Michael N Robertson

Publications of Michael N Robertson

• Extended follow-up confirms early vaccine-enhanced risk of HIV acquisition and demonstrates waning effect over time among participants in a randomized trial of recombinant adenovirus HIV vaccine (Step study).

  Authors: Ann Duerr, Yunda Huang, Susan Buchbinder, Robert W Coombs, Jorge Sanchez, Carlos Del Rio, Martin Casapia, Steven Santiago, Peter Gilbert, Lawrence Corey, Michael N Robertson

  The Journal of infectious diseases. 05/2012;

  BackgroundThe Step study tested whether an adenovirus serotype 5 (Ad5)-vectored HIV vaccine could prevent HIV acquisition and/or reduce viral load set-point after infection. At the first interimBackgroundThe Step study tested whether an adenovirus serotype 5 (Ad5)-vectored HIV vaccine could prevent HIV acquisition and/or reduce viral load set-point after infection. At the first interim analysis non-efficacy criteria were met. Vaccinations were halted; participants were unblinded. In post-hoc analyses, more HIV infections occurred in vaccinees vs. placebo (V: P) recipients in men who had Ad5 neutralizing antibodies and/or were uncircumcised. Follow-up was extended to assess relative risk of HIV acquisition (V: P) over time.MethodsWe used cox proportional hazard models for analyses of vaccine effect on HIV acquisition and analysis of vaccine effect modifiers, and non-parametric and semi-parametric methods for analysis of constancy of relative risk over time.Findings172 of 1836 men were infected. The adjusted V: P hazard ratio (HR) for all follow-up time was 1·40 (95% CI [1·03, 1·92], p=0·03). Vaccine effect differed by baseline Ad5 or circumcision status during first 18 months, but neither was significant for all follow-up time. HR among uncircumcised and/or Ad5 seropositive men waned with time since vaccination. No significant vaccine-associated risk was seen among circumcised, Ad5-negative men (HR = 0·97, p=1·0) over all follow-up time.InterpretationThe vaccine-associated risk seen in interim analysis was confirmed but waned with time from vaccination.

• Sexual risk behaviors, circumcision status and pre-existing immunity to adenovirus type 5 among men who have sex with men participating in a randomized HIV-1 vaccine efficacy trial: Step Study.

  Authors: Beryl A Koblin, Kenneth H Mayer, Elizabeth Noonan, Ching-Yun Wang, Michael Marmor, Jorge Sanchez, Stephen J Brown, Michael N Robertson, Susan P Buchbinder

  Journal of acquired immune deficiency syndromes (1999). 03/2012;

  BACKGROUND: The Step Study found that men who had sex with men (MSM) who received an adenovirus type 5 (Ad5) vector-based vaccine and were uncircumcised or had prior Ad5 immunity had a higher HIVBACKGROUND: The Step Study found that men who had sex with men (MSM) who received an adenovirus type 5 (Ad5) vector-based vaccine and were uncircumcised or had prior Ad5 immunity had a higher HIV incidence than MSM who received placebo. We investigated whether differences in HIV exposure, measured by reported sexual risk behaviors, may explain the increased risk. METHODS: Among 1,764 MSM in the trial, 724 were uncircumcised, 994 had prior Ad5 immunity and 560 were both uncircumcised and had prior Ad5 immunity. Analyses compared sexual risk behaviors and perceived treatment assignment among vaccine and placebo recipients, determined risk factors for HIV acquisition and examined the role of insertive anal intercourse in HIV risk among uncircumcised men. FINDINGS: Few sexual risk behaviors were significantly higher in vaccine vs. placebo recipients at baseline or during follow-up. Among uncircumcised men, vaccine recipients at baseline were more likely to report unprotected insertive anal intercourse with HIV negative partners (25.0% vs. 18.1%; p=0.03). Among uncircumcised men who had prior Ad5 immunity, vaccine recipients were more likely to report unprotected insertive anal intercourse with partners of unknown HIV status (46.0% vs. 37.5%; p=0.05). Vaccine recipients remained at higher risk of HIV infection compared to placebo recipients (HR =2.8; 95% CI:1.7, 6.8) controlling for potential confounders. INTERPRETATION: These analyses do not support a behavioral explanation for the increased HIV infection rates observed among uncircumcised men in the Step Study. Identifying biologic mechanisms to explain the increased risk is a priority.This study is registered with ClinicalTrials.gov, number NCT00095576.

• Human adenovirus-specific T cells modulate HIV-specific T cell responses to an Ad5-vectored HIV-1 vaccine.

  Authors: Nicole Frahm, Allan C DeCamp, David P Friedrich, Donald K Carter, Olivier D Defawe, James G Kublin, Danilo R Casimiro, Ann Duerr, Michael N Robertson, Susan P Buchbinder, Yunda Huang, Gregory A Spies, Stephen C De Rosa, M Juliana McElrath

  The Journal of clinical investigation. 12/2011; 122(1):359-67.

