T cells selectively filter oscillatory signals on the minutes timescale

Abstract

Significance Immune cells in the body encounter stimuli in complex temporal patterns, but our understanding of how the timing of stimulation determines immune responses is incomplete. We engineered T cells obtained from healthy human donors to respond to light as a stimulus in a laboratory setting. We discovered that T cells can filter out specific signals based only on signal frequency by stimulating engineered T cells with light-based temporal stimulation patterns designed to mimic the dynamic patterns a natural T cell might experience in the human body. This filtering mechanism could contribute to how immune cells distinguish between foreign/altered cells versus self-cells in vivo, since foreign/altered and self-cells exhibit highly distinct interaction dynamics with T cells within the body. T cells experience complex temporal patterns of stimulus via receptor–ligand-binding interactions with surrounding cells. From these temporal patterns, T cells are able to pick out antigenic signals while establishing self-tolerance. Although features such as duration of antigen binding have been examined, our understanding of how T cells interpret signals with different frequencies or temporal stimulation patterns is relatively unexplored. We engineered T cells to respond to light as a stimulus by building an optogenetically controlled chimeric antigen receptor (optoCAR). We discovered that T cells respond to minute-scale oscillations of activation signal by stimulating optoCAR T cells with tunable pulse trains of light. Systematically scanning signal oscillation period from 1 to 150 min revealed that expression of CD69, a T cell activation marker, reached a local minimum at a period of ∼25 min (corresponding to 5 to 15 min pulse widths). A combination of inhibitors and genetic knockouts suggest that this frequency filtering mechanism lies downstream of the Erk signaling branch of the T cell response network and may involve a negative feedback loop that diminishes Erk activity. The timescale of CD69 filtering corresponds with the duration of T cell encounters with self-peptide–presenting APCs observed via intravital imaging in mice, indicating a potential functional role for temporal filtering in vivo. This study illustrates that the T cell signaling machinery is tuned to temporally filter and interpret time-variant input signals in discriminatory ways.