Graft-versus-host reactivity and graft-versus-leukemia effect in murine allogeneic bone marrow chimeras conditioned with total body irradiation or total lymphoid irradiation

CTLA-4 blockade in murine bone marrow chimeras induces a host-derived antileukemic effect without graft-versus-host disease

We studied the effect of CTLA-4 blockade on graft-versus-leukemia and graft-versus-host responses in a mouse model of minor histocompatibility-mismatched bone marrow transplantation. Early CTLA-4 blockade induced acute graft-versus-host disease. Delayed CTLA-4 blockade resulted in a lethal condition with lymphosplenomegaly, but with stable mixed T-cell chimerism, unchanged alloreactive T-cell frequencies and absent anti-host reactivity in vitro. In contrast, multiorgan lymphoproliferative disease with autoimmune hepatitis and circulating anti-DNA auto-antibodies were documented. Splenic lymphocytes exhibited ex vivo spontaneous proliferation and a marked proliferative response against host-type dendritic cells pulsed with syngeneic (host-type) tissue-peptides. Both phenomena were exclusively mediated by host and not donor T cells, supporting an autoimmune pathogenesis. Selectively host-derived T-cell immune reactivity was equally documented against leukemia-peptide-pulsed dendritic cells, and this was paralleled by a strong in vivo antileukemic effect in anti-CTLA-4-treated and subsequently leukemia-challenged chimeras. In conclusion, delayed CTLA-4 blockade induced a host-derived antileukemic effect, occurring in the context of an autoimmune syndrome and strictly separated from graft-versus-host disease. Both antileukemic and autoimmune responses depended on the allogeneic component, as neither effect was seen after syngeneic bone marrow transplantation. Our findings reveal the potential of using CTLA-4 blockade to establish antileukemic effects after allogeneic hematopoietic stem cell transplantation, provided autoimmunity can be controlled.

Total lymphoid irradiation nonmyeloablative preconditioning enriches for IL-4-producing CD4+-TNK cells and skews differentiation of immunocompetent donor CD4+ cells

Preconditioning with the nonmyeloablative regimen total lymphoid irradiation (TLI) before hematopoietic cell transplantation facilitates the establishment of mixed chimerism and protects against graft-versus-host disease. We reported that the development of mixed chimerism requires interleukin (IL)-4 and is associated with increased host anti-donor TH2 cells, but the effect of TLI on the differentiation of immunocompetent donor cells has not been investigated. To examine the extent to which TLI preconditioning influences donor T cells, we measured responses of transgenic CD4+cells specific for ovalbumin peptide (OVA-Tg) following in vivo and in vitro antigen stimulation in a TLI-preconditioned environment. OVA-Tg cells that were adoptively transferred into TLI-preconditioned mice that express cross-reactive antigens produced more IL-4 and less interferon-gamma and IL-2 than controls when stimulated with OVA peptide one week later. OVA-Tg primed in vitro with spleen from TLI-preconditioned mice generated more TH2 and fewer TH1 cells when stimulated in recall enzyme-linked immunosorbent spot (ELISPOT) assays with OVA peptide. Naive OVA-Tg up-regulated CD69 and CD25 normally following stimulation with OVA peptide in the presence of spleen from TLI-preconditioned mice, but proliferated less and secreted less IL-2 than controls. Surprisingly, naive OVA-Tg secreted IL-4 in primary cultures that were stimulated with OVA peptide in the presence of spleen from TLI-preconditioned mice. This response depends on CD4+cells from TLI-spleen, which constitutively produce IL-4 and are composed primarily of CD4+-natural killer T (TNK) cells. Thus, TLI preconditioning enriches for IL-4-secreting and TNK-like CD4+cells that may function in the protection from graft-versus-host disease by redirecting the differentiation of immunocompetent donor CD4+cells toward TH2 and away from pathogenic TH1 cells.

