A Study of BION-1301 in Adults With IgA Nephropathy

Inclusion Criteria:

- Male and female participants aged ≥ 18 years at the time of signing the informed
consent form (ICF) prior to initiation of any study specific activities/procedures.

- Biopsy-proven IgAN diagnosed within the past 10 years prior to Screening, that, in
the opinion of the Investigator, is not due to secondary causes. A pseudonymized
copy of the report must be available for review by the Sponsor or designee prior to
randomization. If biopsy report within 10 years is not available, re-biopsy may be
permitted upon discussion with the Medical Monitor.

- eGFR ≥ 30 mL/min/1.73m^2 at Screening based on the 2021 CKD-EPI equation.

- Total urine protein ≥ 1.0 g/day and UPCR ≥ 0.7 g/g (700 mg/g), as measured from an
adequate 24-hour urine collection at Screening by a central laboratory.

- Stable on a maximally tolerated dose of ACEi/ARB for at least 12 weeks prior to
Screening unless intolerant to ACEi/ARB. May also be on a stable and well tolerated
dose of SGLT2i and/or ERAs/MRAs for at least 12 weeks prior to Screening for the
treatment of IgAN. Participants are expected to stay on the ACEi/ARB, SGLT2i and/or
the ERAs/MRAs for the duration of the study.

- Body mass index (BMI) between 18 and 40 kg/m^2.

- Screening weight of 45 to 150 kg.

- Men and women of childbearing potential (WOCBP; per Clinical Trials Facilitation and
Coordination Group [CTFG] 2020) must agree to follow protocol-specified
contraception guidance from Screening through approximately 5 half-lives (24 weeks)
after the final dose of study drug. Use of hormonal contraceptive agents must have
been initiated > 1 month prior to first dose of study drug.

- Provide written informed consent and be willing to comply with study visits and
procedures.

Exclusion Criteria:

- Secondary forms of IgAN as determined by the Investigator, in the setting of
systemic disorders, infections, autoimmune disorders or neoplasias.

- Diagnosis of IgA Vasculitis.

- Current or history of nephrotic syndrome.

- Average blood pressure > 150/90 mm Hg (systolic/diastolic) from 3 readings obtained
at the initial Screening visit. If blood pressure is too high, the 3 readings may be
repeated once within the Screening period if clinically appropriate as per the
Investigator.

- Clinical suspicion of IgAN with rapidly progressive glomerulonephritis (RPGN) based
on KDIGO guidelines

- Chronic Kidney Disease, either clinically suspected or based on biopsy, resulting
from any condition or another glomerulopathy/podocytopathy other than IgAN.

- History of Type 1 Diabetes.

- Participants with Type 2 diabetes are excluded if any of the following are present:

- Screening HbA1c (glycated hemoglobin) of > 8%.

- Evidence of diabetic changes on kidney biopsy, performed for any reason.

- History of diabetic microvascular disease (retinopathy, neuropathy,
nephropathy) and/or macrovascular disease (atherosclerotic heart disease,
peripheral vascular disease, cerebrovascular disease).

- Unstable anti-diabetic regimen:

- Prior exposure to any antibody directed against APRIL.

- History of a previous severe allergic reaction with generalized urticaria,
angioedema, or anaphylaxis, including a history of allergy or hypersensitivity to
any component of BION-1301, or history of severe hypersensitivity reaction to any
monoclonal antibody.

- Received an investigational new drug within 28 days or 5 half-lives, whichever is
longer, prior to Screening.

- Received systemic corticosteroid therapy including budesonide (Tarpeyo/Kinpeygo) for
> 14 days within 12 weeks prior to Screening.

- Use of systemic immunosuppressant medications.

- Any confirmed or suspected immunosuppressive or immune-deficient state, including
but not limited to common variable immunodeficiency (CVID), HIV infection or
asplenia, history of bone marrow or organ transplantation with exception of corneal
transplants.

- Current severe infection requiring antimicrobials or history of recurrent, severe,
infections as determined by the Investigator.

- Positive serology test for hepatitis A virus IgM antibodies (anti-HAV IgM),
hepatitis B surface antigen (HBsAg), detectable hepatitis B virus (HBV) DNA,
hepatitis C virus (HCV) antibodies (participants who completed treatment and are
persistently antibody be allowed), or antibodies to HIV-1 and/or HIV-2 at Screening.

- Received a live vaccination within 12 weeks prior to Screening or plan to have a
live vaccination within 6 months after the last dose of study drug.

- History of malignancy unless cancer free for at least 5 years or non-melanoma skin
cancer that was completely resected. A participant with curatively treated cervical
carcinoma in situ is eligible for the study. Participants with low-risk prostate
cancer (i.e., Gleason score < 7 and prostate specific antigen < 10 ng/mL) are
allowed.

- Pregnancy or breastfeeding or intent to become pregnant or to donate sperm during
the study period and until 24 weeks after last dose.

- History or evidence of any other clinically significant disorder, condition,
disease, or laboratory finding that, in the Investigator's assessment, would place
the participant at unacceptable risk, limit compliance with study requirements, or
confound interpretation of study results.

- IgG levels < 6 g/L at Screening.

- Participation in another interventional trial with an investigational agent/device
is prohibited during the course of this study.