Safety and immunogenicity of a simian-adenovirus-vectored rabies vaccine: an open-label, non-randomised, dose-escalation, first-in-human, single-centre, phase 1 clinical trial.

BACKGROUND: Rabies kills around 60 000 people each year. ChAdOx2 RabG, a simian adenovirus-vectored rabies vaccine candidate, might have potential to provide low-cost single-dose pre-exposure rabies prophylaxis. This first-in-human study aimed to evaluate its safety and immunogenicity in healthy adults. METHODS: We did a single-centre phase 1 study of ChAdOx2 RabG, administered as a single intramuscular dose, with non-randomised open-label dose escalation at the Centre for Clinical Vaccinology and Tropical Medicine, Oxford, UK. Healthy adults were sequentially allocated to groups receiving low (5 × 109 viral particles), middle (2·5 × 1010 viral particles), and high doses (5 x 1010 viral particles) of ChAdOx2 RabG and were followed up to day 56 after vaccination. The primary objective was to assess safety. The secondary objective was to assess immunogenicity with the internationally standardised rabies virus neutralising antibody assay. In an optional follow-up phase 1 year after enrolment, we measured antibody maintenance then administered a licensed rabies vaccine (to simulate post-exposure prophylaxis) and measured recall responses. The trial is registered with ClinicalTrials.gov, NCT04162600, and is now closed to new participants. FINDINGS: Between Jan 2 and Oct 28, 2020, 12 adults received low (n=3), middle (n=3), and high doses (n=6) of ChAdOx2 RabG. Participants reported predominantly mild-to-moderate reactogenicity. There were no serious adverse events. Virus neutralising antibody concentrations exceeded the recognised correlate of protection (0·5 IU/mL) in three middle-dose recipients and six high-dose recipients within 56 days of vaccination (median 18·0 IU/mL). The median peak virus neutralising antibody concentrations within 56 days were 0·7 IU/mL (range 0·0-54·0 IU/mL) for the low-dose group, 18·0 IU/mL (0·7-18·0 IU/mL) for the middle-dose group, and 18·0 IU/mL (6·0-486·0 IU/mL) for the high-dose group. Nine participants returned for the additional follow-up after 1 year. Of these nine participants, virus neutralising antibody titres of more than 0·5 IU/mL were maintained in six of seven who had received middle-dose or high-dose ChAdOx2 RabG. Within 7 days of administration of the first dose of a licensed rabies vaccine, nine participants had virus neutralising antibody titres of more than 0·5 IU/mL. INTERPRETATION: In this study, ChAdOx2 RabG showed an acceptable safety and tolerability profile and encouraging immunogenicity, supporting further clinical evaluation. FUNDING: UK Medical Research Council and Engineering and Physical Sciences Research Council.

A preclinical animal model to assess the effect of pre-existing immunity on AAV-mediated gene transfer.

Hepatic adeno-associated virus (AAV)-serotype 2-mediated gene transfer results in sustained transgene expression in experimental animals but not in human subjects. We hypothesized that loss of transgene expression in humans might be caused by immune memory mechanisms that become reactivated upon AAV vector transfer. Here, we tested the effect of immunological memory to AAV capsid on AAV-mediated gene transfer in a mouse model. Upon hepatic transfer of an AAV2 vector expressing human factor IX (hF.IX), mice immunized with adenovirus (Ad) vectors expressing AAV8 capsid before AAV2 transfer developed less circulating hF.IX and showed a gradual loss of hF.IX gene copies in liver cells as compared to control animals. This was not observed in mice immunized with an Ad vectors expressing AAV2 capsid before transfer of rAAV8-hF.IX vectors. The lower hF.IX expression was primarily linked to AAV-binding antibodies that lacked AAV-neutralizing activity in vitro rather than to AAV capsid-specific CD8(+) T cells.

B cell responses to the 2011/12-influenza vaccine in the aged.

Antibody and B cell responses to influenza A viruses were measured over a period of 2 months in 30 aged and 15 middle-aged individuals following vaccination with the 2011/12 trivalent inactivated influenza vaccine by micro-neutralization assays, ELISAs, ELISpot assays and cell surface staining with lineage-defining antibodies followed by multicolor flow cytometry. Both cohorts developed comparable antibody responses to the H3N2 virus of the vaccine while responses to the H1N1 virus were compromised in the aged. ELISpot assays of peripheral blood mononuclear cells (PBMCs) gave comparable results for the two cohorts. Analysis by flow cytometry upon staining of CD19+IgD-CD20- PBMCs with antibodies to CD27 and CD38 showed markedly reduced increases of such cells following vaccination in the aged. Additional analysis of cells from a subset of 10 younger and 10 aged individuals indicated that in the aged a portion of IgG producing cells lose expression of CD27 and reduce expression of CD38.

Adenoviral vectors persist in vivo and maintain activated CD8+ T cells: implications for their use as vaccines.

CD8(+) T cell-numbers rapidly expand and then contract after exposure to their cognate antigen. Here we show that the sustained frequencies of transgene product-specific CD8(+) T cells elicited by replication-defective adenovirus vectors are linked to persistence of low levels of transcriptionally active adenovirus vector genomes at the site of inoculation, in liver, and lymphatic tissues. Continuously produced small amounts of antigen maintain fully active effector CD8(+) T cells, while also allowing for their differentiation into central memory cells. The long-term persistence of adenoviral vectors may be highly advantageous for their use as vaccines against pathogens for which T-cell-mediated protection requires both fully activated T cells for immediate control of virus-infected cells and central memory CD8(+) T cells that, because of their higher proliferative capacity, may be suited best to eliminate cells infected by pathogens that escaped the initial wave of effector T cells.

Chimpanzee adenovirus CV-68 adapted as a gene delivery vector interacts with the coxsackievirus and adenovirus receptor.

A replication-defective form of chimpanzee adenovirus type 68 (C68) has been developed to circumvent problems posed by widespread preexisting immunity to common human adenovirus vectors. To investigate the determinants of C68 tropism, its interaction with the coxsackievirus and adenovirus receptor (CAR) was studied. Although CHO cells were resistant to transduction by C68 as well as by adenovirus type 5 (Ad5), CHO cells expressing either human or murine CAR were transduced readily. C68 transduction, like Ad5 transduction, was blocked when cells were exposed to anti-CAR antibody or when virus was exposed to a soluble form of the CAR extracellular domain. These results indicate that gene delivery by C68 occurs by a CAR-dependent mechanism.