Graft-versus-tumor induction with donor leukocyte infusions as primary therapy for patients with malignancies

Allogeneic bone marrow transplantation for lymphoma

Registry data show that use of allogeneic transplantation for non-Hodgkin's lymphoma, and to a lesser extent, Hodgkin's disease is increasing. Although no prospective randomized trials have been performed, most comparisons show a significantly lower relapse rate when allogeneic transplant results are compared to results of autologous hematopoietic stem cell transplantation. The lower relapse rate following allogeneic transplantation, as well as several other lines of evidence, support the existence of a graft-versus-lymphoma effect. Nevertheless, in most comparisons, the lower relapse rate following allogeneic transplantation is offset by higher transplant-related mortality. These results make it difficult to find situations where definite overall survival advantages associated with the use of allogeneic transplantation can be demonstrated. The use of low-intensity non-myeloablative regimens for allogeneic transplantation is attracting attention. It is hoped that this approach may harness a graft-versus-lymphoma effect with less morbidity and mortality than conventional allogeneic transplantation, but more data are required to assess the value of this treatment.

Genetic modification of human T cells with CD20: a strategy to purify and lyse transduced cells with anti-CD20 antibodies

A retroviral vector has been constructed that contains the human CD20 cDNA under the control of the Moloney murine leukemia virus (Mo-MuLV) LTR. Freshly isolated mononuclear cells are infected for three consecutive days in the presence of PHA and hrlL-2, and a mean 15.9% of the cells (range, 6.5 to 31.7%) acquire a CD3+CD20+ phenotype. Transduced T lymphocytes grow and expand in vitro for up to 3 weeks like mock-infected cells and, as observed for the T lymphoblastoid CEM cell line, CD20 expression is maintained for several months with no change in the growth curve of the cells. CD20-expressing CEM and fresh T lymphocytes can be positively immunoselected on columns using different anti-CD20 antibodies. Exposure to monoclonal chimeric anti-CD20 IgG1(kappa) Rituximab antibody (Roche), in the presence of complement, results in effective and rapid killing of the transduced CD3+CD20+ human T cells in vitro. This approach represents a new and alternative method to gene manipulation with "suicide" genes for the production of drug-responsive T cell populations, a crucial step for the future management of graft-versus-host disease in bone marrow transplant patients.

Advances in the treatment of graft-versus-host disease

Graft-versus-host disease (GVHD) is a complicated disease whose treatment requires an equally multifaceted approach. Recipient conditioning, donor T cell activation, and end stage effectors all may be potential targets for treatment. Many drugs used in the past are returning to the forefront for investigation. Some of the newer nucleoside analogs that are in various stages of development, such as fludarabine and pentostatin, are showing promising activity in GVHD.

Nonmyeloablative stem cell transplants

Allogeneic stem cell transplantation (SCT) is a curative procedure in a number of hematologic malignancies, but its efficacy is limited by its toxicity, much of which is consequent upon the myeloablative conditioning regimens currently used. The recent demonstration that an immunologically mediated graft-versus-leukemia effect plays a central role in delivering the anti-leukemic effect of an allograft has led to a fundamental reevaluation of the role of conditioning therapy in allogeneic transplantation. Recent animal studies have demonstrated that stem cell engraftment can occur using conditioning regimens that are minimally myelotoxic. This has prompted the development of less toxic nonmyeloablative conditioning protocols, the goal of which is to achieve donor stem cell engraftment allowing the graft-versus-tumor effect of the allograft to be exploited as the primary anti-leukemic strategy. Preliminary results using such nonmyeloablative clinical protocols confirm that durable engraftment of allogeneic stem cells can be achieved with a marked reduction in the immediate toxicity of transplantation. The extent to which this radically different transplant strategy allows the delivery of a sustained anti-leukemic effect is unclear at present, but it is likely that this approach will make an important contribution to allogeneic SCT in the future.