PTK2 and acute lymphoblastic leukemia: Notably, pFAK levels in T-ALL cells were significantly diminished in Icam1-/- mice relative to Icam1+/- littermate controls, with a similar, but non-significant, trend for pPYK2 (Fig. 5d), demonstrating that activation of FAK and PYK2 in T-ALL cells is dependent on ICAM-1 expression in the leukemic microenvironment.