Cumulative incidence (%) of PTLD for patients with 0, 1, 2, or 3 to 4 major risk factors for PTLD. The 4 risk factors were defined as: (1) T-cell depletion methods that selectively target T cells or T + NK cells or E-rosetting; (2) unrelated or ≥2 HLA antigen mismatched related donor; (3) antithymocyte globulin used as prophylaxis or therapy for acute GVHD; and (4) anti-CD3 monoclonal antibody 64.1 given as therapy for acute GVHD (Seattle only). Analysis excludes 2 PTLD and 84 patients with unclassified or other methods of T-cell depletion.