Identification of the antigenic epitopes in staphylococcal enterotoxins A and E and design of a superantigen for human cancer therapy

The Role of Bacterial Superantigens in the Immune Response: From Biology to Cancer Treatment

Aims:

Encouraging results have been indicated preclinically and in patients using the bacterial superantigen. This review article intends to summarize the role of the superantigens that have been recently used in the treatment of cancer. In addition, the vector systems, including lentiviral vectors, adeno-associated vector systems and retroviral vectors that are increasingly being used in basic and applied research, were discussed. Most importantly, the new CRISPR technique has also been discussed in this literature review.

Discussion:

More successful therapies can be achieved by manipulating bacterial vector systems through incorporating genes related to the superantigens and cytokines. The products of SAg and cytokine genes contribute to the strong stimulation of the immune system against tumor cells. They bind to MHC II molecules as well as the V beta regions of TCR and lead to the production of IL2 and other cytokines, the activation of antigen-presenting cells and T lymphocytes. Additionally, superantigens can be used to eradicate tumor cells. Better results in cancer treatment can be achieved by transferring superantigen genes and subsequent strong immune stimulation along with other cancer immunotherapy agents.

Conclusion:

Superantigens induce the proliferation of T lymphocytes and antigen-presenting cells by binding to MHCII molecules and V beta regions in T cell receptors. Therefore, the presentation of tumor cell antigens is increased. Additionally, the production of important cytokines by T cells and APCs contributes to the stimulation of immune response against tumor cells. The manipulation of bacterial vector systems through incorporating genesrelated to SAgs and other immune response factors is a good strategy for the immune system stimulating and eradicating tumor cells along with other immunotherapy agents.

Design of split superantigen fusion proteins for cancer immunotherapy

Several antibody-targeting cancer immunotherapies have been developed based on T cell activation at the target cells. One of the most potent activators of T cells are bacterial superantigens, which bind to major histocompatibility complex class II on antigen-presenting cells and activate T cells through T cell receptor. Strong T cell activation is also one of the main weaknesses of this strategy as it may lead to systemic T cell activation. To overcome the limitation of conventional antibody-superantigen fusion proteins, we have split a superantigen into two fragments, individually inactive, until both fragments came into close proximity and reassembled into a biologically active form capable of activating T cell response. A screening method based on fusion between SEA and coiled-coil heterodimers was developed that enabled detection of functional split SEA designs. The split SEA design that demonstrated efficacy in fusion with coiled-coil dimer forming polypeptides was fused to a single chain antibody specific for tumor antigen CD20. This design selectively activated T cells by split SEA-scFv fusion binding to target cells.

5T4 oncofoetal antigen: an attractive target for immune intervention in cancer

The natural history of a patient's cancer is often characterised by genetic diversity and sequential sweeps of clonal dominance. It is therefore not surprising that identifying the most appropriate tumour-associated antigen for targeted intervention is challenging. The 5T4 oncofoetal antigen was identified by searching for surface molecules shared between human trophoblast and cancer cells with the rationale that they may function to allow survival of the foetus as a semi-allograft in the mother or a tumour in its host. The 5T4 protein is expressed by many different cancers but rarely in normal adult tissues. 5T4 molecules are 72 kD, heavily N-glycosylated proteins with several leucine-rich repeats which are often associated with protein-protein interactions. 5T4 expression is associated with the directional movement of cells through epithelial mesenchymal transition, potentiation of CXCL12/CXCR4 chemotaxis and inhibition of canonical Wnt/beta-catenin while favouring non-canonical pathway signalling; all processes which help drive the spread of cancer cells. The selective pattern of 5T4 tumour expression, association with a tumour-initiating phenotype plus a mechanistic involvement with cancer spread have underwritten the clinical development of different immunotherapeutic strategies including a vaccine, a tumour-targeted superantigen and an antibody drug conjugate. In addition, a chimeric antigen receptor T cell approach targeting 5T4 expressing tumour cells is in pre-clinical development. A key challenge will include how best to combine each 5T4 targeted immunotherapy with the most appropriate standard of care treatment (or adjunct therapy) to maximise the recovery of immune control and ultimately eliminate the tumour.

