Anti-CD45 PBD-based antibody-drug conjugates are effective targeted conditioning agents for gene therapy and stem cell transplant

Stem cell gene therapy and hematopoietic stem cell transplantation (SCT) require conditioning to ablate the recipient's hematopoietic stem cells (HSCs) and create a niche for gene-corrected/donor HSCs. Conventional conditioning agents are non-specific, leading to off-target toxicities and resulting in significant morbidity and mortality. We developed tissue-specific anti-human CD45 antibody-drug conjugates (ADCs), using rat IgG2b anti-human CD45 antibody clones YTH24.5 and YTH54.12, conjugated to cytotoxic pyrrolobenzodiazepine (PBD) dimer payloads with cleavable (SG3249) or non-cleavable (SG3376) linkers. In vitro, these ADCs internalized to lysosomes for drug release, resulting in potent and specific killing of human CD45+ cells. In humanized NSG mice, the ADCs completely ablated human HSCs without toxicity to non-hematopoietic tissues, enabling successful engraftment of gene-modified autologous and allogeneic human HSCs. The ADCs also delayed leukemia onset and improved survival in CD45+ tumor models. These data provide proof of concept that conditioning with anti-human CD45-PBD ADCs allows engraftment of donor/gene-corrected HSCs with minimal toxicity to non-hematopoietic tissues. Our anti-CD45-PBDs or similar agents could potentially shift the paradigm in transplantation medicine that intensive chemo/radiotherapy is required for HSC engraftment after gene therapy and allogeneic SCT. Targeted conditioning both improve the safety and minimize late effects of these procedures, which would greatly increase their applicability.

Abstract 2638: Preclinical development of ADCT-212, a PSMA-targeted antibody-drug conjugate employing the pyrrolobenzodiazepine dimer SG2000 for PSMA-expressing cancers

Prostate-specific membrane antigen (PSMA) is a membrane-bound glutamate carboxypeptidase that is highly expressed in nearly all prostate cancers with the highest expression in metastatic castration-resistant prostate cancer. Moreover, PSMA is expressed in the neovasculature that supplies most non-prostatic solid tumors, including carcinomas of the lung, colon, breast, kidney, liver, and pancreas. ADCT-212 is an antibody-drug conjugate composed of the human IgG1 antibody 2A10 directed against human PSMA, site-specifically conjugated using GlycoConnectTM technology to PL1801, which contains HydraspaceTM, a valine-alanine cleavable linker and the pyrrolobenzodiazepine (PBD) dimer warhead SG2000 (drug-antibody ratio of ~1.8). The purpose of this study was to characterize the in vitro and in vivo anti-tumor activity of ADCT-212 in human cancer cell lines and xenograft models and to determine its tolerability and pharmacokinetic (PK) in the rat. In vitro, ADCT-212 demonstrated potent cytotoxicity in a panel of PSMA-positive prostate cancer cell lines, whereas its activity was greatly reduced in PSMA-negative cell lines. ADCT-212 was efficiently internalized by PSMA-expressing LNCaP cells. Trafficking to the lysosomes started as early as 30 minutes and peaked at 1-2 hours post treatment. In line with the mechanism of action of the PBD dimer, ADCT-212 produced DNA interstrand cross-links (ICLs) that peaked by 12 hours and persisted for up to 36 hours post-treatment. In contrast, the peak of DNA ICLs formation for SG2000, the PBD dimer warhead alone, was observed immediately after 2-hour incubation, while a non-targeted PBD-ADC did not yield any appreciable DNA ICLs. Moreover, ADCT-212 showed indirect bystander killing activity in PSMA-negative PC3 cells incubated with conditioned medium from ADCT-212-treated LNCaP cells. In vivo, ADCT-212 showed strong antitumor activity against CWR22Rv1 and LNCaP prostate cancer xenograft models. In the CWR22Rv1 model, a tumor with heterogeneous PSMA expression, ADCT-212 achieved dose-dependent antitumor activity when administered as single dose at 2, 4 or 6 mg/kg, which resulted in increased survival compared to the control animals. In the LNCaP model, a single dose of ADCT-212 at 5 or 10 mg/kg resulted in strong and specific antitumor activity. Conversely, in the PSMA-negative PC3 xenograft model, ADCT-212 did not show anti-tumor activity compared to the controls, highlighting its target-mediated antitumor activity. ADCT-212 was tolerated as a single 20 mg/kg dose in male rats, with exposure data being indicative of a linear PK profile with a half-life of approximately 12 days. In conclusion, ADCT-212 demonstrated potent and specific in vitro and in vivo anti-tumor activity while it was stable and well tolerated in the rat, warranting further development of ADCT-212 into the clinic.

