Targeting urokinase-type plasminogen activator receptor on human glioblastoma tumors with diphtheria toxin fusion protein DTAT

BACKGROUND

The prognosis for patients with brain cancer is poor, and new therapies are urgently needed. Recombinant toxic proteins that specifically target tumor cells appear to be promising. Urokinase-type plasminogen activator (uPA) receptor (uPAR) is expressed on the surface of glioblastoma and some other tumor cells and endothelial cells. We synthesized a recombinant fusion protein, DTAT, which contains the catalytic portion of diphtheria toxin (DT) for cell killing fused to the noninternalizing amino-terminal (AT) fragment of uPA, and investigated its effectiveness in targeting uPAR-positive tumor cells.

METHODS

In vitro cytotoxicity of DTAT was measured by cell proliferation assays. For in vivo studies, athymic nude mice (four to five animals/group) bearing uPAR-expressing human glioblastoma (U118MG) cell-induced tumors were injected with DTAT or control protein. Tumor volume was assessed over time, and differences between treatments were analyzed by Student's t test. Effects of DTAT on body organ systems were evaluated in normal, tumor-free C57BL/6 mice histologically and functionally by serum enzyme tests. All statistical tests were two-sided.

RESULTS

In vitro, DTAT was highly potent and selective in killing uPAR-expressing glioblastoma cells (U118MG, U373MG, and U87MG) and human umbilical vein endothelial cells. In vivo, compared with mice treated with control proteins, DTAT caused a statistically significant (P =.05) regression of small U118MG cell-induced tumors in all mice. Control fusion proteins that did not react with glioblastoma cells had no effect on tumor growth. DTAT given to tumor-free C57BL/6 mice had little effect on kidney, liver, heart, lung, and spleen histologies. Serum analysis in the same mice showed no elevation in blood urea nitrogen, indicating lack of effect on kidney function but a statistically significant (P =.046), albeit non-life-threatening, elevation in liver alanine aminotransferase levels.

CONCLUSION

DTAT may have potential for intracranial glioblastoma therapy because of its ability to target tumor cells and tumor vasculature simultaneously and its apparent lack of systemic effects.

Gene therapy of murine solid tumors with T cells transduced with a retroviral vascular endothelial growth factor--immunotoxin target gene

Solid tumor growth can be inhibited by targeting its neovasculature with vascular endothelial growth factor (VEGF)-toxin fusion proteins (FPs), but these agents have been limited by their inability to localize at the tumor site. In this study, we devised a gene therapy approach intended to deliver VEGF-toxin directly to tumor. Antigen-specific cytotoxic T lymphocytes (CTLs) served as vehicles to deliver a retroviral VEGF-toxin fusion protein to its specific leukemia cell target in vivo. A retroviral vector was constructed for gene therapy with VEGF positioned downstream of its 27-amino acid leader sequence, which promoted secretion of a catalytic immunotoxin containing either truncated diphtheria toxin or Pseudomonas exotoxin A. VEGF was chosen on the basis of the expression of VEGF receptor on endothelial cells in the tumor neovasculature. The VEGF FP was first expressed and secreted by mammalian NIH 3T3 cells. Intracellular expression of both VEGF and toxin was verified by immunofluorescence. In vitro, supernatants collected from transfected cells specifically inhibited the growth of VEGF receptor-expressing human umbilical vein endothelial cells (HUVECs), but not a control cell line. In vivo findings correlated with in vitro findings. A retroviral vector containing the target gene and a nerve growth factor receptor (NGFR) reporter gene was used to transiently transduce T15, a CD8(+) CTL line that specifically recognizes C1498, a lethal C57BL/6 myeloid tumor. Transduced T15 cells injected intravenously significantly inhibited the growth of subcutaneous tumor, whereas nontransduced controls did not. Together, these data indicate that gene therapy of T cells with retrovirus containing a VEGF-immunotoxin target gene may be a valid means of inhibiting a broad range of solid tumors dependent on angiogenesis.

Peptide toxins directed at the matrix dissolution systems of cancer cells

Growth and spread of tumors requires a variety of membrane and extracellular proteases to modify membrane integrins, dissolve the surrounding matrix and release critical growth factors from both the tumor cell surface and surrounding structures. The two major protease systems involved in this process are the matrix metalloproteases and the serine proteases. Genes and gene products for both protease systems are overexpressed in a variety of neoplasms. Thus, these enzymes serve as excellent targets for the delivery of potent cytotoxic molecules to tumors. A number of peptide toxins have been engineered to bind to tumor cells with high levels of surface proteases and their receptors including anthrax toxins, Pseudomonas exotoxin, saporin and diphtheria toxin. These recombinant fusion proteins provide a novel class of anti-cancer agents that will enter clinical trials in the next several years.

