Suppression of B lymphocyte genesis in the bone marrow by systemic graft-versus-host reactions

Targeting cannabinoid receptors as a novel approach in the treatment of graft-versus-host disease: evidence from an experimental murine model

Allogeneic hematopoietic cell transplantation (HCT) is widely used to treat patients with life-threatening malignant and nonmalignant hematological diseases. However, allogeneic HCT often is accompanied by severe and lethal complications from graft-versus-host disease (GVHD), in which activated donor T cells recognize histocompatibility antigenic mismatches and cause significant toxicity in the recipient. In the current study, we tested the hypothesis that activation of cannabinoid receptors on donor-derived T cells may prevent GVHD. We tested the effect of Δ(9)-tetrahydrocannabinol (THC) in an acute model of GVHD that was induced by transferring parental C57BL/6 (B6) spleen cells into (C57BL/6 × DBA/2) F(1)(BDF1) mice. Transfer of B6 cells into BDF1 mice produced severe acute GVHD in the recipient, characterized by lymphoid hyperplasia, weight loss, T helper l cytokine production and mortality. THC administration led to early recovery from body weight loss, reduced tissue injury in the liver and intestine, as well as complete survival. THC treatment reduced the expansion of donor-derived effector T cells and blocked the killing of host-derived immune cells while promoting Foxp3(+) regulatory T cells. Impaired hematopoiesis seen during GVHD was rescued by treatment with THC. The ability of THC to reduce the clinical GVHD was reversed, at least in part, by administration of cannabinoid receptor (CB) 1 and CB2 antagonists, thereby demonstrating that THC-mediated amelioration of GVHD was cannabinoid receptor-dependent. Our results demonstrate for the first time that targeting cannabinoid receptors may constitute a novel treatment modality against acute GVHD.

Prevention of murine acute graft-versus-host disease by staphylococcal enterotoxin B treatment

Retroviral superantigens such as minor lymphocyte stimulating (Mls) antigen play an important role in the pathogenesis of acute graft-versus-host disease (GVHD). However, it remains unclear how exogenous bacterial superantigens modulate acute GVHD. In this study, we tested the effects of staphylococcal enterotoxin B (SEB) on the development of acute GVHD in a model involving the systemic transfer of parental C57Bl/6 spleen cells into BDF1 mice. SEB treatment suppressed the expansion of donor-derived T cells and blocked the decrease in the number of host cells. Impaired haematopoiesis was actually rescued by treatment with SEB. In SEB-treated mice, both spontaneous proliferation and IL-2 production in T cells were suppressed on day 2 after parental cell infusion. On day 21, the number of donor-derived CD4+ Vbeta8+ T cells markedly decreased in the spleen of SEB-treated mice. Donor-derived CD4+ T cells failed to proliferate in response to host alloantigens, and both donor- and host-derived T cells were unable to produce IL-2 in response to concanavalin A stimulation, suggesting that SEB treatment induced a general immunosuppressive state. Our results indicate that SEB treatment prevents the development of acute GVHD by leading to unresponsiveness of donor-derived T cells against host alloantigens in a Vbeta-restricted and unrestricted manner.

Recombinant CD40L Treatment Protects Allogeneic Murine Bone Marrow Transplant Recipients From Death Caused by Herpes Simplex Virus-1 Infection

Posttransplant infection associated with host immune deficiency is the major cause of nonrelapse mortality of human bone marrow transplant recipients. In a new murine model of posttransplant infection, allogeneic bone marrow transplant recipients were infected with herpes simplex virus-1 (HSV-1) via intraperitoneal inoculation 12 weeks after transplantation. Allogeneic transplant recipients with graft-versus-host disease (GVHD) had significantly increased mortality from HSV-1 encephalitis, with deficiencies of both specific anti–HSV-1 antibody and total serum IgG2a. GVHD mice displayed a Th2 cytokine profile (increased interleukin-4 [IL-4] and decreased interferon-γ) and decreased lipopolysaccharide (LPS) responses, suggesting that both T-cell and B-cell defects contributed to the impaired production of antibody. Because passive transfer of hyperimmune serum protected mice from HSV-1 infection, we hypothesized that CD40 ligand (CD40L), which induces B-cell maturation, would protect mice from HSV-1 infection. CD40L-treated GVHD mice showed elevated IgG2a levels and increased survival compared with vehicle-treated transplant recipients.

