Title: Absence of Graft-versus-Host Disease in Recipients of an Isolated
Vascularized Bone Marrow Transplant
Chau Y. Tai, MD, Louise F. Strande, Riva Eydelman, Xiaoli Sheng, MD, Martha S.
Matthews, MD, and Charles W. Hewitt, PhD
Composite tissue allografts (CTA) such as a hand transplant contain multiple tissue
types including bone, marrow, muscle, vessels, nerves, skin, and immune cells.
Within a CTA is the vascularized bone marrow transplant (VBMT) that contains
immunocompetent stem cells with a potential for inducing graft-versus-host-disease.
However, studies also suggested that the bone marrow is immunomodulatory, and may
facilitate allograft acceptance.1-3 An isolated vascularized bone marrow transplant
model (iVBMT) has been developed in the rat in order to specifically study the
contribution of the bone marrow and its environment in a CTA.4 We hypothesized that
the iVBMT would cause graft-versus-host-disease (GVHD) in a fraction of the
recipients when transplanted across a major semiallogeneic barrier without
immunosuppression.
Methods: Experimental setup - Group A = male Lewis (LEW) donor transplanted across
a semiallogeneic barrier to a female Lewis-Brown-Norway (LBN) rat, n=25. Group B =
control, male LBN to female LBN, n=10. The LBN F1 hybrid cannot reject the parent
LEW graft. However, the LEW graft can react against the Brown-Norway antigen in the
recipient, thereby causing GVHD. No immunosuppression was used.
The extraperitoneal iVBMT model (Fig. 1)- The left donor femur was harvested with
its nutrient vessels and anastomosed to the right femoral vessels of the recipient
in an end-to-end fashion. The graft was then placed subcutaneously in the abdominal
wall.
Clinical assessment - Postoperatively the animals were weighed and examined several
times weekly. Clinical signs of GVHD included hair loss, erythema and/or
desquamation of the skin, diarrhea, and significant weight loss.1 The animals were
sacrificed at various time points from 1 to 14 weeks.
Histology – At sacrifice, tissue samples of the terminal ileum, ear, and tongue
were fixed in Histochoice, processed and embedded in a standard fashion. These
tissues were chosen for examination based on prior limb transplant models that
demonstrated characteristic findings of GVHD in these samples.5 The graft and host
bones were fixed in Histochoice, decalcified in 5% formic acid overnight, stored in
70% cold alcohol, then paraffin embedded. Four micrometer sections were H&E stained
and examined at 200x.
Results: Both groups appeared healthy and gained weight (Table 1). Graft vessels
were patent at necropsy, and histology of the donor grafts demonstrated a viable
marrow compartment (Fig. 2). No animals exhibited clinical signs of GVHD at
sacrifice. Histologic studies also did not find microscopic evidence of GVHD in the
tissue samples. No abnormal infiltrates or desquamation was noted in the ear or
tongue. Instestinal villi and glands were normal, without atrophy or abnormal
lymphocytci infiltrates.
Discussion: The immune cells derived from the bone marrow component did not cause
GVHD in the iVBMT model as hypothesized. This suggests that within a composite
tissue allograft, the vascularized bone marrow component is not highly immunogenic.
The mechanism of graft acceptance across a semiallogeneic barrier in the iVBMT is
unknown. Other immunogeneic components such as the skin and lymph nodes may be more
contributory to the development of GVHD.
Fig. 1 The extraperitoneal isolated vascularized bone marrow transplant model.
Table 1 Preoperative and postoperative weights.
Preoperative Wta (g)
End Wtb (g )
Group A, n=25
206.7  3.53
222.5  1.51
Group B, n=10
211.7  3.64
228.9  4.54
p = 0.66
p = 0.09
a
b
c
Preoperative weight obtained on the day of procedure.
End weight obtained on the day of sacrifice.
 = End weight – preoperative weight.
c
16.4  3.47
18.6  3.47
p = 0.36
Fig. 2 Normal histologic appearance of the donor graft marrow, 103 days posttransplant(H&E 200x).
References
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stable mixed T cell chimerism and transplantation tolerance without immune
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50: 766-772, 1990.
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the induction of transplant tolerance by low-dose UV-B irradiation of BM cells
combined with cyclosporine immunosuppression. Transplantation; 60: 1510-1516, 1995.
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rats: evidence of amplification of hematolymphoid chimerism and freedom from graftversus-host reaction. Transplant Proc; 27: 164-5, 1995.
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