Safety and Efficacy Study of OPC-415 in Patients With Relapsed and/or Refractory Multiple Myeloma

Inclusion Criteria: * Patients aged between 20 and 80 (75 for the phase 1 part) years, both inclusive, at the time of consent * Patients with a definitive diagnosis of active multiple myeloma * Patients who have had 2 or more prior regimens (including all proteasome inhibitors, immunomodulators, and anti-CD38 antibody) * Patients with relapsed and/or refractory Multiple Myeloma * Patients who are positive for MMG49 antigen * Patients with an Eastern Cooperative Oncology Group (ECOG) performance status (PS) score of 0 or 1. Those with an ECOG-PS score of 2 due solely to MM bone lesions can be enrolled * Patients who are expected to survive for at least 3 months Exclusion Criteria: * Patients who are scheduled to receive high-dose chemotherapy in combination with autologous stem cell transplantation as the next treatment. * Patients who have other active double/multiple cancers * Patients on continuous and systemic (oral or intravenous) medication with corticosteroids or other immunosuppressive agents * Patients with graft-versus-host disease that requires treatment. * Patients who underwent a highly invasive and extensive surgical procedure within 2 weeks. * Patients who previously underwent allogeneic stem cell transplantation or organ transplantation. * Patients who underwent autologous stem cell transplantation within 90 days. * Patients with systemic amyloidosis (except localized amyloidosis without organ derangement) or plasma cell leukemia. * Patients with prior or current central nerve involvement in MM. * Patients whose best ever response to MM treatment is PD. * Patients who previously received gene therapy or cell therapy (except hematopoietic stem cell transplantation). * Pregnant women, nursing mothers, or women with a positive pregnancy test.