TAG HIV Basic Science, Vaccines, and Cure Project Blog

Human Herpesvirus Replication & Poor Immune Reconstitution on ART

Evidence from many studies indicates that persistent immune activation is associated with poor CD4 T cell recovery in individuals on antiretroviral therapy (ART), even when HIV viral load is suppressed to undetectable levels. One potential source of ongoing immune activation could be the replication of other co-infecting viruses, such as cytomegalovirus (CMV), Epstein-Barr virus (EBV) and Kaposi's sarcoma herpesvirus (KSHV).

To evaluate this possibility, a group of researchers at UCSF studied the levels of these viruses in both saliva and peripheral blood mononuclear cells (PBMC) of individuals with high CD8 T cell activation and poor CD4 T cell recovery on ART. These individuals were defined as “cases” and compared to controls with low CD8 T cell activation and good CD4 recovery. High CD8 T cell activation was defined as greater than 10% of CD8 T cells co-expressing the activation markers CD38 and HLA-DR, and poor CD4 recovery was defined as levels persistently below 500 cells/mL. Controls were selected based on the opposite criteria (<10% activated CD8 T cells and CD4 cells always >500 cells/mL). A total of 11 cases and five controls were evaluated.

The results showed no differences between the groups, or any correlations between levels of any or all of the viruses and immune activation: “The proportions of all CMV, EBV or KSHV DNA positive specimens between the cases and controls were essentially the same, as were the proportions of subjects in each group that intermittently or continuously shed CMV, EBV or KSHV DNA in saliva. In addition, the median number of copies of CMV, EBV and KSHV DNA longitudinally in cases was virtually identical to that in controls.” The researchers offer the caveats that their study is very small, and sampling relatively infrequent. They are also exploring the same question in a different way, by investigating whether treatment with the anti-CMV drug valganciclovir can reduce immune activation and/or increase CD4 counts in individuals on ART. Results from this trial are expected later this year.

In discussing their findings, the authors write: “Given the strong association between inflammation/immune activation and disease outcomes in treated HIV disease, defining the mechanisms associated with HIV-associated inflammation is of high importance. Our preliminary data do not provide strong evidence for a role of persistent high level herpesvirus replication.”

PLoS ONE 4(4): e5277. doi:10.1371/journal.pone.0005277

Human Herpesvirus Replication and Abnormal CD8+ T Cell Activation and Low CD4+ T Cell Counts in Antiretroviral-Suppressed HIV-Infected Patients

Mark A. Jacobson, Dirk P. Ditmer, Elizabeth Sinclair, Jeffrey N. Martin, Steven G. Deeks, Peter Hunt, Edward S. Mocarski, Caroline Shiboski

Background

Most HIV-infected patients receiving virologically suppressive antiretroviral therapy continue to have abnormal, generalized T cell activation. We explored whether the degree of ongoing cytomegalovirus (CMV), Epstein-Barr virus (EBV) and Kaposi's sarcoma herpesvirus (KSHV) replication was associated with higher virus-specific T cell activation and the failure to achieve normal absolute CD4+ T cell counts in the face of long-term suppressive antiretroviral therapy.

Methodology

Longitudinally collected PBMC and saliva specimens obtained from HIV-infected patients on effective antiretroviral therapy for at least one year (plasma HIV RNA <75 copies/mL) were examined using a multiplex CMV, EBV and KSHV DNA PCR assay. Eleven cases were chosen who had CD8+ T cell CD38+HLA-DR+ expression >10% and plateau absolute CD4+ T cell counts <500 cells/µL. Five controls from the same study had CD8+ T cell CD38 expression <10% and plateau absolute CD4+ T cell counts >500 cells/µL.

Results and Conclusions

Among all subjects combined, 18% of PMBC samples were positive for CMV DNA, and 27%, 73% and 24% of saliva samples were positive for CMV, EBV and KSHV DNA, respectively. No significant differences or trends were observed between cases and controls in proportions of all CMV, EBV or KSHV DNA positive specimens, proportions of subjects in each group that intermittently or continuously shed CMV, EBV or KSHV DNA in saliva, or the median number of genome copies of CMV, EBV and KSHV DNA in saliva. Overall, number of genome copies in saliva were lower for KSHV than for CMV and lower for CMV than for EBV. Although replication of CMV, EBV and KSHV persists in many antiretroviral-suppressed, HIV-infected patients, we observed no evidence in this pilot case-control study that the magnitude of such human herpesvirus replication is associated with abnormally increased CD8+ T cell activation and sub-normal plateau absolute CD4+ T cell counts following virologically suppressive antiretroviral therapy.

