Lung engraftment, however, has not been confirmed in all studies, and more recently the area and methodology have been reevaluated. It is now accepted that previously used methods of detecting engraftment have not been sufficiently rigorous (Table 2
), particularly with the problems of donor-derived inflammatory cells migrating to areas of damage. Techniques used to assess lung chimerism as evidence for engraftment (particularly immunohistochemistry) have been shown to be subject to significant artifacts leading to an overestimation of the amount of engraftment.19–20 One study19 employed a lineage-specific reporter system based on transgenic mice that express the GFP reporter gene only in lung epithelial cells (surfactant protein-C–GFP) to assay for engrafted cells by flow cytometry, histology, and molecular methods. This showed no evidence of bone marrow-derived epithelial cells.19This conclusion was also reached by a related article20that exposed apparently chimeric lung cells as overlapping cells with deconvolution microscopy. Some of the discrepancy and lack of consistency between study outcomes is also attributable to study design. In each experiment, different stem cells have been used as donors (eg, MSCs, side population stem cells, HSCs, whole bone marrow, endothelial progenitor cells [EPCs], multipotent adult progenitor cells21), and the experimental conditions and recipients have differed.