Abstract: Mutant epitopes encoded by cancer genes are virtually always located in the interior of cells, making them invisible to conventional antibodies. We generated single chain variable fragments (scFvs) specific for mutant peptides presented on the cell surface by human leukocyte antigen (HLA) molecules. These scFvs can be converted to full-length antibodies, termed MANAbodies, targeting “Mutation Associated Neo-Antigens” bound to HLA. A phage display library representing a highly diverse array of single-chain variable fragment sequences was first designed and constructed. A competitive selection protocol was then used to identify clones specific for peptides bound to pre-defined HLA types. In this way, we obtained scFvs, including one specific for a peptide encoded by a common KRAS mutant and another by a common EGFR mutant. Molecules targeting MANA can be developed that specifically react with mutant peptide-HLA complexes even when these peptides differ by only one amino acid from the normal, wild-type form.