The central problem these platforms address is the tumor microenvironment, the dynamic and immunosuppressive niche that governs cancer progression, immune evasion, and therapeutic resistance. Tumors are not merely masses of malignant cells; they are complex ecosystems containing cancer stem cells, stromal cells such as fibroblasts and endothelial cells, angiogenic vessels, extracellular matrix, signaling molecules, and a diverse cast of immune populations including macrophages, dendritic cells, neutrophils, natural killer cells, B cells, and T cells. Within this milieu, regulatory T cells, myeloid-derived suppressor cells, and elevated checkpoint molecules conspire to blunt anti-tumor immunity. The review frames tumor–immune dynamics through the cancer immunoediting framework of elimination, equilibrium, and escape, emphasizing that immune evasion during the escape phase is what allows clinically detectable malignancy to emerge and that the microenvironment is an active driver of tumor evolution and therapeutic resistance rather than a passive backdrop.

Immunosuppression within the tumor microenvironment operates through multiple mechanistic layers. An immunosuppressive cytokine milieu dominated by TGF-β, IL-10, and IL-6 suppresses T cell activation while promoting the expansion of myeloid-derived suppressor cells and M2-polarized macrophages. Chemokine gradients, including CCL22 and the CXCR4/CXCL12 axis, actively recruit suppressive cell populations to the tumor site while excluding cytotoxic effector cells, creating spatially organized immunosuppressive niches that shield tumor cells from immune destruction. Tumor-associated macrophages, among the most abundant and plastic immune populations in the microenvironment, are typically driven toward a pro-tumorigenic M2 phenotype through IL-4, IL-13, and IL-10 signaling, converting a potentially anti-tumor force into an active promoter of progression and therapy resistance. Tumors are further classified as inflamed or hot, immune-excluded, or immune-desert or cold, with the latter two categories being largely refractory to immunotherapy, a reality that underscores why models preserving spatial and stromal complexity are so valuable.

At the heart of immune evasion lies the exploitation of checkpoint pathways. PD-L1 on tumor cells engages PD-1 on T cells, inducing a state of exhaustion characterized by reduced proliferation, cytokine production, and cytotoxicity, while CTLA-4 dampens T cell priming by competing with CD28 for B7 ligands. Emerging checkpoints including LAG-3, TIM-3, and TIGIT further contribute to intratumoral T cell exhaustion and represent targets for next-generation immunotherapy. Immune checkpoint inhibitors have demonstrated efficacy across a remarkable range of malignancies, including non-small cell lung cancer, urothelial bladder cancer, head and neck squamous cell carcinoma, breast cancer, cutaneous squamous cell cancer, melanoma, renal cell cancer, and Hodgkin’s lymphoma. Yet predicting which patients will benefit remains difficult, which is precisely where co-culture platforms that preserve viable immune cells alongside living tumor tissue promise to change clinical practice.

The review traces the evolution of cancer models from flat two-dimensional monolayers, which advanced early understanding of tumor biology but fail to capture complex tumor–microenvironment interactions, to three-dimensional systems that more accurately recapitulate in vivo tumor structure and behavior. Gene expression profiling of three-dimensional multicellular tumor spheroids has revealed upregulation of hypoxia-responsive genes and downregulation of cell cycle-related genes compared to two-dimensional models, and enhanced mevalonate pathway activity has been observed in quiescent spheroid cells, underscoring the context-dependent nature of anticancer responses in 3D. Spheroids, typically 200 to 500 micrometers in diameter, form through integrin- and cadherin-mediated self-assembly and can be generated by pellet culture, hanging drop, liquid overlay, or spinner techniques, each with distinct trade-offs in scalability, monitoring, and hypoxic core formation. When co-cultured with immune cells such as PBMCs, spheroids enable modeling of tumor–immune interactions and intratumoral heterogeneity, making them a valuable preclinical research tool.

Organoids, often described as mini-organs, go further by self-organizing to recapitulate native tissue architecture and function through lineage commitment and spatial cell sorting guided by extracellular matrix and culture medium cues. Patient-derived tumor organoids have now been generated across colorectal, pancreatic, breast, lung, and brain cancers, among others, retaining the mutational profiles, histopathology, and cellular diversity of the source tumor. Matrigel-based systems remain the most widely used due to accessibility and standardized workflows, despite batch-to-batch variability, while bioengineered synthetic matrices offer tunable stiffness and improved reproducibility at higher cost. Advanced technologies are pushing the field further: microfluidic organ-on-a-chip systems enable perfused, vascularized organoids modeling fluid flow and immune infiltration; air–liquid interface culture preserves epithelial, stromal, and immune components with improved oxygenation; and microwell arrays, droplet encapsulation, and acoustic aggregation enable high-throughput, size-controlled production, though typically limited to short-term culture.

