Stimulatory Effects Of CpG Oligodeoxynucleotides On Human Na(i|¨)ve B Cells Presenting HBV Epitopes

B lymphocytes are generally thought to be key agents in the humoral immunity againsthepatitis B virus (HBV) infection. However, the role of human na(i|¨)ve B cells in CD8+T cellpriming has been controversial. The failure of B cells to induce CD8+T cell immuneresponses to Ag may caused at least partly by the relatively low expression of costimulatorymolecules, because induction of costimulatory molecules on naive B cells tends toincrease their antigen-presenting-cell (APC) capacity. Another significant limitation fornaive B cell APC capacity is the relative rarity of cells that express specifcity for aparticular Ag, which make Ag recognition and uptake by naive B cells a relatively rareevent.However, recent reports showed B cells have the potential to become potent APCs toinduce immune responses. In the absence of other competent APCs, Ag-specific B cellsinduced CD8+T cell responses in vivo. Memory B cells induced primary CD4+T cellresponse in a CD154-CD40-dependent manner. CD40-activated human B cells can generateautologous antigen-specific T cells and up-regulate the expression of costimulatorymolecules and MHC molecules. Due to the proliferation of B cells from human peripheralblood is easier than dendritic cells (DCs), B cells showed a promising usage of vaccinestrategies.Activated state of APCs determined immune responses of T cells. Resting APCsinduced T cells tolerance and anergy, while activated-APCs triggered efficient T cellresponses. As toll-like receptor (TLR)9agonists, synthetic CpG oligodeoxynucleotides(CpG ODNs) have shown potential applications as immunotherapeutic agents and vaccineadjuvants of infectious disease. In humans, TLR9was shown to be constitutively expressedon B cells. Activation of memory B cells by TLR9leaded to cellular expansion and Igproduction, and increased the expression of costimulatory molecules and MHC moleculesindicated B cells as potent APCs. It also had been shown that CpG-activated na(i|¨)ve B cells enhanced cross-presentation CMV Ag to autologous CD8+T cells, resulting in proliferationof CMV-specific CTLs. However, the role of CpG ODNs in human na(i|¨)ve B cell presentingHBV epitopes to autologous CD8+T cells is not yet well understood.In the present study, we defined the effects of CpG ODNs on the APC capacity ofhuman na(i|¨)ve B cells for HBV epitopes. Firstly, we investigated the interaction betweenthree representative CpG ODNs and four HLA-A2restricted HBV epitopes chosenaccording to the geographical distribution of HBV genotype and the type of humanleukocyte antigen in China. Then, we estimated the effect of blockading PD-1/PD-L1pathway on the APC capacity of CpG-2216-primed human na(i|¨)ve B cells.Part One. Influence of CpG ODNs on APC capacity of human na(i|¨)ve B cellsHuman na(i|¨)ve B cells incubated with CpG-2006, CpG-2216and CpG2395respectivelyfor48hours and then co-incubation with HBV epitopes for additional12h. Cells wereharvested and then analyzed by fluorescence microscopy and flow cytometry. The resultsindicated that CpG ODNs enhanced HBV epitope binding to human na(i|¨)ve B cells atdifferent levels. Compared with other eptiopes, HBx115-123showed the strongest bindingcapacity to human na(i|¨)ve B cells. We next examined costimulatory molecules and MHCmolecules expression of CpG ODN-activated na(i|¨)ve B cells following incubation with HBVepitopes. CpG ODN-activated na(i|¨)ve B cells up-regulated the expression of CD80, CD86,MHC I and MHC II molecules in various degrees. Our results implied that CpGODN-primed na(i|¨)ve B cells have the potential APC capacity. Then we analyzed immuneresponses of autologous CD8+T cells induced by CpG ODN-activated na(i|¨)ve B cells. Theresults showed that CD8+T cells up-regulated the cytotoxic effects, and CpG-2216-primedna(i|¨)ve B cells binding with HBx115-123induced the highest expression ofGamma-interferon and granzyme B. Briefly, the results of this part suggested that CpGODNs discriminately enhanced APC capacity of human na(i|¨)ve B cells to HBV epitopesPart Two. Effects of blockading PD-1/PD-L1pathway on APC capacity of CpGODN-primed human na(i|¨)ve B cells.We blockaded the PD-1/PD-L1pathway of human na(i|¨)ve B cells with PD-L1monoclonal antibody, and analyzed the immune responses of autologous CD8+T cells. Theresults demonstrated that blockading of PD-1/PD-L1pathway can increaseHBx115-123-specific CD8+T cells and up-regulate their IFN-γ secretion. Notably, compare with either of them, priming na(i|¨)ve B cells with CpG-2216and blockading ofPD-1/PD-L1pathway simultaneously resulted in more effective increasingHBx115-123-specific CD8+T cells and the IFN-γsecretion (p<0.01).In conclusion, the present study suggests that CpG ODNs discriminately enhance APCcapacity of human na(i|¨)ve B cells to HBV epitopes, and blockading of PD-1/PD-L1pathwayin human na(i|¨)ve B cells has synergistic effects with CpG ODNs. This novel activity ofhuman na(i|¨)ve B cells showed the potential to exploit for new vaccine strategies...