• Be ≥18 years of age (or the legal age of consent in the jurisdiction in which the study is taking place) at the time of informed consent.

• High-risk SMM defined as having 1 of the following 2 criteria: i) High-risk per Mayo 20-2-20 criteria defined as presence of any ≥2 of the following:

⁃ Serum M-protein ≥2 gm/dL

⁃ Involved to uninvolved FLC ratio ≥20

⁃ BMPC % ≥20% to \<40% OR ii) Presence of ≥95% of BMPC with an aberrant phenotype within the BMPC compartment and immunoparesis present defined as a reduction of at least 25% below the lower normal limit for ≥1 uninvolved immunoglobulin isotype (only IgG, IgA and IgM will be considered).

∙ Have an Eastern Cooperative Oncology Group (ECOG) Performance Status of ≤1.

∙ Have an estimated glomerular filtration rate (eGFR), based on the Modified Diet in Renal Disease (MDRD) 4-variable formula or 24-hour urine collection of ≥40 mL/min during the screening period.

∙ Laboratory values obtained \<21 days prior to Screening: i) Total bilirubin ≤2.0 mg/dL ii) Aspartate aminotransferase (AST) ≤3 x upper limit of normal (ULN) iii) Alanine transaminase (ALT) ≤3 x ULN

∙ Hemoglobin ≥8.0 g/dL (≥5 mmol/L) (without prior red blood cell \[RBC\] transfusion within 7 days before the laboratory test; recombinant human erythropoietin use is permitted). For subjects who meet the inclusion criteria at screening, transfusion of RBCs is permitted after screening as needed to maintain a hemoglobin level ≥8.0 g/dL.

∙ Neutrophils ≥1.0 × 109/L (prior growth factor support is permitted but must be without support in the 7 days prior to the laboratory test)

∙ Platelets ≥75 × 109/L (must be without transfusion support in the 7 days prior to the laboratory test)

∙ Lymphocyte count ≥0.3\*109/L

∙ Participants should be seronegative for human immunodeficiency virus (HIV) or have controlled disease if seropositive.

∙ A female participant of childbearing potential must have a negative serum pregnancy test at screening and within 72 hours of the first dose of study treatment and must agree to further serum or urine pregnancy tests during the study.

∙ A female participant must be either of the following: i) Not of childbearing potential ii) Of childbearing potential and practicing at least 1 highly effective method of contraception throughout the study and through 6 months after the last dose of study treatment. If a female participant becomes of childbearing potential after the start of the study, the female participant must comply with ii).

∙ A female participant using oral contraceptives should use an additional barrier contraceptive method.

∙ A female participant must agree not to donate eggs (ova, oocytes) or freeze for future use for the purposes of assisted reproduction during the study and for a period of 6 months after receiving the cilta-cel infusion. Female participants should consider preservation of eggs prior to study treatment as anti-cancer treatments may impair fertility.

‣ A male participant must wear a condom when engaging in any activity that allows for passage of ejaculate to another person during the study and for 1 year after receiving the cilta-cel infusion. If the male participant's partner is a female of childbearing potential, the male participant must use condoms (with or without spermicide) and the female partner of the male participant must also be practicing a highly effective method of contraception. A male participant who is vasectomized must still use a condom (with or without spermicide), but the partner is not required to use contraception.

‣ A male participant must agree not to donate sperm for the purposes of reproduction during the study and for 1 year after receiving the last dose of study treatment. Male participants should consider preservation of sperm prior to study treatment as anti-cancer treatments may impair fertility.

‣ A male participant must agree not to plan to father a child while enrolled in this study or within 1 year after the last dose of study treatment.

‣ Must sign an informed consent form (ICF) indicating that the participant understands the purpose of, and procedures required for, the study and is willing to participate in the study

‣ An additional ICF will be collected to get participants authorization to collect the necessary samples for performing the Biological studies indicated in this protocol.

‣ Be willing and able to adhere to the lifestyle restrictions specified in this protocol.