Development of a recombinant adenoviral immunocontraceptive vaccine (Ad-GKT) for use in domestic dogs

Abstract

Rabies is a viral disease caused by the rabies lyssavirus (RABV). Despite effective rabies vaccines for humans and animals, this disease continues to pose a major public health challenge, causing an estimated 59 000 human deaths each year, over 99% of which are caused by the domestic dog (Canis familiaris). Current methods of dog population management used in rabies control programs are ineffective. Surgical sterilisation does not reach enough of the dog population to curb population densities and contraceptives need to be administered at a specific phase in the oestrous cycle or cause a range of side effects. Immunocontraception in dogs would allow rabies vaccination coverage to be maintained, in turn reducing the burden of rabies on public health. The aim of this study was to develop an immunocontraceptive vaccine for dogs capable of eliciting a stronger immune response than that of previously constructed vaccines allowing for effective dog population management and allowing rabies vaccination coverage to be maintain, in turn reducing the burden of rabies on public health. By stabilising the dog population size, the 70% vaccination coverage required to interrupt rabies transmission within a population can be maintained. The immunocontraceptive vaccine constructed in this study contained two reproductive hormones, namely GnRH and kisspeptin, in the hope of eliciting a stronger contraceptive effect than either of these could produce alone, as well as the partial tetanus toxoid gene as an immune stimulant. The nucleic acid GnRH, kisspeptin and partial tetanus toxoid gene (GKT) insert fragment was PCR amplified from a DNA construct (pVAC-GKT) and was cloned into the adenoviral vector using In-fusion cloning technology. Transfection of pAdeno-X 293 cells was confirmed using green fluorescent microscopy and expression of the Ad-GKT mRNA in cell culture was confirmed using real-time RT-PCR. The antigenicity of the Ad-GKT construct was evaluated using female Swiss Webster mice. An indirect ELISA was used to detect seroconversion of the GnRH and Kisspeptin insert fragments. The Ad-GKT construct was successful in eliciting an immune response against GnRH and kisspeptin. Future research should include a comparative study to determine the antigenicity of the Ad-GnRH1 and Ad-GKT constructs in a canine trial for potential use in rabies control programs.