Chimeric fusion proteins--diphtheria toxin-based

Most cancer patients receive chemotherapy drugs that target DNA or the cell division apparatus. Many of these patients develop multidrug-resistant tumor cells, thus, novel methods to overcome drug resistance are needed. One approach is to target tumor cell protein synthesis. Peptide toxins, which catalytically inactivate protein synthesis, have been re-engineered to selectively bind and intoxicate tumor cells. Diphtheria toxin (DT), a member of the class of peptide toxins, has been subjected to structural and genetic analysis and protein engineering for several decades. In this review, we will examine the structure, function, synthesis and pharmacology of anticancer DT conjugates.

In vitro efficacy of recombinant diphtheria toxin–murine interleukin-4 immunoconjugate on mouse glioblastoma and neuroblastoma cell lines and the additive effect of radiation

Object

The prognosis for patients with primary malignant brain tumors is poor despite aggressive treatment, and tumor recurrence is common regardless of the chosen therapy. Although multimodal treatment does not provide a cure, it is necessary to determine which treatment modalities have the greatest cytotoxic effect and can potentially prolong survival. Immunotoxin therapy is a novel approach for the treatment of tumors, and it has been successfully used in the central nervous system. Because the interleukin (IL)–4 receptor is commonly expressed on brain tumor cells, the purpose of this study was to evaluate the cytotoxic effect of using a modified diphtheria toxin–murine IL-4 (DT390-mIL4) immunoconjugate for the treatment of murine brain tumor cell lines and to determine whether the addition of radiation therapy could potentiate the effect of this agent.

Methods

Spontaneous murine glioblastoma (SMA-560) and two neuroblastoma (Neuro-2a and NB41A3) cell lines were treated using DT390-mIL4 at different concentrations, and the anti–mouse IL-4 monoclonal antibody (11B11) was used for blocking its cytotoxicity. Other SMA-560 and Neuro-2a cell lines were treated using 500 cGy of radiation 3 hours before DT390-mIL4 treatment. Cytotoxity was evaluated using a trypan blue viability assay.

The immunoconjugate exhibited a dose-dependent cytotoxic effect with 50% inhibitory concentration values of 0.56 × 10−9 M in SMA-560, 1.28 × 10−9 M in Neuro-2a, and 0.95 × 10−10 M in NB41A3 cell lines. The cytotoxicity of DT390-mIL4 was specifically blocked by an excess of 11B11. Cytotoxicity was additive when the DT390-mIL4 at 10−9 M immunoconjugate administration was followed by radiation therapy.

Conclusions

These results indicate that the IL-4 receptor can be a target for diphtheria toxin fusion proteins and that radiation can potentiate the effects of DT390-mIL4. The development of multimodal approaches to treat malignant brain tumors with agents that have different mechanisms of action may be beneficial.

Molecular modification of a recombinant anti-CD3epsilon-directed immunotoxin by inducing terminal cysteine bridging enhances anti-GVHD efficacy and reduces organ toxicity in a lethal murine model

Immunotoxin (IT) therapy shows potential for selectively eliminating GVHD-causing T cells in vivo, but the field has been hampered by toxicity. Previously, we showed that a genetically engineered IT consisting of a single-chain protein, including the anti-CD3sFv spliced to a portion of diphtheria-toxin (DT(390)) has anti-GVHD effects, but pronounced organ toxicity common to this class of agent. A recombinant DT(390) anti-CD3sFv protein previously shown to have anti-GVHD activity was modified to reduce its filtration into kidney by genetically inserting a cysteine residue downstream of the sFv moiety at the c-terminus of the protein. This modification produced an intermolecular disulfide bridge, resulting in a bivalent, rather than a monovalent IT, termed SS2, that selectively inhibited T-cell proliferation in vitro. Although monomer and SS2 were similar in in vitro activity, SS2 had a superior therapeutic index in vivo with at least 8-fold more being tolerated with reduced kidney toxicity. Most importantly, in a lethal model of GVHD, 40 microg SS2 given for 1 day, protected 100% of the mice from lethal GVHD for 3 months, whereas the maximum tolerated dose (MTD) of monomer protected only 33%. To our knowledge, this is the first time disulfide bonded ITs have been created in this way and this simple molecular modification may address several problems in the IT field because it (1) markedly increased efficacy curing mice of GVHD after a single daily treatment, (2) markedly decreased organ toxicity, (3) increased the tolerated dosage, and (4) created a therapeutic window where none existed before.

