Interleukin-6 modulates graft-versus-host responses after experimental allogeneic bone marrow transplantation.

PURPOSE: The graft-versus-tumor (GVT) effect is a potent form of immunotherapy against many hematologic malignancies and some solid tumors. The beneficial GVT effect after allogeneic bone marrow transplantation (BMT) is tightly linked to its most significant complication, graft-versus-host disease (GVHD). The role of interleukin-6 (IL-6) after allogeneic BMT is not well understood. This study used a series of complementary knockout and antibody blockade strategies to analyze the impact of IL-6 in multiple clinically relevant murine models of GVHD and GVT. EXPERIMENTAL DESIGN: We examined the effect of the source of IL-6 by analyzing the role IL-6 deficiency in donor T cells, donor bone marrow or in host tissues. We confirmed and extended the relevance of IL-6 deficiency on GVHD and GVT by treating BMT recipients with anti-mouse IL-6 receptor (IL-6R), MR16-1. RESULTS: Deficiency of IL-6 in donor T cells led to prolongation of survival. Total inhibition of IL-6 with MR16-1 caused an even greater reduction in GVHD-induced mortality. The reduction in GVHD was independent of the direct effects on T effector cell expansion or donor regulatory T cells. GVT responses were preserved after treatment with MR16-1. CONCLUSION: MR16-1 treatment reduced GVHD and preserved sufficient GVT. Tocilizumab, a humanized anti-IL-6R monoclonal antibody (mAb), is approved in several countries including the United States and European Union for the treatment of rheumatoid arthritis and other inflammatory diseases. Blockade of IL-6 with anti-IL-6R mAb therapy may be testable in clinical trials as an adjunct to prevent GVHD in BMT patients without a significant loss of GVT.

A crucial role for host APCs in the induction of donor CD4+CD25+ regulatory T cell-mediated suppression of experimental graft-versus-host disease.

Allogeneic bone marrow transplantation is an effective treatment for a number of malignant and nonmalignant diseases (Applebaum. 2001. Nature. 411: 385-389 and Copelan. 2006. N Engl J Med. 354: 1813-1826). However, the application of this therapeutic modality has been impeded by a number of confounding side effects, the most frequent and severe of which is the development of graft-versus-host disease (GVHD) (Copelan. 2006. N Engl J Med. 354: 1813-1826 and Blazar and Murphy. 2005. Philos Trans R Soc Lond B Biol Sci. 360: 1747-1767). Alloreactive donor T cells are critical for causing GVHD (Fowler. 2006. Crit Rev Oncol Hematol. 57: 225-244 and Ferrara and Reddy. 2006. Semin Hematol. 43: 3-10), whereas recent data demonstrated a significant role for the naturally occurring thymic-derived donor CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs) (Bluestone and Abbas. 2003. Nat Rev Immunol. 3: 253-257 and Shevach. 2006. Immunity. 25: 195-201) in suppressing experimental GVHD after bone marrow transplantation (Blazar and Taylor. 2005. Biol Blood Marrow Transpl. 11: 46-49 and Joffe and van Meerwijk. 2006. Semin Immunol. 18: 128-135) . Host APCs are required for induction of GVHD by the conventional donor T cells. However, it is not known whether they are also obligatory for donor Treg-mediated suppression of GVHD. Using multiple clinically relevant MHC-matched and -mismatched murine models of GVHD, we investigated the role of host APCs in the suppression of GVHD by donor Tregs. We found that alloantigen expression by the host APCs is necessary and sufficient for induction of GVHD protection by donor Tregs. This requirement was independent of their effect on the maintenance of Treg numbers and the production of IL-10 or IDO by the host APCs.

Frequency of CD4(+)CD25(hi)FOXP3(+) regulatory T cells has diagnostic and prognostic value as a biomarker for acute graft-versus-host-disease.

