Utilize a soluble T-cell receptor TCR targeting tumor intracellular antigen PRAME to develop therapeutic and radioactive diagnostic agents for PRAME-positive tumors

T-cell receptor (TCR)-based therapeutics and diagnostics hold great promise for targeting intracellular tumor antigens presented by HLA molecules. The preferentially expressed antigen in melanoma (PRAME) is expressed in many cancers, but is highly restricted in normal tissues, making it a good target for TCR-based therapy. We have established a proprietary high-efficiency TCR discovery platform, enabling rapid identification of antigen-specific TCRs from healthy donors and cancer patients. TCRs specifically targeting PRAME425-433 peptide/ HLA-A*02:01 complex were cloned from healthy donors. T cells transduced with lentivirus encoding PRAME-specific TCR exhibited robust IFN-gamma secretion and cytolytic function in an antigen-specific manner. By engineering the constant regions of both TCR alpha and beta chains, the soluble expression of monovalent and bivalent native TCRs was achieved. We developed an exclusive cell based TCR binding assay to screen and identify the soluble forms of native PRAME-specific TCRs with various affinities. Surface plasmon resonance (SPR) analysis demonstrated that the bivalent native TCR protein HP-002 binds PRAME425-433/HLA-A*02:01 with a KD of 1.08 × 10⁻⁷ M. The Bivalent native TCR was used to develop TCR-CD3 T cell engager and radioactive diagnostic agent for imaging. Iodine-125 (125I)-labeled bivalent native TCR protein HP-002 exhibited in vivo antigen-dependent tumor accumulation in xenograft tumor models by SPECT/CT imaging. These data highlight the capability of our discovery and molecular engineering platform to develop the soluble TCRs for therapeutics and radioactive diagnostics in cancer. Our ongoing work focuses on TCR affinity maturation and molecular optimization of HP-002 to improve its affinity and selectivity, aiming to achieve enhanced tumor accumulation for future diagnostic and therapeutic applications.