Phase I/II Trial of a Combination of Anti-CD3/CD7 Immunotoxins for Steroid-Refractory Acute Graft-versus-Host Disease

Advances in immunotoxin engineering: precision therapeutic strategies in modern oncology

Immunotoxins (ITs) are specialized therapeutic agents designed for targeted treatment, particularly in cancer therapy. They consist of a monoclonal antibody or antibody fragment linked to a potent cytotoxic agent, such as bacterial- or plant-derived toxins like diphtheria toxin, ricin, or pseudomonas exotoxin. The monoclonal antibody component specifically binds to antigens expressed on the surface of target cells, facilitating the internalization of the IT. Once inside the cell, the cytotoxic agent is released, disrupting essential cellular processes and leading to cell death. This targeted approach minimizes damage to healthy tissues while effectively eliminating diseased cells. The production of ITs involves two primary methods: recombinant fusion and chemical conjugation. In recombinant fusion, genetic engineering is used to create a fusion protein that combines the antibody and toxin, ensuring precise control over their ratio and functionality. In chemical conjugation, pre-existing antibodies are chemically linked to toxins, allowing for greater flexibility in combining different antibodies and cytotoxic agents. Each method has its advantages and challenges, influencing the specificity, production complexity, and therapeutic potential of the resulting ITs. As research advances, ITs continue to show promise not only in oncology but also in treating other diseases, including inflammatory conditions and atherosclerosis. The precise targeting and potent effects of ITs make them a valuable tool in the development of new therapeutic strategies.

New investigational drugs for steroid-refractory acute graft-versus-host disease: a review of the literature

INTRODUCTION

Steroid-refractory acute graft-versus-host disease (SR-aGVHD) remains a formidable obstacle in the field of allogeneic hematopoietic cell transplantation (allo-HCT), significantly contributing to patient morbidity and mortality. The current therapeutic landscape for SR-aGVHD is limited, often yielding suboptimal results, thereby emphasizing the urgent need for innovative and effective treatments.

AREAS COVERED

In light of the pivotal REACH2 trial, ruxolitinib phosphate, a Janus kinase inhibitor, has gained prominence as the standard treatment for SR-aGVHD. Nevertheless, a considerable number of patients either do not respond to or cannot tolerate this therapy. This review delves into emerging treatments for SR-aGVHD, including mesenchymal stromal cells (MSCs), fecal microbiota transplantation (FMT), CD3/CD7 blockade, neihulizumab, begelomab, tocilizumab, and vedolizumab. While some of these agents have shown encouraging results in early-phase trials, issues such as treatment-related toxicities and inconsistent responses in larger studies highlight the necessity for ongoing research.

EXPERT OPINION

Current trials exploring new agents and combination therapies offer hope for fulfilling the unmet clinical needs in SR-aGVHD, potentially leading to more effective and precise treatment strategies.

CD7 activation regulates cytotoxicity-driven pathology in systemic sclerosis, yielding a target for selective cell depletion

OBJECTIVES

Cytotoxic T cells and natural killer (NK) cells are central effector cells in cancer and infections. Their effector response is regulated by activating and inhibitory receptors. The regulation of these cells in systemic autoimmune diseases such as systemic sclerosis (SSc) is less defined.

METHODS

We conducted ex vivo analysis of affected skin and blood samples from 4 SSc patient cohorts (a total of 165 SSc vs 80 healthy individuals) using single-cell transcriptomics, flow cytometry and multiplex immunofluorescence staining. We further analysed the effects of costimulatory modulation in functional assays, and in a severely affected SSc patient who was treated on compassionate use with a novel anti-CD3/CD7 immunotoxin treatment.

