Adoptive Transfer of WT1-Specific TCR Gene-Transduced Lymphocytes in Patients with Myelodysplastic Syndrome and Acute Myeloid Leukemia

Wilms' Tumor 1 (WT1) is expressed in a majority of MDS and AML cells and mRNA of WT1 in peripheral blood and bone marrow is monitored as a marker of minimal residual disease of AML and MDS. Several WT1 protein-derived epitopes that are recognized by cytotoxic T lymphocytes (CTLs) along with HLA molecules are determined. In vitro study and WT1 peptide vaccine trials have demonstrated that WT1-specfic CD8+ T cells with cytotoxic activity can be induced. Adoptive T cell therapy using ex vivo expanded WT1-specific CTLs or WT1-specific T-cell receptor (TCR)-gene transduced cells are potentially effective to refractory MDS and AML.

Antigen-specific TCR-gene transfer may cause serious autoimmune disease by mispairing of introduced and endogenous TCR chains that recognize auto-antigens. We established a retroviral vector system encoding siRNAs for endogenous TCR genes to eliminate TCR-mispairing. Using the siRNA-encoding viral vector, we have conducted a first-in-man trial of WT1-specfic TCR-gene transduced T cell transfer. In the trial, we evaluate the safety of the TCR T cell transfer in patients with MDS and AML, and assess in vivo kinetics of the transferred cells. The study was designed as cell-dose escalation with three cohorts of 2x10⁸, 1x10⁹, and 5x10⁹cells per infusion.

Peripheral blood mononuclear cells were collected from each patient. Then, the cells were cultured with IL-2, anti-CD3 antibody, and RetroNectin^®. Proliferating lymphocytes were infected with a retroviral vector, MS3-WT1-siTCR, which was constructed from DNA encoding WT1_235-243/HLA*A24:02 specific TCR-α and -β chains and siRNAs for endogenous TCR genes. After 13-14 days in culture, the lymphocytes were harvested and frozen until infusion.

Patients were enrolled to the clinical trial if they were refractory AML or MDS ineligible for allogeneic stem cell transplant, positive for HLA-A*24:02, had performance status of 0 to 2, and had normal organ function. WT1-TCR T cells were infused intravenously twice on days 0 and 28. Modified WT1_235-243peptide (300μg) emulsified with Montanide, was given subcutaneously on day 2 and 16 after the second infusion.

To date, 5 patients (4 MDS and 1 AML cases) with a median age of 69 years, received WT1-TCR T cells. Three received 2x10⁸ cells (cohort 1) and 2 received 1x10⁹ cells (cohort 2) per infusion, respectively. We did not see any severe adverse events related to the cell infusion or peptide vaccination. No renal or mesothelial damages were observed. We then assessed transduced TCR-gene copy numbers in peripheral blood samples collected at multiple pre-determined time points until day 58.TCR-gene marked cells were detected in all patients after the cell infusion. They appeared immediately after the infusion, reaching peak levels between 1 and 3 days. Then, the levels gradually declined. After the second infusion, which was followed by peptide vaccination, the cells appeared in the similar way to the first cycle. The peptide vaccine did not seem to affect the peripheral cell kinetics. Dose-dependent kinetics were shown between the cohort 1(2 x10⁸ cells) and the cohort 2 (1x10⁹cells). In two patients, transient decline of peripheral abnormal cells that were MDS-related erythroblasts, and decrease of bone marrow blasts were observed, respectively.

Although the clinical trial is still ongoing, transfer of WT1-TCR-gene transduced lymphocyte to MDS and AML patients is safe and tolerable. TCR- T cells appeared in peripheral blood with cell-dose dependent manner.