Patients randomized into the arm blind A. Rituximab is allowed as additional treatment from J12, within the limit of 2 infusions of rituximab. In case of insufficient efficacy of the treatment of acute humoral rejection, investigators may propose an additional infusion of rituximab from J12, without patient withdrawn. In this case (2nd infusion effective in group A and 1st infusion effective group B), a additional consultation (CS) will be provided as part of the study 7 days after infusion. In case of insufficient efficacy of the treatment,in fairness to care for patients between the 2 treatment groups, the investigators may propose to a 3rd infusion patients in group B (2nd infusion effective for this group). To prevent patients from group A will receive a 3rd infusion of rituximab, unblinding will be applied in this case by the investigator before the administration of additional treatment with rituximab.

Patients randomized into the arm blind B. Rituximab is allowed as additional treatment from J12, within the limit of 2 infusions of rituximab. In case of insufficient efficacy of the treatment of acute humoral rejection, investigators may propose an additional infusion of rituximab from J12, without patient withdrawn. In this case (2nd infusion effective in group A and 1st infusion effective group B), a additional consultation (CS) will be provided as part of the study 7 days after infusion. In case of insufficient efficacy of the treatment,in fairness to care for patients between the 2 treatment groups, the investigators may propose to a 3rd infusion patients in group B (2nd infusion effective for this group). To prevent patients from group A will receive a 3rd infusion of rituximab, unblinding will be applied in this case by the investigator before the administration of additional treatment with rituximab.

MabThera 500mg/50ml I.V. infusion, single dose : 375 mg/m2