Programmable Cells Are Emerging as Drug Factories with Context-Dependent Pharmacology

Programmable therapeutic cells challenge a central assumption of conventional pharmacology: that dose is administered as a chemically defined quantity whose subsequent exposure can be separated from the machinery that produced it. Engineered mammalian cells and microorganisms instead remain biologically active after administration. They may sense endogenous or environmental signals, change state, execute genetic logic, migrate or persist in selected compartments, and generate therapeutic molecules only under particular conditions. Consequently, the pharmacologically relevant “dose” may evolve after treatment begins. This Perspective argues that living drug factories should be interpreted through two linked but separable processes: the disposition of the producer cells and the production, disposition, and action of their therapeutic outputs. Evidence from engineered bacteria, programmable immune cells, synthetic gene circuits, local protein secretion, and closed-loop metabolic control demonstrates components of this behavior, but no universal living-cell pharmacokinetic or pharmacodynamic model has been established. We therefore develop a proposed living-pharmacology framework in which therapeutic response emerges from the interaction among viable-cell exposure, sensing performance, circuit state, spatial context, production state, payload disposition, host physiology, and safety constraints. This framing explains why equivalent administered cell numbers need not generate equivalent therapeutic exposure and why apparently identical circuits may behave differently across tissues, hosts, or disease states. Translation will require qualification of these state transitions rather than reliance on administered-cell dose or release testing alone.