Currently no vaccine exists for hepatitis C virus (HCV), a major pathogen thought to infect 170 million people globally. Many studies suggest that host T cell responses are critical for spontaneous resolution of disease, and preclinical studies have indicated a requirement for T cells in protection against challenge. We aimed to elicit HCV-specific T cells with the potential for protection using a recombinant adenoviral vector strategy in a Phase I study of healthy human volunteers. Two adenoviral vectors expressing NS proteins from HCV genotype 1B were constructed based on rare serotypes (Human Adenovirus 6 (Ad6) and Chimpanzee Adenovirus 3 (ChAd3)). Both vectors primed T cell responses against HCV proteins; these T cell responses targeted multiple proteins and were capable of recognizing heterologous strains (genotypes 1A and 3A). HCV-specific T cells consisted of both CD4+ and CD8+ T cells subsets, secreted IL-2, IFNγ, and TNFα, and could be sustained for at least a year after boosting with the heterologous adenoviral vector. Studies using MHC peptide tetramers revealed long-lived central and effector memory pools that retained polyfunctionality and proliferative capacity. These data indicate that an adenoviral vector strategy can induce sustained T cell responses of a magnitude and quality associated with protective immunity, and open the way for studies of prophylactic and therapeutic vaccines for HCV.

Abstract* "This manuscript has been accepted for publication in Science Translational Medicine. This version has not undergone final editing.Please refer to the complete version of record at www.sciencetranslationalmedicine.org/. The manuscript may not be reproduced or used in any manner that does not fall within the fair use provisions of the Copyright Act without the prior, written permission of AAAS."To whom correspondence should be addressed: ellie.barnes@ndm.ox.ac.uk E Barnes Peter Medawar Building, South Parks Rd, Oxford, UK OX1 3SY . + joint author contributions Author contributions: E.B., S. Capone, S. Colloca, J.H., A.F., R.C., C.K., A.N., and P.K. designed the study/protocols; L. Swadling, S. Capone., R.A., A.B., R.R., E.N., J.H., C.K., D.B., J.F., A.K., V.A., M.D.S., F.G., M.L.E., L. Siani., C.T., A.H., M.D., A.F., E.B., and P.K., performed the research and analysis; L. Swadling., E.B., A.F., S. Capone, and P.K. wrote the manuscript; E.B. was the principal investigator. Europe PMC Funders Group Europe PMC Funders Author Manuscripts Europe PMC Funders Author ManuscriptsA protective vaccine against hepatitis C virus (HCV) remains an unmet clinical need. HCV infects millions of people worldwide and is a leading cause of liver cirrhosis and hepatocellular cancer. Animal challenge experiments, immunogenetics studies and assessment of host immunity during acute infection highlight the critical role that effective T-cell immunity plays in viral control. In this first-in-man study we have induced antiviral immunity with functional characteristics analogous to those associated with viral control in natural infection, and improved upon a vaccine based on adenoviral vectors alone. We assessed a heterologous prime-boost vaccination strategy based on a replicative defective simian adenoviral vector (ChAd3) and modified vaccinia Ankara (MVA) vector encoding the NS3, NS4, NS5A and NS5B proteins of HCV genotype-1b.Analysis employed single cell mass cytometry (CyTOF), and HLA class-I peptide tetramer technology in healthy human volunteers. We show that HCV specific T-cells induced by ChAd3 are optimally boosted with MVA, and generate very high levels of both CD8+ and CD4+ HCV specific T-cells targeting multiple HCV antigens. Sustained memory and effector T-cell populations are generated and T-cell memory evolved over time with improvement of quality (proliferation and polyfunctionality) following heterologous MVA boost.We have developed a HCV vaccine strategy, with durable, broad, sustained and balanced T-cell responses, characteristic of those associated with viral control, paving the way for the first efficacy studies of a prophylactic HCV vaccine.