  Recombinant viruses hold promise as vectors for vaccines to prevent infectious diseases with significant global health impacts. One of their major limitations is that preexisting anti-vectorRecombinant viruses hold promise as vectors for vaccines to prevent infectious diseases with significant global health impacts. One of their major limitations is that preexisting anti-vector neutralizing antibodies can reduce T cell responses to the insert antigens; however, the impact of vector-specific cellular immunity on subsequent insert-specific T cell responses has not been assessed in humans. Here, we have identified and compared adenovirus-specific and HIV-specific T cell responses in subjects participating in two HIV-1 vaccine trials using a vaccine vectored by adenovirus serotype 5 (Ad5). Higher frequencies of pre-immunization adenovirus-specific CD4⁺ T cells were associated with substantially decreased magnitude of HIV-specific CD4⁺ T cell responses and decreased breadth of HIV-specific CD8⁺ T cell responses in vaccine recipients, independent of type-specific preexisting Ad5-specific neutralizing antibody titers. Further, epitopes recognized by adenovirus-specific T cells were commonly conserved across many adenovirus serotypes, suggesting that cross-reactivity of preexisting adenovirus-specific T cells can extend to adenovirus vectors derived from rare serotypes. These findings provide what we believe to be a new understanding of how preexisting viral immunity may impact the efficacy of vaccines under current evaluation for prevention of HIV, tuberculosis, and malaria.

• Low-dose penile SIVmac251 exposure of rhesus macaques infected with adenovirus type 5 (Ad5) and then immunized with a replication-defective Ad5-based SIV gag/pol/nef vaccine recapitulates the results of the phase IIb step trial of a similar HIV-1 vaccine.

  Authors: Huma Qureshi, Zhong-Min Ma, Ying Huang, Gregory Hodge, Michael A Thomas, Janet DiPasquale, Veronique DeSilva, Linda Fritts, Andrew J Bett, Danilo R Casimiro, John W Shiver, Marjorie Robert-Guroff, Michael N Robertson, Michael B McChesney, Peter B Gilbert, Christopher J Miller

  Journal of virology. 12/2011; 86(4):2239-50.

  The Step Trial showed that the MRKAd5 HIV-1 subtype B Gag/Pol/Nef vaccine did not protect men from HIV infection or reduce setpoint plasma viral RNA (vRNA) levels but, unexpectedly, it did modestlyThe Step Trial showed that the MRKAd5 HIV-1 subtype B Gag/Pol/Nef vaccine did not protect men from HIV infection or reduce setpoint plasma viral RNA (vRNA) levels but, unexpectedly, it did modestly enhance susceptibility to HIV infection in adenovirus type 5 (Ad5)-seropositive, uncircumcised men. As part of the process to understand the results of the Step Trial, we designed a study to determine whether rhesus macaques chronically infected with a host-range mutant Ad5 (Ad5hr) and then immunized with a replication defective Ad5 SIVmac239 Gag/Pol/Nef vaccine were more resistant or susceptible to SIV infection than unimmunized rhesus macaques challenged with a series of escalating dose penile exposures to SIVmac 251. The Ad5 SIV vaccine induced CD8(+) T cell responses in 70% of the monkeys, which is similar to the proportion of humans that responded to the vaccine in the Step Trial. However, the vaccine did not protect vaccinated animals from penile SIV challenge. At the lowest SIV exposure dose (10(3) 50% tissue culture infective doses), 2 of 9 Ad5-seropositive animals immunized with the Ad5 SIV vaccine became infected compared to 0 of 34 animals infected in the other animal groups (naive animals, Ad5-seropositive animals immunized with the empty Ad5 vector, Ad5-seronegative animals immunized with the Ad5 SIV vaccine, and Ad5-seronegative animals immunized with the empty Ad5 vector). Penile exposure to more concentrated virus inocula produced similar rates of infection in all animal groups. Although setpoint viral loads were unaffected in Step vaccinees, the Ad5 SIV-immunized animals had significantly lower acute-phase plasma vRNA levels compared to unimmunized animals. Thus, the results of the nonhuman primate (NHP) study described here recapitulate the lack of protection against HIV acquisition seen in the Step Trial and suggest a greater risk of infection in the Ad5-seropositive animals immunized with the Ad5 SIV vaccine. Further studies are necessary to confirm the enhancement of virus acquisition and to discern associated mechanisms.

• Raltegravir once daily or twice daily in previously untreated patients with HIV-1: a randomised, active-controlled, phase 3 non-inferiority trial.

  Authors: Joseph J Eron, Jürgen K Rockstroh, Jacques Reynes, Jaime Andrade-Villanueva, Jose Valdez Ramalho-Madruga, Linda-Gail Bekker, Benjamin Young, Christine Katlama, Jose Maria Gatell-Artigas, Jose R Arribas [......] Matthew L Rizk, Larissa Wenning, Michael D Miller, Daria Hazuda, Mark J DiNubile, Randi Leavitt, Robin Isaacs, Michael N Robertson, Peter Sklar, Bach-Yen Nguyen

  The Lancet infectious diseases. 09/2011; 11(12):907-15.

