Evaluation of a CD25-specific immunotoxin for prevention of graft-versus-host disease after unrelated marrow transplantation

Evolution of the role of haploidentical stem cell transplantation: past, present, and future

INTRODUCTION

The accessibility to haplo-donors has led to an increase in the number of haplo-HSCT worldwide. A systematic search of the PubMed database between 2000 to present was performed.

AREAS COVERED

In this review, the authors discussed the most used approaches to perform haplo-HSCT and its results: T-cell depletion (TCD, including Perugia platform and its modifications) and T-cell repleted haplo (TCR, including the high-dose post-transplant cyclophosphamide strategy (Baltimore protocol) and the Beijing protocol). The improvements and modifications made to the different strategies have increased the indications of haplo-HSCT, including both malignant and nonmalignant disorders. Focusing on the Baltimore protocol, the authors review the results of the retrospective studies that have compared it to other donor transplants. The limitations of this strategy in terms of toxicity, graft complications, and GVHD are also discussed in detail. Finally, possible approaches to improve the outcomes of TCR haplo-HSCT are presented.

EXPERT OPINION

The recent advances in the field of haplo-HSCT have allowed a large number of patients with incurable diseases to benefit from this procedure despite not having a matched donor. With all available strategies, virtually no patient who needs an allogeneic transplant should be excluded by the absence of a donor.

Photodepletion with 2-Se-Cl prevents lethal graft-versus-host disease while preserving antitumor immunity

Acute graft-versus-host-disease (GVHD), limits the use of hematopoietic cell transplant (HCT) to treat a variety of malignancies. Any new therapeutic approach must satisfy three requirements: 1) Prevent GVHD, 2) Maintain anti-pathogen immunity, and 3) Maintain anti-tumor immunity. In prior studies we have shown that the selective photosensitizer 2-Se-Cl eliminates highly alloreactive lymphocytes from the graft prior to HCT preventing GVHD and that antiviral immune responses were preserved following incubation with 2-Se-Cl. In this report, we investigated whether 2-Se-Cl treatment preserves antitumor immunity, and then used high dimensional flow cytometry to identify the determinants of successful immune reconstitution. Donor C57BL/6 splenocytes were cocultured for 4 days with irradiated BALB/c splenocytes and then exposed to 2-Se-Cl. Photodepletion (PD)-treated splenocytes were then infused into lethally irradiated BALB/c mice inoculated with A20 leukemia/lymphoma cells. Recipient mice that received PD-treated splenocytes survived > 100 days without evidence of GVHD or leukemia. In contrast, mice that did not receive PD-treated cells at time of HCT died of leukemia progression. Multiparameter flow cytometry of cytokines and surface markers on peripheral blood samples 15 days after HCT demonstrated unique patterns of immune reconstitution. We found that before clinical disease onset GVHD was marked by functionally exhausted T cells, while tumor clearance and long-term survival were associated with an expansion of polyfunctional T cells, monocytes, and DCs early after transplantation. Taken together these results demonstrate that 2-Se-Cl photodepletion is a new treatment that can facilitate HCT by preventing GVHD while preserving antiviral and anti-tumor immunity.

CD25 Blockade Delays Regulatory T Cell Reconstitution and Does Not Prevent Graft-versus-Host Disease After Allogeneic Hematopoietic Cell Transplantation

Daclizumab, a humanized monoclonal antibody, binds CD25 and blocks formation of the IL-2 receptor on T cells. A study of daclizumab as acute graft-versus-host disease (GVHD) prophylaxis after unrelated bone marrow transplantation was conducted before the importance of CD25⁺FOXP3⁺ regulatory T cells (Tregs) was recognized. Tregs can abrogate the onset of GVHD. The relation between Tregs and a graft-versus-malignancy effect is not fully understood. An international, multicenter, double-blind clinical trial randomized 210 adult or pediatric patients to receive 5 weekly doses of daclizumab at 0.3 mg/kg (n = 69) or 1.2 mg/kg (n = 76) or placebo (n = 65) after unrelated marrow transplantation for treatment of hematologic malignancies or severe aplastic anemia. The risk of acute GVHD did not differ among the groups (P = .68). Long-term follow-up of clinical outcomes and correlative analysis of peripheral blood T cell phenotype suggested that the patients treated with daclizumab had an increased risk of chronic GVHD (hazard ratio [HR], 1.49; 95% confidence interval [CI], 1.0 to 2.3; P = .08) and a decreased risk of relapse (HR, 0.57; 95% CI, 0.3 to 1.0; P = .05), but similar survival (HR, 0.89; 95% CI, 0.6 to 1.3; P = .53). T cells from a subset of patients (n = 107) were analyzed by flow cytometry. Compared with placebo, treatment with daclizumab decreased the proportion of Tregs among CD4 T cells at days 11-35 and increased the proportion of central memory cells among CD4 T cells at 1 year. Prophylactic administration of daclizumab does not prevent acute GVHD, but may increase the risk of chronic GVHD and decrease the risk of relapse. By delaying Treg reconstitution and promoting immunologic memory, anti-CD25 therapy may augment alloreactivity and antitumor immunity.

Immunotoxin Against a Donor MHC Class II Molecule Induces Indefinite Survival of Murine Kidney Allografts

Rejection of donor organs depends on the trafficking of donor passenger leukocytes to the secondary lymphoid organs of the recipient to elicit an immune response via the direct antigen presentation pathway. Therefore, the depletion of passenger leukocytes may be clinically applicable as a strategy to improve graft survival. Because major histocompatibility complex (MHC) class II(+) cells are most efficient at inducing immune responses, selective depletion of this population from donor grafts may dampen the alloimmune response and prolong graft survival. In a fully MHC mismatched mouse kidney allograft model, we describe the synthesis of an immunotoxin, consisting of the F(ab')2 fragment of a monoclonal antibody against the donor MHC class II molecule I-A(k) conjugated with the plant-derived ribosomal inactivating protein gelonin. This anti-I-A(k) gelonin immunotoxin depletes I-A(k) expressing cells specifically in vitro and in vivo. When given to recipients of kidney allografts, it resulted in indefinite graft survival with normal graft function, presence of Foxp3(+) cells within donor grafts, diminished donor-specific antibody formation, and delayed rejection of subsequent donor-type skin grafts. Strategies aimed at the donor arm of the immune system using agents such as immunotoxins may be a useful adjuvant to existing recipient-orientated immunosuppression.

