CD8A and cytomegalovirus infection: Since primary CMV-infection occurred only in ATG-treated patients, we analyzed additionally the absolute number of CD3+ and CD8+ T cells, respectively, but could not detect any significant differences between viremic and aviremic patients (S2 Fig), indicating that the immunological scar left by the applied ATG doses was more subtle and absolute CD3+/CD8+ T cell numbers cannot be used as suitable biomarker.