Christian Stemberger, Stefan Dreher, Claudia Tschulik, Christine Piossek, Jeannette Bet, Tori N. Yamamoto, Matthias Schiemann, Michael Neuenhahn, Klaus Martin, Martin Schlapschy, Arne Skerra, Thomas Schmidt, Matthias Edinger, Stanley R. Riddell, Lothar Germeroth, Dirk H. Busch

A general obstacle for clinical cell preparations is limited purity, which causes variability in the quality and potency of cell products and might be responsible for negative side effects due to unwanted contaminants. Highly pure populations can be obtained best using positive selection techniques. However, in many cases target cell populations need to be segregated from other cells by combinations of multiple markers, which is still difficult to achieve--especially for clinical cell products. Therefore, we have generated low-affinity antibody-derived Fab-fragments, which stain like parental antibodies when multimerized via Strep-tag and Strep-Tactin, but can subsequently be removed entirely from the target cell population. Such reagents can be generated for virtually any antigen and can be used for sequential positive enrichment steps via paramagnetic beads. First protocols for multiparameter enrichment of two clinically relevant cell populations, CD4(high)/CD25(high)/CD45RA(high) 'regulatory T cells' and CD8(high)/CD62L(high)/CD45RA(neg) 'central memory T cells', have been established to determine quality and efficacy parameters of this novel technology, which should have broad applicability for clinical cell sorting as well as basic research.