Citation Format: Francesca Zammarchi, Karin Havenith, Lolke de Haan, Ian Kirby, Narinder Janghra, Veronica Gil, Pedro Alves, Kristina Zaitseva, Meghann Kerr, Ben Leatherdale, Afroze Patel, Marie Thoelke, Shiran Huang, John A Hartley, Patrick H van Berkel. Preclinical development of ADCT-212, a PSMA-targeted antibody-drug conjugate employing the pyrrolobenzodiazepine dimer SG2000 for PSMA-expressing cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2638.

Abstract 1604: Preclinical development of ADCT-211, a novel pyrrolobenzodiazepine dimer-based antibody-drug conjugate targeting solid tumors expressing IL13RA2

Interleukin 13 receptor subunit alpha 2 (IL13RA2) is one of the two major receptors for the cytokine interleukin 13 (IL-13). While IL13RA1 has low affinity for IL-13 and it is expressed ubiquitously in humans, IL13RA2 has high binding affinity to IL-13 and its expression in normal tissues is mainly restricted to the testes. IL13RA2 was initially regarded as a decoy receptor because it has a short cytoplasmic tail with no known signaling motifs, and its binding to IL-13 does not lead to activation of the JAK/STAT6 pathway. However, recent studies demonstrated that IL-13-mediated IL13RA2 signaling occurs via STAT6-independent pathways. IL13RA2 is reported to be expressed at a high frequency in glioblastoma multiforme (GBM) as well as in other solid tumors including melanoma, renal cell carcinoma and adrenocortical carcinoma and is correlated with poor prognosis. ADCT-211 is an antibody-drug conjugate composed of HuCl47, a humanized IgG1 antibody directed against human IL13RA2, site-specifically conjugated using GlycoConnectTM technology to PL1801, which contains HydraspaceTM, a valine-alanine cleavable linker and the PBD dimer cytotoxin SG2000 (drug to antibody ratio ~ 1.8). The purpose of this study was to characterize the in vitro and in vivo anti-tumor activity of ADCT-211 in human cancer cell lines and xenograft models, to determine its safety, tolerability and pharmacokinetic (PK) in the rat and to measure IL13RA2 expression by immunohistochemistry (IHC) in human tumor specimens. HuCl47 showed specific binding to recombinant IL13RA2, while it did not bind to IL13RA1. In vitro, ADCT-211 had highly potent and targeted cytotoxicity against various IL13RA2-expressing solid cancer cell lines. In vivo, a single dose of ADCT-211 at 10 mg/kg was able to completely eradicate tumors in the subcutaneous (sc) A375 human melanoma xenograft model and resulted in 8/8 tumor-free survivors (TFS) at the end of the study on day 57. In the sc U251 human glioblastoma xenograft model, a single dose of ADCT-211 at 3.75 mg/kg showed potent and durable antitumor activity and it resulted in 5/10 partial responders and 5/10 complete responders, 2 of which were TFS at the end of the study on day 51. In an MTD study in male rats, ADCT-211 was stable and tolerated up to 24 mg/kg single dose, with exposure data being indicative of a linear PK profile with a half-life of 12-19 days. Expression of membranous IL13RA2 was confirmed by IHC in a panel of primary and refractory GBM samples and malignant melanoma, highlighting them as potential indications for the clinical development of ADCT-211. In conclusion, ADCT-211 demonstrated potent and specific in vitro and in vivo anti-tumor activity and it was stable and well tolerated in the rat, warranting further development of ADCT-211 into the clinic in IL13RA2-expressing cancers.

