Study of Sequential GSK3228836 and Peginterferon Treatment in Participants With Chronic Hepatitis B (CHB)

Inclusion Criteria

• 18 to 75 years of age at the time of signing the informed consent.
• Participants who are eligible to be treated with PegIFN.
• Documented chronic HBV infection >=6 months prior to screening and currently receiving stable NA therapy except telbivudine, defined as no changes to their NA regimen from at least 6 months prior to screening and with no planned changes to the stable regimen over the duration of the study.
• Plasma or serum HBsAg concentration >100 International Units per milliliter (IU/mL).
• Plasma or serum HBV DNA concentration 2 and FibroSure/FibroTest result >0.7. If only one parameter (APRI or FibroSure/FibroTest) result is positive, a discussion with the Medical Monitor is required before inclusion in study is permitted. Regardless of APRI of Fibrosure/FibroTest score, if the participant meets one of the following criteria, they will be excluded from the study: a) Liver biopsy (i.e., Metavir Score F4); b) Liver stiffness >12 kilopascals (kPa).
• Diagnosed or suspected hepatocellular carcinoma as evidenced by the following: Alpha- fetoprotein concentration >=200 nanogram per milliliter (ng/mL); If the screening alpha fetoprotein concentration is >=50 ng/mL and =450 milliseconds (msec) (if single electrocardiogram [ECG] at screening shows QTcF>=450 msec, a mean of triplicate measurements should be used to confirm that participant meets exclusion criterion).
• Laboratory results as follows: Serum albumin 1.25; Platelet count 1.25 times ULN (For participants with benign unconjugated hyperbilirubinemia with total bilirubin >1.25 times ULN, discussion for inclusion to the study is required with the Medical Monitor); Urine albumin to creatinine ratio (ACR) >=0.03 milligram (mg)/mg (or >=30 mg/g). In the event of an ACR above this threshold, eligibility may be confirmed by a second measurement. In cases where participants have low urine albumin and low urine creatinine levels resulting in a urine ACR calculation >=0.03 mg/mg (or >=30 mg/g), the investigator should confirm that the participant does not have a history of diabetes, hypertension or other risk factors that may affect renal function and discuss with the Medical Monitor, or designee.
• History of/sensitivity to GSK3228836 or components thereof or a history of drug or other allergy that, in the opinion of the investigator or Medical Monitor, contraindicates their participation.