Sliced Tumors Keep Their Immune System Alive, Opening a New Window on Bladder Cancer Drug Testing

One of the most stubborn problems in cancer research is that the laboratory models scientists rely on rarely behave like the tumors inside patients. Now a team at Lund University in Sweden has shown that thin slices of freshly removed bladder tumors can keep their full immune machinery alive and functional in a dish for nearly a week, creating what the researchers describe as a versatile human-derived platform for testing immunotherapies outside the body. The work, published in BMC Medicine, addresses a translational gap that has long frustrated the development of cancer immunotherapies: preclinical models that fail to preserve the intricate interactions between tumor cells and the immune cells that surround, attack, and are suppressed by them.

The platform is built on precision-cut tumor slices, or PCTS, a technique borrowed in spirit from lung and liver research but adapted here for urothelial cancer. Fresh bladder cancer specimens, obtained from patients undergoing surgery at Skåne University Hospital in Malmö, were cut into thin, uniform slices and placed in optimized culture conditions designed to maintain both tissue architecture and cellular viability. Unlike single-cell suspensions or organoids, which strip away much of the native structure of a tumor, these slices retain the complete three-dimensional organization of the tissue, including the spatial relationships between cancer cells, stromal cells, blood vessels, and the diverse immune populations that infiltrate the tumor microenvironment.

Preserving that architecture matters because immunotherapy is fundamentally a spatial therapy. Immune checkpoint inhibitors such as nivolumab, which blocks the programmed cell death protein 1, or PD-1, do not kill cancer cells directly. Instead, they release the brakes on T cells that must physically locate and engage their targets within the tumor. A model that scatters the cells into a flat culture dish or grows tumor cells in isolation cannot reproduce that choreography. The Lund team, led by corresponding author Kristina Lundberg of the Department of Immunotechnology, set out to determine whether slices of bladder tumors could sustain the relevant cellular players long enough, and in a functional enough state, to serve as a meaningful testing ground.

The answer, according to their comprehensive characterization, is yes. Using flow cytometry, the researchers performed detailed phenotyping of both the tumor cells and the immune populations within the slices, confirming that a broad repertoire of immune cells survived in culture. Critically, the slices maintained the viability of both cancer cells and diverse immune populations for up to six days, a window long enough to run meaningful drug experiments. The team also demonstrated that the platform could address intra-tumor heterogeneity, the well-known phenomenon in which different regions of the same tumor harbor different cell types and molecular characteristics, while maintaining experimental reproducibility across patient samples, a balance that is notoriously difficult to strike in ex vivo systems.

Viability alone, however, would not be enough. The immune cells inside a preserved tumor slice might simply sit dormant, present but inert, offering no useful signal when a drug is applied. To rule this out, the researchers validated immune functionality directly. They stimulated the T cells within the slices using antibodies against CD3 and CD28, two proteins on the T cell surface whose engagement mimics the activation signals a T cell would normally receive. In response, the cells raised their expression of well-established activation markers, including CD69, CD137, and HLA-DR, and secreted significantly increased amounts of inflammatory mediators such as interferon gamma, or IFNγ, and the chemokine CXCL10, compared with untreated control samples. Those molecules are hallmarks of a genuine, functional immune response, not merely the passive presence of immune cells.

With the platform validated, the team moved to the question that matters most clinically: could the slices predict how real patients respond to real drugs? Nine patient samples were treated with nivolumab, a PD-1 checkpoint inhibitor that is a mainstay of treatment for bladder cancer yet benefits only a minority of patients. In the PCTS model, the responses were heterogeneous, mirroring the clinical reality. Two of the nine samples, roughly 22 percent, demonstrated dose-dependent immune activation after nivolumab treatment, a figure consistent with the response rates published for this drug in bladder cancer patients. For a preclinical model, reproducing that clinical distribution is a striking result, suggesting the slices may capture the biological determinants of response and resistance that simpler models miss.

The platform was also designed to evaluate more than immunotherapy alone. Using multiplex immunofluorescence microscopy on fixed slices, the researchers showed they could visualize the spatial distribution of cells and detect the direct cytotoxic effects of chemotherapy agents on cancer cells. This dual capability, capturing both immune-mediated responses and direct tumor cell killing within the same preparation, means the system can support the evaluation of combination therapies, an increasingly important area as oncology moves toward pairing checkpoint inhibitors with chemotherapy, targeted agents, and other immunomodulators. The technique also preserves the spatial information that pathologists value, allowing researchers to see not just whether a drug works but where in the tumor microenvironment its effects are concentrated.

Bladder cancer presents a particularly compelling case for such a model. The disease encompasses a spectrum from non-muscle-invasive tumors, which are typically managed with intravesical therapies, to muscle-invasive bladder cancer, which often requires aggressive systemic treatment. Molecular subtypes, including the basal/squamous, genomically unstable, and urothelial-like classifications referenced in the study, respond differently to therapy, and the immune landscape varies accordingly. A platform that preserves the native tumor microenvironment of each individual patient’s tumor offers a way to study these differences directly, rather than inferring them from cell lines that have spent decades adapting to plastic or from mouse models engrafted with human tumors.

The broader implications extend to how immunotherapy drugs are developed in the first place. The authors position PCTS among what the field calls new approach methodologies, a class of techniques intended to reduce reliance on animal models while improving translational relevance. Animal models, particularly humanized mice, remain expensive, slow, and imperfect predictors of human immune responses. An ex vivo system that uses a patient’s own tumor, keeps its immune system intact, and yields results within days could accelerate preclinical screening, help prioritize which drug combinations advance to clinical trials, and reduce the number of therapies that fail late in development after showing promise in less faithful models.

The Lund team is careful about what comes next. The current study establishes and validates the technical foundation, but the authors note that future prospective studies will be needed to correlate ex vivo responses in the slices with actual patient clinical outcomes. Only then could the platform move from a research tool toward genuine personalized treatment selection, in which a patient’s tumor is sliced, tested against a panel of therapies, and used to guide clinical decisions. The ethical framework is already in place: the study was approved by the ethics committee at Lund University, conducted in accordance with the Declaration of Helsinki, and all patients provided informed consent. If those prospective correlations hold, the humble tumor slice, a technology conceptually simple enough to be described in a sentence, could become a bridge between the immune complexity of real cancers and the controlled world of the laboratory, bringing precision immunotherapy a measurable step closer to the clinic.

Subject of Research: A precision-cut tumor slice platform preserving the functional immune microenvironment of bladder cancer for ex vivo immunotherapy and drug evaluation

Article Title: Bladder cancer precision-cut tumor slices (PCTS) preserve functional immune microenvironment enabling ex vivo drug evaluation

Article References: Richtmann, S., Radak, M., Sincic, V., Hugoson, J., Werner, N., Skoryk, V., Wagner, D., Liedberg, F., & Lundberg, K. (2026). Bladder cancer precision-cut tumor slices (PCTS) preserve functional immune microenvironment enabling ex vivo drug evaluation. BMC Medicine, 24(1), Article 468. https://doi.org/10.1186/s12916-026-05173-4

Image Credits: AI Generated

DOI: 10.1186/s12916-026-05173-4

Keywords: bladder cancer, precision-cut tumor slices, tumor microenvironment, immunotherapy, nivolumab, PD-1, ex vivo models, drug development, flow cytometry, multiplex immunofluorescence, T cell activation, personalized medicine