Cet-DC315 Enhances Vδ2 T-Cell Activity in Colorectal Models Despite Lower EGFR Affinity

Testing Targeting, Growth and Immune Effects Separately

Researchers at the University of Pisa, IRCCS Ospedale Policlinico San Martino and Fondazione Toscana Life Sciences compared cetuximab conjugates carrying aminobisphosphonates. These payloads were designed to affect tumor cells and stimulate human Vδ2 T-cell responses. The Scientific Reports study evaluated those functions through separate binding, growth, immune-expansion and cytotoxicity experiments.

The two constructs were Cet-DC310 and Cet-DC315. Mass spectrometry estimated drug-to-antibody ratios of approximately 6.8 and 23, respectively. The high loading of Cet-DC315 was accompanied by biological activity, but also by a substantial loss of apparent EGFR binding affinity.

EGFR Recognition Remained Detectable as Affinity Fell

Flow cytometry assessed binding across five colorectal cancer cell lines, with low binding to the EGFR-low SW-620 line. Patient-derived organoids also showed binding by Cet-DC315.

In three cell lines used for quantitative binding curves, native cetuximab had apparent dissociation constants of 0.01–0.02 μg/mL. Cet-DC315 values were 24–189 μg/mL. The conjugate’s higher maximum binding capacity coexisted with this marked loss of affinity.

Functional experiments generally used 2 μg/mL. After 120 hours, Cet-DC315 inhibited approximately 75% of Caco-2 proliferation compared with approximately 25% for native cetuximab. It also reduced Caco-2 spheroid growth: reported mean diameters were 145 μm for controls, 128 μm for cetuximab and 60 μm for Cet-DC315. Neither agent inhibited growth of the KRAS-mutant HCT-116 model under these conditions.

Immune Expansion and Killing Used Different Assay Designs

With IL2 support, Cet-DC315 promoted Vδ2 T-cell expansion in co-cultures involving the LS-180 line. The reported experiment used six healthy blood donors, and Vδ2 cells reached approximately 60% of the population by day 14. Native cetuximab did not produce comparable expansion.

Two patient-derived organoid cultures were separately tested with T cells from two healthy donors, in four experiments. Increased Vδ2 proportions were observed during the longer culture period. Tumor-tissue cell suspensions also supported expansion, with the reported four-patient experiment reaching approximately 30–35% Vδ2 cells by day 25. These assays followed changes in the T-cell population over weeks.

The killing assay used Vδ2 cells expanded from three healthy donors and an effector-to-target ratio of 2:1. Caco-2 or dissociated cells from a separately identified organoid model were assessed after 48 hours. Crystal violet quantified surviving adherent tumor cells after nonadherent cells were washed away. Cet-DC315 reduced the surviving-cell signal more than native cetuximab; the reported optical densities were approximately 0.7 and 1.0.

Cet-DC310 Failed the Functional Assays

Cet-DC310 retained EGFR reactivity but did not significantly inhibit the tested cell lines, expand Vδ2 cells or trigger detectable killing under the corresponding conditions. The authors proposed that its uncleavable linkage prevented useful payload processing.

Payload release and the proposed generation of isopentenyl pyrophosphate or related phosphoantigens were not directly measured. The study also lacked in vivo efficacy and toxicity tests. A drug-to-antibody ratio near 23 raises further questions about stability, aggregation, pharmacokinetics and immunogenicity that the culture assays cannot resolve.

The results support studying this conjugate as an experimental way to combine EGFR targeting with Vδ2 activity. They also show that increased loading, retained recognition and improved function can coexist with poorer affinity. Direct comparisons with other conjugates and more complex tumor environments are needed to determine which properties persist beyond these defined in vitro systems.