A Study to Evaluate a Novel Gene Therapy in Patients With Relapsed and Refractory Multiple Myeloma

• KLN-1010 (Drug): Given at specified dose one time

Primary outcomes

• Incidence and severity of treatment-emergent adverse events (TEAEs), including dose-limiting toxicities (DLTs), and/or establish the recommended Phase 2 Dose [Up to 15 years from dosing of KLN-1010]: All adverse events will be graded according to Common Terminology Criteria for Adverse Events (CTCAE) or American Society for Transplantation and Cell Therapy (ASTCT) criteria

Secondary outcomes

• Pharmacokinetics of KLN-1010 after dosing. [Up to two years after dosing with study drug.]: Peak of virus vector genomes (Cmax of lentivirus) in blood.
• Pharmacokinetics of KLN-1010 (Tmax). [Up to two years after infusion with study drug.]: Measurement of time to the highest amount of viral vector in the blood.
• Pharmacokinetics of KLN-1010 Area Under the Curve (AUC) [Up to two years after infusion with study drug.]: Measurement of the amount of viral vector (AUC of lentivirus) in blood over time.
• Pharmacokinetics of CAR-T cells generated. [Up to two years after infusion with study drug.]: The presence and number of CAR-T (Cmax) cells present in blood.
• Pharmacokinetics of CAR-T cells generated (Tmax). [Up to two years after infusion with study drug.]: Measurement of time to the highest amount of CAR-T cells in the blood.
• Pharmacokinetics of CAR-T cells generated Area Under the Curve (AUC) [Up to two years after infusion with study drug.]: Measurement of the amount of CAR-T cell DNA in blood and bone marrow over time.
• Assessment of Multiple Myeloma [From dosing until disease progression or up to 15 years from receiving study drug, whichever happens first.]: Participants will have multiple myeloma assessed according to the International Myeloma Working Group (IMWG) response criteria.

Sex: All, ages: 18 Years to any

Inclusion Criteria:

* Participants must have relapsed and refractory multiple myeloma (RRMM) with measurable disease
* Participants must have received at least 3 prior lines of therapy including a proteasome inhibitor (PI), an immunomodulatory drug (IMiD), and CD38-directed monoclonal antibody
* Participants must have an Eastern Cooperative Group (ECOG) performance status of 0-1
* Participants must have acceptable laboratory values as defined by the protocol

Exclusion Criteria:

* Participants must not have known central nervous system (CNS) involvement with myeloma
* Participants cannot have plasma cell leukemia, Waldenstrom's macroglobulinemia, POEMS (polyneuropathy, organomegaly, endocrinopathy, and skin changes) syndrome, or primary light chain amyloidosis
* Participants cannot have ongoing acute systemic infection requiring antimicrobial therapy
* Participants cannot require systemic steroids for any condition