Immunogenicity of GagRT VLPs. BALB/c mice were primed on day 0 with the DNA vaccine pVRCgrttnC then boosted on day 28 with the DNA vaccine (DNA+DNA group) or GagRT VLPs (DNA+GagRT group). A further group was left unprimed then vaccinated on day 28 with GagRT VLPs. For all mouse groups spleens were harvested on day 40 and splenocytes used in IFN-γ ELISPOT and IL-2 ELISPOT assays with the indicated Gag and RT CD8 and CD4 peptides. Cumulative ELISPOT responses to the vaccines are shown and are to the sum of responses to the indicated peptides in the IFN-γ ELISPOT or IL-2 ELISPOT assays with the indicated Gag and RT CD8 and CD4 peptides. Data represent results from one of three representative experiments.