Fengshuo Lan

Predominance of NK1.1^+TCRαβ^+ or DX5^+TCRαβ^+ T cells in mice conditioned with fractionated lymphoid irradiation protects against graft-versus-host disease : "natural suppressor" cells

We developed a nonmyeloablative host conditioning regimen in a mouse model of MHC-mismatched bone marrow transplantation that not only reduces radiation toxicity, but also protects against graft-vs-host disease. The regimen of fractionated irradiation directed to the lymphoid tissues and depletive anti-T cell Abs results in a marked change in the residual host T cells, such that NK1.1+ or DX5+asialo-GM1+ T cells become the predominant T cell subset in the lymphoid tissues of C57BL/6 and BALB/c mice, respectively. The latter “natural suppressor” T cells protect hosts from graft-vs-host disease after the infusion of allogeneic bone marrow and peripheral blood cells that ordinarily kill hosts conditioned with sublethal or lethal total body irradiation. Protected hosts become stable mixed chimeras, but fail to show the early expansion and infiltration of donor T cells in the gut, liver, and blood associated with host tissue injury. Cytokine secretion and adoptive transfer studies using wild-type and IL-4−/− mice showed that protection afforded by NK1.1+ and DX5+asialo-GM1+ T cells derived from either donors or hosts conditioned with lymphoid irradiation is dependent on their secretion of high levels of IL-4.

Host Conditioning with Total Lymphoid Irradiation and Antithymocyte Globulin Prevents Graft-versus- Host Disease: The Role of CD1-Reactive Natural Killer T Cells

Our previous studies in mice showed that the nonmyeloablative conditioning regimen of fractionated irradiation of the lymphoid tissues (total lymphoid irradiation; TLI) and depletive anti-T-cell antibodies (anti-thymocyte serum) markedly increased the percentage of regulatory DX5+ and natural killer 1.1+ T cells in the mouse spleen, and prevented acute lethal graft-versus-host disease (GVHD) in BALB/c mice (H-2(d)) following the transplantation of bone marrow (BM) and peripheral blood mononuclear cells (PBMC) from C57BL/6 (H-2(b)) donors. The object of the current study was to determine whether the TLI and anti-thymocyte serum regimen protected natural killer T-cell deficient CD1(-/-) BALB/c mice against GVHD after BM and PBMC transplantation from C57BL/6 donors, and whether a similar conditioning regimen of TLI and anti-thymocyte globulin (ATG) can prevent GVHD in Lewis rat (RT1(l)) hosts after BM and PBMC transplantation from ACI rat (RT1(a)) donors. The experimental results in mice showed that, although wild-type BALB/c hosts are protected in association with a marked increase in CD1- reactive T cells expressing the invariant TCR identified with a CD1 tetramer reagent; CD1(-/-) BALB/c hosts are not. Studies of chimeric donor cells in mice protected from GVHD showed donor T-cell polarization to a Th2 cytokine pattern. Results in rats showed that approximately 1000 fold more donor PBMC cells were required to induce a similar incidence of lethal GVHD in TLI and ATG conditioned hosts as compared with hosts conditioned with single-dose total-body irradiation or total-body irradiation and ATG. Surviving TLI and ATG conditioned rat hosts were complete chimeras. In conclusion, the TLI and ATG/anti-thymocyte serum conditioning regimen protects against GVHD in rats and mice, and regulatory natural killer T cells are required for protection.

Cyclosporine facilitates chimeric and inhibits nonchimeric tolerance after posttransplant total lymphoid irradiation.

BACKGROUND Previous studies showed that Lewis rats given posttransplant total lymphoid irradiation, antithymocyte globulin, and a single infusion of ACI peripheral blood or bone marrow cells develop tolerance to ACI heart allografts. METHODS To determine the effects of cyclosporine on these tolerance induction protocols, groups of Lewis hosts, given either ACI blood or marrow infusions, were given a 60-day course of daily cyclosporine immediately after the cell infusion. RESULTS Cyclosporine treatment was associated with uniform graft rejection in the groups given an ACI blood transfusion, and was associated with uniform graft acceptance in the groups given an ACI bone marrow infusion. Studies of donor-type T and B cell chimerism in the host blood showed that cyclosporine facilitated chimerism in the hosts given ACI bone marrow cells, and stable chimerism over a 300-day observation period was predicted by detectable chimerism by day 30. None of the hosts given ACI blood cells developed chimerism. CONCLUSION Cyclosporine facilitated long-term graft acceptance in a tolerization protocol that induced mixed chimerism, but prevented long-term graft acceptance in a tolerization protocol that did not induce chimerism.

Comparison of chimeric acid and non-chimeric tolerance using posttransplant total lymphoid irradiation: cytokine expression and chronic rejection.

Background. Previous studies showed that an intravenous infusion of donor blood cells facilitates tolerance to ACI heart allografts in Lewis rat hosts given posttransplant total lymphoid irradiation (TLI) and anti-thymocyte globulin (ATG). The object of the current study was to compare tolerance induction using donor cells that do or do not induce chimerism. Methods. Normal peripheral blood mononuclear cells (PBMC), granulocyte colony-stimulating factor (G-CSF)-mobilized PBMC, and bone marrow (BM) cells from ACI donors were tested for their capacity to prolong ACI heart allograft survival in Lewis hosts. Chimerism, anti-donor cell reactivity, and cytokine gene expression in grafts were determined. Results. Intravenous injections of equal numbers of all three donor cells markedly prolonged graft survival (median: >164 to >175 days) as compared to uninjected controls (median: 53 days). Chimerism among T and B cells in the blood was determined by immunofluorescent staining in hosts bearing long-term (>150 days) grafts. Although no chimerism was detected in hosts given normal or G-CSF-mobilized PBMC, chimerism was detected at variable levels in all hosts given BM cells. Vigorous anti-donor reactivity in the mixed leukocyte reaction was present only in non-chimeric hosts. Long-term grafts from hosts given normal ACI PBMC developed chronic rejection, but those from hosts given ACI BM cells did not. The latter hosts showed the lowest levels of intragraft cytokine mRNA. Conclusions. Chimeric tolerance is more robust than non-chimeric tolerance in the model of posttransplant TLI, ATG, and donor cell infusion, and is associated with less chronic rejection.

Suppression of graft-versus-host disease by naturally occurring regulatory T cells.

Studies of graft-versus-host disease after allogeneic bone marrow transplantation have shown that there are subsets of freshly isolated donor T cells that induce the disease and subsets that suppress the disease. The balance of subsets in the graft determines disease severity. The authors’ work on the nature of the regulatory-suppressor T cells and their mechanisms of action is summarized in this article.