We evaluated the safety of adding rituximab 375 mg/m2 only on days +1 and +8 following allo-HCT in 18 patients (M=12, F=6), median age 56 (41–66) years, with advanced CD20+ lymphoid malignancies [CLL=9 (CR2=3, PR2=3; ≥PR3=3); Mantle cell lymphoma (MCL)= 5 (CR1=1, PR2=2, ≥PR3=2); follicular (FL)=3 (CR3=2, ≥PR3=1); DLBC NHL=1 (≥PR3=1). Source of stem cells consisted of matched-related (MRD)=11 (61%), matched-unrelated (MUD)=5 (28%), or mismatched-unrelated (MMUD)=2 (11%) donors. Conditioning regimens consisted of fludarabine plus targeted doses of IV busulfan (FLU-BU) (N=11) or 200 cGy TBI (N=4), or cyclophosphamide (FLU-CY) (N=1). ATG was administered on days −3 and −1 in 2 MMUD cases (FLU-BU-ATG). Fifteen patients received rituximab on day +1 (±3) and all on day +8 (±3). GVHD prophylaxis was tacrolimus plus mycophenolate mofetil (N=11) or methotrexate (N=7). Non-relapse mortality at 100 days was 6%. Median time to neutrophils and platelets engraftment was 15 (6–27) days and 12.5 (9–18) days, respectively. Eight patients never dropped platelets below 20,000/uL. Median CD3 and CD33 chimerisms at day +90 (±10) were 89% (50%–100%) and 100% (15%–100%), respectively. DLI was required in 2 patients (FLU-BU=1, FLU-TBI=1) due to poor CD3 engraftment. Response rates after 90 days post allo-HCT, according to diagnosis, were as follows: CLL (evaluable=8/9; CR=7/8; PR=1/8); MCL (evaluable=4/5; CR=4/4); FL (CR=3/3); DLBC (PD=1/1). Twelve (67%) patients remain alive in remission at a median follow up of 9.4 (2.3–42.3) months. The incidence of grade 0,I, II, and III–IV acute GVHD (aGVHD) was 6%, 33%, 50%, and 11%, respectively. Time to onset of aGVHD was 29 (16–77) days. The incidence of chronic GVHD (cGVHD), per NIH consensus criteria, was as follows in 15 evaluable patients: no cGVHD= 27%, mild= 33%, moderate= 13%, and severe=27%. These findings suggest that administration of rituximab 375 mg/m2 only on days +1 and +8 is safe. Response rates are encouraging; but controlled studies will be needed to conclusively determine the effect of post-transplant rituximab on efficacy.

Disclosures: Off Label Use: rituximab in the setting of allogeneic hematopoietic cell transplantation. Sotomayor:Genetech/IDEC: Speakers Bureau.

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