P319: IL7-RECEPTOR EXPRESSION IS FREQUENT IN T-CELL ACUTE LYMPHOBLASTIC LEUKEMIA AND PREDICTS SENSITIVITY TO JAK-INHIBITION (2023)

Background: T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy with a dismal prognosis related to refractory/relapsing diseases, raising the need for new targeted-therapies. Activating mutations of the IL7-receptor pathway genes (IL7Rp) play a proven leukemia-supportive role in T-ALL. JAK-inhibitors (JAKi) such as ruxolitinib have recently demonstrated preclinical efficacy. However, prediction markers for sensitivity to JAKi are still lacking. Aims: We aimed to provide a biological rationale to address the question of ‘who and how I treat’ with JAK-inhibitors in T-ALL. We thus sought to determine the extent of the IL7 oncogenic addiction in T-ALL and the patient categories who could benefit from JAKi. Methods: We analyzed a large cohort of primary T-ALL samples (n=200) for IL7R-expression (CD127) by flow-cytometry and IL7Rp-mutations using NGS. We compared the characteristics of the identified subgroups from an epigenetic perspective using Chip-Seq (n=26) and EPIC-array (n=26), and at the transcriptomic level (n=85) using RNA-seq. We also investigated their IL7Rp functional properties using pSTAT5 flow assay with (w) or without (w/o) IL7 and w or w/o ruxolitinib in primary derived xenografts (PDX, n=46). Finally, we used an apoptotic assay (Annexin V/ Propidium iodide) to evaluate the cytotoxic reponse to JAKi +/- venetoclax, an inhibitor of BCL2 which is a downstream target of the IL7Rp. Results: We show that IL7R (CD127) expression is more frequent (~70%) than IL7Rp-mutations (~30%) in adult T-ALL (n=200). This delineated 3 T-ALL categories including the so-called non-expressers (no IL7R-expression/IL7Rp-mutation), expressers (IL7R-expression without IL7Rp-mutation) and mutants (IL7Rp-mutations). Noteworthy, these categories were highly preserved from diagnostic to relapse in a cohort of 29 relapsing-T-ALL. Integrative multi-omics analysis outlined IL7R-deregulation in virtually all 3 T-ALL categories: at the epigenetic-level in non-expressers (hypermethylation), genetic-level in mutants (mutation(s)), and post-transcriptional level in expressers (ectopic expression). We then questionned the functionality and druggability of IL7Rp in each of the 3 T-ALL categories by investigating their response to IL7 and IL7+JAKi. Ex-vivo data using PDX support that IL7Rp is functional whenever the IL7R is expressed, regardless of the IL7Rp mutational status. Consequently, ruxolitinib impaired T-ALL survival in both expressers and mutants. Interestingly, we show that expressers displayed ectopic IL7R-expression and IL7Rp-addiction conferring a deeper sensitivity to ruxolitinib. Conversely, mutants were more sensitive to venetoclax than expressers. Overall, combination of ruxolitinib and venetoclax resulted in synergistic effects in both groups. Finally, we illustrate the clinical relevance of this association by reporting achievement of complete remission in two patients with refractory/relapsed-T-ALL that enabled bridge-to-transplant. Summary/Conclusion: Altogether, this study provides valuable information to optimize translation of JAKi and venetoclax to clinics for T-ALL patients with relapse who need therapeutics to bridge to transplant. This treatment protocol may benefit to a larger group of patients who may be selected with an easily applicable flow-cytometry-based companion test. IL7R-expression can be used as a biomarker for sensitivity to JAK-inhibition, thereby expanding the fraction of T-ALL patients eligible to JAKi up to nearly ~70% of T-ALL. Keywords: Signaling, T-ALL, Ruxolitinib, Targeted therapy