Expression of Tumor-Associated Antigens (TAAs) in Acute Myeloid Leukemia (AML) Correlated with Specific T Cell Responses and Survival.

Several Tumor-associated antigens (TAAs) are expressed in acute myeloid leukemia (AML) and elicit specific immune responses of CD8 positive T cells. These specific T cell responses against leukemic blasts expressing TAAs might play a critical role in the control of minimal residual disease (MRD) in AML. Therefore, we investigated whether TAAs inducing specific immune responses in AML patients were associated with the clinical outcome. A DNA-microarray analysis of 116 AML samples was performed to correlate expression of TAAs to the clinical outcome. In these AML patients specific T cell responses to TAAs were assessed by ELISPOT analysis, tetramer staining and chromium release assays. Quantitative RT-PCR based validation of our results demonstrated the power of DNA microarray technology. We found a significant correlation of high mRNA expression of the TAA G250/CA9 with a longer overall survival (P=0.022), a trend for better outcome in patients with high expression levels of PRAME (P=0.103), and a hint for RHAMM/HMMR. In contrast, for other TAAs like WT1, TERT, PRTN3, BCL2, and LAMR1 we found no correlation with clinical outcome of AML patients. Moreover, co-expression of RHAMM/HMMR, PRAME and G250/CA9 provided a favorable prognostic effect (P=0.005). We found specific T cell responses at high frequency for these three antigens in AML patients. Positive immune reactions were detected in 8/17 (47%) AML patients for RHAMM/HMMR-R3-derived, in 7/10 (70%) for PRAME-P3-derived, and in 6/10 (60%) for newly characterized G250/CA9-G2-derived peptides. We detected a significant increased immune response of AML patients in complete remission compared to AML patients with refractory disease (P<0.001). Furthermore, we could demonstrate specific lysis of T2 cells and AML blasts presenting these epitope peptides RHAMM/HMMR-R3, PRAME-P3 and G250/CA9-G2. In conclusion, the expression of the TAAs RHAMM/HMMR, PRAME and G250/CA9 can induce strong anti-leukemic immune responses of CD8 positive T cells possibly enabling the control of MRD in AML patients. Thus, the antigens RHAMM/HMMR, PRAME and G250/CA9 represent interesting target structures for polyvalent immunotherapeutic approaches in AML.