mRNA-2736 for Participants With Relapsed or Refractory Multiple Myeloma (RRMM)

Key Inclusion Criteria: * RRMM with prior exposure to a proteasome inhibitor, an immunomodulatory drug (IMiD), and an anti-cluster of differentiation (CD38) monoclonal antibody. Participants must have received at least 3 prior lines of therapy or be triple-class refractory. Participants that are intolerant of a proteasome inhibitor, IMiD, or aCD38 are eligible. * Measurable disease defined as at least 1 of the following: * Serum M-protein ≥0.5 grams/deciliter * Urine M-protein ≥200 milligrams (mg)/24 hour * Involved free light chain (FLC) ≥100 mg/liter and an abnormal FLC ratio * Plasmacytoma with a single diameter ≥2 centimeters * Bone marrow plasma cells \>30% Key Exclusion Criteria: * Known central nervous system (CNS) myeloma or clinical signs and symptoms of CNS involvement of myeloma. * Active plasma cell leukemia, defined as peripheral blood plasma cells ≥20%. History of plasma cell leukemia is allowed. * Radiotherapy or cytotoxic chemotherapy within 2 weeks prior to Day 1 (Baseline), except palliative radiotherapy of limited field is permissible within 2 weeks after discussion with the Sponsor medical monitor. * Antibody-based immunotherapy (monoclonal antibody, bispecific antibody, antibody drug conjugate, radioimmunoconjugate) within 21 days prior to Day 1 (Baseline). * Proteasome inhibitor therapy within 14 days prior to Day 1 (Baseline). * Immunomodulatory agent therapy within 7 days of Day 1 (Baseline). * Autologous hematopoietic cell transplant within 100 days prior to Day 1 (Baseline). * Allogeneic hematopoietic cell transplant within 180 days prior to Day 1 (Baseline). Participants should have no evidence or ongoing treatment for acute or chronic graft versus host disease. * Genetically modified adoptive cellular therapy (for example, chimeric antigen receptor T cell, chimeric antigen receptor natural killer) within 12 weeks prior to Day 1 (Baseline). * Corticosteroid therapy ≥140 mg prednisone or equivalent cumulative dose within 14 days prior to Day 1 (Baseline). * Active hepatitis B or C, or laboratory evidence for a chronic infection with hepatitis B or C at the time of screening. Participants with a past or resolved hepatitis B infection (presence of hepatitis B core antibody and absence of hepatitis B surface antigen) are eligible. Participants positive for hepatitis C virus (HCV) antibody are eligible only if negative for HCV RNA. Note: Other inclusion and exclusion criteria may apply.