CD28 and acute lymphoblastic leukemia: To further confirm this effect of GSK3β inhibition on the proteolysis of MALT1 substrates, Jurkat T-ALL cells were stimulated with either P/I (Fig. 1C) or agonistic anti-CD3/CD28 antibodies (Fig. 1D) for different time intervals with and without pre-treatment with the GSK3β inhibitor SB216763 (SB21).