Resimmune, an anti-CD3ε recombinant immunotoxin, induces durable remissions in patients with cutaneous T-cell lymphoma

Resimmune is a second-generation recombinant immunotoxin composed of the catalytic and translocation domains of diphtheria toxin fused to two single chain antibody fragments reactive with the extracellular domain of CD3ε. We gave intravenous infusions of Resimmune 2.5 - 11.25 μg/kg over 15 minutes to 30 patients (25 with cutaneous T-cell lymphoma, 3 with peripheral T-cell lymphoma, 1 with T-cell large granular lymphocytic leukemia and 1 with T-cell prolymphocytic leukemia) in an inter-patient dose escalation trial. The most common adverse events were fever, chills, hypotension, edema, hypoalbuminemia, hypophosphatemia, and transaminasemia. Among the 25 patients with cutaneous T-cell lymphoma, there were nine responses for a response rate of 36% (95% CI, 18%-57%) including four complete remissions (16%, 95% CI, 5%-36%). The durations of the complete remissions were 72+, 72+, 60+ and 38+ months. There were five partial remissions lasting 3, 3, 3+, 6+ and 14 months. Of 17 patients with a modified skin weighted assessment tool score <50, 17 patients with stage IB/IIB, and 11 patients with both a score <50 and stage IB/IIB, nine (53%), eight (47%), and eight (73%) had responses, respectively. Further studies of Resimmune in patients with low tumor burden, stage IB-IIB cutaneous T-cell lymphoma are warranted. This trial is registered at clinicaltrials.gov as #NCT00611208.

A truncated diphtheria toxin based recombinant porcine CTLA-4 fusion toxin

Targeted cell therapies are possible through the generation of recombinant fusion proteins that combine a toxin, such as diphtheria toxin (DT), with an antibody or other molecule that confers specificity. Upon binding of the fusion protein to the cell of interest, the diphtheria toxin is internalized which results in protein synthesis inhibition and subsequent cell death. We have recently expressed and purified the recombinant soluble porcine CTLA-4 both with and without N-glycosylation in yeast Pichia pastoris for in vivo use in our preclinical swine model. The glycosylated and non-N-glycosylated versions of this recombinant protein each bind to a porcine CD80 expressing B-cell lymphoma line (LCL13271) with equal affinity (K(D)=13 nM). In this study we have linked each of the glycosylated and non-N-glycosylated soluble porcine CTLA-4 proteins to the truncated diphtheria toxin DT390 through genetic engineering yielding three versions of the porcine CTLA-4 fusion toxins: 1) monovalent glycosylated soluble porcine CTLA-4 fusion toxin; 2) monovalent non-N-glycosylated soluble porcine CTLA-4 fusion toxin and 3) bivalent non-N-glycosylated soluble porcine CTLA-4 fusion toxin. Protein synthesis inhibition analysis demonstrated that while all three fusion toxins are capable of inhibiting protein synthesis in vitro, the non-N-glycosylated porcine CTLA-4 isoforms function most efficiently. Binding analysis using flow cytometry of the porcine CTLA-4 fusion toxins to LCL13271 cells also demonstrated that the non-N-glycosylated porcine CTLA-4 isoforms bind to these cells with higher affinity compared to the glycosylated fusion toxin. The monovalent non-N-glycosylated porcine CTLA-4 fusion toxin was tested in vivo. NSG (NOD/SCID IL-2 receptor γ(-)/(-)) mice were injected with porcine CD80(+) LCL13271 tumor cells. All animals succumbed to tumors and those treated with the monovalent non-N-glycosylated porcine CTLA-4 fusion toxin survived longer based on a symptomatic scoring system compared to the untreated controls. This recombinant protein may therefore provide a novel approach for in vivo depletion of porcine antigen presenting cells (APCs) for studies investigating the induction of transplantation tolerance, autoimmune disease and cancer treatment.

Development of a diphtheria toxin based antiporcine CD3 recombinant immunotoxin

Anti-CD3 immunotoxins, which induce profound but transient T-cell depletion in vivo by inhibiting eukaryotic protein synthesis in CD3+ cells, are effective reagents in large animal models of transplantation tolerance and autoimmune disease therapy. A diphtheria toxin based antiporcine CD3 recombinant immunotoxin was constructed by fusing the truncated diphtheria toxin DT390 with two identical tandem single chain variable fragments (scFv) derived from the antiporcine CD3 monoclonal antibody 898H2-6-15. The recombinant immunotoxin was expressed in a diphtheria-toxin resistant yeast Pichia pastoris strain under the control of the alcohol oxidase promoter. The secreted recombinant immunotoxin was purified sequentially with hydrophobic interaction chromatography (Butyl 650 M) followed by strong anion exchange (Poros 50 HQ). The purified antiporcine CD3 immunotoxin was tested in vivo in four animals; peripheral blood CD3+ T-cell numbers were reduced by 80% and lymph node T-cells decreased from 74% CD3+ cells pretreatment to 24% CD3+ cells remaining in the lymph node following 4 days of immunotoxin treatment. No clinical toxicity was observed in any of the experimental swine. We anticipate that this conjugate will provide an important tool for in vivo depletion of T-cells in swine transplantation models.

Preclinical studies in rats and squirrel monkeys for safety evaluation of the bivalent anti-human T cell immunotoxin, A-dmDT390-bisFv(UCHT1)

The bivalent anti-human T cell immunotoxin A-dmDT390-bisFv(UCHT1) for treatment of patients with T cell malignancies is a single chain fusion protein composed of the catalytic domain and translocation domains of diphtheria toxin fused to two tandem sFv molecules reactive with human CD3 epsilon. This immunotoxin selectively kills CD3 epsilon positive T cells. To determine the maximum tolerated dose (MTD), pharmacokinetics and immunogenicity of A-dmDT390-bisFv(UCHT1), rat and squirrel monkey studies were performed. In both animal studies, animals received either 0, 2.5 (low), 25 (medium), or 56.25 microg/kg (high) of A-dmDT390-bisFv(UCHT1) intravenously twice daily for four consecutive days. Although transient elevation of liver transaminases in the high groups was observed, the A-dmDT390-bisFv(UCHT1) administration did not affect liver function, renal function, the hemogram, or produce serious organ histopathology. Adverse events included transient lethargy, inappetence and weight loss in high groups. A-dmDT390-bisFv(UCHT1) plasma half life was 26.95 min in rats and 18.33 min in squirrel monkeys. Immune responses to A-dmDT390-bisFv(UCHT1) were minimal in squirrel monkeys and mild in rats. In vitro cytokine release, T cell activation and CD3 epsilon receptor occupancy assays using human PBMC were further performed since rat and squirrel monkey T cells do not react with A-dmDT390-bisFv(UCHT1). A-dmDT390-bisFv(UCHT1) did not induce cytokine release or T cell activation. The A-dmDT390-bisFv(UCHT1) concentration for 50% CD3 epsilon receptor occupancy was 7.4 nM. The MTD of 200 microg/kg total provides a dose level sufficient for anti-tumor activity in vitro and in a rodent model. Therefore, we propose that this agent is a promising drug for patients with surface CD3+ T cell malignancies.

A fold-back single-chain diabody format enhances the bioactivity of an anti-monkey CD3 recombinant diphtheria toxin-based immunotoxin

T-cell depleting anti-CD3 immunotoxins have utility in non-human primate models of transplantation tolerance and autoimmune disease therapy. We recently reported that an affinity matured single-chain (scFv) anti-monkey CD3 antibody, C207, had increased binding to T-cells and increased bioactivity in a diphtheria toxin (DT)-based biscFv immunotoxin compared with the parental antibody, FN18. However, FN18 scFvs and their mutant derivatives such as C207 did not exhibit robust bivalent character in the biscFv format. We now report that C207 in a diabody format exhibits a 7-fold increase in binding to T-cells over scFv (C207) indicating considerable divalent character for the diabody. This construct was formed by reducing the V(L)/V(H) linker to five residues and was secreted from Pichia pastoris as the non-covalent dimer. An immunotoxin based on this diabody format was secreted as a non-covalent dimer but was devoid of bioactivity and failed to bind T-cells, suggesting steric hindrance from the two large closely positioned truncated DT moieties. We constructed a single-chain diabody immunotoxin by fusing to the truncated DT C-terminus L1-VL-L1-VH-L2-VL-L1-VH where L1 is a five-residue linker and L2 is the longer (G4S)3 linker permitting interactions between the distal and proximal VL/VH domains. This 'fold-back' immunotoxin was secreted predominantly as the monomer and exhibited a 5- to 7-fold increase in bioactivity over DT390biscFv(C207) and depleted monkey T-cells in vivo.

