PTPA and acute myeloid leukemia: Interestingly, AKT is a downstream target of PP2A, a crucial serine-threonine phosphatase, which associates to CTLA-4 and regulates its inhibitory activity (65), and reduced PP2A activity has been related with enhanced Thr308 phosphorylation, without altering Ser473, in acute myeloid leukemia (66).