Retroviral immunotoxin gene therapy of acute myelogenous leukemia in mice using cytotoxic T cells transduced with an interleukin 4/diphtheria toxin gene

The potential benefit of immunotoxin (IT) for cancer therapy has mostly been limited by the fact that only a small portion of injected dose ever reaches the cancer target. Thus, we set out to determine whether antigen-specific CTLs would be suitable vehicles to deliver IT to the site of cancer cells in vivo. A retroviral vector was constructed for gene therapy with (interleukin 4) IL-4 positioned downstream of its 20-amino-acid leader sequence that permitted cotranslational protein synthesis of IT along with truncated diphtheria toxin (DT). IL-4 was chosen as a ligand based on the expression of IL-4 receptor (IL-4R) on most acute myeloid leukemia cases. The first-time expression and secretion of a cytokine/DT fusion toxin was accomplished in mammalian NIH.3T3 cells, and then a retroviral vector was assembled. The retroviral IT was used to transiently transduce T15, a CD8+ CTL T cell line that specifically recognized C1498 (a lethal murine acute myeloid leukemia cell line). Transduced T15 T cells expressed intracellular DT and IL-4 as determined by immunofluorescence. Secreted IT supernatants collected from T15 had enzymatic activity and killed IL-4R+ C1498 cells, but not IL-4R- EL4 cells. Intravenous injection of transduced T15, but not nontransduced T15, into mice with s.c. tumors significantly inhibited tumor growth. In contrast, systemic therapy with a bacterial preparation of the same IL-4 IT given at its maximum tolerated dose did not protect. Retroviral IT-treated mice showed no sign of the renal or hepatic toxicity that is common to this class of IT. Together, these data indicate that retroviral IT may solve problems relating to systemic IT therapy by delivering reagent more directly to the site of cancer in vivo and may impart new anticancer defense mechanisms to antigen-specific T cells.

Targeting myeloid leukemia with a DT(390)-mIL-3 fusion immunotoxin: ex vivo and in vivo studies in mice

The IL-3 receptor was expressed on a high frequency of myeloid leukemia cells and also on hematopoietic and vascular cells. We previously showed that a recombinant IL-3 fusion immunotoxin (DT(390)IL-3) expressed by splicing the murine IL-3 gene to a truncated diphtheria toxin (DT(390)) gene selectively killed IL-3R(+) expressing cells and was not uniformly toxic to uncommitted BM progenitor cells (Chan,C.-H., Blazar,B.R., Greenfield,L., Kreitman,R.J. and Vallera,D.A., 1996, Blood, 88, 1445-1456). Thus, we explored the feasibility of using DT(390)IL-3 as an anti-leukemia agent. DT(390)IL-3 was toxic when administered to mice at doses as low as 0.1 microg/day. The dose limiting toxicity appeared to be related to platelet and bleeding effects of the fusion toxin. Because of these effects, DT(390)IL-3 was studied ex vivo as a means of purging contaminating leukemia cells from BM grafts in a murine autologous BM transplantation. In this setting, as few as 1000 IL-3R-expressing, bcr/abl transformed myeloid 32Dp210 leukemia cells were lethal. An optimal purging interval of 10 nM/l for 8 h eliminated leukemia cells from 32Dp210/BM mixtures given to lethally irradiated (8 Gy) C3H/HeJ syngeneic mice. Mice given treated grafts containing BM and a lethal dose of 32Dp210 cells survived over 100 days while mice given untreated grafts did not survive (P < 0.00001). DT(390)IL-3 may prove highly useful for ex vivo purging of lethal malignant leukemia cells from autologous BM grafts.

Opposing Roles of CD28:B7 and CTLA-4:B7 Pathways in Regulating In Vivo Alloresponses in Murine Recipients of MHC Disparate T Cells

Blockade with B7 antagonists interferes with CD28:B7 and CTLA-4:B7 interactions, which may have opposing effects. We have examined the roles of CD28:B7 and CTLA-4:B7 on in vivo alloresponses. A critical role of B7:CD28 was demonstrated by markedly compromised expansion of CD28-deficient T cells and diminished graft-versus-host disease lethality of limited numbers of purified CD4+ or CD8+ T cells. When high numbers of T cells were infused, the requirement for CD28:B7 interaction was lessened. In lethally irradiated recipients, anti-CTLA-4 mAb enhanced in vivo donor T cell expansion, but did not affect, on a per cell basis, anti-host proliferative or CTL responses of donor T cells. Graft-versus-host lethality was accelerated by anti-CTLA-4 mAb infusion given early post-bone marrow transplantation (BMT), mostly in a CD28-dependent fashion. Donor T cells obtained from anti-CTLA-4 mAb-treated recipients were skewed toward a Th2 phenotype. Enhanced T cell expansion in mAb-treated recipients was strikingly advantageous in the graft-versus-leukemia effects of delayed donor lymphocyte infusion. In two different systems, anti-CTLA-4 mAb enhanced the rejection of allogeneic T cell-depleted marrow infused into sublethally irradiated recipients. We conclude that blockade of the selective CD28-B7 interactions early post-BMT, which preserve CTLA-4:B7 interactions, would be preferable to blocking both pathways. For later post-BMT, the selective blockade of CTLA-4:B7 interactions provides a potent and previously unidentified means for augmenting the GVL effect of delayed donor lymphocyte infusion.

