Detachment strategies for affinity-adsorbed cells

Target cells adsorbed in affinity separation processes need to be effectively recovered from the adsorption matrix once contaminating cell types have been removed. Although tangential flow can be used to generate detachment forces, the resultant dilution is excessive. In this study, three alternative detachment protocols have been assessed using a membrane-based adsorption surface. Back flushing buffer through the membrane to generate greater detachment forces was studied. However, at the maximum back flush velocity obtainable less than 50% of attached cells were removed and recovered cell concentrations were low. Controlled transmembrane delivery of hydrochloric acid as a non-specific eluent was also investigated. While this allowed complete recovery of cells the effective acid concentration was excessive. The upstream dilution required to maintain cell viability again leads to considerable dilution. Injection of air bubbles into the tangential flow stream to generate elevated detachment forces was found to be the most effective approach. Detachment was found to be a function of both number and size of bubbles. Under optimal conditions, 80% of attached cells can be removed to give a detached cell concentration of 10(8) cells ml(-1). This leads to an essentially reagentless detachment protocol allowing the development of an isocratic affinity cell separator where cells can be attached, washed, and detached in the same buffer. (C) 2002 Elsevier Science Inc. All rights reserved.