Melphalan With or Without Siltuximab

The purpose of this study is to see if siltuximab plus population pharmacokinetic (PK)-dosed melphalan works as well as the usual approach (body surface area \[BSA\]-dosed melphalan) in people with multiple myeloma (MM) who are receiving an autologous stem cell transplant (ASCT) as part of their standard treatment. The researchers will also see if siltuximab in combination with population PK-dosed melphalan works to decrease symptoms after an ASCT, and will study the safety of siltuximab. For the run-in, 15 patients will receive siltuximab, 11 mg/kg, seven days before and 14 days after autologous hematopoietic stem cell infusion (+/-2 day).