Single-arm Study of IgPro20 in Adults With Secondary Immune Deficiencies Due to Hematologic Malignancies Treated With B-cell Targeting Chimeric Antigen Receptor T-cell and T-cell Redirecting Therapies

Inclusion criteria

• Participants greater than or equal to (≥) 18 years of age at the time of providing written informed consent.
• Confirmed diagnosis of B-cell hematologic malignancy (ie, Multiple myeloma \[MM\], Chronic lymphocytic leukemia \[CLL\], Non-Hodgkin lymphoma \[NHL\], or BALL) according to applicable diagnostic criteria.
• Participants treated with Chimeric antigen receptor T-cell (CAR T-cell) therapy or TCE BsAb and are:
• At least 2 months after receipt of an approved CAR T-cell therapy for the B-cell hematologic malignancy at the time of Screening, or
• At least 1 month after initiation of an approved TCE BsAb therapy for the B-cell hematologic malignancy at the time of Screening and expected to continue with the therapy.
• Documented partial or complete response to CAR T-cell or TCE BsAb therapy based on applicable response criteria at the time of Screening:
• CLL based on International Workshop on Chronic Lymphocytic Leukemia response criteria
• MM based on International Myeloma Working Group response criteria
• NHL based on Lugano Classification criteria
• B-ALL based on National Comprehensive Cancer Network guidelines
• IgG level (excluding paraprotein, if relevant) at Screening: If participant has ongoing IgRT (intravenous immunoglobulin \[IVIG\] or subcutaneous immunoglobulin \[SCIG\]) for SID during Screening, then any IgG level at Screening is acceptable for enrollment. Participants with IgG less than (\<) 500 milligrams per deciliter (mg/dL) are assigned to the Loading Cohort, participants with IgG ≥ 500 mg/dL are assigned to the Maintenance-only Cohort.
• IgG level (excluding paraprotein, if relevant) at Screening: If participant does not have ongoing IgRT (IVIG for \> 8 weeks or SCIG for \> 2 weeks) for SID during Screening and are not expected to receive IgRT during Screening, then IgG \< 500 mg/dL is required for enrollment (participant is assigned to the Loading Cohort)

Exclusion criteria

• Documented history of diseases for which IgRT may be indicated: primary immune deficiency, chronic inflammatory demyelinating polyneuropathy, Guillain-Barré syndrome, immune thrombocytopenia, Kawasaki disease, Lambert-Eaton myasthenic syndrome, multifocal motor neuropathy, myasthenia gravis, stiff person syndrome, solid organ transplant, and rejection prior to Screening.
• History of thromboembolic event (TEE) within 6 months before Screening.
• Eastern Cooperative Oncology Group performance status \> 1.
• Presence of any systemic active infection at Screening.
• Participants on any prohibited therapies, including anti-infective treatments.
• Absolute neutrophil count \< 1 × 10\*9/L (Common Terminology Criteria for Adverse Events \[CTCAE\] Grade 3 or worse), unless proven to be due to the underlying disease and raised above the limit by granulocyte colony-stimulating factor.
• Concurrent participation in other interventional clinical studies. Note: a participant may be enrolled if their participation in the other study will not jeopardize their safety and / or the scientific validity of this study (eg, an observational study, a long-term safety follow-up of an interventional study, diagnostic device studies, phase 4 studies with medicines used within their approved indication); the investigator may consult with the medical monitor.