Citation Format: Francesca Zammarchi, Karin Havenith, Ben Leatherdale, Britanny Roberts, Lara Montolio, Afroze Patel, Narinder Janghra, Pedro Alves, Kristina Zaitseva, Cecile Oblette, Ian Kirby, Lolke de Haan, Patrick H van Berkel. Preclinical development of ADCT-211, a novel pyrrolobenzodiazepine dimer-based antibody-drug conjugate targeting solid tumors expressing IL13RA2 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1604.

Re-evaluating the need for chronic toxicity studies with therapeutic monoclonal antibodies, using a weight of evidence approach

To support registration of monoclonal antibodies (mAbs) for chronic indications, 6-month toxicity studies have historically been conducted. Experience with mAb development has shown a relatively benign and well-understood safety profile for this class, with most toxicity findings anticipated based on pharmacology. We evaluated whether a 6-month toxicity study is necessary to assess the long-term safety of mAbs. Data on First-in-Human (FIH)-enabling and chronic toxicity studies were shared for 142 mAbs submitted by 11 companies. Opportunities to further optimize study designs to reduce animal usage were identified. For 71% of mAbs, no toxicities or no new toxicities were noted in chronic studies compared to FIH-enabling study findings. New toxicities of potential concern for human safety or that changed trial design were identified in 13.5% of cases, with 7% being considered critical and 2% leading to program termination. An iterative, weight-of-evidence model which considers factors that influence the overall risk for a mAb to cause toxicity was developed. This model enables an evidence-based justification, suggesting when 3-month toxicity studies are likely sufficient to support late-stage clinical development and registration for some mAbs.

The use of recovery animals in nonclinical safety assessment studies with monoclonal antibodies: further 3Rs opportunities remain

Assessment of reversibility from nonclinical toxicity findings in animals with potential adverse clinical impact is required during pharmaceutical development, but there is flexibility around how and when this is performed and if recovery animals are necessary. For monoclonal antibodies (mAbs) and in accordance with ICH S6(R1) if inclusion of recovery animals is warranted, this need only occur in one study. Data on study designs for first-in-human (FIH)-enabling and later-development toxicity studies were shared from a recent collaboration between the NC3Rs, EPAA, Netherlands Medicines Evaluation Board (MEB) and 14 pharmaceutical companies. This enabled a review of practices on recovery animal use during mAb development and identification of opportunities to reduce research animal use. Recovery animals were included in 68% of FIH-enabling and 69% of later-development studies, often in multiple studies in the same program. Recovery groups were commonly in control plus one test article-dosed group or in all dose groups (45% of studies, each design). Based on the shared data review and conclusions, limiting inclusion of recovery to a single nonclinical toxicology study and species, study design optimisation and use of existing knowledge instead of additional recovery groups provide opportunities to further reduce animal use within mAb development programs.

Characterization of a novel potency endpoint for the evaluation of immune checkpoint blockade in humanized mice

Introduction

Humanized mice are emerging as valuable models to experimentally evaluate the impact of different immunotherapeutics on the human immune system. These immunodeficient mice are engrafted with human cells or tissues, that then mimic the human immune system, offering an alternative and potentially more predictive preclinical model. Immunodeficient NSG mice engrafted with human CD34+ cord blood stem cells develop human T cells educated against murine MHC. However, autoimmune graft versus host disease (GvHD), mediated by T cells, typically develops 1 year post engraftment.

