Inclusion Criteria:

1. MM which initially required a systemic therapy and received a first line treatment, conventional doses of chemotherapies or high dose chemotherapy and an autologous transplantation of hematopoietic cells, followed or not by a consolidation treatment.

2. Residual disease considered as evaluable with:

   • Quantifiable serum M-protein: ≥ 3 g/l, except for spike in the beta globulin area. In this particular case serum M-protein is considered quantifiable if ≥ 10g/l
   • If serum M-protein is < 3g/l, measurable involved Free Light Chains ≥ 100 mg/l and an abnormal Free Light chains ratio (<0.26 or > 1.65)

3. Responses which are partial (PR and VGPR) and in plateau

   • Partial response should meet the IMWG uniform response criteria: a ≥ 50% reduction from value of serum M-protein before the first line chemotherapy treatment and a reduction in 24h urinary M-protein by ≥ 90% or to < 200 mg /24h;
   • Very good partial response according to the IMWG uniform response criteria with 90% or greater reduction in serum M-protein plus urine M-protein level < 100 mg/24h; furthermore the M-protein should spike in the gamma globulin area;

   • Plateau phase is defined by :

     • For patients with serum M-protein ≥ 3g/l: stable levels of M-protein in serum during at least 2 months checked on at least 3 consecutive samples, with the third evaluation performed within 4 weeks before study entry. Fluctuations of ± 25 % and ± 2 g/l in Serum M-protein levels are allowed.
     • For Patients with serum M-protein < 3g/l: stable levels Free Light Chains in serum during at least 2 months checked on at least 3 consecutive samples, with the third evaluation performed within 4 weeks before study entry. Fluctuations of ± 25 % of involved serum Free Light Chain are allowed.
4. ECOG performance status of 0, 1 or 2.

5. Clinical laboratory values at screening:

   • Calculated creatinine clearance (according to MDRD) > 50 ml/min
   • Platelet > 50 x 109 /l
   • ANC > 1 x 109 /l
   • Bilirubin levels < 1.5 ULN; ALT and AST < 2.5 ULN
6. Male or female patient who accepts and is able to use recognised effective contraception (oral contraceptives, IUCD, barrier method of contraception in conjunction with spermicidal jelly) throughout the study.
7. Signed inform consent obtained before any trial-related activities

Exclusion Criteria:

1. Age < 18 years old or > 75 years old
2. Previous consolidation/ maintenance therapy by Imid (thalidomide, lenalidomid) or bortezomib within the last 2 months
3. Treatment with chemotherapy, systemic corticosteroid within the previous 2 months
4. Treatment with growth factors (EPO, G- or GM-CSF) within the previous 1 month
5. Radiotherapy for bone or visceral lesion within the last 3 months
6. Use of any investigational agent within the last 2 months
7. Primary or associated amyloidosis
8. Peripheral neuropathy of grade ≥ III according to the CTCAE of the NCI

9. Abnormal cardiac status with any of the following

   1. NYHA stage III or IV congestive heart failure
   2. myocardial infarction within the previous 6 months
   3. symptomatic cardiac arrhythmia despite treatment
10. Current active infectious disease or positive serology for HIV, HCV or positive Hbs Antigen
11. History of or current auto-immune disease
12. Serious concurrent uncontrolled medical disorder
13. History of other malignancy for less then 5 years (apart from basal cell carcinoma of the skin, or in situ cervix carcinoma)
14. History of allogenic hematopoietic cell or solid organ transplantation
15. Pregnant or lactating women
16. Any medical condition which is regarded by the investigator as incompatible with the study participation
17. Any psychological, familial, sociological or geographical condition potentially hampering compliance with the study protocol and follow-up schedule