Alnuctamab for Refractory SLE (LATTE Study)

Key Inclusion Criteria: * Age 18-60 years. * Documented diagnosis of SLE fulfilling 2019 ACR/EULAR criteria. * Historical documentation of ANA (1:80 or greater) autoantibody on immunofluorescence as well as presence of at least 1 additional autoantibody of the type: anti-dsDNA, anti-histone, anti-chromatin, anti-Smith, anti-RNP, anti-Ro/SSA, anti-La/SSB, anti-cardiolipin (IgG), or anti-beta2-glycoprotein1 (IgG). * History of SLE that is refractory to corticosteroids and at least 2 immunosuppressive therapies with different mechanisms of action (methotrexate, thiopurines, mycophenolate mofetil, calcineurin inhibitors, biologic agents, cyclophosphamide), including at least one biologic therapy (e.g. anti-CD20 therapy, anifrolumab, belimumab) or cyclophosphamide. Of note, hydroxychloroquine is not considered an immunosuppressive therapy, and methotrexate/azathioprine counts as a single drug class). * Total SLEDAI-2K \>6 with clinical SLEDAI-2K \>4, or \>1 BILAG A organ domain score, or \>2 BILAG B, but without active central nervous system (CNS) disease within the past year; a maximum of two participants with only arthritis and/or rash can be included if truly disabling Key Exclusion Criteria: * Autoimmune disease other than SLE, except associated Sjogren's Disease if not primary contributor to symptoms; coexistent fibromyalgia will be allowed if not primary contributor to symptoms. * TTP-like SLE; catastrophic APS; LN WHO class V as primary qualifying criterion (unless overlap with Class III or IV), rapidly progressive LN, or eGFR \<40 mL/min; active CNS pathology attributable to neuropsychiatric SLE. * Active or suspected infection, including HIV. * O2 sat \<92% on room air; ANC \<1500u/L, Hgb \<8g/dL, Plt \<75,000/uL; ALT or AST \> 2X ULN (unless attributed to active myositis), Total Bilirubin \>1.5 X ULN (unless Gilbert's Disease), total B cell count \<12/microliter, hypogammaglobinemia \<500mg/dL.