The Effect Of Genetic Adjuvants On The Kinetics Of Immune Response To Different HBV Vaccines

The effect of genetic adjuvants on the kinetics of immune response to different HBV vaccinesIntroductionAn estimated 400 million people worldwide were chronically infected with HBV, and many of them developed into chronic diseases such as liver cirrhosis and hepatocellular carcinoma. At present there is no efficient drug gainst HBV persistent infection, and then the therapeutic vaccine become a hot spot. The conventional protein-based vaccine induces the humoral immune response which consists mainly of IgG, but it has limited effect on the chronic HBV infection. Although DNA vaccine could induce antigen-specific cytotoxic T lymphocytes, it has relatively low efficacy in large animal species and humans. Construction of genetic adjuvant is an alternative approach in which genes are co-delivered in order to modulate immune responses to vaccine. In this study, we discussed the effect of the different genetic adjuvants on the immune responses to HBV protein-based vaccines and DNA vaccines. T cell responses consist of three distinct phases: ⑴activation and expansion phase, ⑵death phase and ⑶memory phase. Genetic adjuvants might give intervention at any of these three phases: for example, it could increase the expansion of effector T cell populations, alternatively, it might be possible to intervene during the contraction phase to reduce effector T cell death, thereby increasing the percentageof memory T cells that formed.In the expansion phase, the quantities and qualities of T cells are determined by the signals given by antigen presenting cell (APC). Because dentritic cell (DC) is the most potent and important APC and could activate the na?ve T cell, enhancing the function of DC is one of the strategies to improve the efficacy of vaccine. Cytokine flt3 ligand (FL) is one of important factors which could influence the function and quantity of DC. It could induce the proliferation of the lymphoid and myeloid DC, so when used as an adjuvant, it might influence the expansion phase of immune response induced by vaccines.In the memory phase, IL-15 play a key role in the generation and maintenance of CD8+ memory T cells. It is the only one cytokine known that could induce thememory CD44hiCD8+T cell proliferation ex vivo. So when used as an adjuvant, it might influence the memory phase of the immune response induced by vaccines.In this study, we choose the FL as a representative of the genetic adjuvant which could affect the expansion phase induced by the vaccine, the IL-15 as the representative of the genetic adjuvant which could affect the memory phase, to investigate the effect of the genetic adjuvant on the kinetics of immune responses to HBV protein-based vaccines and DNA vaccines.Part I The kinetic and distribution analyses of CD8+ T Cells responses induced by hepatitis B virus core gene DNA vaccine by intracellular cytokine stainingTo study the kinetics of immune responses induced by HBV core gene DNA vaccines,100 μg of a recombinant expression plasmid DNA, harboring DNA encoding the 144 amino acids of the N-terminus of HBV core gene (abbreviated pHBc144) was used to immunize C57BL/6 mice. The percentage of antigen-specific CD8+ T cell (CD8+IFN-γ+T cells ) was detected by intracellular cytokine staining(ICCs)at various time point. On day 8 postimmunization,the percentage of antigen-specific T cells in spleen is 0.10%±0.04%.Then there was a rapid amplification of antigen-specific T cells and peaking at 14 days postimmunization(about 1.84%±0.56% of all splenic CD8+ T cells), then antigen-specific CD8+ T cell decreased gradually,but remained detectable directly ex vivo for one year postinjection(about 0.28% of all splenic CD8+ T cells). And after boosting, the percentage of antigen-specific CD8+ T cell rebounded and reached the peak on 10 days later(about 3.60%±0.35% of all splenic CD8+ T cells), the value is 2 fold higher than the peak of first immunization, then the percentage declined slowly until by day 60 after second immunization it returned back to 0.32%?...