Antithymocyte Globulin and Sirolimus in Treating Patients With Relapsed Multiple Myeloma

DISEASE CHARACTERISTICS: * Previously diagnosed multiple myeloma (MM) based on standard criteria * Soft tissue (not bone only) plasmacytomas allowed * Measurable disease, meeting both of the following criteria: * Monoclonal population of plasma cell in the bone marrow * Quantifiable serum and/or urine monoclonal protein (i.e., generally, but not exclusively, IgG \> 1 g/dL, IgA \> 0.5 g/dL, or urine light-chain excretion ≥ 200 mg/24 hours) * Steroid-refractory disease, defined as less than a minimum response to prior high-dose glucocorticoid therapy * Minimal response requires all of the following criteria: * 25-49% reduction in the level of serum monoclonal paraprotein maintained for ≥ 6 weeks * 50-89% reduction in 24-hour urinary light-chain excretion, but still \> 200 mg/24 hours, maintained for ≥ 6 weeks * 25-49% reduction in the size of soft tissue plasmacytomas (clinically or by CT scan or MRI) * No increase in size or number of lytic bone lesions * High-dose glucocorticoid therapy defined as 480 mg dexamethasone (or equivalent) alone or as part of a vincristine, doxorubicin, and dexamethasone regimen * Must have undergone autologous transplantation OR received ≥ 2 conventional lines of therapy * Currently requiring therapy for progressive disease, as indicated by any of the following criteria: * 25% increase in paraprotein * Development of new or progression of pre-existing lytic bone lesions or soft tissue plasmacytomas * Hypercalcemia not attributable to any other cause * Relapse from complete remission * No nonsecretory MM PATIENT CHARACTERISTICS: * Zubrod performance status 0-2 * 3-4 allowed if, in the opinion of the investigator, secondary to MM-related bone pain * Life expectancy ≥ 3 months * Creatinine ≤ 1.5 times upper limit of normal (ULN) * AST and ALT ≤ 2.5 times ULN * Bilirubin ≤ 1.5 times ULN * Calcium \< 14 mg/dL * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception * HIV negative * Hepatitis B surface antigen and hepatitis C antibody negative * No known history of allergy to rabbit proteins * No history of cardiac amyloidosis * No poorly controlled hypertension, diabetes mellitus, coronary artery disease, or other serious medical or psychiatric illness * No myocardial infarction within the past 6 weeks * No New York Heart Association class III or IV heart failure * No uncontrolled angina * No severe uncontrolled ventricular arrhythmias * No evidence of acute ischemia or active conduction system abnormality by electrocardiogram * No active systemic infection requiring treatment unless adequately controlled with appropriate antimicrobial therapy (e.g., treated central line infection) * No acute viral illness * No pathologic fractures or symptomatic hyperviscosity * No other prior malignancy except adequately treated basal cell or squamous cell skin cancer, cervical cancer in situ, or any other cancer with a disease-free status for ≥ 3 years PRIOR CONCURRENT THERAPY: * See Disease Characteristics * At least 8 weeks since prior immunotherapy or antibody therapy * At least 4 weeks since prior major surgery (except for kyphoplasty) * At least 3 weeks since prior conventional chemotherapy or radiotherapy for MM * At least 3 weeks since prior bortezomib, thalidomide, or clarithromycin for MM * No prior anti-thymocyte globulin * No concurrent radiotherapy * No other concurrent antineoplastic therapy with known activity against MM, including clarithromycin * No other concurrent investigational agents