IL-10 Upregulation in HIV Infection

The cytokine interleukin-10 (IL-10) is considered immunosuppressive because it is involved in shutting down immune responses. A number of studies have reported that IL-10 levels are increased in the setting of chronic progressive HIV infection. More recently, research has shown that blocking the receptor for IL-10 (IL-10R) can enhance virus-specific immune responses in mice chronically infected with lymphocytic choriomeningitis virus (LCMV).

In a new paper in the journal Blood, Mark Brockman and colleagues from the newly-inaugurated Ragon Institute at Massachussetts General Hospital offer a detailed analysis of IL-10 upregulation in HIV and explore the impact of blocking IL-10R in vitro on HIV-specific CD4 and CD8 T cell responses. The key findings include:

• In vitro blockade of IL-10R significantly increased HIV-specific CD4 and CD8 T cell proliferation, but only in the setting of uncontrolled viremia (there was a positive correlation between viral load and fold-increase in p24-specific proliferation). Blockade had no effect on T cell responses in elite controllers or individuals with undetectable viral loads on antiretroviral therapy (ART). CMV-specific T cell responses were not enhanced overall although blockade did increase these responses in a subset of study participants.
• Plasma levels of IL-10 protein correlated strongly with HIV viral load (R=0.6017; p=0.0001). The same held true for levels of IL-10 messenger RNA (mRNA) measured in peripheral blood mononuclear cells (PBMC). Both measures also correlated positively with the fold-increase in HIV-specific CD4 T cell proliferation obtained with IL-10R blockade in vitro.
• IL-10 mRNA levels were comparable between elite controllers and uninfected controls, but slightly higher among individuals with suppressed viral load on ART.
• Longitudinal analysis of several acutely infected study participants showed that IL-10 levels declined significantly after acute infection resolved; levels were significantly higher when measured within 30 days of infection compared to 6-12 months later.
• An investigation of IL-10 mRNA in different cell subsets revealed that, compared to uninfected controls, levels were significantly higher in CD14+ monocytes, CD4+ T cells, CD8+ T cells, CD19+ B cells, and CD56+ NK cells. There was no significant difference for plasmacytoid dendritic cells and levels were lower in monocyte-derived dendritic cells.

The researchers conclude that while IL-10 is clearly upregulated in HIV infection, its relationship with pathogenesis is likely complex. They cite a prior study suggesting that a genetic polymorphism associated with higher IL-10 production may slow disease progression, and note that this would be consistent with a possible beneficial effect of IL-10 in reducing immune activation (which correlates strongly with HIV disease progression). However, they also point out that a short placebo-controlled trial of IL-10 treatment found no benefit on surrogate markers of disease progression. In terms of the therapeutic potential of IL-10R blockade, the researchers argue that it will likely be limited as they observed no impact on HIV-specific immunity when viral load was controlled by ART. To gain a better understanding of the potential positive and negative effects of IL-10 in HIV, the researchers recommend developing strategies that allow specific targeting of the IL-10 production pathway in different cell subsets. 

Blood First Edition Paper, prepublished online April 13, 2009; DOI 10.1182/blood-2008-12-191296.

IL-10 is upregulated in multiple cell types during viremic HIV infection and reversibly inhibits virus-specific T cells

Mark A. Brockman, Douglas S. Kwon, Daniel P. Tighe, David F. Pavlik, Pamela C. Rosato, Jennifer Sela, Filippos Porichis, Sylvie Le Gall, Michael T. Waring, Kristin Moss, Heiko Jessen, Florencia Pereyra, Daniel G. Kavanagh, Bruce D. Walker, and Daniel E. Kaufmann

Ragon Institute of MGH, MIT and Harvard, Massachusetts General Hospital, Charlestown, MA, United States

