Research ArticleCAR–T CELL SIGNALING

Tuning ITAM multiplicity on T cell receptors can control potency and selectivity to ligand density

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Sci. Signal.  22 May 2018:
Vol. 11, Issue 531, eaan1088
DOI: 10.1126/scisignal.aan1088

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ITAM abundance increases receptor potency

T cells transduce extracellular signals by phosphorylating immunoreceptor tyrosine-based activation motifs (ITAMs) within the T cell receptor complex. Why this complex contains more ITAMs than any other immune receptor remains unclear. James engineered drug-responsive synthetic receptors that varied in ITAM abundance to determine how ITAM frequency influenced T cell signaling at the single-cell level. The experimental data fit computational models predicting that increasing ITAM number influenced the efficiency of signal transduction, but not the signal amplitude. Application of these results to human CAR–T cells identified strategies to improve the specificity of these cancer therapeutics.

Abstract

The T cell antigen receptor (TCR) recognizes peptides from pathogenic proteins bound in the major histocompatibility complex (MHC). To convert this binding event into downstream signaling, the TCR complex contains immunoreceptor tyrosine-based activation motifs (ITAMs) that act as docking sites for the cytoplasmic tyrosine kinase ZAP-70. Unique among antigen receptors, the TCR complex uses 10 ITAMs to transduce peptide-MHC binding to the cell interior. Using synthetic, drug-inducible receptor-ligand pairs, it was found that greater ITAM multiplicity primarily enhanced the efficiency with which ligand binding was converted into an intracellular signal. This manifested as an increase in the fraction of cells that became activated in response to antigen, and a more synchronous initiation of TCR-proximal signaling, rather than direct amplification of the intracellular signals. Exploiting these findings, the potency and selectivity of chimeric antigen receptors targeted against cancer were substantially enhanced by modulating the number of encoded ITAMs.

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