Combined PI3K/Akt and Hsp90 targeting synergistically suppresses essential functions of alloreactive T cells and increases Tregs

Acute graft-versus-host disease is still a major cause of transplant-related mortality after allogeneic stem cell transplantation. It requires immunosuppressive treatments that broadly abrogate T cell responses, including beneficial ones directed against tumor cells or infective pathogens. Inhibition of the heat shock protein of 90 kDa has been demonstrated to eliminate tumor cells, as well as alloreactive T cells while preserving antiviral T cell immunity. Here, we show that the suppressive effects of heat shock protein of 90 kDa inhibition on alloreactive T cells were synergistically enhanced by concomitant inhibition of the PI3K/Akt signaling pathway, which is also strongly activated upon allogeneic stimulation. Molecular analyses revealed that this antiproliferative effect was mainly mediated by induction of cell-cycle arrest and apoptosis. In addition, we observed an increased proportion of activated regulatory T cells, which critically contribute to acute graft-versus-host disease control, upon combined heat shock protein of 90 kDa/Akt isoforms 1 and 2 or heat shock protein of 90 kDa/PI3K/p110δ isoform inhibition. Moreover, antiviral T cell immunity was functionally preserved after combined heat shock protein of 90 kDa/Akt isoforms 1 and 2 inhibition. Taken together, our data suggest that the combined heat shock protein of 90 kDa/PI3K/Akt inhibition approach represents a reasonable dual strategy to suppress residual tumor growth and efficiently deplete alloreactive T cells and thus, provide a rationale to prevent and treat acute graft-versus-host disease selectively without impairing pathogen-specific T cell immunity.

Depletion of Alloreactive T-Cells by Anti-CD137-Saporin Immunotoxin

Depletion of alloreactive T-lymphocytes from allogeneic bone marrow tansplants may prevent graft-versus-host disease (GVHD) without impairing donor cell engraftment, immunity, and the graft-versus-leukemia (GVL) effect. Alloreactive T-cells may be identified by their expression, upon activation, of CD137, a costimulatory receptor and putative surrogate marker for antigen-specific effector T-cells. In this context, we tested the use of anti-CD137-saporin immunotoxin to selectively deplete mouse and human alloreactive T-cells. Anti-CD137 antibodies were internalized by cells within 4 h of binding to the cell surface CD137, and anti-CD137-saporin immunotoxin effectively killed polyclonally activated T-cells or antigen-stimulated T-cells. Transfer of donor T-cells after allodepletion with anti-CD137-saporin immunotoxin failed to induce any evident expression of GVHD; however, a significant GVL effect was observed. Targeting of CD137 with an immunotoxin was also effective in killing polyclonally activated or alloreactive human T-cells. Our results indicate that anti-CD137-saporin immunotoxin may be used to deplete alloreactive T-cells prior to bone marrow transplantation and thereby prevent GVHD and the relapse of leukemia.

The allure and peril of hematopoietic stem cell transplantation: overcoming immune challenges to improve success

Since its inception in the mid-twentieth century, the complication limiting the application and utility of allogeneic hematopoietic stem cell transplantation (allo-HSCT) to treat patients with hematopoietic cancer is the development of graft-versus-host disease (GVHD). Ironically, GVHD is induced by the cells (T lymphocytes) transplanted for the purpose of eliminating the malignancy. Damage ensuing to multiple tissues, e.g., skin, GI, liver, and others including the eye, provides the challenge of regulating systemic and organ-specific GVH responses. Because the immune system is also targeted by GVHD, this both: (a) impairs reconstitution of immunity post-transplant resulting in patient susceptibility to lethal infection and (b) markedly diminishes the individual's capacity to generate anti-cancer immunity--the raison d'etre for undergoing allo-HSCT. We hypothesize that deleting alloreactive T cells ex vivo using a new strategy involving antigen stimulation and alkylation will prevent systemic GVHD thereby providing a platform for the generation of anti-tumor immunity. Relapse also remains the major complication following autologous HSCT (auto-HSCT). While GVHD does not complicate auto-HSCT, its absence removes significant grant anti-tumor responses (GVL) and raises the challenge of generating rapid and effective anti-tumor immunity early post-transplant prior to immune reconstitution. We hypothesize that effective vaccine usage to stimulate tumor-specific T cells followed by their amplification using targeted IL-2 can be effective in both the autologous and allogeneic HSCT setting. Lastly, our findings support the notion that the ocular compartment can be locally targeted to regulate visual complications of GVHD which may involve both alloreactive and self-reactive (i.e., autoimmune) responses.

Immunotoxins: the role of the toxin

Immunotoxins are antibody-toxin bifunctional molecules that rely on intracellular toxin action to kill target cells. Target specificity is determined via the binding attributes of the chosen antibody. Mostly, but not exclusively, immunotoxins are purpose-built to kill cancer cells as part of novel treatment approaches. Other applications for immunotoxins include immune regulation and the treatment of viral or parasitic diseases. Here we discuss the utility of protein toxins, of both bacterial and plant origin, joined to antibodies for targeting cancer cells. Finally, while clinical goals are focused on the development of novel cancer treatments, much has been learned about toxin action and intracellular pathways. Thus toxins are considered both medicines for treating human disease and probes of cellular function.

