A Study of the Relationship of the Dynamics of Development and Characteristics of Chimerism with Manifestations of Graft-vs.-Host Disease in the Organs of Mice after Allogeneic Transplantation of Whole Bone Marrow

Abstract

In сlinical practice, allogeneiс bone marrow transplantation (BMT) is often a cause of graft-vs.-host disease (GvHD). GvHD is explained by the fact that T-lymphocytes, which are administered simultaneously with hematopoietic cells during transplantation and form and mature anew in the timus of the recipient from donor progenitor cells thereafter, recognize and attack the cells of the host. However, a complete explanation of the phenomenon of the GvHD does not exist, and chimerization of the recipient’s organism as a possible cause of damage of its organs is not taken into account. Therefore, the aim of this work consisted in modeling of allogeneic transplantation of the whole bone marrow (experiment) and comparing its results with syngeneic transplantation (control) basing on an investigation of engraftment of cells of donor origin in the main GvHD target organs. The bone marrow donors were Tg(ACTB-EGFP)1Osb/J mice carrying a green fluorescent protein gene (EGFP), and the recipients were animals of CBA and C57BL/6 inbred strains of an age of 2–10 months. One day before BMT (1.5 × 10⁷ cells per mouse), all recipients were irradiated at a dose of 6.5 Gy (LD 50/30). After 1, 3, 5, 7, 11, 14, 21, 28, 35, and 55 days, the development of chimerism in the liver, skin, and colon of animals was examined using a fluorescent microscope. Already after 1 day, single fibroblast-like donor cells were found in the colon; after 7 days, in the skin and liver. From 14 to 28 days after BMT, donor cells formed mainly stroma in the liver, as well as fibroblasts and keratinocytes in the skin, and in the colon they substituted the cells of the villi, stroma, and parenchyma of Peyer’s patches that died after irradiation. Unlike control, in the experimental groups, GFP+ giant fibroblasts about 30 μm in length were found in the stroma of the liver, as well as in the skin and in the colon; in the liver there were many GFP+ bulkheads and fibroblast-like Ito’s cells of very intricate configuration. From 35 to 55 days after allogeneic BMT, cells of the donor origin in the liver and in the villi of the colon began to destroy, the villi became overgrown with GFP+ connective tissue cells and warped, the wall of the colon became thin, and the skin was fully replaced with a new one (these things were never observed in the control groups). We propose the hypothesis that, alongside GvHD traits like thinning of the colon wall and a large number of roundish GFP+ cells on the inner surface of the skin, other signs of the studied after allogeneic BMT organs suggest that the cells of the organs that are formed from mesenchymal stem cells of the whole bone marrow become targets for the recipient’s T cells, i.e., suggest the existence of a host-vs.-graft (HVG) reaction. The obvious manifestation of immune reactions after BMT directly coincides with the term of massive engraftment of the studied organs with cells of donor origin and restoration of the host’s own immune system; i.e., the development of chimerism determines the development of organ damage. This explains the GvHD symptoms known from medical practice—atrophy of the mucous membranes, excess production of collagen, sclerosis of the bile ducts, skin damage, colitis—and the timing of its manifestation.