Recombinant CD40L Treatment Protects Allogeneic Murine Bone Marrow Transplant Recipients From Death Caused by Herpes Simplex Virus-1 Infection

Posttransplant infection associated with host immune deficiency is the major cause of nonrelapse mortality of human bone marrow transplant recipients. In a new murine model of posttransplant infection, allogeneic bone marrow transplant recipients were infected with herpes simplex virus-1 (HSV-1) via intraperitoneal inoculation 12 weeks after transplantation. Allogeneic transplant recipients with graft-versus-host disease (GVHD) had significantly increased mortality from HSV-1 encephalitis, with deficiencies of both specific anti–HSV-1 antibody and total serum IgG2a. GVHD mice displayed a Th2 cytokine profile (increased interleukin-4 [IL-4] and decreased interferon-γ) and decreased lipopolysaccharide (LPS) responses, suggesting that both T-cell and B-cell defects contributed to the impaired production of antibody. Because passive transfer of hyperimmune serum protected mice from HSV-1 infection, we hypothesized that CD40 ligand (CD40L), which induces B-cell maturation, would protect mice from HSV-1 infection. CD40L-treated GVHD mice showed elevated IgG2a levels and increased survival compared with vehicle-treated transplant recipients.

Graft-versus-host-disease-associated lymphoid hypoplasia and B cell dysfunction is dependent upon donor T cell-mediated Fas-ligand function, but not perforin function

Allogeneic bone marrow transplant recipients often exhibit a graft-versus-host-disease (GVHD)-associated immune deficiency that can be prolonged and lead to life-threatening infections. We have examined the role of donor T cell-mediated cytotoxic function in the development of GVHD-associated immune deficiency. A major histocompatibility complex-matched model of allogeneic bone marrow transplantation was employed in which lethally irradiated C3H.SW mice received a nonlethal dose of T cells from either perforin-deficient (B6-perforin 0/0), Fas-ligand (FasL)-defective (B6-gld), or normal (B6) allogeneic donor mice. T cell-depleted marrow from B6-Ly-5.1 congenic donor mice was transplanted along with the donor T cell populations to determine the effects of donor T cell-mediated cytotoxicity on engraftment. Our results demonstrate that recipients of perforin-deficient or normal allogeneic T cells exhibit profound lymphoid hypoplasia and severely reduced splenic proliferative responses to lipopolysaccharide in vitro. In contrast, GVHD-associated lymphoid hypoplasia is dramatically reduced and in vitro B cell function is intact in recipients of FasL-defective allogeneic T cells. Engraftment of myeloid and erythroid lineage cells occurs irrespective of donor T cell cytotoxic function. Although recipients of perforin-deficient or normal allogeneic T cells exhibited hematopoietic engraftment exclusively of donor origin, recipients of FasL-defective donor T cells exhibited significant mixed chimerism (Ly-5.1/Ly-5.2). Because only marrow of donor origin was transplanted, this finding suggests that Fas-mediated antirecipient cytotoxicity is required for clearance of residual hematopoietic stem cells of host origin that persist following lethal irradiation.

Host immune suppression after small bowel/liver transplantation in rats

Simultaneous liver grafting in the Lewis (RT1)-to-DA (RT1) rat strain combination protects small intestinal grafts from rejection. The present study examined host immune responses after combined small bowel/liver transplantation (SBL) in this model. Orthotopic liver transplantation and heterotopic small intestinal transplantation were performed simultaneously and compared with isolated small bowel allografts (SBA) and isolated small bowel isografts (SBI). All rats were sacrificed on postoperative day (POD) 7 or 14 for immunological and histological studies. The mean time to rejection of the SBA was 6.6 +/- 0.3 days. In contrast, there was no clinical or histological evidence of intestinal rejection in SBL recipients during the 14 days of follow-up. The SBL recipients showed clinical and histological evidence of graft-versus-host disease (GVHD). Lymphocyte proliferation and IL-2 production in response to donor antigens were suppressed after SBL transplantation compared with the SBA or the SBI controls (P < 0.05). Cell-mediated cytotoxicity and lymphocytotoxic antibody production against donor cells were also significantly inhibited in the SBL recipients compared with the SBA control group (P < 0.05). We conclude that SBL transplantation in the Lewis-to DA rat strain combination: (1) suppresses host alloimmune responses, (2) prevents early intestinal rejection, and (3) favors the development of GVHD.

Host immune suppression after small bowel/liver transplantation in rats

Simultaneous liver grafting in the Lewis (RT1)-to-DA (RT1) rat strain combination protects small intestinal grafts from rejection. The present study examined host immune responses after combined small bowel/liver transplantation (SBL) in this model. Orthotopic liver transplantation and heterotopic small intestinal transplantation were performed simultaneously and compared with isolated small bowel allografts (SBA) and isolated small bowel isografts (SBI). All rats were sacrificed on postoperative day (POD) 7 or 14 for immunological and histological studies. The mean time to rejection of the SBA was 6.6 +/- 0.3 days. In contrast, there was no clinical or histological evidence of intestinal rejection in SBL recipients during the 14 days of follow-up. The SBL recipients showed clinical and histological evidence of graft-versus-host disease (GVHD). Lymphocyte proliferation and IL-2 production in response to donor antigens were suppressed after SBL transplantation compared with the SBA or the SBI controls (P < 0.05). Cell-mediated cytotoxicity and lymphocytotoxic antibody production against donor cells were also significantly inhibited in the SBL recipients compared with the SBA control group (P < 0.05). We conclude that SBL transplantation in the Lewis-to DA rat strain combination: (1) suppresses host alloimmune responses, (2) prevents early intestinal rejection, and (3) favors the development of GVHD.

