A Study of Mezagitamab in Adults With Late Antibody-Mediated Rejection (AMR) After a Kidney Transplant

Key inclusion criteria: 1. The participant aged 18 to 80 years. 2. The participant must have a biopsy-confirmed diagnosis of active or chronic active late AMR (defined as greater than \[\>\] 6 month after kidney transplant) without concurrent definitive TCMR (Grade 1a and above) as defined by the 2022 Banff classification. 3. Biopsy within 30 days prior to screening, or performed during screening period within protocol-defined window. 4. If the participant has received treatment for rejection, then the repeat biopsy and donor specific antibody (DSA) testing must have been performed at least 6 weeks after stopping the treatment. 5. The participant with either human leukocyte antigen (HLA) class I and/or II DSA. 6. eGFR \> 30 milliliters per minute per 1.73 square meters (mL/min/1.73m\^2). Key exclusion criteria: 1. The participant has blood type A, B, AB, or O (ABO) incompatible transplant. 2. The participant has a history of multiple organ transplants, including en bloc and dual kidney transplants. 3. Participant likely to require renal replacement therapy within the subsequent 30 days. 4. Participants who have received an anti-cluster of differentiation 38 (CD38) therapy in the last 1 year or have past history of failing to achieve AMR resolution despite treatment with an anti-CD38 therapy. 5. The participant has received any previous treatment with other immunosuppressant or immunomodulatory therapy: a) Within 6 months of signing the informed consent form (ICF) as listed below: * Complement system inhibitors (such as, eculizumab). * Proteasome inhibitors (such as, bortezomib). * Interleukin-6 (IL-6)/IL-6R antibody (such as, tocilizumab). * Anti-cluster of differentiation 20 (CD20) antibody (such as, rituximab). b) Within 6 weeks of signing the ICF as listed below: * Intravenous immunoglobulin (IVIG) or subcutaneous immunoglobulin (SCIG) or plasmapheresis 6. The participant has active infection with hepatitis B virus, hepatitis C virus (HCV), or human immunodeficiency virus (HIV). 7. Participant with serious infection within 2 weeks or with opportunistic infection within 2 months prior to signing ICF. Participant with active or untreated tuberculosis, or those with high suspicion of tuberculosis are also excluded. 8. History of malignancy (including myelodysplastic syndrome) within 5 years of signing the ICF, except for adequately treated non-melanoma skin cancer, superficial bladder cancer, and curatively treated cervical carcinoma-in-situ. Key Note: Other protocol specified inclusion and exclusion criteria apply.