  Twice-daily raltegravir with once-daily tenofovir-emtricitabine is an effective initial antiretroviral regimen for patients with HIV-1. On the basis of pharmacokinetic data suggesting efficacy ofTwice-daily raltegravir with once-daily tenofovir-emtricitabine is an effective initial antiretroviral regimen for patients with HIV-1. On the basis of pharmacokinetic data suggesting efficacy of once-daily raltegravir and because adherence is often improved with once-daily dosing, we aimed to compare these dosing schedules. In our international, double-blind, randomised, phase 3 non-inferiority study, we enrolled antiretroviral-naive patients with HIV RNA loads of more than 5000 copies per mL and no baseline resistance to tenofovir or emtricitabine at 83 centres worldwide. We randomly allocated patients (1:1) by use of a computer-generated sequence to receive raltegravir once daily (two 400 mg tablets taken together every 24 h), or twice daily (one 400 mg tablet every 12 h), both in combination with once-daily co-formulated tenofovir 300 mg plus emtricitabine 150 mg. The primary outcome was virological response at 48 weeks (viral RNA loads <50 copies per mL) in patients who received at least one dose of study drug, counting non-completers as failure. We assessed non-inferiority in terms of the proportion of patients in both treatment groups who achieved the primary outcome, with a non-inferiority margin of -10%. This study is registered with ClinicalTrials.gov, number NCT00745823. From Oct 15, 2008, to Nov 2, 2009, we randomly allocated 775 patients, of whom 382 (99%) of 386 patients in the once-daily group and 388 (99%) of 389 in the twice-daily group received at least one dose of study drug. At baseline, 304 (39%) of 770 treated patients had viral loads of more than 100,000 copies per mL and 188 (24%) had CD4 cell counts of fewer than 200 cells per μL. 318 (83%) of 382 patients in the once-daily group had virological response compared with 343 (89%) of 386 in the twice-daily group (difference -5·7%, 95% CI -10·7 to -0·83; p=0·044). Serious adverse events were reported in 26 (7%) of 382 once-daily recipients and 40 (10%) of 388 twice-daily recipients, and adverse events leading to discontinuation occurred in four (1%) patients in each group. Despite high response rates with both regimens, once-daily raltegravir cannot be recommended in place of twice-daily dosing. Merck.

• Host genetic determinants of T cell responses to the MRKAd5 HIV-1 gag/pol/nef vaccine in the step trial.

  Authors: Jacques Fellay, Nicole Frahm, Kevin V Shianna, Elizabeth T Cirulli, Danilo R Casimiro, Michael N Robertson, Barton F Haynes, Daniel E Geraghty, M Juliana McElrath, David B Goldstein

  The Journal of infectious diseases. 03/2011; 203(6):773-9.

  Understanding how human genetic variation impacts individual response to immunogens is fundamental for rational vaccine development. To explore host mechanisms involved in cellular immune responsesUnderstanding how human genetic variation impacts individual response to immunogens is fundamental for rational vaccine development. To explore host mechanisms involved in cellular immune responses to the MRKAd5 human immunodeficiency virus type 1 (HIV-1) gag/pol/nef vaccine tested in the Step trial, we performed a genome-wide association study of determinants of HIV-specific T cell responses, measured by interferon γ enzyme-linked immunospot assays. No human genetic variant reached genome-wide significance, but polymorphisms located in the major histocompatibility complex (MHC) region showed the strongest association with response to the HIV-1 Gag protein: HLA-B alleles known to be associated with differences in HIV-1 control were responsible for these associations. The implication of the same HLA alleles in vaccine-induced cellular immunity and in natural immune control is of relevance for vaccine design. Furthermore, our results demonstrate the importance of considering the host immunogenetic background in the analysis of immune responses to T cell vaccines.

• Genetic impact of vaccination on breakthrough HIV-1 sequences from the STEP trial.

  Authors: Morgane Rolland, Sodsai Tovanabutra, Allan C deCamp, Nicole Frahm, Peter B Gilbert, Eric Sanders-Buell, Laura Heath, Craig A Magaret, Meera Bose, Andrea Bradfield [......] Fusheng Li, Steve G Self, Jerome Kim, Susan Buchbinder, Danilo R Casimiro, Michael N Robertson, Ann Duerr, M Juliana McElrath, Francine E McCutchan, James I Mullins

  Nature medicine. 02/2011; 17(3):366-71.

  We analyzed HIV-1 genome sequences from 68 newly infected volunteers in the STEP HIV-1 vaccine trial. To determine whether the vaccine exerted selective T cell pressure on breakthrough viruses, weWe analyzed HIV-1 genome sequences from 68 newly infected volunteers in the STEP HIV-1 vaccine trial. To determine whether the vaccine exerted selective T cell pressure on breakthrough viruses, we identified potential T cell epitopes in the founder sequences and compared them to epitopes in the vaccine. We found greater distances to the vaccine sequence for sequences from vaccine recipients than from placebo recipients. The most significant signature site distinguishing vaccine from placebo recipients was Gag amino acid 84, a site encompassed by several epitopes contained in the vaccine and restricted by human leukocyte antigen (HLA) alleles common in the study cohort. Moreover, the extended divergence was confined to the vaccine components of the virus (HIV-1 Gag, Pol and Nef) and not found in other HIV-1 proteins. These results represent what is to our knowledge the first evidence of selective pressure from vaccine-induced T cell responses on HIV-1 infection in humans.

• Safety and Immunogenicity of the MRKAd5 gag HIV Type 1 Vaccine in a Worldwide Phase 1 Study of Healthy Adults.

  Authors: Ouzama Nicholson, Fay Dicandilo, James Kublin, Xiao Sun, Erin Quirk, Michelle Miller, Glenda Gray, Jean Pape, Michael N Robertson, Devan V Mehrotra, Steven Self, Katherine Turner, Jorge Sanchez, Punnee Pitisuttithum, Ann Duerr, Sheri Dubey, Lisa Kierstead, Danilo Casimiro, Scott M Hammer

  AIDS research and human retroviruses. 11/2010;

