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Analysis of the specificity of neutralizing antibodies to Ad5 PowerPoint Presentation

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On : Mar 14, 2014

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  • Slide 1 - Analysis of the specificity of neutralizing antibodies to Ad5 and correlation with vaccine-induced immunity and infection in the STEP study: interim report Cheng Cheng, PhD Dr. Nabel’s group/VRC/NIAID/NIH
  • Slide 2 - Exposure of Ad5 to the immune system elicits neutralizing antibodies directed to different components of the virus, including the fiber or external capsid (largely hexon) independent of fiber. Natural Ad5 infection and rAd5 vaccination induce neutralizing antibodies with different specificities likely to due to the lack of viral replication in rAd5 vectors. In the STEP study, we have asked whether vaccinated subjects who became HIV-infected may have had distinct neutralizing antibodies responses to individual Ad5 capsid proteins compared to non-infected controls. Neutralizing antibodies to individual Ad5 capsid proteins have reduced vaccine-induced Gag immunogenicity in VRC studies. We therefore are analyzing whether similar effects would be seen with the rAd vaccine immunization in STEP. Background and Study Objectives
  • Slide 3 - Sera used from the STEP trial: 88 samples from 22 subjects at 4 time points Ad5 Serostatus at pre-vaccination: 11 seropositives; 11 seronegatives Time points: pre-vaccination (Day 1) 4 weeks post first vaccination (Week 4) 4 weeks post second vaccination (Week 8) 4 weeks post third vaccination (Week 30) Is There any Differences Between Nab Induced by Natural Ad5 Infection and Vaccination?
  • Slide 4 - rAd35 5Fiber (rAd35 F5) rAd5 35Fiber (rAd5 F35) Ad5 Nab Specificity: Ad5 Fiber All rAd5 rAd35 Ad5 Capsid(Non-Fiber) Wild Type and Chimeric Vectors Based on Ad5 and Ad35 Used to Analyze Ad5 Neutralizing Antibodies None(Rare serotype) rAd encodes luciferase as the marker to assay for viral neutralization.
  • Slide 5 - Vaccination Generated Nab to Both Fiber and Capsid in Ad5-Seropositive Subjects
  • Slide 6 - Vaccination Stimulated a Significant Increase in the Titer of Capsid-directed Neutralizing Antibodies in Ad5-Seropositive Subjects
  • Slide 7 - Evolution of Neutralizing Antibodies to Ad5 in Seronegative Subjects after Vaccination
  • Slide 8 - Increased Titer of Capsid-Directed Nab in Ad5-Seronegative Subjects Post Vaccination
  • Slide 9 - Ad5 Seropositives Had Higher Nab Titers Post Vaccination Compared to Ad5 Seronegatives Anti-Capsid Nab Anti-Fiber Nab p<0.05
  • Slide 10 - Summary-Pilot Study of Uninfected Subjects Anti-Fiber Nab were detected in Ad5 seropositives (due to natural infections) with high titers. Vaccination generated Capsid-directed Nabs more efficiently than Fiber Nabs, both in Ad5-seropositive and seronegative subjects. After three rAd5 vaccines, all rAd5-seronegative subjects were converted to seropositive. In these individuals, Fiber Nabs were much lower than in the initial Ad5-seropositive volunteers (p<0.05, 10X).
  • Slide 11 - Any Unique Features About Pre-existing anti-Ad5 Neutralizing Antibodies in HIV Case Volunteers? 71 seropositive sera at Day 1 (pre-vaccination) from HIV case volunteers in the STEP trial.
  • Slide 12 - Neutralizing Antibodies are Directed Largely Both to Fiber and Capsid
  • Slide 13 - Titer of Neutralizing Antibodies Directed to Fiber and Capsid
  • Slide 14 - Are There Lower Fiber Nab Titers in HIV Cases Compared to Control Non-cases? Non-case: 11 sera used in the first study. More non-case sera will be analyzed to do statistical analysis. p=0.8 p=0.06 p=0.6
  • Slide 15 - Summary The Nab generated by natural infection and rAd5 vaccination are different. may reflect differences in the route of exposure, viral replication. Higher anti-fiber Nab titers were seen after three injections of rAd5 vaccine in Ad5 seropositive subjects compared to initial rAd5 seronegative volunteers. Preliminary analysis of the HIV case subjects showed a trend of ~2.5-fold lower anti-fiber Nab compared to controls but significance has not been reached. Further analysis of 160 control sera will determine whether there is a correlation with fiber-directed Nab and infection. We will further evaluate whether there is a correlation of the fiber and capsid Nab responses with vaccine-induced immunogenicity.
  • Slide 16 - Acknowledgments Nabel lab GenVec Inc HVTN, STEP volunteers, trial sponsors,

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