Multiplexed Elispot assay.

Micron scale latex beads are well established as highly biocompatible reagents. Imbibing two fluorescent dyes into the interior of the beads enables the creation of a family of combinatorially colored labels. Previous use of such beads, in flow cytometry for example, has focused on beads of approximately 5 microm diameter. We show here that 280 nm combinatorially labeled particles can be used to create ELISA-style assays in 200 microm scale virtual wells, using digital microscopy as the readout. The utility of this technique is illustrated by profiling the secreted cytokine footprints of peripheral blood mononuclear cells in a multiparametric version of the popular Elispot assay. Doing so reveals noncanonical classes of T lymphocytes. We further show that the secreting cell type can be concurrently identified by surface staining with a cell type specific antibody conjugated to the same multiplexed beads.

Antibody discovery via multiplexed single cell characterization.

The secreted immunoglobulin footprint of single hybridoma cells, containing ~10 fg of antibody purified in situ, has been probed for 9 properties concurrently by use of detection labels comprising 280 nm combinatorially colored fluorescent latex beads functionalized with proteins. Specificity of each individual hybridoma cell's product has thereby been assessed in a primary screen. Varying the density of antigen on beads to modulate the avidity of the interaction between bead and secreted antibody footprint allowed rank ordering by affinity in the same primary screen. As more criteria were added to the selection process, the frequency of positive cells went down; in some cases, the favorable cell was present at <1/50,000. Recovery of the cell of interest was accomplished by plating the cells in a viscous medium on top of a membrane. After collecting the antibody footprint on a capture surface beneath the membrane, the immobilized cells were transferred to an incubator while the footprints were analyzed to locate the hybridoma cells of interest. The desired cells were then cloned by picking them from the corresponding locations on the membrane.