Post-Transplant Prophylactic Cellular Immunotherapy with Anti- Leukemic WT1-Specific CTLs for High-Risk Acute Myelogenous Leukemia

High-level expression of Wilm’s tumor 1 (WT1) gene or its mutations correlates with the clinical outcome in patients with acute myeloid leukemia (AML), making WT1 a valuable immunotherapeutic target for AML and a critical prognostic factor for minimal residual disease (MRD). We developed a novel strategic immunotherapeutic tool to eradicate MRD by enhancing the graft-versus-leukemia effect following conventional allogeneic hematopoietic stem cell transplantation (HSCT) in patients with relapse highrisk AML. For the potent induction of anti-leukemic WT1-specific cytotoxic T cells (CTLs), whole leukemic cell-challenged dendritic cells were used as antigen-presenting cells for presentation of a truncated form of WT1, expressed using an adenoviral vector system. Four male and four female patients, with a median age of 40 years (range, 28–49), who were categorized mostly as cytogenetically high-risk for AML or initially resistant to standard induction chemotherapy, received allogeneic sibling donor HSCT, followed by anti-leukemic WT1-specific CTL induction as consolidation chemotherapy at our center. The preparative regimen consisted of cyclophosphamide 60 mg/kg/day for 2 days and total body irradiation with a total dose of 1,320 cGy for 4 days. Cyclosporine A and a short course of standard-dose methotrexate were used to prevent GVHD. Beginning day+35 post-transplantation, WT1-specific CTLs were infused four consecutive times at 1-week intervals in those patients with no moderate to severe acute graft-versus-host disease (GvHD). If no acute GvHD occurred, the CsA was tapered over 4–8 weeks, with the intent to discontinue by 3–5 months. Every 1–3 months after the CTLs infusion, for at least 1 year post-transplantation, we serially monitored the peripheral blood lymphocyte subpopulations, using flow cytometry; the in vitro activity of interferon-γ (IFN-γ), using an ELISPOT assay; and the WT1 level, using real-time quantitative polymerase chain reaction (RQ-PCR). All patients were engrafted successfully, and none relapsed. Seven patients were alive at a median follow-up of 6 months (range, 3–15). Five (63%) of the eight patients developed acute GvHD, but none were grade >II. Three (50%) of the six evaluable patients developed chronic extensive type GvHD; however, all but one were manageable. The cause of death in the one patient who died at 11 months post-transplantation was progressive pneumonia with sepsis, combined with chronic extensive type GvHD. The patients exhibited a high variability of WT1 expression by RQ-PCR, but decreased median WT1 levels were apparent post-transplantation. All of the patients exhibited a decreased CD4/CD8 ratio and persistently increased IFN-γ level by ELISPOT assay. Despite the short-term follow-up period, these findings are promising and suggest the possible future use of a similarly specific therapeutic strategy of combining elective allogeneic HSCT with WT1-CTLs infusion post-transplantation, in a manner tailored to individual patients.