Harvard Medical School, Boston, MA, United States

Howard Hughes Medical Institute, Chevy Chase, MD, United States

Jessen Praxis, Berlin, Germany

Brigham and Women's Hospital, Boston, MA, United States

Murine models indicate that IL-10 can suppress viral clearance, and interventional blockade of IL-10 activity has been proposed to enhance immunity in chronic viral infections. Increased IL-10 levels have been observed during HIV infection and IL-10 blockade has been shown to enhance T cell function in some HIV-infected subjects. However, the categories of individuals in whom the IL-10 pathway is upregulated are poorly defined, and the cellular sources of IL-10 in these subjects remain to be determined. Here we report that blockade of the IL-10 pathway augmented in vitro proliferative capacity of HIV-specific CD4 and CD8 T cells in individuals with ongoing viral replication. IL-10 blockade also increased cytokine secretion by HIV-specific CD4 T cells. Spontaneous IL-10 expression, measured as either plasma IL-10 protein or IL-10 mRNA in PBMC, correlated positively with viral load and diminished following successful antiretroviral therapy. IL-10 mRNA levels were upregulated in multiple PBMC subsets in HIV infected subjects compared to HIV-negative controls, particularly in T, B, and NK cells, whereas monocytes were a major source of IL-10 mRNA in HIV-infected and uninfected individuals. These data indicate that multiple cell types contribute to IL-10-mediated immune suppression in the presence of uncontrolled HIV viremia.

Guiseppe Pantaleo’s Lausanne Patient

Eleven years ago, a plethora of media stories described the case of “The Berlin Patient,” an individual who received antiretroviral therapy during acute HIV infection and subsequently maintained viral load below 50 copies for many years after stopping treatment. This individual turned out to possess the HLA B*57 allele which is strongly and consistently associated with long term non-progression of HIV infection, and it remains somewhat uncertain if he might have become an elite controller even in the absence of any treatment. At the recent Keystone HIV pathogenesis meeting in Colorado, Guiseppe Pantaleo described another similar case, but in this instance lacking known favorable HLA alleles.

The individual -- dubbed patient 1010 -- was a participant in one of Pantaleo’s studies of acute infection treatment. The protocol compared ART alone to ART together with a short course (8 weeks) of treatment with cyclosporin A (CSA); there were 59 individuals in the trial, ten who received ART and 49 assigned to ART + CSA. Results were published in the Journal of Clinical Investigation in 2002, and showed that receipt of CSA was associated with significantly higher CD4 counts, a difference which Pantaleo reported has been maintained out to four years of follow up.

Patient 1010 enrolled in the study in March of 1999, approximately two weeks after becoming HIV-infected, with a baseline viral load of 26 million copies. He was randomized to receive ART + CSA and was adherent until stopping ART on December 31, 2000. Surprisingly, viral load rose to just 63 copies two weeks later, and has remained below 50 copies without further treatment during the subsequent eight years of follow up; his CD4 count has stayed stable at around 2,000. Pantaleo noted that he is wild-type for the delta32 CCR5 mutation and also lacks any of the major HLA alleles that have been associated with elite control (his class I HLA types are A*0301, B*0702 and B*4002)

Pantaleo went on to describe the profiles of HIV-specific T cell responses in patient 1010. Around 3.5% of CD8 T cells are HIV-specific, targeting Gag, Vif, and Env proteins. An unusually large proportion of these cells (~80%) produce both IL-2 and interferon gamma, and they have what Pantaleo describes as a “massive capacity” for proliferation upon stimulation with antigen, the highest his lab has ever seen. The proportion of cells making IL-2 is also far greater than Pantaleo has previously seen in studies of untreated elite controllers. The differentiation profile of the HIV-specific CD8 T cells equates with a quiescent central memory phenotype, with over 80% of the cells expressing CCR7, CD127, CD27 and CD28.

Based on this anecdotal case, Pantaleo provocatively hypothesized that the ideal immune profile associated with virological control may be the “quiescent, non-effector” CD8 T cell response he has documented in patient 1010. It appears that the virus is so robustly controlled in this individual that HIV-specific T cells are hardly ever encountering antigen. Pantaleo mentioned that Tae-Wook Chun from NIAID has looked for HIV in the patient and found only 1.7 copies of HIV DNA per microgram of genomic DNA, and 11 copies of HIV DNA per million peripheral blood mononuclear cells (PBMC). Chun has calculated that there are approximately 0.0027 infective units of virus out of 360 million CD4 T cells sampled, the lowest he has ever documented. HIV DNA levels were extremely low even in the gut.

The case adds to a number of reports suggesting that a very small proportion of individuals who interrupt ART after being treated for acute infection can maintain control of viral load for variable periods of time. It is generally unclear if these individuals might have gone on to become elite controllers without treatment, but the high viral load and lack of protective HLA alleles in Pantaleo’s patient appear to argue against this possibility. The individual is also clearly an outlier in terms of the extremely low levels of HIV DNA that are detectable and the strong proliferative capacity and IL-2 producing potential of his HIV-specific T cell responses. The duration of time off therapy -- over 8 years -- is also unusual. Whether CSA may have somehow contributed to this salutary outcome is unclear and almost certainly unanswerable without additional studies.

