Pathophysiology of capillary leak syndrome, the probable cause of pre-engraftment syndrome. Conditioning chemoradiotherapy can damage the endothelial lining of the gastrointestinal tract, allowing immunostimulatory microbial products such as LPS to enter the circulation. These molecules can stimulate the secretion of inflammatory cytokines (TNF-α, IL-1), leading to secondary release of inflammatory cytokines (cytokine storms). In addition, potentially toxic materials such as G-CSF and the cryoprotectant DMSO, donor stem cells expressing proinflammatory cytokines, and alloreactive donor T cells can also enhance the cytokine storms, thereby contributing to increased vascular permeability to fluids and low-molecular-weight substances.

Abbreviations: LPS, lipopolysaccharide; TNF, tumor necrosis factor; IL, interleukin; G-CSF, granulocyte colony-stimulating factor; DMSO, dimethylsulfoxide.