Validation and promise of a TCR mimic antibody for cancer immunotherapy of hepatocellular carcinoma

Abstract

Monoclonal antibodies are at the vanguard of the most promising cancer treatments. Whereas traditional therapeutic antibodies have been limited to extracellular antigens, T cell receptor mimic (TCRm) antibodies can target intracellular antigens presented by cell surface major histocompatibility complex (MHC) proteins. TCRm antibodies can therefore target a repertoire of otherwise undruggable cancer antigens. However, the consequences of off-target peptide/MHC recognition with engineered T cell therapies are severe, and thus there are significant safety concerns with TCRm antibodies. Here we explored the specificity and safety profile of a new TCRm-based T cell therapy for hepatocellular carcinoma (HCC), a solid tumor for which no effective treatment exists. We targeted an alpha-fetoprotein peptide presented by HLA-A*02 with a highly specific TCRm, which crystallographic structural analysis showed binds directly over the HLA protein and interfaces with the full length of the peptide. We fused the TCRm to the γ and δ subunits of a TCR, producing a signaling AbTCR construct. This was combined with an scFv/CD28 co-stimulatory molecule targeting glypican-3 for increased efficacy towards tumor cells. This AbTCR + co-stimulatory T cell therapy showed potent activity against AFP-positive cancer cell lines in vitro and an in an in vivo model and undetectable activity against AFP-negative cells. In an in-human safety assessment, no significant adverse events or cytokine release syndrome were observed and evidence of efficacy was seen. Remarkably, one patient with metastatic HCC achieved a complete remission after nine months and ultimately qualified for a liver transplant.

Computationally profiling peptide:MHC recognition by T-cell receptors and T-cell receptor-mimetic antibodies

“…CTA: cancer testis antigen, MHCA: MHC alpha chain, MHCB: MHC beta chain, Neo: neoantigen. *We have labelled the TCRm from 7RE7 as AFP-TCRm as it has no name in the seminal paper (28).…”

“…Experimental peptidome binding assays performed on three early-generation TCRms (17,19,20) suggested that they were unlikely to achieve the levels of specificity required for therapeutic applications (21,22). However, several TCRms with apparently high specificity have been reported in the past year, fostering renewed interest in this therapeutic modality and resulting in a more than doubling of the num-ber of crystal structures of TCRm:pMHC complexes (23)(24)(25)(26)(27)(28). These include an anti-Wilms' Tumor Antigen 1 (WT1) TCRm ( 23) and an anti-alpha ferroprotein (AFP) TCRm (28) that have both progressed to clinical trials (23).…”

“…However, several TCRms with apparently high specificity have been reported in the past year, fostering renewed interest in this therapeutic modality and resulting in a more than doubling of the num-ber of crystal structures of TCRm:pMHC complexes (23)(24)(25)(26)(27)(28). These include an anti-Wilms' Tumor Antigen 1 (WT1) TCRm ( 23) and an anti-alpha ferroprotein (AFP) TCRm (28) that have both progressed to clinical trials (23). Two neoantigen peptide:MHC-specific TCRms were also identified that achieve complete selectivity over their wildtype peptide equivalents each differing by just a single residue mutation (24,25).…”

“…TCRs seem to avoid this behavior, instead reliably exploiting energy hotspots on the peptide surface. Finally, we highlight TCR-like pMHC recognition features in the first TCRms to achieve sufficient specificity to reach the clinic (11D06 (23) and AFP-TCRm (28)) versus a TCRm with several known off-targets (ESK1). Overall, our analysis begins to quantify TCR-likeness across TCRms, enabling rational TCRm selection, optimisation, and design based on the natural cognate partners of pMHCs.…”

Computationally profiling peptide:MHC recognition by T-cell receptors and T-cell receptor-mimetic antibodies

“…Experimental peptidome binding assays performed on three early-generation TCRms ( 17 , 19 , 20 ) suggested that they were unlikely to achieve the levels of specificity required for therapeutic applications ( 22 , 23 ). However, several TCRms with apparently high specificity have been reported in the past year, fostering renewed interest in this therapeutic modality and resulting in a more than doubling of the number of crystal structures of TCRm:pMHC complexes ( 24 – 29 ). These include an anti-Wilms’ Tumor Antigen 1 (WT1) TCRm ( 24 ) and an anti-alpha ferroprotein (AFP) TCRm ( 29 ) that have both progressed to clinical trials.…”