Development and validation of monoclonal antibodies against N6-methyladenosine for the detection of RNA modifications.

RNA contains various chemical modifications, among which N6-methyladenosine (m6A) is the most prevalent modified nucleotide in eukaryotic mRNA. Emerging evidence suggests that m6A plays an important role in regulating a variety of cellular functions by controlling mRNA processing, translation and degradation. Because m6A is not detectable by standard chemical modification-based approaches, immunological methods, such as ELISA, immunoblotting, immunohistochemistry, m6A RNA immunoprecipitation sequencing and m6A individual-nucleotide resolution cross-linking and immunoprecipitation, have been employed to detect m6A in RNA. Although the most important factor determining the success of these methods is the integrity of highly specific antibodies against m6A, the development of m6A-specific monoclonal antibodies has been challenging. We developed anti-m6A monoclonal antibodies using our recently developed single cell-based monoclonal antibody production system. The binding of one selected antibody, #B1-3, to RNA oligoribonucleotide containing a single m6A had an equilibrium dissociation constant of 6.5 nM, and this antibody exhibited negligible binding to oligoribonucleotides containing a single N1-methyladenosine and unmodified adenosine. The binding was competed by the addition of increasing concentrations of N6-methyl-ATP but not N1-methyl-ATP or ATP. Furthermore, this mAb specifically crosslinked m6A-containing oligoribonucleotide by ultraviolet light, resulting in the induction of cDNA truncation at m6A position. These results show the feasibility of using the validated m6A monoclonal antibody for the specific detection of m6A in RNA.

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

Intracellular tumor-associated antigens are targeted by antibodies known as T-cell receptor mimic antibodies (TCRm-Abs), which recognize T-cell epitopes with better stabilities and higher affinities than T-cell receptors. However, TCRm-Abs have been proven difficult to produce using conventional techniques. Here, we developed TCRm-Abs that recognize the survivin-2B-derived nonamer peptide, AYACNTSTL (SV2B80-88), presented on HLA-A*24 (SV2B80-88/HLA-A*24) from immunized mice by using a fluorescence-activated cell sorting-based antigen-specific plasma cells isolation method combined with a high-throughput single-cell-based immunoglobulin-gene-cloning technology. This approach yielded a remarkable efficiency in generating candidate antibody clones that recognize SV2B80-88/HLA-A*24. The screening of the antibody clones for their affinity and ability to bind key amino-acid residues within the target peptide revealed that one clone, #21-3, specifically recognized SV2B80-88/HLA-A*24 on T2 cells. The specificity of #21-3 was further established through survivin-2B-positive tumor cell lines that exogenously or endogenously express HLA-A*24. A bispecific T-cell engager comprised of #21-3 and anti-CD3 showed specific cytotoxicity towards cells bearing SV2B80-88/HLA-A*24 by recruiting and activating T-cells in vitro. The efficient development of TCRm-Ab overcomes the limitations that hamper antibody-based immunotherapeutic approaches and enables the targeting of intracellular tumor-associated antigens.