Methods

Here, we have used the development of GvHD in NSG mice, using donors with HLA alleles predisposed to autoimmunity (psoriasis) to weight in favor of GvHD, as an endpoint to evaluate the relative potency of monoclonal and BiSpecific antibodies targeting PD-1 and CTLA-4 to break immune tolerance.

Results

We found that treatment with either a combination of anti-PD-1 & anti-CTLA-4 mAbs or a quadrivalent anti-PD-1/CTLA-4 BiSpecific (MEDI8500), had enhanced potency compared to treatment with anti-PD-1 or anti-CTLA-4 monotherapies, increasing T cell activity both in vitro and in vivo. This resulted in accelerated development of GvHD and shorter survival of the humanized mice in these treatment groups commensurate with their on target activity.

Discussion

Our findings demonstrate the potential of humanized mouse models for preclinical evaluation of different immunotherapies and combinations, using acceleration of GvHD development as a surrogate of aggravated antigenic T-cell response against host.

Use of human splenocytes in an innovative humanised mouse model for prediction of immunotherapy-induced cytokine release syndrome

OBJECTIVES

Humanised mice have emerged as valuable models for pre-clinical testing of the safety and efficacy of immunotherapies. Given the variety of models available, selection of the most appropriate humanised mouse model is critical in study design. Here, we aimed to develop a model for predicting cytokine release syndrome (CRS) while minimising graft-versus-host disease (GvHD).

METHODS

To overcome donor-induced variation, we directly compared the in vitro and in vivo immune phenotype of immunodeficient NSG mice reconstituted with human bone marrow (BM) CD34+ haematopoietic stem cells (HSCs), peripheral blood mononuclear cells (PBMCs) or spleen mononuclear cells (SPMCs) from the same human donors. SPMC engraftment in NSG-dKO mice, which lack MHC class I and II, was also evaluated as a strategy to limit GvHD. Another group of mice was engrafted with umbilical cord blood (UCB) CD34+ HSCs. Induction of CRS in vivo was investigated upon administration of the anti-CD3 monoclonal antibody OKT3.

RESULTS

PBMC- and SPMC-reconstituted NSG mice showed short-term survival, with engrafted human T cells exhibiting mostly an effector memory phenotype. Survival in SPMC-reconstituted NSG-dKO mice was significantly longer. Conversely, both BM and UCB-HSC models showed longer survival, without demonstrable GvHD and a more naïve T-cell phenotype. PBMC- and SPMC-reconstituted mice, but not BM-HSC or UCB-HSC mice, experienced severe clinical signs of CRS upon administration of OKT3.

CONCLUSION

PBMC- and SPMC-reconstituted NSG mice better predict OKT3-mediated CRS. The SPMC model allows generation of large experimental groups, and the use of NSG-dKO mice mitigates the limitation of early GvHD.

Opportunities for use of one species for longer-term toxicology testing during drug development: A cross-industry evaluation

An international expert working group representing 37 organisations (pharmaceutical/biotechnology companies, contract research organisations, academic institutions and regulatory bodies) collaborated in a data sharing exercise to evaluate the utility of two species within regulatory general toxicology studies. Anonymised data on 172 drug candidates (92 small molecules, 46 monoclonal antibodies, 15 recombinant proteins, 13 synthetic peptides and 6 antibody-drug conjugates) were submitted by 18 organisations. The use of one or two species across molecule types, the frequency for reduction to a single species within the package of general toxicology studies, and a comparison of target organ toxicities identified in each species in both short and longer-term studies were determined. Reduction to a single species for longer-term toxicity studies, as used for the development of biologicals (ICHS6(R1) guideline) was only applied for 8/133 drug candidates, but might have been possible for more, regardless of drug modality, as similar target organ toxicity profiles were identified in the short-term studies. However, definition and harmonisation around the criteria for similarity of toxicity profiles is needed to enable wider consideration of these principles. Analysis of a more robust dataset would be required to provide clear, evidence-based recommendations for expansion of these principles to small molecules or other modalities where two species toxicity testing is currently recommended.

