These include: serum cytokines (REG3α and ST2; the MAGIC Algorithm Probability/Ann Arbor Score [MAP/AA]), where increased levels can predict GVHD onset, and are associated with increased severity, inferior response and survival [72, 73]; and stool assessment of GI tract microbiome, where decreased microbial diversity has been correlated with GI-GVHD incidence, severity, and mortality [74–76]. This evidence concerns the gene REG3A and graft versus host disease.