Regulation of graft-versus-host-reaction by Mlsa-reactive donor T cells

Injection of A/J splenocytes (H-2Dd, Mlsc) into unirradiated (A/J x CBA)F1 (BAF1) host mice (H-2Dd/k, Mlsd) results in an acute suppressive graft-vs.-host reaction (GVHR), characterized by immune dysfunction and appreciable donor cell engraftment; injection of the CBA/J parent (H-2Dk, Mlsd), which recognizes no Mls disparity in the host, results in little or no GVHR. Furthermore, the Mlsa-reactive V beta 6 and V beta 8.1 T cell subsets in A/J T cells expand significantly in the GVHR host. Finally, depletion of V beta 6+ and V beta 8.1+ from the A/J population abrogates the proliferative response to BAF1 in vitro and the development of GVHR in vivo. Thus, the response to Mls determinants can contribute to the generation of a GVHR.

Dynamics of early B lymphocyte precursor cells in mouse bone marrow: proliferation of cells containing terminal deoxynucleotidyl transferase

Three populations of early B lymphocyte precursor cells lacking mu heavy chains have been defined in mouse bone marrow, based on immunofluorescence labeling for terminal deoxynucleotidyl transferase (TdT) and B220 glycoprotein, as detected by monoclonal antibody 14.8 (TdT+14.8- cells; TdT+14.8+ cells; TdT-14.8+ cells). We have now analyzed the frequency, size distribution, proliferation and production rates of TdT+ cells in mouse bone marrow. These formed well-defined populations of medium-sized cells, the TdT+14.8+ cells tending to be larger than TdT+14.8- cells (modal cell diameters in cytocentrifuge preparations; 10.0 microns and 9.0 microns, respectively). Some TdT+ cells (1%-2%) were normally in metaphase, the TdT being dispersed through the cytoplasm. After inducing mitotic arrest with vincristine, the incidence of TdT+ cells in metaphase increased linearly from 2 to 4 h, indicating a turnover of 5.1%/h for TdT+14.8- cells and 9.0%/h for TdT+14.8+ cells. Subtraction of turnover data for TdT+14.8+ cells from those previously obtained for 14.8+ mu- cells gave values for the population of TdT-14.8+ cells. The calculated daily turnover of cells in the three compartments increased progressively (TdT+14.8-, 2.5 x 10(6) cells; TdT+14.8+, 5.0 x 10(6) cells; TdT-14.8+, 36.0 x 10(6) cells), accompanied by a shortening of the average apparent cell cycle time (TdT+14.8-, 20 h; TdT+14.8+, 11 h; TdT-14.8+, 8 h). The results demonstrate a progressive expansion of cell production at three putatively successive stages of early B lymphocyte development before the expression of mu chains. The findings contribute to a kinetic model of primary B cell genesis in mouse bone marrow.

Hematopoietic factors in graft-versus-host reaction

Graft-versus-host (GVH) reaction has a curious unsolved area in the immunopathogenesis and pathophysiology of the immunohematopoietic system, and GVH disease remains one of the major obstacles in clinical allogeneic bone marrow transplantation. T lymphocytes and T lymphocyte subpopulations are now recognized to be initiators of this GVH reaction and disease. Also, T lymphocytes are known to be accessory cells in the regulation of hematopoiesis, and produce a variety of lymphokines relevant to hematopoiesis. Admittedly, remarkable hematopoietic changes can be found in GVH reaction, but the cellular mechanisms underlying these changes are so complex they have yet to be fully elucidated. In fact, elevated serum levels of myeloid and erythroid colony-stimulating activities were found in mice suffering from GVH disease in which marked granulopoiesis and suppression of erythropoietic differentiation were seen. In addition, each granulocyte/macrophage colony-stimulating factor (GM-CSF) or burst-promoting activity (BPA) could be detected in sera from patients with GVH disease following allogeneic bone marrow transplantation. There seems to be at least two mechanisms involved in the control of hematopoiesis with either humoral or local environmental factor, probably via the T lymphocytes or T lymphocyte subpopulations activated by alloantigens or autologous non-T cells.