Control of T cell responses by accessory receptors revealed by phenotypic models

T cells orchestrate immune responses crucial for the elimination of infections and cancers. They do this by initiating a diverse set of effector responses when their T cell surface receptors (TCRs) recognise these threats. It is now appreciated that a large number of other, “accessory”, receptors shape these responses. Indeed, the remarkable clinical success of checkpoint inhibitors and chimeric antigen receptors is based on perturbing accessory receptor signalling. Despite extensive research into the underlying biochemistry, we have yet to formulate canonical models of signalling that can predict how accessory receptors shape T cell responses. Here, we propose to use a mathematical method known as adaptive inference to identify signalling models directly from T cell response data, without prior biochemical assumptions. The method produces what we term "phenotypic models" because it coarse-grains over molecular information. These models provide effective pathway architectures showing how accessory receptors integrate (or not) with TCR signalling to shape response phenotypes. This will move the field beyond the current stimulatory/inhibitory binary paradigm of accessory receptors. The work offers a different way to study receptor regulated signalling pathways and the predictive power of the phenotypic model will be exploited for T cell-based therapies.