Very recently, we demonstrated that the replacement of the human immunodeficiency virus type-1 (HIV-1) gp41 transmembrane protein by an Epstein-Barr virus gp220/350-derived membrane anchor resulted in the incorporation of chimeric envelope (Env) oligomers into Pr55gag virus-like particles (VLPs), exceeding that of wild-type gp160 by a factor of 10. In this study, we examined the immunostimulatory properties of Pr55gag VLPs to both (i) chimeric HIV-1 gp120 external envelope proteins and (ii) full-length gp160 presented on the outer surface of the particles. Immunization studies carried out with VLPs presenting different derivatives of the chimeric and wild-type Env proteins elicited a consistent anti-Pr55gag as well as anti-Env antibody response in complete absence of additional adjuvants. In both cases, the immune sera exhibited an in vitro neutralizing activity against homologous HIV-1 infection in MT4 cells. Noteworthy, these VLPs were also capable of inducing a strong CD8+ cytotoxic T-cell (CTL) response in immunized BALB/c mice that was directed toward a known CTL epitope in the third variable domain V3 of the gp120 external glycoprotein. However, the induction of V3-loop-specific CTLs critically depended on the amounts of Env proteins that were presented by the Pr55gag VLPs. Moreover, the CD8+ CTL response was not significantly altered by adsorbing the VLPs to alum or by repeated booster immunizations. These results illustrate that Pr55gag VLPs provide a safe and effective means of enhancing neutralizing humoral responses to particle-entrapped gp120 proteins and are also capable of delivering these proteins to the MHC class I antigen processing and presentation pathway. Therefore, antigenically expanded Pr55gag VLPs represent an attractive approach in the design of vaccines for which specific stimulation of neutralizing antibodies and cytotoxic effector functions to complex glycoproteins is desired.