Improvement of a Recombinant Anti-Monkey Anti-CD3 Diphtheria Toxin Based Immunotoxin by Yeast Display Affinity Maturation of the scFv

Recently, a bivalent recombinant anti-human CD3 diphtheria toxin (DT) based immunotoxin derived from the scFv of UCHT1 antibody has been made that shows enhanced bioactivity and is free from the side effects of Fc receptor interaction. In this case, the diminution of CD3 binding due to the placement of the scFv domain at the C-terminus of the truncated DT in single scFv immunotoxins was compensated by adding an additional scFv domain. However, this strategy was less successful for constructing an anti-rhesus recombinant immunotoxin derived from the scFv of FN18 antibody due to poor binding of the anti-rhesus bivalent immunotoxin. We report here that, by increasing the FN18 scFv affinity through random mutagenesis and selection with a dye-labeled monkey CD3epsilongamma recombinant heterodimer, we greatly improved the bioactivity of FN18 derived immunotoxin. The best mutant, C207, contained nine mutations, two of which were located in CDRs that changed the charge from negative to positive. Binding affinity of the C207 scFv to the monkey T cell line HSC-F increased 9.8-fold. The potency of the C207 bivalent immunotoxin assayed by inhibition of protein synthesis increased by 238-fold.

Polymorphisms of CD3epsilon in cynomolgus and rhesus monkeys and their relevance to anti-CD3 antibodies and immunotoxins

The monoclonal antibody FN18 has been used as a marker for monkey T cells and as a T-cell-depleting reagent when conjugated to diphtheria toxin that was mutated to prevent binding to non-targeted cells. The antibody recognizes a conformational epitope on the ectodomain of monkey CD3epsilon and displays a range of binding activity to the T cells from different rhesus and cynomolgus monkeys. Our quantitative fluorescence-activated cell sorting analysis of the FN18 reactivity to T cells from different rhesus and cynomolgus monkeys showed that there are at least three levels of FN18 reactivity in the monkeys tested: high, moderate and low. On the basis of available DNA sequence information, we determined the gene structure of rhesus CD3epsilon chain and designed primers that can be used to amplify and quickly sequence the ectodomain of monkey CD3epsilon. Our sequence analysis revealed that the extent of nucleotide sequence variation in this area is greater than that previously reported. In addition to the amino acids at positions 45 and 50, we demonstrated that position 35 of CD3epsilon was also important and substitution of amino acid A for V at this position greatly reduced T-cell reactivity to FN18. We found that T cells from monkeys with high FN18 reactivity all had V, E and R at positions 35, 45 and 50 in CD3epsilon, respectively; those having low FN18 reactivity were homozygous in CD3epsilon with at least one of the changes: V35 to A, E45 to G and R to 50Q, whereas members in the moderate group are heterozygous, having both V and A, E and G, R and Q at these locations. A cytotoxicity assay revealed that T cells from a heterozygous rhesus monkey with moderate FN18 reactivity were much (about 40 times) less sensitive to a FN18-derived immunotoxin than those from a homozygous rhesus monkey having high FN18 reactivity.

Stable multilineage chimerism without graft versus host disease following nonmyeloablative haploidentical hematopoietic cell transplantation

BACKGROUND

Hematopoietic cell transplantation may offer the only cure for patients with hematological diseases. The clinical application of this therapy has been limited by toxic conditioning and lack of matched donors. Haploidentical transplantation would serve to extend the potential donor pool; however, transplantation across major histocompatibility complex barriers is often associated with severe graft-versus-host disease. Here we evaluate a novel protocol to achieve engraftment across mismatch barriers without toxic conditioning or significant posttransplant complications.

METHODS

Nine major histocompatibility complex (MHC)-defined miniature swine received haploidentical hematopoietic cell transplantation following standard myeloablative conditioning. Nine additional animals received haploidentical hematopoietic cell transplantation following a minimally myelosuppressive regimen, consisting of 100 cGy total body irradiation, immunotoxin mediated T-cell depletion, and a short course of cyclosporine. Donor cell engraftment and peripheral chimerism was assessed by polymerase chain reaction and flow cytometry. Graft-versus-host disease was monitored by clinical grading and histology of skin biopsy specimens.

RESULTS

All animals conditioned for haploidentical hematopoietic cell transplantation using myeloablative conditioning were euthanized within 2 weeks due to engraftment failure or graft-versus-host disease. All animals conditioned with the nonmyeloablative regimen developed multilineage peripheral blood chimerism during the first 2 months following transplantation. Six animals evaluated beyond 100 days maintained multilineage chimerism in the peripheral blood and lymphoid tissues, showed evidence of progenitor cell engraftment in the bone marrow, and had minimal treatment-related complications.

CONCLUSIONS

Here we report that stable multilineage chimerism and engraftment can be established across haploidentical major histocompatibility complex barriers with minimal treatment-related toxicity and without significant risk of graft-versus-host disease.

Minimization of aggregation of secreted bivalent anti-human T cell immunotoxin in Pichia pastoris bioreactor culture by optimizing culture conditions for protein secretion

In a bioreactor culture of genetically engineered Pichia pastoris secreting a bivalent immunotoxin, 64% of the secreted immunotoxin was present in aggregate forms and this resulted in a loss of bioactivity. Biochemical analyses of the secreted immunotoxin and an in vitro aggregation study using purified monomeric immunotoxin suggested that aggregation was primarily an extracellular event. By employing limited methanol feeding at 0.75 mlmin(-1) per 10l initial medium, oxygen consumption was reduced, permitting a lowering of the bioreactor agitation speed from 800 to 400 rpm. By increasing the anti-foam reagent to 0.6 mll(-1), the thickness of the air/liquid interfacial foam layer was reduced by 80%. These steps reduced the immunotoxin aggregates from 64% to 5%. Consequently immunotoxin purification yield was increased from 53.0% to 73.8%. Simultaneously this methodology enhanced immunotoxin secretion to 120 mgl(-1) at 163 h of methanol induction in a toxin resistant production strain. We conclude that minimizing shearing force and reducing the air/liquid interfacial foam area are crucial factors in reducing hydrophobic protein aggregation upon secretory expression in yeast bioreactor cultures.

Vascularized Thymic Lobe Transplantation in a Pig-to-Baboon Model: A Novel Strategy for Xenogeneic Tolerance Induction and T-cell Reconstitution

BACKGROUND

This laboratory has previously demonstrated the induction of allogeneic tolerance by vascularized thymic lobe (VTL) transplantation in miniature swine. We report here our initial attempt to induce tolerance by VTL transplantation in the clinically relevant, discordant, pig-to-baboon model of xenotransplantation.

METHODS

Six baboons received xenografts of hDAF VTLs. Four of these baboons also received omental thymic tissue implants. All recipients were treated with an immunosuppressive conditioning regimen that included thymectomy, splenectomy, extracorporeal immunoadsorption of anti-alpha Gal antibodies, and T-cell depletion. Two control baboons received sham operations, of which one also received 5x10 hDAF porcine thymocytes/kg intravenously.

RESULTS

Transplanted VTL grafts supported early thymopoiesis of recipient-type immature thymocytes, and facilitated engraftment of nonvascularized thymic omental implants. Recipients of the VTL grafts demonstrated donor-specific unresponsiveness in MLR assays, development of peripheral CD45RAhigh/CD4 double positive (DP) cells, and positive cytokeratin staining of thymic stroma in the grafts for 2 months following xenotransplantation. The control baboons did not show these markers of thymic reconstitution. The eventual return of Gal natural antibodies led to the destruction of graft epithelial cells and the rejection of all VTL grafts by 3 months posttransplantation.

CONCLUSIONS

VTL transplantation from hDAF swine to baboons induced early thymopoiesis in the recipients and donor-specific cellular unresponsiveness in vitro. When coupled with additional strategies aimed at silencing humoral rejection, VTL transplantation may significantly prolong xenograft survival and result in long-term tolerance.

