The extended lifespan induced by forced expression of inducible STAT5 mutants described in this paper provides a tool to expand in vitro cultured single human memory B cells to obtain monoclonal cell lines. However these cell lines do not express any immunoglobulins when the inducible active STAT5 mutant is ''on''. By subsequently inactivating STAT5 the cells regained the capacity to produce immunoglobulin offering an opportunity to screen the clones for secretion of specific antibodies. It should be noted that antigen specificity was not selected for by a functional assay. Instead, we used a binding assay (ELISA) to screen for antitetanus toxoid specific antibodies. It has been described previously however that TT specific antibodies selected through binding assays (ELISA) are functional as shown in a Toxin Binding Inhibition test (ToBI) and in in vivo TT challenge models in mice [43] [44] . Following selection of the antigen-specific clones the immunoglobulin genes can be retrieved from the clones. An obvious next step would be to scale up the production of antibodies through recombinant expression of the identified immunoglobulin genes in suitable cell lines. These recombinant antibody proteins can then be tested for other effector functions like antigen dependent cellular cytotoxicity (ADCC), complement activation or in vivo in mice for toxin inactivation properties.