Introduction: This study aimed to assess programmed death-1 (PD-1) and programmed death ligand-1 (PDL-1) expression in newly diagnosed pediatric cases of acute B-lymphoblastic leukemia (B-ALL) and at 6 months of treatment and to explore their value as biomarkers.

Methods: Fifty newly diagnosed B-ALL patients and 30 controls were recruited. Bone marrow samples or peripheral blood were obtained from children at diagnosis and 6 months after cytotoxic therapy. Flow cytometric analysis of obtained samples was done and the PD-1, PDL-1, and CD3 (cluster of differentiation) expressions were recorded.

Results: Percentages of PD-1, PDL-1, and CD3 in the control and B-ALL groups at initial presentation were 7.9% ± 2.8% vs. 16.45% ± 7.7% (p = 0.023), 8.6% ± 3.4% vs. 19.05% ± 13.7% (p < 0.001), and 30.8% ± 1.2% vs. 11.05% ± 7.3% (p < 0.001), respectively. CD3 expression increased significantly at 6 months; PD-1 and PDL-1 expression showed insignificant decrease from initial presentation. There was a negative correlation between PD-1 and HB level (p = 0.03) and a positive correlation between PD-1 and PDL-1 at 6 months of treatment (p = 0.002). Remission rates increased significantly with the decrease of PD-1and PDL-1.

Conclusion: Initially, PD-1 and PDL-1 were higher in patients than in controls and decreased 6 months after treatment. PD-1 and PDL-1 expression was associated with increased remission rates, implicating that modulation of PD-1 and PDL-1 expression may be a therapeutic approach for B-ALL. Moreover, this study created a new method for the assessment of PD-1 and PDL-1 in B-ALL.

Clinical trial: Trial Registration: NCT05428111.