Patent ID: 8321145

Claim:
A method of determining when to harvest cells from a cell growth chamber of a closed cell expansion system comprising the steps of: measuring a number of cells initially loaded into the cell growth chamber; removing, through a sampling port, fluid from a fluid circulation path of the closed cell expansion system while maintaining sterility of the closed cell expansion system; measuring a concentration of lactate in the fluid; and based on the measured number of cells initially loaded and the measured concentration of lactate, determining when to harvest the cells from the cell growth chamber of the closed cell expansion system, wherein the determining comprises: executing an algorithm, the algorithm comprising: ln m L =c+ln N 0 , wherein m L denotes a lactate mass, N 0 denotes the number of cells initially loaded, and c denotes a constant, the constant c comprising: c=ln g L +d′ ln 2, wherein g L denotes a generation rate of lactate, and d′ denotes a number of cell doublings that will be needed to obtain a desired number of cells to harvest.