ODC1 and graft versus host disease: Spermine restrains innate immune responses by inhibiting M1 macrophage activation via suppression of ornithine decarboxylase and pro-inflammatory cytokine synthesis without perturbing anti-inflammatory TGFβ and IL-10 (Figure 2).113,114 Spermidine also modulates systemic and mucosal adaptive immunity by modulating T cell differentiation.122,123 Clinically, N-acetyl putrescine and N-acetyl spermidine are enriched in allo-hematopoietic stem cell transplantation (HSCT) recipients free from graft versus host disease (GvHD) compared to those with GvHD124 (Table 5).