Infections and immunodeficiency in bone marrow transplantation.

After allogeneic bone marrow transplantation certain patterns of infectious complications emerge that follow the clinical course, are correlated to the immunobiology of transplantation and are almost predictable in their character and expression. The preparative regimen, designed to generate complete aplasia, will be associated with severe and sometimes life-threatening bacterial infections, predominantly with Gram-negative organisms derived from bowel flora, but also Gram-positive skin saprophytes. In this early aplastic phase, life-threatening viral infections are less common, consisting mainly of herpes simplex and possibly Epstein-Barr stomatitis and BK papovavirus cystitis. Systemic infections with invasive filamentous fungi are rare and are seen only when the induced aplasia is markedly prolonged. Once early marrow recovery has been achieved, systemic infections will generally disappear unless acute graft-vs.-host disease develops. This complication, which will lead to the breakdown of natural barriers such as skin and gastrointestinal epithelium and the marked impairment of all systemic defense mechanisms, can cause polymicrobial infections as well as set the stage for life-threatening viral infections. Such opportunistic viral infections, leading to either interstitial pneumonia or hemorrhagic gastroenteritis, are the major threat in the early recovery phase after engraftment has taken place. Usually caused by cytomegalovirus and rotavirus, respectively, these infections are the primary expression of the severe combined immunodeficiency post transplant, statistically associated with the presence of acute graft-vs.-host disease and amenable to immunologic manipulations. With the recovery of cellular and humoral immune function derived from transplanted donor lymphoid cells, the third phase of infectious complications is reached, covering 3 months to 2 years post grafting.(ABSTRACT TRUNCATED AT 250 WORDS)