Long-term donor chimerism after MHC (RT1) mismatched bone marrow transplantation in the rat: the role of host alloreactive NK cells

We have investigated the role of major histocompatibility complex (MHC) (RT1) disparities in the engraftment of bone marrow (BM) cells after whole body irradiation of rats. Mononuclear BM cells from PVG.RT7.2 (RT1c) rats were injected i.v. into sublethally (10Gy) whole body irradiated PVG (RT1c) rats and RT1 congenic and recombinant PVG rats. Repopulation of the BM, spleen, and blood with donor cells was assessed by FACS analysis of cells labelled with the fluorescein isothiocyanate (FITC)-labelled HIS41 monoclonal antibody (MoAb) against the RT7.2 marker. In RT1 matched (PVG.RT7.2 --> PVG) and RT1-mismatched combinations (PVG.RT7.2 --> PVG.1AV1), where radioresistant host natural killer (NK) cells could not recognize the BM inoculum as foreign, a donor chimerism close to 100% was observed after 6-8 weeks. However, in rat strain combinations where host NK cells could recognize an RT1 mismatch, almost no donor cells survived, and the rats were repopulated with leukocytes of host origin. In intra-MHC recombinant rat strains the element determining rejection or acceptance of the allograft mapped to the RT1-B/D-C/E/M region in PVG.R8 and PVG.R23 rats, in accordance with the patterns of NK alloreactivity in these strain combinations. NK cells may therefore be a primary obstacle to successful allogeneic BM engraftment in this model.

Transforming growth factor-beta inhibits lymphokine activated killer cytotoxicity of bone marrow cells: implications for the graft-versus-leukemia effect in irradiation allogeneic bone marrow chimeras

BACKGROUND

We have previously shown that allogeneic bone marrow (BM) chimeras preconditioned with total lymphoid irradiation and low-dose total body irradiation (TLI/TBI) develop a stronger graft-versus-leukemia (GVL) effect than chimeras preconditioned with high-dose total body irradiation only (TBI). Here, we report on the possible role of cytokines in the mechanism underlying this GVL effect.

METHODS

Splenic mRNA levels of the cytokines interleukin (IL)-1, IL-2, IL-4, IL-6, IL-7, IL-10, IL-12, IL-15, interferon-gamma, tumor necrosis factor-alpha, and transforming growth factor-beta (TGF-beta), and of inducible nitric oxide synthetase were determined by reverse transcription-polymerase chain reaction in TLI/TBI- or TBI-conditioned C3H/AKR BM chimeras challenged with AKR-type BW5147.3 leukemia cells. Ex vivo TGF-beta protein production by splenocytes was determined using ELISA. The possibility that cytokines influence the GVL effect by modulating the activity of IL-2-activated lymphocytes (LAK cells) was investigated by in vitro assays on donor-type BM cells.

RESULTS

Of all cytokine mRNA levels studied, those of TGF-beta and IL-7 were different between groups; both were significantly more elevated in TBI- than in TLI/ TBI-conditioned or normal mice. Differences were apparent after conditioning and were not influenced by additionally injected BM or leukemia cells. Cultured splenocytes of TBI-conditioned animals produced significantly more TGF-beta protein than those of TLI/TBI-conditioned ones or normal controls. r-TGF-beta but not r-IL-7 suppressed in vitro LAK activity of donor-type BM cells against BW5147.3 cells in a dose-dependent way.

CONCLUSIONS

High-dose TBI-induced, host-derived splenic TGF-beta may inhibit generation of LAK cells from subsequently transplanted donor BM cells, suppressing their capacity to generate cytotoxicity upon injection of leukemia cells. The cytokine profile, induced by irradiation in host hematopoietic organs, can significantly modify posttransplant immunological processes such as the GVL effect and graft-versus-host disease (GVHD).

Graft-versus-leukemia effect in minor antigen mismatched chimeras given delayed donor leucocyte infusion: immunoregulatory aspects and role of donor T and ASGM1-positive cells

BACKGROUND

Previous studies have demonstrated that delayed donor leukocyte infusion (DLI) can increase graft-versus-leukemia (GVL) without increasing graft-versus-host-disease (GVHD) in MHC mismatched bone marrow (BM) chimeras. In our report, the immune status of minor antigen mismatched BM chimeras given DLI was studied. Particularly the role of donor ASGM1 positive or T cells in the graft-versus-leukemia effect (GVL) was investigated.

