CASP6 and acute myeloid leukemia: We suspect that the caspase 8 activation seen in our caspase activation studies (Fig. 5A) is a non-essential process for CTL killing of AML cells and is not mediated by death receptor engagement but rather by (a) downstream caspases that have been shown to cleave caspase 8, such as caspase 6 and/or (b) by granzyme B itself, which has also been shown to cleave caspase 8 [89–91].