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Comparison of subcutaneous versus intranasal immunization of male koalas (Phascolarctos cinereus) for induction of mucosal and systemic immunity against Chlamydia pecorum

Waugh, CA, Timms, P, Andrew, D, Rawlinson, G, Brumm, J, Nilsson, K & Beagley, KW 2015, Vaccine, vol. 33, no. 1, pp. 855-860.

An anti-chlamydial vaccine delivered either subcutaneously or intranasally elicited significant and long-term immune responses in immunised male koalas. The subcutaneous, or systemic, route of delivery elicited a stronger cell-mediated response than the intranasal, or mucosal, route, which induced a greater humoral response including at the mucosal sites where chlamydial infections begin.

  Twelve healthy male koalas at Lone Pine Koala Sanctuary were immunised with a three-dose regimen of a vaccine consisting of Chlamydia pecorum major outer membrane protein and adjuvanted with immunostimulating complex (ISC). Six were immunised via the subcutaneous route and six via the intranasal route to compare the effectiveness of these different routes for eliciting mucosal immunity at urogenital and ocular sites. In both groups, the vaccine produced a prolonged (52-week) antigen-specific peripheral blood mononuclear cell (PBMC) proliferative response to intact C. pecorum elementary bodies as well as an antigen-specific Immunoglobin G antibody response in plasma, although these responses were stronger when the vaccine was delivered subcutaneously. The intranasal immunisation caused a significant increase in Immunoglobin G antibody titres in urogenital and ocular secretions, while the subcutaneous immunisation had this effect only for ocular secretions and to a lesser extent. In vitro, a C. pecorum infection was neutralised with antibodies present in plasma and mucosal secretions that were developed following immunisation via either route; however, the response was slightly stronger for animals in the intranasal delivery group.

  Depending on the route of immunisation, the effects of a vaccine can vary. Because Chlamydia first manifests via mucosal pathways such as the conjunctiva, respiratory, gastrointestinal and genitourinary tracts, mucosal immunisation is expected to elicit a greater immune response at these sites than systemic immunisation. Given the differences observed between the immune responses elicited by immunisation via different routes in this study, the authors suggest that there is merit in trialling a combined systemic and mucosal anti-chlamydial vaccination in koalas. Importantly, this study is the first to test a Chlamydia vaccine in male koalas. Although previous studies have demonstrated the effectiveness of MOMP-based anti-chlamydial vaccines in females, these findings could not be extrapolated to determine the expected outcomes of the same vaccine in males given important anatomical and physiological differences between the sexes that can alter the immune response to a vaccine.

  This study may be the first to assess a mucosal vaccination route in the koala, and its outcomes suggest that vaccination with a chlamydial MOMP vaccine can elicit mucosal immunity to chlamydial infection in male koalas. The next step in determining the vaccine’s suitability for combating Chlamydia in wild populations is to evaluate the protection it affords for an immunised koala that is already or subsequently becomes infected.

 

Summarised by Joanna Horsfall

 

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