Introduction Acute Lymphoblastic Leukemia (ALL) remains the most prevalent childhood malignancy. While chemotherapy has improved survival rates, multidrug resistance (MDR) mediated by P-glycoprotein (P-gp/ABCB1) overexpression persists as a major cause of treatment failure and relapse. Natural Killer (NK) cells are pivotal for anti-leukemic surveillance but are often compromised during treatment due to their susceptibility to chemotherapy, a vulnerability intrinsically linked to their own expression of P-gp. Strategies to transiently enhance NK cell chemoresistance could therefore preserve immune function and improve therapeutic outcomes. We hypothesized that stimulating Toll-Like Receptor 2 (TLR2) on NK cells could modulate P-gp expression or activity, enhancing their resilience to cytotoxic drugs. Methods In this study, we first characterized NK cells from pediatric ALL patients, confirming the constitutive expression of both the therapeutic target (TLR2) and the drug efflux pump (P-gp) across all major subpopulations. Using a healthy donor model, we then dissected the functional consequences of specific TLR2 heterodimer engagement. Results While agonists for both TLR2/1 (PCSK) and TLR2/6 (LTA, MALP-2) induced functional activation, their effects on P-gp were divergent. In a PBMC context, stimulation with the TLR2/1 agonist PCSK significantly enhanced the efflux of the chemotherapeutic agent Methotrexate (MTX), but not Rhodamine 123. This functional enhancement occurred without increasing P-gp surface expression, suggesting a modulation of transporter kinetics. Crucially, mechanistic assays in purified NK cells revealed that this MTX efflux enhancement relies on the cellular microenvironment, whereas direct high-dose TLR2/1 stimulation paradoxically led to P-gp loss. Furthermore, we demonstrated that the immunomodulatory effects of PCSK extend beyond chemoresistance to directly potentiate anti-leukemic effector functions; PCSK stimulation significantly enhanced NK cell cytotoxicity against RS4;11 leukemic blasts without compromising effector viability. Discussion These findings identify a novel immunomodulatory axis where TLR2 signaling differentially regulates P-gp function and effector capacity in NK cells depending on the specific heterodimer engaged and the cellular context. We propose that controlled TLR2/1 stimulation represents a potential dual-benefit strategy to protect NK cells from chemotherapy-induced suppression while boosting their anti-leukemic activity in ALL.
Álvarez-Carrasco et al. (Wed,) studied this question.