METHODS

AKR mice (H2k, Mls1a, Thy1.1) received TBI (9,5 Gy) and T cell-depleted (TCD) C3H (H2k, Mls2a, Thy1.2) BM alone (BM chimeras), or TCD BM together with immunocompetent C3H spleen cells at the time of BM transplantation (BM+SP chimeras), or TCD BM and 3 weeks later C3H spleen cells (DLI chimeras). Chimerism and T lymphocyte subsets were scored using FACS and anti-Thy, anti-Vbeta6, anti-IL2-beta receptor, anti-CD4, anti-CD3, and anti-CD8 mAbs. Leukemia challenge consisted of 5 x 10(6) AKR T cell lymphoma (BW4157) cells injected i.v. ASGM1 positive (ASGM1+) cells and T cells were depleted using anti-ASGM1 or anti-Thy1.2 antibodies, respectively. Immune tolerance was studied using MLR and CML tests.

RESULTS

BM + SP chimeras developed acute and lethal GVHD, whereas DLI chimeras were totally free from GVHD. In DLI chimeras, host-reactive cytotoxic T cells (CTL) could not be induced and host-reactive CD8Vbeta6 cells were deleted whereas CD4Vbeta6 cells and MLR reactivity persisted temporarily. In contrast, in BM+SP chimeras, anti-host CTL were easily generated and an expansion of both host-reactive CD8Vbeta6 and CD4Vbeta6 T cells was found as well as high anti-host MLR reactivity. Depletion of either ASGM1 + cells or T cells from the DLI inoculum resulted in an abrogation of GVL reactivity, suggesting that both cell populations were involved in the protection against BW4157 leukemia. Three weeks after DLI, the GVL effect waned which correlated with the disappearance of host-reactive CD4 cells and MLR reactivity.

CONCLUSION

In minor antigen mismatched BM chimeras, anti-host reactivity after DLI is characterized by (1) an absence of clinical GVHD, (2) clonal deletion of host-reactive CD8 cells, (3) an absence of anti-host CTL induction, and ( 4) a temporary persistence of host-reactive CD4 T cells and of MLR reactivity. In addition, either donor ASGM1+ cells or an interaction between these cells and T cells contribute to the GVL effect.

Extramedullary relapse despite graft-versus-leukemia effect after bone marrow transplantation in a girl with juvenile myelomonocytic leukemia

A 12 year-old girl with juvenile myelomonocytic leukemia (JMML) and monosomy 7 underwent allogeneic bone marrow transplantation (BMT) from her HLA-matched brother. To monitor the engraftment and the course of the disease we used fluorescence in situ hybridization (FISH) with probes specific for the centromeres of chromosomes X, Y and 7. Complete hematological remission was achieved and confirmed by the virtually exclusive presence of normal male cells in the bone marrow (BM). Acute graft-versus host disease (GvHD) was treated with prednisone and cyclosporine A (CSA) and female cells with monosomy 7 reoccurred in the peripheral blood (PB) and BM. After discontinuation of the immunosuppressive therapy, the leukemic cells with monosomy 7 disappeared again from these compartments. One year after transplantation, isolated extramedullary relapses occurred in lymph nodes and skin, followed by dissemination of blast cells into the BM, whereas the PB cells remained of donor origin. The fact that the leukemic cells fluctuated with the intensity of the immunosuppressive treatment provides evidence of a graft versus leukemia (GvL) effect in this unusually old girl with JMML with a unique extramedullary disease progression.

Induction of specific transplantation tolerance across xenogeneic barriers in the T-independent immune compartment

After transplantation of primarily vascularized xenografts (Xgs), T-independent mechanisms may lead to Xg rejection before T-cell activation even takes place. The possibility of achieving T-independent xenotolerance was evaluated in nude rats that normally reject hamster cardiac Xgs within 4 days by non-T cell-mediated mechanisms. After donor antigen infusion, temporary NK-cell depletion and a 4-week administration of Leflunomide, hamster heart grafts survived even after withdrawal of immunosuppression. Tolerant rats accepted second hamster hearts, but promptly rejected mouse heart Xgs. In vivo immunization and in vitro cytotoxicity assays indicated that this species-specific tolerance was based on B-lymphocyte and NK-cell tolerance respectively.

