Immunogenicity of full length and truncated SIV envelope proteins.

We have compared the immunogenicity of the full-length (FL) SIV envelope (Env) protein and a truncated (T) form of the Env protein which has a short cytoplasmic tail. The Env(T) protein was previously shown to be more fusogenic than Env(FL), has a higher level of incorporation into virus-like particles (VLPs) and membrane vesicles, and expands the viral host range. We have found that mice immunized with VLPs which contained an equal amount of Env(FL) or Env(T) produced similar titres of neutralizing antibody. Comparison of immune responses between animals that received DNA vaccines encoding Env(T) vs. Env (FL) by epidermal delivery demonstrated that a higher level of specific antibody was elicited by Env(T) than Env(FL). This result correlated with a higher level of expression of pCMVEnv(T) than pCMVEnv(FL) observed in vitro. DNA immunization combined with VLP boosting elicited a similar level of neutralizing antibody with both forms of Env proteins. These data indicate that the immunogenicity of Env(FL) and Env(T) is similar, and that either form of Env protein appears to be potentially suitable for use in further development of vaccine preparations.