Adult Umbilical Cord Blood Transplantation Following Non-Myeloablative Conditioning; Impact of Increased Cell Dose and 200cGy TBI on Engraftment and Survival.

Reliable engraftment following transplantation of partially matched umbilical cord blood is dependent upon adequate immunosuppression and myelosuppression. The lowest intensity conditioning regimen that will provide reliable cord blood engraftment in adult patients has not been determined. 26 adult patients with a contraindication for myeloablative marrow conditioning due to advanced age or comorbidities, underwent non-myeloablative umbilical cord blood transplantation for hematologic malignancies. The first 13 patients (Cohort 1) were conditioned with Fludarabine 120mg/m², Cyclophosphamide 2g/m² and horse Antithymocyte globulin 90mg/kg. Cyclosporine and Mycophenolate Mofetil was administered for GvHD prophylaxis. The median cell nucleated dose was 2.1 × 10⁷/kg and median follow-up is 60 months (Chao 2004 BBMT 10:569). After protocol revision, 200 cGy total body irradiation was added to the regimen described above. In addition, the minimum nucleated cell dose provided from up to two cord blood units was increased to 3 × 10⁷/kg (Cohort 2). With a median follow-up of 12 months, we now report the outcome of cohort 2. Fourteen patients with AML CR1 (2), CR≥2 (5), CML (1), MDS/AML (1), MDS (4), or Follicular Lymphoma (1) and a median age of 54 (range 21–72) were transplanted. Eight patients required dual cord blood grafts to achieve the minimum cell dose. All grafts were at least 4/6 HLA matches (antigen level class I, allele level class II) with the patient, and with each other (dual cord blood grafts). The median cryopreserved and infused nucleated cell dose was 3.6 × 10⁷/kg and 3.5 × 10⁷/kg respectively. Two patients were not evaluable for engraftment due to early toxic death. Two patients experienced primary graft failure. Acute GvHD (grade II skin) was observed in 2 patients. Limited chronic GvHD developed in 2 patients. Parainfluenza type 3 sinusitis and pneumonitis caused significant morbidity in 5 patients. Day 100 treatment-related mortality occurred in 4 patients (30%) due to; infection (2), hemorrhage (2). Relapse occurred in 5 patients (36%). The estimated one year overall and disease-free survival is 25% and 17%, respectively. T-cell recovery was slow. The median CD4 count/ul for engrafted patients was 44 (range 4–516) and 61(range 2–237) at 3 and 6 months following transplantation, respectively. The median CD8 count/ul was 7 (range 0–359) and 108 (range 0–728) at 3 and 6 months following transplantation, respectively. A comparison of results from the two cohorts is presented in the table. The addition of 200cGy and increasing the cell dose facilitated by dual cord blood transplantation doubled the chance for sustained donor engraftment. Improved engraftment was accompanied by increased treatment-related morbidity and mortality, erasing the potential for improved disease-free survival. Disease relapse, in part due to slow immune recovery resulting in impaired anti-tumor response, was the other major impediment to successful outcome. Techniques focused on enhancing immune recovery would significantly improve outcomes of adult cord blood transplantation.