Contribution of activated macrophages to the process of delayed xenograft rejection

BACKGROUND

When hyperacute rejection, involving natural xenoreactive antibodies (XAb) and/or complement (C), can be prevented, xenografts (Xgs) undergo delayed xenograft rejection associated with a progressive mononuclear cell infiltration. We have previously shown that XAb formation can be totally suppressed in leflunomide (LF)-treated, T-deficient nude rats receiving hamster hearts. Hence, this model was well-suited to study a role played by other factors, e.g., natural killer (NK) cells and macrophages (Mphi). The relative contribution of Mphi to delayed xenograft rejection was investigated.

METHODS

In addition to LF (20 mg/kg/24 hr p.o.), anti-asialoGM-1 serum (1 mg/48 hr i.v.) and N omega-nitro-L-arginine methyl ester (L-NAME; 100 mg/kg/24 hr i.v.) were given. Graft-infiltrating cells, deposition of cytokines (interferon-gamma [IFN-gamma] and tumor necrosis factor-alpha [TNF-alpha]), IgM and C, and expression of endothelial cell (EC) P- and E-selectins were investigated by immunohistochemistry. In some cases, rat rTNF-alpha or anti-TNF-alpha antibodies were injected intravenously.

RESULTS

Xgs rejected after 3 days by LF-treated rats showed an absence of IgM, C, and T cells, but the infiltration of NK cells and Mphi, together with the presence of IFN-gamma and TNF-alpha. Addition of NK cell depletion resulted in a significantly prolonged survival of Xgs (6 days; P<0.001) in which NK cells and IFN-gamma had disappeared, but Mphi were still prominent. Additional blockade of Mphi nitric oxide (NO) with L-NAME further prolonged Xg survival (11 days; P<0.001). In these rejected Xgs, Mphi, TNF-alpha, and EC expression of P- and E-selectins was still found, together with platelet thrombi, neutrophil-EC adhesion, and vessel intima lesions. The role of TNF-alpha in initiating this Xg rejection was further demonstrated by the acceleration of Xg rejection after injection of rTNF-alpha and by a synergism between L-NAME and anti-TNF-alpha antibodies in hampering the acceleration of Xg rejection seen after transfer of sensitized Mphi.

CONCLUSION

In the absence of XAb, T cells, and NK cells, Mphi can still reject Xgs. Both NO-dependent and NO-independent mechanisms are involved. In the latter case, Mphi-derived, TNF-alpha-associated EC activation may play a role.

Factors involved in rejection of concordant xenografts in complement-deficient rats

BACKGROUND

Factors that contribute to xenograft (Xg) rejection were investigated in complement C6-deficient (C-) PVG rats.

METHODS

First and second hamster hearts were transplanted in C6-deficient and C6-sufficient PVG rats. Xenoantibody (XAb) formation, hemolytic C (CH50) activity and immunohistochemistry were studied.

RESULTS

PVG C6-deficient rats rejected Xgs 3 days later than PVG C6-sufficient rats. Surprisingly, C activation participated in the rejection in PVG C- rats, as shown by partially recovered serum CH50 levels and deposition of C factors in the Xgs. As we found that cultured endothelial cells produced C6 in vitro, we hypothesized that Xg endothelial cells corrected the C6 defect in PVG C- rats. This was probably induced by IgM XAbs as: (1) it did not occur in immunosuppressed PVG C- rats in which XAb formation was prevented, and (2) transfer of IgM XAbs to naive, xenotransplanted PVG C- rats accelerated the recovery of CH50 and concomitantly Xg rejection. Thirty days after rejection of a first Xg, when no IgM XAbs or CH50 activity but high levels of IgG XAbs were detected in PVG C- rats, second Xgs underwent a hyperacute rejection. This time, complement was not involved, as no serum CH50 nor C deposition was found in the Xg. Instead, IgG antibody-dependent cellular cytotoxicity was involved as: (1) IgG XAbs were deposited in the Xg and (2) hyperacute rejection was induced in naive PVG C- rats by transfer of IgG XAbs, and (3) this rejection was delayed to 5+/-3 days if the adoptive hosts were first irradiated.

CONCLUSIONS

In the face of a defect of host C factors, IgM XAb may induce cells of the Xg to secrete C factors which may correct the C defect of the host. Even if activation of lytic C can be prevented, IgG XAb may still provoke an acute Xg rejection by antibody-dependent cellular cytotoxicity.