Longitudinal multiparameter assay of lymphocyte interactions from onset by microfluidic cell pairing and culture

Abstract

Resolving how the early signaling events initiated by cell-cell interactions are transduced into diverse functional outcomes necessitates correlated measurements at various stages. Typical approaches that rely on bulk cocultures and population-wide correlations, however, only reveal these relationships broadly at the population level, not within each individual cell. Here, we present a microfluidics-based cell-cell interaction assay that enables longitudinal investigation of lymphocyte interactions at the single-cell level through microfluidic cell pairing, on-chip culture, and multiparameter assays, and allows recovery of desired cell pairs by micromanipulation for off-chip culture and analyses. Well-defined initiation of interactions enables probing cellular responses from the very onset, permitting singlecell correlation analyses between early signaling dynamics and later-stage functional outcomes within same cells. We demonstrate the utility of this microfluidic assay with natural killer cells interacting with tumor cells, and our findings suggest a possible role for the strength of early calcium signaling in selective coordination of subsequent cytotoxicity and IFN-gamma production. Collectively, our experiments demonstrate that this new approach is well-suited for resolving the relationships between complex immune responses within each individual cell.microfluidics | cell pairing | single-cell analysis | cell-cell interactions | multiparameter assay I nitiation and progression of immune responses require direct cell-cell interactions. Molecular interactions at the contact interface mediate cellular cross-talk and trigger a series of wellorchestrated downstream signaling events. The magnitude and dynamics of these signals promote and coordinate immune cell activation, and underlie a broad array of functional outcomes, such as target cell elimination, secretory activity, and proliferation (1, 2). Understanding how these early signaling events are transduced into functional responses demands correlated measurements at different stages as these responses unfold.Typically, these relationships are probed by first activating cells in bulk cocultures, often mixing cell populations and initiating contacts via a brief centrifugal cosedimentation, and then piecing together measurements from independent assays performed at different time points. This approach may determine broad outcomes of intercellular interactions, but it suffers from three major limitations. First, individual assay measurements are averaged over many different combinations of interactions due to the uncontrolled and indefinite nature of cell-cell interactions in bulk cocultures. For example, varying times of initiation and duration of contacts (1, 3), number of interacting partners (4), and differences in antigen presenting cells (5) can all modulate immune cell responses. Unpredictable variation is therefore introduced into measured responses, masking the true intrinsic cellular heterogeneity and blurring the correlations. Second, conventional as...

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