Elevated T Regulatory Cells in Long-Term Stable Transplant Tolerance in Rhesus Macaques Induced by Anti-CD3 Immunotoxin and Deoxyspergualin

Regulatory T cells (Tregs) are implicated in immune tolerance and are variably dependent on IL-10 for in vivo function. Brief peritransplant treatment of multiple nonhuman primates (NHP) with anti-CD3 immunotoxin and deoxyspergualin has induced stable (5-10 years) rejection-free tolerance to MHC-mismatched allografts, which associated with sustained elevations in serum IL-10. In this study, we demonstrate that resting and activated PBMC from long-term tolerant NHP recipients are biased to secrete high levels of IL-10, compared with normal NHP PBMC. Although IL-10-producing CD4+ Tregs (type 1 regulatory cells (TR1)/IL-10 Tregs) were undetectable (<0.5%) in normal rhesus monkeys, 7.5 +/- 1.7% of circulating CD4+ T cells of tolerant rhesus recipients expressed IL-10. In addition to this >15-fold increase in Tr1/IL-10 Tregs, the tolerant monkeys exhibited a nearly 3-fold increase in CD4+CD25+ Tregs, 8.1 +/- 3.0% of CD4 T cells vs 2.8 +/- 1.4% in normal cohorts (p < 0.02). The frequency of CD4+CD25+IL-10+ cells was elevated 5-fold in tolerant vs normal NHP (1.8 +/- 0.9% vs 0.4 +/- 0.2%). Rhesus CD4+CD25+ Tregs exhibited a memory phenotype, and expressed high levels of Foxp3 and CTLA-4 compared with CD4+CD25- T cells. Also, NHP CD4+CD25+ Tregs proliferated poorly after activation and suppressed proliferation of CD4+CD25- effector T cells, exhibiting regulatory properties similar to rodent and human CD4+CD25+ Tregs. Of note, depletion of CD4+CD25+ Tregs restored indirect pathway antidonor responses in tolerant NHP. Our study demonstrates an expanded presence of Treg populations in tolerant NHP recipients, suggesting that these adaptations may be involved in maintenance of stable tolerance.

Overexpression of an anti-CD3 immunotoxin increases expression and secretion of molecular chaperone BiP/Kar2p by Pichia pastoris

We previously reported that the secretory capacity of Pichia pastoris is limited with respect to the secretion of a 96.5-kDa bivalent anti-CD3 immunotoxin; double-copy expression generated more translation products than single-copy expression but did not increase the secretion of the immunotoxin. In Saccharomyces cerevisiae heterologous protein secretion has been reported to increase the expression of molecular chaperones, most prominently BiP/Kar2p. We therefore investigated the relationships between immunotoxin secretion and Kar2p expression in P. pastoris. We found that expression of the immunotoxin in P. pastoris increased the expression of Kar2p to levels that surpassed the retrieval capacity of the cell, leading to secretion of Kar2p into the medium. The level of Kar2p secretion was correlated with the copy number of the immunotoxin gene. Intracellular Kar2p was found to bind exclusively to the unprocessed immunotoxin containing the prosequence of alpha-factor in the endoplasmic reticulum. These results show that Kar2p is intimately involved in immunotoxin secretion in P. pastoris. The limited capacity of P. pastoris to retain a sufficiently high level of intracellular Kar2p may be a factor restricting the production of the immunotoxin.

A new yeast display vector permitting free scFv amino termini can augment ligand binding affinities

Yeast surface display and sorting by flow cytometry are now widely used to direct the evolution of protein binding such as single-chain antibodies or scFvs. The available commercial yeast display vector pYD1 (Invitrogen) displays the protein of interest flanked on the N-terminus by Aga2, the disulfide of which binds the myristylated surface membrane protein Aga1. We have noted that two anti-CD3epsilon scFvs expressed as fusion proteins suffer a 30- to 100-fold loss of affinity when placed NH(2) terminal to either truncated toxins or human serum albumin. In the course of affinity maturing one of these scFv (FN18) using pYD1 we noted that the affinity towards the ectodomain of monkey CD3epsilongamma was too low to measure. Consequently we rebuilt pYD1 tethering the scFv off the NH(2) terminus of Aga2. This display vector, pYD5, now gave a positive signal displaying FN18 scFv with its ligand, monkey CD3epsilongamma. The apparent equilibrium association constant of the higher affinity scFv directed at human CD3epsilongamma increased approximately 3-fold when displayed on pYD5 compared with pYD1. These data show that for certain yeast-displayed scFvs a carboxy-tethered scFv can result in increased ligand-scFv equilibrium association constants and thereby extend the low range of affinity maturation measurements.

Increasing secretion of a bivalent anti-T-cell immunotoxin by Pichia pastoris

The bivalent anti-T-cell immunotoxin A-dmDT390-bisFv(G(4)S) was developed for treatment of T-cell leukemia and autoimmune diseases and for tolerance induction for transplantation. This immunotoxin was produced extracellularly in toxin-sensitive Pichia pastoris JW102 (Mut(+)) under control of the AOX1 promoter. There were two major barriers to efficient immunotoxin production, the toxicity of the immunotoxin for P. pastoris and the limited capacity of P. pastoris to secrete the immunotoxin. The immunotoxin toxicity resulted in a decrease in the methanol consumption rate, cessation of cell growth, and low immunotoxin productivity after the first 22 h of methanol induction. Continuous cell growth and continuous immunotoxin secretion after the first 22 h of methanol induction were obtained by adding glycerol to the methanol feed by using a 4:1 methanol-glycerol mixed feed as an energy source and by continuously adding a yeast extract solution during methanol induction. The secretory capacity was increased from 22.5 to 37 mg/liter by lowering the induction temperature. A low temperature reduced the methanol consumption rate and protease activity in the supernatant but not cell growth. The effects of adding glycerol and yeast extract to the methanol feed were synergistic. Adding yeast extract primarily enhanced methanol utilization and cell growth, while adding glycerol primarily enhanced immunotoxin production. The synergy was further enhanced by decreasing the induction temperature from 23 to 15 degrees C, which resulted in a robust process with a yield of 37 mg/liter, which was sevenfold greater than the yield previously reported for a toxin-resistant CHO cell expression system. This methodology should be applicable to other toxin-related recombinant proteins in toxin-sensitive P. pastoris.

Risk factors for the development of post-transplant lymphoproliferative disorder in a large animal model

A high incidence of a post-transplant lymphoproliferative disorder (PTLD) is observed in miniature swine conditioned for allogeneic hematopoietic cell transplantation using a protocol involving T-cell depletion and cyclosporine therapy. This study was designed to assess contributing factors to disease development. Forty-six animals were studied including 12 (26%) that developed PTLD. A number of risk factors for PTLD were examined, including degree of immunosuppression, degree of MHC mismatch and infection by a porcine lymphotrophic herpesvirus (PLHV-1). Flow cytometry was used to measure host and donor T- and B-cell levels in the peripheral blood. Porcine lymphotrophic herpesvirus viral load was determined by quantitative PCR. Animals developing PTLD had significantly lower levels of T cells on the day of transplant. Cyclosporine levels did not differ significantly between animals with and without PTLD. Animals receiving transplants across a two-haplotype mismatch barrier showed an increased incidence of PTLD. All animals with PTLD had significant increases in PLHV-1 viral loads. Porcine lymphotrophic herpesvirus viral copy numbers remained at low levels in the absence of disease. The availability of a preclinical large-animal model with similarities to PTLD of humans may allow studies of the pathogenesis and treatment of that disorder.

Expression and characterization of recombinant soluble monkey CD3 molecules: mapping the FN18 polymorphic epitope

The monoclonal antibody FN18 has been used as a marker for monkey T cells and as a T cell depleting reagent when conjugated to binding site mutants of diphtheria toxin. This anti-CD3 antibody shares certain properties with its anti-human counterparts UCHT1, OKT3 and Leu-4 in that it precipitates two different CD3 chains from membrane detergent extracts. However, in contrast to human CD3, rhesus and cynomolgus monkeys display CD3 polymorphisms producing FN18 negative phenotypes. Using recently published sequence data, we have expressed the ectodomains of cynomolgus CD3-epsilon CD3-gamma and CD-delta chains in E. coli, and have refolded these chains separately and in pairs to produce CD3 homo- and heterodimeric proteins. These proteins were fractionated by anion exchange according to their differing isoelectric points and further identified by size differences on SDS gels. On the basis of ELISA, the FN18 epitope is restricted to the CD3-epsilongamma ectodomain heterodimer, CD-epsilondelta and CD-epsilonepsilon being non-reactive. Either of the two amino acid polymorphisms reported in the CD3-epsilon chain were sufficient to degrade the bioactivity of the CD3-epsilongamma towards FN18.

Tolerance to composite tissue allografts across a major histocompatibility barrier in miniature swine1

BACKGROUND

Tolerance to composite tissue allografts might allow the widespread clinical use of reconstructive allotransplantation if protocols to achieve this could be rendered sufficiently nontoxic. The authors investigated whether tolerance could be generated in miniature swine to composite tissue allografts across a major histocompatibility (MHC) barrier. A clinically relevant tolerance protocol involving hematopoietic cell transplantation without the need for irradiation or myelosuppressive drugs was tested.