Although it’s clearly possible -- some might say likely -- that anecdotes such as this one reflect some rare and unknown trait possessed by the individuals involved, they might also be hinting that prolonged and robust immune control of HIV is an achievable goal. 

Mapping the Antiviral Battlefield

In a study published in the March 27 issue of Science, Ashley Haase and colleagues offer an unprecedented insight into the battle between host and virus. The study employs two different models: SIV infection in rhesus macaques and LCMV infection in mice. Many years ago, Haase pioneered a technique called in situ hybridization (ISH) that allows the visualization and quantification of virus-infected cells in tissue samples by staining the viral RNA with silver grains. He has now married this approach to a complementary method that identifies virus-specific CD8 T cells in tissues, using a modified version of the widely used tetramer assay (tetramers can identify CD8 T cells based on the specific epitope they are targeting). Tissue images captured using the two techniques are overlayed to create what Haase describes as a “battlefield map” which shows the spatial organization of both virus-infected cells and virus-specific CD8 T cells.

In the Science paper Haase describes results obtained in a study of rhesus macaques challenged intravaginally with SIVmac239. Staining of both viral RNA and SIV Gag-specific CD8 T cells showed that the number of detectable conjugates correlated with the magnitude of the viral load reduction from peak (around days 10-14 post-challenge) to day 21. This finding held true in both cervix and lymph nodes. Haase also used the images to calculate an effector to target cell ratio (E:T ratio) and found that there was a statistically significant correlation between the E:T ratio and the extent of post-peak viral load control.

To explore the value of the approach in another model, Haase collaborated with Rafi Ahmed’s group at Emory University to study the impact of E:T ratios in murine LCMV infection. Two strains of LCMV were compared: the Armstrong strain, which causes a time-limited acute infection that is rapidly cleared, and clone 13, which establishes a chronic persistent infection.  The results demonstrate that the different outcomes are associated with clone 13’s rapid infection of far greater numbers of macrophages  and fibroreticular cells compared to the Armstrong strain. This propensity of clone 13 causes the number of infected target cells to far outnumber effector cells. In contrast, the Armstrong strain infected a limited number of cells which were rapidly outnumbered by effector cells, leading to rapid clearance. Specifically, the E:T ratio for the Armstrong strain was 4 at day 3 post-infection, which was higher by a factor of 20 than the ratio for clone 13 at the same timepoint.

Haase and colleagues conclude that “location, timing, and numbers of effectors and targets all count in determining outcome.” The methodology, which Haase dubs ISTH, will now be used to ascertain if there are vaccination strategies that can create enough effector cells to overwhelm SIV at the portal of entry, before systemic infection can take hold. Ultimately, the hope is that this research can guide the development of a protective HIV vaccine.

This image from the paper shows the individual images of Gag-specific CD8 T cells (top right), SIV-infected cells (middle right) and the two images overlayed (bottom right). CREDIT: Science Magazine, 27 March 2009, Li et al., pp. 1726 – 1729. Reproduced for non-profit educational presentation use only. 

Science 27 March 2009: Vol. 323. no. 5922, pp. 1726 - 1729

DOI: 10.1126/science.1168676

REPORTS

Visualizing Antigen-Specific and Infected Cells in Situ Predicts Outcomes in Early Viral Infection

Qingsheng Li,1 Pamela J. Skinner,2 Sang-Jun Ha,3 Lijie Duan,1 Teresa L. Mattila,2 Aaron Hage,2 Cara White,2 Daniel L. Barber,4 Leigh O'Mara,3 Peter J. Southern,1 Cavan S. Reilly,5 John V. Carlis,6 Christopher J. Miller,7 Rafi Ahmed,3 Ashley T. Haase1

1 Department of Microbiology, Medical School, University of Minnesota, Minneapolis, MN 55455, USA.

2 Department of Veterinary and Biomedical Sciences, University of Minnesota, St. Paul, MN55108, USA.

3 Emory Vaccine Center, Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, GA 30322, USA.

4 Immunobiology Section, National Institute of Allergy and Infectious Diseases, Bethesda, MD 20892, USA.

5 Division of Biostatistics, School of Public Health, University of Minnesota, Minneapolis, MN 55455, USA.

6 Department of Computer Science and Engineering, Institute of Technology, University of Minnesota, Minneapolis, MN 55455, USA.

