A conformation-specific ON-switch for controlling CAR T cells with an orally available drug

Proc Natl Acad Sci U S A. 2020 Jun 30;117(26):14926-14935. doi: 10.1073/pnas.1911154117. Epub 2020 Jun 17.


Molecular ON-switches in which a chemical compound induces protein-protein interactions can allow cellular function to be controlled with small molecules. ON-switches based on clinically applicable compounds and human proteins would greatly facilitate their therapeutic use. Here, we developed an ON-switch system in which the human retinol binding protein 4 (hRBP4) of the lipocalin family interacts with engineered hRBP4 binders in a small molecule-dependent manner. Two different protein scaffolds were engineered to bind to hRBP4 when loaded with the orally available small molecule A1120. The crystal structure of an assembled ON-switch shows that the engineered binder specifically recognizes the conformational changes induced by A1120 in two loop regions of hRBP4. We demonstrate that this conformation-specific ON-switch is highly dependent on the presence of A1120, as demonstrated by an ∼500-fold increase in affinity upon addition of the small molecule drug. Furthermore, the ON-switch successfully regulated the activity of primary human CAR T cells in vitro. We anticipate that lipocalin-based ON-switches have the potential to be broadly applied for the safe pharmacological control of cellular therapeutics.

Keywords: CAR T cell; CID; alternative scaffold; lipocalin; protein engineering.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Line
  • Cytokines / immunology
  • Humans
  • Lipocalins / genetics
  • Lipocalins / immunology
  • Molecular Conformation
  • Piperidines / chemistry
  • Piperidines / pharmacology
  • Receptors, Chimeric Antigen / genetics
  • Receptors, Chimeric Antigen / immunology*
  • Retinol-Binding Proteins, Plasma / genetics
  • Retinol-Binding Proteins, Plasma / immunology
  • T-Lymphocytes / drug effects
  • T-Lymphocytes / immunology*


  • A1120 agent
  • Cytokines
  • Lipocalins
  • Piperidines
  • RBP4 protein, human
  • Receptors, Chimeric Antigen
  • Retinol-Binding Proteins, Plasma

Associated data

  • PDB/6QBA