METHODS

Seven recipient animals were transiently T-cell depleted and a short course of cyclosporine was initiated. Twenty-four hours later, a donor hematopoietic cell transplant consisting of cytokine-mobilized peripheral blood mononuclear cells or bone marrow cells and a heterotopic limb transplant were performed. In vitro anti-donor responsiveness was assessed by mixed-lymphocyte reaction and cell-mediated lympholysis assays. Acceptance of the limb allografts was determined by gross and histologic appearance. Chimerism in the peripheral blood and lymphohematopoietic organs was assessed by flow cytometry.

RESULTS

All seven experimental animals accepted the musculoskeletal elements but rejected the skin of the allografts. All but one of the animals displayed donor-specific unresponsiveness in vitro. The animals that received cytokine mobilized-peripheral blood mononuclear cells showed chimerism but had clinical evidence of graft-versus-host disease (GVHD). None of the animals that received bone marrow cells showed stable chimerism and none developed GVHD.

CONCLUSIONS

This protocol can achieve tolerance to the musculoskeletal elements of composite tissue allografts across an MHC barrier in miniature swine. Stable chimerism does not appear to be necessary for tolerance and may not be desirable because of the risk of GVHD.

Separation of bivalent anti-T cell immunotoxin from Pichia pastoris glycoproteins by borate anion exchange

A major problem encountered in the large-scale purification of the bivalent anti-T cell immunotoxin, A-dmDT390-bisFv(G4S), from Pichia pastoris supernatants was the presence of host glycoproteins exhibiting similar charge, size, and hydrophobicity characteristics. We overcame this problem by employing borate anion exchange chromatography. The borate anion has an affinity for carbohydrates and imparts negative charges to these structures. We found that at a concentration of sodium borate between 50 and 100 mM, the nonglycosylated immunotoxin did not bind to Poros 50 HQ anion exchanger resin, but glycoproteins, including aggregates related to the immunotoxin, did. By using this property of the immunotoxin in the presence of sodium borate, we successfully developed a 3-step purification procedure: (i) Butyl-650M hydrophobic interaction chromatography, (ii) Poros 50 HQ anion exchange chromatography in the presence of borate, and (iii) HiTrap Q anion exchange chromatography. The final preparation exhibited a purity of greater than 98% and a yield of greater than 50% from the supernatant. Previously, boronic acid resins have been used to separate glycoproteins from proteins. However, combining borate anion with conventional anion exchange resins accomplishes the separation of the immunotoxin from glycoproteins and eliminates the need to evaluate nonstandard resins with respect to good manufacturing practice guidelines.

Targeted introduction of a diphtheria toxin resistant mutation into the chromosomal EF-2 locus of Pichia pastoris and expression of immunotoxin in the EF-2 mutants

In an attempt to increase the production of a diphtheria toxin (DT) based immunotoxin by Pichia pastoris, we have created DT-resistant mutants that contain a substitution of arginine for glycine at position 701 in elongation factor 2 (EF-2). To achieve this, we first cloned and characterized the EF-2 gene (PEF1), and then made a construct pBLURA-Delta5'mutEF-2 that efficiently introduces specific mutations into the chromosomal EF-2 gene in P. pastoris by in vivo homologous recombination. pBLURA-Delta5(')mutEF-2 contains a selection marker URA3 and a 5' truncated form of the P. pastoris PEF1 that had been modified in vitro to carry the nucleotide mutations for the Gly(701) to Arg transition. Unlike the non-mutated strains, the EF-2 mutants are resistant to high-level intracellular expression of DT A chain that can catalyze the ADP-ribosylation. When used to express the secreted bivalent anti-T cell immunotoxin, A-dmDT390-bisFv(G4S), the EF-2 mutant strains showed increased viability compared to the non-mutated strains. However, they did not show an advantage over the non-mutated expressing strain in the production of the immunotoxin. Western blotting analysis revealed that although the EF-2 mutants did not increase the accumulation of intact A-dmDT390-bisFv(G4S) in the culture medium, they generated larger amounts of degraded products found in both the medium and cell pellets compared to the non-mutant expressing clone. In addition, double copy expression resulted in greater amounts of intact immunotoxin being retained within cellular compartments as well as degraded products. Based on these findings, we suggest that the secretory capacity may be rate limiting for divalent immunotoxin production in P. pastoris.

Immunotoxin therapy of hematologic malignancies

Patients with chemotherapy relapsed or refractory hematologic malignancies may be effectively treated with allogeneic or autologous stem cell transplants. However, many patients cannot be transplanted due to age, comorbidities, or lack of suitable donors. Further, a fraction of patients relapse post-transplant. Novel therapeutic agents that can kill multidrug-resistant malignant stem cells and are not myelosuppressive are needed. One class of such agents is immunotoxins. Immunotoxins consist of cell-selective ligands covalently linked to peptide toxins. The ligand delivers the molecule to specific cell surface receptors on malignant cells. The toxin triggers cell death either by reaching the cytosol and catalytically inactivating vital cell processes or by modifying the tumor cell surface membrane. We have synthesized immunotoxins for therapy of chemoresistant hematologic diseases. In this review, we will detail the synthesis of a number of these drugs and describe their preclinical and clinical activity. Several of these agents have shown dramatic antitumor effects in patients with hematologic neoplasms, and one immunotoxin has been approved for use by the US Food and Drug Administration (FDA). Over the next several decades, a growing number of these agents should reach the clinic.

Xenogeneic thymus transplantation in a pig-to-baboon model

BACKGROUND

We have tested whether fetal porcine thymic tissue transplantation can lead to tolerance across a discordant (pig-to-baboon) xenogeneic barrier.

METHODS

Six baboons underwent a conditioning regimen with thymectomy, splenectomy, and anti-monkey CD3 antibody conjugated to a diphtheria toxin binding site mutant (FN18-CRM9). Porcine fetal or neonatal thymic tissue was transplanted into three baboons. Three control baboons received either no transplanted pig tissue (n=1) or adult pig lymph node (n=2). Cellular responses and skin xenografts were used to test for tolerance.

RESULTS

After T-cell depletion and thymic transplantation, recovery of thymus-dependent naïve-type CD4 cells (CD4/CD45RA ) and in vitro xenogeneic hyporesponsiveness were observed. No sensitization of alpha-galactosyl antibody responses was observed. The thymic grafts survived up to 48 days. Porcine skin xenografts were performed in two of these animals with survival of 22 and 24 days. Only two of these animals were completely T-cell depleted, and both failed to recover thymus-dependent T cells (CD4/CD45RA ). In one animal, general in vitro hyporesponsiveness was observed, with subsequent death from infection. The second animal demonstrated delayed recovery of T cells and prolonged general hyporesponsiveness in vitro. Neither animal demonstrated prolongation of porcine skin grafts compared with allografts (both rejected by day 13).

CONCLUSIONS

Porcine thymic tissue is able to induce xenogeneic hyporesponsiveness. More efficient thymic engraftment may allow this approach to induce xenograft tolerance.

Stable alpha- and beta-islet cell function after tolerance induction to pancreatic islet allografts in diabetic primates

Pancreatic islet transplantation (PIT) is an attractive alternative for type 1 diabetic patients. PIT is not yet an effective clinical reality due in part to early loss of functional islet mass. In addition, current immunosuppressive drugs have toxic effects on islets and increase the risk of morbidity and mortality. Precise and durable alpha- and beta-cell function is essential for the success of PIT. Therefore, it is important to establish whether PIT can produce adequate long-term metabolic control, especially in the absence of chronic immunosuppressive therapy (CIT). In the present study, the stability of functional alpha- and beta-cell mass and metabolic function was assessed in streptozotocin (STZ)-induced diabetic primates following PIT in the absence of CIT. Diabetes was induced in rhesus macaques with STZ, 140 mg/kg. Hyperglycemia was reversed rapidly by PIT coupled with a 14-day tolerance induction protocol based on F(Ab)2-IT and DSG (n = 7). Two diabetic animals received the tolerance induction protocol without PIT. Acute rejection was presented in three animals at 70, 353 and 353 days post transplant in the tolerance induction protocol, whereas the controls [F(Ab)2-IT or DSG alone] showed early 10-day function but all lost islet function by days 15-70. One recipient [F(Ab)2-IT or DSG] died euglycemic after a surgical procedure on day 187. At 2 years, three animals studied had a normal FIM evaluated by oral glucose tolerance test, mixed meal test, acute insulin response to glucose, glucose disposal rate, and hyperinsulinemic hypoglycemic clamp. PIT in STZ-induced diabetic primates resulted in restoration of normal alpha- and beta-cell function. Operational tolerance induction was achieved with only peritransplant administration of F(Ab)2-IT and DSG sparing the animals from chronic exposure of diabetogenic immunosuppressive drugs. These results offer an exciting new potential for treatment of type 1 diabetes mellitus.

