Heteroclitic CD33 peptide with enhanced anti-acute myeloid leukemic immunogenicity

The goal of these studies was to engineer a synthetic CD33 peptide with enhanced immunogenicity for the induction of acute myeloid leukemia (AML)-specific CTLs. Eight modified CD33 peptides (YL) under bar ISGDSPV, (Y) under barI (G) under bar SGDSPV, (Y) under bar IIIGDSPV, (Y) under bar II (L) under bar GDSPV, (Y) under bar IISGI (S) under bar PV, (Y) under bar IISGD (L) under bar PV, (Y) under bar IISGDS (W) under barV and (Y) under bar IISGDSP (L) under bar were designed for increased HLA-A2.1 or T cell receptor affinity and compared with the native CD33(65-73) peptide, AIISGDSPV, for enhanced immunogenicity. The (YL) under bar ISGDSPV peptide was found to be the most immunogenic epitope producing highly cytolytic CTLs against AML target cells. The CTLs generated with (YL) under bar ISGDSPV peptide showed CD33 peptide-specificity through targeting of both native (AIISGDSPV) and modified ((YL) under bar ISGDSPV) peptide presenting EBV-BLCL. The CTL cultures displayed a distinct phenotype consisting of a high percentage of activated memory (CD69(+)/CD45RO(+))-CD8(+) and a low percentage of naive (CD45R(+)/CCR7(+))-CD8(+) cells. In addition, T-cell clones specific to the (YL) under bar ISGDSPV peptide were isolated and characterized to target AML cells. The clones exhibited both HLA-A2.1-restricted and AML cell-specific cytotoxicity that was mediated through a granule-dependent pathway. More importantly, the CTL clones did not lyse or inhibit the proliferation of normal CD34(+) progenitor cells. In conclusion, we report on the identification of a highly immunogenic heteroclitic (YL) under bar ISGDSPV CD33 epitope that is a promising candidate for immunotherapy targeting AML.