Opposing roles of CD28:B7 and CTLA-4:B7 pathways in regulating in vivo alloresponses in murine recipients of MHC disparate T cells

Blockade with B7 antagonists interferes with CD28:B7 and CTLA-4:B7 interactions, which may have opposing effects. We have examined the roles of CD28:B7 and CTLA-4:B7 on in vivo alloresponses. A critical role of B7:CD28 was demonstrated by markedly compromised expansion of CD28-deficient T cells and diminished graft-versus-host disease lethality of limited numbers of purified CD4+ or CD8+ T cells. When high numbers of T cells were infused, the requirement for CD28:B7 interaction was lessened. In lethally irradiated recipients, anti-CTLA-4 mAb enhanced in vivo donor T cell expansion, but did not affect, on a per cell basis, anti-host proliferative or CTL responses of donor T cells. Graft-versus-host lethality was accelerated by anti-CTLA-4 mAb infusion given early post-bone marrow transplantation (BMT), mostly in a CD28-dependent fashion. Donor T cells obtained from anti-CTLA-4 mAb-treated recipients were skewed toward a Th2 phenotype. Enhanced T cell expansion in mAb-treated recipients was strikingly advantageous in the graft-versus-leukemia effects of delayed donor lymphocyte infusion. In two different systems, anti-CTLA-4 mAb enhanced the rejection of allogeneic T cell-depleted marrow infused into sublethally irradiated recipients. We conclude that blockade of the selective CD28-B7 interactions early post-BMT, which preserve CTLA-4:B7 interactions, would be preferable to blocking both pathways. For later post-BMT, the selective blockade of CTLA-4:B7 interactions provides a potent and previously unidentified means for augmenting the GVL effect of delayed donor lymphocyte infusion.

A critical role for CD48 antigen in regulating alloengraftment and lymphohematopoietic recovery after bone marrow transplantation

The binding of CD2, present on T cells, to its counterreceptor CD48 facilitates adhesion, signaling, alloantigen-induced cytokine production, and cytotoxic T-lymphocyte responses. Because these T-cell functions have been implicated in graft-versus-host disease (GVHD) pathogenesis, we have analyzed the effects of the CD2:CD48 pathway on GVHD mediated by CD4(+) and CD8(+) T cells infused into sublethally irradiated recipients. CD4(+) T-cell-mediated, and to a lesser extent, CD8(+) T-cell-mediated GVHD was inhibited by CD2 + 48 monoclonal antibody (MoAb) infusion. To assess the effects of combined MoAb infusion on alloengraftment, two different alloengraftment bone marrow transplantation (BMT) models were used. In both, MoAb infusion markedly inhibited alloengraftment and hematopoietic recovery post-BMT. To determine if the adverse effects on lymphohematopoiesis in the allogeneic BMT recipients were caused by an immune or nonimmune mechanism, studies were performed in congenic BMT recipients to preclude an immune mechanism as the cause for delayed recovery post-BMT. MoAb infusion resulted in impaired lymphohematopoietic recovery in congenic BMT recipients and markedly reduced day 12 colony-forming unit-spleen formation in syngeneic BMT recipients, consistent with a nonimmune mediated mechanism. Because the spleen is a site of early hematopoietic recovery post-BMT, studies were performed using adult splenectomized syngeneic BMT recipients. MoAb infusion delayed recovery in both nonsplenectomized and splenectomized recipients post-BMT, indicating that the delayed hematopoietic recovery was not the consequence of an abnormal homing pattern of hematopoietic progenitors to the spleen early post-BMT. CD48 MoAb was necessary and sufficient for the inhibition of GVHD lethality and delayed lymphohematopoietic effects of the combined MoAb regimen. CD48 MoAb was found to induce a profound modulation of CD48 antigen expression on BM cells, suggesting that the CD48 antigen may have an important function in hematopoiesis in the BM compartment. Taken together, these data provide evidence that the CD48 antigen plays a critical role in regulating hematopoiesis in post-BMT.

Interleukin-10 dose-dependent regulation of CD4+ and CD8+ T cell-mediated graft-versus-host disease

BACKGROUND

Endogenous interleukin (IL)-10 production has been associated with the lack of graft-versus-host disease (GVHD) in human recipients of MHC-disparate donor grafts. Paradoxically, we have shown that the exogenous administration of high doses (30 microg/dose) of IL-10 to murine recipients of MHC-disparate grafts accelerates GVHD lethality.

METHODS

The effects of IL-10 on GVHD mediated by either CD4+ or CD8+ T cells was examined in studies involving exogenous IL-10 administration or the infusion of T cells from IL-10-deficient (-/-) donor mice. The role of interferon (IFN)-gamma on IL-10-induced GVHD acceleration was studied using IFN-gamma-deficient (-/-) donor mice or neutralizing monoclonal antibody.

RESULTS

IL-10 was found to have a dose-dependent effect on the GVHD lethality mediated by either CD4+ or CD8+ T cells. High doses of exogenous IL-10 accelerated GVHD lethality. IFN-gamma release was not responsible for the IL-10 facilitation of GVHD lethality. Paradoxically, low doses of IL-10 protected mice against GVHD lethality. The GVHD protective effect of the bioavailability of small amounts of IL-10 was confirmed by demonstrating that the infusion of T cells from IL-10 -/- donors accelerated GVHD lethality.

