CD28-Targeted Enzyme-Responsive Conformation-Switching Peptide Self-Assembly for Selective T-Cell Acute Lymphoblastic Leukemia (T-ALL) Therapy.

T-cell acute lymphoblastic leukemia (T-ALL) is a highly aggressive hematologic malignancy with limited targeted therapies. CD28, a costimulatory receptor aberrantly overexpressed on T-ALL cells, presents a promising underexplored therapeutic target. In this study, we developed an enzyme-responsive self-assembling peptide, SAp-CD28, designed to target CD28 and undergo receptor-mediated self-assembly in the tumor microenvironment. Upon dephosphorylation by overexpressed phosphatases, SAp-CD28 transitions from an α-helix to a β-sheet/β-turn rich structure, facilitating the formation of nanooligomers that engage CD28 and activate cytotoxic pathways. Transcriptomic and biochemical analyses reveal that SAp-CD28 induces a profound dysregulation of CD28 downstream signaling, characterized by the suppression of the PLCγ and Akt pathways. These signaling perturbations lead to oxidative stress and disruption of intracellular calcium homeostasis, resulting in calcium overload, calpain activation, and cytoskeletal collapse. Besides, confocal imaging suggested that the peptide self-assembly can enter the nucleus and disrupt it. In Jurkat xenograft models, SAp-CD28 demonstrated potent antitumor activity, and its combination with cytarabine resulted in near-complete tumor suppression, highlighting its potential for T-ALL treatment. This work introduces a CD28-targeted, enzyme-activated nanotherapeutic strategy that synergizes biochemical and mechanical mechanisms to selectively eliminate T-ALL cells. This multi-mechanistic tumor-killing strategy can also be extended to inspire therapeutic approaches for other diseases.