Investigating host versus donor T cell chimerism in cutaneous graft versus host disease

BACKGROUND: Graft versus host disease (GVHD) is a significant cause of morbidity and mortality following stem cell transplantation. Donor T cells are thought to be the main mediators of this disease, although we have recently identified that host T cells are present and active during acute GVHD suggesting contributions from both donor and host T cells. Whether both donor and host T cells can survive GVHD and coexist harmoniously after disease resolves is unknown. \nOBJECTIVE: The goals of this thesis are two-fold: (i) to study T cell chimerism in post-GVHD skin and (ii) to understand what effect, if any, treatment has on T cell chimerism in skin. \nMETHODS: Acute GVHD and post-GVHD skin samples were obtained from male patients that had been transplanted with female donor cells. Chimerism was assessed using fluorescence in situ hybridization for the X and Y chromosomes concurrently with immunofluorescence staining for CD3, a T cell marker. Regulatory T cells were stained by immunofluorescence for CD3, CD4 and Foxp3. Medical record data was collected for all patients. \nRESULTS: We found that the percent of host T cells decreased significantly after resolution of acute skin GVHD compared to during active acute skin GVHD in skin samples obtained from five male patients that had been transplanted with female donor cells. The T cell composition in these patients in post-GVHD skin was primarily donor. We identified chimerism shifted toward donor T cells in patients treated with systemic steroids and this correlated with an increased number of donor T cells infiltrating into skin rather than a decrease in the number of host T cells in skin. With regard to frequency of Tregs, there was no significant difference between the group that had been treated with systemic steroids prior to biopsy and the group that had not. \nCONCLUSIONS: We discovered that donor chimerism predominates in post-GVHD skin and in active skin GVHD of patients who received systemic steroids, suggesting a role of donor cells in acute GVHD resolution. We were not able to identify a higher frequency of regulatory T cells in the treatment group. It is possible that the Treg recruited to skin by steroid treatment is Foxp3 negative, and therefore missed by our staining approach. The use of another marker is required for future studies.