Variable relationship between chimerism and tolerance after hematopoietic cell transplantation without myelosuppressive conditioning

BACKGROUND

We have previously described a mixed chimerism protocol that avoids myelosuppressive conditioning and permits hematopoietic cell transplantation across MHC barriers without the need for whole body irradiation in miniature swine. Here, we report our current experience including animals conditioned without thymic irradiation, and we attempt to define the relationship between long-term chimerism and stable tolerance in these animals.

METHODS

Recipient swine received in vivo T-cell depletion, with or without thymic irradiation on day -2. Cyclosporine was administered for 30 to 60 days beginning on day -1. A total of 1 to 2 x 10(10) /kg cytokine-mobilized donor hematopoietic cells were infused during 3 days. Chimerism was determined by flow cytometry. In vitro tolerance assays and donor-matched kidney transplantation were performed after cessation of cyclosporine.

RESULTS

Most recipients maintained stable chimerism (26 of 35) and were specifically tolerant to donor-matched cells in vitro regardless of whether they received thymic irradiation. Donor-matched kidney transplantations performed in chimeric animals without in vitro antidonor immune responses were accepted without immunosuppression. Some animals developed in vitro evidence of antidonor MHC responsiveness despite the persistence of donor cells in the peripheral blood. Donor-matched kidney transplantations performed in the face of these responses were rejected.

CONCLUSIONS

These data indicate that this nonmyelosuppressive protocol can induce stable chimerism and robust tolerance even in animals conditioned without thymic irradiation. However, the data also demonstrate that macrochimerism does not always correlate with tolerance. Lack of in vitro antidonor immune responses in chimeric animals is an important predictor of renal allograft acceptance in this model.

Gene optimization is necessary to express a bivalent anti-human anti-T cell immunotoxin in Pichia pastoris

The bivalent anti-human anti-T cell immunotoxin A-dmDT390-bisFv(G(4)S) was developed for treatment of T cell leukemia, autoimmune diseases, and tolerance induction for transplantation. The multi-domain structure of the bivalent immunotoxin hinders efficient production in Escherichia coli and most eukaryotes are sensitive to the toxin. However, Pichia pastoris has a tolerance to levels of DT (diphtheria toxin) that were previously observed to intoxicate wild type eukaryotic cells, including Saccharomyces cerevisiae. This tolerance has permitted the optimization of the secreted expression of A-dmDT390-bisFv(G(4)S) in P. pastoris under the control of AOX1 (alcohol oxidase 1) promoter. The original DNA sequence of A-dmDT390-bisFv(G(4)S) was not expressed in P. pastoris because of several AT-rich regions, which induce an early termination of transcription. After DNA rebuilding for abolishing AT-rich regions and codon optimization, the immunotoxin could be expressed up to 10mg/L in the shake flask culture. No differences in the expression levels of immunotoxin were observed by using different secretional signal sequences, Mut(s) (methanol utilization slow phenotype) or Mut(+) (methanol utilization plus phenotype) phenotypes. Buffered complex medium (pH 7.0) having 1% casamino acids provided the highest expression in shake flask culture and PMSF (phenylmethylsulfonyl fluoride) in the range of 1 to 3mM further improved the expression level presumably by inhibiting protein degradation. The immunotoxin was purified by DEAE (diethylaminoethyl) Sepharose ion exchange chromatography and Protein L affinity chromatography. The immunotoxin purified from P. pastoris culture was as fully functional as that expressed in a toxin resistant mutant CHO (Chinese hamster ovary) cell line. Our results demonstrate that P. pastoris is an ideal system for expression of toxin-based fusion proteins.

Improved binding of a bivalent single-chain immunotoxin results in increased efficacy for in vivo T-cell depletion

Anti-CD3 immunotoxins exhibit considerable promise for the induction of transplantation tolerance in pre-clinical large animal models. Recently an anti-human anti-CD3epsilon single-chain immunotoxin based on truncated diphtheria toxin has been described that can be expressed in CHO cells that have been mutated to diphtheria toxin resistance. After the two toxin glycosylation sites were removed, the bioactivity of the expressed immunotoxin was nearly equal to that of the chemically conjugated immunotoxin. This immunotoxin, A-dmDT390-sFv, contains diphtheria toxin to residue 390 at the N-terminus followed by VL and VH domains of antibody UCHT1 linked by a (G(4)S)(3) spacer (sFv). Surprisingly, we now report that this immunotoxin is severely compromised in its binding affinity toward CD3(+) cells as compared with the intact parental UCHT1 antibody, the UCHT1 Fab fragment or the engineered UCHT1 sFv domain alone. Binding was increased 7-fold by adding an additional identical sFv domain to the immunotoxin generating a divalent construct, A-dmDT390-bisFv (G(4)S). In vitro potency increased 10-fold over the chemically conjugated immunotoxin, UCHT1-CRM9 and the monovalent A-dmDT390-sFv. The in vivo potency of the genetically engineered immunotoxins was assayed in the transgenic heterozygote mouse, tgepsilon 600, in which the T-cells express human CD3epsilon as well as murine CD3epsilon. T-cell depletion in the spleen and lymph node observed with the divalent construct was increased 9- and 34-fold, respectively, compared with the monovalent construct. The additional sFv domain appears partially to compensate for steric hindrance of immunotoxin binding due to the large N-terminal toxin domain.

Influence of relative binding affinity on efficacy in a panel of anti-CD3 scFv immunotoxins

The in vitro cell killing potency of an immunotoxin reflects the aggregate of several independent biochemical properties. These include antigen binding affinity; internalization rate, intracellular processing and intrinsic toxin domain potency. This study examines the influence of antigen binding affinity on potency in various immunotoxin fusion proteins where target antigen binding is mediated by single chain antibody variable region fragments (scFv). Firstly, the relationship between affinity and potency was examined in a panel of four scFv immunotoxins generated from different anti-CD3 monoclonal antibodies fused to the 38 kDa fragment of Pseudomonas aeruginosa exotoxin A (PE38). Of these four scFv-PE38 immunotoxins, the one derived from the anti-CD3 monoclonal antibody UCHT1 has highest cell killing potency. Analysis of these four scFv-PE38 immunotoxins indicated a correlation between antigen binding affinity and immunotoxin potency in the cell killing assay with the exception of the scFvPE38 immunotoxin derived from the antibody BC3. However this scFv appeared to suffer a greater drop in affinity ( approximately 100x), relative to the parent Mab than did the other three scFvs used in this study (2-10x). Secondly, the scFv(UCHT1)-PE38 immunotoxin was then compared with a further panel of scFv(UCHT1)-derived immunotoxins including a divalent PE38 version and both monovalent and divalent Corynebacterium diphtheriae toxin (DT389) fusion proteins. When the scFv-UCHT1 domain was amino-terminally positioned relative to the toxin, as in the scFv(UCHT1)-PE38, an approximately 10-fold higher antigen-binding affinity was observed than with the C-terminal fusion, used in the DT389-scFv(UCHT1) molecule. Despite this lower antigen-binding activity, the DT389-scFv immunotoxin had a 60-fold higher potency in the T-cell-killing assay. Thirdly, a divalent form of the DT389-scFv construct, containing tandem scFv domains, had a 10-fold higher binding activity, which was exactly reflected in a 10-fold increase in potency. Therefore, when comparing immunotoxins in which scFvs from different antibodies are fused to the same toxin domain (DT or PE) a broad correlation appears to exist between binding affinity and immunotoxin potency. However, no correlation between affinity and potency appears to exist when different toxin domains are combined with the same scFv antibody domain.

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.

