Increased Frequency and Responsiveness of PSA-Specific T Cells After Allogeneic Hematopoetic Stem-Cell Transplantation

Autologous and allogeneic cellular therapies for high-risk pediatric solid tumors

Since the 1950s, the overall survival of children with cancer has gone from almost zero to approaching 80%. Although there have been notable successes in treating solid tumors such as Wilms tumor, some childhood solid tumors have continued to elude effective therapy. With the use of megatherapy techniques such as tandem transplantation, dose escalation has been pushed to the edge of dose-limiting toxicities, and any further improvements in event-free survival will have to be achieved through novel therapeutic approaches. This article reviews the status of autologous and allogeneic hematopoietic stem cell transplantation (HSCT) for many pediatric solid tumor types. Most of the clinical experience in transplant for pediatric solid tumors is in the autologous setting, so some general principles of autologous HSCT are reviewed. The article then examines HSCT for diseases such as Hodgkin disease, Ewing sarcoma, and neuroblastoma, and the future of cell-based therapies by considering some experimental approaches to cell therapies.

The allogeneic graft-versus-cancer effect

Allogeneic haematological stem cell transplantation (HSCT) has developed into immunotherapy. Donor CD4+, CD8+ and natural killer (NK) cells have been reported to mediate graft-versus-leukaemia (GVL) effects, using Fas-dependent killing and perforin degranulation to eradicate malignant cells. Cytokines, such as interleukin-2, interferon-gamma and tumour necrosis factor-alpha potentiate the GVL effect. Post-transplant adoptive therapy of cytotoxic T-cells (CTL) against leukaemia-specific antigens, minor histocompatibility antigens, or T-cell receptor genes may constitute successful approaches to induce anti-tumour effects. Clinically, a significant GVL effect is induced by chronic rather than acute graft-versus-host disease (GVHD). An anti-tumour effect has also been reported for myeloma, lymphoma and solid tumours. Reduced intensity conditioning enables HSCT in older and disabled patients and relies on the graft-versus-tumour effect. Donor lymphocyte infusions promote the GVL effect and can be given as escalating doses with response monitored by minimal residual disease. A high CD34+ cell dose of peripheral blood stem cells increases GVL. There is a balance between effective immunosuppression, low incidence of GVHD and relapse. For instance, T-cell depletion of the graft increases the risk of relapse. This paper reviews the current knowledge in graft-versus-cancer effects. Future directions, such as immunotherapy using leukaemia-specific CTLs, allo-depleted T-cells and suicide gene manipulated T-cells, are presented.