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.