RESULTS

Here, we show that SSc-affected skin contains elevated numbers of proliferating T cells, cytotoxic T cells and NK cells. These cells selectively express the costimulatory molecule CD7 in association with cytotoxic, proinflammatory and profibrotic genes, especially in recent-onset and severe disease. We demonstrate that CD7 regulates the cytolytic activity of T cells and NK cells and that selective depletion of CD7+ cells prevents cytotoxic cell-induced fibroblast contraction and inhibits their profibrotic phenotype. Finally, anti-CD3/CD7 directed depletive treatment eliminated CD7+ skin cells and stabilised disease manifestations in a severely affected SSc patient.

CONCLUSION

Together, the findings imply costimulatory molecules as key regulators of cytotoxicity-driven pathology in systemic autoimmune disease, yielding CD7 as a novel target for selective depletion of pathogenic cells.

Antibody-drug conjugates come of age in oncology

Antibody-drug conjugates (ADCs) combine the specificity of monoclonal antibodies with the potency of highly cytotoxic agents, potentially reducing the severity of side effects by preferentially targeting their payload to the tumour site. ADCs are being increasingly used in combination with other agents, including as first-line cancer therapies. As the technology to produce these complex therapeutics has matured, many more ADCs have been approved or are in late-phase clinical trials. The diversification of antigenic targets as well as bioactive payloads is rapidly broadening the scope of tumour indications for ADCs. Moreover, novel vector protein formats as well as warheads targeting the tumour microenvironment are expected to improve the intratumour distribution or activation of ADCs, and consequently their anticancer activity for difficult-to-treat tumour types. However, toxicity remains a key issue in the development of these agents, and better understanding and management of ADC-related toxicities will be essential for further optimization. This Review provides a broad overview of the recent advances and challenges in ADC development for cancer treatment.

Recent advances in graft-versus-host disease

Acute and chronic graft-versus-host disease (GVHD) continue to present a significant challenge to physicians, accounting for considerable haematopoietic stem cell transplant (HSCT)-related morbidity and mortality, particularly those patients with steroid-refractory disease. In this review, we discuss recent advances in understanding the underlying pathophysiology, prevention and management of acute and chronic GVHD. Barriers to progress include the difficulty in obtaining high-quality evidence with sufficient patient numbers to identify optimal preventative and treatment strategies, with the heterogeneity of multiple patient, donor, graft and transplant-related factors, in addition to limited availability of human tissue to study the underlying pathophysiology, particularly in steroid-refractory disease. Continued collaborative efforts to improve our understanding of the pathophysiology involved, particularly in steroid-refractory disease, identification of biomarkers to permit risk stratification, and further well-designed randomised clinical trials are essential to help physicians determine optimal GVHD preventative and treatment strategies for each individual patient.

Synthesis of an Anti-CD7 Recombinant Immunotoxin Based on PE24 in CHO and E. coli Cell-Free Systems

Recombinant immunotoxins (RITs) are an effective class of agents for targeted therapy in cancer treatment. In this article, we demonstrate the straight-forward production and testing of an anti-CD7 RIT based on PE24 in a prokaryotic and a eukaryotic cell-free system. The prokaryotic cell-free system was derived from Escherichia coli BL21 StarTM (DE3) cells transformed with a plasmid encoding the chaperones groEL/groES. The eukaryotic cell-free system was prepared from Chinese hamster ovary (CHO) cells that leave intact endoplasmic reticulum-derived microsomes in the cell-free reaction mix from which the RIT was extracted. The investigated RIT was built by fusing an anti-CD7 single-chain variable fragment (scFv) with the toxin domain PE24, a shortened variant of Pseudomonas Exotoxin A. The RIT was produced in both cell-free systems and tested for antigen binding against CD7 and cell killing on CD7-positive Jurkat, HSB-2, and ALL-SIL cells. CD7-positive cells were effectively killed by the anti-CD7 scFv-PE24 RIT with an IC50 value of 15 pM to 40 pM for CHO and 42 pM to 156 pM for E. coli cell-free-produced RIT. CD7-negative Raji cells were unaffected by the RIT. Toxin and antibody domain alone did not show cytotoxic effects on either CD7-positive or CD7-negative cells. To our knowledge, this report describes the production of an active RIT in E. coli and CHO cell-free systems for the first time. We provide the proof-of-concept that cell-free protein synthesis allows for on-demand testing of antibody−toxin conjugate activity in a time-efficient workflow without cell lysis or purification required.

