Breaking Immune Tolerance in Chronic Hepatitis B by Dendritic Cell Vaccination in HBV Trimera Mice

Introduction: Whereas spontaneous resolution from hepatitis B is associated with strong antiviral T cell responses, only weak immune responses are found in patients with chronic infection. Thus, induction of strong HBV-specific T cell reactivities might represent a new therapeutic strategy. Dendritic cells (DC) are highly specialised antigen presenting cells (APC) and might therefore serve as an effective therapeutic vaccine. Methods: DC were generated from MACS -seperated monocytes of patients and healthy cnotrols by incubation in IL–4 and GM-CSF. Apoptosis of HepG2 cells transfected with a 1.3 overlength HBV plasmid was induced by UV irradiation. Balb/c mice were irradiated, transplanted with nod.scid mouse bone marrow and reconstituted with human PBMC from donors with chronic HBV infection (HBsAg seropositive) or controls. Vaccination of such trimera was performed i.p. with DC pulsed with apoptotic HBV-transfected or non-transfected HepG2 cells, rHBcAg or HBc18–27 peptide; vaccination with rHBc antigen and EBV peptide280–288 served as controls. HBV specific human T cell frequencies were analysed from peritoneal lavage by IFNy ELISpot with autologous APC pulsed with HBV core (HBc) and surface (HBs) antigens or one core and five envelope peptides 10 days after vaccination. Results: Cross presentation of HBV core antigen by DC from chronic HBV patients and controls was similarly effective, as demonstrated by stimulation of an HLA A2-restricted HBc18–27-specific CTL clone by IFNy Elispot. Patient PBMC revealed no or very weak Th cell and CTL responses against core or envelope epitopes, indicating their antiviral immune tolerance. However, when DC pulsed with apoptotic HBV-transfected HepG2 cells were transferred together with autologous PBMC from chronic HBV carriers into trimera mice, strong and multispecific HBc and HBs specific Th cell and CTL responses were detected. Conclusions: Our studies demonstrate that HBV transfected apoptotic body pulsed DC might represent a tool for therapeutic vaccination of chronic HBV patients. Moreover, core specific CTL, that are barely detectable ex vivo in chronic HBV patients, can rapidly be recovered under our experimental conditions, arguing against deletion of such cells in patient PBMC.