Safety, pharmacokinetics and pharmacodynamics of SYN023 alone or in combination with a rabies vaccine: An open, parallel, single dose, phase 1 bridging study in healthy Chinese subjects.

BACKGROUND: SYN023, a mixture of two anti-rabies humanized monoclonal antibodies (mAbs), namely, CTB011 and CTB012, has been developed as a safe and cost-effective alternative to RIG in the use of postexposure prophylaxis (PEP) after rabies exposure. METHODS: This phase I bridging study was designed to compare the pharmacokinetics (PK) of SYN023 (0.3 mg/kg) alone (cohort A, n = 8) or in combination with a rabies vaccine (cohort B, n = 24) in healthy Chinese subjects with those in American subjects to guide the design of further clinical trials. Their safety was assessed for the development of adverse events (AEs) by laboratory examinations. The levels of serum CTB011, CTB012 and anti-drug antibodies (ADAs) were measured longitudinally for 85 days. Serum rabies virus neutralizing antibody (RVNA) levels were measured as a pharmacodynamic (PD) surrogate. RESULTS: Some subjects with injectable SYN023 at 0.3 mg/kg developed temporary AEs and adverse drug reactions (ADRs) of Grade 1 or 2, particularly in cohort B, probably due to vaccine coadministration. SYN023 injection displayed a typical and reliable PK, similar to that of human IgGs. Following injection with SYN023, Chinese subjects had slower absorption with higher exposures for CTB011 but lower exposures for CTB012 than American subjects. The SYN023 recipients achieved protective levels of RVNA (≥0.5 IU/mL) on day 3 post injection. A few subjects developed temporary ADA, which did not affect the safety and PK/PD of SYN023 in Chinese subjects. CONCLUSION: SYN023 at 0.3 mg/kg is relatively saf e and effective and can be selected for further clinical trials in Chinese subjects. The clinical trial registration number is CTR20190281. http://www.chinadrugtrials.org.cn/eap/clinicaltrials.searchlist?a=a®_no=CTR20190281.

Nonclinical safety assessment of repeated administration and biodistribution of a novel rabies self-amplifying mRNA vaccine in rats.

The novel self-amplifying mRNA (SAM) technology for vaccines consists of an engineered replication-deficient alphavirus genome encoding an RNA-dependent RNA polymerase and the gene of the target antigen. To validate the concept, the rabies glycoprotein G was chosen as antigen. The delivery system for this vaccine was a cationic nanoemulsion. To characterize the local tolerance, potential systemic toxicity and biodistribution of this vaccine, two nonclinical studies were performed. In the repeated dose toxicity study, the SAM vaccine was administered intramuscularly to rats on four occasions at two-week intervals followed by a four-week recovery period. SAM-related changes consisted of a transient increase in neutrophil count, alpha-2-macroglobulin and fibrinogen levels. Transient aspartate aminotransferase and alanine aminotransferase increases were also noted in females only. At necropsy, observations related to the elicited inflammatory reaction, such as enlargement of the draining lymph nodes were observed that were almost fully reversible by the end of the recovery period. In the biodistribution study, rats received a single intramuscular injection of SAM vaccine and then were followed until Day 60. Rabies RNA was found at the injection sites and in the draining lymph nodes one day after administration, then generally decreased in these tissues but remained detectable up to Day 60. Rabies RNA was also transiently found in blood, lungs, spleen and liver. No microscopic changes in the brain and spinal cord were recorded. In conclusion, these results showed that the rabies SAM vaccine was well-tolerated by the animals and supported the clinical development program.

Oral vaccination of wildlife against rabies: Differences among host species in vaccine uptake efficiency.

Oral vaccination using attenuated and recombinant rabies vaccines has been proven a powerful tool to combat rabies in wildlife. However, clear differences have been observed in vaccine titers needed to induce a protective immune response against rabies after oral vaccination in different reservoir species. The mechanisms contributing to the observed resistance against oral rabies vaccination in some species are not completely understood. Hence, the immunogenicity of the vaccine virus strain, SPBN GASGAS, was investigated in a species considered to be susceptible to oral rabies vaccination (red fox) and a species refractory to this route of administration (striped skunk). Additionally, the dissemination of the vaccine virus in the oral cavity was analyzed for these two species. It was shown that the palatine tonsils play a critical role in vaccine virus uptake. Main differences could be observed in palatine tonsil infection between both species, revealing a locally restricted dissemination of infected cells in foxes. The absence of virus infected cells in palatine tonsils of skunks suggests a less efficient uptake of or infection by vaccine virus which may lead to a reduced response to oral vaccination. Understanding the mechanisms of oral resistance to rabies virus vaccine absorption and primary replication may lead to the development of novel strategies to enhance vaccine efficacy in problematic species like the striped skunk.

