Abstract: Improved colony forming cell (CFC) assays are described. The improved assay comprises modifications to the standard CFC assay that enable analysis of temporal, real-time changes in antigen expression during colony development without need to fixate or destroy the culture. The improved assay is applicable to hematopoietic CFC assays as well as to CFC assays for other cells, such as neural cells and mammary cells. In one embodiment, the invention comprises adding a detection reagent, most likely a fluorescently labeled antibody, that is specific for antigens (most likely a cell-surface antigen) expressed on progenitors or on specific mature cell types to a culture at the start or during culture. The invention also comprises modifications to the culture medium and cell preparations used in standard CFC assays to selectively promote the development of one colony type while preventing or suppressing the development of other colony types.

Abstract: A method for preventing or inhibiting non-specific binding reactions between a detection reagent and an antigen in an immunological assay is described. The method involves using tetrameric antibody complexes that can bind to the antigen and are comprised of two monoclonal antibodies of a first animal species linked to two monoclonal antibodies of a second animal species that can bind the antibodies of the first animal species. Preferably, the antigen is an Fc Receptor and the method reduces the binding of a detection antibody with Fc receptors present on the surface of many cells.