Dendritic Cell / Multiple Myeloma Fusion Vaccine

This research is being done to determine if the combination of the Dendritic Cell (DC)/ Multiple Myeloma (MM) fusion vaccine with elranatamab is safe and effective in treating Relapsed or Refractory Multiple Myeloma (MM). The names of the study drugs and vaccine involved in this study are: * DC/MM fusion vaccine (a personalized cancer vaccine in which harvested participant tumor cells are fused with harvested participant dendritic blood cells) * Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF) (a type of growth factor) * Elranatamab (a type of T-cell engager antibody)