Construction and evaluation of novel rhesus monkey adenovirus vaccine vectors

Adenovirus vectors are widely used as vaccine candidates for a variety of pathogens, including HIV-1. To date, human and chimpanzee adenoviruses have been explored in detail as vaccine vectors. The phylogeny of human and chimpanzee adenoviruses is overlapping, and preexisting humoral and cellular immunity to both are exhibited in human populations worldwide. More distantly related adenoviruses may therefore offer advantages as vaccine vectors. Here we describe the primary isolation and vectorization of three novel adenoviruses from rhesus monkeys. The seroprevalence of these novel rhesus monkey adenovirus vectors was extremely low in sub-Saharan Africa human populations, and these vectors proved to have immunogenicity comparable to that of human and chimpanzee adenovirus vaccine vectors in mice. These rhesus monkey adenoviruses phylogenetically clustered with the poorly described adenovirus species G and robustly stimulated innate immune responses. These novel adenoviruses represent a new class of candidate vaccine vectors. IMPORTANCE Although there have been substantial efforts in the development of vaccine vectors from human and chimpanzee adenoviruses, far less is known about rhesus monkey adenoviruses. In this report, we describe the isolation and vectorization of three novel rhesus monkey adenoviruses. These vectors exhibit virologic and immunologic characteristics that make them attractive as potential candidate vaccine vectors for both HIV-1 and other pathogens

Attenuation of Replication-Competent Adenovirus Serotype 26 Vaccines by Vectorization

Replication-competent adenovirus (rcAd)-based vaccine vectors may theoretically provide immunological advantages over replication-incompetent Ad vectors, but they also raise additional potential clinical and regulatory issues. We produced replication-competent Ad serotype 26 (rcAd26) vectors by adding the E1 region back into a replication-incompetent Ad26 vector backbone with the E3 or E3/E4 regions deleted. We assessed the effect of vectorization on the replicative capacity of the rcAd26 vaccines. Attenuation occurred in a stepwise fashion, with E3 deletion, E4 deletion, and human immunodeficiency virus type 1 (HIV-1) envelope (Env) gene insertion all contributing to reduced replicative capacity compared to that with the wild-type Ad26 vector. The rcAd26 vector with E3 and E4 deleted and containing the Env transgene exhibited 2.7- to 4.4-log-lower replicative capacity than that of the wild-type Ad26 in vitro. This rcAd26 vector is currently being evaluated in a phase 1 clinical trial. Attenuation as a result of vectorization and transgene insertion has implications for the clinical development of replication-competent vaccine vectors

Rapid Cloning of Novel Rhesus Adenoviral Vaccine Vectors

ABSTRACT Human and chimpanzee adenovirus vectors are being developed to circumvent preexisting antibodies against common adenovirus vectors such as Ad5. However, baseline immunity to these vectors still exists in human populations. Traditional cloning of new adenovirus vaccine vectors is a long and cumbersome process that takes 2 months or more and that requires rare unique restriction enzyme sites. Here we describe a novel, restriction enzyme-independent method for rapid cloning of new adenovirus vaccine vectors that reduces the total cloning procedure to 1 week. We developed 14 novel adenovirus vectors from rhesus monkeys that can be grown to high titers and that are immunogenic in mice. All vectors grouped with the unusual adenovirus species G and show extremely low seroprevalence in humans. Rapid cloning of novel adenovirus vectors is a promising approach for the development of new vector platforms. Rhesus adenovirus vectors may prove useful for clinical development. IMPORTANCE: To overcome baseline immunity to human and chimpanzee adenovirus vectors, we developed 14 novel adenovirus vectors from rhesus monkeys. These vectors are immunogenic in mice and show extremely low seroprevalence in humans. Rhesus adenovirus vectors may prove useful for clinical development

