Research ArticleIMMUNOTHERAPY

Bispecific antibodies targeting mutant RAS neoantigens

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Science Immunology  01 Mar 2021:
Vol. 6, Issue 57, eabd5515
DOI: 10.1126/sciimmunol.abd5515

Diabodies see the unseeable

RAS oncogene mutations are common in various cancers, controlling their growth and survival. Targeting mutant RAS proteins with antibodies has been unsuccessful due to low surface expression, even when targeting mutant RAS peptides presented via HLA on the surface of cancer cells. Douglass et al. used phage display to generate single-chain variable fragments (scFvs) specific for mutant RAS peptide-HLA complexes. The authors tested various bispecific, T cell–engaging antibody formulations, finding that single-chain diabodies (scDbs) combining the aforementioned scFv with an anti-CD3 scFv were able to induce T cell activation and subsequent killing of tumor cells expressing mutant RAS peptide-HLA complexes. This scDb approach opens the door for antibody-based therapies against mutant neoantigens expressed at very low levels on the surface of cancer cells.

Abstract

Mutations in the RAS oncogenes occur in multiple cancers, and ways to target these mutations has been the subject of intense research for decades. Most of these efforts are focused on conventional small-molecule drugs rather than antibody-based therapies because the RAS proteins are intracellular. Peptides derived from recurrent RAS mutations, G12V and Q61H/L/R, are presented on cancer cells in the context of two common human leukocyte antigen (HLA) alleles, HLA-A3 and HLA-A1, respectively. Using phage display, we isolated single-chain variable fragments (scFvs) specific for each of these mutant peptide-HLA complexes. The scFvs did not recognize the peptides derived from the wild-type form of RAS proteins or other related peptides. We then sought to develop an immunotherapeutic agent that was capable of killing cells presenting very low levels of these RAS-derived peptide-HLA complexes. Among many variations of bispecific antibodies tested, one particular format, the single-chain diabody (scDb), exhibited superior reactivity to cells expressing low levels of neoantigens. We converted the scFvs to this scDb format and demonstrated that they were capable of inducing T cell activation and killing of target cancer cells expressing endogenous levels of the mutant RAS proteins and cognate HLA alleles. CRISPR-mediated alterations of the HLA and RAS genes provided strong genetic evidence for the specificity of the scDbs. Thus, this approach could be applied to other common oncogenic mutations that are difficult to target by conventional means, allowing for more specific anticancer therapeutics.

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