Antibody Engineering Program

Division Of Basic Sciences - Nci

Investigators

Linked publications, trials & patents

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 FY21, the AEP published two articles and several other manuscripts in preparation. One article was published in Molecular Cancer Therapeutics [Duan and Ho Mol Cancer Ther 2021]. 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 major histocompatibility complex 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 understand their mechanisms of action and selection of target epitopes for immunotherapy. Our review summarized and discuss 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 in the clinic. In the other article published in Antibody Therapeutics [Sun and Ho, Antib Ther 2020], we summarized the development of neutralizing antibodies against SARS-CoV-2, with a focus on discussing various antibody discovery strategies (animal immunization, phage display and B cell cloning), describing binding epitopes and comparing neutralizing activities. Broad-neutralizing antibodies targeting the spike proteins of SARS-CoV-2 and SARS-CoV might be helpful for treating COVID-19 and future infections. VIR-7831/7832 based on S309 is the only antibody in late clinical development, which can neutralize both SARS-CoV-2 and SARS-CoV although it does not directly block virus receptor binding. Thus far, the only cross-neutralizing antibody that is also a receptor binding blocker is nanobody VHH-72. The feasibility of developing nanobodies as inhaled drugs for treating COVID-19 and other respiratory diseases is an attractive idea that is worth exploring and testing. A cocktail strategy such as REGN-COV2, or engineered multivalent and multispecific molecules, combining two or more antibodies might improve the efficacy and protect against resistance due to virus escape mutants. Besides the receptor-binding domain, other viral antigens such as the S2 subunit of the spike protein and the viral attachment sites such as heparan sulfate proteoglycans that are on the host cells are worth investigating.