Impaired regulatory T cell reconstitution in patients with acute graft-versus-host disease and cytomegalovirus infection after allogeneic bone marrow transplantation

To elucidate the correlation between regulatory T cells (Tregs) and acute graft-versus-host disease (aGVHD) or cytomegalovirus infection following allogeneic bone marrow transplantation (allo-BMT), we evaluated either CD4⁺CD25(high) or FOXP3⁺ Treg-enriched cells in peripheral blood (PB) from 20 patients who received allo-BMT, and in biopsies of skin with aGVHD. Proportions of CD4⁺CD25(high)FOXP3⁺ cells in total lymphocytes, but not other types of T cells, were lower in patients who eventually developed grades II-IV aGVHD (n = 13) than in others (n = 7, P < 0.001). Proportions of CD62L⁺ cells in CD4⁺CD25(high) cells at day +30 were lower (P < 0.01) in patients who eventually showed cytomegalovirus viremia (n = 6) than in others (n = 14). Incidence of aGVHD (P < 0.05) or cytomegalovirus viremia (P < 0.05) was higher in patients without these complications, but with lower proportions of PB CD4⁺CD25(high)FOXP3⁺ cells at day +30 (n = 8) than in others (n = 8). However, in skin with aGVHD (n = 5), there was marked or slightly increased infiltration of CD8⁺ cells (P < 0.001) or CD3⁺FOXP3⁺ cells (P < 0.05), respectively, when compared with control (n = 5), resulting in threefold higher ratio of CD8⁺/CD3⁺FOXP3⁺ cells in aGVHD relative to controls (P < 0.05). Thus, impaired reconstitution of Tregs may be associated with aGVHD and CMV infection. Moreover, imbalance of Tregs and CD8⁺ cells may play a role in aGVHD tissue.

Passive and active vaccination strategies to prevent ricin poisoning

Ricin toxin (RT) is derived from castor beans, produced by the plant Ricinus communis. RT and its toxic A chain (RTA) have been used therapeutically to arm ligands that target disease-causing cells. In most cases these ligands are cell-binding monoclonal antibodies (MAbs). These ligand-toxin conjugates or immunotoxins (ITs) have shown success in clinical trials [1]. Ricin is also of concern in biodefense and has been classified by the CDC as a Class B biothreat. Virtually all reports of RT poisoning have been due to ingestion of castor beans, since they grow abundantly throughout the world and are readily available. RT is easily purified and stable, and is not difficult to weaponize. RT must be considered during any "white powder" incident and there have been documented cases of its use in espionage [2,3]. The clinical syndrome resulting from ricin intoxication is dependent upon the route of exposure. Countermeasures to prevent ricin poisoning are being developed and their use will depend upon whether military or civilian populations are at risk of exposure. In this review we will discuss ricin toxin, its cellular mode of action, the clinical syndromes that occur following exposure and the development of pre- and post-exposure approaches to prevent of intoxication.

Immunotoxins and anticancer drug conjugate assemblies: the role of the linkage between components

Immunotoxins and antibody-drug conjugates are protein-based drugs combining a target-specific binding domain with a cytotoxic domain. Such compounds are potentially therapeutic against diseases including cancer, and several clinical trials have shown encouraging results. Although the targeted elimination of malignant cells is an elegant concept, there are numerous practical challenges that limit conjugates’ therapeutic use, including inefficient cellular uptake, low cytotoxicity, and off-target effects. During the preparation of immunoconjugates by chemical synthesis, the choice of the hinge component joining the two building blocks is of paramount importance: the conjugate must remain stable in vivo but must afford efficient release of the toxic moiety when the target is reached. Vast efforts have been made, and the present article reviews strategies employed in developing immunoconjugates, focusing on the evolution of chemical linkers.

Depletion of alloreactive T-cells in vitro using the proteasome inhibitor bortezomib preserves the immune response against pathogens

Current graft-versus-host disease (GVHD) inhibition approaches lead to abrogation of pathogen-specific T-cell responses. We propose an approach to inhibit GVHD without hampering immunity against pathogens: in vitro depletion of alloreactive T cells with the preoteasome inhibitor bortezomib. We show that PBMCs stimulated with allogeneic cells and treated with bortezomib greatly reduce their ability to produce IFN-γ when re-stimulated with the same allogeneic cells, but mainly preserve their ability to respond to citomegalovirus stimulation. Unlike in vivo administration of immunosuppressive drugs or other strategies of allodepletion, in vitro allodepletion with bortezomib maintains pathogen-specific T cells, representing a promising alternative for GVHD prophylaxis.

HLA-F is a surface marker on activated lymphocytes

Of the three nonclassical class I antigens expressed in humans, HLA-F has been least characterized with regard to expression or function. In this study, we examined HLA-F expression focusing on lymphoid cells, where our previous work with homologous cell lines had demonstrated surface HLA-F expression. HLA-F protein expression was observed by Western blot analysis in all resting lymphocytes, including B cells, T cells, NK cells, and monocytes, all of which lacked surface expression in the resting state. Upon activation, using a variety of methods to activate different lymphocyte subpopulations, all cell types that expressed HLA-F intracellularly showed an induction of surface HLA-F protein. An examination of peripheral blood from individuals genetically deficient for TAP and tapasin expression demonstrated the same activation expression profiles for HLA-F,but with altered kinetics post-activation. Further analysis of CD41+CD25+1 Treg showed that HLA-F was not upregulated on the major fraction of these cells when they were activated,whereas CD41+CD25- T cells showed strong expression of surface HLA-F when activated under identical conditions. These findings are discussed with regard to possible functions for HLA-F and its potential clinical use as a marker of an activated immune response.

Toxin-based therapeutic approaches

Protein toxins confer a defense against predation/grazing or a superior pathogenic competence upon the producing organism. Such toxins have been perfected through evolution in poisonous animals/plants and pathogenic bacteria. Over the past five decades, a lot of effort has been invested in studying their mechanism of action, the way they contribute to pathogenicity and in the development of antidotes that neutralize their action. In parallel, many research groups turned to explore the pharmaceutical potential of such toxins when they are used to efficiently impair essential cellular processes and/or damage the integrity of their target cells. The following review summarizes major advances in the field of toxin based therapeutics and offers a comprehensive description of the mode of action of each applied toxin.

Allogeneic hematopoietic cell transplantation for chronic myelomonocytic leukemia: relapse-free survival is determined by karyotype and comorbidities

Hematopoietic cell transplantation (HCT) offers potentially curative therapy for chronic myelomonocytic leukemia (CMML). We evaluated HCT outcomes in 85 patients with CMML, 1.0-69.1 (median 51.7) years of age, with follow-up extending to 19 years. CMML was considered de novo in 71 and secondary in 14 patients. Conditioning regimens were of various intensities. Thirty-eight patients had related (34 HLA identical), and 47 (39 HLA matched) unrelated donors. The source of stem cells was marrow in 32 and peripheral blood progenitor cells in 53 patients. Acute graft-versus-host disease (aGVHD) grades II-IV occurred in 72% and chronic GVHD (cGVHD) in 26% of patients. Relapse incidence was 27% at 10 years. Relapse correlated with increasing scores by the MD Anderson prognostic score (P = .01). The major causes of death were relapse and infections ±GVHD. Progression-free survival (PFS) was 38% at 10 years. Mortality was negatively correlated with pre-HCT hematocrit (P = .007), and increased with high-risk cytogenetics (P = .02), higher HCT Comorbidity Index (P = .0008), and increased age (P = .02). WHO classification did not statistically significantly affect outcome. Thus, a proportion of patients with CMML have lasting remissions following allogeneic HCT and appear to be cured of their disease.

