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GVHD remains a major problem in allo-SCT. We explored the presence of APC in skin biopsies of GVHD patients, using the IgG receptor CD64 expression as a hallmark for activated APC. By immunohistochemistry we demonstrated CD64 to be upregulated on host APC in skin biopsies of patients with acute GVHD and, less prominently, in chronic GVHD. Double staining for CD32 polymorphism revealed CD64-positive cells to be mainly of host origin. The majority of CD64-positive cells coexpressed CD68, indicating a macrophage phenotype. Given its very restricted cellular distribution, CD64 may represent an excellent target for APC-directed therapies in GVHD.

Cardiomyocytes are a stable cell population with only limited potential for renewal after injury. Tissue regeneration may be due to infiltration of stem cells, which differentiate into cardiomyocytes. We have analysed the influx of stem cells in the heart of patients who received either a gender-mismatched BMT (male donor to female recipient) or a gender-mismatched cardiac transplant (HTX; female donor to male recipient). The proportion of infiltrating cells was determined by Y-chromosome in situ hybridization combined with immunohistochemical cell characterization. In BM transplanted patients and in cardiac allotransplant recipients, cardiomyocytes of apparent BM origin were detected. The proportions were similar in both groups and amounted up to 1% of all cardiomyocytes. The number of stem cell-derived cardiomyocytes did not alter significantly in time, but were relatively high in cases where large numbers of BM-derived Y-chromosome-positive infiltrating inflammatory cells were present. The number of Y-chromosome-positive endothelial cells was small and present only in small blood vessels. The number of BM-derived cardiomyocytes in both BMT and HTX is not significantly different between the two types of transplantation and is at most 1%.