ABSTRACT
Over the last several decades, allogeneic hematopoietic stem cell transplantation (SCT)
has emerged as an important therapeutic option for a number of malignant and nonma-
lignant conditions. Unfortunately, this treatment strategy is limited by several side
effects including pulmonary toxicity. Diffuse lung injury is a major complication of
SCT that occurs in 25-55% of SCT recipients and can account for approximately
50% of transplant-related mortality (1-6). Noninfectious lung injury can be either
acute (termed idiopathic pneumonia syndrome, or IPS) or chronic, depending on the
time of onset after SCT and the tempo of disease progression. Historically, approxi-
mately 50% of all pneumonias seen after SCT have been secondary to infection, but
the judicious use of broad-spectrum antimicrobial prophylaxis in recent years has
tipped the balance of pulmonary complications from infectious to noninfectious causes
(7). Chronic lung injury (by definition occurring in patients over 100 days posttrans-
plant) is further subdivided into two types: obstructive and restrictive (8-16). Each
form of noninfectious lung injury is associated with significant morbidity and mortality
and responds poorly to standard therapeutic approaches. A significant body of exper-
imental literature demonstrates that both acute and chronic noninfectious lung injuries
after SCT are immunologically mediated and share similar pathogenetic mechanisms
with graft-vs.-host disease (GVHD). This chapter will review the definitions, risk
factors, and pathogeneses of noninfectious lung injury occurring both early and late
after allogeneic SCT.