Increase in FOXP3+ regulatory T cells in GVHD skin biopsies is associated with lower disease severity and treatment response

In animal models, CD4+/CD25+ T-regulatory cells (Tregs) have been reported to prevent/delay the onset of graft-versus-host disease (GVHD). Recently, an insufficient upregulation of Tregs was found in target organ (intestinal) biopsies from patients with GVHD. We have analyzed by immunohistochemistry the number of CD3+ T lymphocytes and FOXP3+ Tregs in skin biopsies from (1) recipients of allogeneic hematopoietic stem cell transplantation (HSCT, n = 26), (2) nontransplanted patients diagnosed with cutaneous drug reaction (n = 12), and (3) healthy donors (n = 10). Infiltrating CD3+ cells were significantly higher in both transplanted patients showing acute GVHD (aGVHD) and drug reaction when compared to healthy donors and patients without GVHD. Tregs number in aGVHD was higher than in patients without GVHD or healthy subjects and lower than in drug reaction. Interestingly, the number of infiltrating FOXP3+ Tregs was significantly higher in patients responding to GVHD treatment and with a low GVHD grade. Increase in FOXP3+ Tregs in GVHD skin biopsies correlates with less severe GVHD and is associated with response to GVHD treatment. Larger studies are required to confirm that evaluation of Tregs in minimally invasive skin biopsies assists the diagnosis and prognosis of GVHD patients.

Treatment with bortezomib of human CD4+ T cells preserves natural regulatory T cells and allows the emergence of a distinct suppressor T-cell population

BACKGROUND

In vitro depletion of alloreactive T cells using the proteasome inhibitor bortezomib is a promising approach to prevent graft-versus-host disease after allogeneic stem cell transplantation. We have previously described the ability of bortezomib to selectively eliminate alloreactive T cells in a mixed leukocyte culture, preserving non-activated T cells. Due to the role of regulatory T cells in the control of graft versus host disease, in the current manuscript we have analyzed the effect of bortezomib in regulatory T cells.

DESIGN AND METHODS

Conventional or regulatory CD4(+) T cells were isolated with immunomagnetic microbeads based on the expression of CD4 and CD25. The effect of bortezomib on T-cell viability was analyzed by flow cytometry using 7-amino-actinomycin D staining. To investigate the possibility of obtaining an enriched regulatory T-cell population in vitro with the use of bortezomib, CD4(+) T cells were cultured during four weeks in the presence of anti-CD3 and anti-CD28 antibodies, IL-2 and bortezomib. The phenotype of these long-term cultured cells was studied, analyzing the expression of CD25, CD127 and FOXP3 by flow cytometry, and mRNA levels were determined by RT-PCR. Their suppressive capacity was assessed in co-culture experiments, analyzing proliferation and IFN-gamma and CD40L expression of stimulated responder T cells by flow cytometry.

RESULTS

We observed that naturally occurring CD4(+)CD25(+) regulatory T cells are resistant to the pro-apoptotic effect of bortezomib. Furthermore, we found that long-term culture of CD4(+) T cells in the presence of bortezomib promotes the emergence of a regulatory T-cell population that significantly inhibits proliferation, IFN-gamma production and CD40L expression among stimulated effector T cells.

CONCLUSIONS

These results reinforce the proposal of using bortezomib in the prevention of graft versus host disease and, moreover, in the generation of regulatory T-cell populations, that could be used in the treatment of multiple T-cell mediated diseases.

Immunomodulatory effects of mixed hematopoietic chimerism: immune tolerance in canine model of lung transplantation

Long-term survival after lung transplantation is limited by acute and chronic graft rejection. Induction of immune tolerance by first establishing mixed hematopoietic chimerism (MC) is a promising strategy to improve outcomes. In a preclinical canine model, stable MC was established in recipients after reduced-intensity conditioning and hematopoietic cell transplantation from a DLA-identical donor. Delayed lung transplantation was performed from the stem cell donor without pharmacological immunosuppression. Lung graft survival without loss of function was prolonged in chimeric (n = 5) vs. nonchimeric (n = 7) recipients (p < or = 0.05, Fisher's test). There were histological changes consistent with low-grade rejection in 3/5 of the lung grafts in chimeric recipients at > or =1 year. Chimeric recipients after lung transplantation had a normal immune response to a T-dependent antigen. Compared to normal dogs, there were significant increases of CD4+INFgamma+, CD4+IL-4+ and CD8+ INFgamma+ T-cell subsets in the blood (p < 0.0001 for each of the three T-cell subsets). Markers for regulatory T-cell subsets including foxP3, IL10 and TGFbeta were also increased in CD3+ T cells from the blood and peripheral tissues of chimeric recipients after lung transplantation. Establishing MC is immunomodulatory and observed changes were consistent with activation of both the effector and regulatory immune response.

Immunomodulation and pharmacological strategies in the treatment of graft-versus-host disease

BACKGROUND

Allogeneic hematopoietic stem cell transplantation offers great promise for the treatment of a variety of diseases including malignancies and other diseases of hematopoietic origin. However, morbidity and mortality due to graft-versus-host disease (GVHD) remain a major barrier to its application.

OBJECTIVE

This review will provide an overview of the pathophysiology of GVHD and discuss the recent advances in GVHD management in both preclinical and clinical studies.

METHODS

An extensive literature search on PubMed from 1995 to 2008 was performed.

RESULTS/CONCLUSION

There has been much progress in our understanding of GVHD and finding new means to control acute GVHD. While these approaches hold promise, as yet none has been able to replace the standard methods we may use routinely to decrease the incidence of the condition.