Successful reversal of streptozotocin-induced diabetes with stable allogeneic islet function in a preclinical model of type 1 diabetes

The recent focus on islet transplantation as primary therapy for type 1 diabetes has heightened interest in the reversal of type 1 diabetes in preclinical models using minimal immunosuppression. Here, we demonstrated in a preclinical rhesus model a consistent reversal of all measured glycemic patterns of streptozotocin-induced type 1 diabetes. The model used single-donor islet transplantation with induction of operational tolerance. The term "operational tolerance" is used to indicate durable survival of single-donor major histocompatibility complex (MHC)-mismatched islet allografts without maintenance immunosuppressive therapy and without rejection or loss of functional islet mass or insulin secretory reserve. In this operational tolerance model, all immunosuppression was discontinued after day 14 posttransplant, and recipients recovered with excellent health. The operational tolerance induction protocol combined peritransplant anti-CD3 immunotoxin to deplete T-cells and 15-deoxyspergualin to arrest proinflammatory cytokine production and maturation of dendritic cells. T-cell deficiency was specific but temporary, in that T-cell-dependent responses in long-term survivors recovered to normal, and there was no evidence of increased susceptibility to infection. Anti-donor mixed lymphocyte reaction responses were positive in the long-term survivors, but all showed clear evidence of systemic T-helper 2 deviation, suggesting that an immunoregulatory rather than a deletional process underlies this operational tolerance model. This study provides the first evidence that operational tolerance can protect MHC nonhuman primate islets from rejection as well as loss of functional islet mass. Such an approach has potential to optimize individual recipient recovery from diabetes as well as permitting more widespread islet transplantation with the limited supply of donor islets.

Phenotypic and functional analysis of T-cell recovery after anti-CD3 immunotoxin treatment for tolerance induction in rhesus macaques

T-cell reduction utilizing specific antibody has been widely used in human transplantation, and is a cornerstone of several tolerance induction strategies in nonhuman primates. We have established a population of long-term tolerant rhesus macaques induced with an anti-CD3epsilon immunotoxin (IT). This treatment effects transient, specific and profound ablation of T cells in blood and lymphoid tissues. In most instances the IT was used in combination with the NF-kappaB inhibitor, 15-Deoxyspergualin. This 2-week long protocol produces a "window of opportunity" for tolerization in which the animal exhibits an enduring quiescent state of unresponsiveness to the allograft, all accomplished without maintenance immunosuppressive drugs. During this induction period, the treated immune system bears some resemblance to that of the neonate, in that T cell numbers are abnormally low and antigen presentation by dendritic cells is precluded by an arrest in their NF-kappaB dependant maturation. In addition, IL-4 production is prominent during and after the tolerance induction interval. For this study we focused on measuring the monkey's ability to repopulate T cells with particular emphasis on the memory T-cell phenotype. Three "memory" phenotypes were utilized; CD3(+)CD45RO(+), CD3(+)CRTH2(+), and CD3(+)CD4(+)CD8(+). All three phenotypes exhibited different patterns of recovery, all of which included transient bursts in their numbers during repopulation. We also estimated thymic activity after T-cell ablation with the use of a newly-described RTE or recent thymic émigré phenotype (a naïve CD8(+)CD103(+) T cell). This marker revealed production of RTE cells including supranormal levels at approximately 6 months post-transplant, implicating thymic function in the repopulation of T-cells. Finally, we measured antibody responses to a panel of antigens (vaccines, environmental antigen, and foreign proteins) that indicated there was no apparent loss of immunologic function during or after the tolerance induction period. Results of studies of T-cell receptor repertoire expression suggest preservation of the pretreatment repertoire, which is consistent with rapid recovery of immune competence to the test antigens. Taken together, these results suggest that while aggressive, this tolerance induction protocol does not appear to incur a prolonged immunologically-compromised state, if at all.

Expression of an anti-CD3 single-chain immunotoxin with a truncated diphtheria toxin in a mutant CHO cell line

ADP-ribosylating immunotoxins are generally expressed in Escherichia coli and then refolded in vitro. Because the efficiency of the in vitro refolding process decreases with the number of protein domains and internal disulfide bonds, these immunotoxins have been generally limited to single-chain monovalent structures. We now show that using the hamster cell line CHO K1 RE1.22c (J. M. Moehring and T. J. Moehring, 1979, Somat. Cell Genet. 5, 453-468) that has been mutated to ADP-ribosylation insensitivity, a level of 4 microg/ml of a truncated anti-T cell immunotoxin, DT390-scFvUCHT1, can be secreted into the medium. This immunotoxin is glycosylated at the two potential N-linked glycosylation sites in the toxin moiety: positions 16-18 in the A chain and residues 235-237 in the B chain. The glycosylated immunotoxin is relatively nontoxic (IC(50) 4.8 x 10(-10) M). Removal of the N-linked oligosaccharides by N-glycosidase F treatment or mutations at the two N-linked glycosylation sites results in a highly active immunotoxin with an IC(50) of 4 x 10(-12) M toward CD3(+) Jurkat cells. This is a 12-fold increase in toxicity over the same immunotoxin harvested from E. coli periplasm without refolding. A single Asn(235) Ala mutation that removed the B chain glycosylation was nearly as toxic as the double mutant. This suggests that B chain glycosylation is the major cause for the loss of toxicity.

Durable donor-specific T and B cell tolerance in rhesus macaques induced with peritransplantation anti-CD3 immunotoxin and deoxyspergualin: absence of chronic allograft nephropathy

Tolerance induction can prevent acute kidney allograft rejection without chronic immunosuppression. It is uncertain whether specific tolerance can prevent chronic allograft nephropathy (CAN), which involves both nonimmune and immune injury. This report provides evidence that immunologically tolerant macaques, induced with immunotoxin and deoxyspergualin, developed neither acute rejection nor CAN. Long survivors, bearing MHC-mismatched grafts without chronic immunosuppression for 0.8 to 3.4 years, exhibited general immune competence with donor-specific T and B cell tolerance and no functional or histological evidence of CAN. Stringent criteria for tolerance were satisfied by specific prolongation of donor skin grafts with rapid rejection of third-party skin, followed by indefinite acceptance of a second donor kidney graft and establishment of microchimerism. Primate tolerance with documented absence of CAN may give impetus to the clinical application of tolerance.

Mixed chimerism and tolerance without whole body irradiation in a large animal model

Mixed hematopoietic chimerism may provide a treatment for patients with nonmalignant hematologic diseases, and may tolerize patients to organ allografts without requiring chronic immunosuppression. However, the toxicity of the usual conditioning regimens has limited the clinical applicability of this approach. These regimens generally include some level of whole body irradiation (WBI), which is thought to facilitate engraftment either by making room for donor hematopoietic stem cells or by providing sufficient host immunosuppression to enable donor cells to engraft. Here, we have established mixed chimerism across both minor and major histocompatibility barriers in swine, by using high doses of peripheral blood stem cells in the absence of WBI. After mixed chimerism was established, swine leukocyte antigen-matched (SLA-matched) donor skin grafts were tolerated and maintained for a prolonged period, whereas third-party SLA-matched skin was rejected promptly. Donor-matched kidney allografts were also accepted without additional immunosuppression. Because of its low toxicity, this approach has potential for a wide range of clinical applications. Our data may indicate that niches for engrafting stem cells are filled by mass action and that WBI, which serves to empty some of these niches, can be omitted if the donor inoculum is sufficiently large and if adequate host T-cell depletion is achieved before transplant.

Long-term functional islet mass and metabolic function after xenoislet transplantation in primates

BACKGROUND

Pancreatic islet transplantation (PIT) is an attractive alternative for patients with type I diabetes mellitus. PIT is not yet an effective clinical reality due in part to the high incidence of rejection and early loss of functional islet mass. In addition, current immunosuppressive drugs have toxic effects on islets and increase the risk of morbidity and mortality. In the present study, the effects of PIT on glycemic parameters were assessed in spontaneously diabetic primates.

METHODS

Five insulinopenic nonhuman primates (three Macacca fascicularis, one Ceropithecus aethiops, and one Macacca mulatta) were studied. All required twice-daily treatment with 4-10 U of insulin. For immunosuppression, the animals received anti-CD3-immunotoxin (100 microg/kg(initially infused 2 hr before transplantation and again on day +1), cyclosporine (CsA) (20 mg/kg(i.v./2 hr before transplantation), cyclosporine microemulsion (Neoral) 60 mg/kg/b.i.d. on days +1 to +3 with dose adjusted by blood levels, and methylprednisolone (15 mg/kg day 0 to +3). Three recipients were given islets from a single donor (M mulatta). The islets were prepared by a semiautomated technique using Liberase. A mean of 13,136 islet equivalents/kg was infused into the portal vein. Two animals (M fascicularis and M mulatta) were used as a diabetic, nontransplanted control. Several metabolic parameters were evaluated.

