Interleukin signaling mitigates the inhibitory effects of combined Src/BCR-ABL1 blockade on T-cell activity in Philadelphia chromosome-positive acute lymphoblastic leukemia

Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ ALL), driven by the BCR-ABL1 fusion gene, remains a high-risk malignancy despite therapeutic advances. Tyrosine kinase inhibitors (TKIs) targeting BCR-ABL1 have significantly improved outcomes, but resistance and relapse persist, necessitating novel strategies such as combining TKIs with bispecific T-cell engagers (BiTEs) like blinatumomab. Blinatumomab redirects T cells to eliminate CD19+ leukemia cells and has shown impressive clinical activity in Ph+ ALL when combined with Src+BCR-ABL1 TKIs. However, this contrasts with preclinical observations reporting that Src kinase inhibition by Src/BCR-ABL1 TKIs antagonizes blinatumomabmediated T-cell activation. Consistent with prior preclinical studies, we demonstrate that dasatinib and ponatinib, unlike SRC sparing TKIs (imatinib, nilotinib), antagonize blinatumomab's T-cell engaging efficacy by potently inhibiting LCK Y394 phosphorylation, a critical step in proximal TCR signaling. This inhibition impairs T-cell proliferation, cytokine production, and NFAT activation. To reconcile this in vitro antagonism with favorable clinical combination outcomes, we confirmed that the mechanism of SRC inhibition is T-cell intrinsic and explored the impact of interleukins. We show that TKI-induced T-cell suppression and antagonism can be significantly improved by supplementing co-cultures with common gamma-chain cytokines, particularly IL-7. IL-7 robustly enhances human T-cell proliferation, reduces exhaustion, and significantly improves blinatumomab's cytotoxic efficacy in the presence of Src/BCRABL1 TKIs.