Strategies to mitigate the on- and off-target toxicities of recombinant immunotoxins: an antibody engineering perspective

Targeted cancer therapies using immunotoxins has achieved remarkable efficacies in hematological malignancies. However, the clinical development of immunotoxins is also faced with many challenges like anti-drug antibodies and dose-limiting toxicity issues. Such a poor efficacy/safety ratio is also the major hurdle in the research and development of antibody-drug conjugates. From an antibody engineering perspective, various strategies were summarized/proposed to tackle the notorious on target off tumor toxicity issues, including passive strategy (XTENylation of immunotoxins) and active strategies (modulating the affinity and valency of the targeting moiety of immunotoxins, conditionally activating immunotoxins in the tumor microenvironments and reconstituting split toxin to reduce systemic toxicity etc.). By modulating the functional characteristics of the targeting moiety and the toxic moiety of immunotoxins, selective tumor targeting can be augmented while sparing the healthy cells in normal tissues expressing the same target of interest. If successful, the improved therapeutic index will likely help to address the dose-limiting toxicities commonly observed in the clinical trials of various immunotoxins.

Natural Killer Cells in Hepatic Ischemia-Reperfusion Injury

Ischemia-reperfusion injury can be divided into two phases, including insufficient supply of oxygen and nutrients in the first stage and then organ injury caused by immune inflammation after blood flow recovery. Hepatic ischemia-reperfusion is an important cause of liver injury post-surgery, consisting of partial hepatectomy and liver transplantation, and a central driver of graft dysfunction, which greatly leads to complications and mortality after liver transplantation. Natural killer (NK) cells are the lymphocyte population mainly involved in innate immune response in the human liver. In addition to their well-known role in anti-virus and anti-tumor defense, NK cells are also considered to regulate the pathogenesis of liver ischemia-reperfusion injury under the support of more and more evidence recently. The infiltration of NK cells into the liver exacerbates the hepatic ischemia-reperfusion injury, which could be significantly alleviated after depletion of NK cells. Interestingly, NK cells may contribute to both liver graft rejection and tolerance according to their origins. In this article, we discussed the development of liver NK cells, their role in ischemia-reperfusion injury, and strategies of inhibiting NK cell activation in order to provide potential possibilities for translation application in future clinical practice.

The Role of Fecal Microbiota Transplantation in the Treatment of Acute Graft-versus-Host Disease

The number of allogeneic hematopoietic stem cell transplantations conducted worldwide is constantly rising. Together with that, the absolute number of complications after the procedure is increasing, with graft-versus-host disease (GvHD) being one of the most common. The standard treatment is steroid administration, but only 40–60% of patients will respond to the therapy and some others will be steroid-dependent. There is still no consensus regarding the best second-line option, but fecal microbiota transplantation (FMT) has shown encouraging preliminary and first clinically relevant results in recent years and seems to offer great hope for patients. The reason for treatment of steroid-resistant acute GvHD using this method derives from studies showing the significant immunomodulatory role played by the intestinal microbiota in the pathogenesis of GvHD. Depletion of commensal microbes is accountable for aggravation of the disease and is associated with decreased overall survival. In this review, we present the pathogenesis of GvHD, with special focus on the special role of the gut microbiota and its crosstalk with immune cells. Moreover, we show the results of studies and case reports to date regarding the use of FMT in the treatment of steroid-resistant acute GvHD.

