Wilms Tumor Protein 1 (WT1) Peptide Vaccination-induced Complete Remission in a Patient With Acute Myeloid Leukemia Is Accompanied by the Emergence of a Predominant T-cell Clone Both in Blood and Bone Marrow

Within the last few years, the first peptide vaccination trials for treatment of acute myeloid leukemia (AML) have been initiated. Athough the presence of epitope-specific T cells could be seen both in bone marrow (BM) and peripheral blood (PB), nothing is known about their clonal composition. In this study, we analyzed material from a patient with recurrent AML vaccinated with Wilms Tumor Protein 1 (WT1) peptide, who achieved a complete remission (CR) lasting for 12 months. For identification of expanded WT1-specific T-cell clones, enrichment by tetramer and IFN gamma secretion were followed by comparative quantitative reverse transcribed PCR (qRT PCR) quantification of all TCR V beta-families. V beta-families with increase in the enriched fraction were cloned and sequenced. A predominant clone was quantified by clonotypic qRT PCR from PB and BM. Quantity and functionality of WT1-specific cells were assessed by tetramer analyses and intracellular IFN gamma staining. A specific predominant clone was identified during clinical remission. Clone-specific qRT PCR showed an increase both in PB and BM after 8 vaccinations. Six months after achieving CR, the transcript levels in BM decreased. Relapse was accompanied by secondary rise of the WT1-specific clone in PB but not in BM. In parallel, a lack of vaccine-induced WT1 specific IFN gamma production was observed at that timepoint. In conclusion, we provide first data regarding evolution and compartmentalization of a peptide vaccine-induced T-cell clone in PB and BM of an AML patient. At the time of relapse, the same clone reappeared spontaneously in PB but not in BM showing impaired functionality.