Therefore, the attenuating effect of AZM on GVHD might be due partly to its control of bacteria. Concerning the timing and dose of oral AZM, we chose a regimen of 100 mg/kg orally for 5 days starting from day −2 to day 2. Amsden et al. [55] reported that the blood concentration of the drug in humans became stable (0·5–1·0 mg/ml) after 3 or 5 days of oral AZM. The 100 mg/kg/day Mdm2 antagonist dosage was used because

it corresponds to the human dosage after size correction [56]. Accumulating evidence indicates that early interaction between allogeneic T lymphocytes and residual recipient APCs immediately after allo-BMT is critical for eliciting acute GVHD [6, 10]. Zhang et al. [57] studied the kinetic window during which recipient APCs elicited acute GVHD in a murine model and demonstrated that recipient DCs were activated and aggregated rapidly in T lymphocyte-rich areas of the spleen within 6 h after lethal irradiation. By 5 days after irradiation, <1% of recipient DCs were detectable, but the activated donor CD8+ T lymphocytes had already undergone as many as seven divisions. This indicates that, although recipient DCs disappear rapidly after allo-BMT, they first prime donor

T lymphocytes and play a critical role in BGJ398 concentration triggering donor CD8+ T lymphocyte-mediated GVHD. In our transplantation model, AZM-treated recipients developed GVHD in the later phase. Although Zhang et al. [57] demonstrated the critical, early role of DCs in initiating acute GVHD, they also found that a small number of radio-resistant recipient DCs remained even at 4 months after allo-BMT

and pointed out the possibility that they might be important in amplifying the GVHD response. Further studies are necessary to elucidate later events in the induction of acute GVHD. Taken together, Methocarbamol our results suggest that blockade of DC–T lymphocyte interaction by inactivating DCs with AZM, i.e. DC targeting, might require administration of the drug for a short period before and after BMT. It is this period that should be targeted in an attempt to attenuate acute GVHD. Moreover, this treatment might not be accompanied by suppression of the beneficial GVL effect, as oral AZM had no effect on the lymphocyte functions of mice. AZM already has a history of use in the treatment of bacterial infections, so its administration should also be safe in patients undergoing BMT for haematological disorders. Similarly to bortezomib [23], AZM could be used singly or in conjunction with immunosuppressants to prevent acute GVHD in various clinical settings. AZM also seems to have potential for use in treating already developed GVHD. Further studies of the in-vivo effects of AZM in allogeneic BMT are clearly warranted. We thank Dr Takashi Iwamoto of Chubu College of Life and Health Sciences for technical advice and Miyuki Namikata for technical assistance.