The STORE.2 model of the T cell proliferative phase considering c-Myc
The generation of antigen-specific CD8+ T cell responses is dictated by the affinity of the cognate antigen, the stimulatory capacity of antigen presenting cells (APCs), and the metabolic pathways required for rapid cell proliferation. The complexity of these pathways is a significant challenge in designing vaccines against diseases that require a protective CD8+ T cell response. To understand the mechanisms underlying CD8+ T cell responses, the STORE.2 model was developed to simulate the early events of T cell priming and expansion at the site of priming. STORE.2 is a mathematical, stochastic, and agent-based model based on first-principles that tracks every individual CD8+ T cell and APC. It allows for the simulation of different antigen affinity (Signal 1) as well as levels of costimulation (Signal 2) and inflammatory cytokines (Signal 3) provided by APCs. The impact of Signals 1-3 is translated to T cell responses via the transcription factor c-Myc, which supports T cell proliferation. Enhanced glycolysis during T cell activation results in a change in the metabolic environment that includes an increase in extracellular lactate concentration. STORE.2 models the role of lactate in the inhibition of T cell metabolism and proliferation as a negative feedback mechanism on c-Myc production. STORE.2 accurately recapitulated the CD8+ T cell response during in vitro T cell priming assays that control for Signals 1-3 as well as lactate concentration. Finally, application of STORE.2 to an in vivo response to immunization demonstrated that the model accurately simulates CD8+ T cell activation at the site of priming.