  Abstract The safety and immunogenicity of the MRK adenovirus type 5 (Ad5) HIV-1 clade B gag vaccine was assessed in an international Phase I trial. Three-hundred and sixty healthy HIV-uninfectedAbstract The safety and immunogenicity of the MRK adenovirus type 5 (Ad5) HIV-1 clade B gag vaccine was assessed in an international Phase I trial. Three-hundred and sixty healthy HIV-uninfected adults were enrolled on five continents. Subjects received placebo or 1 × 10(9) or 1 × 10(10) viral particles (vp) per dose of the MRKAd5 HIV-1 gag vaccine at day 1, week 4, and week 26. Immunogenicity was evaluated using an IFN-γ ELISPOT gag 15-mer assay with positive responses defined as ≥55 SFC/10(6) PBMCs and ≥4-fold over mock control. The vaccine was well tolerated. The most common adverse events were injection site reactions, headache, pyrexia, diarrhea, fatigue, and myalgia. At week 30, geometric mean ELISPOT responses were 24, 114, and 226 SFC/10(6) PBMCs in the placebo, 1 × 10(9) vp/dose, and 1 × 10(10) vp/dose groups, respectively. Overall, responses to 1 × 10(10) vp were 85% and 68% in subjects with low (≤200) and high (>200) baseline Ad5 titers, respectively. The MRKAd5 HIV-1 gag vaccine was immunogenic in diverse geographic regions. Gag ELISPOT responses were greater in the 1 × 10(10) vp/dose groups than in the 1 × 10(9) vp/dose groups. Data from this first international study indicate that adenovirus-vectored vaccines are well tolerated and may be immunogenic in subjects from regions with high prevalence of preexisting Ad5 immunity.

• Comparison of T cell immune responses induced by vectored HIV vaccines in non-human primates and humans.

  Authors: Andrew J Bett, Sheri A Dubey, Devan V Mehrotra, Liming Guan, Romnie Long, Kiersten Anderson, Kelly Collins, Christine Gaunt, Rose Fernandez, Suzanne Cole, Steve Meschino, Aimin Tang, Xiao Sun, Sanjay Gurunathan, Jim Tartaglia, Michael N Robertson, John W Shiver, Danilo R Casimiro

  Vaccine. 10/2010; 28(50):7881-9.

  Following the disappointing outcome of the phase IIb test-of-concept step study in which Merck's adenovirus type 5 (Ad5) HIV-1 clade B gag/pol/nef vaccine failed to demonstrate efficacy in HIVFollowing the disappointing outcome of the phase IIb test-of-concept step study in which Merck's adenovirus type 5 (Ad5) HIV-1 clade B gag/pol/nef vaccine failed to demonstrate efficacy in HIV high-risk individuals, an extensive review of the trial and preclinical studies which supported the trial is ongoing. One point of interest is how well preclinical nonhuman primate immunogenicity studies predicted what was observed in humans. Here we compare the HIV-1-specific cellular immune responses elicited in nonhuman primates and human clinical trial subjects to several HIV-1 vaccine candidates. We find that although rhesus macaques are immunologically more responsive to vaccination than humans, the hierarchy in potency of single-modality prime-boost regimens using several vector approaches (adenovirus, DNA, and pox vectors) was well predicted. Vaccine approaches using complex formulations such as novel adjuvants (DNA+CRL1005) or mixed-modality prime-boost (DNA/Ad5; Ad5/ALVAC) did not correlate as well between rhesus macaques and humans. Although the immunogenicity of the vaccines and vaccine regimens evaluated were not all accurately predicted, testing in rhesus macaques generally offers an indispensable tool for ranking the immunological potential of HIV-1 vaccine candidates.

• Vaccination with Ad5 vectors expands Ad5-specific CD8 T cells without altering memory phenotype or functionality.

  Authors: Natalie A Hutnick, Diane G Carnathan, Sheri A Dubey, Kara S Cox, Lisa Kierstead, George Makadonas, Sarah J Ratcliffe, Marcio O Lasaro, Michael N Robertson, Danilo R Casimiro, Hildegund C J Ertl, Michael R Betts

  PloS one. 01/2010; 5(12):e14385.

  Adenoviral (Ad) vaccine vectors represent both a vehicle to present a novel antigen to the immune system as well as restimulation of immune responses against the Ad vector itself. To what degreeAdenoviral (Ad) vaccine vectors represent both a vehicle to present a novel antigen to the immune system as well as restimulation of immune responses against the Ad vector itself. To what degree Ad-specific CD8(+) T cells are restimulated by Ad vector vaccination is unclear, although such knowledge would be important as vector-specific CD8(+) T cell expansion could potentially further limit Ad vaccine efficacy beyond Ad-specific neutralizing antibody alone. Here we addressed this issue by measuring human Adenovirus serotype 5 (Ad5)-specific CD8(+) T cells in recipients of the Merck Ad5 HIV-1 vaccine vector before, during, and after vaccination by multicolor flow cytometry. Ad5-specific CD8(+) T-cells were detectable in 95% of subjects prior to vaccination, and displayed primarily an effector-type functional profile and phenotype. Peripheral blood Ad5-specific CD8(+) T-cell numbers expanded after Ad5-HIV vaccination in all subjects, but differential expansion kinetics were noted in some baseline Ad5-neutralizing antibody (Ad5 nAb) seronegative subjects compared to baseline Ad5 nAb seropositive subjects. However, in neither group did vaccination alter polyfunctionality, mucosal targeting marker expression, or memory phenotype of Ad5-specific CD8(+) T-cells. These data indicate that repeat Ad5-vector administration in humans expands Ad5-specific CD8(+) T-cells without overtly affecting their functional capacity or phenotypic properties. This is a secondary analysis of samples collected during the 016 trial. Results of the Merck 016 trial safety and immunogenicity have been previously published in the journal of clinical infectious diseases [1]. ClinicalTrials.gov NCT00849680[http://www.clinicaltrials.gov/show/NCT00849680].

• Comparative Cell-Mediated Immunogenicity of DNA/DNA, DNA/Adenovirus Type 5 (Ad5), or Ad5/Ad5 HIV-1 Clade B gag Vaccine Prime-Boost Regimens.

