Mucosal calprotectin is associated with severity of aGI-GVHD and poor outcomes after allogeneic stem cell transplantation.

Calprotectin, a calcium- and zinc-binding protein that comprises the subunits S100A8 and S100A9, has been extensively studied as a biomarker of gastrointestinal (GI) inflammation through fecal and serum analyses. However, its role in intestinal tissue remains poorly understood because of the limited availability of biopsy specimens. In this study, we analyzed S100A8 and S100A9 messenger RNA (mRNA) expression in 579 intestinal biopsy specimens from allogeneic stem cell transplantation recipients and observed a strong association with acute GI graft-versus-host disease (aGI-GVHD; P< .001). Neutrophil infiltration correlated with the severity of aGI-GVHD (P< .001), and calprotectin expression was strongly linked to Toll-like receptor 4 (TLR4; P< .001) and TLR2 (P< .001) expression. Both TLR4 and aGI-GVHD were associated with elevated calprotectin mRNA levels (P< .001). When patients received broad-spectrum antibiotics at disease onset, calprotectin expression was suppressed (S100A8, P = .001; S100A9, P = .01). GI site-specific differences in calprotectin expression were identified: during severe aGI-GVHD, levels increased up to 30-fold in the small intestine and up to fivefold in the large intestine with respect to mild or no aGI-GVHD, whereas under homeostasis, the large intestine exhibited higher baseline calprotectin (P = .001). The high clinical relevance of this finding is evident from the observation that calprotectin expression was prognostic for transplant-related mortality. Our study suggests that (1) calprotectin is a potential biopsy biomarker in aGI-GvHD and (2) calprotectin expression and neutrophil infiltration possibly indicate translocation of microbiota, which (3) may be modulated by antibiotics.