Background:  Given the extreme sequence diversity of circulating HIV strains, the most effective therapeutic vaccines may be those using antigens derived from autologous virus. The safety and immunogenicity of vaccine protocols using monocyte-derived dendritic cells (MDDC) transfected with synthetic mRNA encoding tumor antigens have been demonstrated in previous clinical trials. Chimeric antigens expressed in the lysosome of antigen-presenting cells have been shown to be processed and presented to T cells in the context of both class I and class II MHC. We hypothesized that MDDC transfected with lysosome-targeted chimeric HIV nef antigen, using consensus or autologous sequence, would induce in vitro activation and expansion of nef-specific CD4 and CD8 T cells. The in vitro immunogenicity of transfected MDDC will be used in the evaluation of potential vaccines.

Methods:  MDDC derived from chronic HIV patients were transfected with synthetic mRNA encoding a chimeric open reading frame composed of an ER-translocation signal sequence, nef sequence, and a lysosomal targeting sequence. Nef sequences were derived either from a synthetic gene representing consensus nef or from clinical isolate HIV sequences. Autologous T cells were co-cultured with transfected MDDC for 1 to 3 weeks and the frequency of nef-specific T cells before and after co-culture was assessed by flow cytometry.

Results:  Co-culture of autologous T cells with MDDC expressing chimeric nef induced specific expansion of IFNg-producing nef-reactive CD4 and CD8 T cells, as determined by ICS. For some patients, nef-specific T-cell frequency increased from nearly undetectable to ~15% of CD4 and CD8 T cells. In other cases, CD4 T cells expanded to a lesser degree or not at all. Patient T cells responded both to consensus nef and to nef derived from autologous HIV.

Conclusions:  Transfection of MDDC with lysosome-targeted nef constructs permits efficient presentation of nef-derived antigens in the context of MHC class I and class II. Co-culture of autolgous T cells with chimeric nef-transfected MDDC induced specific expansion of nef-reactive CD4 and CD8 T cells for some patients. The reason other patients’ T cells failed to respond to stimulation by MDDC is a topic of ongoing investigation. Immune therapy with autolgous MDDC-expressing chimeric HIV antigens derived from autologous clinical isolate HIV sequences is a promising method to boost antiviral CD4 and CD8 T-cell responses in chronic HIV patients.

Keywords: therapeutic vaccine; dendritic cell; autologous HIV