High throughput development of TCR-mimic antibody that targets survivin-2B80-88/HLA-A*A24 and its application in a bispecific T-cell engager

TCR mimic compounds for pHLA targeting with high potency modalities in oncology

pHLA complexes represent the largest class of cell surface markers on cancer cells, making them attractive for targeted cancer therapies. Adoptive cell therapies expressing TCRs that recognize tumor specific pHLAs take advantage of the unique selectivity and avidity of TCR: pHLA interactions. More recently, additional protein binding domains binding to pHLAs, known as TCR mimics (TCRm), were developed for tumor targeting of high potency therapeutic modalities, including bispecifics, ADCs, CAR T and -NK cells. TCRm compounds take advantage of the exquisite tumor specificity of certain pHLA targets, including cell lineage commitment markers and cancer testis antigens (CTAs). To achieve meaningful anti-tumor responses, it is critical that TCRm compounds integrate both, high target binding affinities and a high degree of target specificity. In this review, we describe the most advanced approaches to achieve both criteria, including affinity- and specificity engineering of TCRs, antibodies and alternative protein scaffolds. We also discuss the status of current TCRm based therapeutics developed in the clinic, key challenges, and emerging trends to improve treatment options for cancer patients treated with TCRm based therapeutics in Oncology.

Evaluation of chimeric antigen receptor of humanized rabbit-derived T cell receptor-like antibody

T-cell receptor (TCR)-like antibodies that specifically recognize antigenic peptides presented on major histocompatibility complex (MHC) molecules have been developed for next-generation cancer immunotherapy. Recently, we reported a rapid and efficient method to generate TCR-like antibodies using a rabbit system. We humanized previously generated rabbit-derived TCR-like antibodies reacting Epstein-Barr virus peptide (BRLF1p, TYPVLEEMF) in the context of HLA-A24 molecules, produced CAR-T cells, and evaluated their anti-tumor effects using in vitro and in vivo tumor models. Humanization of the rabbit-derived TCR-like antibodies using the complementarity-determining region grafting technology maintained their specificity and affinity. We prepared a second-generation chimeric antigen receptor (CAR) using scFv of the humanized TCR-like antibodies and then transduced them into human T-cells. The CAR-T cells specifically recognized BRLF1p/MHC molecules and lysed the target cells in an antigen-specific manner in vitro. They also demonstrated anti-tumor activity in a mouse xenograft model. We report the generation of CAR-T cells using humanized rabbit-derived TCR-like antibodies. Together with our established and efficient generation procedure for TCR-like antibodies using rabbits, our platform for the clinical application of humanized rabbit-derived TCR-like antibodies to CAR-T cells will help improve next-generation cancer immunotherapy.

Identification of Neoantigens in Cancer Cells as Targets for Immunotherapy

The clinical benefits of immune checkpoint blockage (ICB) therapy have been widely reported. In patients with cancer, researchers have demonstrated the clinical potential of antitumor cytotoxic T cells that can be reinvigorated or enhanced by ICB. Compared to self-antigens, neoantigens derived from tumor somatic mutations are believed to be ideal immune targets in tumors. Candidate tumor neoantigens can be identified through immunogenomic or immunopeptidomic approaches. Identification of neoantigens has revealed several points of the clinical relevance. For instance, tumor mutation burden (TMB) may be an indicator of immunotherapy. In various cancers, mutation rates accompanying neoantigen loads may be indicative of immunotherapy. Furthermore, mismatch repair-deficient tumors can be eradicated by T cells in ICB treatment. Hence, immunotherapies using vaccines or adoptive T-cell transfer targeting neoantigens are potential innovative strategies. However, significant efforts are required to identify the optimal epitopes. In this review, we summarize the recent progress in the identification of neoantigens and discussed preclinical and clinical studies based on neoantigens. We also discuss the issues remaining to be addressed before clinical applications of these new therapeutic strategies can be materialized.