Control of established colon cancer xenografts using a novel humanized single chain antibody-streptococcal superantigen fusion protein targeting the 5T4 oncofetal antigen

Superantigens (SAgs) are microbial toxins that cross-link T cell receptors with major histocompatibility class II (MHC-II) molecules leading to the activation of large numbers of T cells. Herein, we describe the development and preclinical testing of a novel tumor-targeted SAg (TTS) therapeutic built using the streptococcal pyrogenic exotoxin C (SpeC) SAg and targeting cancer cells expressing the 5T4 tumor-associated antigen (TAA). To inhibit potentially harmful widespread immune cell activation, a SpeC mutation within the high-affinity MHC-II binding interface was generated (SpeC_D203A) that demonstrated a pronounced reduction in mitogenic activity, yet this mutant could still induce immune cell-mediated cancer cell death in vitro. To target 5T4⁺ cancer cells, we engineered a humanized single chain variable fragment (scFv) antibody to recognize 5T4 (scFv5T4). Specific targeting of scFv5T4 was verified. SpeC_D203A fused to scFv5T4 maintained the ability to activate and induce immune cell-mediated cytotoxicity of colorectal cancer cells. Using a xenograft model of established human colon cancer, we demonstrated that the SpeC-based TTS was able to control the growth and spread of large tumors in vivo. This required both TAA targeting by scFv5T4 and functional SAg activity. These studies lay the foundation for the development of streptococcal SAgs as ‘next-generation’ TTSs for cancer immunotherapy.

The tumor targeted superantigen ABR-217620 selectively engages TRBV7-9 and exploits TCR-pMHC affinity mimicry in mediating T cell cytotoxicity

The T lymphocytes are the most important effector cells in immunotherapy of cancer. The conceptual objective for developing the tumor targeted superantigen (TTS) ABR-217620 (naptumomab estafenatox, 5T4Fab-SEA/E-120), now in phase 3 studies for advanced renal cell cancer, was to selectively coat tumor cells with cytotoxic T lymphocytes (CTL) target structures functionally similar to natural CTL pMHC target molecules. Here we present data showing that the molecular basis for the anti-tumor activity by ABR-217620 resides in the distinct interaction between the T cell receptor β variable (TRBV) 7-9 and the engineered superantigen (Sag) SEA/E-120 in the fusion protein bound to the 5T4 antigen on tumor cells. Multimeric but not monomeric ABR-217620 selectively stains TRBV7-9 expressing T lymphocytes from human peripheral blood similar to antigen specific staining of T cells with pMHC tetramers. SEA/E-120 selectively activates TRBV7-9 expressing T lymphocytes resulting in expansion of the subset. ABR-217620 selectively triggers TRBV7-9 expressing cytotoxic T lymphocytes to kill 5T4 positive tumor cells. Furthermore, ABR-217620 activates TRBV7-9 expressing T cell line cells in the presence of cell- and bead-bound 5T4 tumor antigen. Surface plasmon resonance analysis revealed that ABR-217620 binds to 5T4 with high affinity, to TRBV7-9 with low affinity and to MHC class II with very low affinity. The T lymphocyte engagement by ABR-217620 is constituted by displaying high affinity binding to the tumor cells (K_D approximately 1 nM) and with the mimicry of natural productive immune TCR-pMHC contact using affinities of around 1 µM. This difference in kinetics between the two components of the ABR-217620 fusion protein will bias the binding towards the 5T4 target antigen, efficiently activating T-cells via SEA/E-120 only when presented by the tumor cells.

Perspectives in drug development for metastatic renal cell cancer

Patients with renal cell carcinoma (RCC) exhibit a spectrum of clinical outcomes, with some patients following an indolent clinical course and others displaying rapidly advancing disease. As evidence points to RCC being largely refractory to traditional chemotherapy and radiotherapy strategies, immunotherapeutic approaches played a dominant role in the management of metastatic RCC for a quarter of a century. Management of this challenging tumor has been revolutionized by the incorporation of molecularly targeted therapies such as inhibitors of pathways involving tyrosine kinase signaling and the mammalian target of rapamycin (mTOR). The improvements in disease stabilization and survival seen with these agents has meant that molecularly targeted therapy now forms the foundation for treating RCC and has resulted in a multitude of studies investigating similar compounds for efficacy in RCC. Despite this, the rationale for using immunomodulatory regimens remains strong and its ongoing place in this era of targeted treatments continues to pose interesting clinical questions. The challenge of maintaining durable responses from our current therapies persists and this review highlights the plethora of options now available in RCC treatment and the directions in which modern management are heading.

