• Patients with newly diagnosed multiple myeloma status post 1st auto-HCT (day 60 - 180 post-transplant).

• Disease status (MRD positive or negative), partial response, or better.

• Age \> 18-year and 75-year. Non-English speaking patients are eligible.

• Karnofsky performance status 70 (Appendix A.).

• Adequate organ function (Please see Table 2. below). Participant agrees to not donate blood while taking lenalidomide and for 28 days after stopping lenalidomide.

• Patient agrees to enroll in the lenalidomide REMS program.

• Woman of child-bearing potential (WOCPB) must abstain from hetersosexual sexual contact or agrees to use a contraceptive method that is highly effective (with a failure rate of \<1% per year), preferably with low user dependency (as described in Appendix C), plus one additional effective method at least 28 days before starting therapy (for lenalidomide), during the intervention period, at least 28 days after the last dose of lenalidomide and at least 4 months after the last dose of belantamab mafodotin, and agrees not to donate eggs (ova, oocytes) for reproduction during this period. The investigator should evaluate the effectiveness of the contraceptive method in relation to the first dose of the study intervention.

⁃ A WOCBP must have a negative highly sensitive serum pregnancy test (as required by local regulations) within 10-14 days and also within 24 hours before the first dose of the study intervention.

⁃ Nonchildbearing potential is defined as follows (by other than medical reasons):

• ≥ 45 years of age and has not had menses for \>1 year.

• Patients who have been amenorrhoeic for \<2 years without a history of a hysterectomy and oophorectomy must have a follicle-stimulating hormone value in the postmenopausal range upon screening evaluation.

• Post-hysterectomy, post-bilateral oophorectomy, or post-tubal ligation. 9. Male participant agrees to contraceptive use that should be consistent with institutional guidelines regarding the methods of contraception for those participating in clinical studies.

⁃ Male participants are eligible to participate if they agree to the following during the intervention period and for 6 months after the last dose of study treatment to allow for clearance of any altered sperm:

⁃ • Refrain from donating sperm during treatment (including dose interruptions) and for 4 weeks after their last dose of lenalidomide.

⁃ PLUS, either:

⁃ • Be abstinent from heterosexual intercourse as their preferred and usual lifestyle (abstinent on a long term and persistent basis) and agree to remain abstinent.

⁃ OR Must agree to use contraception/barrier as detailed in Appendix C.

⁃ • All prior auto-HCT- related toxicities (defined by National Cancer Institute - Common Toxicity Criteria for Adverse Events (NCI-CTCAE), version 5 must be ≤ Grade 1 at the time of enrollment except for alopecia, fatigue, and amenorrhea.