The relationship between regulatory T cells (Tregs) and acute graft-versus-host disease (aGVHD) in clinical allogeneic bone marrow transplantation (BMT) recipients is not well established. We conducted a prospective analysis of peripheral blood Tregs as determined by the frequency of CD4(+)CD25(hi)FOXP3(+) lymphocytes in 215 BMT patients. Autologous BMT patients (N = 90) and allogeneic BMT patients without GVHD (N = 65) had similar Treg frequencies, whereas allogeneic patients with GVHD (N = 60) had Treg frequencies that were 40% less than those without GVHD. Treg frequencies decreased linearly with increasing grades of GVHD at onset, and correlated with eventual maximum grade of GVHD (P < .001). In addition, frequency of Tregs at onset of GVHD predicted the response to GVHD treatment (P = .003). Patients with Treg frequencies less than the median had higher nonrelapse mortality (NRM) than patients with Tregs greater than the median, but experienced equivalent relapse mortality, resulting in an inferior survival at 2 years (38% versus 63%, P = .03). Treg frequency may therefore have important prognostic value as a biomarker of aGVHD.

Immunization with host-type CD8{alpha}+ dendritic cells reduces experimental acute GVHD in an IL-10-dependent manner.

Little is known about the role of active immunization in suppressing undesirable immune responses. Because CD8alpha(+) dendritic cells (DCs) suppress certain immune responses, we tested the hypothesis that immunization of donors with host-derived CD8alpha(+) DCs will reduce host-specific donor T-cell responses. BALB/c T cells from the animals that were immunized with B6 CD8alpha(+) DCs demonstrated, in vitro and in vivo, significantly reduced proliferation and secretion of inflammatory cytokines but showed enhanced secretion of interleukin-10 (IL-10). The responses against third-party and model antigens were preserved demonstrating antigen specificity. The in vivo relevance was further demonstrated by the reduction on graft-versus-host disease (GVHD) in both a major histocompatibility complex-mismatched clinically relevant BALB/c --> B6 model and major histocompatibility complex-matched, minor-mismatched C3H.SW --> B6 model of GVHD. Immunization of the donors that were deficient in IL-10 (IL-10(-/-)) or with CD8alpha(+) DCs from B6 class II (class II(-/-)) failed to reduce T-cell responses, demonstrating (1) a critical role for secretion of IL-10 by donor T cells and (2) a direct contact between the T cells and the CD8alpha(+) DCs. Together, these data may represent a novel strategy for reducing GVHD and suggest a broad counterintuitive role for vaccination strategies in mitigating undesirable immune responses in an antigen-specific manner.

Mesenchymal stem cells for treatment and prevention of graft-versus-host disease after allogeneic hematopoietic cell transplantation.

Allogeneic hematopoietic cell transplantation (allo-HCT) is an effective therapy for hematological malignancies and inherited diseases. However, acute graft-versus-host-disease (aGVHD) is a major life-threatening complication after allo-HCT and there are few therapeutic options for severe steroid-refractory aGVHD. Preliminary studies on co-transplantation of mesenchymal stem cells (MSCs) have shown an improvement in or resolution of severe aGVHD. However, the mechanism underlying this immunosuppressive effect has not been elucidated. Most of the data suggest that the immunosuppressive effect involves soluble factors such as IL-6 or TGF-beta as well as cell-cell contact dependence. MSCs interact either directly with T cells or indirectly via other immune cells such as dendritic cells and NK cells. Here we review the immunomodulatory function of MSCs in allo-HCT and their potential usefulness in the treatment or prevention of severe acute GVHD.

Combined Th2 cytokine deficiency in donor T cells aggravates experimental acute graft-vs-host disease.

