This clinical trial is looking at a new gene therapy for people with relapsed and refractory multiple myeloma, a type of blood cancer. "Relapsed" means the cancer has come back after treatment, and "refractory" means it didn't respond to treatments. The study aims to find out if the therapy is safe and how much of it should be given in the next phase of research. To join, patients need to have tried at least three different treatments before, including specific types of cancer drugs. They should also be in good overall health and not have other serious health issues like infections or certain other types of cancer. People who have cancer affecting their brain or need regular steroid medications cannot participate. If you're eligible, you might help researchers learn more about this potential new treatment for multiple myeloma.

• The study checks a new treatment's safety and proper dosing.
• Participants must have tried at least three prior treatments for multiple myeloma.
• Certain health conditions might prevent participation.