Mesencephalic Astrocyte-derived Neurotrophic Factor Supports Hepatitis B Virus-induced Immunotolerance

The immune tolerance induced by hepatitis B virus (HBV) is a major challenge for achieving effective viral clearance, and the mechanisms involved are not well-understood. One potential factor involved in modulating immune responses is mesencephalic astrocyte-derived neurotrophic factor (MANF), which has been reported to be increased in patients with chronic hepatitis B. In this study, our objective is to examine the role of MANF in regulating immune responses to HBV.

We utilized a commonly used HBV-harboring mouse model, where mice were hydrodynamically injected with the pAAV/HBV1.2 plasmid. We assessed the HBV load by measuring the levels of various markers including hepatitis B surface antigen, hepatitis B envelope antigen, hepatitis B core antigen, HBV DNA, and HBV RNA.

Our study revealed that following HBV infection, both myeloid cells and hepatocytes exhibited increased expression of MANF. Moreover, we observed that mice with myeloid-specific MANF knockout (Manf^Mye-/-) displayed reduced HBV load and improved HBV-specific T cell responses. The decreased HBV-induced tolerance in Manf^Mye-/- mice was associated with reduced accumulation of myeloid-derived suppressor cells (MDSCs) in the liver. Restoring MDSC levels in Manf^Mye-/- mice through MDSC adoptive transfer reinstated HBV-induced tolerance. Mechanistically, we found that MANF promoted MDSC expansion by activating the IL-6/STAT3 pathway. Importantly, our study demonstrated the effectiveness of a combination therapy involving an hepatitis B surface antigen vaccine and nanoparticle-encapsulated MANF siRNA in effectively clearing HBV in HBV-carrier mice.

The current study reveals that MANF plays a previously unrecognized regulatory role in liver tolerance by expanding MDSCs in the liver through IL-6/STAT3 signaling, leading to MDSC-mediated CD8⁺ T cell exhaustion.