PARTIAL PROTECTION BY VACCINATION WITH RECOMBINANT FELINE IMMUNODEFICIENCY VIRUS SURFACE GLYCOPROTEINS

In an effort to induce a strong immune response that might protect aga inst feline immunodeficiency virus (FIV) challenge infection, three gr oups of five specified pathogen-free (spf) cats each were immunized su bcutaneously with different FIV antigen preparations, Immunizations we re done at weeks 0, 2, and 4 with 100 mu g of recombinant SU from an F IV Zurich 2 (FIV Z2) strain expressed by E. coli (group 1) or the bacu lovirus expression system (groups 2 and 3) adsorbed on aluminum hydrox yde and administered with QS-21 (groups 1 and 2) or Freund's adjuvant together with the recombinant nucleocapsid protein (protein NC) of rab ies virus (group 3), Protein NC was described to act as an exogenous s uperantigen. Group 3 cats demonstrated the highest detectable antibody response to the vaccine antigen as determined by ELISA and Western bl ot analysis, All immunized cats together with seven control animals we re challenged with 20 CID50 of cat lymphocyte-grown FIV Z2 3 weeks fol lowing the last immunization, Whereas virus was readily recovered from peripheral blood lymphocytes of seven of seven nonvaccinated control cats following this challenge dose, virus was not recovered from two c ats of groups 1 and 2, All cats in groups 2 and 3 showed a provirus lo ad significantly decreased to 3% of that of controls up to week 8 afte r challenge infection, Eleven of 15 vaccinated cats and 5 of 7 control cats developed virus-neutralizing antibodies by week 8 after challeng e infection, The two cats negative on virus isolation remained seroneg ative, developed no detectable virus-neutralizing activities, but were repeatedly positive in provirus PCR, Moreover, starting at week 1 aft er challenge, both cats showed the lowest provirus load in their respe ctive groups, These results indicate that immunization with recombinan t FIV SU in conjunction with appropriate adjuvants may lead to partial protection against FIV challenge infection.