  Authors: David M Asmuth, Elizabeth L Brown, Mark J DiNubile, Xiao Sun, Carlos Del Rio, Clayton Harro, Michael C Keefer, James G Kublin, Sheri A Dubey, Lisa S Kierstead, Danilo R Casimiro, John W Shiver, Michael N Robertson, Erin K Quirk, Devan V Mehrotra

  The Journal of infectious diseases. 11/2009;

  Background. We report composite results from the Merck phase I program of near-consensus clade B human immunodeficiency virus (HIV) type 1 gag vaccines. Methods. Healthy HIV-uninfected adults wereBackground. We report composite results from the Merck phase I program of near-consensus clade B human immunodeficiency virus (HIV) type 1 gag vaccines. Methods. Healthy HIV-uninfected adults were enrolled in 6 blinded placebo-controlled studies evaluating the immunogenicity of (1) a 4-dose regimen of a DNA vaccine, (2) a 3-dose priming regimen of the DNA vaccine with a booster dose of an adenovirus type 5 (Ad5)-vectored vaccine, or (3) a 3-dose regimen of the Ad5 vaccine. The DNA plasmid was provided with or without an aluminum phosphate or CRL1005 adjuvant. The primary end point was the unfractionated HIV-1 gag-specific interferon gamma enzyme-linked immunospot (ELISpot) response 4 weeks after the final dose. Results. Overall, 254 (83%) of 307 subjects randomized to the vaccine groups were evaluable. Adjuvants did not enhance immunogenicity of the DNA vaccine. Postboost ELISpot responder frequencies were higher for Ad5-containing regimens than for the DNA/DNA regimen (33%) but were similar for DNA/Ad5 (55%) and Ad5/Ad5 (50%). DNA/DNA elicited mainly a CD4 response, whereas Ad5/Ad5 elicited mainly a CD8 response; DNA/Ad5 generated CD4 and CD8 responses comparable to those of DNA/DNA and Ad5/Ad5, respectively. Conclusions. The DNA vaccine alone or as a priming regimen for the Ad5 vaccine did not increase unfractionated ELISpot responses compared with the Ad5 vaccine alone. Qualitative T cell responses to different vaccine regimens deserve further study.

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

  Authors: Natalie A Hutnick, Diane G Carnathan, Sheri A Dubey, Kara S Cox, Lisa Kierstead, Sarah J Ratcliffe, Michael N Robertson, Danilo R Casimiro, Hildegund C J Ertl, Michael R Betts

  Nature medicine. 09/2009; 15(8):876-8.

  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 Ad5The 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.

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

  Authors: Kara L O'Brien, Jinyan Liu, Sharon L King, Ying-Hua Sun, Joern E Schmitz, Michelle A Lifton, Natalie A Hutnick, Michael R Betts, Sheri A Dubey, Jaap Goudsmit, John W Shiver, Michael N Robertson, Danilo R Casimiro, Dan H Barouch

  Nature medicine. 09/2009; 15(8):873-5.

  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 studyThe 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.

• HIV Seroconversion without Infection after Receipt of Adenovirus-Vectored HIV Type 1 Vaccine.

  Authors: Erin K Quirk, Robin Mogg, Deborah D Brown, Michelle A Lally, Devan V Mehrotra, Mark J DiNubile, Michael N Robertson

  Clinical infectious diseases : an official publication of the Infectious Diseases Society of America. 01/2009; 47(12):1593-9.

  Background. @nbsp; We analyzed human immunodeficiency virus (HIV) seroresponses from 3 phase I HIV-1 vaccine trials to assess the frequency of vaccine-induced seroconversion. Methods. @nbsp; HIV-1Background. @nbsp; We analyzed human immunodeficiency virus (HIV) seroresponses from 3 phase I HIV-1 vaccine trials to assess the frequency of vaccine-induced seroconversion. Methods. @nbsp; HIV-1 and HIV-2 enzyme-linked immunosorbent assay (ELISA) was performed during trials of adenovirus type 5 (Ad5)-vectored clade B HIV-1 monovalent gag and trivalent gag/pol/nef vaccines given to HIV-seronegative adults. Doses were administered at day 1, week 4, and week 26. Results were analyzed by vaccine formulation and dose and were stratified by baseline Ad5 titer. ELISA-positive samples were reflexively tested by Western blotting. Results. @nbsp; Overall, 165 (41%) of 406 evaluable vaccine recipients had positive ELISA results but negative PCR results by week 78. Seroconversion rates were directly related to vaccine dose, were inversely related to baseline Ad5 titer, and were unaffected by vaccine valency. One hundred (89%) of 113 evaluable patients with low baseline Ad5 antibody titers (</=200) who were given >/=1 dose of vaccine with >/=[Formula: see text] gag-containing Ad5 particles per dose experienced seroconversion. Of 163 vaccine recipients who had positive ELISA results and available Western blot results, 150 (92%) had indeterminate results of Western blot, typically involving bands at p24, p40, and/or p55. Thirteen uninfected patients (8%) had equivocally positive Western blot results, usually because of an additional weak glycoprotein 41 band. Env-specific enzyme immunoassay results were falsely positive for 2 uninfected vaccine recipients. Conclusions. @nbsp; Positive ELISA results were similarly common for monovalent and trivalent vaccine recipients. Vaccine dose and baseline Ad5 immunity were major determinants of vaccine-induced seroconversion rates. Corresponding Western blots characteristically showed bands directed only at Gag proteins, which helped to distinguish HIV-uninfected vaccine recipients who experienced seroconversion from true HIV-infected patients. If available, an enzyme immunoassay exclusively targeting proteins not expressed by the vaccine should be the screening test of first choice for vaccine recipients.

