A Study to Evaluate the Safety, Tolerability, Drug Levels, and Preliminary Efficacy of Relatlimab Plus Nivolumab in Pediatric and Young Adults With Hodgkin and Non-Hodgkin Lymphoma

Inclusion Criteria:

1. Participants with pathologically confirmed high-risk R/R cHL, after non-response to or failure of 1or more lines of standard therapy.
2. Participants with pathologically confirmed R/R NHL after non-response to or failure of 1or more lines of standard therapy, including, but not limited to, R/R primary mediastinal B-cell lymphoma, diffuse large B-cell lymphoma (DLBCL), mediastinal gray zone lymphoma (MGZL), anaplastic large cell lymphoma (ALCL), or peripheral T-cell lymphoma (PTCL).
3. Participants with pathologically confirmed R/R NHL after non-response to or failure of 2 or more lines of standard therapy, including Burkitt lymphoma (blast count <25% malignant Burkitt cells and/or per the investigator's clinical assessment of risk status), lymphoblastic lymphoma (blast count < 25% of marrow nucleated cells and/or per the investigator's clinical assessment of risk status), NK/T-cell lymphoma (nasal and non-nasal NK/T-cell lymphoma subtypes, but not aggressive NK/T-cell leukemia/lymphoma subtype).
4. The participant's current disease state must be R/R to standard therapy.
5. Participants must have measurable PET positive disease in both cHL and NHL cohorts.

Exclusion Criteria:

1. Primary CNS lymphoma of the brain or spinal cord, and secondary CNS lymphoma (ie, from systemic non-Hodgkin lymphoma) involving the brain, spinal cord, or with leptomeningeal seeding.
2. Prior treatment with an anti-cytotoxic T-lymphocyte-associated protein 4 (anti-CTLA-4) antibody, or any other antibody or drug specifically targeting T-cell co-stimulation or checkpoint pathways, with the exception of anti-PD(L)-1 targeted therapies.
3. Prior treatment with lymphocyte activation gene-3 (LAG-3)-targeted agents.
4. Participants with clinically significant systemic illnesses unrelated to the cancer as judged by the investigators, which would compromise the participant's ability to tolerate the study treatment.
5. Participants with autoimmune disease.
6. Prior allogeneic bone marrow transplantation.

Other protocol-defined inclusion/exclusion criteria apply