Serum HBsAg and ddPCR HBV-DNA as predictive parameters of HBsAg loss after nucleo(s)tide analogue (NA) treatment discontinuation in non-cirrhotic patients with Chronic Hepatitis B

Introduction: Stopping nucleo(s)tide analogue (NA) treatment in selected non-cirrhotic Chronic Hepatitis B (CHB) often leads to virus-induced flares, which may result to life-threatening liver failure. Aim: to identify predictive parameters of off-NAs response at the end of treatment and their association with HBsAg loss or HBsAg < 100IU/ml, for a safe discontinuation of treatment. Materials and Methods: 38 non-cirrhotic CHB patients, with complete virological suppression ( > 4 years), were prospectively monitored after suspending NA treatment for a median (IQR) time of 16 (10-19) months. Plasma samples at suspension date (baseline, BL) were collected and used to quantify serum HBV-DNA by highly sensitive droplet digital PCR (ddPCR). HBsAg was quantified by the ARCHITECT HBsAg assay at BL, every 2 weeks from suspension in the first month, followed by every month until the sixth month, then every 3 months. Results: At BL, 28 (73.7%) pts had detectable serum HBV-DNA (median[ IQR] 5[2-11] IU/mL), while 10 (26.3%) were completely negative to HBV-DNA. After NA suspension, 7 (18.4%) achieved HBsAg < 100IU/mL (median [IQR]: 43 [35-53]IU/ml) and 8 (21.1%) lost HBsAg at last follow-up. Patients achieving HBsAg loss had lower HBsAg levels at BL (140 [70-480]IU/ml with vs 1162 [439- 3135] without HBsAg loss, p = 0.014). The negativity to HBV-DNA by ddPCR at BL strongly correlated with the achievement of HBsAg < 100IU/mL or HBsAg loss after NA suspension (70% [7/10] with vs 28.6% [8/28] without negative BL HBV-DNA; OR [95%CI]: 5.8 [1.3- 23.6], p = 0.03).The combination of HBsAg < 500IU/mL + negativity HBV-DNA by ddPCR at BL was the best predictor for achieving HBsAg < 100IU/mL or HBsAg loss (85.7% with vs 27.6% without this combination; OR [95%CI]: 15.8 (1.6-152.2; p = 0.008; PPV = 86%; NPV = 72%). Conclusions: Residual HBV replicative activity at NA suspension, measured by highly sensitive assays, provides an added value in identifying patients more prone to achieve HBV functional cure.