Steroid-Refractory Gut Graft-Versus-Host Disease: What We Have Learned From Basic Immunology and Experimental Mouse Model

Intestinal graft-versus-host disease (Gut-GVHD) is one of the major causes of mortality after allogeneic hematopoietic stem cell transplantation (allo-HSCT). While systemic glucocorticoids (GCs) comprise the first-line treatment option, the response rate for GCs varies from 30% to 50%. The prognosis for patients with steroid-refractory acute Gut-GVHD (SR-Gut-aGVHD) remains dismal. The mechanisms underlying steroid resistance are unclear, and apart from ruxolitinib, there are no approved treatments for SR-Gut-aGVHD. In this review, we provide an overview of the current biological understanding of experimental SR-Gut-aGVHD pathogenesis, the advanced technology that can be applied to the human SR-Gut-aGVHD studies, and the potential novel therapeutic options for patients with SR-Gut-aGVHD.

OUP accepted manuscript

Graft-versus-host disease (GVHD) is a common complication of allogeneic hematopoietic cell transplantation (HCT) and is associated with significant morbidity and mortality. For many years, there have been few effective treatment options for patients with GVHD. First-line systemic treatment remains corticosteroids, but up to 50% of patients will develop steroid-refractory GVHD and the prognosis for these patients is poor. Elucidation of the pathophysiological mechanisms of acute and chronic GVHD has laid a foundation for novel therapeutic approaches. Since 2017, there have now been 4 approvals by the US Food and Drug Administration (FDA) for GVHD. Ruxolitinib, an oral selective JAK1/2 inhibitor, received FDA approval for the treatment of steroid-refractory acute GVHD in 2019 and remains the only agent approved for acute GVHD. There are currently 3 FDA approvals for the treatment of chronic GVHD: (1) ibrutinib, a BTK inhibitor traditionally used for B-cell malignancies, was the first agent approved for chronic GVHD after failure of one or more lines of systemic therapy, (2) belumosudil, an oral selective inhibitor of ROCK2, for patients with chronic GVHD who received at least 2 prior lines of treatment, and (3) ruxolitinib for chronic GVHD after failure of one or two lines of systemic therapy. In this review, we highlight the clinical data which support these FDA approvals in acute and chronic GVHD with a focus on mechanism of actions, clinical efficacy, and toxicities associated with these agents.

New therapeutic targets and biomarkers for acute graft-versus-host disease (GVHD)

INTRODUCTION

Acute Graft-versus-Host Disease (GVHD) is the major toxicity of allogeneic hematopoietic cell transplantation (HCT). Systemic steroids are the standard primary treatment but only half of the patients will respond completely and the survival of steroid-refractory patients is poor. The gastrointestinal (GI) tract is a key target organ that usually determines a patient's response to therapy.

AREAS COVERED

This review summarizes the use of clinical grading systems and biomarkers in GVHD treatment and highlights pathophysiologic phases of acute GVHD as context for the mechanisms of action and therapeutic targets of various approaches. We reviewed >100 publications and performed a search of ongoing, current clinical trials on the emerging therapeutic targets for prophylaxis and treatment of acute GVHD. Search databases included clinicaltrials.gov and PUBMED. Search terms and keywords included 'acute graft-versus-host disease,' 'GVHD,' 'graft versus host,' 'treatment.'

EXPERT OPINION

Future strategies will employ a risk-adapted therapy using biomarkers, which more accurately predict 6-month NRM. Strategies for high-risk patients will inhibit GI tract damage by selective targeting of effectors (e.g. inhibition of JAK signaling in T cells), blockade of trafficking through mAbs against integrin receptors, or enhancement of target cell survival. Future strategieswill reduce immunosuppression to avoid risk of infections and relapse.

