Clonal Deletion Established via Invariant NKT Cell Activation and Costimulatory Blockade Requires In Vivo Expansion of Regulatory T Cells

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.

A novel approach inducing transplant tolerance by activated invariant natural killer T cells with costimulatory blockade

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. Here, we describe the potential of a novel approach using a ligand for iNKT cells and suboptimal dosage of antibody for CD40-CD40 ligand (L) blockade as a powerful method for mixed chimerism establishment after allogenic bone marrow transplantation in sublethally irradiated fully allo recipients. Mixed-chimera mice accepted subsequent cardiac allografts in a donor-specific manner. High amounts of type 2 helper T cytokines were detected right after iNKT cell activation, while subsequent interferon-gamma production by NK cells was effectively inhibited by CD40/CD40L blockade. Tolerogenic components, such as CD11c(low) mPDCA1(+) plasmacytoid dendritic cells and activated regulatory T cells (Tregs) expressing CD103, KLRG-1 and PD-1, were subsequently augmented. Those activating Tregs seem to be required for the establishment of chimerism because depletion of the Tregs 1 day before allogenic cell transfer resulted in a chimerism brake. These results collectively suggest that our new protocol makes it possible to induce donor-specific tolerance by enhancement of the innate ability for immune tolerance in place of the conventional immunosuppression.