Bone Marrow Reaction in Chronic Graft-Versus-Host Disease.
Authors: Hill Wolfgang , Sotlar Karl , Diem Heinz , Hausmann Andreas , Kolb Hans Jochem 
Published: April 2020

Abstract
Hematopoiesis of the host is a primary target organ of the graft-versus-host reaction. However histological analyses of the bone marrow are rarely reported. Here we report histological changes in the bone marrow of patients (pts) with and without chronic graft-versus-host disease (cGvHD). Bone marrow biopsies were obtained between 101 days and 4623 days (median:419 days) after transplantation as part of a controlled prospective phase ll study of patients with osteopenia/osteoporosis after allogeneic hematopoietic stem cell transplantation (HCT). Previously we reported an increased density of microvessels using an antibody against v. Willebrand factor (vW) (Hill W. et al Blood110, abstract No 1963; 2007). Here we report additional immunohistological and immunocytological findings in marrow and blood. We analyzed the number of CD34+ and vW+ microvessels as well as CD8+ suppressor/cytotoxic T-cells/mm² (T-S) in sequential biopsies of pts with (n=9) or without (n=6) cGvHD after median 2 years apart. Biopsies of 3 pts without HCT and without lymphoma involvement served as controls. Simultaneously lymphocyte subpopulations were evaluated in peripheral blood samples of pts with (n=16) or without (n=8) cGvHD. The pts were divided in 5 groups:
neither aGvHD nor cGvHD; no cGvHD but acute GvHD before entry; cGvHD limited; cGvHD extensive without immunosuppression; cGvHD extensive with immunosuppression.
Results: In the first biopsies the content of CD34+, vW+ microvessels and T-S cells were significantly higher in pts with cGvHD (group 3–5) than in those without cGvHD (group 1–2) (21,3 vs 8,2 p=0,03; 22,0 vs 9,2 p=0,002 respectively 106,2 vs 32,1 p=0,04). In the second biopsies these parameters were also increased in cGvHD: CD34+ (18,3 vs 11,2 p=0,02), vW+ (17,3 vs 9,0 p=0,08) microvessels and T-S cells (63,2 vs 37,8 p=0,27). The increased density of CD34+ and vW+ microvessels correlated with the number of T-S cells (p=0,05). As compared to normal controls we observed a significantly higher content of vW+ microvessels in all groups of transplanted pts (16,9 vs 4,2 p=0,03). In pts with cGvHD (group 3–5) CD34+ and vW+ microvessels were further increased (p=0,02 respectively p=0,002). At the time of the first biopsy the absolute T-S cell content in peripheral blood was moderately increased in group 5 (1124/ul) and minimally increased in group 2 (993/ul) (normal 270 – 880), whereas the overall T cell (CD3) content was normal in all groups. The percentage of activated T-S (HLA-DR+) cells was increased in all groups of transplanted pts (61,8% vs normal =33%; p=0,05). After two years T-S cells content was reduced in pts under immunosuppressive therapy (group 5) (1415 vs 900/ul; p=0.000) but remained increased over the norm. In group 4 T-S cell content was increased over the norm (800 vs 920/ul; p=0,043). In conclusion, sequential immunohistology and immunocytology analyses on bone marrow biopsies and peripheral blood provide evidence for the existence of a chronic graft-versus-host reaction of the bone marrow in pts with cGvHD. This is characterized by an increased content of CD34+ and vW+ microvessels and an increased content of T-S cells at least initially. However this reaction does not lead to a generalized hematopoietic insufficiency.