In vitro generation of Epstein-Barr virus-specific cytotoxic T cells in patients receiving haplo-identical allogeneic stem cell transplantation

Cellular therapy of Epstein-Barr-virus-associated post-transplant lymphoproliferative disease

During the immunodeficiency that follows hemopoietic stem cell transplant or solid organ transplant, lymphoproliferation can develop due to uncontrolled expansion of Epstein-Barr-virus (EBV)-infected B cells that express the full spectrum of EBV latent antigens. As development of post-transplant lymphoproliferative disease (PTLD) in these patients is clearly associated with a deficient EBV-specific cellular immune response, immunotherapy strategies to restore the EBV-specific immune response have been evaluated. In hemopoietic stem cell transplant recipients, adoptively transferred donor-derived EBV-specific T cells have been able to restore immunity and eradicate overt lymphoproliferation. Autologous or closely matched allogeneic EBV-specific cytotoxic T lymphocytes have also shown promise in recipients of solid organ transplant. The use of genetically modified T cells or newer suicide genes may result in improved safety and efficacy. Current challenges are to define indications for immunotherapy or antibody therapy in patients with incipient or overt PTLD.

Adoptive immunotherapy for posttransplantation viral infections

Viral diseases are a major cause of morbidity and mortality after hemopoietic stem cell transplantation. Because viral complications in these patients are clearly associated with the lack of recovery of virus-specific cellular immune responses, reconstitution of the host with in vitro expanded cytotoxic T lymphocytes is a potential approach to prevent and treat these diseases. Initial clinical studies of cytomegalovirus and Epstein-Barr virus in human stem cell transplant patients have shown that adoptively transferred donor-derived virus-specific T cells may restore protective immunity and control established infections. Preclinical studies are evaluating this approach for other viruses while strategies for generating T cells specific for multiple viruses to provide broader protection are being evaluated in clinical trials. The use of genetically modified T cells or the use of newer suicide genes may result in improved safety and efficacy.

Allogeneic transplantation across major HLA barriers

Only one-fourth of patients with fatal haematological disorders and malignancies will have an HLA-matched sibling donor to create access to potentially curative allogeneic stem cell transplantation. Advances in medical management, preparation of the graft and prevention of transplant-related complications, particularly rejection and GVHD, now make it possible to use alternative donors who are not genetically HLA-histocompatible with the patient. Some patients identify unrelated donor options using adult volunteers or cord blood units. All patients have immediate access to one or more genetically half-matched (haplo-identical), HLA partially-mismatched related donors. Using safer non-cytotoxic therapies to ablate the patient's immune system, graft preparation to decrease T-lymphocyte and/or increase CD 34+ cell doses, and post-transplant GVHD and infection prophylaxis, rates >95% for engraftment and <25% for grade II-IV GVHD can be achieved. Thus, disease-free survival rates are comparable to other alternative donors with all outcomes adversely influenced by advanced disease status, poor medical performance and older age.