Naptumomab estafenatox: a new immunoconjugate

IMPORTANCE OF THE FIELD

New agents that specifically engage the immune system are being tested in a variety of malignancies. This review provides an overview of naptumomab, an immunotoxin, with encouraging clinical activity in Phase I trials.

AREAS COVERED IN THIS REVIEW

This review examines the preclinical and the published clinical data with regards to naptumomab.

WHAT THE READER WILL GAIN

This review provides the reader with an understanding of the mechanism of action, immunology, pharmacokinetics and clinical activity of this agent.

TAKE HOME MESSAGE

Naptumomab has a unique mechanism of action and appears to be an active agent in the treatment of refractory solid tumors such as renal cell carcinoma.

Directed evolution of chemotaxis inhibitory protein of Staphylococcus aureus generates biologically functional variants with reduced interaction with human antibodies

Chemotaxis inhibitory protein of Staphylococcus aureus (CHIPS) is a protein that binds and blocks the C5a receptor (C5aR) and formylated peptide receptor, thereby inhibiting the immune cell recruitment associated with inflammation. If CHIPS was less reactive with existing human antibodies, it would be a promising anti-inflammatory drug candidate. Therefore, we applied directed evolution and computational/rational design to the CHIPS gene in order to generate new CHIPS variants displaying lower interaction with human IgG, yet retaining biological function. The optimization was performed in four rounds: one round of random mutagenesis to add diversity into the CHIPS gene and three rounds of DNA recombination by Fragment INduced Diversity (FIND). Every round was screened by phage selection and/or ELISA for decreased interaction with human IgG and retained C5aR binding. The mean binding of human anti-CHIPS IgG decreased with every round of evolution. For further optimization, new amino acid substitutions were introduced by rational design, based on the mutations identified during directed evolution. Finally, seven CHIPS variants with low interaction with human IgG and retained C5aR blocking capacity could be identified.

Phase I dose escalation, pharmacokinetic and pharmacodynamic study of naptumomab estafenatox alone in patients with advanced cancer and with docetaxel in patients with advanced non-small-cell lung cancer

PURPOSE

Two phase I studies were conducted of ABR-217620 alone or in combination with docetaxel. This is a recombinant fusion protein consisting of a mutated variant of the superantigen staphylococcal enterotoxin E (SEA/E-120) linked to fragment antigen binding moiety of a monoclonal antibody recognizing the tumor-associated antigen 5T4.

PATIENTS AND METHODS

Patients with non-small-cell lung cancer (NSCLC), pancreatic cancer (PC), and renal cell cancer (RCC) received 5 daily boluses of ABR-217620 (3-month cycles) in escalating doses to determine the maximum-tolerated dose (MTD; ABR-217620 dose escalation monotherapy [MONO] study). Doses were selected based on individual patient anti-SEA/E-120 titers pretreatment. Patients with NSCLC received 4 daily, escalating doses of ABR-217620 followed by docetaxel in 21-day cycles (ABR-217620 dose escalation combination with docetaxel [COMBO] study).

RESULTS

Thirty-nine patients were enrolled in the MONO study and 13 were enrolled in the COMBO study. The monotherapy MTD was 26 microg/kg (NSCLC and PC) and 15 microg/kg (RCC). Dose-limiting toxicities (DLTs) in the MONO study were fever, hypotension, acute liver toxicity, and vascular leak syndrome. In the COMBO study, the MTD was 22 microg/kg (neutropenic sepsis). Adverse events included grade 1 to 2 fever, hypotension, nausea, and chills. Treatment caused a systemic increase of inflammatory cytokines and selective expansion of SEA/E-120 reactive T-cells. Tumor biopsies demonstrated T-cell infiltration after therapy. Fourteen patients (36%) had stable disease (SD) on day 56 of the MONO study. Two patients (15%) in the COMBO study had partial responses, one in a patient with progressive disease on prior docetaxel, and five patients (38%) had SD on day 56.

