Umbilical Cord Blood a source of hematopoietic stem cells
Umbilical cord blood (UCB) collected from the umbilical vessels in the placenta at the time of delivery is a rich source of hematopoietic stem cells. Because these cells are immunologically relatively naive, recipients may have satisfactory outcomes, even when crossing major histocompatibility barriers, thus extending the donor pool to individuals for whom finding allele-matched adult donors can be difficult if not impossible.
Histocompatible umbilical cord blood units
Registries have been established that can be searched for histocompatible cord blood units. A significant advantage of Umbilical cord blood is that the cells are fully typed before cryopreservation and, therefore, are available, avoiding long search times. A major limitation has been the relatively small number of cells available in the cord blood unit, which has made transplantation feasible mainly for pediatric patients.
Multiple recent studies on umbilical cord blood
A limited number of studies have been performed in adults and most confirmed prolonged engraftment times. An analysis of approximately 100 umbilical cord blood transplants showed that recipients who received <1.7 x 107 cells/kg body weight had a high rate of graft failure that led to high nonrelapse mortality.
Thus, it is prudent to anticipate the need for a backup graft given that umbilical cord blood transplantation is associated with an increased risk of graft failure even when using well-matched, suitably sized, cord blood units. The majority of patients who had graft failure were rescued by this type of a planned approach initiated before day +50 after transplantation. Double-unit umbilical cord blood transplantation with two closely and suitably matched cord bloods may provide better engraftment by providing a higher CD34+ and CD3+ cell dose.
Efforts have also been made to expand hematopoietic stem cells from cord blood or potentially use multiple cord blood samples for transplantation to accelerate hematopoietic immune reconstitution.