Evaluation of novel single-dose vaccine candidates against gonadotropin-releasing hormone (GnRH) in mice

Immunocontraceptive vaccines targeting gonadotropin-releasing hormone (GnRH) are in high demand for controlling population growth and managing the temperament of both wild and domesticated animals. Achieving adequate efficacy, especially with a single-dose immunization, requires potent vaccines and adjuvants. However, commercial vaccines face challenges: some, like Gonacon®, have regulatory issues with veterinary authorities, while others, like Bopriva®, lack potency and require multiple booster doses. Thus, there is a critical need for highly effective vaccines with robust adjuvants suitable for easy, less invasive single-dose administration. Recent studies have shown that peptide vaccines adjuvanted with 15-mer polyleucine (L₁₅) or poly(methyl acrylate) (PMA) demonstrate potent immunogenicity, comparable to complete Freund's adjuvant (CFA), after a single dose against Streptococcus pyogenes. Our research aims to evaluate the performance of these promising vaccine adjuvant as single-dose contraceptive vaccines in mice, compared to well-established commercial and experimental adjuvants, such as AddaVax®, Incomplete Freunds Adjuvant (IFA), and CFA. To develop a vaccine with sufficient HLA coverage for cattle immunocontraception, we evaluated a peptide vaccine incorporating three cattle-compatible helper T cell epitopes. We evaluated the immunogenicity of constructs in mice to that of a construct with the universal mouse-compatible PADRE (P) helper T cell epitope. Various vaccines were prepared to investigate: (A) the impact of incorporating cattle-compatible helper T cells on immunogenicity, and (B) the effectiveness of different adjuvant systems compared to CFA. The vaccines were administered subcutaneously to C57BL/6 mice, and serological assays revealed that the L₁₅/Quil A-based vaccine system was highly immunogenic, with performance comparable to CFA without the need for reactogenic mycobacterial components. Our vaccines significantly reduced serum progesterone levels in mice, making the L₁₅/Quil A system a strong candidate for single-dose anti-fertility application, followed by PMA, and AddaVax® adjuvanted GnRH.