DIFFERENT MEASURES OF HUMAN HEMATOPOIETIC-CELL CULTURE PERFORMANCE ARE OPTIMIZED UNDER VASTLY DIFFERENT CONDITIONS

Hematopoiesis, the formation of mature blood cells from stem (LTC-IC) and progenitor (CFU-GM) cells in the bone marrow, is a complex tissue- forming process that leads to many important physiological functionali ties. Consequently, a functioning ex vivo hematopoietic system has a v ariety of basic scientific and clinical uses. The design and operation of such a system presents the tissue engineer with challenges and cho ices. In this study, three culture variables were used to control ex v ivo human hematopoiesis. Systematic variation of inoculum density (ID) , medium exchange interval (MEI), and the use of preformed stroma (PFS ) showed that (1) all three variables significantly influenced culture performance, (2) the three variables interacted strongly, and (3) the variables could be manipulated to achieve the optimization of differe nt performance criteria. Donor-to-donor variability in culture perform ance was great at low ID but was minimized at higher ID. PFS had a lar ge positive effect on cell and CFU-GM output at low ID, but had minima l effect at higher ID. In fact, PFS caused a decrease in LTC-IC output at high ID. The effects of PFS indicated that stromal cell elements b ecame more limiting than proliferative cell elements as ID was reduced . In cultures without PFS, maximum cell output was obtained with high ID using a short MEI, whereas the greatest cell expansion ratio was ob tained at low ID with an intermediate MEI. Maximum CFU-GM output was o btained from cultures with high ID using a short to intermediate MEI, whereas the greatest CFU-GM expansion ratio was obtained at intermedia te ID with an intermediate MEI. The addition of PFS altered the locati ons of these maxima. In general, PFS moved the maxima to lower ID, and culture output became more sensitive to MEI. Therefore, the optimizat ion of one performance criterion always resulted in a decline of the o thers. This study demonstrates that ex vivo tissue function is sensiti ve to many culture variables in an interactive fashion and that system atic multivariable studies are required to characterize tissue functio n. Once the effects of individual variables and their interactions are known, this knowledge can be used to optimize tissue performance with respect to desired criteria. (C) 1996 John Wiley & Sons, Inc.