Vaccine Protection Against Zika Virus from Brazil

Zika virus (ZIKV) is a flavivirus that is responsible for an unprecedented current epidemic in Brazil and the Americas1,2. ZIKV has been causally associated with fetal microcephaly, intrauterine growth restriction, and other birth defects in both humans3–8 and mice9–11. The rapid development of a safe and effective ZIKV vaccine is a global health priority1,2, but very little is currently known about ZIKV immunology and mechanisms of immune protection. Here we show that a single immunization of a plasmid DNA vaccine or a purified inactivated virus vaccine provides complete protection in susceptible mice against challenge with a ZIKV outbreak strain from northeast Brazil. This ZIKV strain has recently been shown to cross the placenta and to induce fetal microcephaly and other congenital malformations in mice11. We produced DNA vaccines expressing full-length ZIKV pre-membrane and envelope (prM-Env) as well as a series of deletion mutants. The full-length prM-Env DNA vaccine, but not the deletion mutants, afforded complete protection against ZIKV as measured by absence of detectable viremia following challenge, and protective efficacy correlated with Env-specific antibody titers. Adoptive transfer of purified IgG from vaccinated mice conferred passive protection, and CD4 and CD8 T lymphocyte depletion in vaccinated mice did not abrogate protective efficacy. These data demonstrate that protection against ZIKV challenge can be achieved by single-shot subunit and inactivated virus vaccines in mice and that Env-specific antibody titers represent key immunologic correlates of protection. Our findings suggest that the development of a ZIKV vaccine for humans will likely be readily achievable

Mechanisms of Avian Retroviral Host Range Extension

Alpharetroviruses provide a useful system for the study of the molecular mechanisms of host range and receptor interaction. These viruses can be divided into subgroups based on diverse receptor usage due to variability within the two host range determining regions, hr1 and hr2, in their envelope glycoprotein SU (gp85). In previous work, our laboratory described selection from a subgroup B avian sarcoma-leukosis virus of an extended-host-range variant (LT/SI) with two adjacent amino acid substitutions in hr1. This virus retains its ability to use the subgroup BD receptor but can also infect QT6/BD cells, which bear a related subgroup E receptor (R. A. Taplitz and J. M. Coffin, J. Virol 71:7814-7819, 1997). Here, we report further analysis of this unusual variant. First, one (L154S) of the two substitutions is sufficient for host range extension, while the other (T155I) does not alter host range. Second, these mutations extend host range to non-avian cell types, including human, dog, cat, mouse, rat, and hamster. Third, interference experiments imply that the mutants interact efficiently with the subgroup BD receptor and possibly the related subgroup E receptor, but they have another means of entry that is not dependent on these interactions. Fourth, binding studies indicate that the mutant SU proteins retain the ability to interact as monomers with subgroup BD and BDE receptors but only bind the subgroup E receptor in the context of an Env trimer. Further, the mutant SU proteins bind well to chicken cells but do not bind any better than wild-type subgroup B to QT6 or human cells, even though the corresponding viruses are capable of infecting these cells

Protective efficacy of a global HIV-1 mosaic vaccine against heterologous SHIV challenges in rhesus monkeys

The global diversity of HIV-1 represents a critical challenge facing HIV-1 vaccine development. HIV-1 mosaic antigens are bioinformatically optimized immunogens designed for improved coverage of HIV-1 diversity. However, the protective efficacy of such global HIV-1 vaccine antigens has not previously been evaluated. Here, we demonstrate the capacity of bivalent HIV-1 mosaic antigens to protect rhesus monkeys against acquisition of infection following heterologous challenges with the difficult-to-neutralize simian-human immunodeficiency virus SHIV-SF162P3. Adenovirus/poxvirus and adenovirus/adenovirus vector-based vaccines expressing HIV-1 mosaic Env, Gag, and Pol afforded a significant reduction in the per-exposure acquisition risk following repetitive, intrarectal SHIV-SF162P3 challenges. Protection against acquisition of infection correlated with vaccine-elicited binding, neutralizing, and functional nonneutralizing antibodies, suggesting that the coordinated activity of multiple antibody functions may contribute to protection against difficult-to-neutralize viruses. These data demonstrate the protective efficacy of HIV-1 mosaic antigens and suggest a potential strategy for the development of a global HIV-1 vaccine. PAPERCLIP

First-in-human randomized controlled trial of an oral, replicating adenovirus 26 vector vaccine for HIV-1.

