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

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±79pg/ml vs. 320±82pg/ml) and IFNγ (77±35pg/ml vs. 401±121pg/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.