The safety of ONRAB® in select non-target wildlife.

ONRAB(®) is a recombinant human adenovirus type 5 (HAd5) with the rabies glycoprotein gene incorporated into its genome. ONRAB(®) has been used in Canada as an oral rabies vaccine in target wildlife species such as: red fox (Vulpes vulpes), raccoon (Procyon lotor), and striped skunk (Mepthis mephitis). We evaluated the safety of ONRAB(®) in non-target wildlife species likely to contact the vaccine baits during oral rabies vaccine campaigns in the United States. We investigated the effects of oral inoculation of high titer ONRAB(®), approximately ten times the dose given to target species, in wood rats (Neotoma spp.), eastern cottontail rabbits (Sylvilagus floridanus), Virginia opossums (Didelphis virginiana), eastern wild turkeys (Meleagris gallopavo silvestri), and fox squirrels (Sciurus niger). We performed real-time polymerase chain reaction (PCR) on fecal swabs, oral swabs, and tissues, including lung, liver, kidney, small intestine, large intestine, and when appropriate nasal turbinates, to detect ONRAB(®) DNA from inoculated animals. By seven days post-inoculation, turkeys, opossums, and cottontails had all stopped shedding ONRAB(®) DNA. One wood rat and one fox squirrel still had detectable levels of ONRAB(®) DNA in fecal swabs 14 days post-inoculation. Real-time PCR analysis of the tissues revealed some ONRAB(®) DNA persisting in certain tissues; however, there were no significant gross or histologic lesions associated with ONRAB(®) in any of the species studied. Our results suggest that many non-target species are not likely to be impacted by the distribution of ONRAB(®) as part of oral rabies vaccination programs in the United States.

A vaccine measured with a highly variable assay: rabies.

Manufacturers and regulators are challenged when evaluating stability of vaccines when potency is measured using a highly variable assay. Participants in the IABS Workshop on Stability Evaluation of Vaccines, a Life Cycle Approach, were offered a case study from a series of stability studies of a rabies vaccine, using the NIH potency assay. The case study was introduced with a scenario in which a new manufacturer was to formulate, lyophilize and fill the vaccine from bulk supplied by another manufacturer. The regulatory authority requested that data from the new manufacturer be supplied, to supplement that of the original producer. Participants were asked to answer a series of questions posed by the regulator, and critique the study design and data analysis according to principles described during the workshop.

Monosynaptic restriction of transsynaptic tracing from single, genetically targeted neurons.

There has never been a wholesale way of identifying neurons that are monosynaptically connected either to some other cell group or, especially, to a single cell. The best available tools, transsynaptic tracers, are unable to distinguish weak direct connections from strong indirect ones. Furthermore, no tracer has proven potent enough to label any connected neurons whatsoever when starting from a single cell. Here we present a transsynaptic tracer that crosses only one synaptic step, unambiguously identifying cells directly presynaptic to the starting population. Based on rabies virus, it is genetically targetable, allows high-level expression of any gene of interest in the synaptically coupled neurons, and robustly labels connections made to single cells. This technology should enable a far more detailed understanding of neural connectivity than has previously been possible.

Effective transfection of rabies DNA vaccine in cell culture using an artificial lipoprotein carrier system.

PURPOSE: To evaluate the transfection efficiency in cell culture of rabies plasmid DNA vaccine carried by a novel artificial lipoprotein system. METHODS: Phospholipid nanoemulsions resembling the lipid core of natural lipoproteins were prepared. The artificial lipoprotein carrier system for DNA was constructed by assembling of the nanoemulsion (NE)-palmitoyl-poly-L-lysine (p-PLL)-rabies DNA complex. Agarose gel electrophoresis, zeta potential, and mobility measurement were conducted to determine the surface charge balance in various complex compositions. Transfection and transfection efficiency were examined by fluorescence microscopy and flow cytometry, respectively. RESULTS: The artificial lipoprotein system was successfully constructed and the rabies DNA vaccine was effectively transfected in glioma cell line SF-767. The amount of p-PLL incorporated into the artificial lipoprotein formulations had a significant effect on transfection efficiency. The new system also proved to be more efficient in cellular transfection of rabies DNA vaccine than the commercial lipofectamine formulation. CONCLUSIONS: Effective transfection of rabies DNA vaccine in cell culture can be achieved using the novel artificial lipoprotein carrier system, and the charge balance of the NE-p-PLL-DNA complex appears an important factor.