• Safety and Immunogenicity of Adenovirus-Vectored Near-Consensus HIV Type 1 Clade B gag Vaccines in Healthy Adults.

  Authors: Clayton D Harro, Michael N Robertson, Michelle A Lally, Lori D O'Neill, Srilatha Edupuganti, Paul A Goepfert, Mark J Mulligan, Frances H Priddy, Sheri A Dubey, Lisa S Kierstead, Xiao Sun, Danilo R Casimiro, Mark J DiNubile, John W Shiver, Randi Y Leavitt, Devan V Mehrotra

  AIDS research and human retroviruses. 12/2008;

  Abstract Vaccines inducing pathogen-specific cell-mediated immunity are being developed using attenuated adenoviral (Ad) vectors. We report the results of two independent Phase I trials of similarAbstract Vaccines inducing pathogen-specific cell-mediated immunity are being developed using attenuated adenoviral (Ad) vectors. We report the results of two independent Phase I trials of similar replication-deficient Ad5 vaccines containing a near-consensus HIV-1 clade B gag transgene. Healthy HIV-uninfected adults were enrolled in two separate, multicenter, dose-escalating, blinded, placebo-controlled studies to assess the safety and immunogenicity of a three-dose homologous regimen of Ad5 and MRKAd5 HIV-1 gag vaccines given on day 1, week 4, and week 26. Adverse events were collected for 29 days following each intradeltoid injection. The primary immunogenicity endpoint was the proportion of subjects with a positive unfractionated Gag-specific IFN-gamma ELISPOT response measured 4 weeks after the last dose (week 30). Analyses were performed after combining data for each dose group from both protocols, stratifying by baseline Ad5 titers. Overall, 252 subjects were randomized to receive either vaccine or placebo, including 229 subjects (91%) who completed the study through week 30. Tolerability and immunogenicity did not appear to differ between the Ad5 and MRKAd5 vaccines. The frequency of injection-site reactions was dose dependent. Systemic adverse events were also dose dependent and more frequent in subjects with baseline Ad5 titers <200 versus >/=200, especially after the first dose. The percent of ELISPOT responders and the ELISPOT geometric means overall were significantly higher for all four vaccine doses studied compared to placebo, and were generally higher in vaccine recipients with baseline Ad5 titers <200 versus >/=200. Ad5 titers increased after vaccination in a dose-dependent fashion. Both Ad5-vectored HIV-1 vaccines were generally well tolerated and induced cell-mediated immune responses against HIV Gag-peptides in the majority of healthy adults with baseline Ad5 titers <200. Preexistent and/or vaccine-induced immunity to the Ad5 vector may dampen the CMI response to HIV Gag.

• HIV-1 vaccine-induced immunity in the test-of-concept Step Study: a case-cohort analysis.

  Authors: M Juliana McElrath, Stephen C De Rosa, Zoe Moodie, Sheri Dubey, Lisa Kierstead, Holly Janes, Olivier D Defawe, Donald K Carter, John Hural, Rama Akondy, Susan P Buchbinder, Michael N Robertson, Devan V Mehrotra, Steven G Self, Lawrence Corey, John W Shiver, Danilo R Casimiro

  Lancet. 12/2008;

  BACKGROUND: In the Step Study, the MRKAd5 HIV-1 gag/pol/nef vaccine did not reduce plasma viraemia after infection, and HIV-1 incidence was higher in vaccine-treated than in placebo-treated men withBACKGROUND: In the Step Study, the MRKAd5 HIV-1 gag/pol/nef vaccine did not reduce plasma viraemia after infection, and HIV-1 incidence was higher in vaccine-treated than in placebo-treated men with pre-existing adenovirus serotype 5 (Ad5) immunity. We assessed vaccine-induced immunity and its potential contributions to infection risk. METHODS: To assess immunogenicity, we characterised HIV-specific T cells ex vivo with validated interferon-gamma ELISPOT and intracellular cytokine staining assays, using a case-cohort design. To establish effects of vaccine and pre-existing Ad5 immunity on infection risk, we undertook flow cytometric studies to measure Ad5-specific T cells and circulating activated (Ki-67+/BcL-2(lo)) CD4+ T cells expressing CCR5. FINDINGS: We detected interferon-gamma-secreting HIV-specific T cells (range 163/10(6) to 686/10(6) peripheral blood mononuclear cells) ex vivo by ELISPOT in 77% (258/354) of people receiving vaccine; 218 of 354 (62%) recognised two to three HIV proteins. We identified HIV-specific CD4+ T cells by intracellular cytokine staining in 58 of 142 (41%) people. In those with reactive CD4+ T cells, the median percentage of CD4+ T cells expressing interleukin 2 was 88%, and the median co-expression of interferon gamma or tumor necrosis factor alpha (TNFalpha), or both, was 72%. We noted HIV-specific CD8+ T cells (range 0.4-1.0%) in 117 of 160 (73%) participants, expressing predominantly either interferon gamma alone or with TNFalpha. Vaccine-induced HIV-specific immunity, including response rate, magnitude, and cytokine profile, did not differ between vaccinated male cases (before infection) and non-cases. Ad5-specific T cells were lower in cases than in non-cases in several subgroup analyses. The percentage of circulating Ki-67+BcL-2(lo)/CCR5+CD4+ T cells did not differ between cases and non-cases. INTERPRETATION: Consistent with previous trials, the MRKAd5 HIV-1 gag/pol/nef vaccine was highly immunogenic for inducing HIV-specific CD8+ T cells. Our findings suggest that future candidate vaccines have to elicit responses that either exceed in magnitude or differ in breadth or function from those recorded in this trial. FUNDING: National Institute of Allergy and Infectious Diseases, US National Institutes of Health; and Merck Research Laboratories.

