Multivalent ligands to control stem cell behaviour in vitro and in vivo

There is broad interest in designing nanostructured materials that can interact with cells and regulate key downstream functions(1–7). In particular, materials with nanoscale features may enable control over multivalent interactions, which involve the simultaneous binding of multiple ligands on one entity to multiple receptors on another and are ubiquitous throughout biology(8–10). Cellular signal transduction of growth factor and morphogen cues that play critical roles in regulating cell function and fate often begins with such multivalent binding of ligands, either secreted or cell-surface tethered, to target cell receptors, leading to receptor clustering(11–18). Cellular mechanisms that orchestrate ligand-receptor oligomerisation are complex, however, and the capacity to control multivalent interactions and thereby modulate key signaling events within living systems is therefore currently very limited. Here we demonstrate the design of potent multivalent conjugates that can organise stem cell receptors into nanoscale clusters and control stem cell behaviour in vitro and in vivo. The ectodomain of ephrin-B2, normally an integral membrane protein ligand, was conjugated to a soluble biopolymer to yield multivalent nanoscale conjugates that potently induced signaling in neural stem cells and promoted their neuronal differentiation both in culture and within the brain. Super-resolution microscopy analysis yielded insights into the organisation of receptor-ligand clusters at the nanoscale. We also found that synthetic multivalent conjugates of ephrin-B1 strongly enhanced human embryonic and induced pluripotent stem cell differentiation into functional dopaminergic neurons. Multivalent bioconjugates thus represent powerful tools and potential nanoscale therapeutics for controlling the behaviour of target stem cells in vitro and in vivo.