Reviewing the Utility of Two Species in General Toxicology Related to Drug Development

As part of the safety assessment of new drugs, the use of two species (a rodent and a nonrodent) for regulatory toxicology studies is the typical approach taken for small molecules. For biologics, species selection is dictated by pharmacological relevance, and single species toxicology packages (typically using the nonhuman primate) are common. The UK National Centre for the Replacement, Refinement, and Reduction of Animals in Research and the Association of the British Pharmaceutical Industry are collaborating on a project to review the utility of two species in regulatory toxicology studies, with the aim to explore whether there are wider circumstances when data from a single species could be sufficient to enable safe progression in humans. An international working group consisting of 37 representatives from pharmaceutical and biotechnology companies, contract research organizations, academia, and regulatory bodies is coordinating a large-scale data sharing exercise to examine the potential for changes in current practice to reduce the number of species used for nonclinical safety testing at different stages of development. The challenge will be to determine whether two species toxicology adds significant value or whether in some instances data from a single species are sufficient (across a broader range of molecules than is currently the case) without compromising human safety.

Potent Immune Modulation by MEDI6383, an Engineered Human OX40 Ligand IgG4P Fc Fusion Protein

Ligation of OX40 (CD134, TNFRSF4) on activated T cells by its natural ligand (OX40L, CD252, TNFSF4) enhances cellular survival, proliferation, and effector functions such as cytokine release and cellular cytotoxicity. We engineered a recombinant human OX40L IgG4P Fc fusion protein termed MEDI6383 that assembles into a hexameric structure and exerts potent agonist activity following engagement of OX40. MEDI6383 displayed solution-phase agonist activity that was enhanced when the fusion protein was clustered by Fc gamma receptors (FcγRs) on the surface of adjacent cells. The resulting costimulation of OX40 on T cells induced NFκB promoter activity in OX40-expressing T cells and induced Th1-type cytokine production, proliferation, and resistance to regulatory T cell (Treg)-mediated suppression. MEDI6383 enhanced the cytolytic activity of tumor-reactive T cells and reduced tumor growth in the context of an alloreactive human T cell:tumor cell admix model in immunocompromised mice. Consistent with the role of OX40 costimulation in the expansion of memory T cells, MEDI6383 administered to healthy nonhuman primates elicited peripheral blood CD4 and CD8 central and effector memory T-cell proliferation as well as B-cell proliferation. Together, these results suggest that OX40 agonism has the potential to enhance antitumor immunity in human malignancies. Mol Cancer Ther; 17(5); 1024-38. ©2018 AACR.

MEDI1873, a potent, stabilized hexameric agonist of human GITR with regulatory T-cell targeting potential

Glucocorticoid-induced tumor necrosis factor receptor-related protein (GITR) is part of a system of signals involved in controlling T-cell activation. Targeting and agonizing GITR in mice promotes antitumor immunity by enhancing the function of effector T cells and inhibiting regulatory T cells. Here, we describe MEDI1873, a novel hexameric human GITR agonist comprising an IgG1 Fc domain, a coronin 1A trimerization domain and the human GITRL extracellular domain (ECD). MEDI1873 was optimized through systematic testing of different trimerization domains, aglycosylation of the GITRL ECD and comparison of different Fc isotypes. MEDI1873 exhibits oligomeric heterogeneity and superiority to an anti-GITR antibody with respect to evoking robust GITR agonism, T-cell activation and clustering of Fc gamma receptors. Further, it recapitulates, in vitro, several aspects of GITR targeting described in mice, including modulation of regulatory T-cell suppression and the ability to increase the CD8⁺:CD4⁺ T-cell ratio via antibody-dependent T-cell cytotoxicity. To support translation into a therapeutic setting, we demonstrate that MEDI1873 is a potent T-cell agonist in vivo in non-human primates, inducing marked enhancement of humoral and T-cell proliferative responses against protein antigen, and demonstrate the presence of GITR- and FoxP3-expressing infiltrating lymphocytes in a range of human tumors. Overall our data provide compelling evidence that MEDI1873 is a novel, potent GITR agonist with the ability to modulate T-cell responses, and suggest that previously described GITR biology in mice may translate to the human setting, reinforcing the potential of targeting the GITR pathway as a therapeutic approach to cancer.