• Efficacy assessment of a cell-mediated immunity HIV-1 vaccine (the Step Study): a double-blind, randomised, placebo-controlled, test-of-concept trial.

  Authors: Susan P Buchbinder, Devan V Mehrotra, Ann Duerr, Daniel W Fitzgerald, Robin Mogg, David Li, Peter B Gilbert, Javier R Lama, Michael Marmor, Carlos Del Rio, M Juliana McElrath, Danilo R Casimiro, Keith M Gottesdiener, Jeffrey A Chodakewitz, Lawrence Corey, Michael N Robertson

  Lancet. 12/2008;

  BACKGROUND: Observational data and non-human primate challenge studies suggest that cell-mediated immune responses might provide control of HIV replication. The Step Study directly assessed theBACKGROUND: Observational data and non-human primate challenge studies suggest that cell-mediated immune responses might provide control of HIV replication. The Step Study directly assessed the efficacy of a cell-mediated immunity vaccine to protect against HIV-1 infection or change in early plasma HIV-1 levels. METHODS: We undertook a double-blind, phase II, test-of-concept study at 34 sites in North America, the Caribbean, South America, and Australia. We randomly assigned 3000 HIV-1-seronegative participants by computer-generated assignments to receive three injections of MRKAd5 HIV-1 gag/pol/nef vaccine (n=1494) or placebo (n=1506). Randomisation was prestratified by sex, adenovirus type 5 (Ad5) antibody titre at baseline, and study site. Primary objective was a reduction in HIV-1 acquisition rates (tested every 6 months) or a decrease in HIV-1 viral-load setpoint (early plasma HIV-1 RNA measured 3 months after HIV-1 diagnosis). Analyses were per protocol and modified intention to treat. The study was stopped early because it unexpectedly met the prespecified futility boundaries at the first interim analysis. This study is registered with ClinicalTrials.gov, number NCT00095576. FINDINGS: In a prespecified interim analysis in participants with baseline Ad5 antibody titre 200 or less, 24 (3%) of 741 vaccine recipients became HIV-1 infected versus 21 (3%) of 762 placebo recipients (hazard ratio [HR] 1.2 [95% CI 0.6-2.2]). All but one infection occurred in men. The corresponding geometric mean plasma HIV-1 RNA was comparable in infected male vaccine and placebo recipients (4.61 vs 4.41 log(10) copies per mL, one tailed p value for potential benefit 0.66). The vaccine elicited interferon-gamma ELISPOT responses in 75% (267) of the 25% random sample of all vaccine recipients (including both low and high Ad5 antibody titres) on whose specimens this testing was done (n=354). In exploratory analyses of all study volunteers, irrespective of baseline Ad5 antibody titre, the HR of HIV-1 infection between vaccine and placebo recipients was higher in Ad5 seropositive men (HR 2.3 [95% CI 1.2-4.3]) and uncircumcised men (3.8 [1.5-9.3]), but was not increased in Ad5 seronegative (1.0 [0.5-1.9]) or circumcised (1.0 [0.6-1.7]) men. INTERPRETATION: This cell-mediated immunity vaccine did not prevent HIV-1 infection or reduce early viral level. Mechanisms for insufficient efficacy of the vaccine and the increased HIV-1 infection rates in subgroups of vaccine recipients are being explored. FUNDING: Merck Research Laboratories; the Division of AIDS, National Institute of Allergy and Infectious Diseases, in the US National Institutes of Health (NIH); and the NIH-sponsored HIV Vaccine Trials Network (HVTN).

• DNA gag/adenovirus type 5 (Ad5) gag and Ad5 gag/Ad5 gag vaccines induce distinct T-cell response profiles.

  Authors: Kara S Cox, James H Clair, Michael T Prokop, Kara J Sykes, Sheri A Dubey, John W Shiver, Michael N Robertson, Danilo R Casimiro

  Journal of virology. 08/2008; 82(16):8161-71.

  Results from Merck's phase II adenovirus type 5 (Ad5) gag/pol/nef test-of-concept trial showed that the vaccine lacked efficacy against human immunodeficiency virus (HIV) infection in a high-riskResults from Merck's phase II adenovirus type 5 (Ad5) gag/pol/nef test-of-concept trial showed that the vaccine lacked efficacy against human immunodeficiency virus (HIV) infection in a high-risk population. Among the many questions to be explored following this outcome are whether (i) the Ad5 vaccine induced the quality of T-cell responses necessary for efficacy and (ii) the lack of efficacy in the Ad5 vaccine can be generalized to other vector approaches intended to induce HIV type 1 (HIV-1)-specific T-cell responses. Here we present a comprehensive evaluation of the T-cell response profiles from cohorts of clinical trial subjects who received the HIV CAM-1 gag insert delivered by either a regimen with DNA priming followed by Ad5 boosting (n = 50) or a homologous Ad5/Ad5 prime-boost regimen (n = 70). The samples were tested using a statistically qualified nine-color intracellular cytokine staining assay measuring interleukin-2 (IL-2), tumor necrosis factor alpha, macrophage inflammatory protein 1beta, and gamma interferon production and expression of CD107a. Both vaccine regimens induced CD4(+) and CD8(+) HIV gag-specific T-cell responses which variably expressed several intracellular markers. Several trends were observed in which the frequencies of HIV-1-specific CD4(+) T cells and IL-2 production from antigen-specific CD8(+) T cells in the DNA/Ad5 cohort were more pronounced than in the Ad5/Ad5 cohort. Implications of these results for future vaccine development will be discussed.

