Emergence of chiral multi-armed spirals in an open system of migrating cells under continuous cell supply

From molecular assemblies to multicellular tissues, chirality organizes living and active-matter systems into striking collective states. Across cellular collectives and active materials, weak microscopic chiral cues in motion and interaction can systematically skew how constituents coordinate, flow, and break spatial symmetries. Yet the principles that govern chiral ordering in open systems, where elements are continuously supplied and removed, remain poorly understood. Here, we show that chemotaxis-deficient Dictyostelium discoideum mutants (KI cells) form centimeter-scale, clockwise, multi-armed spirals. Each arm is a traveling band produced by short-range alignment interactions and guided by a polar-ordered rotating core that encircles the cell source. A subtle clockwise bias in single-cell migration is amplified by collective ordering into tissue-scale chirality. To uncover the minimal ingredients, we developed an open chiral Vicsek model and found that intrinsic chirality, polar alignment, and continuous cell supply are the key factors. Our study establishes a general route by which weak microscopic chirality and sustained material flux generate macroscopic chiral order, offering new insight into chiral patterning in multicellular systems.