Graft-vs.-host reactions: mechanisms and contemporary theories

Sulfur mustard induces immune sensitization in hairless guinea pigs

Sulfur mustard (SM, bis-(2-chloroethyl) sulfide) is a well known chemical warfare agent that may cause long-term debilitating injury. Because of the ease of production and storage, it has a strong potential for chemical terrorism; however, the mechanism by which SM causes chronic tissue damage is essentially unknown. SM is a potent protein alkylating agent, and we tested the possibility that SM modifies cellular antigens, leading to an immunological response to "altered self" and a potential long-term injury. To that end, in this communication, we show that dermal exposure of euthymic hairless guinea pigs induced infiltration of both CD4(+) and CD8(+) T cells into the SM-exposed skin and strong upregulated expression of proinflammatory cytokines and chemokines (TNF-alpha, IFN-gamma, and IL-8) in distal tissues such as the lung and the lymph nodes. Moreover, we present evidence for the first time that SM induces a specific delayed-type hypersensitivity response that is associated with splenomegaly, lymphadenopathy, and proliferation of cells in these tissues. These results clearly suggest that dermal exposure to SM leads to immune activation, infiltration of T cells into the SM-exposed skin, delayed-type hypersensitivity response, and molecular imprints of inflammation in tissues distal from the site of SM exposure. These immunological responses may contribute to the long-term sequelae of SM toxicity.

Spleen cells from antithymocyte serum pretreated mice do not induce GVHD but exert increased repopulating activity in irradiated semiallogeneic recipients

Graft-versus-host disease (GVHD) due to allogeneic bone marrow transplantation can be prevented by depleting the T cells from the marrow graft in vitro. However, the elimination of the donor T cells results in a higher frequency of graft failure, secondary infections and, in case of leukaemia, relapse. We found, that, in contrast to normal spleen cells, spleen cells from A or B10 donor mice pretreated with xenogeneic antithymocyte serum (ATS) in vivo did not induce GVHD in non-irradiated (B10 x A)F1 hybrids. Spleen cells of ATS-pretreated A donors did not cause GVHD in allogeneic CBA mice made neonatally tolerant to the A donor strain either. Furthermore, spleen cells from ATS-treated donors did not cause GVHD in irradiated F1 hybrid recipients, moreover, they decreased the lethal effect of irradiation. The in vivo ATS pretreatment improved the repopulating capacity of spleen cells in irradiated syngeneic recipients, too. The effect of the ATS treatment does not rely solely upon the elimination of T cells, since flow cytofluorometric analysis revealed only a partial depletion of both the CD4+ and CD8+ T cells of the ATS-pretreated animals. These observations may also have clinical relevance.

Protection from lethal graft-vs.-host disease by donor stem cell repopulation

Graft-vs.-host reaction (GVHR) induced in non-irradiated F1 mice with DBA/2J parental spleen and lymph node (LN) cells usually does not lead to acute GVH disease (GVHD). This contrasts with the GVHR induced in other parent-F1 combinations involving both major histocompatibility complex (MHC) class I and class II differences between donor and host. Most signs of acute GVHD in non-irradiated F1 mice relate to immunodeficiency following destruction of the lymphohemopoietic system of the host, which leads to wasting and death due to infections. This sequence of events is prevented when donor lymphoid cells, originating from grafted stem cells, repopulate the destroyed lymphohemopoietic system of the host. To examine whether a "silent" repopulation of the F1 host by donor stem cells might underly the absence of clinical signs of acute GVHD when GVHR is induced with DBA/2J lymphoid cells, GVHR was induced with LN cells, which do not contain stem cells. Indeed, GVHR induced in (C57BL/10 x DBA/2J)F1 (BDF1) mice with 80 x 10(6) DBA/2J LN cells led to acute GVHD. Signs of acute GVHD such as wasting and death did not occur when donor stem cells, from an inoculum of DBA/2J spleen and LN cells, were allowed to repopulate the lymphohemopoietic system of the host. The effect of donor stem cells on clinical signs of acute GVHD was more apparent when (B10.D2 x DBA/2J)F1, instead of DBA/2J, lymphoid cells were used to induce GVHR. The detection of alloreactive anti-host cytotoxic T lymphocyte (CTL) activity during acute GVHD induced with DBA/2J donor lymphoid cells supports the hypothesis that such CTL contribute to the destruction of the host immune system in acute GVHD.

