Gut graft-versus-host disease (GVHD) contributes significantly to lethality after allogeneic hematopoietic stem-cell transplantation (HSCT). In murine models, macrophage secretion of interleukin 1α (IL-1α) and tumor necrosis factor α (TNF-α) contributes to gut GVHD pathogenesis. To help characterize whether human gut GVHD has similar biological characteristics, monocyte IL-1α and TNF-α production were evaluated after HSCT.

Patients with refractory hematologic malignancy (n = 17) underwent reduced-intensity conditioning, HLA-matched sibling HSCT, and cyclosporine A GVHD prophylaxis. After HSCT, monocyte IL-1α and TNF-α levels were measured using intracellular flow cytometry (IC-FCM), and results were correlated with clinical GVHD.

Incidences of acute GVHD were none (n = 3), grades I-II (n = 9), or grades III-IV (n = 5; each case with stage 2–3 gut GVHD). Posttransplantation monocyte IL-1α production (percentage of CD14⁺IL-1⁺ cells) increased significantly from 8.7% ± 3.7% (week 2) to 40.3% ± 7.3% (week 4; P = 0.0065) and was not associated with GVHD severity (P = 1.00). Conversely, increases in monocyte TNF-α were quantitatively reduced and temporally delayed, from 0.6% ± 0.2% (week 2) to 3.6% ± 1.4% (week 6; P = 0.076). Most importantly, elevation of monocyte TNF-α level correlated with increased gut GVHD severity (P = 0.0041); increases in monocyte TNF-α levels typically preceded the onset of gut GVHD symptoms.

Human gut GVHD after reduced-intensity allogeneic HSCT is associated with monocyte cytokine secretion initially involving IL-1α, followed by TNF-α. Serial measurement of monocyte cytokines, in particular, TNF-α, by IC-FCM may represent a noninvasive method for GVHD monitoring, potentially allowing the identification of patients appropriate for early-intervention strategies.