Histologic Evidence of Peripheral Lymphatic Organ Reconstitution Following Vascularized Bone Marrow Transplant (VBMT)

Abstract

Purpose We hypothesized that VBMT can repopulate the peripheral lymphatic centers of an irradiated (XRT) semiallogenic recipient. Methods Control groups were LBNs: non-transplanted, non-irradiated (CT1) and non-transplanted, XRT (CT2). Experimental female LBN rats received 900cGy and a VBMT. Donor femurs were from male LEW rats. Results CT2 Lymph nodes: no lymphatic germinal centers; evidence of profound fibroplasia and focal areas of tissue necrosis; significant numbers of hemosiderin laden macrophages (HLM) and multinucleated giant cells. Bone marrow: areas of hypoplasia and necrosis; decreased ratio of cellular to fatty elements secondary to cellular depletion; foci of lymphocytic infiltrates; prominent HLM. Spleen: white pulp atrophy; increased HLM in red pulp; scarce small, hypochromatic lymphocytes; fibrohistiocytes present with fibroplasia. VBMT Lymph nodes: absence of tissue necrosis and multinucleated giant cells; less HLM; germinal centers present; cortical areas display more cellular depletion than paracortical areas; increased lymphocytes compared to CT2; increased fibrohistiocytes compared to CT1. Bone marrow: Host bone has normal appearing marrow with an average ratio of hematopoietic to fatty elements; hyperchromatic nuclei present. Donor bone marrow appears to be entirely normal. Spleen appears normal. Conclusions This model is capable of hematopoeitically reconstituting the peripheral lymphatic centers of XRT recipients without the development of GVHD. We speculate that the VBMT syngeneic microenvironment can serve as an extra-thymic site for immune development and tolerance induction.