Episode 78: Covalently PD‐L1 Anchoring Drives Bispecific Nanostructure Assembly for Spatial Control of T Cell Recruitment and Activation

**Monday Immune Engager** — our weekly pick from the latest immune-engager digest. **Paper:** [Covalently PD‐L1 Anchoring Drives Bispecific Nanostructure Assembly for Spatial Control of T Cell Recruitment and Activation](https://doi.org/10.1002/anie.5894316) **Authors:** Fengzhen Zhang, Yuhan Dong, Kailu Liu, Hui Hu, et al. **Journal:** Angewandte Chemie International Edition, 2025 **Why it matters:** Rather than passively blocking tumor immune checkpoints, this work shows it is possible to chemically hijack a tumor's own surface machinery to build synthetic nanostructures that simultaneously relieve immune suppression and actively recruit and activate T cells. **Summary** Current immune checkpoint therapies that block the PD-1/PD-L1 axis — the suppressive signaling pathway tumors use to exhaust T cells — benefit only around 20% of patients. Blocking the pathway removes an inhibitory signal but does not actively stimulate T cells to attack, a distinction the authors liken to releasing a parking brake without pressing the accelerator. This paper introduces a two-step "localized oxidation–covalent assembly" strategy designed to do both at once. The first component, the P1 probe, is a conjugate of a PD-L1-targeting peptide (Kd ≈ 4.5 µM) and the enzyme galactose oxidase (GAO). Once the probe transiently binds PD-L1, GAO oxidizes the C6 hydroxyl groups on PD-L1's N-linked glycans, converting them to aldehydes. Specificity was confirmed using a glycosylation-deficient PD-L1 mutant (4NQ) and the inhibitor tunicamycin, both of which sharply reduced oxidation. These aldehyde groups serve as covalent anchors for the second component: a hydrazide-functionalized self-assembling peptide (HSP) incorporating an anti-CD3 sequence. Covalent attachment of HSP to the oxidized membrane dramatically lowers its critical aggregation concentration (CAC) from 38.26 µM to 2.18 µM, driving rapid β-sheet and π–π stacking assembly into stable artificial topological nanostructures (ATNs) directly on the tumor surface. The resulting ATNs act as membrane-anchored bispecific T cell engagers (BiTEs): they block PD-1/PD-L1 interaction while projecting anti-CD3 sequences outward to recruit and activate passing T cells. In vivo in MC38 tumor-bearing mice, this achieved 62.6% tumor inhibition, with increased intratumoral PD-1⁺ T cells and interferon-γ secretion. Efficacy also translated to patient-derived lung cancer organoids. A key limitation the authors acknowledge is the potential for off-target glycan oxidation by the GAO enzyme in a systemic context, which will require tumor-microenvironment-responsive activation strategies in future iterations. **Three takeaways** 1. Covalent anchoring via PD-L1 glycan oxidation drops the peptide CAC nearly 18-fold (38.26 µM → 2.18 µM), triggering localized self-assembly of ATNs specifically on PD-L1-overexpressing tumor cells rather than on bystander tissue. 2. ATN-treated co-cultures showed 2.61-fold higher tumor cell killing versus non-assembling controls, alongside a doubling of interferon-γ secretion and a peak in CD69 expression at ~8 hours — demonstrating genuine T cell activation rather than mere recruitment. 3. The covalent assembly strategy significantly outperformed a non-covalent analogue under mildly acidic, physiologically dynamic conditions, and this stability advantage translated to 62.6% tumor volume inhibition in vivo and efficacy in patient-derived lung cancer organoids. **Read the source:** https://doi.org/10.1002/anie.5894316