Immune checkpoint inhibitors (ICIs) have transformed cancer immunotherapy, but clinical benefits are limited by low response rates and immune‑related adverse events from on‑target off‑tumor effects. To mitigate these limitations, the authors developed a chemically masked anti‑PD‑L1 nanobody‑sialidase conjugate named CAPS. CAPS is intended to provide spatial control of protein function so that PD‑L1 blockade and enzymatic desialylation occur preferentially within the tumor microenvironment.
The construct integrates a nanobody that targets PD‑L1 with a fused sialidase enzyme, enabling simultaneous modulation of two immunosuppressive pathways. The design seeks to increase tumor specificity of activity while limiting systemic exposure to the active conjugate.
CAPS is produced using genetic code expansion to incorporate a non‑canonical amino acid (ncAA) at a defined site. Following ncAA incorporation, a chemical mask is installed via site‑specific PEGylation. This masking reduces nanobody affinity and blocks sialidase activity systemically, thereby minimizing off‑tumor engagement and circulating enzyme activity.
The mask is engineered to be removable by a tumor‑associated protease, permitting restoration of the conjugate’s functions where the protease is present.
The chemical mask on CAPS is designed to be cleaved by MMP2, a protease that is enriched in many tumor microenvironments. Cleavage by MMP2 removes the PEG mask locally and restores both nanobody binding capability and enzymatic activity of the sialidase component. This protease‑responsive activation provides a mechanism for tumor‑selective re‑activation of the therapeutic functions.
The masked design yields what the authors describe as “one construct, three functions.” By reversible masking and protease‑triggered unmasking, CAPS allows simultaneous control over three parameters:
These coordinated controls aim to concentrate both PD‑L1 blockade and sialic acid removal within tumor tissue while sparing normal tissues.
CAPS is intended to interrupt two immunosuppressive pathways concurrently. The anti‑PD‑L1 nanobody component targets the PD‑1/PD‑L1 immune checkpoint axis, while the sialidase removes terminal sialic acids to disrupt the Sialoglycan/Siglec immunosuppressive axis. Localized desialylation may enhance immune recognition and activation in the tumor microenvironment when combined with PD‑L1 blockade.
When compared with the unmasked control construct (anti‑PD‑L1 nanobody‑sialidase, referred to as APS), CAPS demonstrated markedly altered pharmacokinetics and biodistribution. The masked CAPS showed a 144‑fold extension in systemic half‑life over APS and achieved a 9.3‑fold increase in tumor‑site accumulation. These differences were reported by the authors as evidence that masking can substantially modify circulation time and tumor delivery.
In murine models of immune checkpoint inhibitor‑resistant colorectal cancer, CAPS produced superior antitumor efficacy relative to controls. The authors report that CAPS enhanced immune activation within treated tumors and showed an improved safety profile, suggesting reduced on‑target off‑tumor toxicity compared with the unmasked conjugate.
Specific experimental details, numerical results beyond the reported fold‑changes in half‑life and tumor accumulation, and methods were presented in the full article; those procedural and quantitative specifics are not reproduced here beyond what the source abstract reports.
The authors propose CAPS as a new class of glyco‑ICIs that combine checkpoint blockade with targeted glycan editing to potentiate antitumor immunity. The protease‑responsive, chemically masked approach is intended to improve the therapeutic index by enhancing efficacy in tumors while minimizing systemic enzymatic activity and off‑tumor immune modulation.
Taken together, the reported enhancements in systemic half‑life, tumor accumulation, antitumor activity, and safety in preclinical models support further investigation of CAPS‑type constructs as a strategy to overcome limitations of current ICIs. The abstract emphasizes keywords and enabling technologies including genetic code expansion, ncAAs, protease responsivity, PD‑L1 targeting, and sialidase activity.
CAPS represents a rationally engineered, protease‑activated anti‑PD‑L1 nanobody‑sialidase conjugate that the authors report can localize dual immunomodulatory functions to tumors. According to the source, this design improved pharmacokinetics and tumor targeting and yielded superior efficacy and safety in mouse models of ICI‑resistant colorectal cancer, supporting the concept of tumor‑selective glyco‑ICIs. Detailed experimental protocols, full datasets, and translational considerations are available in the full text of the cited article.