Recombinant adenovirus vaccines, a comprehensive investigation of T cell immunity.

摘要

Vaccination is arguably the most effective tool at our disposal to prevent the morbidity and mortality associated with infectious disease. However, there are currently several infectious diseases, notably HIV, malaria and tuberculosis, for which we do not posses effective vaccines. Further complicating matters, traditional methods to construct vaccines for these diseases have been unsuccessful. Advances in our understanding of adaptive immunity have demonstrated that vaccines for these diseases likely rely upon potent T cell immunity to be effective. Recombinant adenovirus (rAd) vectors have shown great promise as vaccination platforms since they are easily constructed, stable, well-tolerated and elicit robust T cell responses. The robust activity of rAd vectors based on the human serotype 5 virus (rHuAd5) in murine and simian models merits futher investigation as a prototypic T cell vaccine. To this end, we have undertaken a comprehensive evaluation of T cell immunity following rAd vaccination. Our previous observations determined that the CD8+ T cell response produced by rHuAd5 vaccines displayed a prolonged effector phase that was associated with long-lived antigen presentation. We have further investigated the mechanisms underlying the maintenance of this memory population. Our results have revealed that the memory phenotype is not due to continual recruitment of naive CD8+ T cells. Rather, the sustained effector phenotype appears to depend upon prolonged expression of the antigen-encoding transgene from the rHuAd5 vector. Interestingly, transgene expression was only required for 60 days after which point the memory population stabilized. Further investigation of the relationship between antigen structure and the CD8+ T cell response revealed that antigens which traffic through the ER produce a CD8+ T cell response that expands more rapidly and displays a more pronounced contraction phase than antigens which are produced within the cytosol. While the exact mechanism underlying this phenomenon is not known, we suspect that pathways related to ER stress may be involved. Despite the more dramatic contraction phase associated with antigens that traffic through the ER, the memory phenotype was unchanged. Interestingly, the CD4+ T cell response was not influenced by antigen structure and displays a sharp contraction phase regardless of whether the antigen traffics through the ER or is produced in the cytosol. We further investigated the relationship between CD4+ T cell help and CD8+ T cell immunity produced by rHuAd5. Based on the partially-exhausted phenotype of the CD8+ T cells produced by rHuAd5 (diminished TNF-alpha production and little IL-2 production), we suspected that inadequate CD4+ T cell help may have been responsible. However, removal of CD4+ T cells did not further impair the CD8+ T cell response produced by rHuAd5. Rather, a lack of CD4+ T cell help only impacted the magnitude of the primary CD8+ T cell response generated by rHuAd5; the functionality of the CD8+ T cell population, including the ability to proliferate following secondary stimulation, were not affected by the absence of CD4+ T cells. Thus, although CD8+ T cell expansion following immunization with rHuAd5 is dependent upon the availability of CD4+ T cell help, the memory functions of the CD8+ T cell population appears to be independent of CD4+ T cell help. Finally, we compared the magnitude of the CD8+ T cell response produced by rHuAd5 and recombinant vaccinia virus. Our results demonstrated that the functionality of the early T cell response produced by both vectors were identical. However, the primary transgene-specific CD8+ T cell responses produced by rHuAd5 were significantly larger than rVV because the vector specific responses were negligible in the case of rAd but very strong following rVV inoculation. This research has contributed to our understanding of T cell immunity following rAd immunization and will assist in the construction and implementation of future vaccines.