institute, Philadelphia, Pennsylvania, USA.

Nature Medicine

Published online: 20 July 2009 | doi:10.1038/nm.1991

Brief Communication abstract

Adenovirus-specific immunity after immunization with an Ad5 HIV-1 vaccine candidate in humans

Kara L O'Brien1, Jinyan Liu1, Sharon L King1, Ying-Hua Sun1, Joern E Schmitz2, Michelle A Lifton2, Natalie A Hutnick3, Michael R Betts3, Sheri A Dubey4, Jaap Goudsmit5, John W Shiver4, Michael N Robertson4, Danilo R Casimiro4 & Dan H Barouch1,6

The immunologic basis for the potential enhanced HIV-1 acquisition in adenovirus serotype 5 (Ad5)-seropositive individuals who received the Merck recombinant Ad5 HIV-1 vaccine in the STEP study remains unclear. Here we show that baseline Ad5-specific neutralizing antibodies are not correlated with Ad5-specific T lymphocyte responses and that Ad5-seropositive subjects do not develop higher vector-specific cellular immune responses as compared with Ad5-seronegative subjects after vaccination. These findings challenge the hypothesis that activated Ad5-specific T lymphocytes were the cause of the potential enhanced HIV-1 susceptibility in the STEP study.

1. Division of Vaccine Research, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA.

2. Division of Viral Pathogenesis, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA.

3. Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA.

4. Merck Research Laboratories, West Point, Pennsylvania, USA.

5. Crucell Holland BV, Leiden, The Netherlands.

6. Ragon Institute of Massachusetts General Hospital, Massachusetts Institute of Technology and Harvard, Cambridge, Massachusetts, USA.

Journal of Virology, March 2009, p. 2417-2428, Vol. 83, No. 6

Latent Species C Adenoviruses in Human Tonsil Tissues

C. T. Garnett ,1,, G. Talekar,1, J. A. Mahr,1,¶ W. Huang,1 Y. Zhang,1,|| D. A. Ornelles,2 and L. R. Gooding1

Emory University School of Medicine, Department of Microbiology and Immunology, Atlanta, Georgia 30322,1 Wake Forest University School of Medicine, Department of Microbiology and Immunology, Winston-Salem, North Carolina 271572

Although species C human adenoviruses establish persistent infections, the molecular details of this lifestyle remain poorly understood. We previously reported that adenovirus DNA is found in human mucosal T lymphocytes in a noninfectious form (C. T. Garnett, D. Erdman, W. Xu, and L. R. Gooding, J. Virol. 76:10608-10616, 2002). In this study, human tonsil and adenoid tissues were analyzed to determine the dynamics of infection, the rate of clearance of viral DNA, and the possibility of reactivation of virus from these tissues. The presence of viral DNA peaked at 4 years of age and declined thereafter. The average number of viral genomes declined with the age of the donor. The frequency of virus-bearing cells ranged from 3 x 10–7 to 3.4 x 10–4, while the amount of viral DNA per cell varied less, with an average of 280 copies per cell. All species C serotypes were represented in these tissues, although adenovirus type 6 was notably rare. Infectious virus was detected infrequently (13 of 94 of donors tested), even among donors with the highest levels of adenoviral DNA. Adenovirus transcripts were rarely detected in uncultured lymphocytes (2 of 12 donors) but appeared following stimulation and culture (11 of 13 donors). Viral DNA replication could be stimulated in most donor samples by lymphocyte stimulation in culture. New infectious virus was detected in 13 of 15 donors following in vitro stimulation. These data suggest that species C adenoviruses can establish latent infections in mucosal lymphocytes and that stimulation of these cells can cause viral reactivation resulting in RNA transcription, DNA replication, and infectious virus production.

Journal of Virology, November 2002, p. 10608-10616, Vol. 76, No. 21

Prevalence and Quantitation of Species C Adenovirus DNA in Human Mucosal Lymphocytes

C. T. Garnett,1 D. Erdman,2 W. Xu,2, and Linda R. Gooding1

Department of Microbiology and Immunology, Emory University, Atlanta, Georgia 30322,1 Centers for Disease Control and Prevention, Atlanta, Georgia 303332