RESULTS

All monkeys that underwent transplantation experienced reversal of diabetes mellitus with normalization of all diabetic glycemic parameters. In the nontransplanted primates given the same immunosuppression but no PIT, diabetic metabolic parameters were unchanged after 9 months of follow-up. In contrast, all three PIT recipients established fasting and nonfasting euglycemia within 1-2 weeks, and none required exogenous insulin after day 10. Normal intravenous glucose tolerance tests were observed at day 15, and no significant differences in the glucose disappearance rate (Kg) were observed at days 15, 45, 190, and 365 days after transplantation. The acute insulin response to glucose indicated no significant reduction of functional islet mass.

CONCLUSIONS

PIT in severely insulinopenic type I diabetes mellitus primates resulted in restoration of normal glycemic parameters and durable islet mass. Operational tolerance was achieved with only 4 days of drug administration, sparing the animals from chronic exposure to potentially diabetogenic immunosuppressive drugs. These results offer an exciting new potential for type I diabetes mellitus treatment.

Stable mixed chimerism and tolerance using a nonmyeloablative preparative regimen in a large-animal model

Bone marrow transplantation (BMT) has considerable potential for the treatment of malignancies, hemoglobinopathies, and autoimmune diseases, as well as the induction of transplantation allograft tolerance. Toxicities associated with standard preparative regimens for bone marrow transplantation, however, make this approach unacceptable for all but the most severe of these clinical situations. Here, we demonstrate that stable mixed hematopoietic cell chimerism and donor-specific tolerance can be established in miniature swine, using a relatively mild, non-myeloablative preparative regimen. We conditioned recipient swine with whole-body and thymic irradiation, and we depleted their T-cells by CD3 immunotoxin-treatment. Infusion of either bone marrow cells or cytokine-mobilized peripheral blood stem cells from leukocyte antigen-matched animals resulted in stable mixed chimerism, as detected by flow cytometry in the peripheral blood, thymus, and bone marrow, without any clinical evidence of graft-versus-host disease (GvHD). Long-term acceptance of donor skin and consistent rejection of third-party skin indicated that the recipients had developed donor-specific tolerance.

Peritransplant tolerance induction in macaques: early events reflecting the unique synergy between immunotoxin and deoxyspergualin

BACKGROUND

Day of transplant T cell depletion with anti-CD3 immunotoxin or F(Ab)2 immunotoxin induces stable tolerance to renal allografts in rhesus monkeys given 15-deoxyspergualin (DSG), a NF-kappaB inhibitor that suppresses proinflammatory cytokine (PC) production. Because PC and NF-kappaB are involved in dendritic cell (DC) maturation, we asked if impaired DC maturation and Th2-type cytokine deviation might be related to the synergistic effect of DSG in this novel model.

METHODS

Immunosuppression was initiated 4 hr before transplanting a major histocompatibility complex mismatched renal allograft. Some groups received a supplemental 5-day course of cyclosporine A or DSG or a 15-day course of DSG. Peripheral lymph nodes were sequentially examined for presence of mature DC. In vitro effects of DSG on PC-induced maturation of DC were also examined.

RESULTS

Allografts survived without rejection in 87% of recipients given immunotoxin or F(Ab)2 immunotoxin with DSG x 15 days, in 50% with DSG x 5 days, and 0% with cyclosporine A. The longest DSG survivors are >1000 days with normal graft function and tolerance validated, including acceptance of challenge second donor kidneys without treatment. DSG-treated recipients were unique in developing polarized Th2-type plasma cytokines. In DSG recipients, mature DC were significantly reduced in day +5 lymph node biopsies, with complete repopulation by 30 days. In vitro studies verified an inhibitory effect of DSG on DC maturation.

CONCLUSIONS

The study suggests DSG arrests DC maturation. The unusual synergy of immunotoxin and DSG apparently involves coincidental reduction in lymph node T cell mass and mature DC, a transient circumstance favoring development of stable tolerance.

In vivo T cell depletion in miniature swine using the swine CD3 immunotoxin, pCD3-CRM9

BACKGROUND

Partially inbred miniature swine developed in this laboratory provide a unique preclinical large animal model for studying transplant tolerance. The importance of in vivo T cell depletion for establishing stable mixed hematopoietic cell chimerism using a clinically relevant sublethal regimen has been well documented in murine studies (1). Until now, the lack of an effective in vivo T cell-depleting reagent in swine has limited the progress of studies involving hematopoietic cell transplants.

METHODS

The swine CD3 immunotoxin, pCD3-CRM9, was prepared by conjugating our porcine-specific CD3 monoclonal antibody 898H2-6-15 to the diphtheria toxin derivative, CRM9. The resultant immunotoxin was administered i.v. to several miniature swine at doses ranging from 0.15-0.2 mg/kg either in a single dose or two doses 2 days apart. T-cell depletion was monitored in the peripheral blood, mesenteric lymph node, and thymus by flow cytometric analysis and histological examination.

RESULTS

T cells were depleted to less than 1% of their pretreatment levels based on absolute numbers in the peripheral blood. Fluorescence activated cell sorter analysis and histological examination of serial lymph node biopsies confirmed depletion of the CD3+ T cells rather than down modulation or masking of the surface CD3 expression. Depletion of the CD3 bright medullary thymocytes could also be detected by flow cytometry and histological examination after immunotoxin treatment.

CONCLUSIONS

Administration of the immunotoxin i.v. drastically depletes mature T cells from the peripheral blood, lymph node, and thymus compartments of the pig. This first description of an effective in vivo T-cell depleting reagent for the pig provides a valuable tool for studies of transplant tolerance in this large animal model. It also makes possible preclinical studies of T cell depletion with anti-CD3 immunotoxin in this large animal model.

Tolerability and side effects of anti-CD3-immunotoxin in preclinical testing in kidney and pancreatic islet transplant recipients

INTRODUCTION

Anti-CD3-immunotoxin (alpha-CD3-IT) promotes allograft tolerance in nonhuman primates owing to efficient depletion of sessile and circulating T cells. Common side effects of vascular leak syndrome, hepatotoxicity, and nephrotoxicity have limited tolerability of other immunotoxins. We report on preclinical studies of alpha-CD3-IT-related side effects.

METHODS

Normal rhesus monkeys received a kidney transplant and alpha-CD3-IT alone (on day -to +2) or in combination with brief peritransplant adjunctive immunosuppressive therapy. Some received donor CD34+ cells. Blood chemistries, complete blood count, weight, liver, and kidney biopsies were examined for immunotoxin-related changes. Five spontaneously diabetic primates also received alpha-CD3-IT, three of whom had a pancreas islet transplant.

RESULTS

The main side effect of alpha-CD3-IT, vascular leak syndrome, was entirely prevented by adjunctive immunosuppressive therapy. Renal and liver function tests and biopsies revealed a lack of nephrotoxicity and hepatotoxicity. All had transient weight loss (14+/-5%). Without infusion of donor CD34+ cells, 97% had full weight recovery. Of those given donor CD34+ cells, 50% were euthanized for wasting.

CONCLUSIONS

Side effects of alpha-CD3-IT are manageable and should not prevent therapeutic application.

Reversal of naturally occuring diabetes in primates by unmodified islet xenografts without chronic immunosuppression

BACKGROUND

Isolated pancreatic islet transplantation (IPITx) is an attractive alternative for treatment of insulin-dependent diabetes mellitus (IDDM). However, IPITx has been difficult to implement clinically because islets frequently fail to function, have a high incidence of rejection, and are susceptible to autoimmune recurrence and damage by chronic immunosuppressive therapy. Tolerance induction may be a rational approach to resolve several of these limitations. Because anti-CD3 immunotoxin (IT) has been successful in promoting stable primate kidney transplant tolerance in our experience, we considered that tolerance induction with IT might be duplicated in IPITx.

MATERIALS AND METHODS

Three monkeys with spontaneous IDDM (two Macaca fascicularis and one Ceropithecus aethiops) were treated with xenogeneic pancreatic islets (Macaca mulatta). Intrahepatic islet transplantation was performed at a mean of 13136+/-3860 islet equivalents/kg. Islet xenograft acceptance was accomplished by tolerance induction with two injections of IT given on day 0 at 2 hr before transplantation and on day +1, respectively. IT treatment was supplemented with cyclosporine and steroids administered on days 0 through 4. No additional immunosuppression was given thereafter. Two additional control macaques with spontaneous IDDM received the immunosuppressive protocol without islet infusion.

RESULTS

All recipients were restored to stable euglycemia, off exogenous insulin, within 1-2 weeks after transplantation. Glucose tolerance, C-peptide, and glycosylated hemoglobin tests confirmed the restoration of normal glucose homeostasis after islet transplantation. All three islet recipients have remained euglycemic at 410, 255, and 100 days of follow-up despite recovery of peripheral T cells to normal levels. In contrast, none of the controls presented changes in the diabetic status 4 and 8 months after treatment.