Immunotoxins and nanobody-based immunotoxins: review and update

Immunotoxins (ITs) are protein-based drugs that compose of targeting and cytotoxic moieties. After binding the IT to the specific cell-surface antigen, the IT internalises into the target cell and kills it. Targeting and cytotoxic moieties usually include monoclonal antibodies and protein toxins with bacterial or plant origin, respectively. ITs have been successful in haematologic malignancies treatment. However, ITs penetrate poorly into solid tumours because of their large size. Use of camelid antibody fragments known as nanobodies (Nbs) as a targeting moiety may overcome this problem. Nbs are the smallest fragment of antibodies with excellent tumour tissue penetration. The ability to recognise cryptic (immuno-evasive) target antigens, low immunogenicity, and high-affinity are other fundamental characteristics of Nbs that make them suitable candidates in targeted therapy. Here, we reviewed and discussed the structure and function of ITs, Nbs, and nanobody-based ITs. To gain sound insight into the issue at hand, we focussed on nanobody-based ITs.

GVHD Prophylaxis 2020

Graft-vs. host disease (GVHD), both acute and chronic are among the chief non-relapse complications of allogeneic transplantation which still cause substantial morbidity and mortality despite significant advances in supportive care over the last few decades. The prevention of GVHD therefore remains critical to the success of allogeneic transplantation. In this review we briefly discuss the pathophysiology and immunobiology of GVHD and the current standards in the field which remain centered around calcineurin inhibitors. We then discuss important translational advances in GVHD prophylaxis, approaching these various platforms from a mechanistic standpoint based on the pathophysiology of GVHD including in-vivo and ex-vivo T-cell depletion alongwith methods of selective T-cell depletion, modulation of T-cell co-stimulatory pathways (checkpoints), enhancing regulatory T-cells (Tregs), targeting T-cell trafficking as well as cytokine pathways. Finally we highlight exciting novel pre-clinical research that has the potential to translate to the clinic successfully. We approach these methods from a pathophysiology based perspective as well and touch upon strategies targeting the interaction between tissue damage induced antigens and T-cells, regimen related endothelial toxicity, T-cell co-stimulatory pathways and other T-cell modulatory approaches, T-cell trafficking, and cytokine pathways. We end this review with a critical discussion of existing data and novel therapies that may be transformative in the field in the near future as a comprehensive picture of GVHD prophylaxis in 2020. While calcineurin inhibitors remain the standard, post-transplant eparinsphamide originally developed to facilitate haploidentical transplantation is becoming an attractive alternative to traditional calcinuerin inhibitor based prophylaxis due to its ability to reduce severe forms of acute and chronic GVHD without compromising other outcomes, even in the HLA-matched setting. In addition T-cell modulation, particularly targeting some important T-cell co-stimulatory pathways have resulted in promising outcomes and may be a part of GVHD prophylaxis in the future. Novel approaches including targeting early events in GVHD pathogenesis such as interactions bvetween tissue damage associated antigens and T-cells, endothelial toxicity, and T-cell trafficking are also promising and discussed in this review. GVHD prophylaxis in 2020 continues to evolve with novel exicitng therapies on the horizon based on a more sophisticated understanding of the immunobiology of GVHD.

Immunopathology and biology-based treatment of steroid-refractory graft-versus-host disease

Acute graft-versus-host disease (GVHD) is 1 of the major life-threating complications after allogeneic cell transplantation. Although steroids remain first-line treatment, roughly one-half of patients will develop steroid-refractory GVHD (SR-GVHD), which portends an extremely poor prognosis. Many agents that have shown encouraging response rates in early phase 1/2 trials for prevention and treatment have been unsuccessful in demonstrating a survival advantage when applied in the setting of SR-GVHD. The discovery of novel treatments has been further complicated by the absence of clinically informative animal models that address what may reflect a distinct pathophysiology. Nonetheless, the combined knowledge of established bone marrow transplantation models and recent human trials in SR-GVHD patients are beginning to illuminate novel mechanisms for inhibiting T-cell signaling and promoting tissue tolerance that provide an increased understanding of the underlying biology of SR-GVHD. Here, we discuss recent findings of newly appreciated cellular and molecular mechanisms and provide novel translational opportunities for advancing the effectiveness of treatment in SR-GVHD.