CONCLUSIONS

The results suggest that IL-10 has a dose-dependent effect on the GVHD lethality mediated by CD4+ or CD8+ T cells, such that high doses accelerate lethality, while low amounts of bioavailable IL-10 are protective.

Engraftment of severe combined immune deficient mice receiving allogeneic bone marrow via In utero or postnatal transfer

Although in utero transplantation (IUT) has been shown to be effective in treating human severe combined immune deficiency (SCID), the relative merit of IUT as compared with postnatal bone marrow transplantation (BMT) for SCID is unknown. Therefore, comparative studies were undertaken in mice to determine the engraftment outcome in these two settings. Because T-cell depletion (TCD) reduces graft-versus-host disease (GVHD) severity but compromises alloengraftment, studies were performed with TCD or non-TCD BM and GVHD risk was assessed using a tissue scoring system and by the adoptive transfer of splenocytes from engrafted mice into secondary recipients. Non-SCID recipients received pre-BMT irradiation to simulate those circumstances in which conditioning is required for alloengraftment. IUT recipients of non-TCD and especially TCD BM cells in general had higher levels of donor T-cell and myeloid peripheral blood (PB) engraftment than nonconditioned SCID recipients. Increased TCD or non-TCD BM cell numbers in adult SCID recipients resulted in similar levels of PB engraftment as IUT recipients. However, under these conditions, mean GVHD scores were higher than in IUT recipients. The majority of adoptive transfer recipients of splenocytes from IUT recipients were GVHD-free, consistent with the in vitro evidence of tolerance to host alloantigens. Total body irradiation (TBI)-treated mice that had the highest engraftment had evidence of thymic damage as denoted by a higher proportion of thymic and splenic T cells with a memory phenotype as compared with IUT recipients. IUT mice had vigorous thymic reconstitution by 3 weeks of age. Our data indicate that IUT has a number of advantages as compared with postnatal BMT. Future studies examining the fine specificity of immunoreconstitution in IUT versus postnatal BMT are indicated.

Keratinocyte growth factor administered before conditioning ameliorates graft-versus-host disease after allogeneic bone marrow transplantation in mice

Keratinocyte growth factor (KGF) is important in tissue repair and wound healing and its administration can abrogate chemical- and radiation-induced tissue damage in rodents. We investigated KGF as a therapeutic agent for the prevention of graft-versus-host disease (GVHD)-induced tissue damage, morbidity, and mortality in an established murine allogeneic bone marrow transplantation (BMT) model. B10.BR (H2(k)) recipient mice were lethally irradiated and transplanted with C57BL/6 (H2(b)) bone marrow (BM) with spleen cells (BMS) as a source of GVHD-causing T cells. KGF-treated mice (5 mg/kg/d subcutaneously days -6, -5, and -4 pre-BMT) receiving BMS exhibited better survival than those not receiving KGF (P =.0027). Cyclophosphamide (Cy), a common component of total body irradiation (TBI)-containing regimens, was administered to other cohorts of mice at a dose of 120 mg/kg/d intraperitoneally on days -3 and -2 before BMT. KGF-treated mice again exhibited a better survival rate than those not receiving KGF (P =.00086). However, KGF-treated recipients receiving TBI or Cy/TBI BMS were not GVHD-free, as shown by lower body weights compared with BM groups. GVHD target tissues were assessed histologically during a 38-day post-BMT observation period. KGF ameliorated GVHD-induced tissue damage in the liver, skin, and lung (completely in some recipients) and moderately so in the spleen, colon, and ileum, even with Cy conditioning. These studies demonstrate that KGF administration, completed before conditioning, has potential as an anti-GVHD therapeutic agent.

Differential effects of the absence of interferon-gamma and IL-4 in acute graft-versus-host disease after allogeneic bone marrow transplantation in mice

Graft-versus-host disease (GVHD), in which immunocompetent donor cells attack the host, remains a major cause of morbidity after allogeneic bone marrow transplantation (BMT). To understand the role of cytokines in the pathobiology of GVHD, we used cytokine knockout (KO) mice as a source of donor T cells. Two different MHC-disparate strain combinations were examined: BALB/c (H2(d)) donors into lethally irradiated C57BL/6 (H2(b)) recipients or C57BL/6 (H2(b)) donors into B10.BR (H2(k)) recipients. Donor cells were from mice in which either the interferon-gamma (IFN-gamma) or the IL-4 gene was selectively disrupted to understand the role of these cytokines in acute GVHD. In both strain combinations the same pattern was noted with regard to GVHD onset and morbidity. All mice exhibited the classic signs of acute GVHD: weight loss with skin, gut, and liver pathology resulting in morbidity and mortality. Surprisingly, donor cells obtained from mice lacking IFN-gamma gave rise to accelerated morbidity from GVHD when compared with cells from wild-type control donors. Similar results were obtained using normal donors when neutralizing antibodies to IFN-gamma were administered immediately after the BMT. These results suggest that IFN-gamma plays a role in protection from acute GVHD. In marked contrast, cells obtained from IL-4 KO mice resulted in protection from GVHD compared with control donors. Splenocytes from IFN KO mice stimulated with a mitogen proliferated to a significantly greater extent and produced more IL-2 compared with splenocytes obtained from IL-4 KO or control mice. Additionally, there was increased IL-2 production in the spleens of mice undergoing GVHD using IFN-gamma KO donors. These results therefore indicate, with regard to the TH1/ TH2 cytokine paradigm, the absence of a TH1-type cytokine can be deleterious in acute GVHD, whereas absence of a TH2 cytokine can be protective.

