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      Understanding the Dynamics of T-Cell Activation in Health and Disease Through the Lens of Computational Modeling

      1 , 1 , 1
      JCO Clinical Cancer Informatics
      American Society of Clinical Oncology (ASCO)

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          Abstract

          T cells in the immune system are activated by binding to foreign peptides (from an external pathogen) or mutant peptide (derived from endogenous proteins) displayed on the surface of a diseased cell. This triggers a series of intracellular signaling pathways, which ultimately dictate the response of the T cell. The insights from computational models have greatly improved our understanding of the mechanisms that control T-cell activation. In this review, we focus on the use of ordinary differential equation–based mechanistic models to study T-cell activation. We highlight several examples that demonstrate the models’ utility in answering specific questions related to T-cell activation signaling, from antigen discrimination to the feedback mechanisms that initiate transcription factor activation. In addition, we describe other modeling approaches that can be combined with mechanistic models to bridge time scales and better understand how intracellular signaling events, which occur on the order of seconds to minutes, influence phenotypic responses of T-cell activation, which occur on the order of hours to days. Overall, through concrete examples, we emphasize how computational modeling can be used to enable the rational design and optimization of immunotherapies.

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          Most cited references65

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          Phase separation of signaling molecules promotes T cell receptor signal transduction.

          Activation of various cell surface receptors triggers the reorganization of downstream signaling molecules into micrometer- or submicrometer-sized clusters. However, the functional consequences of such clustering have been unclear. We biochemically reconstituted a 12-component signaling pathway on model membranes, beginning with T cell receptor (TCR) activation and ending with actin assembly. When TCR phosphorylation was triggered, downstream signaling proteins spontaneously separated into liquid-like clusters that promoted signaling outputs both in vitro and in human Jurkat T cells. Reconstituted clusters were enriched in kinases but excluded phosphatases and enhanced actin filament assembly by recruiting and organizing actin regulators. These results demonstrate that protein phase separation can create a distinct physical and biochemical compartment that facilitates signaling.
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            Kinetic proofreading: a new mechanism for reducing errors in biosynthetic processes requiring high specificity.

            J Hopfield (1974)
            The specificity with which the genetic code is read in protein synthesis, and with which other highly specific biosynthetic reactions take place, can be increased above the level available from free energy differences in intermediates or kinetic barriers by a process defined here as kinetic proofreading. A simple kinetic pathway is described which results in this proofreading when the reaction is strongly but nonspecifically driven, e.g., by phosphate hydrolysis. Protein synthesis, amino acid recognition, and DNA replication, all exhibit the features of this model. In each case, known reactions which otherwise appear to be useless or deleterious complications are seen to be essential to the proofreading function.
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              Serial triggering of many T-cell receptors by a few peptide-MHC complexes.

              T lymphocytes can recognize and be activated by a very small number of complexes of peptide with major histocompatibility complex (MHC) molecules displayed on the surface of antigen-presenting cells (APCs). The interaction between the T-cell receptor (TCR) and its ligand has low affinity and high off-rate. Both findings suggest that an extremely small number of TCRs must be engaged in interaction with APCs and raise the question of how so few receptors can transduce an activation signal. Here we show that a small number of peptide-MHC complexes can achieve a high TCR occupancy, because a single complex can serially engage and trigger up to approximately 200 TCRs. Furthermore, TCR occupancy is proportional to the T cell's biological response. Our findings suggest that the low affinity of the TCR can be instrumental in enabling a small number of antigenic complexes to be detected.
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                Author and article information

                Journal
                JCO Clinical Cancer Informatics
                JCO Clinical Cancer Informatics
                American Society of Clinical Oncology (ASCO)
                2473-4276
                2473-4276
                January 2019
                January 2019
                : 3
                : 1-8
                Affiliations
                [1 ]1University of Southern California, Los Angeles, CA
                Article
                10.1200/CCI.18.00057
                517f76e0-020b-49ac-aced-64e4629aec6a
                © 2019
                History

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