Figure 1: Quantitative HLA I expression (a) in primary childhood ALL and AML blasts measured by Qifikit (Dako). HLA I molecules/cell mean 211064 ± 25800 (range: 13149 to 436661) in ALL and 416339 ± 55329 in AML (range: 35724 to 741641). AML showed significantly higher HLA I expression than ALL (, ; ). (b) Cellular cytotoxicity (BATDA europium release assay, Perkin Elmer) of freshly isolated CD56+ enriched and CD3+ depleted NK cells from healthy volunteer donors towards ALL (only 1 donor, ) versus AML (2 different donors, ) blasts with and without IL2 prestimulation at E : T ratio 10 : 1 revealed significantly higher lysis in AML than ALL without IL2 prestimulation (filled symbols) and with IL2 prestimulation (blank symbols) (; ). Comparing ALL versus AML lysis in single donor comparison also revealed significantly higher lysis for AML blasts. The ALL data was already published in Br J Haematology 2007 [11].