CCL21-ICAM1 synthetic niche accelerates lytic hit delivery by OT-I T cells against B16 melanoma in vitro

In a two-dimensional cell-culture study, CD8+ T cells expanded on a synthetic immune niche coated with CCL21 and ICAM1 killed OVA- and GFP-expressing B16 melanoma cells more efficiently than cells cultured on uncoated surfaces. Model analysis estimated that the lytic hit-delivery rate was approximately fourfold higher for niche-treated T cells, while differences in target-encounter rates could not be reliably determined.

Researchers isolated naïve ovalbumin-specific CD8+ T cells from spleens of female OT-I mice, activated them with anti-CD3/CD28-coated microbeads and interleukin-2, and cultured them for seven days on either uncoated plates or plates coated with recombinant mouse CCL21 and ICAM1. On day 7, the T cells were combined with OVA/GFP-expressing B16 melanoma cells at a 3:1 effector-to-target ratio. Time-lapse imaging then tracked the cultures for 48 hours.

Target-cell death was operationally defined by morphological rounding followed by complete loss of cytoplasmic GFP signal. The investigators used Cellpose-assisted segmentation, Fiji analysis and single-cell event tracking to quantify target-cell trajectories, T-cell–tumor-cell conjugates and the interval between rounding and loss of GFP. A mean death interval of approximately 164 minutes was measured, while mean T-cell–tumor-cell attachment duration was approximately 400 minutes.

The study combined these observations with a mean-field ordinary differential equation model representing tumor growth, T-cell binding and unbinding, and delivery of lytic hits. Tumor cells occupied successive damage states before entering an apoptotic state. Model comparison favored approximately four hits as the consensus number required for irreversible target-cell death: the Akaike information criterion reached its minimum at four hits for the synthetic-niche condition and at three hits for the untreated condition, with similar values at four hits in the latter group.

To limit problems with parameter identifiability, the researchers fixed the target-cell decay rate and T-cell dissociation rate using direct image-based measurements and fitted the remaining parameters to population-level tumor trajectories. Initial fits to individual regions of interest produced broad likelihood profiles. Co-fitting synthetic datasets with different initial effector and target numbers constrained the parameters, and the same strategy was then applied to the experimental data.

The estimated lytic hit-delivery rate, k3, was approximately four times higher for synthetic-niche-treated T cells than for untreated cells, a statistically significant difference reported with p=0.0003. Conjugate stability was not measurably different between conditions. By contrast, the target-encounter rate, k1, was practically non-identifiable in the untreated dataset, so the study could not establish whether CCL21 and ICAM1 altered that rate. The comparison of tumor growth rates was also not statistically significant at p=0.06.

Global sensitivity analysis supported the kinetic finding. The study evaluated cumulative tumor burden over 48 hours using the area under the tumor-population curve, with lower values representing less tumor burden. Both target encounter and lytic hit delivery were negatively associated with tumor burden, but k3 explained the largest fraction of outcome variance in the first-order Sobol analysis. The authors described this model-based pattern as “synaptic lethality,” meaning enhanced cytotoxic performance after a T cell has engaged a target.

Previously reported experiments conducted under matched culture conditions found that synthetic-niche-treated T cells had improved survival, a shift toward an effector phenotype, reduced expression of proapoptotic and exhaustion-associated genes, and increased expression of the cytotoxicity-associated gene Gzmm, while granzyme B and perforin expression remained unchanged. The current analysis did not directly measure the timing of individual lytic events, and the authors said direct validation of the inferred increase in k3 would require single-cell measurements of granule polarization, degranulation timing and frequency, CD107a exposure, and cytotoxic-molecule release.

The findings are limited to an in vitro OT-I T-cell and B16 melanoma system using two-dimensional culture and a mean-field model that assumes a well-mixed population. The experiments do not reproduce the three-dimensional architecture, extracellular-matrix barriers or immunosuppressive cytokine environment of an in vivo tumor. The model also treats lytic hit delivery as an effective rate and does not identify the specific molecular pathways responsible. Accordingly, the results support faster lytic execution and improved tumor-cell clearance in this experimental system, but do not establish clinical efficacy or prove benefits in human cancer or solid tumors.

Subject of Research: In vitro analysis of CCL21-ICAM1 conditioning and lytic hit delivery by OT-I CD8+ T cells against B16 melanoma cells

Article Title: Decoupling T cell cytotoxicity: a CCL21+ICAM1-based synthetic immune niche enhances tumor elimination by accelerating lytic hit delivery

Article References: Gupta, M. K., Zoabi, R., Yado, S., Starruß, J., Geiger, B., & Hatzikirou, H. (2026). Decoupling T cell cytotoxicity: a CCL21+ICAM1-based synthetic immune niche enhances tumor elimination by accelerating lytic hit delivery. BMC Cancer, 26(1), Article 1235. https://doi.org/10.1186/s12885-026-16748-y

Image Credits: AI Generated

DOI: 10.1186/s12885-026-16748-y

Keywords: synthetic immune niche, CCL21, ICAM1, OT-I T cells, B16 melanoma, lytic hit delivery, live-cell imaging, ordinary differential equation model, in vitro cytotoxicity, Decoupling, cell, cytotoxicity