A Study of Teclistamab in Participants With Relapsed or Refractory Multiple Myeloma

Inclusion Criteria: -

* Documented diagnosis of multiple myeloma according to IMWG diagnostic criteria

* Eastern Cooperative Oncology Group (ECOG) Performance Status score of 0 or 1

* Measurable disease: Cohort A and Cohort C: Multiple myeloma must be measurable by central laboratory assessment

* A female participant of childbearing potential must have a negative pregnancy test at screening

* Willing and able to adhere to the prohibitions and restrictions specified in this protocol

* Cohort A: received at least >=3 prior lines of therapy and previously received a PI, an IMiD and an anti-CD38 monoclonal antibody; Cohort C: received >= 3 prior lines of therapy that included a PI, an IMiD, an anti-CD38 monoclonal antibody, and an anti-B cell maturation antigen (BCMA) treatment (with CART-T cells or an antibody drug conjugate (ADC)

Exclusion Criteria:

* Plasma cell leukemia, Waldenström's macroglobulinemia, POEMS syndrome, or primary amyloid light-chain amyloidosis

* The following medical conditions: Pulmonary compromise requiring supplemental oxygen use to maintain adequate oxygenation, human immunodeficiency virus (HIV) infection, hepatitis B or C infection, stroke or seizure less than or equal to (<=) 6 m, autoimmune disease, uncontrolled systemic infection, cardiac conditions (Myocardial Infarction <= 6 m, stage III-IV congestive heart failure, etc)

* Received any therapy that is targeted to BCMA, with the exception of Cohort C in Part 3

* Prior antitumor therapy, within 21 days (PI or radiotherapy within 14 days, IMiDs within 7 days, Gene modified adoptive cell therapy within 3 months) prior to first dose of study drug

* Toxicities from previous anticancer therapies that have not resolved to baseline or to <= grade 1 (except for alopecia or peripheral neuropathy)

* Received a cumulative dose of corticosteroids equivalent to >=140 mg of prednisone within the 14-day period before the first dose of study drug (does not include pretreatment medication)

* Known active central nervous system (CNS) involvement or exhibits clinical signs of meningeal involvement of multiple myeloma (MM)

* Myelodysplastic syndrome or active malignancies other than relapsed/refractory multiple myeloma with exceptions are: 1) Non-muscle invasive bladder cancer treated within the last 24 months that is considered completely cured 2) Skin cancer (non-melanoma or melanoma) treated within the last 24 months that is considered completely cured. 3) Noninvasive cervical cancer treated within the last 24 months that is considered completely cured. 4) Localized prostate cancer (N0M0) 5) Breast cancer: Adequately treated lobular carcinoma in situ or ductal carcinoma in situ, or history of localized breast cancer and receiving antihormonal agents and considered to have a very low risk of recurrence. 6) Malignancy that is considered cured with minimal risk of recurrence

* Prior allogenic stem cell transplant <=6 months

* Prior autologous stem cell transplant <=12 weeks

* Live, attenuated vaccine within 4 weeks prior to the first dose of teclistamab