Variables not listed in Table 4—including alternative conditioning regimens, hematopoietic recovery status, GVHD prophylaxis, lymphocyte subpopulation counts, absolute lymphocyte counts, and serial measurements of immunoglobulins (IgM, IgA, IgG), complements (C3, C4), and blood LDH at reactivation—showed no significant association with PTLD in univariate analysis. The gene discussed is C4A; the disease is graft versus host disease.