The potential applications of T cell receptor (TCR)-like antibody in cervical cancer immunotherapy

Cervical cancer is ranked as the fourth most common cancer in women worldwide. Monoclonal antibody has created a new dimension in the immunotherapy of many diseases, including cervical cancer. The antibody's ability to target various aspects of cervical cancer (oncoviruses, oncoproteins, and signaling pathways) delivers a promising future for efficient immunotherapy. Besides, technologies such as hybridoma and phage display provide a fundamental platform for monoclonal antibody generation and create the opportunity to generate novel antibody classes including, T cell receptor (TCR)-like antibody. In this review, the current immunotherapy strategies for cervical cancer are presented. We have also proposed a novel concept of T cell receptor (TCR)-like antibody and its potential applications for enhancing cervical cancer therapeutics. Finally, the possible challenges in TCR-like antibody application for cervical cancer therapeutics have been addressed, and strategies to overcome the challenges have been highlighted to maximize the therapeutic benefits.

Bringing Together the Power of T Cell Receptor Mimic and Bispecific Antibodies for Cancer Immunotherapy: Still a Long Way to Go

Antibody-based cancer immunotherapy has revolutionized oncology. The first successful therapeutic antibodies relied on eliciting immune-mediated cytotoxicity (rituximab) or modulation of intracellular signaling (trastuzumab). Further attempts to enhance the antitumor effects led to the development of immunoconjugates with radioactive or cytotoxic compounds (tositumomab, brentuximab vedotin). Another line of research led to the bispecific antibodies that can enhance the formation of immunological synapse between cancer and cytotoxic T cells (blinatumomab). Despite the constant advances in design and production, the application of monoclonal antibodies in cancer treatment remains limited by the presence of specific cell surface markers. A rational approach to target intracellular cancer antigens was proposed almost two decades ago by the development of anti-peptide human leukocyte antigen (HLA) complex (T cell receptor-like/mimic) antibodies. They could recognize specifically cancer neoantigens expressed in the context of specific HLA molecules theoretically providing unprecedented specificity. Furthermore, they can be developed in a semigeneric format, that is, to target common neoantigens expressed in the context of common HLA molecules. It is rationale to expect that the development of such antibodies in the format of bispecific antibody constructs can bring together the power of specific antibody-based recognition and that of T cell-mediated lysis. There are already some preliminary reports that suggest such constructs would be an achievable goal. In this brief review, we discuss some of the successful preclinical developments in the field and the major challenges that are yet to be addressed.

Rapid and efficient generation of T-cell receptor-like antibodies using chip-based single-cell analysis

Generation of TCR-like monoclonal antibodies using conventional methods is markedly laborious and inefficient. We have proposed improvements of ISAAC (chip-based Ab-secreting cell [ASC] screening method), allows comprehensive analysis of ASCs at the single-cell level to obtain TCR-like antibodies; blocking procedure enables us to avoid the detection of non-TCR-like antibodies.

Overcoming Challenges for CD3-Bispecific Antibody Therapy in Solid Tumors

Immunotherapy of cancer with CD3-bispecific antibodies is an approved therapeutic option for some hematological malignancies and is under clinical investigation for solid cancers. However, the treatment of solid tumors faces more pronounced hurdles, such as increased on-target off-tumor toxicities, sparse T-cell infiltration and impaired T-cell quality due to the presence of an immunosuppressive tumor microenvironment, which affect the safety and limit efficacy of CD3-bispecific antibody therapy. In this review, we provide a brief status update of the CD3-bispecific antibody therapy field and identify intrinsic hurdles in solid cancers. Furthermore, we describe potential combinatorial approaches to overcome these challenges in order to generate selective and more effective responses.

Development of a T-cell receptor mimic antibody targeting a novel Wilms tumor 1-derived peptide and analysis of its specificity

Wilms tumor 1 (WT1) is an intracellular tumor‐associated antigen that remains inaccessible to antibodies. Recently, T‐cell receptor (TCR) mimic antibodies (TCRm‐Abs), which recognize peptides loaded on human leukocyte antigen (HLA) with higher specificity and affinity than TCR, have been developed as a new antibody class that can target intracellular antigens. To expand the therapeutic targets in tumors with WT1, we developed TCRm‐Abs targeting a novel HLA‐A*02:01‐restricted peptide, WT1C (ALLPAVPSL), and validated their specificity using multiple techniques. Screening of these antibodies by ELISA with a panel of peptide/HLA complexes and by glycine scanning of peptide‐pulsed T2 cells identified one specific clone, #25‐8. Despite the low risk for eliciting broad cross–reactivity of this TCRm‐Ab, analysis of a panel of cell lines, in conjunction with exogenous expression of either or both the HLA‐A*02:01 and WT1 genes in HeLa cells, revealed that #25‐8 reacts with WT1C but also with unknown peptides in the context of HLA‐A*02:01. This potentially dangerous cross–reactivity was confirmed through analysis using chimeric antigen receptor T‐cells carrying the single‐chain variable fragment of #25‐8, which targets WT1‐negative HeLa/A02 cells. To determine the cross–reactive profiles of #25‐8, we applied the PresentER antigen presentation platform with the #25‐8‐recognition motif, which enables the identification of potential off–target peptides expressed in the human proteome. Our results demonstrate the potential of TCRm‐Abs to target a variety of peptides in the context of HLA but also depict the need for systematic validation to identify the cross–reactive peptides for the prediction of off–target toxicity in future clinical translation.

