A Study to Assess Change in Disease Activity and Adverse Events (AE)s in Adult Participants With Immunoglobulin Light Chain (AL) Amyloidosis Receiving Etentamig (ABBV-383) as an Intravenous (IV) Infusion

Age

18–any

Sex

ALL

Healthy volunteers

Not accepted

Diagnosis of primary systemic immunoglobulin light chain (AL) amyloidosis.
Eastern Cooperative Oncology Group (ECOG) performance status of \<= 2.
Have at least 1 organ historically impacted by AL amyloidosis.
Considered AL amyloidosis cardiac risk stage 1, 2, or 3a, or considered risk stage 3b with stable cardiac function and markers for 3 months prior to dosing, and have measurable disease of AL amyloidosis as defined by difference between involved and uninvolved free light chains (dFLC) \>= 50 mg/L or meeting high-risk dFLC progression criteria after immediate prior line of therapy.
Has previously been exposed to a proteasome inhibitor (PI) and an anti-CD38 monoclonal antibody.

Known history of clinically significant (per investigator's judgment) drug or alcohol abuse within the last 6 months.
Known allergic reaction, significant sensitivity, or intolerance to constituents of the study treatment (and excipients) and/or other products in the same class.
Participant has the following conditions:
* Other non-AL amyloid disease;
* Previous or current diagnosis of symptomatic multiple myeloma (MM), including the presence of lytic bone disease, plasmacytomas, \>= 60% plasma cells in the bone marrow, or hypercalcemia (defined as corrected calcium \> 11 mg/dL);
* Active plasma cell leukemia (i.e., either 20% of peripheral white blood cells or \> 2.0 × 109/L circulating plasma cells by standard differential);
* Waldenström's macroglobulinemia;
* Acute diffuse infiltrative pneumopathy;
* Major surgery within 28 days prior first dose or planned during study participation;
* History of organ transplant requiring continued use of immunosuppressants;
* Acute infections within 14 days prior first dose requiring parenteral therapy (antibiotic, antifungal, or antiviral);
* Participant has received an autologous stem cell transplant (SCT) within 12 weeks or an allogeneic SCT within 1 year of the first dose of study treatments.