Study design and endpoints in graft-versus-host disease

The design of clinical trials for prevention or treatment of acute or chronic graft-versus-host disease poses many challenges. These challenges include the selection of primary and secondary endpoints that demonstrate clinical benefit, and the identification of measures indicating success both for individual patients and groups. Assessment of response in treatment trials should ideally encompass the prior trajectory of change before treatment. The criteria, timing and duration of response should be specified, and the potential effects of concomitant treatment and complications other than GVHD should be taken into account in assessing outcomes. A crucial element in clinical trial design is the pre-specification of the hypothesis to be tested in quantitative terms. Potential barriers to enrollment should be carefully considered in order to ensure timely completion of the trial.

Partial reduction of human FOXP3+ CD4 T cells in vivo after CD25-directed recombinant immunotoxin administration

The regulation of tolerance to self-proteins and the suppression of T-cell responses have in part been attributed to the activity of CD25+CD4+ T regulatory (Treg) cells. Further, Treg cells can inhibit the antitumor effectiveness of adoptive immunotherapy and active immunization approaches in preclinical models. In an effort to selectively eliminate Treg cells from human peripheral blood mononuclear cell to potentially bolster antitumor responses, we have evaluated the Treg-cell depleting capacity of the CD25-directed immunotoxin, RFT5-SMPT-dgA. In preclinical studies, incubation of human peripheral blood mononuclear cell with RFT5-SMPT-dgA mediated a partial reduction in the levels of CD25+, Foxp3-expressing CD4+ T cells in vitro. Administration of RFT5-SMPT-dgA to 6 patients with metastatic melanoma induced a transient but robust reduction in the number of CD25high CD4 T cells in vivo (a 97.5% mean reduction at nadir; from 69.4 +/- 12.4 cells/miroL to 1.7 +/- 0.3 cells/microL). The reduction in FOXP3+ CD4 T-cell number was less comprehensive (a 71.3% mean reduction at nadir; from 66.6 +/- 16.5 cells/microL to 14.2 +/- 3.9 cells/tL). This resulted in the selective persistence of a stable number of CD25(low/neg) FOXP3+ CD4+ T cells in vivo. No objective antitumor responses were seen in any patient. Our results indicate that the CD25-directed, RFT5-SMPT-dgA immunotoxin can mediate a transient, partial reduction in Treg-cell frequency and number in vitro and in vivo and suggest that comprehensive eradication of human Treg cells in vivo may require the ability to target and eliminate FOXP3+ CD4+ T cells expressing both high and low levels of CD25.

The effects of antibody treatment on regulatory CD4(+)CD25(+) T cells

Current therapeutic antibodies, at least some, possess the capacity to induce immune tolerance in experimental models with allo-grafts or autoimmune diseases. Clinical application of humanized or chimeric antibodies to treat graft rejection or autoimmune diseases is presently underway. It is now becoming clear that immune tolerance can be acquired in some cases due to the action of regulatory T cells (Tregs), especially CD4(+)CD25(+) Tregs. In addition to their inhibition on immune response, some antibodies could promote tolerance induction in organ transplantation and autoimmune diseases essentially through the induction of Tregs. In this manuscript, we review the recent progress on the effects of therapeutic antibodies on the development, phenotypic changes and functions of CD4(+)CD25(+) Tregs.

Administration of a CD25-directed immunotoxin, LMB-2, to patients with metastatic melanoma induces a selective partial reduction in regulatory T cells in vivo

CD25+ CD4+ T regulatory (Treg) cells regulate peripheral self tolerance and possess the ability to suppress antitumor responses, which may in part explain the poor clinical response of cancer patients undergoing active immunization protocols. We have previously shown that in vitro incubation of human PBMC with LMB-2, a CD25-directed immunotoxin, significantly reduced CD25+ FOXP3+ CD4+ Treg cells without impairing the function of the remaining lymphocytes. In the current study, eight patients with metastatic melanoma were treated with LMB-2 followed by MART-1 and gp100-specific peptide vaccination. LMB-2 administration resulted in a preferential, transient reduction in mean circulating CD25+ CD4+ T cell number, from 83 +/- 16 cells/microl to a nadir of 17 +/- 5 cells/microl, a 79.1% reduction. FOXP3 analysis revealed a less robust depletion with mean FOXP3+ CD4+ Treg cell number decreasing from 74 +/- 15 cells/microl to 36 +/- 8 cells/microl, a 51.4% reduction. FOXP3+ CD4+ Treg cells that survived LMB-2-mediated cytotoxicity expressed little or no CD25. Similar to the peripheral blood, immunohistochemical analysis showed a 68.9% mean reduction in FOXP3+ CD4+ Treg cell frequency in evaluable lesions. Despite inducing a reduction in Treg cell numbers in vivo, LMB-2 therapy did not augment the immune response to cancer vaccination and no patient experienced an objective response or autoimmunity. These data demonstrate the capacity of a CD25-directed immunotoxin to selectively mediate a transient partial reduction in circulating and tumor-infiltrating Treg cells in vivo, and suggest that more comprehensive Treg cell elimination may be required to bolster antitumor responses in patients with metastatic melanoma.

Reconstitution of FOXP3+ regulatory T cells (Tregs) after CD25-depleted allotransplantation in elderly patients and association with acute graft-versus-host disease

Selective depletion (SD) of host-reactive donor T cells from allogeneic stem-cell transplants (SCTs) using an anti-CD25 immunotoxin (IT) is a strategy to prevent acute graft-versus-host disease (aGvHD). There is concern that concurrent removal of regulatory T cells (T(regs)) with incomplete removal of alloactivated CD25(+) T cells could increase the risk of aGvHD. We therefore measured T(regs) in the blood of 16 patients receiving a T-cell-depleted allograft together with anti-CD25-IT-treated SD lymphocytes, in 13 of their HLA-identical donors, and in 10 SD products. T(regs) were characterized by intracellular staining for forkhead box protein 3 (FOXP3) and by quantitative reverse-transcription-polymerase chain reaction (qRT-PCR) for FOXP3 gene in CD4(+) cells. Patients received a median of 1.0 x 10(8)/kg SD T cells and a stem cell product containing a median of 0.25 x 10(4)/kg residual T cells. T(regs) reconstituted promptly after SCT and underwent further expansion. Of the CD4(+) T cells in SD products, 1.5% to 4.8% were CD25(-) T(regs). Acute GvHD (>or= grade II) was restricted to 5 patients whose donors had significantly (P = .019) fewer T(regs) compared with those without clinically significant aGvHD. These results suggest that rapid T(reg) reconstitution can occur following SD allografts, either from CD25(-) T(regs) escaping depletion, or from residual CD25(-) and CD25(+) T(regs) contained in the stem-cell product that expand after transplantation and may confer additional protection against GvHD.

