Improving anti-chlamydial responses in NSW koalas with a Chlamydia-koala retrovirus combination vaccine.

Koalas are an endangered species under threat of extinction from several factors, including infections agents. Chlamydia pecorum infection results in morbidity and mortality from ocular and urogenital dis eases while Koala Retrovirus (KoRV) infection has been linked to increased rates of cancer and chlamy diosis. Both C. pecorum and KoRV are endemic in many wild Australian koala populations, with limited treatment options available. Fortunately, vaccines for these pathogens are under development and have generated effective immune responses in multiple trials.

The current study aimed to improve vaccine for mulations by testing a novel peptide version of the Chlamydia vaccine and a combination Chlamydia – KoRV vaccine. Utilising a monitored wild population in Southeast Queensland, this trial followed koalas given either a ‘Chlamydia only’ vaccine (utilising four peptides from the chlamydial Major Outer Membrane Protein, MOMP), a combination ‘Chlamydia and KoRV’ vaccine (comprised of the chlamydial peptides plus a KoRV recombinant envelope protein (rEnv)) or no treatment. Clinical observations, C. pecorum and KoRV gene expression, serum IgG, and mucosal immune gene expression were assessed over a 17-month period. Overall, both vaccine formulations resulted in a decrease in chlamydiosis mortality, with decreases in C. pecorum, CD4, CD8b and IL-17A gene expression observed. In addition, the combina tion vaccine group also showed an increase in anti-KoRV IgG production that corresponded to a decrease in detected KoRV-B expression. While these results are favourable, the chlamydial peptide vaccine did not appear to outperform the established recombinant chlamydial vaccine and suggests that a combina tion vaccine formulated with recombinant MOMP plus KoRV rEnv could capitalize on the demonstrated benefits of both for the betterment of koalas into the future.