The role of T helper (Th) 1 and Th2 polarization in acute graft-vs-host-disease (GVHD) is unclear. We investigated the role of Th2 cytokine secretion by utilizing donor T cells that cannot make interleukin (IL)-4, IL-5, IL-9, and IL-13 from quadruple cytokine-deficient (Quad-KO) animals in a well-characterized BALB/c-->C57BL/6 model of allogeneic bone marrow transplantation. B6 recipients of BALB/c Quad-KO T cells demonstrated greater clinical severity, target organ damage, and mortality from GVHD than recipients of BALB/c wild-type (WT) T cells. When compared with donor T cells that are deficient in signal transducers and activators of transcription 6 signaling or the signature Th2 cytokine, IL-4, Quad-KO T cells demonstrated greater GVHD mortality. Mechanistic studies demonstrated that Quad-KO T cells demonstrated enhanced T-cell proliferation than WT T cells when stimulated with either allogeneic antigen-presenting cells or with nonspecific stimuli, such as anti-CD3 monoclonal antibody. Quad-KO T cells also secreted greater amounts of Th1 cytokines and IL-17 compared to WT T cells. Deficiency of Th2 cytokines, however, did not alter the allospecific cytotoxic responses, the numbers of immunoregulatory CD4(+)CD25(+) Foxp3(+) T cells or their suppressive functions. Our data thus unequivocally demonstrate that deficiency of the four classical Th2 cytokine enhances T-cell proliferative responses and aggravates GVHD.

Extracorporeal photopheresis reverses experimental graft-versus-host disease through regulatory T cells.

Extracorporeal photopheresis (ECP), a technique that exposes isolated white blood cells to photoactivatable 8-methoxypsoralen and ultraviolet A radiation, is used clinically to treat cutaneous T-cell lymphoma and immune-mediated diseases such as graft-versus-host disease (GVHD). ECP is thought to control these diseases in part through direct induction of lymphocyte apoptosis, but its effects on the immune system beyond apoptosis remain poorly characterized. We have developed a novel method for incorporating ECP treatment into well-established and clinically relevant murine models of GVHD to examine its effects during an ongoing immune response. We demonstrate that the transfer of cells treated with ECP reverses established GVHD by increasing donor regulatory T cells and indirectly reducing the number of donor effector lymphocytes that themselves had never been exposed to psoralen and ultraviolet A radiation.

Critical role of host gammadelta T cells in experimental acute graft-versus-host disease.

Gammadelta T cells localize to target tissues of graft-versus-host disease (GVHD) and therefore we investigated the role of host gammadelta T cells in the pathogenesis of acute GVHD in several well-characterized allogeneic bone marrow transplantation (BMT) models. Depletion of host gammadelta T cells in wild-type (wt) B6 recipients by administration of anti-T-cell receptor (TCR) gammadelta monoclonal antibody reduced GVHD, and gammadelta T-cell-deficient (gammadelta-/-) BM transplant recipients experienced markedly improved survival compared with normal controls (63% vs 10%, P < .001). gammadelta T cells were responsible for this difference because reconstitution of gammadelta-/- recipients with gammadelta T cells restored GVHD mortality. gammadelta-/- recipients showed decreased serum levels of tumor necrosis factor alpha (TNF-alpha), less GVHD histopathologic damage, and reduced donor T-cell expansion. Mechanistic analysis of this phenomenon demonstrated that dendritic cells (DCs) from gammadelta-/- recipients exhibited less allostimulatory capacity compared to wt DCs after irradiation. Normal DCs derived from BM caused greater allogeneic T-cell proliferation when cocultured with gammadelta T cells than DCs cocultured with medium alone. This enhancement did not depend on interferon gamma (IFN-gamma), TNF-alpha, or CD40 ligand but did depend on cell-to-cell contact. These data demonstrated that the host gammadelta T cells exacerbate GVHD by enhancing the allostimulatory capacity of host antigen-presenting cells.

Immunologic response to cryoablation of breast cancer.