Immunobiology of allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) has evolved into an effective adoptive cellular immunotherapy for the treatment of a number of cancers. The immunobiology of allogeneic HSCT is unique in transplantation in that it involves potential immune recognition and attack between both donor and host. Much of the immunobiology of allogeneic HSCT has been gleaned from preclinical models and correlation with clinical observations. We review our current understanding of some of the issues that affect the success of this therapy, including host-versus-graft (HVG) reactions, graft-versus-host disease (GVHD), graft-versus-tumor (GVT) activity, and restoration of functional immunity to prevent transplant-related opportunistic infections. We also review new strategies to optimize the GVT and improve overall immune function while reducing GVHD and graft rejection.

Risk assessment in haematopoietic stem cell transplantation: GvHD prevention and treatment

Graft-versus-host disease (GvHD) is the major cause of transplant-related mortality and morbidity. As it is closely related to the major therapeutic principle, graft-versus-leukaemia (GvL) effect, risk assessment has to balance both risks depending on the pre-transplant status. This is clearly demonstrated when comparing the two major strategies for prevention of GvHD. While the majority of approaches aiming at T-cell depletion show efficacy in reducing acute and chronic GvHD and transplant-related mortality, T-cell depletion also affects graft-versus-leukaemia effects and thus results in a higher relapse rate. Thus, standard prophylaxis relying on calcineurin inhibitors frequently results in at least equivalent or even superior long-term disease-free survival, and the risk of relapse has to be considered when selecting regimens for prevention of GvHD. In addition to this general dilemma, drug-specific side-effects and risks have to be considered when selecting regimens for GvHD prevention and treatment.

Immunotoxin treatment of cancer

Immunotoxins are proteins used to treat cancer that are composed of an antibody fragment linked to a toxin. The immunotoxin binds to a surface antigen on a cancer cell, enters the cell by endocytosis, and kills it. The most potent immunotoxins are made from bacterial and plant toxins. Refinements over many years have produced recombinant immunotoxins; these therapeutic proteins are made using protein engineering. Individual immunotoxins are designed to treat specific cancers. To date, most success has been achieved treating hematologic tumors. Obstacles to successful treatment of solid tumors include poor penetration into tumor masses and the immune response to the toxin component of the immunotoxin, which limits the number of cycles that can be given. Strategies to overcome these limitations are being pursued.

Encouraging results with inolimomab (anti-IL-2 receptor) as treatment for refractory acute graft-versus-host disease

Inolimomab [corrected] an anti-interleukin-2 receptor (anti-IL-2R) monoclonal antibody, may be useful in the treatment of steroid-refractory acute graft-versus-host disease (aGVHD) by inhibiting 1 of its putative immunopathogenic pathways. We retrospectively analyzed 40 consecutive patients who received inolimomab [corrected] as salvage treatment for steroid refractory aGVHD at a single institution between June 1999 and December 2004. Inolimomab [corrected] was given intravenously at a dose of 11 mg/d for 3 consecutive days, followed by 5.5 mg/d for 7 consecutive days and then 5.5 mg every other day for 5 doses. No infusion-related side effects were noted. Twenty-three patients (58%) responded, including 15 (38%) complete and 8 (20%) partial responses. Median overall survival was 294 days (58-996 days) for responders versus 14 days for nonresponders (P < .001), with a 1 year probability of 59% vs 0% for overall survival (P < .0001). Patients without gastrointestinal (GI) involvement showed a higher response rate (100% versus 50% for those without versus with GI involvement, P = .03) In addition, patients who showed some response by day 15 had a higher overall survival (73 +/- 12% vs 24 +/- 12%, respectively, P = .02). The results of this study suggest that inolimomab [corrected] may be an effective salvage therapy for patients with steroid-refractory aGVHD, particularly for those without GI disease, and supports further studies with this agent in prospective controlled trials.

Immunotoxins for targeted cancer therapy

Immunotoxins are proteins that contain a toxin along with an antibody or growth factor that binds specifically to target cells. Nearly all protein toxins work by enzymatically inhibiting protein synthesis. For the immunotoxin to work, it must bind to and be internalized by the target cells, and the enzymatic fragment of the toxin must translocate to the cytosol. Once in the cytosol, 1 molecule is capable of killing a cell, making immunotoxins some of the most potent killing agents. Various plant and bacterial toxins have been genetically fused or chemically conjugated to ligands that bind to cancer cells. Among the most active clinically are those that bind to hematologic tumors. At present, only 1 agent, which contains human interleukin-2 and truncated diphtheria toxin, is approved for use in cutaneous T-cell lymphoma. Another, containing an anti-CD22 Fv and truncated Pseudomonas exotoxin, has induced complete remissions in a high proportion of cases of hairy-cell leukemia. Refinement of existing immunotoxins and development of new immunotoxins are underway to improve the treatment of cancer.

Pitfalls in the design of clinical trials for prevention or treatment of acute graft-versus-host disease

This review addresses pitfalls of clinical trials to evaluate new approaches for prevention or treatment of graft-versus-host disease. Determination of end points poses a difficult challenge in the design of clinical trials, and examples from previous studies are used to illustrate some of the pitfalls. Also discussed is the need for a new conceptual approach for evaluation of graft-versus-host disease after non-myeloablative conditioning regimens, because the donor anti-recipient alloimmune reaction is the primary mechanism of benefit with this type of treatment. Finally, investigators should be aware of regulatory and socioeconomic pitfalls that apply to all clinical trials.