The common species C adenoviruses (serotypes Ad1, Ad2, Ad5, and Ad6) infect more than 80% of the human population early in life. Following primary infection, the virus can establish an asymptomatic persistent infection in which infectious virions are shed in feces for several years. The probable source of persistent virus is mucosa-associated lymphoid tissue, although the molecular details of persistence or latency of adenovirus are currently unknown. In this study, a sensitive real-time PCR assay was developed to quantitate species C adenovirus DNA in human tissues removed for routine tonsillectomy or adenoidectomy. Using this assay, species C DNA was detected in Ficoll-purified lymphocytes from 33 of 42 tissue specimens tested (79%). The levels varied from fewer than 10 to greater than 2 x 106 copies of the adenovirus genome/107 cells, depending on the donor. DNA from serotypes Ad1, Ad2, and Ad5 was detected, while the rarer serotype Ad6 was not. When analyzed as a function of donor age, the highest levels of adenovirus genomes were found among the youngest donors. Antibody-coated magnetic beads were used to purify lymphocytes into subpopulations and determine whether viral DNA could be enriched within any purified subpopulations. Separation of T cells (CD4/8- expressing and/or CD3-expressing cells) enriched viral DNA in each of nine donors tested. In contrast, B-cell purification (CD19-expressing cells) invariably depleted or eliminated viral DNA. Despite the frequent finding of significant quantities of adenovirus DNA in tonsil and adenoid tissues, infectious virus was rarely present, as measured by coculture with permissive cells. These findings suggest that human mucosal T lymphocytes may harbor species C adenoviruses in a quiescent, perhaps latent form.

Webcasts & Abstracts from the 5th IAS Conference on HIV Pathogenesis, Treatment and Prevention

The 5th International AIDS Society Conference on HIV Pathogenesis, Treatment and Prevention got underway yesterday in Cape Town, South Africa. For the first time, webcasts of several sessions are available via the conference website; in addition to a list of the presentations due to be made available, direct links are included in the Programme-at-a-Glance. The opening session is already online, as are presentations from Monday morning including Wafaa El-Sadr's talk on the role of inflammation in HIV infection. Late breaker abstract sessions on Wednesday will also be webcast, and these include an interesting study pointing to differences in background levels of immune activation has a potential explanation for the increased efficiency of heterosexual HIV transmission in the African setting. UK website AIDSMap is also providing official news coverage from the IAS conference. 

Short Cuts To Memory

Two papers in last week’s issue of Nature report that memory CD8 T cell responses can be enhanced by drugs that alter cellular metabolism. In one of the studies, the drug rapamycin – generally used as an immune suppressant – also accelerated the development of functional memory CD8 T cells. The findings may assist efforts to develop more effective CD8 T cell vaccines and therapeutics, because one of the inconvenient aspects of T cell biology is that the differentiation process by which naïve T cells become fully functional memory T cells takes time (several weeks in mice and considerably longer in people). Furthermore, restimulation of the T cells during this differentiation process can be counterproductive, reducing the quality of the resultant memory response.

On a somewhat similar theme, the new issue of Nature Medicine includes a paper showing that manipulation of the Wnt signaling pathway can also arrest the normal T cell differentiation process, leading to the generation of memory CD8 T cells with stem cell-like self-renewal properties.

Nature 460, 41-42 (2 July 2009) | doi:10.1038/460041a; Published online 1 July 2009

News and Views

Immunology: A metabolic switch to memory

Martin Prlic & Michael J. Bevan

Abstract

Two therapeutic drugs have been found to enhance memory in immune cells called T cells, apparently by altering cellular metabolism. Are changes in T-cell metabolism the key to generating long-lived immune memory?

Nature 460, 103-107 (2 July 2009) | doi:10.1038/nature08097; Received 23 January 2009; Accepted 23 April 2009; Published online 3 June 2009

Enhancing CD8 T-cell memory by modulating fatty acid metabolism

Erika L. Pearce1, Matthew C. Walsh1, Pedro J. Cejas1, Gretchen M. Harms1, Hao Shen2, Li-San Wang1,3, Russell G. Jones4 & Yongwon Choi1

1. Department of Pathology and Laboratory Medicine,

2. Department of Microbiology,

3. Penn Center for Bioinformatics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA

4. McGill Cancer Centre, Department of Physiology, McGill University, Montreal, QC, H3G 1Y6, Canada

CD8 T cells, which have a crucial role in immunity to infection and cancer, are maintained in constant numbers, but on antigen stimulation undergo a developmental program characterized by distinct phases encompassing the expansion and then contraction of antigen-specific effector (TE) populations, followed by the persistence of long-lived memory (TM) cells Although this predictable pattern of CD8 T-cell responses is well established, the underlying cellular mechanisms regulating the transition to TM cells remain undefined. Here we show that tumour necrosis factor (TNF) receptor-associated factor 6 (TRAF6), an adaptor protein in the TNF-receptor and interleukin-1R/Toll-like receptor superfamily, regulates CD8 TM-cell development after infection by modulating fatty acid metabolism. We show that mice with a T-cell-specific deletion of TRAF6 mount robust CD8 TE-cell responses, but have a profound defect in their ability to generate TM cells that is characterized by the disappearance of antigen-specific cells in the weeks after primary immunization. Microarray analyses revealed that TRAF6-deficient CD8 T cells exhibit altered expression of genes that regulate fatty acid metabolism. Consistent with this, activated CD8 T cells lacking TRAF6 display defective AMP-activated kinase activation and mitochondrial fatty acid oxidation (FAO) in response to growth factor withdrawal. Administration of the anti-diabetic drug metformin restored FAO and CD8 TM-cell generation in the absence of TRAF6. This treatment also increased CD8 TM cells in wild-type mice, and consequently was able to considerably improve the efficacy of an experimental anti-cancer vaccine.

