Novel Chimeric Antigen Receptor Signaling Domains Derived via Activity-based Directed Evolution

Provided herein are chimeric antigen receptor (CAR) viral libraries and methods of making the same. In some embodiments, the CAR comprises an intracellular domain (ICD) with at least one immune activation signaling domain, one co-stimulatory domain, and one or more inhibitory signaling domain or signaling domain from non-T cell lineages. In some embodiments, the signaling domains of the ICD are joined by distinct linkers of 10 amino acids. In some embodiments, the CARs contain a 18-nucleotide barcode in the 3' untranslated region. Also provided herein, are CAR cell libraries and methods of making the same.