CONCLUSION

ABR-217620 was well tolerated with evidence of immunological activity and antitumor activity.

A phase II study of a 5T4 oncofoetal antigen tumour-targeted superantigen (ABR-214936) therapy in patients with advanced renal cell carcinoma

In a phase II study, 43 renal cell carcinoma patients were treated with individualised doses of ABR-214936; a fusion of a Fab recognising the antigen 5T4, and Staphylococcal enterotoxin A. Drug was given intravenously on 4 consecutive days, treatment was repeated 1 month later. Treatment was associated with moderate fever and nausea, but well tolerated. Of 40 evaluable patients, 28 had disease control at 2 months, and at 4 months, one patient showed partial response (PR) and 16 patients stable disease. Median survival, with minimum follow-up of 26 months was 19.7 months with 13 patients alive to date. Stratification by the Motzer's prognostic criteria highlights prolonged survival compared to published expectation. Patients receiving higher drug exposure had greater disease control and lived almost twice as long as expected, whereas the low-exposure patients survived as expected. Sustained interleukin-2 (IL-2) production after a repeated injection appears to be a biomarker for clinical effect, as the induced-IL-2 level on the day 2 of treatment correlated with survival. The high degree of disease control and the prolonged survival suggest that this treatment can be effective. These findings will be used in the trial design for the next generation of drug, with reduced antigenicity and toxicity.

Staphylococcal superantigens of the enterotoxin gene cluster (egc) for treatment of stage IIIb non-small cell lung cancer with pleural effusion

There has been renewed interest in the superantigens as antitumor agents with the discovery of a group of bacterial superantigens known as the enterotoxin gene cluster (egc staphylococcal enterotoxins [SEs]). This article discusses the mechanisms by which egc SEs induce tumor killing and pleurodesis. The application of SE homolog and nucleic acid compositions as vaccines and for treatment of established tumors is reviewed. Finally, the use of native SEs ex vivo-intratumorally and intravesicularly administered superantigens against established tumors-is described and the interrelation between superantigen therapy and chemoradiotherapy.

Stable, soluble, high-affinity, engineered T cell receptors: novel antibody-like proteins for specific targeting of peptide antigens

The recent development of T cell receptor phage display opens up the possibility of engineering human T cell receptors with antibody-like binding properties for cell-surface peptide antigens. In this review we briefly discuss recent developments in molecular targeting of peptide antigens. We then discuss potential clinical applications of engineered high-affinity T cell receptors in autoimmunity and cancer.

Preclinical evaluation of superantigen (staphylococcal enterotoxin B) in the intravesical immunotherapy of superficial bladder cancer

Superantigens are potent activators of T lymphocytes; therefore, their characteristics can be exploited in diseases where immunomodulation is known to be effective. In this study, we evaluated a new approach for the intravesical therapy of superficial bladder cancer. We investigated in coculture experiments if staphylococcal enterotoxin B (SEB)-activated PBMCs are able to induce apoptosis in human transitional cell carcinoma (TCC) cells. Additionally, we tested the toxicity and efficacy of SEB dissolved in NaCl 0.9% administered intravesically once weekly for 6 weeks in a rat bladder cancer model. To validate the coculture in vitro findings, we evaluated tumor stage, grade, apoptotic cells in the urothelium and stroma of the bladder and infiltration of the bladder wall by lymphocytes, macrophages and mononuclear cells. Coculture experiments revealed that SEB-activated PBMCs are able to kill TCC cells by inducing apoptosis. The intravesical toxicity study with a maximum dose of 100 microg/ml SEB demonstrated no side effects. In the intravesically SEB-treated animals (10 microg/ml), only 3 tumors remained vs. 15 persisting tumors in the control group. The remaining tumors of the therapy group showed a significant amount of apoptosis and granulocytes, mainly in the urothelium, whereas no relevant apoptosis or infiltration of the bladder with lymphocytes or macrophages was found in the control group. These preclinical findings suggest that SEB might be an interesting candidate for further clinical evaluation.