Intrathecal therapy of leptomeningeal CEM T-cell lymphoma in nude rats with anti-CD7 ricin toxin A chain immunotoxin

We have established a new xenogeneic animal model of leptomeningeal metastasis (LM) by intracisternal inoculation of human CEM T-cell lymphoma into nude rats, and used it to evaluate the anti-lymphoma efficacy of an anti-CD7 ricin A chain immunotoxin (DA7). In vitro incubation with 2 microg/ml DA7 for 72 h inhibited CEM cells by 90% in a trypan blue exclusion assay. To establish its anti-lymphoma activity, one and four days after cisternal inoculation of 10(6) CEM cells, eight animals each were treated cisternally with 10 microg DA7 in 50 microl PBS or sham-treated with 50 microl PBS. Histopathologically, all eight sham-treated and five of eight DA7 treated animals showed typical features of LM with multilayers of tumor cells along the whole subarachnoid space and the ventricular walls, as well as subependymal and diffuse parenchymal tumor cell infiltration. Three DA7 treated animals were free of tumor. Two of these animals were asymptomatic long-term survivors (> 90 days). The third tumor-free animal suddenly died on day 51. Histology revealed viral myocarditis. Median symptom-free survival was 51 days (range 29-90+ days) in DA7 treated and 34 days (range 29-87 days) in sham-treated animals (p = 0.12, log-rank test). Histologically, no signs of neurotoxicity or systemic toxicity was found. However, DA7 treated animals showed a tendency to a slower weight increase on days 6-28 after tumor cell inoculation. Our results indicate that this model is useful in studying leptomeningeal seeding and intracisternal treatment of lymphoma. The demonstrated anti-tumor effect of DA7 treatment deserves further evaluation especially regarding the application of DA7 in early stages of LM from T-cell lymphoma.

CD4(+) T cells tolerized ex vivo to host alloantigen by anti-CD40 ligand (CD40L:CD154) antibody lose their graft-versus-host disease lethality capacity but retain nominal antigen responses

A major goal of the transplant field is to tolerize donor T cells to prevent graft-versus-host disease (GVHD) (1). We describe an ex vivo approach in which the blockade of CD40 ligand (CD40L:CD154):CD40 interactions, a pathway required for optimal T cell expansion, induces donor CD4(+) T cells to become tolerant to host alloantigens (2). High doses of tolerized cells did not cause GVHD lethality in vivo. T cells had intact responses to antigens not present during tolerization. Tolerance was long lived and not readily reversible in vivo. These data have significant implications for the use of tolerization approaches to prevent human GVHD.

Rapamycin Inhibits the Generation of Graft-Versus-Host Disease- and Graft-Versus-Leukemia-Causing T Cells by Interfering with the Production of Th1 or Th1 Cytotoxic Cytokines

Rapamycin (RAPA), an inhibitor of cytokine responses, is under investigation in humans for graft-vs-host disease (GVHD) prevention. The mechanisms responsible for GVHD prevention are unknown. We show that RAPA is more effective in inhibiting CD8+ or TCR γδ+ than CD4+ T cell-mediated murine GVHD. To determine how RAPA inhibited GVHD, thoracic duct lymphocytes (TDL) were isolated from recipients of allogeneic donor grafts. Compared with controls, RAPA-treated recipients had a marked decrease in donor TDL T cell number between days 5 and 24 posttransplant. CD8+ T cell expansion was preferentially inhibited. RAPA inhibited Th1 or Th1 cytotoxic (Tc1) cytokines, but not Th2 or Tc2, cell generation. In situ mRNA hybridization also showed that TDL T cells from RAPA-treated mice had a lower frequency of granzyme B+ cells, indicating that RAPA inhibited the generation of CTL capable of mediating cytolysis through the release of granzyme B. In another system, RAPA was found to inhibit the GVL response of delayed donor lymphocyte infusions. Since CD8+ T cells are the primary effectors in this system, these data suggest that RAPA directly interfered with GVL effector cell expansion or function. We conclude that RAPA is effective in inhibiting Th1 or Tc1 cytokine production and CD8+ and TCRγδ+ T cell-mediated GVHD, but abrogates GVL.

