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A multi-subunit chlamydial vaccine induces antibody and cell-mediated immunity in immunised koalas (Phascolarctos cinereus): comparison of three different adjuvants

Carey, AJ, Timms, P, Rawlinson, G, Brumm, J, Nilsson, K, Harris, JM & Beagley, KW 2009, American Journal of Reproductive Immunology, vol. 63, no. 1, pp. 161-172.

An experimental vaccine against Chlamydia induced Chlamydia-specific cell-mediated and antibody responses in immunised koalas. Of three different adjuvants tested, each in combination with a selection of recombinant chlamydial antigens, one caused adverse reactions in immunised koalas and was therefore considered unsafe and removed from the experiment. The remaining two adjuvants had no adverse effects, and both resulted in long-term (270 days) neutralising antibody responses in plasma against the three antigens as well as Chlamydia-specific peripheral blood mononuclear cell proliferative responses. In an artificial environment, plasma antibodies inhibited infections from two different species of Chlamydia, suggesting the approach trialled may be effective for combating chlamydial infections in koalas.

  Eighteen healthy female koalas at Lone Pine Koala Sanctuary were immunised subcutaneously with a combination of three chlamydial antigens mixed with one of three adjuvants. The antigens were different recombinant chlamydial proteins and the adjuvants trialled were immunostimulating complex (ISC), Aluminium hydroxide Gel (Alhydrogel), and TiterMax Gold. A vaccine consists of an antigen, which elicits an immune response, and an adjuvant, which is added to enhance and, in some cases, modify the immune response elicited by the antigen. Previously, no information was available about which adjuvants were safe to use in vaccines for koalas. The purpose of this study was in part, therefore, to investigate this problem to assist in the development of a safe and effective vaccine for Chlamydia, which is one of the greatest threats to the species. Such a vaccine will be essential for combating the disease for which current treatment options are limited to antibiotics. Antibiotics are not ideal for this purpose as they can cause adverse effects to the koala’s gut microflora as well as increase the persistence of chlamydial infections in the longer-term. Although the TiterMax Gold-formulated vaccine caused koalas to develop abscesses at the point of vaccination, ISC and Alhydrogel appeared to be safe for use in koalas. In addition to the strong neutralising antibody responses in plasma and Chlamydia-specific peripheral blood mononuclear cell proliferative responses induced by the Alhydrogel- and ISC-formulated vaccines, the latter vaccine also induced long-term cloacal antibody responses.

  The promising outcomes of this study suggest that a multi-subunit chlamydial vaccine such as that described may induce cell-mediated and antibody responses that provide effective protection against Chlamydia in koalas. By comparing the outcomes generated by the vaccines with different components, we can gain a more comprehensive understanding of which components are responsible for inducing the desired response and, importantly, if they are safe to include in immunisations for koalas.

 

Summarised by Joanna Horsfall

 

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