Study to Investigate Alternative Dosing Regimens of Belantamab Mafodotin in Participants With Relapsed or Refractory Multiple Myeloma

Inclusion Criteria:

Participant must be 18 years of age inclusive at the time of signing the informed consent form (ICF).
Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2.
Histologically or cytologically confirmed diagnosis of MM and a. Has undergone stem cell transplant or is considered transplant ineligible, and b. Has failed at least 3 prior lines of anti-MM therapies, including an anti-cluster of differentiation (CD)38 antibody (e.g., daratumumab) alone or in combination and is refractory to an immunomodulatory agent (e.g., lenalidomide, pomalidomide) and a proteasome inhibitor (e.g., bortezomib, ixazomib, carfilzomib).
Participant has measurable disease per modified IMWG criteria.
Life expectancy of at least 6 months, in the opinion of the investigator.
Male and female participants agree to abide by protocol-defined contraceptive requirements.
Participant is capable of giving signed informed consent.
Participant meets country-specific inclusion criteria described in the protocol.

Exclusion Criteria:

Symptomatic amyloidosis, active POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, myeloma protein, and skin changes), or active plasma cell leukemia at the time of screening.
Current corneal epithelial disease, except nonconfluent superficial punctate keratitis (SPK).
Evidence of active mucosal or internal bleeding.
Presence of an active renal condition.
Any serious and/or unstable pre-existing medical condition, psychiatric disorder, or other conditions that could interfere with the participant's safety, obtaining informed consent, or compliance with the study procedures.
Malignancies other than the disease under study, except for any other malignancy from which the participant has been disease free for >2 years and, will not affect the evaluation of the effects of the study treatment on the currently targeted malignancy (MM). Participants with curatively treated non-melanoma skin cancer may be enrolled without a 2-year restriction.
Evidence of cardiovascular risk as per the protocol criteria.
Pregnant or lactating female.
Active infection requiring antibiotic, antiviral, or antifungal treatment.
Known human immunodeficiency virus (HIV) infection, unless the criteria in protocol can be met.
Hepatitis B and C will be excluded unless the criteria in protocol can be met.
Cirrhosis or current unstable liver or biliary disease.
Alanine aminotransferase (ALT) >2.5× upper limit of normal (ULN).
Total Bilirubin >1.5×ULN.
Systemic anti-MM therapy within <=14 days or 5 half-lives, whichever is shorter.
Systemic therapy with high dose steroids within <=14 days before the first dose of study treatment.
Prior allogenic stem cell transplant.
Prior treatment with a monoclonal antibody <=30 days before the first dose of study treatment.
Prior treatment with an anti-B cell maturation antigen (BCMA) targeted therapy or hypersensitivity reactions to any components of the study treatment..
Treatment with an antibody-drug conjugate.
Participant has received any major surgery <=4 weeks before the first dose of study treatment. An exception may be allowed for bone stabilizing surgery after consultation with the GSK medical director.
Inadequate bone marrow reserve or organ functions as demonstrated by any of the following: a. Absolute neutrophil count <1.0×10^9/L, b. Hemoglobin <8 gram/deciliter (g/dL), c. Platelet count <50×10^9/L, d. Spot urine (albumin/creatinine ratio) >500 milligram/gram (mg/g), e. Estimated glomerular filtration rate (eGFR) <30 milliliter per minute per 1.73 meter square (mL/min/1.73m^2).