CpG oligonucleotides increase HBV-specific cytokine responses in whole blood and enhance cytokine release assay sensitivity

Abstract Background Chronic hepatitis B leads to liver cirrhosis and hepatocellular carcinoma. To develop a therapeutic vaccine for chronic hepatitis B patients it is necessary to assess cellular immune responses to hepatitis B virus (HBV) antigens. We investigated the potential of toll-like receptor (TLR) 9 agonists, i.e. CpG oligonucleotides, as costimulators to increase diagnostic sensitivity and specificity of our HBV- specific cytokine release assay. Methods Whole blood from 80 healthy individuals (n = 51 hepatitis B vaccinated, n = 29 unvaccinated) was stimulated with hepatitis B surface antigen (HBsAg) or hepatitis B core antigen (HBcAg) in presence or absence of CpG oligonucleotides. IL2 and IFNγ secretion in plasma was assessed using ELISA. Results CpG oligonucleotides specifically enhanced HBsAg-mediated IL2 (276 ± 79 pg/ml vs. 320 ± 82 pg/ml) and IFNγ (77 ± 35 pg/ml vs. 401 ± 121 pg/ml) responses in whole blood. When IFNγ release was considered as readout depicting the hepatitis B vaccination status, the according assay reached a diagnostic sensitivity of 61% without, but of 76% with additional CpG oligonucleotide stimulation at a diagnostic specificity of 90%. Conclusions We show that innate signals mediated via TLRs contribute to HBV-specific cellular immune responses. CpG oligonucleotides can be used to make whole blood based cytokine release assays even more powerful as screening tools in HBV immunology.