The research, led by Franziska Köhler and Sonja Kallendrusch of Leipzig University and the HMU Health and Medical University, together with colleagues in Erfurt and Potsdam, compared two complementary patient-derived culture systems side by side. The first, patient-derived neurospheres (PDNS), are compact, free-floating spheroids grown from dissociated tumor cells under serum-free conditions. They offer a controlled, tumor-cell-intrinsic system in which variables can be manipulated with relative ease. The second, patient-derived tissue slice cultures (PDTC), preserve the tumor’s native architecture: thin, 350-micrometer slices of fresh surgical tissue are cultured at an air–liquid interface, retaining the extracellular matrix, vascular structures, immune cells, and stromal compartments that neurospheres inevitably discard. The team systematically exposed both models to two AAV serotypes, AAV2 and AAV6, each carrying a green fluorescent protein (GFP) reporter gene, and then tracked transduction with live confocal microscopy, quantitative PCR, flow cytometry, and immunofluorescence.

The technical rigor of the workflow is central to the study’s credibility. Thirteen surgical specimens from 25 collected samples ultimately entered the analysis, twelve of them IDH-wildtype glioblastomas under the WHO 2021 classification. Tissue not required for diagnosis was obtained with informed consent and ethical approval. For neurospheres, tumor tissue was mechanically and enzymatically dissociated with Accutase, filtered, and seeded at 100,000 cells per well; after 10 to 15 days, spheroids of 100 to 150 micrometers in diameter were ready for experiments. Slice cultures were punched into 2 to 3 millimeter discs and maintained on membrane inserts. After testing several media formulations, the researchers selected NeuroCult-XF, a serum-free proliferation medium, because it preserved tissue architecture and histopathological features better than serum-containing alternatives or other defined formulations. Blinded pathological review confirmed that fibrillary architecture and even characteristic gemistocytic features—enlarged cell bodies with eccentric nuclei—were retained in both models.

The cellular composition analysis revealed stark differences between the two systems, exactly as the team had hypothesized. Slice cultures retained expression of immune markers such as CD68, the vascular marker CD31, and the hypoxia marker HIF1α in organotypic patterns closely mirroring the original tumors. Neurospheres, by contrast, showed virtually no CD31, scarce and disorganized CD68-positive cells, and only weak HIF1α restricted to larger spheroids. More subtly, sphere-forming conditions selectively enriched stem-like populations: the mean SOX2-positive cell fraction rose from 0.114 in native tissue to 0.328 in PDNS, and Nestin positivity climbed from 0.132 to 0.393, while the mesenchymal marker CD44 fell. This finding matters because it confirms that neurosphere culture is not a neutral act of preservation but an active selection process that reshapes the cellular landscape before any vector is ever introduced.

When the vectors were applied, the serotype differences were unambiguous. In neurospheres, AAV6 drove significantly greater GFP expression than AAV2 across a dose range of 10^6 to 10^9 particles, with significant signal appearing as early as day 2 at higher doses, while AAV2 reached significance only at the highest dose after 5 days. Quantitative PCR corroborated the fluorescence data: five days after exposure to 10^8 particles, PLAT-normalized vector genome abundance averaged 146.7 copies per cell for AAV2 but 1,074.0 for AAV6 in EGF-containing medium. Notably, epidermal growth factor supplementation itself proved to be a critical experimental variable. Because AAV6 is known to use EGFR as a co-receptor for cellular entry, the team deliberately compared EGF-containing and EGF-free conditions. In neurospheres, EGF presence modified both the magnitude and temporal stability of AAV6-mediated GFP expression, and marker-defined analysis showed that EGF deprivation broadened GFP positivity across GFAP-, CD44-, Nestin-, and SOX2-positive populations, whereas under EGF-containing conditions only the Nestin-positive fraction showed significant GFP signal.

Exploratory flow cytometry from two independent experiments added an intriguing layer. GFP positivity was markedly enriched among SOX2-positive cells (40.8 percent versus 7.2 percent in SOX2-negative cells) and among cells triple-positive for CD133, Nestin, and SOX2 (41.0 percent versus 7.5 percent). The authors are careful to stress that these figures, based on limited sample numbers, are descriptive and cannot distinguish preferential vector uptake from differences in population abundance, survival, or promoter activity. Still, the pattern suggests that the most stem-like, aggressive cellular states within a glioblastoma may be among those most efficiently engaged by AAV6—a hypothesis with obvious therapeutic implications if it can be confirmed with larger datasets and mechanistic studies.