7 Center for Comparative Medicine, California National Primate Research Center, University of California, Davis, CA 95616, USA.

In the early stages of viral infection, outcomes depend on a race between expansion of infection and the immune response generated to contain it. We combined in situ tetramer staining with in situ hybridization to visualize, map, and quantify relationships between immune effector cells and their targets in tissues. In simian immunodeficiency virus infections in macaques and lymphocytic choriomeningitis virus infections in mice, the magnitude and timing of the establishment of an excess of effector cells versus targets were found to correlate with the extent of control and the infection outcome (i.e., control and clearance versus partial or poor control and persistent infection). This method highlights the importance of the location, timing, and magnitude of the immune response needed for a vaccine to be effective against agents of persistent infection, such as HIV-1.

Gag Orders – Targeting of HIV-Specific CD4 T Cell Responses in Clade C HIV Infection

A new paper from Bruce Walker’s group follows up on their prior work regarding the importance of Gag-specific CD8 T cell responses by evaluating Gag-specific CD4 T cells in chronic clade C HIV infection. The study found that the presence of Gag-specific CD4 T cells (as measured solely by interferon gamma production) was associated with significantly lower viral load on average compared to participants lacking these responses (29,900 copies vs. 91,900 copies). However, there was considerable overlap between the two groups, as would be expected given that previous studies have found that the magnitude of HIV-specific CD4 T cell responses measured by interferon gamma production does not correlate with control of viral load.

To compare CD4 T cell responses to Gag with those targeting other HIV antigens, 32 randomly selected participants were screened for CD4 T cell responses to a pool of peptides (protein fragments) derived from all clade C HIV proteins. This analysis revealed 33 peptides targeted by CD4 T cells, and 27 of the 33 were located in Gag. On average, responses to Gag made up at least 50% of the total HIV-specific CD4 T cell response among study participants. 

The researchers also found that while the magnitude of the total HIV-specific CD4 T cell response did not correlate with viral load, there was a significant inverse correlation with the breadth of the response (i.e. targeting of more peptides was associated with lower viral loads). When responses to just Gag were analyzed, there were significant correlations between both the number of peptides targeted and the magnitude of the response and viral load; broader and stronger Gag-specific CD4 T cell responses were associated with lower viral load.

The authors of the paper emphasize that it will be important to verify these results in larger cohorts and also look in more detail at production of other cytokines as well as interferon gamma. They also note the important caveat that some of the bias toward Gag is likely explained by the relative conservation of this protein; since the T cell assays use peptides based on the most common circulating viruses (consensus peptides), there may be responses present to variant peptides from other less conserved proteins that the assays can't detect. But, even with these caveats, the data represent another addition to the growing literature on the potential contribution to viral load control of broad T cell responses targeting Gag. Unfortunately, to date, HIV vaccine candidates have abjectly failed to induce T cell responses to multiple epitopes within the Gag protein.

PLoS ONE. 2009;4(4):e5013. Epub 2009 Apr 7.

Immunodominant HIV-1 CD4+ T cell epitopes in chronic untreated clade C HIV-1 infection.

Ramduth D, Day CL, Thobakgale CF, Mkhwanazi NP, de Pierres C, Reddy S, van der Stok M, Mncube Z, Nair K, Moodley ES, Kaufmann DE, Streeck H, Coovadia HM, Kiepiela P, Goulder PJ, Walker BD.

HIV Pathogenesis Programme, Doris Duke Medical Research Institute, Nelson R Mandela School of Medicine, University of KwaZulu-Natal, Durban, South Africa. [email protected]

