The purpose of this study is to assess the safety of the study drug, talquetamab when administered with carfilzomib for patients with multiple myeloma. This study also aims to identify the safe dose(s) of the study drug combination, as well as how long talquetamab stays in the body and how this combination fights the cancer.

Talquetamab is a bispecific antibody (an antibody that can bind to two different things bringing them together) that has two arms: one targets a protein on myeloma cells called GPRC5D and another targets CD3, a cluster of proteins that is expressed on T-cells in the body. Talquetamab is considered experimental which means that it is not yet approved by the United States Food and Drug Administration (FDA).

Carfilzomib is an anti-tumor drug that works by stopping or slowing the growth of tumor cells. The group of drugs that carfilzomib belongs to are called proteasome inhibitors. Inhibiting proteasome pathways can delay cell proliferation and kill some cancer cells. Carflizomib is approved by the FDA for the treatment of multiple myeloma.

Medication will be given in 28-day cycles. The study team will discuss and determine the dosing schedule for participants. Talquetamab is administered subcutaneously with a short needle injected under the skin and carflizomib is administered intravenously through an IV into a vein.

Study participation length will vary from participant to participant and may last as long as the study drug is beneficial, or the study team feels that someone should stop participating. Participation also includes hospital stays for initial drug administration during the first cycle, as well as study visits for health exams and tests during future cycles.