Combined laser-assisted microdissection and short tandem repeat analysis for detection of in situ microchimerism after solid organ transplantation.

Following the transplantation of a solid organ leukocytes of donor origin migrate out of the organ, contributing to a chimeric blood cell population ("peripheral microchimerism"). At the same time, leukocytes and pluripotent precursor cells of the recipient migrate into the organ, creating an "in situ microchimerism." A method is described for the identification of cells with the recipient's genotype in the transplanted organ by combining laser-assisted microdissection and short tandem repeat analysis. The microdissection allows the contamination-free isolation of morphologically and immunohistochemically characterized cells or groups of cells from histological tissue sections. The subsequent analysis of highly polymorphic short tandem repeats enables unequivocal genotyping in nearly all donor-recipient instances. Employing this new methodological approach, we could identify in individual transplanted organs differentiated parenchymal cells of recipient's origin, which most probably are derived from circulating precursor cells from the bone marrow.

Increased chimerism of bronchial and alveolar epithelium in human lung allografts undergoing chronic injury.

Chimerism on the parenchymal level has been shown for several human allografts, including liver, heart, and kidney, with the integrated recipient-derived cells most likely originating from multipotent bone marrow precursors. We investigated whether chimerism also occurs within epithelial structures of the lung. For this purpose archival tissue biopsies from seven explanted human lung allografts were obtained. We performed laser microdissection of the target structures with subsequent short tandem repeat analysis to detect chimerism within the isolated cells. We found integration of recipient-derived cells in the bronchial epithelium, in type II pneumocytes and in seromucous glands lying adjacent to larger bronchi in all lung allografts studied. Quantitative analysis revealed that the epithelial structures displaying signs of chronic injury, such as squamous metaplasia, showed a markedly higher degree of chimerism (24% versus 9.5%). We therefore conclude that in human lungs, epithelial chimerism occurs at least within bronchi, type II pneumocytes, and seromucous peribronchial glands. Although a bone marrow origin of immigrating host-derived stem cells has been suggested by previous studies in rodents, analysis of lung biopsies from bone marrow-transplanted patients (n = 3) could not prove such delineation in this study. The observation of an enhanced integration of recipient cells into chronically damaged epithelial structures suggests that extrapulmonary precursor cells are able to contribute to pulmonary regeneration.