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.

Pharmacokinetics and antibody responses to the CD3 antibody otelixizumab used in the treatment of type 1 diabetes

Otelixizumab is a chimeric CD3 antibody that has been genetically engineered to remove the glycosylation site in the Fc domain. This limits its ability to bind to complement or Fc receptors and reduces the risk of adverse clinical reactions due to cytokine release. In a trial for treatment of type 1 diabetes, a short treatment with otelixizumab resulted in a reduced requirement for insulin lasting at least 18 months. In the course of this trial, the blood concentrations of the antibody were measured by flow cytometry to determine its pharmacokinetic profile. Dose-dependent accumulation of otelixizumab was demonstrated and modeling of the data indicated that the terminal half-life was approximately 1.5 days. Antibody responses to otelixizumab were measured by 2 methods: a bridging enzyme-linked immunosorbent assay and surface plasmon resonance. The surface plasmon resonance method had a greater sensitivity and was able to detect responses in all patients, starting at 8 days after the commencement of therapy. Neutralizing antibodies were detected in a significant proportion of patients by days 22 to 29. Although no adverse clinical effects were associated with these antibody responses and they did not appear to affect the clearance of the drug, they might have important implications for possible retreatment of the patients.