Reduced Adverse Effects and Improved Engraftment in the Pediatric Transplant Population upon Dilution of HPC, Cord Blood Products Prior to Infusion

Patient specific adverse reactions are common when HPC, Cord Blood (HPC-C) units, cryopreserved in dimethylsulfoxide (DMSO) are warmed to 37°C and infused into pediatric patients. Adverse reactions, including hemodynamic instability, fever, chills, nausea, cardiomyopathy, unconsciousness, and even death have been described in the pediatric population. Additionally, hematopoietic stem cells (HSC) cryopreserved in DMSO have limited viability upon thawing due to the cellular cytotoxicity of DMSO, resulting in the potential for significant loss of cells available for transplantation and subsequent engraftment. Although DMSO is essential as a cryoprotectant for long-term preservation of hematopoeitic stem cells, standardized techniques are required to mitigate the cellular cytotoxicity and acute onset adverse events witnessed in unwashed/undiluted cord blood transplantation. Immediate mixing of thawed cord blood units with a hypertonic reconstitution solution can ameliorate many of these problems by restoring the osmolarity of the suspension, promoting colloidal-osmotic intracellular equilibrium, and reducing DMSO concentration in the infused product. In general, studies examining the benefits of dilution and/or washing of HPC-C prior to infusion have largely been confined to adult populations with varying results. Since pediatric patients often experience more significant adverse reactions, even when DMSO concentrations in the infused unit are well below the recommended maximum of 5 mL of 20% DMSO/kg body weight, examination of effective and robust techniques for minimizing these effects in the pediatric patient is crucial. The studies presented demonstrate successful utilization of diluted HPC-C products in HSC transplants in pediatric patients. HPC-C products were either infused immediately after thaw or infused after dilution with a solution of 8% Gentran-40 and 5% HSA (ReCon solution). Dilution of HPC-C products immediately after thaw appears to ensure maximal HSC recovery and viability--essential for transplant and engraftment. In experimental studies, improved HPC recovery and viability was observed in all diluted HPC-C products as compared to undiluted products. As well, the number and viability of CD34⁺ cells remains constant for >24 hours post thaw when HPC-C products are diluted in ReCon solution. In contrast, thawed and undiluted HPC-C units experience a significant reduction in number and viability of CD34⁺ cells 15–30 minutes post-thaw. Most importantly, pediatric patients displayed reduced adverse reactions when infused with diluted HPC-C products as compared to undiluted products. Dilution of HPC-C products with ReCon solution did not affect engraftment of neutrophils and/or platelets in these patients. In a specific case study, a diluted HPC-C product resulted in engraftment when a double-cord transplant with undiluted HPC-C products did not. As well, the negative adverse reaction experienced by the patient following infusion of undiluted product was not experienced when the diluted HPC-C product was infused. In the pediatric HSC transplant population it is essential not only to ensure optimal recovery and potency of HSCs in the transplant graft but also to alleviate adverse reactions. Application of HPC-C dilution protocols employing a solution of Gentran-40 and HSA provide an effective, safe, and efficient strategy for diminishing DMSO related toxicities in the pediatric HSCT patient.