Potency evaluation of rabies vaccine for human use: The impact of the reduction in the number of animals per dilution

Potency evaluation of rabies vaccine for human use: The impact of reducing the number of animals per dilution - Part 2

The most critical parameter for the quality control of the rabies vaccine is potency, which is evaluated by challenge test in mice while using a large animal number. Because the 3Rs concept is applied worldwide, it becomes necessary to develop alternative methods to demonstrate the production consistency of these vaccines and reduce the number of animals used for performing assays. Hence, the present study evaluated the impacts of reducing the number of mice used in the NIH test for such vaccines. A retrospective data analysis compared vaccines tested in the standard test with the results of the reduced test using only the first cages of each dilution and considering the second cages as their replicates. The relevance of the reduced assay was evaluated using Bland- Altman plot and CCC. Reliability was assessed by CV% and confidence intervals, while the impact of the reduced mouse number was evaluated by the analysis of the confidence interval of potency results and regression, linearity and parallelism parameters. The results demonstrated the feasibility of reducing to eight mice per dilution in routine assays, with complete statistical validation of the resulting potency, allowing the number of animals used for the test vaccines to be reduced by 50%.

Immunogenicity and protective efficacy of an EV71 virus-like particle vaccine against lethal challenge in newborn mice

Enterovirus 71(EV71) has caused severe epidemics of hand, foot and mouth disease (HFMD) in the Asia Pacific in recent years, particularly in infants and pre-school children. It has become a serious public health threat, as currently there are no approved vaccines or antiviral drugs for EV71 infection. Many EV71 vaccines have been under development worldwide, however the main focus is inactivated EV71 vaccines. For example, the inactivated EV71 vaccine has recently finished phase III clinical trial in Mainland China. There have been very few studies on EV71 virus like particles (VLPs). In this study, the immunogenicity and protective potency of the EV71 VLPs produced in insect cells were evaluated in mice with different dosages. Our results showed that EV71 VLPs could elicit high titers of neutralizing antibodies (NTAbs) in a dose-dependent manner and NTAbs were sustained after the second injection with an average GMT (geometric mean titer) level from 19 to 2960 in immunized mice. Survival rates were 100%, 100%, 85%, and 40% after challenge with 15 LD50 (median lethal dose) of EV71 in these newborn mice, respectively. ED50 (50% effective dose) of VLPs was 0.20 μg/dose in newborn mice, while NTAb titer under this dosage was about 50. Passive protection was determined with 2 methods and demonstrated that the survival rates were positively correlated with NTAb titers, which at 24 and 54 induced 50% survival rates in experimental animals. The ED50 of VLP vaccines and the passive NTAb titers were also analyzed. The maternal NTAb titer was similar as the passive NTAb titer in the mouse model challenged with our lethal mouse EV71 strain. Hence, our work has provided preliminary data on the protection potency of VLPs as a vaccine candidate and would facilitate future VLP vaccine development.

Laboratory animal: biological reagent or living being?

The duties of humans toward non-human animals and their rights in society have been debated for a long time. However, a discussion on the terminology used for the identification of laboratory animals is usually not considered, although the employment of inadequate terminology may generate disastrous consequences for the animals before, during, and after the experiment. This study intends to defend the use of appropriate terminology, call attention to an unethical attitude of certain professionals when dealing with experimental animals, and also propose operational mechanisms, which allow for those distortions to be corrected.