A Study to Assess the Safety, Tolerability, and Pharmacokinetics of GIGA-2339 in Participants With Chronic Hepatitis B Virus Infection

Key Inclusion Criteria:

• Hepatitis B envelope antigen (HBeAg) negative chronic HBV infection for ≥ 6 months,defined as presence of Hepatitis B surface antigen (HBsAg) in serum for ≥ 6 months.

• Serum HBsAg concentration between ≥ 100 international units per milliliter (IU/mL)and 2000 IU/mL at screening.

• Currently on stable dose of nucleot(s)ide analogues (NAs) (≥ 6 months) and expectedto continue while in study.

• Serum HBV deoxyribonucleic acid (DNA) concentration ≤ 50 IU/mL at screening.

• Male participants must refrain from donating spermatozoa and agree to use highlyeffective contraception.

• Female participants must not be pregnant, or breastfeeding; either should not be awoman of childbearing potential (WOCBP) or if WOCBP should use highly effectivecontraceptive methods.

Key Exclusion Criteria:

• Positive for co-infection with hepatitis C virus (HCV), human immunodeficiency virus (HIV), hepatitis D virus (HDV) at screening.

• Participants that weigh less than 50 kilograms (kg) and/or have a body mass index (BMI) less than 18.5.

• History of documented liver cirrhosis at screening. Patients under liver cirrhosisevaluation at screening will not be eligible until cirrhosis is ruled out.

• Liver stiffness > 8 kilopascal (kPa) at screening.

• History of chronic liver disease from another cause, immune complex disease, orautoimmune diseases that in the opinion of the investigator would precludeparticipation.

• Family history of hepatocellular carcinoma (HCC).

• Alpha fetoprotein > 20 nanograms per milliliter (ng/mL).

• Presence of a liver imaging reporting and data system (LI-RADS) 4 or 5 liver lesionon imaging 12 months prior to Screening OR, LI-RADS-US findings of US-3 grade onimaging 12 months prior to Screening, OR LIRADS-US grade 3 done prior to the D1infusion visit, if prior LI-RADS or LI-RADS-US results are not available atScreening.

• History of hematopoietic stem cell transplant or solid organ transplant.

• Receipt of anti-HBV monoclonal antibody (mAb) therapy of any kind in the past (including hepatitis B immunoglobulin [HBIG]).

• History of cardiovascular disease (e.g., coronary artery disease, cardiomyopathy,congestive heart failure, family history of congenital long QT syndrome).

• Malignancy diagnosed and/or treated within 5 years prior to Screening, and/or withongoing treatment for malignancy, with the exception of localized non-metastaticbasal cell or squamous cell carcinoma of the skin or in-situ carcinoma of the cervixexcised with curative intent.

• Participants requiring anti-coagulation therapies (for example warfarin, Factor Xainhibitors, or anti-platelet agents like clopidogrel).

• Male participants with a corrected QT interval using Fridericia's formula (QTcF) > 450 milliseconds (msec) and female participants with QTcF > 470 msec on ECG recordedat screening. Participants with evidence of intraventricular conduction delay,defined as QRS interval greater than 110 msec, will be excluded if the QTcF is > 500msec for both males and females.

• Known hypersensitivity to any GIGA-2339 excipients or any confirmed significantallergic reactions (urticaria or anaphylaxis) against any drug, or multiple drugallergies (nonactive hay fever is acceptable), or a history of drug or other allergythat, in the opinion of the Investigator, contraindicates participation.

• Received or will receive live-attenuated virus vaccinations such as measles, mumps,rubella or varicella within 4 weeks before and up to three months afteradministration of investigational product (IP).