Inclusion Criteria:

          -  Documented diagnosis of relapsed/refractory multiple myeloma (MM) with measurable
             disease (serum, urine, or free light chain [FLC]) per International Myeloma Working
             Group (IMWG) criteria

          -  At least 3 prior lines of MM therapy, including a proteasome inhibitor,
             immunomodulatory agent, and anti-CD38 antibody (unless contraindicated), and
             refractory to the last treatment line.

          -  Eastern Cooperative Oncology Group (ECOG) 0 or 1

          -  Absence of donor (product)-specific anti-HLA antibodies

          -  Adequate hematologic, renal, hepatic, pulmonary, and cardiac function

        Exclusion Criteria:

          -  Current or history of Central Nervous System (CNS) involvement of myeloma or plasma
             cell leukemia

          -  Clinically significant CNS disorder

          -  Current or history of thyroid disorder

          -  Autologous stem cell transplant within the last 6 weeks, or any allogeneic stem cell
             transplant

          -  Prior treatment with anti-BCMA therapy, any gene therapy, any genetically modified
             cell therapy, or adoptive T cell therapy

          -  History of HIV infection or acute or chronic active hepatitis B or C infection

          -  Patients unwilling to participate in an extended safety monitoring period

        Additional Exclusion Criteria for Nirogacestat plus ALLO-715 Cohorts

          -  Inability to swallow tablets

          -  Subject has known malabsorption syndrome or preexisting gastrointestinal conditions
             that may impair absorption of nirogacestat

          -  Use of strong/moderate CYP3A4 inhibitors, and strong CYP3A4 inducers within 14 days
             before starting nirogacestat.

          -  Use of concomitant medications that are known to prolong the QT/QTcF interval