Rapamycin inhibits the generation of graft-versus-host disease- and graft-versus-leukemia-causing T cells by interfering with the production of Th1 or Th1 cytotoxic cytokines

Rapamycin (RAPA), an inhibitor of cytokine responses, is under investigation in humans for graft-vs-host disease (GVHD) prevention. The mechanisms responsible for GVHD prevention are unknown. We show that RAPA is more effective in inhibiting CD8+ or TCR gammadelta+ than CD4+ T cell-mediated murine GVHD. To determine how RAPA inhibited GVHD, thoracic duct lymphocytes (TDL) were isolated from recipients of allogeneic donor grafts. Compared with controls, RAPA-treated recipients had a marked decrease in donor TDL T cell number between days 5 and 24 posttransplant. CD8+ T cell expansion was preferentially inhibited. RAPA inhibited Th1 or Th1 cytotoxic (Tc1) cytokines, but not Th2 or Tc2, cell generation. In situ mRNA hybridization also showed that TDL T cells from RAPA-treated mice had a lower frequency of granzyme B+ cells, indicating that RAPA inhibited the generation of CTL capable of mediating cytolysis through the release of granzyme B. In another system, RAPA was found to inhibit the GVL response of delayed donor lymphocyte infusions. Since CD8+ T cells are the primary effectors in this system, these data suggest that RAPA directly interfered with GVL effector cell expansion or function. We conclude that RAPA is effective in inhibiting Th1 or Tc1 cytokine production and CD8+ and TCRgammadelta+ T cell-mediated GVHD, but abrogates GVL.

Anti-CD3 epsilon F(ab')2 fragments inhibit T cell expansion in vivo during graft-versus-host disease or the primary immune response to nominal antigen

This study was undertaken to distinguish between several mechanisms responsible for graft-vs-host disease (GVHD) protection in anti-CD3epsilonF(ab')2 fragment (Fr)-treated recipients: TCR down-modulation, deletion, failure of expansion, or anergy induction. To quantify alloreactive T cell expansion and function, thoracic duct lymphocytes (TDL) were analyzed. Sixfold fewer donor TDL T cells were recoverable from anti-CD3epsilonF(ab')2 Fr as compared with irrelevant F(ab')2 Fr-treated recipients at the time of peak T cell expansion in vivo. Kinetic analysis revealed that donor T cell expansion was inhibited and not simply delayed by anti-CD3epsilonF(ab')2 Fr. Similar proportions of TDL T cells in irrelevant and anti-CD3epsilonF(ab')2 Fr were undergoing apoptosis. Although TCR modulation was observed, donor TDL T cells had intact anti-host alloresponses as compared with irrelevant F(ab')2 Fr-treated recipients. Because donor CD4+ T cells are primarily responsible for GVHD in this model, an adoptive transfer system was used in which the function and kinetics of expansion of OVA-specific CD4+ TCR transgenic cells could be physically tracked. Relevant Fr severely blunted CD4+ TCR transgenic T cell clonal expansion after OVA administration. Nonviable transgenic and nontransgenic T cells were proportionally similar in OVA-pulsed recipients, regardless of whether relevant or irrelevant F(ab')2 Fr were given. After discontinuing Fr, transgenic T cells were found to have intact in vitro OVA-specific responses. Our current and previous results suggest that reduced donor T cell expansion and T cell depletion both contribute to GVHD protection by anti-CD3epsilonF(ab')2 Fr. These data have implications for designing therapeutic approaches directed toward TCR targeting in humans.

Anti-CD3 epsilon F(ab')2 fragments inhibit T cell expansion in vivo during graft-versus-host disease or the primary immune response to nominal antigen

This study was undertaken to distinguish between several mechanisms responsible for graft-vs-host disease (GVHD) protection in anti-CD3epsilonF(ab')2 fragment (Fr)-treated recipients: TCR down-modulation, deletion, failure of expansion, or anergy induction. To quantify alloreactive T cell expansion and function, thoracic duct lymphocytes (TDL) were analyzed. Sixfold fewer donor TDL T cells were recoverable from anti-CD3epsilonF(ab')2 Fr as compared with irrelevant F(ab')2 Fr-treated recipients at the time of peak T cell expansion in vivo. Kinetic analysis revealed that donor T cell expansion was inhibited and not simply delayed by anti-CD3epsilonF(ab')2 Fr. Similar proportions of TDL T cells in irrelevant and anti-CD3epsilonF(ab')2 Fr were undergoing apoptosis. Although TCR modulation was observed, donor TDL T cells had intact anti-host alloresponses as compared with irrelevant F(ab')2 Fr-treated recipients. Because donor CD4+ T cells are primarily responsible for GVHD in this model, an adoptive transfer system was used in which the function and kinetics of expansion of OVA-specific CD4+ TCR transgenic cells could be physically tracked. Relevant Fr severely blunted CD4+ TCR transgenic T cell clonal expansion after OVA administration. Nonviable transgenic and nontransgenic T cells were proportionally similar in OVA-pulsed recipients, regardless of whether relevant or irrelevant F(ab')2 Fr were given. After discontinuing Fr, transgenic T cells were found to have intact in vitro OVA-specific responses. Our current and previous results suggest that reduced donor T cell expansion and T cell depletion both contribute to GVHD protection by anti-CD3epsilonF(ab')2 Fr. These data have implications for designing therapeutic approaches directed toward TCR targeting in humans.