BACKGROUND:Live, attenuated viral vectors that express HIV-1 antigens are being investigated as an approach to generating durable immune responses against HIV-1 in humans. We recently developed a replication-competent, highly attenuated Ad26 vector that expresses mosaic HIV-1 Env (rcAd26.MOS1.HIV-Env, "rcAd26"). Here we present the results of a first-in-human, placebo-controlled clinical trial to test the safety, immunogenicity and mucosal shedding of rcAd26 given orally. METHODS:Healthy adults were randomly assigned to receive a single oral dose of vaccine or placebo at 5:1 ratio in a dosage escalation of 10^8 to 10^11 rcAd26 VP (nominal doses) at University of Rochester Medical Center, Rochester, NY, USA. Participants were isolated and monitored for reactogenicity for 10 days post-vaccination, and adverse events were recorded up to day 112. Rectal and oropharyngeal secretions were evaluated for shedding of the vaccine. Humoral and cellular immune responses were measured. Household contacts were monitored for secondary vaccine transmission. RESULTS:We enrolled 22 participants and 11 household contacts between February 7 and June 24, 2015. 18 participants received one dose of HIV-1 vaccine and 4 participants received placebo. The vaccine caused only mild to moderate adverse events. No vaccine-related SAEs were observed. No infectious rcAd26 viral particles were detected in rectal or oropharyngeal secretions from any participant. Env-specific ELISA and ELISPOT responses were undetectable. No household contacts developed vaccine-induced HIV-1 seropositivity or vaccine-associated illness. CONCLUSIONS:The highly attenuated rcAd26.MOS1.HIV-Env vaccine was well tolerated up to 10^11 VP in healthy, HIV-1-uninfected adults, though the single dose was poorly immunogenic suggesting the replicative capacity of the vector was too attenuated. There was no evidence of shedding of infectious virus or secondary vaccine transmission following the isolation period. These data suggest the use of less attenuated viral vectors in future studies of live, oral HIV-1 vaccines. TRIAL REGISTRATION:ClinicalTrials.gov NCT02366013

Data from: First-in-human randomized controlled trial of an oral, replicating Adenovirus 26 vector vaccine for HIV-1

Background: Live, attenuated viral vectors that express HIV-1 antigens are being investigated as an approach to generating durable immune responses against HIV-1 in humans. We recently developed a replication-competent, highly attenuated Ad26 vector that expresses mosaic HIV-1 Env (rcAd26.MOS1.HIV-Env, “rcAd26”). Here we present the results of a first-in-human, placebo-controlled clinical trial to test the safety, immunogenicity and mucosal shedding of rcAd26 given orally. Methods: Healthy adults were randomly assigned to receive a single oral dose of vaccine or placebo at 5:1 ratio in a dosage escalation of 10^8 to 10^11 rcAd26 VP (nominal doses) at University of Rochester Medical Center, Rochester, NY, USA. Participants were isolated and monitored for reactogenicity for 10 days post-vaccination, and adverse events were recorded up to day 112. Rectal and oropharyngeal secretions were evaluated for shedding of the vaccine. Humoral and cellular immune responses were measured. Household contacts were monitored for secondary vaccine transmission. Results: We enrolled 22 participants and 11 household contacts between February 7 and June 24, 2015. 18 participants received one dose of HIV-1 vaccine and 4 participants received placebo. The vaccine caused only mild to moderate adverse events. No vaccine-related SAEs were observed. No infectious rcAd26 viral particles were detected in rectal or oropharyngeal secretions from any participant. Env-specific ELISA and ELISPOT responses were undetectable. No household contacts developed vaccine-induced HIV-1 seropositivity or vaccine-associated illness. Conclusions: The highly attenuated rcAd26.MOS1.HIV-Env vaccine was well tolerated up to 10^11 VP in healthy, HIV-1-uninfected adults, though the single dose was poorly immunogenic suggesting the replicative capacity of the vector was too attenuated. There was no evidence of shedding of infectious virus or secondary vaccine transmission following the isolation period. These data suggest the use of less attenuated viral vectors in future studies of live, oral HIV-1 vaccines. Clinical Trials Registration: NCT0236601

Mosaic HIV-1 vaccines expand the breadth and depth of cellular immune responses in rhesus monkeys

The worldwide diversity of HIV-1 presents an unprecedented challenge for vaccine development. Antigens derived from natural HIV-1 sequences have elicited only a limited breadth of cellular immune responses in nonhuman primate studies and clinical trials to date. Polyvalent 'mosaic' antigens, in contrast, are designed to optimize cellular immunologic coverage of global HIV-1 sequence diversity. Here we show that mosaic HIV-1 Gag, Pol and Env antigens expressed by recombinant, replication-incompetent adenovirus serotype 26 vectors markedly augmented both the breadth and depth without compromising the magnitude of antigen-specific T lymphocyte responses as compared with consensus or natural sequence HIV-1 antigens in rhesus monkeys. Polyvalent mosaic antigens therefore represent a promising strategy to expand cellular immunologic vaccine coverage for genetically diverse pathogens such as HIV-1