Non-clinical Safety Evaluation of Biotherapeutics - Challenges, Opportunities and new Insights

New challenges and opportunities in nonclinical safety testing of biotherapeutics were presented and discussed at the 5th European BioSafe Annual General Membership meeting in November 2015 in Ludwigshafen. This article summarizes the presentations and discussions from both the main and the breakout sessions. The following topics were covered in six main sessions: The following questions were discussed across 4 breakout sessions (i-iv) and a case-study based general discussion (v).

Nonclinical safety testing of biopharmaceuticals--Addressing current challenges of these novel and emerging therapies

Non-clinical safety testing of biopharmaceuticals can present significant challenges to human risk assessment with these often innovative and complex drugs. Hot Topics in this field were discussed recently at the 4th Annual European Biosafe General Membership meeting. In this feature article, the presentations and subsequent discussions from the main sessions are summarized. The topics covered include: (i) wanted versus unwanted immune activation, (ii) bi-specific protein scaffolds, (iii) use of Pharmacokinetic (PK)/Pharmacodynamic (PD) data to impact/optimize toxicology study design, (iv) cytokine release and challenges to human translation (v) safety testing of cell and gene therapies including chimeric antigen receptor T (CAR-T) cells and retroviral vectors and (vi) biopharmaceutical development strategies encompassing a range of diverse topics including optimizing entry of monoclonal antibodies (mAbs) into the brain, safety testing of therapeutic vaccines, non-clinical testing of biosimilars, infection in toxicology studies with immunomodulators and challenges to human risk assessment, maternal and infant anti-drug antibody (ADA) development and impact in non-human primate (NHP) developmental toxicity studies, and a summary of an NC3Rs workshop on the future vision for non-clinical safety assessment of biopharmaceuticals.

Recommendations from a global cross-company data sharing initiative on the incorporation of recovery phase animals in safety assessment studies to support first-in-human clinical trials

An international expert group which includes 30 organisations (pharmaceutical companies, contract research organisations, academic institutions and regulatory bodies) has shared data on the use of recovery animals in the assessment of pharmaceutical safety for early development. These data have been used as an evidence-base to make recommendations on the inclusion of recovery animals in toxicology studies to achieve scientific objectives, while reducing animal use. Recovery animals are used in pharmaceutical development to provide information on the potential for a toxic effect to translate into long-term human risk. They are included on toxicology studies to assess whether effects observed during dosing persist or reverse once treatment ends. The group devised a questionnaire to collect information on the use of recovery animals in general regulatory toxicology studies to support first-in-human studies. Questions focused on study design, the rationale behind inclusion or exclusion and the impact this had on internal and regulatory decisions. Data on 137 compounds (including 53 biologicals and 78 small molecules) from 259 studies showed wide variation in where, when and why recovery animals were included. An analysis of individual study and programme design shows that there are opportunities to reduce the use of recovery animals without impacting drug development.

Challenges and approaches for the development of safer immunomodulatory biologics

Immunomodulatory biologics are a class of biotechnology-derived therapeutic products that are designed to engage immune-relevant targets and are indicated in the treatment and management of a range of diseases, including immune-mediated inflammatory diseases and malignancies.

Despite their high specificity and therapeutic advantages, immmunomodulatory biologics have been associated with adverse reactions such as serious infections, malignancies and cytokine release syndrome, which arise owing to the on-target or exaggerated pharmacological effects of these drugs. Immunogenicity resulting in the generation of antidrug antibodies is another unwanted effect that leads to loss of efficacy and — rarely — hypersensitivity reactions.

