Response to OSE-127 was detected in 9/11 (82%) PDX samples in vivo, including BCR-ABL+, MLLr and E2A-PBX1+-relapse samples. Accordingly, OSE-127 immunotherapy led to a significant increase in median overall survival (85 days versus 55 days; P=0.0122). Of note, OSE-127 therapy response associated with IL7R expression levels on BCP-ALL cells...Taken together, our data demonstrate that IL7R-targeting using OSE-127, which has already demonstrated a good safety profile in healthy volunteers, is an efficient approach for BCP-ALL immunotherapy and may be particularly beneficial for patients with high IL7R-expression and/or relapsed/refractory disease after CD19-directed therapy.