CD28/B7 interactions are required for sustaining the graft-versus-leukemia effect of delayed post-bone marrow transplantation splenocyte infusion in murine recipients of myeloid or lymphoid leukemia cells

Graft-vs-leukemia (GVL) can reduce relapse rates after bone marrow transplantation (BMT). Delayed lymphocyte infusion (DLI) post-BMT can mediate a potent GVL effect with less graft-vs-host disease (GVHD) than would be observed if given early post-BMT. In vivo CD28/B7 blockade can reduce GVHD lethality, and B7 ligand expression can augment an antitumor immune response in mice. To examine the role of CD28/B7 interactions in DLI-mediated GVL, we established murine allogeneic BMT models in C57BL/6 (B6) recipients of C1498 (B6 acute myeloid leukemia) or EL4 (B6 acute T cell leukemia) that closely mimic human GVL. Recipients of C1498 and DLI had a marked reduction in relapse. GVL was blocked by anti-B7 mAb infusion. In contrast, recipients of EL4 cells and B10.BR DLI had a more modest GVL effect. The forced expression of B7-1 on EL4 cells markedly augmented the GVL effect of DLI, in contrast to the forced expression of B7-2 on EL4 cells. Relapse rates observed in recipients of C1498-B7-1 and DLI were significantly lower than in recipients of parental C1498 cells. We conclude that the administration of anti-B7 mAbs may impair the GVL effect of DLI and that the forced expression of B7-1 ligands stimulates a GVL effect without adversely affecting the GVHD lethality effect of DLI.

CD28/B7 interactions are required for sustaining the graft-versus-leukemia effect of delayed post-bone marrow transplantation splenocyte infusion in murine recipients of myeloid or lymphoid leukemia cells

Graft-vs-leukemia (GVL) can reduce relapse rates after bone marrow transplantation (BMT). Delayed lymphocyte infusion (DLI) post-BMT can mediate a potent GVL effect with less graft-vs-host disease (GVHD) than would be observed if given early post-BMT. In vivo CD28/B7 blockade can reduce GVHD lethality, and B7 ligand expression can augment an antitumor immune response in mice. To examine the role of CD28/B7 interactions in DLI-mediated GVL, we established murine allogeneic BMT models in C57BL/6 (B6) recipients of C1498 (B6 acute myeloid leukemia) or EL4 (B6 acute T cell leukemia) that closely mimic human GVL. Recipients of C1498 and DLI had a marked reduction in relapse. GVL was blocked by anti-B7 mAb infusion. In contrast, recipients of EL4 cells and B10.BR DLI had a more modest GVL effect. The forced expression of B7-1 on EL4 cells markedly augmented the GVL effect of DLI, in contrast to the forced expression of B7-2 on EL4 cells. Relapse rates observed in recipients of C1498-B7-1 and DLI were significantly lower than in recipients of parental C1498 cells. We conclude that the administration of anti-B7 mAbs may impair the GVL effect of DLI and that the forced expression of B7-1 ligands stimulates a GVL effect without adversely affecting the GVHD lethality effect of DLI.

Renal dysfunction accounts for the dose limiting toxicity of DT390anti-CD3sFv, a potential new recombinant anti-GVHD immunotoxin

The toxicity of a highly selective, recombinant fusion immunotoxin, DT390anti-CD3sFv, was examined in mice. The protein was expressed from a hybrid gene in which the single chain Fv of the anti-murine CD3 epsilon antibody cDNA was spliced to truncated diphtheria toxin cDNA. DT390anti-CD3sFv, previously shown to have significant anti-GVHD effects when administered to mice given transplants of allogeneic MHC-disparate donor T cells (Vallera et al., Blood 88, 2342-2353, 1996), preferentially localized to kidney and had profound renal toxicity as assessed by histology and serum levels of blood urea nitrogen (BUN), and creatinine. Kidney effects were more severe than liver effects at the maximum tolerated dose (MTD) of 10 microg/day BID given over a six day interval. Toxic injury was attributed in part to the toxin moiety since DT390 administered alone was more toxic than equivalent doses of DT390 given in the context of DT390anti-CD3sFv fusion protein. The presence of anti-CD3sFv ligand reduced toxicity since DT390anti-CD3sFv was twice as toxic to severe combined immunodeficiency disease (scid) mice which do not have CD3epsilon expressing T cells as compared to their normal counterparts. Together, these findings further our understanding of the toxicities limiting the in vivo administration of DT fusion immunotoxins in mice and provide a foundation for future genetic modifications which should be directed at reducing these effects.