Antibody Engineering Program

Division Of Basic Sciences - Nci

Investigators

Linked publications & trials

Abstract

While antibody-based therapeutics have emerged as a major component in cancer treatment, the generation of antibodies to important targets such as cell surface receptors and ion channels remains difficult. These proteins contain buried functional sites that are often unreachable by classical mouse or human IgG-based antibodies. Single domain antibodies have shown a promising ability to target difficult antigens and hidden epitopes. Dr. Mitchell Ho at the NCI has demonstrated that single domain antibodies are capable of targeting buried functional sites in cancer signaling complexes [Feng et al. PNAS, 2013; Gao et al Nature Communications, 2015; Li et al. PNAS, 2017; Li et al. Hepatology, 2019]. The Ho lab has constructed large shark and camel single-domain ('nanobody') libraries and isolated binders to a wide range of antigens [Feng et al. Antibody Therapeutics, 2019], indicating that the phage-displayed single domain antibody libraries can be a valuable source to isolate therapeutic antibodies. Two areas of research are being pursued at the AEP with collaborators using the shark and camel single domain phage libraries created by the Ho lab. One is focused on targeting intracellular cancer targets via binding of nanobodies to the MHC associated peptide complexes. The other is to isolate nanobodies to important and emerging viruses such as Lassa virus and SARS-CoV-2. In FY22, the AEP published three review articles [Duan and Ho. Molecular Cancer Therapeutics 2021; Duan and Ho. Antibody Therapeutics 2022; Yerabham and Ho. Antibody Therapeutics 2022] and one methodology paper [Duan et al. Current Protocols 2022]. Antibody-based immunotherapies show clinical effectiveness in various cancer types. However, the target repertoire is limited to surface or soluble antigens, which are a relatively small percentage of the cancer proteome. Most proteins of the human proteome are intracellular. Short peptides from intracellular targets can be presented by MHC class I (MHC-I) molecules on cell surface, making them potential targets for cancer immunotherapy. Antibodies can be developed to target these peptide/MHC complexes, similar to the recognition of such complexes by the T-cell receptor (TCR). These antibodies are referred to as T-cell receptor mimic (TCRm) or TCR-like antibodies. Ongoing preclinical and clinical studies will help us understand their mechanisms of action and selection of target epitopes for immunotherapy. Our review article published in Molecular Cancer Therapeutics (AACR) [Duan and Ho 2021] summarized and discussed the selection of intracellular antigens, production of the peptide/MHC complexes, isolation of TCRm antibodies for therapeutic applications, limitations of TCRm antibodies, and possible ways to advance TCRm antibody-based approaches into the clinic. Single-domain antibodies, including the antigen-binding variable domains of the shark immunoglobulin new antigen receptor and the camelid variable region of the heavy chain, are the smallest antigen recognition domains (15 kDa) and have unique characteristics compared to conventional antibodies. They are capable of binding epitopes that are hard to access for classical antibodies and can also be used for therapeutics or diagnostics or as modular building blocks for multi-domain constructs, antibody-drug conjugates, immunotoxins, or chimeric antigen receptor therapy. Our method paper contains detailed procedures for the purification and validation of two single-domain antibodies (one shark and one camel), which bind to the S2 subunit of the SARS-CoV-2 spike protein, using both bacterial and mammalian cell expression systems [Duan et al. Current Protocols. 2022]. It provides a comprehensive reference for the production of single-domain antibodies with high yield, good quality, and purity. In FY2022, the AEP also published two research papers as co-authors [Hong et al. PNAS 2022; Pan et al. Molecular Cancer Therapeutics 2022].