A Study to Investigate the Safety and Pharmacological Effect of a Single Intravenous Infusion of Belantamab in Male and Female Participants Aged 18 to 75 With Autoimmune Disease

Inclusion Criteria: * Body mass index (BMI) from 18 to 40 kilograms per square meter (kg/m\^2) (BMI = weight/height\^2), inclusive, and body weight of \>=40 kilogram (kg) * IgM \>= lower limit of normal (LLN) (40 milligram per deciliter \[mg/dL\]) at initial screening visit (ISV) Participants with systemic lupus erythematosus (SLE) must also meet the following inclusion criteria: * Documented clinical diagnosis of SLE according to the European League Against Rheumatism (EULAR) or American College of Rheumatology (ACR) Classification Criteria * Positive anti-double stranded deoxyribonucleic acid (anti-dsDNA) autoantibody and/or positive antinuclear antibody (ANA) test results, using central lab test, at ISV. * SLE Disease Activity Index 2000 (SLEDAI-2K) total score of \>=6 at ISV. * Failure to adequately respond to at least two immunosuppressive therapies. Participants with Rheumatoid Arthritis (RA) must also meet the following inclusion Criteria: * Meets ACR/EULAR 2010 RA Classification Criteria with a duration of RA disease of \>=6 months at time of ISV * Positive rheumatoid factor (RF) and/or anti-cyclic citrullinated peptide (anti-CCP) test results, using central lab test, at ISV. * Have moderate to severe active disease as defined by \>=3/68 Tender and \>=3/66 Swollen joint count at ISV and Baseline. * Failure to adequately respond to at least two immunosuppressive therapies. Participants with antiphospholipid syndrome (APS) must also meet the following inclusion criteria: * Documented diagnosis of APS meeting the 2023 ACR/EULAR APS classification criteria * Positive lupus anticoagulant test or moderate to high titers of positive IgG/IgM anticardiolipin (aCL) or moderate to high titers of IgG/IgM anti-beta2-glycoprotein I antibody using central lab test, at ISV * Clinical features attributable to antiphospholipid antibodies that are resistant to warfarin and/or heparin: * Thrombotic event within last 18 months despite adequate anti-coagulation therapy and/or * Persistent thrombocytopenia and/or * Persistent autoimmune hemolytic anemia * Sex and Contraceptive /Barrier requirements for females. Exclusion criteria: SLE specific exclusion: * Any acute, severe lupus related flare during the Screening Period that needs immediate treatment * Has any unstable or progressive manifestation of SLE * Significant, likely irreversible organ damage related to SLE RA specific exclusions: * RA functional status class IV according to the ACR 1991 revised criteria * Adult Juvenile RA APS specific exclusions: * Acute thrombosis (arterial or venous acute thrombosis diagnosis) less than 30 days before study ISV * Catastrophic APS classification within the prior 90 days of ISV