Primary Cells as Feeder Cells for Coculture Expansion of Human Hematopoietic Stem Cells from Umbilical Cord Blood-A Comparative Study

Although umbilical cord blood (UCB) has been widely accepted as an alternative source of hematopoietic stem cells (HSC) for transplantation, its use in adults is restricted because of low absolute HSC numbers. To overcome this obstacle, expansion of HSC in coculture with feeder cells is a promising possibility. In this study, we compared the potential of three human primary cell types, namely, mesenchymal stem cells (MSC), human umbilical cord vein endothelial cells (HUVEC), and Wharton's jelly cells (WJC), for use as feeder cells in a potentially clinically applicable coculture system. In first experiments, we evaluated procedures needed to obtain feeder cells, the possibility to separate them from cells derived from CD34(+) cells after coculture, their ability to activate allogeneic T cells, and their survival in CD34(+)-adapted medium. Finally, we compared their support for UCB-derived CD34(+) expansion. MSC and WJC were superior to HUVEC in terms of ease and reliability of isolation procedures needed. None of the potential feeder cells expressed CD34 or CD45, thus providing markers for cell sorting after coculture. Other markers (CD31, CD90, CD105, CD166) were expressed differently on feeder cell types. While MSC in higher concentrations did not activate allogeneic T cells, those were stimulated by lower concentrations of MSC as shown by CD25, CD69, and CD71 expression. In contrast, HUVEC and WJC were proven to activate T cells at all ratios tested. Feeder cells survived a 7-day culture in CD34(+)-adapted medium. In cocultures of UCB CD34(+) cells with primary feeder cells, mononuclear cell expansion was 30- to 60-fold, colony-forming cell expansion 20- to 40-fold, and cobblestone area-forming cell expansion 10- to 50-fold. We conclude that after a careful further evaluation especially of their immunological properties, all three primary cell types might possibly be suitable for use in a potentially clinically applicable system for expansion from UCB CD34(+) cells, with WJC being best choice and MSC still superior to HUVEC.