HIV-1 CTL epitope-based DNA vaccine(VaxOnco, Inc.)

A DNA vaccine encoding sequence-conserved human immunodeficiency virus type 1 (HIV-1)-derived cytotoxic T-lymphocyte (CTL) epitopes from multiple HIV-1 gene products (designated EP HIV-1090) was evaluated in a placebo-controlled, dose escalation phase 1 clinical trial of HIV-1-infected subjects receiving potent combination antiretroviral therapy. Patients received four intramuscular immunizations with EP HIV-1090 over a 4-month period at one of four doses (0.5, 1.0, 2.0, or 4.0 mg) or received a placebo. The vaccine was determined to be safe and well tolerated at all doses tested. CTL responses were measured from cryopreserved peripheral blood mononuclear cells using gamma interferon enzyme-linked immunospot assays, with and without in vitro peptide stimulation (IVS). Responses to one or more vaccine epitopes were detected throughout the course of vaccination in 37.5% (12/32) and 47% (15/32) of vaccine recipients measured without and with IVS, respectively, indicating possible vaccine-induced priming of epitope-specific T cells. However, differences in rates of response to HIV-1 epitopes between vaccine and placebo recipients did not achieve statistical significance. The HIV-1 epitope-specific CTL responses measured in the peripheral blood after vaccination were often low level and short-lived, and therefore, alternative immunization schedules, routes of delivery, or vaccine formulations may be required to increase vaccine potency.

Epitope-based vaccines designed to induce CTL responses specific for HIV-1 are being developed as a means for addressing vaccine potency and viral heterogeneity. We identified a set of 21 HLA-A2, HLA-A3, and HLA-B7 restricted supertype epitopes from conserved regions of HIV-1 to develop such a vaccine. Based on peptide-binding studies and phenotypic frequencies of HLA-A2, HLA-A3, and HLA-B7 allelic variants, these epitopes are predicted to be immunogenic in greater than 85% of individuals. Immunological recognition of all but one of the vaccine candidate epitopes was demonstrated by IFN-γ ELISPOT assays in PBMC from HIV-1-infected subjects. The HLA supertypes of the subjects was a very strong predictor of epitope-specific responses, but some subjects responded to epitopes outside of the predicted HLA type. A DNA plasmid vaccine, EP HIV-1090, was designed to express the 21 CTL epitopes as a single Ag and tested for immunogenicity using HLA transgenic mice. Immunization of HLA transgenic mice with this vaccine was sufficient to induce CTL responses to multiple HIV-1 epitopes, comparable in magnitude to those induced by immunization with peptides. The CTL induced by the vaccine recognized target cells pulsed with peptide or cells transfected with HIV-1 env or gag genes. There was no indication of immunodominance, as the vaccine induced CTL responses specific for multiple epitopes in individual mice. These data indicate that the EP HIV-1090 DNA vaccine may be suitable for inducing relevant HIV-1-specific CTL responses in humans.