• Age ≥18 years.

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

⁃ - Serum M spike ≥ 2 gm/dL, Involved to uninvolved free light chain (FLC) ratio≥ 20, Bone marrow Plasma Cell (BMPC) % ≥ 20%

• OR total score of 9 using the following scoring system:

‣ FLC Ratio \>10-25 = 2, \>25-40 = 3, \> 40 = 5

⁃ Serum M-Protein (g/dL) \>1.5-3 = 3, \>3 = 4

⁃ BMPC% \>15-20 = 2, \>20-30 = 3, \>30-40 = 5, \>40 = 6

• Fluorescence In Situ Hybridization (FISH) abnormality (t(4,14), t(14,16), 1q gain, or del13q = 2

• 2) Presence of ≥10% BMPC and at least one of the following:

⁃ - Evolving pattern:

⁃ evolving Monoclonal Protein (eMP) (≥10% increase in Monoclonal Protein/Immunoglobulin (Ig)) within the first 6 months (only if M-protein ≥3 g/dl) and/or ≥25% increase in M/Ig within the first 12 months, with a minimum required increase of 0.5 g/dl in M-protein and/or 500 mg/dl in Ig.

⁃ Evolving change in hemoglobin (eHb) ≥0.5 g/dl decrease within 12 months of diagnosis;

⁃ Progressive involved light chain increase on two successive evaluation

⁃ Abnormal Plasma Cell immunophenotype (≥ 95% of BMPCs are clonal) and reduction of ≥1 uninvolved immunoglobulin isotype. (Only IgG; IgA and IgM will be considered)

⁃ High risk cytogenetics defined as presence of t(4;14), t(14;16), t(14;20), 17p deletion, TP53 mutation, 1q21 gain

• No evidence of CRAB criteria\* or new criteria of active MM (SLIM-CRAB) which include the following:

‣ Increased calcium levels: Corrected serum calcium \>0.25 mmol/L (\>1mg/dL) above the upper limit of normal or \>2.75 mmol/L (\>11mg/dL);

⁃ Renal insufficiency (attributable to myeloma);

⁃ Anemia (Hgb 2g/dL below the lower limit of normal or \<10g/dL);

⁃ Bone lesions (lytic lesions or generalized osteoporosis with compression fractures)

⁃ No evidence of the following new criteria for active MM including the following:

• Bone marrow plasma cells \>60%

∙ Serum involved/uninvolved FLC ratio ≥100

∙ MRI with more than one focal lesion

• Participants with CRAB criteria that are attributable to conditions other than the disease under study may be eligible after discussion with the Sponsor Investigator.

• Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) 0, 1, or 2

• The following laboratory values obtained \<28 days prior to registration:

‣ Absolute Neutrophil Count (ANC) \>1000/mL

⁃ Platelets Count (PLT) \>75,000/mL

⁃ Total bilirubin ≤ 2.0 mg/dL (If total is elevated check direct and if normal patient is eligible.)

⁃ Aspartates Aminotransferase (AST) \<2.5 x institutional upper limit of normal (ULN)

⁃ Alanine Transaminase (ALT) \<2.5 x institutional upper limit of normal (ULN)

⁃ Estimated creatinine clearance (CLcr) ≥60 mL/min (Cockcroft Gault equation).

• Voluntary written informed consent will be obtained before performance of any study-related procedure not part of normal medical care, with the understanding that consent may be withdrawn by the subject at any time without prejudice to future medical care.

• Females of child-bearing potential\* randomized to Lenalidomide must have a negative serum or urine pregnancy test with a sensitivity of at least 50 mIU/mL within 10 - 14 days and again within 24 hours prior to prescribing lenalidomide for Cycle 1 (prescriptions must be filled within 7 days as required by Revlimid Risk Evaluation and Mitigation Strategies (REMS®) and must either commit to continued abstinence from heterosexual intercourse or begin TWO acceptable methods of birth control, one highly effective method and one additional effective method AT THE SAME TIME, at least 28 days before she starts taking lenalidomide.

‣ A female of child-bearing potential is a sexually mature female who: has not undergone a hysterectomy (the surgical removal of the uterus) or bilateral oophorectomy (the surgical removal of both ovaries), or has not been naturally postmenopausal (amenorrhea following cancer therapy does not rule out childbearing potential) for at least 24 consecutive months (i.e., has had menses at any time during the preceding 24 consecutive months)

⁃ A woman must be . A Not of childbearing potential, or b. Of childbearing potential and Practicing true abstinence; or Have a sole partner who is vasectomized; or Practicing ≥1 highly-effective, user-independent method of contraception NOTE: Participant must agree to continue the above throughout the study and for 90 days after the last dose of study treatment.

⁃ NOTE: If a woman becomes of childbearing potential after start of the study the woman must comply with point (b) as described above.

⁃ NOTE: An interaction between hormonal contraception and teclistamab has not been formally studied. Therefore, it is unknown whether teclistamab may reduce the efficacy of the contraception method.

• A woman must agree not to donate eggs (ova, oocytes) or freeze for future use, for the purposes of assisted reproduction during the study and for 90 days after receiving the last dose of study treatment

• A man must wear a condom (with or without spermicidal foam/gel/film/cream/suppository) when engaging in any activity that allows for passage of ejaculate to another person during the study and for a minimum of 90 days after receiving the last dose of study treatment. If a female partner is of childbearing potential, she must also be practicing a highly effective method of contraception

• If the male participant is vasectomized, he still must wear a condom (with spermicidal foam/gel/film/cream/suppository), but his female partner is not required to use contraception.

• A male participant must agree not to donate sperm for the purpose of reproduction during the study and for a minimum of 90 days after receiving the last dose of study treatment.

• Must be willing and able to adhere to the lifestyle restrictions specified in this protocol

• All study participants randomized to lenalidomide must be registered into the mandatory Revlimid REMS® program and be willing and able to comply with the requirements of the REMS® program.

• Females of child-bearing potential must adhere to the scheduled pregnancy testing as required in the Revlimid REMS® program if randomized to lenalidomide

• Men must agree to use a latex condom during sexual contact with a female of childbearing potential even if they have had a successful vasectomy

• Ability to understand and the willingness to sign a written informed consent.