PURPOSE: With improvements in breast imaging and image-guided interventions, there is interest in ablative techniques for breast cancer. Cryosurgery initiates inflammation and leaves tumor-specific antigens intact, which may induce an anti-tumor immune response. To help define the mechanisms involved in the cryoimmunologic response, we compared cryosurgery to surgery in a murine model of breast cancer. EXPERIMENTAL DESIGN: BALB/c mice with MT-901 tumors underwent cryoablation or resection. Mice successfully treated were re-challenged with MT-901 or RENCA. Serum cytokine levels were analyzed by ELISA. Tumor draining lymph nodes (TDLN) and spleens were harvested, lymphocytes were activated and assessed for a specific anti-tumor response by both an interferon-gamma (IFNgamma) release assay and ELISPOT. NK cell activity was assessed by cytotoxicity against YAC-1, an NK-susceptible cell line. RESULTS: After re-challenge, tumors developed in 86% of mice treated by surgical excision compared to 16% of mice treated by cryosurgery (p=0.025). Cryoablation of MT-901 had no effect on re-challenge with RENCA. Cryoablation led to significantly higher levels of interleukin (IL)-12 (383.6 pg/ml +/- 32.8 versus 251.6 +/- 16.5, p=0.025) and IFN-gamma (1564 pg/ml +/- 49 versus 1244 pg/ml +/- 101, p=0.009), but no changes in IL-4 or IL-10. Tumor-specific T-cell responses were evident after cryosurgery in lymphocytes from TDLN but not from spleen. Cryoablation also increased NK activity compared to surgery (24.5% +/- 17.3 versus 16.5% +/- 5.9, p < 0.001). CONCLUSION: Cryoablation results in the induction of both a tumor-specific T-cell response in the TDLN and increased systemic NK cell activity, which correlates with rejection of tumors upon re-challenge.

Paradoxical effects of interleukin-18 on the severity of acute graft-versus-host disease mediated by CD4+ and CD8+ T-cell subsets after experimental allogeneic bone marrow transplantation.

Administration of exogenous interleukin-18 (IL-18) regulates experimental acute graft-versus-host disease (GVHD) in a Fas-dependent manner when donor CD4(+) T cells are required for mortality after experimental allogeneic bone marrow transplantation (BMT). However, CD4(+) and CD8(+) T cells can induce acute GVHD after clinical allogeneic BMT, and the role of IL-18 in CD8(+)-mediated acute GVHD is unknown. We, therefore, determined the role of IL-18 in GVHD mediated by CD4(+) or CD8(+) T cells across major histocompatibility complex (MHC) class II- and class I-disparate allogeneic BMT, respectively. Administering IL-18 significantly increased survival in CD4(+)-mediated GVHD but reduced survival in CD8(+)-mediated GVHD. This increase in deaths was associated with significantly greater clinical, biochemical, and histopathologic parameters of GVHD damage and was independent of Fas expression on donor T cells. Administering IL-18 significantly enhanced allospecific cytotoxic function and expansion of CD8(+) cells. Endogenous IL-18 was critical to GVHD mediated by CD8(+) donor T cells because IL-18 receptor-deficient donors caused significantly less GVHD but exacerbated CD4(+)-mediated, GVHD-related death. Furthermore, administering anti-IL-18 monoclonal antibody significantly reduced CD8(+)-mediated, GVHD-related death. Together these findings demonstrate that IL-18 has paradoxical effects on CD4(+) and CD8(+) cell-mediated GVHD.

Blockade of CXCR3 receptor:ligand interactions reduces leukocyte recruitment to the lung and the severity of experimental idiopathic pneumonia syndrome.

Idiopathic pneumonia syndrome (IPS) is a frequently fatal complication after allogeneic stem cell transplantation (allo-SCT) that responds poorly to standard immunosuppressive therapy. The pathophysiology of IPS involves the secretion of inflammatory cytokines including IFN-gamma and TNF-alpha along with the recruitment of donor T cells to the lung. CXCR3 is a chemokine receptor that is expressed on activated Th1/Tc1 T cell subsets and the expression of its ligands CXCL9 (monokine induced by IFN-gamma (Mig)) and CXCL10 (IFN-gamma-inducible protein 10 (IP-10)) can be induced in a variety of cell types by IFN-gamma alone or in combination with TNF-alpha. We used a lethally irradiated murine SCT model (B6 --> bm1) to evaluate the role of CXCR3 receptor:ligand interactions in the development of IPS. We found that Mig and IP-10 protein levels were significantly elevated in the bronchoalveolar lavage fluid of allo-SCT recipients compared with syngeneic controls and correlated with the infiltration of IFN-gamma-secreting CXCR3(+) donor T cells into the lung. The in vivo neutralization of either Mig or IP-10 significantly reduced the severity of IPS compared with control-treated animals, and an additive effect was observed when both ligands were blocked simultaneously. Complementary experiments using CXCR3(-/-) mice as SCT donors also resulted in a significant decrease in IPS. These data demonstrate that interactions involving CXCR3 and its primary ligands Mig and IP-10 significantly contribute to donor T cell recruitment to the lung after allo-SCT. Therefore, approaches focusing on the abrogation of these interactions may prove successful in preventing or treating lung injury that occurs in this setting.