Induction of antigen-specific CD8+ T cells offers the prospect of immunization against many infectious diseases, but no subunit vaccine has induced CD8+ T cells that correlate with efficacy in humans. Here we demonstrate that a replication-deficient chimpanzee adenovirus vector followed by a modified vaccinia virus Ankara booster induces exceptionally high frequency T-cell responses (median >2400 SFC/106 peripheral blood mononuclear cells) to the liver-stage Plasmodium falciparum malaria antigen ME-TRAP. It induces sterile protective efficacy against heterologous strain sporozoites in three vaccinees (3/14, 21%), and delays time to patency through substantial reduction of liver-stage parasite burden in five more (5/14, 36%), P=0.008 compared with controls. The frequency of monofunctional interferon-γ-producing CD8+ T cells, but not antibodies, correlates with sterile protection and delay in time to patency (Pcorrected=0.005). Vaccine-induced CD8+ T cells provide protection against human malaria, suggesting that a major limitation of previous vaccination approaches has been the insufficient magnitude of induced T cells.

Replication defective Adenovirus vectors based on the human serotype 5 (Ad5) have been shown to induce protective immune responses against diverse pathogens and cancer in animal models and to elicit robust and sustained cellular immunity in humans. However, most humans have anti-Ad5 neutralising antibodies that can impair the immunological potency of such vaccines. Here we show that most other human Adenoviruses from rare serotypes are far less potent as vaccine vectors than Ad5 in mice and non-human primates, casting doubt on their potential efficacy in humans. To identify novel vaccine carriers suitable for vaccine delivery in humans we isolated and sequenced over a thousand Adenovirus strains from chimpanzees (ChAd). Replication-defective vectors were generated from different ChAd serotypes and were screened for neutralization by human sera and for ability to grow in human cell lines already approved for clinical studies. Most importantly, we devised a screening strategy to rank the ChAd vectors by immunological potency in mice which predicts their immunogenicity in non-human primates and humans. The vectors studied varied by up to a thousand-fold in potency for CD8 T cell induction in mice. Two of the Europe PMC Funders Group

BACKGROUNDThe West African outbreak of Ebola virus disease that peaked in 2014 has caused more than 11,000 deaths. The development of an effective Ebola vaccine is a priority for control of a future outbreak. METHODSIn this phase 1 study, we administered a single dose of the chimpanzee adenovirus 3 (ChAd3) vaccine encoding the surface glycoprotein of Zaire ebolavirus (ZEBOV) to 60 healthy adult volunteers in Oxford, United Kingdom. The vaccine was administered in three dose levels -1×10 10 viral particles, 2.5×10 10 viral particles, and 5×10 10 viral particles -with 20 participants in each group. We then assessed the effect of adding a booster dose of a modified vaccinia Ankara (MVA) strain, encoding the same Ebola virus glycoprotein, in 30 of the 60 participants and evaluated a reduced prime-boost interval in another 16 participants. We also compared antibody responses to inactivated whole Ebola virus virions and neutralizing antibody activity with those observed in phase 1 studies of a recombinant vesicular stomatitis virus-based vaccine expressing a ZEBOV glycoprotein (rVSV-ZEBOV) to determine relative potency and assess durability. RESULTSNo safety concerns were identified at any of the dose levels studied. Four weeks after immunization with the ChAd3 vaccine, ZEBOV-specific antibody responses were similar to those induced by rVSV-ZEBOV vaccination, with a geometric mean titer of 752 and 921, respectively. ZEBOV neutralization activity was also similar with the two vaccines (geometric mean titer, 14.9 and 22.2, respectively). Boosting with the MVA vector increased virus-specific antibodies by a factor of 12 (geometric mean titer, 9007) and increased glycoprotein-specific CD8+ T cells by a factor of 5. Significant increases in neutralizing antibodies were seen after boosting in all 30 participants (geometric mean titer, 139; P<0.001). Virus-specific antibody responses in participants primed with ChAd3 remained positive 6 months after vaccination (geometric mean titer, 758) but were significantly higher in those who had received the MVA booster (geometric mean titer, 1750; P<0.001). CONCLUSIONSThe ChAd3 vaccine boosted with MVA elicited B-cell and T-cell immune responses to ZEBOV that were superior to those induced by the ChAd3 vaccine alone. (Funded by the Wellcome Trust and others; ClinicalTrials.gov number, NCT02240875.)A BS TR AC T