Aptamers Targeting Immune Checkpoints for Tumor Immunotherapy.

Tumor immunotherapy has revolutionized cancer treatment by harnessing the immune system to recognize and eliminate malignant cells, with immune checkpoint inhibitors targeting programmed death receptor 1 (PD-1), programmed death-ligand 1 (PD-L1), and cytotoxic T-lymphocyte-associated protein-4 (CTLA-4) demonstrating remarkable clinical success. However, challenges such as treatment resistance, immune-related adverse effects, and high costs highlight the need for novel therapeutic approaches. Aptamers, short, single-stranded oligonucleotides with high specificity and affinity for target molecules, have emerged as promising alternatives to conventional antibody-based therapies. This review provides a comprehensive analysis of aptamer-based strategies targeting immune checkpoints, with a particular focus on PD-1/PD-L1 and CTLA-4. We summarize recent advances in aptamer design, including bispecific and multifunctional aptamers, and explore their potential in overcoming immune resistance and improving therapeutic efficacy. Additionally, we discuss strategies to enhance aptamer stability, bioavailability, and tumor penetration through chemical modifications and nanoparticle conjugation. Preclinical and early clinical studies have demonstrated that aptamers can effectively block immune checkpoint pathways, restore T-cell activity, and synergize with other immunotherapeutic agents to achieve superior anti-tumor responses. By systematically reviewing the current research landscape and identifying key challenges, this review aims to provide valuable insights into the future directions of aptamer-based cancer immunotherapy, paving the way for more effective and personalized treatment strategies.