BACKGROUND: A dominance of Gag-specific CD8+ T cell responses is significantly associated with a lower viral load in individuals with chronic, untreated clade C human immunodeficiency virus type 1 (HIV-1) infection. This association has not been investigated in terms of Gag-specific CD4+ T cell responses, nor have clade C HIV-1-specific CD4+ T cell epitopes, likely a vital component of an effective global HIV-1 vaccine, been identified. METHODOLOGY/PRINCIPAL FINDINGS: Intracellular cytokine staining was conducted on 373 subjects with chronic, untreated clade C infection to assess interferon-gamma (IFN-gamma) responses by CD4+ T cells to pooled Gag peptides and to determine their association with viral load and CD4 count. Gag-specific IFN-gamma-producing CD4+ T cell responses were detected in 261/373 (70%) subjects, with the Gag responders having a significantly lower viral load and higher CD4 count than those with no detectable Gag response (p<0.0001 for both parameters). To identify individual peptides targeted by HIV-1-specific CD4+ T cells, separate ELISPOT screening was conducted on CD8-depleted PBMCs from 32 chronically infected untreated subjects, using pools of overlapping peptides that spanned the entire HIV-1 clade C consensus sequence, and reconfirmed by flow cytometry to be CD4+ mediated. The ELISPOT screening identified 33 CD4+ peptides targeted by 18/32 patients (56%), with 27 of the 33 peptides located in the Gag region. Although the breadth of the CD4+ responses correlated inversely with viral load (p = 0.015), the magnitude of the response was not significantly associated with viral load. CONCLUSIONS/SIGNIFICANCE: These data indicate that in chronic untreated clade C HIV-1 infection, IFN-gamma-secreting Gag-specific CD4+ T cell responses are immunodominant, directed at multiple distinct epitopes, and associated with viral control.

VRC Ad5 Vaccine: Decreased Adenovirus Protein Synthesis & Vector-Specific Immunity

A new paper from scientists at the Vaccine Research Center reports that their Ad5 vaccine may induce less vector-specific immunity than other similar constructs. The original prototype of the Merck Ad5 vaccine had deletions in the E1 and E3 adenovirus genes, but this prototype turned out to be genetically unstable and the E3 gene was restored to the final vector that was used in the STEP trial. A part of the Merck vector called the 5’ packaging region was also modified “to make it more like wild-type adenovirus.”

In contrast, the VRC Ad5 vector has the E1, E3 and E4 genes deleted. In the paper, the researchers compare adenoviral protein synthesis after in vitro infection with a vector containing deletions in E1/E3 versus deletions in E1, E3 and E4. The results show that synthesis of the early adenoviral protein ssDNA binding protein (DBP) and the capsid proteins (hexon, penton base and fiber) is significantly lower with the triple-deleted vector; the capsid proteins in particular appear barely detectable. 

An additional analysis of CD4 and CD8 T cell responses to vector proteins in 31 human recipients of the VRC vaccine is consistent with the protein synthesis data. At four weeks after immunization, statistically significant increases in CD4 and CD8 T cell responses to the HIV Env antigen encoded by the vector were detectable At the same time point, only CD8 T cell responses to the Ad5 hexon protein showed a significant increase in magnitude. CD4 T cell responses to the hexon protein increased slightly overall, but the change did not reach statistical significance. There were no significant changes in either CD4 or CD8 T cell responses to the adenovirus E2A protein. Echoing several other recent studies, no correlation was found between baseline adenovirus-specific CD4 T cell responses and anti-Ad5 neutralizing antibody titers.

In sum, if the enhancement of susceptibility to HIV infection documented in a subset of STEP participants was somehow related to Ad5 protein expression by the Merck vector, these data might suggest that the VRC Ad5 vaccine would not be similarly affected. However, unless some clear correlate of the enhanced susceptibility in STEP emerges – which at this point seems unlikely – then it is hard to imagine a scenario in which the FDA would approve another test of an Ad5 vaccine among the population that was most at risk for enhancement in STEP (uncircumcised men, particularly those with pre-existing neutralizing antibodies to Ad5).

J. Virol. doi:10.1128/JVI.00384-09

Multiply-deleted replication-defective adenovirus vectors do not induce measurable vector-specific T cells in human trials

Richard A. Koup, Laurie Lamoreaux, David Zarkowsky, Robert T. Bailer, C. Richter King, Jason G. D. Gall, Douglas E. Brough, Barney S. Graham, and Mario Roederer

Immunology Laboratory, Immunology Core Section, Clinical Trials Core, and ImmunoTechnology Section, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA; GenVec Inc. Gaithersburg, MD, USA

The magnitude and character of adenovirus type 5 (Ad5) -specific T cells was determined in volunteers with and without pre-existing neutralizing antibodies (NA) to Ad5 who received rAd5-based HIV vaccines. There was no correlation between T cell responses and NA to Ad5. There was no increase in magnitude or activation state of Ad5-specific CD4+ T cells at time points where antibodies to Ad5 and T cell responses to the recombinant gene products could be measured. These data indicate that rAd5-based vaccines containing deletions in the E1, E3 and E4 region do not induce appreciable expansion of vector-specific CD4+ T cells.