A Study of Modakafusp Alfa on Adult Participants With Relapsed/Refractory Multiple Myeloma

The main aims of this 3-part study are as follows: Part 1: To determine any side effects from modakafusp alfa single treatment and how often they occur. The dose of modakafusp alfa will be increased a little at a time until the highest dose that does not cause harmful side effects is found. Part 2: To assess clinical activity of one or more dosing schedules of modakafusp alfa alone in participants with relapsed/refractory multiple myeloma. Dexamethasone standard dose will be administered with one or more selected dose of modakafusp alfa in selected group of participants. Part 3: To find the optimal dose with the more favorable risk-benefit profile of modakafusp alfa. Participants will receive modakafusp alfa at one of two doses which will be given through a vein.