Recently, the immune-regulating potential of invariant natural killer T (iNKT) cells has attracted considerable attention. We previously reported that a combination treatment with a liposomal ligand for iNKT cells and an anti-CD154 antibody in a sublethally irradiated murine bone marrow transplant (BMT) model resulted in the establishment of mixed hematopoietic chimerism through in vivo expansion of regulatory T cells (Tregs). Herein, we show the lack of alloreactivity of CD8(+) T cells in chimeras and an early expansion of donor-derived dendritic cells (DCs) in the recipient thymi accompanied by a sequential reduction in the donor-reactive Vβ-T cell receptor repertoire, suggesting a contribution of clonal deletion in this model. Since thymic expansion of donor DCs and the reduction in the donor-reactive T cell repertoire were precluded with Treg depletion, we presumed that Tregs should preform before the establishment of clonal deletion. In contrast, the mice thymectomized before BMT failed to increase the number of Tregs and to establish CD8(+) T cell tolerance, suggesting the presence of mutual dependence between the thymic donor-DCs and Tregs. These results provide new insights into the regulatory mechanisms that actively promote clonal deletion.
The role of B cells in graft rejection and tolerance has aroused great interest. We previously reported that rituximab (RIT) induction prior to kidney transplantation (KTx) reduced the incidence rate of chronic rejection. Here, we performed a cross sectional investigation to determine the characteristics of B cells after RIT induction for KTx. We sampled blood from 29 patients with (N = 16) and without (N = 13) RIT induction 3 to 18 months after KTx. In the RIT group, the majority of repopulating B cells was the transitional type, while memory B cells were scarce. Although transitional B cells are believed to have immune-regulatory functions by producing IL-10, transcriptional levels of IL-10 in the peripheral blood mononuclear cells were similar in both groups. In contrast, transcription levels of BAFF-receptor relatively increased in patients with RIT induction. In conclusion, BAFF-receptor expressing highly proliferating transitional B cell was the major subset after RIT induction for KTx.
Background: Invariant natural killer T (iNKT) cells are one of the innate lymphocytes that regulate immunity, although it is still elusive how iNKT cells should be manipulated for transplant tolerance. We previously reported that the liposomal formulation of α-galactosylceramide (Lipo-aGC) could enhance an immune-regulative aspect of iNKT cells compared to the conventional aGC. Here we describe a novel approach to induce mixed chimerism (MC) by activating iNKT cells with Lipo-aGC under CD40-CD40L blockade (MR1). Methods and Results: 3Gy irradiated BALB/c mice were transplanted B6 bone marrow cells (BMCs) with/without Lipo-aGC and/or several dosage of MR1. Only combination therapy of Lipo-aGC plus suboptimal-MR1 could establish robust MC (table). Mice established MC completely accepted subsequent cardiac allografts in a donor-specific manner (figure). High amounts of Th2-cytokines were detected right after iNKT-cell activation, while subsequent IFN-γ production by NK cells was effectively inhibited by MR1. Expansion of regulatory T cells (Tregs) was observed in MC mice, and Treg-depletion on 1 day before transplantation resulted in a MC brake. Further, iNKT-cell knockout mice failed both MC establishment and Tregs expansion (table). Conclusion: These results collectively suggest that our new protocol makes it possible to induce donor-specific tolerance by enhancement of the innate regulatory mechanism in place of the conventional immunosuppression.Table: No Caption available.Figure: No Caption available.
