A Study of Melphalan With or Without Siltuximab in People With Multiple Myeloma Having an Autologous Stem Cell Transplant

Inclusion Criteria: * Histologically-confirmed symptomatic multiple myeloma undergoing autologous HCT with plan off study for melphalan 140 or 200 mg/m2 undergoing HCT within 12 months of diagnosis. * At least 60 years of age * Have at least 3 million x 10\^6 CD34+ cells/kg to be infused * KPS performance status \>60% or ECOG Performance Status score of 0-2 Within 6 weeks prior to enrollment: * Diffusion capacity \>45% (adjusted for hemoglobin) as predicted by pulmonary function testing. * LVEF \>45% by MUGA or rest ECHO * Clinical laboratory values meeting the following criteria * Platelet count ≥ 20 x 10\^9/L * ALT and AST ≤ 2.5 x ULN o Total bilirubin ≤ 2.5 x ULN; except if the elevation is due to Gilbert's syndrome * Calculated creatinine clearance \> 40 mL/min * Before enrollment, all women are expected to be not of childbearing potential as they will be age 60+. * A man who is sexually active with a woman of childbearing potential and has not had a vasectomy must agree to use a barrier method of birth control eg, either condom with spermicidal foam/gel/film/cream/suppository or partner with occlusive cap (diaphragm or cervical/vault caps) with spermicidal foam/gel/film/cream/suppository, and all men must also not donate sperm during the study and for 3 months after receiving the last dose of study drug Exclusion Criteria: * Prior exposure to agents targeting IL-6 or the IL-6 receptor * Other malignancy within the past 2 years, except for the following if tre…