Phase 1/2a Study of Belantamab Mafodotin in Relapsed or Refractory AL Amyloidosis

Inclusion Criteria: 1. Participants medically diagnosed with relapsed or refractory Amyloid Light Chain Amyloidosis (AL amyloidosis) with one or more line of treatment as below: 1. Must have received a proteosome inhibitor, alkylator and anti-cluster of differentiation 38 (CD38) antibody (e.g., daratumumab - for patients who were eligible to receive in newly diagnosed AL Amyloidosis) and autologous stem cell transplant (for transplant eligible candidates). OR 2. Failed treatment and/or intolerant/ineligible for above agents NOTE: Patients who fail to achieve Partial Hematological Response or better after 2 cycles of induction therapy for newly diagnosed AL Amyloidosis are also eligible. 2. Participant must be over 18 years of age inclusive, at the time of signing the informed consent. 3. Participant and Disease Characteristics: Patient must have primary systemic AL amyloidosis, histologically confirmed at the initial diagnosis before initiation of 1st-line treatment by positive Congo red stain with green birefringence on polarized light microscopy, Or characteristic appearance by electron microscopy AND confirmatory AL amyloid typing (mass spectrometry-based proteomic analysis or immunofluorescence). 4. Patient must have measurable disease within 28 days prior to registration; serum quantitative immunoglobulins (immunoglobulin G (IgG), immunoglobulin A (IgA), and immunoglobulin M (IgM), serum free kappa and lambda, and serum protein electrophoresis (SPEP) with M-protein quantification must be obtained within 14 days prior to registration. 5. Measurable disease of amyloid light chain amyloidosis as defined by at least One of the following: a. Serum M-protein ≥0.5 g/dL by protein electrophoresis (routine serum protein electrophoresis and immunofixation). b. Serum free light chain ≥50 mg/L with an abnormal kappa: lambda ratio or the difference between the involved and uninvolved free light chains (dFLC) ≥50 mg/L. 6. One or more organs impacted by AL Amyloidosis according to consensus guidelines below per National Comprehensive Cancer Network (NCCN)Guidelines Version 1.2016: a. Cardiac Involvement i. Mean left ventricular wall thickness on echocardiogram greater than or equal to 12 mm in the absence of hypertension or valvular heart disease, OR N-terminal fragment brain natriuretic protein (NT-pro) brain natriuretic peptide (BNP) greater than 332 ng/mL provided that patient does not have impaired renal function (as defined by calculated creatinine clearance less than 25 mL/min) within 14 days prior to registration, OR prior cardiac biopsy (at time of diagnosis) showing amyloid deposition with past documented or presently noted clinical symptoms and signs supportive of a diagnosis of heart failure in the absence of an alternative explanation for heart failure. b. Non-Cardiac Organ Involvement i. Kidney: albuminuria greater than or equal to 500 mg per day on a 24-hour urine specimen within 35 days prior to registration, OR prior kidney biopsy (at the time of diagnosis) showing amyloid deposition. ii. Liver: hepatomegaly (total liver span \> 15 cm) as demonstrated by computed tomography (CT) or magnetic resonance imaging (MRI) within 35 days prior to registration OR alkaline phosphatase (ALP) greater than 1.5 times the institutional upper limit of normal within 14 days prior to registration, OR prior liver biopsy (at the time of diagnosis) showing amyloid deposition. iii. Gastrointestinal tract: direct biopsy verification with symptoms. iv. Lung: biopsy verifications with symptoms and interstitial radiographic pattern. v. Soft tissue: tongue enlargement, clinical, arthropathy, claudication, presumed vascular amyloid, skin involvement, carpal tunnel syndrome, myopathy by biopsy or pseudohypertrophy. 7. Patients must have completed other systemic therapy or investigational drug ≥ 28 days or five half-lives prior to registration, surgery (other than biopsies) ≥ 28 days prior to registration, and any autologous stem cell transplant (ASCT) ≥ 100 days prior to registration. 8. Patients must have a complete medical history and physical exam within 14 days prior to registration. 9. New York Heart Association (NYHA) Class 1 - 3a which has been clinically stable for 56 days before registration 10. Eastern Cooperative Oncology Group (ECOG) performance score 0, 1 or 2 11. Left ventricular ejection fraction (LVEF) by echocardiogram (ECHO) \> 35% within 28 days prior to registration. 12. Adequate organ system functions within 14 days of registration as defined by the laboratory assessments below: a) Hematologic i) Absolute neutrophil count (ANC): ≥1.0 × 10(9)/ L \* ii) Hemoglobin: ≥8.0 g/dL \* iii) Platelets: ≥50 × 10(9)/L \* b) Hepatic i) Total bilirubin: ≤1.5 × upper limit of normal (ULN); (Isolated bilirubin ≥1.5 × ULN is acceptable if bilirubin is fractionated, and direct bilirubin is \<35%) ii) Alanine aminotransferase (ALT): ≤2.5 × ULN c) Renal i) Estimated glomerular rate (eGFRª): ≥30 mL/min/1.73 m2 Note: Laboratory results obtained during Screening should be used to determine eligibility criteria. In situations where laboratory results are outside the permitted range, the investigator may re-test the participant and the subsequent within range screening result may be used to confirm eligibility. \* Without growth factor or cell transfusion support for the past 14 days prior to testing, excluding erythropoietin. ª As calculated by Modified Diet in Renal Disease (MDRD) formula (Appendix 4 in Protocol) 13. Females of childbearing potential: These participants must have a negative baseline pregnancy test using serum or urine within 14 days prior to starting therapy and a confirmatory negative serum pregnancy test with a sensitivity of at least 50 mIU/mL within 72 hours prior to registration; females of childbearing potential must also agree: (1) to have a pregnancy test prior to the start of each treatment cycle and (2) to e