Current and Emerging Targeted Therapies for Acute Graft-Versus-Host Disease

Acute graft-versus-host disease (GVHD), the major complication after allogeneic hematopoietic cell transplant (HCT), develops in approximately 50% of patients. The primary treatment is high-dose systemic steroids, but treatment failure is common, and steroid-refractory (SR) GVHD is the leading cause of non-relapse mortality after allogeneic HCT. Ruxolitinib became the first treatment for SR GVHD to obtain US Food and Drug Administration approval, and other new treatments are actively being studied. We searched the literature using the PubMed database and clinical trials using ClinicalTrials.gov to identify the most promising new treatments for GVHD. In this review, we categorize potential new treatments for GVHD by their mechanism of action (e.g., antibodies that deplete T cells or prevent their trafficking to target tissues, proteasome inhibitors, tyrosine kinase inhibitors, and other agents) and summarize the results from clinical trials.

Experimental Pharmaceuticals for Steroid-Refractory Acute Graft-versus-Host Disease

Acute GVHD (aGVHD) is a significant complication after allogeneic hematopoietic cell transplantation (HCT), occurring in up to 70% of HCT recipients. Steroid-refractory aGVHD represents a subset of patients failing initial therapy and is particularly morbid, with only 30% of patients surviving long term. Better therapies are urgently required for these patients. Here, we discuss recent advancements in the management of SR-aGVHD. We review the currently available therapies for SR-aGVHD including the results of the REACH1 and REACH2 trials, which provide the basis for the use of ruxolitinib for the treatment of SR-aGVHD. We additionally discuss newer agents under clinical investigation and will highlight the niche these agents may fill to further improve outcomes in aGVHD patient care.

Immunogenicity of Immunotoxins Containing Pseudomonas Exotoxin A: Causes, Consequences, and Mitigation

Immunotoxins are cytolytic fusion proteins developed for cancer therapy, composed of an antibody fragment that binds to a cancer cell and a protein toxin fragment that kills the cell. Pseudomonas exotoxin A (PE) is a potent toxin that is used for the killing moiety in many immunotoxins. Moxetumomab Pasudotox (Lumoxiti) contains an anti-CD22 Fv and a 38 kDa portion of PE. Lumoxiti was discovered in the Laboratory of Molecular Biology at the U.S. National Cancer Institute and co-developed with Medimmune/AstraZeneca to treat hairy cell leukemia. In 2018 Lumoxiti was approved by the US Food and Drug Administration for the treatment of drug-resistant Hairy Cell Leukemia. Due to the bacterial origin of the killing moiety, immunotoxins containing PE are highly immunogenic in patients with normal immune systems, but less immunogenic in patients with hematologic malignancies, whose immune systems are often compromised. LMB-100 is a de-immunized variant of the toxin with a humanized antibody that targets mesothelin and a PE toxin that was rationally designed for diminished reactivity with antibodies and B cell receptors. It is now being evaluated in clinical trials for the treatment of mesothelioma and pancreatic cancer and is showing somewhat diminished immunogenicity compared to its un modified parental counterpart. Here we review the immunogenicity of the original and de-immunized PE immunotoxins in mice and patients, the development of anti-drug antibodies (ADAs), their impact on drug availability and their effect on clinical efficacy. Efforts to mitigate the immunogenicity of immunotoxins and its impact on immunogenicity will be described including rational design to identify, remove, or suppress B cell or T cell epitopes, and combination of immunotoxins with immune modulating drugs.

Development of Glypican-3 Targeting Immunotoxins for the Treatment of Liver Cancer: An Update

Hepatocellular carcinoma (HCC) accounts for most liver cancers and represents one of the deadliest cancers in the world. Despite the global demand for liver cancer treatments, there remain few options available. The U.S. Food and Drug Administration (FDA) recently approved Lumoxiti, a CD22-targeting immunotoxin, as a treatment for patients with hairy cell leukemia. This approval helps to demonstrate the potential role that immunotoxins can play in the cancer therapeutics pipeline. However, concerns have been raised about the use of immunotoxins, including their high immunogenicity and short half-life, in particular for treating solid tumors such as liver cancer. This review provides an overview of recent efforts to develop a glypican-3 (GPC3) targeting immunotoxin for treating HCC, including strategies to deimmunize immunotoxins by removing B- or T-cell epitopes on the bacterial toxin and to improve the serum half-life of immunotoxins by incorporating an albumin binding domain.

