A Novel Chemical Compound, NK026680, Targets Dendritic Cells to Prolong Recipient Survival After Rat Liver Grafting

Triazolopyrimidine derivative NK026680 and donor-specific transfusion induces CD4+CD25+Foxp3+ T cells and ameliorates allograft rejection in an antigen-specific manner

We have previously demonstrated the unique properties of a new triazolopyrimidine derivative, NK026680, which exerts immunosuppressive effects in rat heart transplant model and confers tolerogeneic properties on ex vivo-conditioned dendritic cells in mice. We herein demonstrate that NK026680 promotes the expansion of regulatory T cells (Tregs) with potent immunoregulatory effects when used in combination with donor-specific transfusion (DST). BALB/c (H-2^d) heart graft were transplanted into C57BL/6 (H-2^b) mice following intravenous injection of donor splenocytes (DST) and oral administration of NK026680. The NK026680 plus DST treatment markedly prolonged the survival time of the donor-graft, but not that of the 3rd party-graft (C3H; H-2^k). Treg cells in the recipient spleen on day 0 expanded when stimulated with donor-antigens in vivo and in vitro. After heart transplantation, Treg cells accumulated into the graft and increased in the spleen. NK026680 plus DST also decreased activated CD8⁺ T cells in the spleen and inhibited infiltration of CD8⁺ T cells into the graft. Depletion of CD25⁺ cells inhibited the graft prolonging effect of the NK026680 plus DST treatment. NK026680 administration together with DST induces potent immunoregulatory effects in an antigen-specific manner, likely due to the in vivo generation of donor-specific Tregs.

5-Aminolevulinic acid with ferrous iron induces permanent cardiac allograft acceptance in mice via induction of regulatory cells

BACKGROUND

5-Aminolevulinic acid (5-ALA), a precursor of heme biosynthesis, plays a fundamentally important role in aerobic energy metabolism. Heme oxygenase (HO)-1 cleaves heme to form biliverdin, carbon monoxide (CO) and iron (Fe(2+)). The anti-inflammatory properties of biliverdin and CO help to alleviate ischemia/reperfusion injury as well as acute and/or chronic allograft rejection. We investigated whether 5-ALA and Fe(2+) exerts salutary effects in the setting of organ transplantation.

METHODS

An in vitro mixed-lymphocyte reaction (MLR) assay and cardiac allotransplantation model (CBA to C57BL/10) were used to evaluate the effects of 5-ALA and Fe(2+) on transplantation tolerance.

RESULTS

Treatment with 5-ALA and sodium ferrous citrate (SFC) resulted in permanent acceptance in the murine cardiac allografts in a dose-, SFC- and HO-1-dependent manner. The number of graft-infiltrating CD8 T cells was lower and the survival response of recipient spleen T cells to donor-type alloantigens was less compared with control recipients; however, numbers of both regulatory T cells and dendritic cells were significantly increased in 5-ALA/SFC-treated recipients.

CONCLUSIONS

Our findings show that 5-ALA/SFC inhibits T-cell proliferation in response to alloantigens and an increased number of regulatory cells, resulting in permanent cardiac allograft acceptance in mice. These findings highlight the major roles of CO and/or HO-1 in inducing tolerance and suggest that 5-ALA/SFC may be a clinically effective treatment for allograft rejection.