Envelope determinants of EIAV vaccine protection and the effects of sequence variation on immune recognition

Developing an effective lentiviral vaccine has been an elusive goal, largely due to immune evasion mechanisms of lentiviruses. Lentiviral envelope (Env) proteins pose a major obstacle to vaccine development due to extreme antigenic variation, but research with equine infectious anemia virus (EIAV) has indicated Env to be a primary determinant of vaccine efficacy. We have developed an attenuated EIAV vaccine capable of protecting horses from disease after homologous challenge. However, when variant challenge strains with divergent Env proteins are utilized, vaccine protection is incrementally decreased with increasing divergence from the homologous Env. I hypothesize there may be Env-specific immune responses associated with vaccine protection and believe antigenic variation may have profound effects on immune recognition. Utilizing thymidine incorporation and chromium release assays on PBMC from vaccinated horses challenged with the homologous strain, I identified broadly reactive regions of Env recognized by T-helper and CTL cells. With PBMC from vaccinated ponies challenged with divergent EIAV strains I identified Env-specific immune responses associated with vaccine protection from disease. Although I was unable to correlate antibody neutralization with protection, I found one T-helper and eight CTL peptide responses associated with vaccine protection. Three of the CTL peptides were located in variable domains of Env. To understand the effects of variation on immune recognition, I utilized sera and PBMC from vaccinated and variant infected ponies to analyze the cross-reactivity of humoral and cellular immune responses. Due to limited proliferative activity, I was unable to fully analyze the effects of Env variation on lymphoproliferation; however, CTL analysis indicated Env variation had profound effects on immune recognition in EIAV vaccinated and infected ponies. The most remarkable effects of Env variation were observed in in vitro neutralization assays, where there was no detectable cross-reactivity of neutralizing antibodies. Collectively, these results indicate that eliciting key immune responses to more conserved regions of the EIAV Env may be crucial in developing an effective EIAV vaccine. The peptide-specific responses identified in this dissertation could serve as important targets for future EIAV vaccines and this analysis may be a valuable complement to ongoing work in SIV and HIV.