Abstract
Enhancing the affinity of therapeutic T cell receptors (TCR) without altering their specificity is a significant challenge for adoptive immunotherapy. Current efforts have primarily relied on empirical approaches. Here, we used structural analyses to identify a glycine-serine variation in the TCR that modulates antigen sensitivity. A G at position 107 within the CDR3β stalk is encoded within a single mouse and human TCR, TRBV13-2 and TRBV12-5 respectively. Most TCR bear a S107. The S hydroxymethyl side chain intercalates into the core of the CDR3β loop, stabilizing it. G107 TRBV possess a gap in their CDR3β where this S hydroxymethyl moiety would fit. We predicted based on modeling and molecular dynamics simulations that a G107S substitution would increase CDR3β stability and thereby augment receptor sensitivity. Experimentally, a G107S replacement led to an ∼10–1000 fold enhanced antigen sensitivity in 3 of 4 TRBV13-2+ TCR tested. Analysis of fine specificity indicated a preserved binding orientation. These results support the feasibility of developing high affinity antigen specific TCR for therapeutic purposes through the identification and manipulation of critical framework residues. They further indicate that amino acid variations within TRBV not directly involved in ligand contact can program TCR sensitivity, and suggest a role for CDR3 stability in this programming.
Highlights
T cells endowed with new specificities by T cell receptor (TCR) transduction have shown promise in cancer and other diseases [1,2,3]
Biased TRBV use need not indicate a clonal or oligoclonal response, but may be associated with heterogeneous TRAV and CDR3b sequences, a feature we identified after sequencing TCR from myelin oligodendrocyte glycoprotein (MOG)-specific T cell clones [25,26]
As the hydroxymethyl side chain of the more common S is positioned to intercalate into the core of the CDR3b loop, we reasoned that alternative amino acids at that position should distort the CDR3b’s conformation and thereby influence peptide MHC (pMHC) recognition
Summary
T cells endowed with new specificities by T cell receptor (TCR) transduction have shown promise in cancer and other diseases [1,2,3]. Inadequate affinity may limit the activity of introduced TCR, and engineering enhanced responsiveness to peptide MHC (pMHC) ligand is an important challenge [4]. Random mutations that increase TCR affinity will often non-selectively increase affinity for MHC. T cells modified with TCR mutated and selected for high affinity have been found to lose Ag specificity, responding to APCs alone [5,8,13]. It would be anticipated that mutant TCR with smaller affinity increases will likewise possess some increased reactivity to MHC. This may convert subthreshold engagements with self or other Ags into productive responses. By using known TCR structures to direct mutations to residues less likely to alter Ag selectivity, may be a useful alternative to empirical approaches to modulate TCR affinity
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