Treatment and unmet needs in steroid-refractory acute graft-versus-host disease

Acute graft-versus-host disease (aGVHD) is a common complication of allogeneic hematopoietic stem cell transplantation (alloHCT) and is a major cause of morbidity and mortality. Systemic steroid therapy is the first-line treatment for aGVHD, although about half of patients will become refractory to treatment. As the number of patients undergoing alloHCT increases, developing safe and effective treatments for aGVHD will become increasingly important, especially for those whose disease becomes refractory to systemic steroid therapy. This paper reviews current treatment options for patients with steroid-refractory aGVHD and discusses data from recently published clinical studies to outline emerging therapeutic strategies.

Ruxolitinib: a potential treatment for corticosteroid refractory acute graft-versus-host disease

INTRODUCTION

Allogeneic transplantation represents a potentially curative procedure for various lethal conditions; however, it is associated with serious immune mediated complications. The most serious complication is graft-versus-host disease (GVHD). Acute GVHD (aGVHD) is unresponsive to initial corticosteroid therapy in ~40% of cases. Corticosteroid-refractory aGVHD (CR-aGVHD) represents a significant unmet need with nearly 60% mortality in patients developing this state.

AREAS COVERED

We review landmark trials which led to the US FDA approval of Ruxolitinb for the treatment of CR-aGVHD. Ruxolitinib phosphate is a Janus Kinase 1 and 2 inhibitor which inhibits pro-inflammatory signaling, and modulates T-cell subsets to an anti-inflammatory phenotype. Ruxolitinib was recently prospectively studied for the treatment of CR-aGVHD in the REACH1 trial, which added Ruxolitinib to corticosteroid therapy. This trial demonstrated favorable results with 73% of patients ultimately responding. Among responders, over 70% remained alive at 6 months. These results led to the US FDA to approve ruxolitinib as treatment for CR-aGVHD, the first approval of its kind.

EXPERT OPINION

Ruxolitinib represents the standard option for CR-aGVHD. Future studies should identify patients less likely to respond to ruxolitinib and/or focus on a more targeted approaches to reduce infectious complications and cytopenias seen with this drug.

Treatment of steroid resistant acute graft versus host disease with an anti-CD26 monoclonal antibody-Begelomab

We have treated 69 patients with steroid refractory acute graft versus host disease (SR-aGvHD), with an anti-CD26 monoclonal antibody (Begelomab): 28 patients in two prospective studies (EudraCT No. 2007-005809-21; EudraCT No. 2012-001353-19), and 41 patients on a compassionate use study. The median age of patients was 42 and 44 years; the severity of GvHD was as follows: grade II in 8 patients, grade III in 33, and grade IV in 28 patients. There were no adverse events directly attributable to the antibody. Day 28 response was 75% in the prospective studies and 61% in the compassionate use patients, with complete response rates of 11 and 12%. Response for grade III GvHD was 83 and 73% in the two groups; response in grade IV GvHD was 66 and 56% in the two groups. Non relapse mortality (NRM) at 6 months was 28 and 38%. Overall there were 64, 56, 68% responses for skin, liver, and gut stage 3-4 GvHD. The overall survival at 1 year was 50% for the prospective studies and 33% for the compassionate use patients. In conclusion, Begelomab induces over 60% responses in SR-aGvHD, including patients with severe gut and liver GvHD, having failed one or more lines of treatment.