For some adverse reactions, mitigating and preventive strategies are in place, such as stratifying patients on the basis of responsiveness to therapy and the risk of developing adverse reactions. These strategies depend on the availability of robust biomarkers for therapeutic efficacy and the risk of adverse reactions: for example, seropositivity for John Cunningham virus is a risk factor for progressive multifocal leukoencephalopathy. The development of effective biomarkers will greatly aid these strategies.

The development and design of safer immunomodulatory biologics is reliant on a detailed understanding of the nature of the disease, target biology, the interaction of the target with the immunomodulatory biologic and the inherent properties of the biologic that elicit unwanted effects.

The availability of in vitro and in vivo models that can be used to predict adverse reactions associated with immunomodulatory biologics is central to the development of safer immunomodulatory biologics. Some progress has been made in developing in vitro and in silico tests for predicting cytokine release syndrome and immunogenicity, but there is still a lack of models for effectively predicting infections and malignancies.

Two pathways can be followed in designing and developing safer immunomodulatory biologics. The first pathway involves generating a biologic that engages an alternative target or mechanism to produce the desired pharmacodynamic effect without the associated adverse reaction, and is followed when the adverse reaction cannot be dissociated from the target biology. The second pathway involves redesigning the biologic to 'engineer out' components within the biologic structure that trigger adverse effects or to alter the nature of the target–biologic interactions.

Owing to their specificity, immunomodulatory biologics generally have better safety profiles than small-molecule drugs. However, adverse effects such as an increased risk of infections or cytokine release syndrome are of concern. Here, Park and colleagues discuss the current strategies used to predict and mitigate these adverse effects and consider how they can be used to inform the development of safer immunomodulatory biologics.

Immunomodulatory biologics, which render their therapeutic effects by modulating or harnessing immune responses, have proven their therapeutic utility in several complex conditions including cancer and autoimmune diseases. However, unwanted adverse reactions — including serious infections, malignancy, cytokine release syndrome, anaphylaxis and hypersensitivity as well as immunogenicity — pose a challenge to the development of new (and safer) immunomodulatory biologics. In this article, we assess the safety issues associated with immunomodulatory biologics and discuss the current approaches for predicting and mitigating adverse reactions associated with their use. We also outline how these approaches can inform the development of safer immunomodulatory biologics.

The design of chronic toxicology studies of monoclonal antibodies: implications for the reduction in use of non-human primates

The changing environment of monoclonal antibody (mAb) development is impacting on the cost of drug development and the use of experimental animals, particularly non-human primates (NHPs). The drive to reduce these costs is huge and involves rethinking and improving nonclinical studies to make them more efficient and more predictive of man. While NHP use might be unavoidable in many cases because of the exquisite specificity and consequent species selectivity of mAbs, our increasing knowledge base can be used to improve drug development and maximise the output of experimental data. Data on GLP regulatory toxicology studies for 58mAbs were obtained from 10 companies across a wide range of therapeutic indications. These data have been used to investigate current practice and identify study designs that minimise NHP use. Our analysis shows that there is variation in the number of animals used for similar studies. This information has been used to develop practical guidance and make recommendations on the use of science-based rationale to design studies using fewer animals taking into account the current regulatory guidance. There are eight recommendations intended to highlight areas for consideration. They include guidance on the main group size, the inclusion of recovery groups and the number of dose groups used in short and long term chronic toxicology studies.