Phase I/II trial of melanoma therapy with dendritic cells transfected with autologous tumor-mRNA

We have developed an individualized melanoma vaccine based on transfection of autologous dendritic cells (DCs) with autologous tumor-mRNA. Dendritic cells loaded with complete tumor-mRNA may generate an immune response against a broad repertoire of antigens, including unique patient-specific antigens. The purpose of the present phase I/II trial was to evaluate the feasibility and safety of the vaccine, and the ability of the DCs to elicit T-cell responses in melanoma patients. Further, we compared intradermal (i.d.) and intranodal (i.n.) vaccine administration. Twenty-two patients with advanced malignant melanoma were included, each receiving four weekly vaccines. Monocyte-derived DCs were transfected with tumor-mRNA by electroporation, matured and cryopreserved. We obtained successful vaccine production for all patients elected. No serious adverse effects were observed. A vaccine-specific immune response was demonstrated in 9/19 patients evaluable by T-cell assays (T-cell proliferation/interferon-gamma ELISPOT) and in 8/18 patients evaluable by delayed-type hypersensitivity (DTH) reaction. The response was demonstrated in 7/10 patients vaccinated intradermally and in 3/12 patients vaccinated intranodally. We conclude that immuno-gene-therapy with the described DC-vaccine is feasible and safe, and that the vaccine can elicit in vivo T-cell responses against antigens encoded by the transfected tumor-mRNA. The response rates do not suggest an advantage in applying i.n. vaccination.

Bortezomib induces selective depletion of alloreactive T lymphocytes and decreases the production of Th1 cytokines

We explored the ability of the proteasome inhibitor bortezomib, which prevents nuclear factor kappaB (NF-kappaB) activation, to block T-cell activation, proliferation, and survival within alloreactive compared with resting T cells. For this purpose, T cells were stimulated with PHA, alphaCD3/alphaCD28, or allogeneic dendritic cells or through mixed lymphocyte cultures. NF-kappaB expression increased in activated T lymphocytes compared with resting T cells. Of interest, the higher the NF-kappaB expression, the more intense the proliferative blockade induced by bortezomib. Moreover, after mixed lymphocyte reaction (MLR) cultures, alloreactive T cells were 2 logs more sensitive to bortezomib-induced apoptosis than the resting T-cell counterpart. This effect was due to a selective induction of apoptosis among activated T cells that was related to caspase activation and cleavage of the antiapoptotic bcl-2 protein and was partially abolished by the addition of the pancaspase inhibitor Z-VAD-FMK. In addition, after secondary MLR, the number of activated T cells was significantly reduced among T lymphocytes previously cultured with bortezomib when cells from the same donor were used as stimulating cells. By contrast, when third-party donor cells were used as stimulating cells, no significant differences were observed between T lymphocytes previously exposed or not to the drug, indicating a highly specific depletion of T lymphocytes alloreactive against primary donor antigens. The addition of bortezomib decreased not only the proliferation and viability of activated T lymphocytes but also the levels of IFNgamma and IL-2, which were significantly decreased among activated T cells cultured with bortezomib at doses ranging from 10 to 100 nM. In conclusion, at concentrations reached in the clinical setting, bortezomib induces selective apoptosis and decreases Th1 response among alloreactive T lymphocytes while it barely affects unstimulated T cells. These results establish the basis for the clinical use of bortezomib in the management of graft-versus-host disease (GVHD).

High donor FOXP3-positive regulatory T-cell (Treg) content is associated with a low risk of GVHD following HLA-matched allogeneic SCT

Regulatory T cells (T(reg)s) that constitutively express FOXP3 are instrumental to the maintenance of tolerance and may suppress graft-versus-host disease (GVHD) in humans. To determine whether regulatory T cells in allogeneic stem cell transplants (SCTs) ameliorate GVHD after transplantation, we quantitated the coexpression of FOXP3 on CD4(+) T cells in 32 donor SCTs infused into HLA-matched siblings and examined GVHD incidence in respective recipients. High CD4(+)FOXP3(+) T-cell count in the donor was associated with a reduced risk of GVHD. We monitored T(reg)s during immune reconstitution in 21 patients with leukemia undergoing a T-cell-depleted allogeneic SCT. Early after SCT, there was a significant expansion in the CD4(+)FOXP3(+) T-cell compartment. A low CD4(+)FOXP3(+) T-cell count early after SCT (day 30) was associated with an increased risk of GVHD, and the ratio of CD4(+)FOXP3(+) T cells to CD4(+)CD25(+)FOXP3(-) T cells was significantly reduced in patients with GVHD, suggesting diminished control of effector T cells. Our findings suggest that graft T(reg) content may predict for risk of GVHD after SCT. Determining the T(reg) levels in the donor and manipulating T(reg)s early after transplantation may provide a new approach to controlling GVHD.

CD4+CD25+ regulatory T cells in human hematopoietic cell transplantation

Naturally occurring CD4+CD25+ regulatory T cells (T(reg)) are differentiated T lymphocytes actively involved in the control of peripheral immunity. Over the past few years, a number of animal studies have demonstrated the critical role of these cells in the outcome of allogeneic hematopoietic stem cell transplantation (HCT). In these models, T(reg) can exert a potent suppressive effect on immune effector cells reactive to host antigens and prevent graft versus host disease (GVHD) while preserving the graft-versus-leukemia effect (GVL). The present review summarizes current knowledge on the role of T(reg) populations in humans following allogeneic HCT. Recent investigations focusing on T(reg) in transplant patients have generated conflicting results mostly due to the use of different parameters to assess T(reg). Nonetheless, these studies suggested that an imbalance between T(reg) and effector cells during immune reconstitution can substantially impair regulatory mechanisms and contributes to the development of GVHD. Building on these studies, a number of therapeutic strategies are being developed to positively modulate T(reg) pools in vivo and prevent or even correct GVHD. Conversely, clinical interventions can also be envisaged to decrease T(reg) activity in vivo and enhance the GVL effect. These potential strategies are discussed herein. Coming years will undoubtedly yield additional knowledge on how to use T(reg) subsets in vivo and successfully control and modulate immune responses in patients post-HCT.

