Abstract
The efficient induction of CD8 T cell immunity is dependent on the processing and presentation of antigen on MHC class I molecules by professional antigen presenting cells (APC). To develop an improved T cell vaccine for HIV we investigated whether fusing the ubiquitin gene to the N terminus of the HIV gag gene enhanced targeting to the proteasome resulting in better CD8 T cell responses. Human monocyte derived dendritic cells (moDC), transduced with adenovirus vectors carrying either ubiquitinated or non-ubiquitinated gag transgene constructs, were co-cultured with autologous naïve T cells and T cell responses were measured after several weekly cycles of stimulation. Despite targeting of the ubiquitin gag transgene protein to the proteasome, ubiquitination did not increase CD8 T cell immune responses and in some cases diminished responses to gag peptides. There were no marked differences in cytokines produced from ubiquitinated and non-ubiquitinated gag stimulated cultures or in the expression of inhibitory molecules on expanded T cells. However, the ability of moDC transduced with ubiquitinated gag gene to upregulate co-stimulatory molecules was reduced, whilst no difference in moDC maturation was observed with a control ubiquitinated and non-ubiquitinated MART gene. Furthermore moDC transduced with ubiquitinated gag produced more IL-10 than transduction with unmodified gag. Thus failure of gag ubiquitination to enhance CD8 responses may be caused by suppression of moDC maturation. These results indicate that when designing a successful vaccine strategy to target a particular cell population, attention must also be given to the effect of the vaccine on APCs.
Highlights
The urgency for a prophylactic HIV vaccine is evident by the sustained global increase in HIV-1 infection
Despite IFNc responses to the non-ubiquitinated transgene construct, ubiquitination of the transgene did not enhance IFNc production nor did it result in a broader response by CTLs, though in some donors the recognition of the odd epitope was enhanced by the ubiquitinated transgene (Figure 3B)
Our results illustrated that unmodified CN54 gag is already very efficiently targeted to the proteasome (Figure 1) suggesting that further targeting of the presentation pathway would result in little enhancement of responses and that fusion to ubiquitin suppressed responses
Summary
The urgency for a prophylactic HIV vaccine is evident by the sustained global increase in HIV-1 infection. Despite the best efforts of over 20 years of research an effective HIV vaccine remains elusive, compounded by the diversity of the virus and its ability to evade immune responses. Recent progress has been in isolating broadly neutralising antibodies from HIV infected individuals. Such antibodies only appear after infection for several years with high virus loads and require very extensive changes in germ line immunoglobulin changes which will be difficult to achieve with vaccinations [2]. Induction of effective neutralising antibodies remains at the forefront of developing a preventative vaccine that provides long term immunity.
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