Trafficking of exogenous peptides into proteasome-dependent major histocompatibility complex class I pathway following enterotoxin B subunit-mediated delivery

The B-subunit component of Escherichia coli heat-labile enterotoxin (EtxB), which binds to cell surface GM1 ganglioside receptors, was recently shown to be a highly effective vehicle for delivery of conjugated peptides into the major histocompatibility complex (MHC) class I pathway. In this study we have investigated the pathway of epitope delivery. The peptides used contained the epitope either located at the C terminus or with a C-terminal extension. Pretreatment of cells with cholesterol-disrupting agents blocked transport of EtxB conjugates to the Golgi/endoplasmic reticulum, but did not affect EtxB-mediated MHC class I presentation. Under these conditions, EtxB conjugates entered EEA1-positive early endosomes where peptides were cleaved and translocated into the cytosol. Endosome acidification was required for epitope presentation. Purified 20 S immunoproteasomes were able to generate the epitope from peptides in vitro, but 26 S proteasomes were not. Only presentation from the C-terminal extended peptide was proteasome-dependent in cells, and this was found to be significantly slower than presentation from peptides with the epitope at the C terminus. These results implicate the proteasome in the generation of the correct C terminus of the epitope and are consistent with proteasome-independent N-terminal trimming. Epitope presentation was blocked in a TAP-deficient cell line, providing further evidence that conjugated peptides enter the cytosol as well as demonstrating a requirement for the peptide transporter. Our findings demonstrate the utility of EtxB-mediated peptide delivery for rapid and efficient loading of MHC class I epitopes in several different cell types. Conjugated peptides are released from early endosomes into the cytosol where they gain access to proteasomes and TAP in the "classical" pathway of class I presentation.

Mutant Escherichia coli heat-labile toxin B subunit that separates toxoid-mediated signaling and immunomodulatory action from trafficking and delivery functions

The homopentameric B-subunit components of Escherichia coli heat-labile enterotoxin (EtxB) and cholera toxin (CtxB) possess the capacity to enter mammalian cells and to activate cell-signaling events in leukocytes that modulate immune cell function. Both properties have been attributed to the ability of the B subunits to bind to GM1-ganglioside receptors, a ubiquitous glycosphingolipid found in the plasma membrane. Here we describe the properties of EtxB(H57S), a mutant B subunit with a His-->Ser substitution at position 57. The mutant was found to be severely defective in inducing leukocyte signaling, as shown by failure to (i) trigger caspase 3-mediated CD8(+)-T-cell apoptosis, (ii) activate nuclear translocation of NF-kappaB in Jurkat T cells, (iii) induce a potent anti-B-subunit response in mice, or (iv) serve as a mucosal adjuvant. However, its GM1 binding, cellular uptake, and delivery functions remained intact. This was further validated by the finding that EtxB(H57S) was as effective as EtxB in delivering a conjugated model class I epitope into the major histocompatibility complex class I pathway of a dendritic cell line. These observations imply that GM1 binding alone is not sufficient to trigger the signaling events responsible for the potent immunomodulatory properties of EtxB. Moreover, they demonstrate that its signaling properties play no role in EtxB uptake and trafficking. Thus, EtxB(H57S) represents a novel tool for evaluating the complex cellular interactions and signaling events occurring after receptor interaction, as well as offering an alternative means of delivering attached peptides in the absence of the potent immunomodulatory signals induced by wild-type B subunits.

Bacterial toxins as versatile delivery vehicles

An ability to deliver macromolecules into the intracellular compartments of mammalian cells offers enormous potential for development of new therapeutics directed against intracellular targets. Unfortunately, most peptides or proteins are too large to enter the cell cytosol unaided, and any uptake that does occur primarily results in their entry into lysosomes for degradation. However, one group of proteins that possesses an inherent capacity to interact with and enter mammalian cells are bacterial toxins. These are being developed as efficient vehicles for the attachment and intracellular delivery of other macromolecules, including peptides, proteins and DNA. To date, most studies have concentrated on the delivery of immunological epitopes into the endogenous major histocompatibility class I (MHC-I) pathway for development of antiviral or anticancer vaccines. However, opportunities to use toxins to modulate inflammatory autoimmune disorders and cell-specific targeting of DNA for gene therapy illustrates the versatility of toxin molecules as delivery vehicles.