Pathology of bone marrow in transplant recipients

This article has outlined the special problems associated with evaluation of bone marrow before and after BMT. Marrow grafting has become a major form of therapy in oncology and hematology whose potential is only beginning to be fully realized. The transplantation of healthy hematopoietic and lymphoid cells has made possible the use of otherwise superlethal doses of radiation and chemotherapy in preparing the patient for engraftment. In the case of tumors, this allows massive doses of tumorocidal therapy prior to rescue with a BMT. In the case of aplastic anemia, it allows massive immunosuppression and ablation of the residual host marrow in preparation for replacement by the healthy donor marrow. The complications of this procedure include the toxicity of chemotherapy and irradiation upon the liver, lung, and gut as well as less serious toxicity to skin and other organs. The double barrier associated with marrow transplantation consists of rejection and GVHD. Marrow graft failure occurs by two distinct mechanisms, graft resistance and graft rejection. The former is marked by a total failure of any evidence of engraftment and the latter by engraftment followed by disappearance of the graft. GVHD is the immunologic attack upon host tissues by donor lymphoid cells (predominantly mature T cells). In the acute phase, it attacks liver, skin, and gut, with the latter producing the most life-threatening syndrome. Chronic GVHD resembles scleroderma. Treatment of GVHD includes the use of prednisone, cyclosporin A, ATG, and monoclonal antilymphoid antibodies. Prevention includes the attempt to remove T cells from the donor marrow with monoclonal antibodies using complement-mediated cytolysis and other approaches such as conjugation of antibodies to ricin and other toxins. GVHD also produces severe immunosuppression in and of itself added to that produced by chemoirradiation therapy. As a result, the marrow transplant recipient is extremely susceptible to infections. During the early period, the patient is granulocytopenic and susceptible to bacterial and fungal infections, which are dealt with by antibiotics and isolation procedures. Later, viral infections become very important, particularly CMV and other herpes viruses. The relative success in dealing with bacterial and, to some extent, viral infections has brought fungal infections to the fore as major causes of death, especially in higher risk categories of patients. Hemorrhage is a frequent complication owing to delayed megakaryocyte engraftment and thrombocytopenia during the early period and is a serious problem in patients with GVHD of the gut.