Abstract
Pediatric B-cell precursor acute lymphoblastic leukemia (BCP-ALL) has a favorable prognosis when treated according to contemporary protocols. Nevertheless, patients subjected to intensive chemotherapy suffer from significant short- and long-term toxicity, which supports the need for novel targeted therapies. Here, we study the role of IL-7Rα in BCP-ALL development in preclinical model and show gene expression data of patient cohorts suggesting that targeting IL-7Rα may be beneficial for treating ALL patients, especially those with CNS involvement.
IL-7Rα is expressed in almost all BCP-ALL patients with particularly high expression levels in E2A-PBX1 leukemias. Therefore, we analyzed mRNA levels of IL-7Rα in diagnostic BM of 61 E2A-PBX1+ pediatric BCP-ALL patients at initial diagnosis. High IL-7Rα expression was associated with an increased white blood cell count (p= 0.0206), which is a poor prognostic indicator in patients. Importantly, high IL-7Rα expression was also associated with CNS positivity (p= 0.0162). There were no correlations between IL-7Rα expression and sex, age, prednisone response or risk group. To further investigate the role of IL-7Rα in CNS infiltration, we determined IL-7Rα expression levels in an expanded BCP-ALL cohort of 98 patients. The cohort was selected to contain 26 CNS-positive (only 1 patient was E2A-PBX1 +) and 72 CNS-negative patients. IL-7Rα expression was significantly elevated in CNS-positive as compared to CNS-negative patients (p= 0.0284). There were no statistical differences in sex, age, prednisone response and MRD risk groups between the CNS-negative and CNS-positive patients. These data suggest that IL-7Rα expression is associated with CNS infiltration in both E2A-PBX1 positive and negative BCP-ALL patients
To study the effect of inhibiting IL-7Rα signaling in xenograft models, we injected E2A-PBX1 + primary BCP-ALL cells into NSG mice. We monitored the survival of recipient mice under ruxolitinib treatment, which targets IL-7Rα downstream signaling via JAK1/2. Interestingly, ruxolitinib treated mice showed a significantly prolonged survival as compared to untreated mice (median survival 76 vs. 64 days, respectively, p= 0.0002). However, there were no significant differences in leukemic burden in spleen, bone marrow or CNS. Ruxolitinib abrogates IL-7Rα signaling via JAK1/2, but not via JAK3. Therefore, we investigated whether interfering with IL-7Rα expression directly would block infiltration more efficiently than ruxolitinib treatment. For that purpose, the E2A-PBX1 + cell line 697 was lentivirally transduced with specific shRNAs against IL-7Rα (shIL-7Rα) or a non-targeting green fluorescent protein (shGFP) control. The cells were then injected intravenously into NSG mice, which were sacrificed when leukemia symptoms developed. Leukemic bone marrow and splenic infiltration was significantly reduced in shIL-7Rα animals as compared to the control group (median % blasts 64% vs. 21%, p= 0.0167 and 52% vs. 9%, p= 0.0238, respectively). Similarly, immunohistochemical scoring of CNS infiltration revealed that 6/6 animals (100%) in the shGFP group and only 1/6 animals (17%) in the shIL-7Rα group were CNS-positive (p= 0.0152). This suggests that interfering with IL-7Rα expression impairs the proliferation as well as the CNS-positive phenotype of 697 cells in vivo . To test if treatment with anti-IL-7Rα antibody can also interfere with leukemia development, NSG mice bearing 697 cells were treated with anti-human IL-7Rα antibody in the presence or absence of ruxolitinib. Spleen volumes of mice treated with anti-IL-7Rα antibody were significantly smaller than controls (median size 0.1130 cm3 vs. 0.0885 cm3, respectively, p= 0.0079) whereas mice treated with ruxolitinib alone were not significantly different from controls. Similarly, leukemic infiltration in spleen and bone marrow was significantly reduced in mice treated with antibody or with both antibody and ruxolitinib compared to control mice or mice treated with ruxolitinib alone (Figure 1). These data suggest that anti-IL-7Rα therapy is highly efficient in abrogating leukemia development in xenograft mice and outperforms ruxolitinib blockade.
Altogether, we show that expression of IL-7Rα is a hallmark of primary BCP-ALL and associated with CNS leukemia. Importantly, we propose the use of IL-7Rα antibodies as a potential therapeutic alternative for treating BCP-ALL.
Schrappe: JAZZ Pharma: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; SigmaTau: Consultancy, Research Funding; Baxalta: Consultancy, Research Funding; Medac: Consultancy, Research Funding.
