To investigate disease progression, we focused on studying a population of 44 privately owned domestic cats infected with FIV, in collaboration with Dr Annette Litster (Purdue University). Using assays to assess the strength and breadth of neutralising antibodies, we found that neutralising antibodies did not appear to influence the course of natural FIV infection. These findings argue against a role for neutralising antibodies in controlling infection and disease progression.
A commercial FIV vaccine is licenced in the US, Australia, New Zealand and Japan and we have conducted studies in order to understand how this vaccine affords protection against FIV infection. We analysed samples from cats vaccinated against FIV, in collaboration with Dr Julia Beatty (University of Sydney) and demonstrated that vaccination did not induce cross-reactive neutralising antibodies. Furthermore, in one Australian cat vaccinated against FIV, we identified and characterised a virus strain that we speculated might have overcome vaccine-induced immunity. We are currently testing methods to induce high levels of neutralising antibodies in order to develop improved vaccines.
Another notable finding was that the FIV env gene sequence was relatively stable following natural infection, perhaps explaining why many naturally infected cats remain healthy and do not progress to AIDS. Moreover, by examining the receptor usage of viral variants, we observed that sick cats were more likely to harbour viruses displaying a distinct receptor usage phenotype compared to healthy cats, echoing the switch in co-receptor usage observed during the progression of HIV infection. We are now developing an algorithm that may be used to predict the prognosis for individual cats infected with FIV, based on the properties of the infecting strain.
Overall, this research has broadened our understanding of natural FIV infection and highlights that much can be learned from studying the differences between the feline and human lentivirus infections. Such comparative studies will contribute to the design of novel, safe and fully efficacious lentiviral vaccines.