Granulomatous pneumonitis, sclerosing cholangitis, and pancreatitis in a child with Crohn disease: response to infliximab

Fulminating acute ulcerative colitis (UC) is a potentially life threatening medical emergency. Up to 30% of individuals respond poorly to corticosteroids alone and second line medical or surgical therapies are indicated. We describe the successful use of chimeric anti-CD25 therapy in 4 such children poorly responsive to combined therapy with intravenous steroids and calcineurin inhibitors with a pretreatment predictive risk of colectomy of 85-100%. Clinical disease activity scores normalized within 72 hours of anti-CD25 administration and colonic histology provided evidence of mucosal healing within 10-14 days. None required emergency colectomy. Anti-CD25 is efficacious in fulminating UC and randomized placebo controlled trials appear indicated.

Chronic Graft-Versus-Host Disease

Chronic graft-versus-host disease (cGVHD) is the most common and severe complication among patients surviving >100 days after allogeneic transplantation. It starts with the expansion of donor T cells in response to alloantigens or autoantigens that are unchecked by normal thymic or peripheral mechanisms of deletion. The T cells induce damage to target organs either directly through cytolytic attack, inflammatory cytokines and fibrosis, or by promoting B cell activation and production of autoantibodies. HLA disparity, donor and patient age and sex, source of progenitor cells, graft composition and previous acute GVHD are the main factors that predict the risk of developing cGVHD. Once the diagnosis has been established, patients needing treatment (extensive cGVHD) must be identified. Poor prognostic factors such as extensive skin involvement, thrombocytopenia and progressive-type onset of cGVHD must be considered in order to define the immunosuppressive treatment requirements. Prednisone, together with a calcineurin inhibitor such as ciclosporin or tacrolimus, can be considered the standard regimen as primary treatment for cGVHD. Using that approach, among high-risk patients (identified as those with extensive cGVHD plus thrombocytopenia) 3-year survival reached 52%. Concerning salvage regimens, to date there is no clear standard regimen for cGVHD treatment, the best choice being to enter the patient into a clinical trial. Immunosuppressive drugs that inhibit T cell activation, proliferation or survival, such as mycophenolate mofetil, the anti-interleukin-2 alpha receptor antagonist daclizumab, sirolimus (rapamycin), extracorporeal photopheresis and pentostatin (deoxycoformycin), among other agents, have been used with a very wide range of complete responses ranging from 5% to 50%. In addition, anti-cytokine or B cell inhibitors such as etanercept or rituximab have also been evaluated. The severe immunosuppression induced by those drugs increases the risk of infectious complications and may have a deleterious effect on the graft versus tumour effect after transplant so that newer strategies based on the selective depletion of alloreactive T cells and induction of more specific immunotolerance against host tissues are required.

CD4+CD25+ Regulatory T Cells and Graft-Versus-Host Disease

Peripheral suppression of autoreactive T cells by specialized T-cell populations is one of several mechanisms ensuring self-tolerance within the adaptive immune system. Thymus-derived CD4+CD25+ T cells expressing the transcriptional repressor FOXP3 mediate such immunoregulatory functions and are pivotal for the prevention of autoimmunity. As peripheral tolerance induction is a prerequisite for successful treatment outcome after allogeneic hematopoietic stem cell transplantation (HSCT), the role of CD4+CD25+ T cells in transplantation models and clinical trials is now under investigation in many laboratories. Here we summarize recent results regarding protection from graft-versus-host disease (GVHD) by adoptively transferred CD4+CD25+ T cells in mice and discuss early findings from clinical studies in HSCT.

Selective depletion strategies in allogeneic stem cell transplantation

Despite improved prophylaxis and treatment, GvHD remains a major limitation to optimal allogeneic stem cell transplantation. Ex vivo selective depletion (SD) is a strategy to prevent GvHD, in which host-reactive donor lymphocytes are selectively eliminated from a PBSC allograft while useful donor immune function is preserved. The elimination of alloreactive and thereby GvHD-mediating T cells has been shown to be feasible in both pre-clinical and more recently clinical studies. However, SD techniques and the translational research needed for clinical application are still under development. Here we summarize and discuss the following aspects of the SD approach: selection of an appropriate allogeneic stimulator; the responder population; the alloresponse; methods for removal of alloreacting T cells; product testing; clinical considerations. Our review highlights the diversity of possible approaches and the need to develop different techniques for specific clinical applications.

Anti-CD25 monoclonal antibody (basiliximab) for prevention of graft-versus-host disease after haploidentical bone marrow transplantation for hematological malignancies

Haploidentical donors are available for most patients who need allografts but do not have matched donors. However, GVHD, rejection, delayed immune reconstitution, and infections have been significant barriers. We designed a haploidentical BMT protocol focusing on prevention of GVHD and rejection. A total of 53 leukemic patients underwent haploidentical G-CSF-primed BMT without ex vivo T-cell depletion. GVHD prophylaxis consisted of antithymocyte globulin, cyclosporine, methotrexate, and mycophenolate mofetil. In all, 38 patients (the CD25 group) received additional anti-CD25 monoclonal antibody basiliximab. The results were compared to 15 patients who did not receive basiliximab. All patients achieved trilineage engraftment with full-donor chimerism. The incidence of acute II-IV GVHD was 11% in the CD25 group vs 33% in the control group (P=0.046). The overall incidence of extensive chronic GVHD was 15%. T, B, and NK cells recovered within 12 months post transplant. The disease-free survival at 2 years was 53% with a median follow-up of 31 months. In conclusion, G-CSF primed haploidentical BMT along with sequential immunosuppressive agents as described here deserves further study.

Graft-versus-host disease: How to translate new insights into new therapeutic strategies

Graft-versus-host disease occurs when transplanted donor-derived T lymphocytes recognize major or minor histocompatibility complex proteins and their associated peptides expressed by recipient antigen-presenting cells. A widely accepted paradigm for the pathophysiology of acute GVHD is based on the existence of 3 sequential steps: (1) injury to the host environment (as would occur during conditioning regimens); (2) donor T-cell activation, proliferation, and differentiation; and (3) damage to the target tissue caused by either cytotoxicity or indirectly by inflammatory cytokines. In order to reduce the incidence of GVHD, recent studies have focused on methods of prophylaxis as well as novel treatments for established GVHD. We review each phase in the development of acute GVHD and discuss recently developed interventions aimed to prevent or treat GVHD by interfering with these pathways.