Comparison of Pre-Cryopreserved and Post Thaw and Wash Total Nucleated Cell Count On Major Outcomes Following Unrelated Cord Blood Transplant in Children.

Abstract 3336

Poster Board III-224

Engraftment and overall survival after umbilical cord blood transplant is highly dependent on the total nucleated cell count (TNC). Current standard post thaw processing includes a wash step to remove dimethyl sulfoxide (DMSO), lysed red cells and stroma. The contribution of the wash step to cell loss and ultimately the dose of cells available for transplant is not well described. To investigate the amount of cell loss after washing and its impact on major outcomes compared to pre-cryopreserved TNC, we analyzed data from 310 patients prospectively enrolled on a National Heart Lung Blood Institute (NHLBI) sponsored cord blood transplant study between 1999 and 2003. Dataset was obtained after signed agreement with the NHLBI and local IRB approval. There were 310 patients ≤18 years of age with malignant (N=217) or non-malignant (N=93) disease enrolled on this trial. Only single cord units were used. All cord blood units were thawed and washed using an identical process developed by Rubinstein et al. All patients received myeloablative preparative regimen with either total body irradiation or busulfan based regimens with cyclosporine and prednisone GVHD prophylaxis. All patients received anti-thymocyte globulin as part of their conditioning regimen. For the overall survival, Cox proportional hazard models were generated for pre-wash cell dose and post-wash cell dose separately and then combined in one model. All models included identical covariates. Total cell dose was modeled as a continuous variable with appropriate transformation using restricted cubic lines to account for non-linear relationships. For transplant related mortality (TRM) and neutrophil engraftment, competing risk analyses were used. These analyses were done with adjustment for age, gender, disease (malignant versus nonmalignant), performance status (<90 versus ≥90), HLA (3-4/6 versus 5-6/6 match), and CMV status. The median age was 4.59 years (range 0.04 – 17.90) with 188 (61%) male, 249 patients (80%) had a performance status of ≥90. 166 patients (54%) received a cord blood unit matched at 3/6 or 4/6 HLA antigens and 144 patients (46%) received a cord blood unit matched at 5/6 or 6/6 HLA antigens. The median pre-cryopreserved TNC per kg was 6.93 × 10⁷/kg (range 1.5-80.9 × 10⁷/kg). The median TNC recovery after thawing and washing (PTW) was 5.43 × 10⁷/kg (range 1-31.6 × 10⁷/kg). The average cell recovery was 89% after thawing and washing. Neutrophil engraftment was significantly associated with higher pre-cryopreserved (p=0,003) and PTW TNC infused (p=0.005); younger age (p=0.03), better HLA match (p=0.03). The risk of transplant related mortality was significantly higher among older patients (p=0.02), female patients (p=0.02) and those receiving 3-4/6 HLA matched cord units (p=0.02). Neither the pre-cryopreserved or PTW TNC were significant contributing factors. The risk of grade II-IV acute GVHD was significantly higher among older patients (p=0.04) and those receiving higher pre-cryopreserved TNC (p=0.02) but not higher PTW TNC (p=0.07). Overall survival was significantly better among younger patients (p=0.02), male recipients (p<0.001), patients with non-malignant diseases (p<0.001), patients with performance status >90 (p=0.04) and those receiving 5-6/6 HLA matched cord units (p=0.04). Pre-cryopreserved and PTW TNC did not influence overall survival. In conclusion, pre-cryopreserved and post thaw and wash TNC were equally predictive for major outcomes of unrelated cord blood transplant in children.