CONCLUSIONS

These results represent the first demonstration in nonhuman primates of stable, long-term acceptance of nonencapsulated xenogeneic islets off all immunosuppression, suggesting operational tolerance. The findings have potential implications for islet transplantation as well as improved and more cost-effective therapy for IDDM.

Primate renal transplants using immunotoxin

BACKGROUND

T-lymphocyte depletion 7 days before transplantation with immunotoxin FN 18-CRM9 has resulted in tolerance to subsequent renal allografts. We tested the effect of giving immunotoxin on the day of the transplantation and evaluated its effect on rhesus monkey and allograft survival, on antibody production, and on T-cell recovery.

METHODS

Major histocompatibility complex mismatched renal allografts were performed in rhesus monkeys. Immunotoxin was given starting on the day of transplantation, with and without prednisone and mycophenolate mofetil for 3 days. T-cell subsets and alloantibody levels were measured by flow cytometry. The ability of treated monkeys to develop antibody to tetanus, diphtheria, and xenoantibody was measured. Histology of renal transplants was read in a blinded manner.

RESULTS

Immunotoxin started on the day of transplantation resulted in prolonged allograft survival in all treatment groups. Graft loss between days 50 and 135 was most often due to interstitial nephritis. Later graft loss was due to chronic rejection. Monkeys had intact antibody responses to alloantigen, tetanus, diphtheria, and xenoantibody. Their CD4 cells recovered gradually over 6 months.

CONCLUSIONS

Immunotoxin reliably prolongs renal allograft survival when started on the day of transplantation, but interstitial nephritis and chronic rejection limit the development of long-term tolerance. T-cell-dependent B-cell responses remain intact after treatment.

Peritransplant tolerance induction with anti-CD3-immunotoxin: a matter of proinflammatory cytokine control

BACKGROUND

Tolerance is gaining momentum as an approach to reduce lifelong immunosuppressive therapy while improving transplant longevity. Anti-CD3 immunotoxin (IT), FN18-CRM9, has potential to induce tolerance owing to its exceptional ability to deplete sessile lymph node T cells. However, if initiated at the time of transplantation, alpha-CD3-IT alone elicits a proinflammatory cytokine response, precluding establishment of tolerance.

METHODS

Four groups of rhesus monkeys received kidney allografts and immunosuppression. Three groups received alpha-CD3-IT alone or alpha-CD3-IT supplemented with 15-deoxyspergualin (DSG) and/or methylprednisolone (MP). One group received alpha-CD3-monoclonal antibody with DSG and MP. Cytokines were measured by enzyme-linked immunosorbent assay.

RESULTS

Supplementing peritransplant alpha-CD3-IT treatment with a brief course of DSG and MP promoted rejection-free kidney allograft acceptance in 75% of macaques followed for up to 550 days. Among those given alpha-CD3-IT alone or with MP, none were long-term survivors. Tolerance developed after alpha-CD3-IT, DSG, and MP treatment, but not when the unconjugated a-CD3 monoclonal antibody was substituted for IT. Systemic production of proinflammatory cytokines interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha induced after peritransplant alpha-CD3-IT was prevented only in animals given DSG. Despite high levels of interleukin (IL)-12 in the first month after transplant, tolerant recipients exhibited IL-12 resistance, as evidenced by baseline plasma levels of IFN-gamma but elevated IL-4. DSG was shown to inhibit IL-12-driven IFN-gamma production by a mechanism associated with inhibition of nuclear factor kappa-B.

CONCLUSIONS

In this model, peritransplant induction of tolerance is promoted by efficient elimination of sessile lymph node T cells and control of the proinflammatory IFN-gamma response by a mechanism that appears to involve resistance to IL-12.

Genetic construction and characterization of an anti-monkey CD3 single-chain immunotoxin with a truncated diphtheria toxin

We have previously developed a chemically conjugated anti-rhesus monkey CD3 immunotoxin FN18-CRM9 that can deplete in vivo T cells and induce long term tolerance of mismatched renal allograft in rhesus monkeys. This immunotoxin is a monkey analogue of anti-human CD3 immunotoxin UCHT1-CRM9. In this study, we cloned the light and heavy chain variable regions of anti-monkey CD3 monoclonal antibody FN18 and constructed a single-chain Fv (sFv) by linking variable light and variable heavy regions with a (Gly4Ser)3 linker. The single-chain immunotoxin DT390-FN18sFv was constructed by ligating the sFv to the carboxyl terminus of DT390, a truncated form of diphtheria toxin. The DT390-FN18sFv fusion protein was expressed in Escherichia coli and purified with Ni-RTA affinity and anion exchange columns. Similar to the chemically conjugated immunotoxin FN18-CRM9, DT390-FN18sFv can also specifically inhibit protein synthesis in primary monkey T cells in a dose-dependent manner. DT390-FN18sFv at 10(-7) mol/L or FN18-CRM9 at 10(-8) mol/L is sufficient to reduce protein synthesis of monkey primary T cells to less than 5% of the control. The 50% inhibition dosage (IC50) of FN18-CRM9 is 1 x 10(-10) mol/L, while the IC50 of DT390-FN18sFv is 1 x 10(-8) mol/ L, reflecting the lowered affinity of monovalent Fab' FN18 to its parental divalent antibody. The availability of functional FN18sFv will provide the basis for the construction of divalent anti-CD3 immunotoxins for preclinical studies on the induction of tolerance in organ transplantation and experimental autoimmune diseases.

Preclinical studies of allograft tolerance in rhesus monkeys: a novel anti-CD3-immunotoxin given peritransplant with donor bone marrow induces operational tolerance to kidney allografts

A major challenge in clinical transplantation today is to design a practical and effective protocol for tolerance induction compatible with cadaver organ transplantation. A preclinical rhesus monkey kidney allograft model using immediate peritransplant anti-CD3 immunotoxin (anti-CD3-IT) and donor bone marrow (DBM) is shown here to induce operational tolerance with prolonged graft survival in the absence of chronic immunosuppressive drugs. Bone marrow harvested from the kidney donor was depleted of mature alloantigen-presenting cells and T cells by removing DR(bright) cells and CD3(bright) cells, respectively. In outbred, major histocompatibility complex-incompatible donor-recipient pairs with high pretransplant mixed lymphocyte response and cytotoxic T lymphocyte precursor activity, four of six allografts survived for periods of 120 days to >1.5 years. Graft acceptance after peritransplant treatment followed robust elimination of both peripheral blood T cells and lymph node T cells. In most recipients given anti-CD3-IT and DBM infusion, anti-donor immunoglobulin G responses were completely inhibited. Microchimerism was observed in all recipients studied, including those not given DBM, but levels of microchimerism did not correlate with graft survival. Anti-CD3-IT induction in combination with modified DBM protocols such as the depletion of mature T cells and DR(bright) antigen-presenting cells may offer new opportunities to improve clinical tolerance protocols beyond those attempted in the clinic to date. Overall, these results with anti-CD3-IT show promise for development of cadaver transplant tolerance induction.

Split tolerance induced by immunotoxin in a rhesus kidney allograft model

BACKGROUND

Renal allografts were performed in rhesus monkeys using FN18-CRM9, a potent immunotoxin capable of depleting T cells to less than 1% of baseline levels in blood and lymph nodes, as a preparative agent. We have recently reported that animals pretreated with FN18-CRM9 1 week before transplantation without further immunosuppression had prolonged graft survival time compared with control animals, and frequently became tolerant.

METHODS

This report examines the alloimmune responses of recipient monkeys to the donor, including cytotoxic T lymphocyte precursor (CTLp) frequency, mixed lymphocyte response, and antidonor IgG response.

RESULTS

CTLp frequencies declined significantly (P<0.01) after FN18-CRM9 treatment and renal transplantation. This decline in CTLp was initially nonspecific, as CTLp frequencies against third-party animals also declined (P<0.01). The decrease in CTLp was maintained in five of five animals tested 6 months after transplant. However, unresponsiveness was limited to the CTL arm of the immune response as antidonor IgG was detected in four of four animals tested, and the 5-day mixed lymphocyte response stimulation index and relative response were not significantly different before and after transplant. In long-term survivors (>150 days), an increase in anti-third-party CTLp was detected 1 month after grafting with third-party skin. No change was seen in the antidonor CTLp frequency after donor skin grafting, indicating that a specific defect in the antidonor CTL response had developed.

CONCLUSIONS

These data suggest that FN18-CRM9 treatment of rhesus monkeys allows the development of specific down-regulation of antidonor CTL activity in renal allograft recipients.