Engineered DNA plasmid encoding proinsulin (BHT-3021) preserves β cell function in T1D patients through a reduction in insulin-specific T cells when comparing the islet-specific CD8+ T cell frequencies assessed with multimers of monomeric human leukocyte antigen class I molecules loaded with peptides containing pancreatic or unrelated antigens. This evidence concerns the gene INS and type 1 diabetes mellitus.