CD25-Targeted Aptamer–Drug Conjugate for the Treatment of CD25-Expressing Hematological Malignancies

<b>Background</b>: CD25, the α-chain of the interleukin-2 (IL-2) receptor, is highly expressed on malignant cells and tumor-infiltrating regulatory T-cells (Tregs) in hematologic malignancies, making it an attractive therapeutic target for tumor elimination and immunomodulation. <b>Methods</b>: We developed a CD25-specific aptamer-drug conjugate (CD25-ApDC) by linking a CD25 aptamer to monomethyl auristatin E via a cathepsin B-cleavable Val-Cit linker. <b>Results</b>: The aptamer exhibited high affinity for CD25 (Kd = 16.4 ± 0.29 nM), rapid receptor-mediated uptake (half-time = 9.6 min), and selective inhibition of IL-2 signaling in CD25^high cells, with no activity in CD25^low cells. In vitro, CD25-ApDC induced selective cytotoxicity, confirmed by apoptosis and G2/M arrest in CD25-positive cancer cells while having no effect on CD25-negative cells. Co-culture studies confirmed selective depletion of CD25^high Treg-like cells, suggesting potential to relieve immune suppression within the tumor microenvironment. In vivo, CD25-ApDC achieved complete tumor remission in xenograft and disseminated models with optimized dosing, showing efficacy and tolerability comparable to Brentuximab vedotin. Increasing drug-to-aptamer ratios further enhanced outcomes, supporting flexible dosing strategies. <b>Conclusions</b>: These findings highlight CD25-ApDC as a promising therapeutic modality for hematologic malignancies, offering advantages in specificity, tissue penetration, and manufacturability over conventional antibody-based therapies.