Functional restoration of CD56 bright NK cells facilitates immune control via IL-15 and NKG2D in patients under antiviral treatment for chronic hepatitis B.

BACKGROUND AND AIMS: Hepatitis B virus (HBV) is intrinsically immunogenic, with long-lasting immune control in many patients. However, the mechanisms and key cell types underlying effective immune control are incompletely understood.

METHODS: We studied the restoration of natural killer (NK) cell numbers and function post antiviral treatment in 52 hepatitis B e antigen (HBeAg)-positive chronic hepatitis B (CHB) patients who received telbivudine (LdT) for 48 weeks. Blood samples were collected at week 0, 12, 24, 36, and 48 and tested for HBV DNA, hepatitis B surface antigen (HBsAg), HBeAg, liver enzymes, and NK cell parameters.

RESULTS: Compared with baseline, the number of peripheral CD3- CD56bright NK cells increased significantly from week 24 to 48, especially in patients with baseline alanine transaminase (ALT) two- to fivefold the upper line of normal (ULN) or HBV DNA <9 log10 copies/ml. Expression (number and density) of activating receptors NKG2D and NKp46 on CD3- CD56bright NK cells was enhanced, while inhibitory receptor NKG2A decreased. Notably, numbers of CD3- CD56bright or NKG2D+ CD3- CD56bright NK cells were significantly better restored in patients with HBeAg seroconversion. NK cell activating serum interleukin 15 (IL-15) was significantly increased during LdT treatment, especially in HBeAg seroconverters. LdT significantly enhanced expression of NKG2D and IL-15 in cultures of purified peripheral NK cells from treatment-naïve HBeAg-positive CHB patients.

CONCLUSIONS: Functional restoration of CD56bright NK cells via upregulation of IL-15 and NKG2D is a novel activity of LdT and likely other antivirals, independent of its effect on HBV replication. This also demonstrates the importance of host immune restoration in controlling chronic HBV infection.