Nature 460, 108-112 (2 July 2009) | doi:10.1038/nature08155; Received 27 April 2009; Accepted 15 May 2009; Published online 21 June 2009

mTOR regulates memory CD8 T-cell differentiation

Koichi Araki1, Alexandra P. Turner2, Virginia Oliva Shaffer2, Shivaprakash Gangappa2, Susanne A. Keller3, Martin F. Bachmann3, Christian P. Larsen2 & Rafi Ahmed1

1. Emory Vaccine Center and Department of Microbiology and Immunology,

2. Emory Transplant Center and Department of Surgery, Emory University School of Medicine, Atlanta, Georgia 30322, USA

3. Cytos Biotechnology AG, Wagistrasse 25, 8952 Zürich-Schlieren, Switzerland

Memory CD8 T cells are a critical component of protective immunity, and inducing effective memory T-cell responses is a major goal of vaccines against chronic infections and tumours. Considerable effort has gone into designing vaccine regimens that will increase the magnitude of the memory response, but there has been minimal emphasis on developing strategies to improve the functional qualities of memory T cells. Here we show that mTOR (mammalian target of rapamycin, also known as FRAP1) is a major regulator of memory CD8 T-cell differentiation, and in contrast to what we expected, the immunosuppressive drug rapamycin has immunostimulatory effects on the generation of memory CD8 T cells. Treatment of mice with rapamycin following acute lymphocytic choriomeningitis virus infection enhanced not only the quantity but also the quality of virus-specific CD8 T cells. Similar effects were seen after immunization of mice with a vaccine based on non-replicating virus-like particles. In addition, rapamycin treatment also enhanced memory T-cell responses in non-human primates following vaccination with modified vaccinia virus Ankara. Rapamycin was effective during both the expansion and contraction phases of the T-cell response; during the expansion phase it increased the number of memory precursors, and during the contraction phase (effector to memory transition) it accelerated the memory T-cell differentiation program. Experiments using RNA interference to inhibit expression of mTOR, raptor (also known as 4932417H02Rik) or FKBP12 (also known as FKBP1A) in antigen-specific CD8 T cells showed that mTOR acts intrinsically through the mTORC1 (mTOR complex 1) pathway to regulate memory T-cell differentiation. Thus these studies identify a molecular pathway regulating memory formation and provide an effective strategy for improving the functional qualities of vaccine- or infection-induced memory T cells.

Nature Medicine 15, 731 - 732 (2009), doi:10.1038/nm0709-731

Tumor immunotherapy: making an immortal army

Brent H. Koehn1 & Stephen P. Schoenberger1

Laboratory of Cellular Immunology, La Jolla Institute for Allergy and Immunology, La Jolla, California, USA.

Abstract

Manipulation of cell renewal pathways creates T memory stem cells that can generate a sustained and targeted immune response. These findings have broad implications for vaccine development and immunotherapy (pages 808–813).

Nature Medicine 15, 808 - 813 (2009)

Published online: 14 June 2009 | doi:10.1038/nm.1982

Wnt signaling arrests effector T cell differentiation and generates CD8+ memory stem cells

Luca Gattinoni1,2, Xiao-Song Zhong1,2, Douglas C Palmer1, Yun Ji1, Christian S Hinrichs1, Zhiya Yu1, Claudia Wrzesinski1, Andrea Boni1, Lydie Cassard1, Lindsay M Garvin1, Chrystal M Paulos1, Pawel Muranski1 & Nicholas P Restifo1

1. Center for Cancer Research, National Cancer Institute, US National Institutes of Health, Bethesda, Maryland, USA.

2. These authors contributed equally to this work.

Self-renewing cell populations such as hematopoietic stem cells and memory B and T lymphocytes might be regulated by shared signaling pathways1. The Wnt–-catenin pathway is an evolutionarily conserved pathway that promotes hematopoietic stem cell self-renewal and multipotency by limiting stem cell proliferation and differentiation2, 3, but its role in the generation and maintenance of memory T cells is unknown. We found that induction of Wnt–-catenin signaling by inhibitors of glycogen sythase kinase-3 or the Wnt protein family member Wnt3a arrested CD8+ T cell development into effector cells. By blocking T cell differentiation, Wnt signaling promoted the generation of CD44lowCD62LhighSca-1highCD122highBcl-2high self-renewing multipotent CD8+ memory stem cells with proliferative and antitumor capacities exceeding those of central and effector memory T cell subsets. These findings reveal a key role for Wnt signaling in the maintenance of 'stemness' in mature memory CD8+ T cells and have major implications for the design of new vaccination strategies and adoptive immunotherapies.