Biased usage of T cell receptor β-chain variable region genes of Wilms' tumor gene (WT1)-specific CD8+ T cells in patients with solid tumors and healthy donors

Spontaneous high clonal expansion of Wilms' tumor gene 1-specific cytotoxic T-lymphocytes in patients with Wilms' tumor gene 1-expressing solid tumor

Wilms' tumor protein 1 (WT1)-targeted immunotherapy has been used in patients with leukemia and solid tumors. However, the spontaneous WT1-specific immune response before WT1 peptide vaccination in patients with WT1-expressing tumors (PTs) remains unclear. Therefore, we investigated whether WT1-specific cytotoxic CD8+ T-lymphocytes (CTLs) are clonally expanded in the peripheral blood outside of tumor sites. Clonal expansion of WT1126 peptide (a.a.126-134)-specific CTLs (WT1126-CTLs) was compared between seven PTs and five healthy volunteers (HVs), and their T-cell receptors (TCRs) were analyzed at the single-cell level. Overall, 433 and 351 TCR β-chains of WT1126-CTLs were detected from PTs and HVs, respectively, and complementarity-determining region 3 was sequenced for clonality analysis. The frequencies of WT1126-CTLs were higher in human leukocyte antigen (HLA)-A*02:01+ PTs than in HLA-A*02:01+ HVs, although the difference was not statistically significant. WT1126-CTLs of differentiated types, including memory and effector, were higher in PTs than in HVs; whereas, those of the naïve type were higher in HVs than in PTs. WT1126-CTL clonality was significantly higher in PTs than in HVs. Furthermore, the frequency of effector WT1126-CTLs positively correlated with WT1126-CTL clonality in PTs; whereas, the frequency of naïve phenotype WT1126-CTLs tended to be negatively correlated with clonality. In conclusion, these results suggest that the WT1 protein in tumor cells is highly immunogenic, thereby stimulating endogenous naïve-type WT1126-CTLs and enabling them to clonally expand and differentiate into effector-type WT1126-CTLs.

Preclinical development of T-cell receptor-engineered T-cell therapy targeting the 5T4 tumor antigen on renal cell carcinoma

5T4 (trophoblast glycoprotein, TPBG) is a transmembrane tumor antigen expressed on more than 90% of primary renal cell carcinomas (RCC) and a wide range of human carcinomas but not on most somatic adult tissues. The favorable expression pattern has encouraged the development and clinical testing of 5T4-targeted antibody and vaccine therapies. 5T4 also represents a compelling and unexplored target for T-cell receptor (TCR)-engineered T-cell therapy. Our group has previously isolated high-avidity CD8⁺ T-cell clones specific for an HLA-A2-restricted 5T4 epitope (residues 17-25; 5T4_p17). In this report, targeted single-cell RNA sequencing was performed on 5T4_p17-specific T-cell clones to sequence the highly variable complementarity-determining region 3 (CDR3) of T-cell receptor α chain (TRA) and β chain (TRB) genes. Full-length TRA and TRB sequences were cloned into lentiviral vectors and transduced into CD8⁺ T-cells from healthy donors. Redirected effector T-cell function against 5T4_p17 was measured by cytotoxicity and cytokine release assays. Seven unique TRA-TRB pairs were identified. All seven TCRs exhibited high expression on CD8⁺ T-cells with transduction efficiencies from 59 to 89%. TCR-transduced CD8⁺ T-cells demonstrated redirected cytotoxicity and cytokine release in response to 5T4_p17 on target-cells and killed 5T4⁺/HLA-A2⁺ kidney-, breast-, and colorectal-tumor cell lines as well as primary RCC tumor cells in vitro. TCR-transduced CD8⁺ T-cells also detected presentation of 5T4_p17 in TAP1/2-deficient T2 target-cells. TCR-transduced T-cells redirected to recognize the 5T4_p17 epitope from a broadly shared tumor antigen are of interest for future testing as a cellular immunotherapy strategy for HLA-A2⁺ subjects with 5T4⁺ tumors.

Analysis of cytotoxic T lymphocytes from a patient with hepatocellular carcinoma who showed a clinical response to vaccination with a glypican‑3‑derived peptide

Glypican-3 (GPC3), which is a carcinoembryonic antigen, is overexpressed in human hepatocellular carcinoma (HCC). Previously, we performed a phase I clinical trial of GPC3-derived peptide vaccination in patients with advanced HCC, and reported that GPC3 peptide vaccination is safe and has clinical efficacy. Moreover, we proposed that a peptide-specific CTL response is a predictive marker of overall survival in patients with HCC who receive peptide vaccination. In this study, we established GPC3-derived peptide-specific CTL clones from the PBMCs of an HLA-A ^* 02:07-positive patient with HCC who was vaccinated with an HLA-A2-restricted GPC3 peptide vaccine and showed a clinical response in the phase I clinical trial. Established CTL clones were analyzed using the IFN-γ ELISPOT assay and a cytotoxicity assay. GPC3 peptide-specific CTL clones were established successfully from the PBMCs of the patient. One CTL clone showed cytotoxicity against cancer cell lines that expressed endogenously the GPC3 peptide. The results suggest that CTLs have high avidity, and that natural antigen-specific killing activity against tumor cells can be induced in a patient with HCC who shows a clinical response to vaccination with the GPC3 _144–152 peptide.