This study looks at HDP-101, a new treatment for people with relapsed refractory multiple myeloma, a type of blood cancer. The study has two parts: the first finds a safe dose, and the second tests how well it works. Participants must be 18 or older and have tried other treatments that no longer work for them. They also need to be healthy enough to participate, with good organ function, and not have other serious health issues like active infections or recent cancer treatments.

• The study includes two phases: dose finding and expansion to test safety and effectiveness.
• Participants must have tried other treatments and be healthy enough to join.
• Exclusion criteria include other active cancers or infections.

This study helps researchers learn about HDP-101's safety and potential benefits for multiple myeloma patients.