Bi- and Tri-Specific T Cell Engager-Armed Oncolytic Viruses: Next-Generation Cancer Immunotherapy

Oncolytic viruses (OVs) are potent anti-cancer biologics with a bright future, having substantial evidence of efficacy in patients with cancer. Bi- and tri-specific antibodies targeting tumor antigens and capable of activating T cell receptor signaling have also shown great promise in cancer immunotherapy. In a cutting-edge strategy, investigators have incorporated the two independent anti-cancer modalities, transforming them into bi- or tri-specific T cell engager (BiTE or TriTE)-armed OVs for targeted immunotherapy. Since 2014, multiple research teams have studied this combinatorial strategy, and it showed substantial efficacy in various tumor models. Here, we first provide a brief overview of the current status of oncolytic virotherapy and the use of multi-specific antibodies for cancer immunotherapy. We then summarize progress on BiTE and TriTE antibodies as a novel class of cancer therapeutics in preclinical and clinical studies, followed by a discussion of BiTE- or TriTE-armed OVs for cancer therapy in translational models. In addition, T cell receptor mimics (TCRm) have been developed into BiTEs and are expected to greatly expand the application of BiTEs and BiTE-armed OVs for the effective targeting of intracellular tumor antigens. Future applications of such innovative combination strategies are emerging as precision cancer immunotherapies.

Bispecific antibodies in cancer immunotherapy

Among antibody-based cancer therapies, bispecific antibodies (biAbs) have gained momentum in preclinical and clinical investigations following the regulatory approvals of the trailblazing T-cell engaging biAb (T-biAb) blinatumomab. Discussed herein are recent strategies that aim at boosting the potency and mitigating the toxicity of T-biAbs, broadening their therapeutic utility from hematologic to solid malignancies, and generating T-biAbs in situ. In cancer immunotherapy, T-biAbs are facing fierce competition with chimeric antigen receptor T cells (CAR-Ts), a battle for clinical and commercial viability that will be closely watched. However, innovative combinations of T-biAbs and CAR-Ts have also transpired. NK-cell engaging biAbs (NK-biAbs) are reemerging as an alternative that addresses liabilities of T-biAbs. Beyond NK-biAbs, other biAbs designed to recruit cellular and molecular components of the innate immune system will be covered in this reflection on new tools, technologies, and targets.

Cancer therapeutics using survivin BIRC5 as a target: what can we do after over two decades of study?

Survivin (also named BIRC5) is a well-known cancer therapeutic target. Since its discovery more than two decades ago, the use of survivin as a target for cancer therapeutics has remained a central goal of survivin studies in the cancer field. Many studies have provided intriguing insight into survivin's functional role in cancers, thus providing promise for survivin as a cancer therapeutic target. Despite this, moving survivin-targeting agents into and through the clinic remains a challenge. In order to address this challenge, we may need to rethink current strategies in order to develop a new mindset for targeting survivin. In this Review, we will first summarize the current survivin mechanistic studies, and then review the status of survivin cancer therapeutics, which is classified into five categories: (i) survivin-partner protein interaction inhibitors, (ii) survivin homodimerization inhibitors, (iii) survivin gene transcription inhibitors, (iv) survivin mRNA inhibitors and (v) survivin immunotherapy. We will then provide our opinions on cancer therapeutics using survivin as a target, with the goal of stimulating discussion that might facilitate translational research for discovering improved strategies and/or more effective anticancer agents that target survivin for cancer therapy.