The purpose of this study is to evaluate the tolerability,safety and efficacy of OPC-415 in patients with relapsed and/or refractory Multiple Myeloma (MM).

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.

:The focus of this study is a rare disease.