Repifermin (keratinocyte growth factor-2) reduces the severity of graft-versus-host disease while preserving a graft-versus-leukemia effect.

Graft-versus-host disease (GVHD) is the principal complication after allogeneic bone marrow transplantation (BMT). Reductions in systemic GVHD are frequently associated with a corresponding diminishment of the graft-versus-leukemia (GVL) response. In this study, we tested the effects of a novel recombinant human keratinocyte growth factor, repifermin (keratinocyte growth factor-2), on the induction of GVHD in a well-defined murine BMT model (B6 --> B6D2F1). Administration of repifermin (5 mg/kg/d) to allogeneic BMT recipients resulted in a significant decrease in both systemic GVHD and target organ histopathology. Repifermin treatment also reduced serum levels of tumor necrosis factor alpha and lipopolysaccharide compared with control mice. In contrast, repifermin did not affect T-cell proliferation, cytokine production, or cytotoxic responses to host antigens. When 2000 host-derived P815 (H-2(d)) leukemia cells were added to the bone marrow inoculum, repifermin preserved GVL effects and resulted in significantly delayed mortality compared with control-treated allogeneic BMT recipients. Collectively, these data suggest that repifermin administration may represent a novel strategy to separate the toxicity of GVHD from the beneficial GVL effects after allogeneic BMT.

Flt3 ligand therapy for recipients of allogeneic bone marrow transplants expands host CD8 alpha(+) dendritic cells and reduces experimental acute graft-versus-host disease.

Recent evidence suggests that dendritic cells (DCs) can regulate and amplify immune responses. Flt3 ligand (FL)-derived DC function was tested as a stimulator of allogeneic lymphocytes in vitro and in vivo. Treatment of mice with FL dramatically expanded DC number, but DCs isolated from FL-treated mice (FL DCs) were poor stimulators of allogeneic T-cell responses in vitro. Further activation of FL DCs did not restore their stimulatory ability, and FL DCs did not suppress the stimulation of the allogeneic T cells by normal DCs. FL treatment significantly increased the CD8 alpha(+) DC subset, which appeared to be the reason for their poor stimulatory capacity. These observations were confirmed in vivo using a mouse model of acute graft-versus-host disease (GVHD) wherein host DCs play a critical role. FL treatment of recipients before allogeneic bone marrow transplantation dramatically suppressed donor T-cell responses to host antigens, thereby reducing GVHD mortality (P <.01). These data represent a novel strategy that alters host DCs and reduces acute GVHD.

Donor leukocyte infusion from immunized donors increases tumor vaccine efficacy after allogeneic bone marrow transplantation.

Donor T cells play a critical role in mediating both harmful graft-versus-host disease (GVHD) and beneficial graft-versus-tumor effect after allogeneic bone marrow transplantation (BMT). We have recently demonstrated a novel treatment strategy to stimulate specific antitumor activity with preservation of tolerance to host antigens after T cell-depleted allogeneic BMT by vaccination of recipients with irradiated B16 melanoma cells engineered to secrete granulocyte-macrophage colony-stimulating factor. In this murine system, donor leukocyte infusion from a donor immunized with the recipient-derived B16 vaccines enhanced clinical activity of tumor vaccines without exacerbating GVHD. CD4(+) T cells are essential for this enhancement. In vitro analysis of splenocytes from donor leukocyte infusion donor mice demonstrated that immunization of donors with the recipient-derived B16 vaccines elicited potent T-cell proliferation and cytokine responses specific to B16 antigens. These results demonstrate that immunization of donors with recipient-derived tumor vaccines preferentially induces tumor-specific T-cell responses and that vaccination of both donors and recipients can generate potent antitumor immunity without exacerbating GVHD. This strategy has important implications to prevent recurrence of malignancies after BMT.