The unphysiological formation of biological chimeras after allogeneic hematopoietic cell transplantation is not free of consequences. Recent findings suggest that in the transplant recipient some epithelial cells reveal, unexpectedly, donor-derived genotype and/or acquire genomic alterations. Since both phenomena are presented in the host epithelium, one could argue that they might be etiologically linked through a common background mechanism. We recently proposed that the incessant charge of the transplant recipient with donor-DNA and its integration in host epithelium by horizontal DNA transference may indeed be operative in the generation of epithelial cells with donor derived genome. On the other hand, the incessant incorporation of the foreign DNA into the host genome may result in genomic alterations. Lymphocyteepithelial interactions between the two genetically distinct cell populations in the transplant recipient should be investigated more precisely not only in cellular but also in molecular level.