T cell circuits that sense antigen density with an ultrasensitive threshold

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Science  12 Mar 2021:
Vol. 371, Issue 6534, pp. 1166-1171
DOI: 10.1126/science.abc1855

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Designing smarter anticancer T cells

Biological signaling systems can exhibit a large, nonlinear—or “ultrasensitive”—response, which would be useful to engineer into therapeutic T cells to allow for better discrimination between cancer cells and normal tissues. Hernandez-Lopez et al. modified human T cells using a two-step mechanism that allowed them to kill cells expressing large amounts of cancer marker protein but not cells expressing a small amount of the same protein. A first synthetic receptor recognized the antigen with low affinity. That receptor signaled to increase expression of a chimeric antigen receptor (CAR) with high affinity for the same antigen. The circuit proved effective in cell culture and mouse cancer models, offering hope of extending the CAR T cell strategy against solid tumors.

Science, this issue p. 1166


Overexpressed tumor-associated antigens [for example, epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER2)] are attractive targets for therapeutic T cells, but toxic “off-tumor” cross-reaction with normal tissues that express low levels of target antigen can occur with chimeric antigen receptor (CAR)–T cells. Inspired by natural ultrasensitive response circuits, we engineered a two-step positive-feedback circuit that allows human cytotoxic T cells to discriminate targets on the basis of a sigmoidal antigen-density threshold. In this circuit, a low-affinity synthetic Notch receptor for HER2 controls the expression of a high-affinity CAR for HER2. Increasing HER2 density thus has cooperative effects on T cells—it increases both CAR expression and activation—leading to a sigmoidal response. T cells with this circuit show sharp discrimination between target cells expressing normal amounts of HER2 and cancer cells expressing 100 times as much HER2, both in vitro and in vivo.

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