Prediction, diagnosis and treatment of experimental graft-versus-host disease : an investigation of genomic, molecular and cellular factors in graft-versus-host disease and mesenchymal stromal cell therapy in a rat model of allogeneic stem cell transplantation

Abstract

Patients who suffer from leukemia or lymphoma can be cured by the transplantation of bone marrow stem cells from a volunteer donor (allogeneic hematopoietic cell transplantation). Recipients frequently acquire an immune disorder known as graft-versus-host disease (GvHD) which represents the main hindrance of this therapeutic procedure at present. Graft-borne donor T cells are activated by disparate antigens in the host leading to a cascade of adverse immune reactions and damage of host tissues that give rise to clinical GvHD.

The objectives of this thesis were twofold: firstly, to develop diagnostic tools and identify reliable biomarkers of GvHD; secondly, to improve GvHD treatment by mesenchymal stromal cell (MSC) therapy.

In a collaborative effort, we helped develop the rat skin explant, an ex-vivo assay of GvHD, as well as a DNA microarray for the study of genetic factors that regulate GvHD. Analysis of gene expression in rat skin explants revealed MHC and innate immune receptor genes that were associated with graft-versus-host reactions and are thus of potential use as diagnostic biomarkers of GvHD. In a model of MHC-mismatched bone marrow transplantation that caused acute GvHD in rats, we isolated natural killer cell and T cell subsets including regulatory T cells that were differentially distributed in disease. Using this animal model, we also tested whether MSC injections could prevent GvHD. We concluded that repeated interventions failed to alleviate disease or improve survival in transplanted rats. In contrast, MSC potently suppressed T cell proliferation and cytokine secretion in vitro. Proliferation was inhibited through the enzymatic synthesis of nitric oxide.

In summary, this work resulted in the characterization of genetic and cellular markers of GvHD in the skin ex vivo and after transplantation in vivo as well as the isolation of nitric oxide synthesis as a key pathway used by rat MSC to inhibit allogeneic T cell responses in vitro.