Analysis of 120 Pediatric Patients with Non-Malignant Disorders Transplanted Using Unrelated Plasma Depleted Cord Blood and the Role of Post-Thaw Wash

Unrelated cord blood (UCB) is an important stem cell source for unrelated hematopoietic cell transplantation of patients with non-malignant disorders. Cell dosage is a critical factor for successful UCB hematopoietic stem cell transplantation (HSCT). The red cell reduced (RCR) and post-thaw wash techniques that are widely used incur significant nucleated cell loss. Three strategies were employed to maximize cell dose and improve outcome–use of cord blood processed with plasma depletion without red blood cell reduction (PD CB), avoidance of post-thaw wash, and the use of double cords (2X) when necessary. A CIBMTR-audited analysis was performed on all 120 pediatric patients with non-malignant disorders transplanted with PD CB at 29 U.S. and 17 international centers. Transplant characteristics: median age 3.5 years (range 0.1–14); median patient weight 15 kg (range 4–61); male 58%. The majority of patients (n=58; 55%) were Asian. Twenty-two (21%) patients were Hispanic, 15 (14%) were Caucasian, 6 (6%) were African-American, and three (3%) were of Middle Eastern background. HLA ABDR matches: 6/6–26; 5/6–48; 4/6–47; 3/6 or 2/6–6; median pre-freeze nucleated cell dose 10.5×10⁷/kg; median pre-freeze CD34⁺ dose 3.7×10⁵/kg; non-myeloablative regimen 24%; 58% infused without post-thaw wash (NW). Myeloid engraftment defined as ANC≥500 and 6-month platelet engraftment defined as ≥ 20K and ≥ 50K are 89±8%, 88±8%, and 84±6% respectively. The median time to myeloid and platelet engraftment are 21 days (range 11–64), 49 days (range 13–155), and 61.5 days (range 21–205) respectively. No major adverse event was observed in either the W or the NW group. The cumulative incidence of reported grade II–IV acute GVHD was 38±5%, and 19±4% had grade III–IV acute GVHD. 36±6% developed limited chronic GVHD, and 12±4% developed extensive chronic GVHD. With a median follow-up of 329 days (range 3–1928 days), the Kaplan-Meier estimates of 1-year TRM, OS and diseasefree survival were 20±6%, 88±6% and 72±6% respectively. Foregoing post-thaw wash for PD CB transplantation improved neutrophil (RR=1.75; p=0.01) and platelet engraftment (RR=1.72; p=0.02) and reduced TRM (RR=0.38; p=0.04). This series demonstrated that unrelated PD CB transplantation can be performed safely and effectively in children with life-threatening, non-malignant disorders. Additionally, the results demonstrate possible improvement in myeloid and platelet engraftment, overall and disease-free survival when post-thaw wash is not employed.

Table 1. Summary of overall results