Expression of CD30 in diagnostic intestinal biopsy specimens as assessed by immunohistochemistry. (A) Patient without aGVHD who was diagnosed with C difficile colitis; CD30⁺ cells are rare (mean 0.4 per 400× field). (B) Patient with clinical grade 2 intestinal aGVHD, with numerous CD30⁺ cells (mean 4.7 per 400× field). (C) Patient with clinical grade 4 intestinal aGVHD, with numerous CD30⁺ cells (mean 3.5 per 400× field).