The translational centerpiece of the review is the PDTO–PBMC co-culture system, which the authors describe as enabling reconstitution of autologous immune responses in an antigen-agnostic manner. The landmark study by Dijkstra and colleagues established that co-culturing peripheral blood lymphocytes with tumor organoids expands CD8-positive T cells that kill tumor organoids but spare healthy tissue-derived organoids, with killing efficiency of 20 to 80 percent depending on tumor type, and confirmed antigen-specificity through HLA-blocking experiments. The review is careful to define what constitutes genuine functional immune reconstitution rather than mere physical co-localization: HLA-dependent tumor-selective killing, CD137 upregulation as a marker of tumor-reactive T cell activation, interferon-gamma secretion, and granzyme B-mediated cytotoxicity must all be demonstrated. Checkpoint blockade responsiveness has been validated in immune-enhanced organoid platforms, with anti-PD-1 treatment increasing CD3-positive and CD8-positive T cell recruitment, and air–liquid interface models showing organoid responses to PD-1/PD-L1 blockade correlating with clinical outcomes in approximately 85 percent of cases.

Beyond T cells, the platforms extend across the immune repertoire. Cancer-associated fibroblasts co-cultured with organoids enhance tumor growth, promote epithelial–mesenchymal transition, and confer therapy resistance across colorectal, pancreatic, hepatocellular, and esophageal cancers, while endothelial co-culture illuminates tumor-induced angiogenesis and vascular niche-dependent drug resistance. Macrophage co-cultures reveal that sirtuin-1 promotes M2 polarization and suppresses CD8-positive T cell activity in colorectal cancer, and that the CCL5–Sp1–AREG axis mediates tumor–macrophage crosstalk in pancreatic cancer. Dendritic cell co-cultures expose tolerogenic shifts in tumor microenvironments, and natural killer cell studies in breast and pancreatic cancer models have demonstrated both therapeutic potential and tumor-induced immune impairment. CAR T cell evaluation has been particularly transformative: patient-derived bladder cancer organoids have been validated as reliable preclinical platforms for CAR T testing, neuroblastoma organoids have modeled CAR T infiltration and antigen loss, and glioblastoma organoids now serve as real-time avatars for assessing responses to clinical CAR T cell therapy.

The review does not shy away from sobering limitations. Most published work remains at the proof-of-concept stage, with prospective clinical validation data still sparse and no defined response thresholds for what magnitude of in vitro cytotoxicity reliably predicts clinical benefit. Organoid establishment success rates vary dramatically, from 22 percent rising to 75 percent with optimized protocols in metastatic colorectal cancer, 58 percent in pancreatic cancer, and as low as 17 percent for conventional lung cancer protocols versus over 90 percent with optimized free-floating platforms. PBMC viability after cryopreservation, delays exceeding 24 hours between blood collection and processing, and inter-patient immune repertoire variation all confound outcomes. Turnaround from biopsy to functional readout typically spans three to six weeks, though accelerated platforms have demonstrated feasibility within 7 to 14 days. Clonal evolution poses a further threat, as culture-adapted subclones may displace clinically relevant immune-evasive populations, and therapy-induced changes can alter neoantigen repertoires and checkpoint expression. The authors call for the newly proposed Minimum Information about Organoid Research reporting standard, reference organoid lines, external quality control programs, and a structured evidentiary roadmap toward companion diagnostic status under FDA and EU IVDR frameworks.

Looking forward, the convergence of microfluidics, spatial transcriptomics, single-cell multi-omics, and artificial intelligence promises to expand both the biological fidelity and translational utility of these platforms. Three-dimensional bioprinting allows spatially controlled deposition of tumor, immune, and stromal components that better recapitulate immune exclusion zones and stromal barriers, while machine learning applied to high-dimensional co-culture datasets holds promise for predicting patient-specific immunotherapy responses. The authors conclude that clinical validation of tumor–immune co-culture systems will be fundamental to achieving truly personalized cancer immunotherapy, in which each patient’s tumor is prospectively tested against their own immune cells to guide individualized treatment decisions, transforming organoid co-culture from a research curiosity into a functional companion diagnostic for precision oncology.

Subject of Research: Patient-derived tumor organoid co-culture systems for modeling tumor–immune interactions and evaluating cancer immunotherapy and precision oncology

Article Title: Patient-derived tumor organoid co-culture systems as translational platforms for cancer immunotherapy and precision oncology

Article References: Gadelkarim, M., Elsayed, A., Abaza, T., Bahr, A. R., Elsayed, Y., & Iqbal, O. (2026). Patient-derived tumor organoid co-culture systems as translational platforms for cancer immunotherapy and precision oncology. Clinical Cancer Bulletin, 5(1), Article 18. https://doi.org/10.1007/s44272-026-00067-1

Image Credits: AI Generated

DOI: 10.1007/s44272-026-00067-1

Keywords: tumor organoids, co-culture, tumor microenvironment, cancer immunotherapy, immune checkpoint inhibitors, CAR T cells, PBMC, precision oncology, patient-derived models, adoptive cell therapy, organ-on-a-chip, companion diagnostics