A novel platform, termed TRACeR, has been developed to create proteins that specifically bind to peptide-MHC-I (pMHC-I) complexes. This innovation allows for targeted recognition of tumor-associated antigens presented on cancer cells, opening new avenues for cancer immunotherapy. The study, published in Nature Biotechnology, details the design, validation, and application of TRACeR proteins in redirecting T cells to eliminate tumor cells.
Design and Validation of TRACeR Proteins
The TRACeR platform leverages computational modeling and combinatorial library screening to identify proteins with high affinity and specificity for target pMHC-I complexes. Researchers used the crystal structure of a TRACeR bound to HLA-A*02:01/NY-ESO-1 to guide the design process. Through iterative rounds of Rosetta high-resolution docking and interface sequence design, they optimized TRACeR variants for binding to specific pMHC-I targets. The designed proteins were then expressed on the surface of yeast cells and screened using fluorescence-activated cell sorting (FACS) to identify binders with desired characteristics.
Versatility in Therapeutic Applications
The TRACeR platform's versatility was demonstrated through the creation of bispecific T-cell engagers (BiTEs) and CAR-T cells. A TRACeR-based BiTE was engineered to target the NY-ESO-1 antigen presented on tumor cells, redirecting T cells to kill these cells. In vitro cytotoxicity assays showed that the TRACeR BiTE effectively eliminated NY-ESO-1-positive diffuse large B-cell lymphoma (DLBCL) cell lines. Similarly, TRACeR-based CAR-T cells were generated and shown to specifically kill tumor cells expressing the targeted antigen.
In Vivo Efficacy and Safety
In vivo studies were conducted to evaluate the efficacy and safety of TRACeR-based therapeutics. Mice treated with TRACeR-based BiTEs exhibited potent anti-tumor responses, with significant reduction in tumor volume compared to control groups. Immunogenicity assays revealed that TRACeR proteins were well-tolerated and did not elicit significant off-target immune responses. These findings suggest that TRACeR-based therapeutics have the potential to be safe and effective in clinical applications.
Addressing the Challenge of Intracellular Tumor Antigens
Traditional antibody-based therapies often struggle to target intracellular tumor antigens. The TRACeR platform overcomes this limitation by targeting pMHC-I complexes, which present processed intracellular antigens on the cell surface. This approach expands the repertoire of targetable tumor antigens and offers new opportunities for precision cancer immunotherapy.
Sequence-Based Selection of Cross-Reactive Peptides
To identify peptides that cross-react with TRACeR, researchers searched the Immune Epitope Database for linear peptides that bind to HLA-A*02:01 with a specific SMW motif. Three peptides (FTIAMWLLL, CINMWCWTV, and TSDMWLYR) were selected for further analysis, demonstrating the platform's ability to identify and target cross-reactive antigens.
Future Directions
The TRACeR platform represents a significant advancement in targeted cancer immunotherapy. Future research will focus on expanding the platform to target a wider range of tumor-associated antigens and optimizing the design of TRACeR-based therapeutics for clinical applications. The ability to precisely target and redirect T cells to kill tumor cells holds great promise for improving cancer treatment outcomes.
