Engineering a PD-L1-sensing synthetic receptor for programmable macrophage response.

Cellular decision-making relies on the integration of multiple extracellular cues into coordinated functional responses. Synthetic biology provides tools to rewire this process by engineering receptors that convert defined inputs into programmable outputs. Here, we describe a synthetic receptor-based architecture that enables monocytic-like cells to sense an immune-regulatory ligand and conditionally activate a phagocytic program. We engineered a synthetic Notch-based receptor (SNIPR) that detects programmed death-ligand 1 (PD-L1), a broadly expressed immune-regulatory ligand. Upon PD-L1 engagement, the circuit triggers programmable outputs, including expression of a fluorescent reporter or CV1-Fc, as model effector that interferes with CD47-mediated inhibition of phagocytosis. We show that circuit activation scales with PD-L1 levels, partially attenuates PD-1/PD-L1 signaling, and that conditional CV1-Fc expression enhances engulfment of SKOV-3 ovarian cancer cells by THP-1-derived macrophages in vitro. Collectively, this work reframes PD-L1 from an end-point therapeutic target to a programmable input signal for synthetic circuit activation and establishes a modular framework for ligand-responsive control of engineered macrophage behaviour.