Modulation of experimental allergic encephalomyelitis by a host-versus-graft reaction: a clinicopathological study

The effect of timing of a local host-versus-graft reaction on the induction of acute experimental allergic encephalomyelitis (EAE) was studied in guinea pigs. 20 x 10(7) gamma-irradiated allogeneic cells injected 4 days after encephalitogenic challenge resulted in the development of EAE with an earlier onset, an increased delayed-type hypersensitivity (DTH) response and an increase in lymphoid cell infiltration in the spinal cord. Challenge with allogeneic cells on days -4 and -7, however, produced a delay in onset and a protracted course of disease, with 30-40% of the animals recovering. Evidence of disease was confirmed histologically.

Immunomagnetic T-lymphocyte depletion (ITLD) of rat bone marrow using OX-19 monoclonal antibody

Graft versus host disease (GVHD) may be abrogated and host survival prolonged by in vitro depletion of T lymphocytes from bone marrow (BM) prior to allotransplantation. Using a mouse anti-rat pan T-lymphocyte monoclonal antibody (OX19) bound to monosized, magnetic, polymer beads, T lymphocytes were removed in vitro from normal bone marrow. The removal of the T lymphocytes was confirmed by flow cytometry. Injection of the T-lymphocyte-depleted bone marrow into fully allogeneic rats prevents the induction of GVHD and prolongs host survival.

Regulation of delayed type hypersensitivity to host histocompatibility antigens during graft-versus-host reactions

During GvH reactions in irradiated mice a variety of specific anti-host immune responses may occur. One of these is the occurrence of DTH to the host histocompatibility antigens, which may account for the inflammatory aspects of GvH. During acute as well as delayed GvH reactions the occurrence of anti-host DTH precedes the clinical symptoms of GvH disease. The anti-host DTH is mediated by long-lived, recirculating Lyt-1 + 2- T cells that need to proliferate in the irradiated recipients in order to display maximum activity. Not all host histocompatibility antigens can elicit anti-host DTH. H-2I and Mls-locus coded alloantigens do, but H-2K/D coded alloantigens and non-H-2 alloantigens other than Mls-locus coded alloantigens do not. This correlates with the ability to elicit proliferative mixed lymphocyte reactions in vitro but is in contrast to the response of nonirradiated mice to sc administered alloantigens. Under the latter conditions, all histocompatibility antigens induce a state of antigen-specific DTH. While the anti-host DTH is mediated by long-lived, recirculating Lyt-1 + 2- T cells, their response can be amplified by short-lived, sessile Lyt-1 + 2 + T cells. The latter T cell subset reacts to the host H-2K/D alloantigens and/or to non-H-2 alloantigens other than Mls-locus coded products. These cells alone cannot mount an anti-host DTH response. The anti-host DTH can be mitigated by Ts cells and non-T suppressor cells. Appropriate Ts cells can be readily induced by iv preimmunization of the donors with 5 X 10(7) irradiated, recipient-type spleen cells. Non-T suppressor cells can be induced by iv injection of bacterial LPS and simultaneous sc injection of 1 X 10(7) recipient type spleen cells. The suppression induced by these protocols shares several characteristics. In both cases the suppression is long-lasting, i.e., lasts at least 50 d, is transferable to syngeneic mice by spleen and lymph node cells, and both suppressive systems affect the induction of anti-host DTH as well as already activated anti-host DTH reactive T cells. Furthermore, while Ts cells and non-T suppressor cells are specific with regard to their antigen recognition, they are both able to suppress the DTH to a completely different set of host alloantigens. This, however, only occurs if the latter are inherited by the irradiated recipients as bystanders to the type of alloantigens that had activated the suppressor cells in the lymphoid cell donors.