• Safety and immunogenicity of a replication-incompetent adenovirus type 5 HIV-1 clade B gag/pol/nef vaccine in healthy adults.

  Authors: Frances H Priddy, Deborah Brown, James Kublin, Kathleen Monahan, David P Wright, Jacob Lalezari, Steven Santiago, Michael Marmor, Michelle Lally, Richard M Novak [......] Sheri A Dubey, Lisa S Kierstead, Danilo R Casimiro, Robin Mogg, Mark J DiNubile, John W Shiver, Randi Y Leavitt, Michael N Robertson, Devan V Mehrotra, Erin Quirk

  Clinical infectious diseases : an official publication of the Infectious Diseases Society of America. 06/2008; 46(11):1769-81.

  BACKGROUND: The safety and immunogenicity of the MRK adenovirus type 5 human immunodeficiency virus type 1 clade B gag/pol/nef vaccine, a replication-incompetent adenovirus type 5-vectored vaccineBACKGROUND: The safety and immunogenicity of the MRK adenovirus type 5 human immunodeficiency virus type 1 clade B gag/pol/nef vaccine, a replication-incompetent adenovirus type 5-vectored vaccine designed to elicit cell-mediated immunity against conserved human immunodeficiency virus proteins, was assessed in a phase 1 trial. METHODS: Healthy adults not infected with human immunodeficiency virus were enrolled in a multicenter, dose-escalating, blind, placebo-controlled study to evaluate a 3-dose homologous prime-boost regimen of the trivalent MRK adenovirus type 5 human immunodeficiency virus type 1 vaccine containing from 3 x 10(6) to 1 x 10(11) viral particles per 1-mL dose administered on day 1, during week 4 and during week 26. Adverse events were recorded for 29 days after each intradeltoid injection. The primary immunogenicity end point was the proportion of study participants with a positive unfractionated Gag-, Pol-, or Nef-specific interferon-gamma enzyme-linked immunosorbent spot response measured 4 weeks after administration of the last dose. RESULTS: Of 259 randomized individuals, 257 (99%) received > or = 1 dose of vaccine or placebo and were included in the safety analyses. Enzyme-linked immunosorbent spot results were available for 217 study participants (84%) at week 30. No serious vaccine-related adverse events occurred. No study participant discontinued participation because of vaccine-related adverse events. The frequency of injection-site reactions was dose dependent. Vaccine doses of > or = 3 x 10(9) viral particles elicited positive enzyme-linked immunosorbent spot responses to > or = 1 vaccine component in > 60% of recipients. High baseline antibody titers against adenovirus type 5 diminished enzyme-linked immunosorbent spot responses at all doses except the 3 x 10(10) viral particle dose. CONCLUSIONS: The vaccine was generally well tolerated and induced cell-mediated immune responses against human immunodeficiency virus type 1 peptides in most healthy adults. Despite these findings, vaccination in a proof-of-concept trial with use of this vaccine was discontinued because of lack of efficacy.

• Primary human immunodeficiency virus type 1 (HIV-1) infection during HIV-1 Gag vaccination.

  Authors: Arumugam Balamurugan, Martha J Lewis, Christina M R Kitchen, Michael N Robertson, John W Shiver, Eric S Daar, Jacqueline Pitt, Ayub Ali, Hwee L Ng, Judith S Currier, Otto O Yang

  Journal of virology. 03/2008; 82(6):2784-91.

  Vaccination for human immunodeficiency virus type 1 (HIV-1) remains an elusive goal. Whether an unsuccessful vaccine might not only fail to provoke detectable immune responses but also could actuallyVaccination for human immunodeficiency virus type 1 (HIV-1) remains an elusive goal. Whether an unsuccessful vaccine might not only fail to provoke detectable immune responses but also could actually interfere with subsequent natural immunity upon HIV-1 infection is unknown. We performed detailed assessment of an HIV-1 gag DNA vaccine recipient (subject 00015) who was previously uninfected but sustained HIV-1 infection before completing a vaccination trial and another contemporaneously acutely infected individual (subject 00016) with the same strain of HIV-1. Subject 00015 received the vaccine at weeks 0, 4, and 8 and was found to have been acutely HIV-1 infected around the time of the third vaccination. Subject 00016 was a previously HIV-1-seronegative sexual contact who had symptoms of acute HIV-1 infection approximately 2 weeks earlier than subject 00015 and demonstrated subsequent seroconversion. Both individuals reached an unusually low level of chronic viremia (<1,000 copies/ml) without treatment. Subject 00015 had no detectable HIV-1-specific cytotoxic T-lymphocyte (CTL) responses until a borderline response was noted at the time of the third vaccination. The magnitude and breadth of Gag-specific CTL responses in subject 00015 were similar to those of subject 00016 during early chronic infection. Viral sequences from gag, pol, and nef confirmed the common source of HIV-1 between these individuals. The diversity and divergence of sequences in subjects 00015 and 00016 were similar, indicating similar immune pressure on these proteins (including Gag). As a whole, the data suggested that while the gag DNA vaccine did not prime detectable early CTL responses in subject 00015, vaccination did not appreciably impair his ability to contain viremia at levels similar to those in subject 00016.