Therefore, in-vivo DC expansion system using such cytokines might not be preferable to examine the essential function of AZM in the present

report. However, our in-vivo SAHA HDAC chemical structure data suggest that acute GVHD was clearly suppressed, clinically and pathologically, by oral AZM (Figs 1 and 2). It is tempting to speculate that AZM-treated DCs may be related functionally to regulatory DCs, not only in vitro but also in vivo, and might induce Treg in an allogeneic BMT setting. We are also interested in testing whether injection of AZM-treated DCs to recipients following allogeneic BMT could attenuate acute GVHD, as observed with regulatory DCs [38]. However, it might be difficult to develop and expand these DCs ex vivo. Simply administering AZM orally to recipients would be much more practical from the clinical viewpoint. Next, we confirmed the effects of AZM on donor lymphocytes. Tomazic et al. [44] reported that the absence of impairment of T and B lymphocytes by AZM might be an important property of this drug, especially in immunocompromised individuals. Our data for C57BL/6 murine lymphocytes are compatible with their results (Fig. 3). The fact that AZM has no deleterious effects on T lymphocyte functions in this setting

is important for preservation of the graft-versus-leukaemia (GVL) effect of AZM therapy. Conversely, commonly used immunosuppressants such as tacrolimus (a 23-membered ring-macrolide) and cyclosporin inhibit T lymphocyte functions strongly by blocking the phosphatase activity of calcineurin, resulting in susceptibility to infections and a find more decreased GVL effect. Moreover, potential concerns for the use of these calcineurin inhibitors include renal toxicity, veno-occlusive disease of the liver, hypertension, hyperglycaemia and neurological side effects [45]. In contrast, AZM has been used safely worldwide as an antibiotic. Nevertheless, AZM is not without its own safety issues: reversible hearing

loss with high doses (600 mg daily for 1·5–20 weeks) [46] and long-term treatment (600 mg once weekly for 1 year) [47] and cardiovascular effects; specifically, prolongation of the QT interval that leads to torsades de pointes, an abnormal heart rhythm that can be fatal [48]. In addition to the immunoregulatory effects of AZM, its anti-microbial Bumetanide effect may also be important in BMT as bacteria and bacterial products, especially LPS, are associated with exacerbation of GVHD [49, 50]. In the clinical setting, Gram-negative gut decontamination has actually been found to reduce the incidence of GVHD [51-53]. Interestingly, some investigators reported that changes in the microbial flora, due to intestinal inflammation caused by TBI as preconditioning for murine recipients of allogeneic BMT, influenced the severity of acute GVHD, and that manipulation of the intestinal flora enabled regulation of acute GVHD [53, 54].