Delayed Tolerance Through Mixed Chimerism

Months-Years after standard transplant, patients will undergo bone marrow transplant (either from prospective collection of stem cells from their living donor, or from bone marrow collected at the time of deceased donation)

PBSC will be collected from the LD via leukapheresis 1-4 weeks before the scheduled HSCT. The donor will first undergo standard GCSF mobilization: GCSF (can be TBO-GCSF) dosed at 10 mcg/kg/d (rounded to nearest pre-filled syringe) administered subcutaneously daily for 5 consecutive days. On the 5th day, the donor will undergo standard large volume leukapheresis. The target yield will be 2-3 x 106 CD34+ cells / kg of actual recipient body weight. A maximum of 3 days of pheresis will be allowed. A minimum of 2 x 106 CD34+ cells / kg of actual recipient body weight will be required to proceed.

Fludarabine 15 mg/m2/day on days -5 to -3 (3 doses)

Cyclophosphamide (CP) 30 mg/kg/day on days -5 and -4

Rituximab on study day -6

Siplizumab (anti-CD2 mAb) on days, -2, -1, 0 and +1.