Breaking tolerance: autoantibodies can target protein posttranslational modifications

Abstract

Autoantibodies (AAb) are an immunological resource ripe for exploitation in cancer detection and treatment. Key to this translation is a better understanding of the self-epitope that AAb target in tumor tissue, but do not bind to in normal tissue. Posttranslational modifications (PTMs) on self-proteins are known to break tolerance in many autoimmune diseases and have also recently been described in cancer. This scope of possible autoantigens is quite broad and new high-dimensional and -throughput technologies to probe this repertoire will be necessary to fully exploit their potential. Here, we discuss the strengths and weaknesses of existing high-throughput platforms to detect AAb, review the current methods for characterizing immunogenic PTMs, describe the main challenges to identifying disease-relevant antigens and suggest the properties of future technologies that may be able to address these challenges. We conclude that exploiting the evolutionary power of the immune system to distinguish between self and nonself has great potential to be translated into antibody-based clinical applications.

Figure 1.

PubMed citations of autoantibodies (AAb) described in autoimmunity or cancer have steadily risen since 1963. In the last decade, AAb citations have almost doubled for a total of 2565 autoimmunity and 908 cancer publications in 2022.

Figure 2.. Two approaches to high-throughput autoantibody identification

(A) Platforms like SEREX, NAPPA, and HuProt use recombinant proteins bound to a coated slide or other surface in a spatially specific manner in order to map protein identification. Human serum or plasma are then added, unbound autoantibodies are washed away, and bound autoantibodies are often detected by a fluorescent anti-human immunoglobulin secondary antibody. (B) Platforms like PhIP-Seq or REAP produce barcoded proteins and after incubation with human serum or plasma, autoantibodies are immunoprecipitated by antibody-binding magnetic beads or columns. The identify of autoantibody-bound proteins are then identified by barcode sequencing. Image created with BioRender.com.

Figure 3.. Approaches for PTM-targeting autoantibody identification

(A) Methods like SERPA use tumor or cancer cell lysates that are separated on 2D electrophoresis gels and probed with serum from diseased or healthy patients. Bound autoantibodies are detected with a fluorescent or chemiluminescent secondary antibody. Proteins with autoantibody binding in diseased but not healthy patients are excised and sent for identification via mass spectrometry. (B) Commercially available antibodies are spotted on coated microarray slides in a specific spatial orientation and used to capture autoantibody-antigen complexes upon incubation with patient serum or plasma. Bound autoantibody-antigen complexes are detected by a fluorescent secondary antibody. Image created with BioRender.com