Engineering of Ribosome-inactivating Proteins for Improving Pharmacological Properties

Ribosome-inactivating proteins (RIPs) are N-glycosidases, which depurinate a specific adenine residue in the conserved α-sarcin/ricin loop (α-SRL) of rRNA. This loop is important for anchoring elongation factor (EF-G for prokaryote or eEF2 for eukaryote) in mRNA translocation. Translation is inhibited after the attack. RIPs therefore may have been applied for anti-cancer, and anti-virus and other therapeutic applications. The main obstacles of treatment with RIPs include short plasma half-life, non-selective cytotoxicity and antigenicity. This review focuses on the strategies used to improve the pharmacological properties of RIPs on human immunodeficiency virus (HIV) and cancers. Coupling with polyethylene glycol (PEG) increases plasma time and reduces antigenicity. RIPs conjugated with antibodies to form immunotoxins increase the selective toxicity to target cells. The prospects for future development on the engineering of RIPs for improving their pharmacological properties are also discussed.

Critical Issues in the Development of Immunotoxins for Anticancer Therapy

Immunotoxins (ITs) are attractive anticancer modalities aimed at cancer-specific delivery of highly potent cytotoxic protein toxins. An IT consists of a targeting domain (an antibody, cytokine, or another cell-binding protein) chemically conjugated or recombinantly fused to a highly cytotoxic payload (a bacterial and plant toxin or human cytotoxic protein). The mode of action of ITs is killing designated cancer cells through the effector function of toxins in the cytosol after cellular internalization via the targeted cell-specific receptor-mediated endocytosis. Although numerous ITs of diverse structures have been tested in the past decades, only 3 ITs-denileukin diftitox, tagraxofusp, and moxetumomab pasudotox-have been clinically approved for treating hematological cancers. No ITs against solid tumors have been approved for clinical use. In this review, we discuss critical research and development issues associated with ITs that limit their clinical success as well as strategies to overcome these obstacles. The issues include off-target and on-target toxicities, immunogenicity, human cytotoxic proteins, antigen target selection, cytosolic delivery efficacy, solid-tumor targeting, and developability. To realize the therapeutic promise of ITs, novel strategies for safe and effective cytosolic delivery into designated tumors, including solid tumors, are urgently needed.

Outcomes and Predictors of Response in Steroid-Refractory Acute Graft-versus-Host Disease

The prognosis of steroid-refractory acute graft-versus-host disease (aGVHD) is poor, and predictors of response and survival are unclear. In an exploratory analysis of 203 steroid-refractory aGVHD patients with prospectively collected GVHD data who received antithymocyte globulin, etanercept, or mycophenolate mofetil (MMF) as second-line treatment, we determined the predictors of day 28 response, 2-year overall survival, and 2-year nonrelapse mortality (NRM). To minimize the risk of finding false-positive results, we used least absolute shrinkage and selection operator regression, aggressively eliminating variables that are unlikely to be associated with outcome. Day 28 response to second-line therapy was 38% (complete response, 23%), with a 2-year overall survival of 25% and a 2-year NRM of 62%. Factors associated with response were GVHD prophylaxis, organ involvement, and initial aGVHD to steroid-refractory aGVHD interval. Specifically, compared with cyclosporine/MMF as GVHD prophylaxis, the odds ratio (OR) for calcineurin inhibitor/methotrexate was .8 and for cyclosporine/prednisone .6. The OR for aGVHD to steroid-refractory aGVHD interval ≥ 14 versus <14 days was 1.3. The ORs for skin only involvement and gut or liver only involvement when compared with multiorgan involvement were 1.4 and 1.2, respectively. The only variable associated with worse survival was age, with a hazard ratio (HR) per decade of 1.04 for overall mortality. Similarly, age was the only variable associated with NRM (HR per decade, 1.02). When compared with complete response, no response at day 28 increased the risk of death (HR, 2.4; 95% confidence interval, 1.5 to 3.7). In conclusion, by means of an underused statistical technique in the field of transplantation, we identified predictors of response and survival in steroid-refractory aGVHD. Our results highlight the importance of developing novel treatment strategies because current treatments yield poor outcomes.