Evaluation of Tumor Vaccine Generation in a Phase II Multicenter Trial of Single Autologous Hematopoietic Cell Transplant (AutoHCT)Followed By Lenalidomide Maintenance for Multiple Myeloma (MM) with or without Vaccination with Dendritic Cell/ Myeloma Fusions (DC/MM fusion vaccine): Blood and Marrow Transplant Clinical Trials Network (BMT CTN) 1401