The most sobering results came from the tissue slice cultures. Overall GFP readouts were comparable to, or in some cases higher than, those in neurospheres, but interpatient variability was dramatically greater. Some patient specimens transduced robustly; others showed little or no detectable GFP despite identical conditions. Mean fluorescence intensities of 4,989 for AAV2, 4,232 for AAV6, and 6,448 for AAV6 without EGF in slice cultures contrasted with far lower values in matched neurospheres, but the spread between patients was wide enough that no single-patient result could be generalized. The authors argue that this variability should not be dismissed as experimental noise. Instead, it may represent a biologically faithful reflection of the heterogeneity that any real-world gene therapy for glioblastoma would confront. A vector that performs uniformly in a homogeneous spheroid panel may still fail in a substantial fraction of patients, and only multi-patient tissue-based validation can expose that vulnerability before clinical translation.

Spatial analysis added another dimension. In neurospheres, GFP-positive cells clustered predominantly at the spheroid periphery, consistent with diffusion-limited vector transport through densely packed three-dimensional tissue, although the authors caution that GFP fluorescence reflects the downstream consequence of delivery and expression rather than physical particle penetration itself. Slice cultures showed a more homogeneous distribution of fluorescence across the tissue, an effect not associated with preferential vascular localization and therefore likely driven by preserved microarchitecture rather than vascular entry routes. Equally notable was the observation of occasional GFP-positive cells in two samples of adjacent non-neoplastic brain tissue, a preliminary but cautionary signal that off-target transduction of tumor-adjacent cells can occur under experimental conditions, consistent with the broad central nervous system tropism of naturally occurring AAV serotypes.

The study’s self-imposed limitations are candidly acknowledged. Vector dose escalation could not be performed in slice cultures because of limited tissue availability, preventing fully matched comparisons between models. Flow cytometric findings rested on only two experiments. Vector genome quantification cannot distinguish entry, trafficking, persistence, or processing, and GFP expression additionally depends on transcription and translation. Slice cultures themselves, while architecturally faithful, remain ex vivo systems that cannot reproduce systemic immunity, vascular dynamics, or long-term tumor evolution. The significant increase in SOX2 expression observed in neurospheres after AAV6 treatment without EGF likewise supports an association rather than a demonstrated causal effect of vector exposure on tumor-cell state.

What the study ultimately delivers is a framework rather than a verdict. The authors explicitly do not claim that both models are mandatory for every preclinical AAV program, nor that either predicts in vivo performance. Instead, they advocate a question-driven approach: neurospheres, with their lower variability and experimental tractability, are well suited to initial serotype screening and dissection of tumor-cell-intrinsic effects; candidate vectors that pass that filter can then be challenged against panels of slice cultures from multiple patients, where preserved architecture, stromal and vascular compartments, and honest interpatient heterogeneity reveal how performance holds up in tissue that more closely resembles what a surgeon would leave behind in a resection cavity. In a disease where nearly every promising preclinical result has eventually collided with clinical reality, the insistence that model selection itself is a determinant of apparent vector efficacy may prove to be one of the more consequential methodological messages glioblastoma gene therapy has received in years.

Subject of Research: Preclinical evaluation of AAV-mediated gene delivery in patient-derived glioblastoma cultures

Article Title: Patient-derived tissue cultures complement neurospheres for preclinical evaluation of AAV-mediated gene delivery in glioblastoma

Article References: Köhler, F., Hess, K., Koloske, C., Gaunitz, F., Rosahl, S. K., Gerlach, R., & Kallendrusch, S. (2026). Patient-derived tissue cultures complement neurospheres for preclinical evaluation of AAV-mediated gene delivery in glioblastoma. Journal of Neuro-Oncology, 179(3), Article 93. https://doi.org/10.1007/s11060-026-05807-w

Image Credits: AI Generated

DOI: 10.1007/s11060-026-05807-w

Keywords: glioblastoma, AAV vectors, gene therapy, patient-derived models, neurosphere cultures, tissue slice cultures, tumor microenvironment, viral vectors, EGF, transduction, preclinical testing, gene delivery

Transduction is a form of horizontal gene transfer, the phenomenon that allows bacteria to acquire genes from organisms other than their own offspring. Unlike transformation, in which cells take up naked DNA from their environment, or conjugation, which relies on direct cell-to-cell contact, transduction depends on virus-like particles, or VLPs. These particles, produced by bacteria themselves or by the viruses that infect them, can accidentally encapsulate fragments of bacterial DNA instead of viral genomes. When the particles deliver that cargo to new cells, they can spread traits such as antibiotic resistance, virulence factors, and metabolic capabilities across microbial communities with striking efficiency.

Detecting this hidden traffic of DNA has been the province of transductomics, a sequencing-based method introduced to catalog the DNA carried by VLPs in a sample. The approach is conceptually elegant. Researchers first purify virus-like particles from a biological sample, such as a fecal pellet, and sequence the DNA inside them. They then assemble metagenomic contigs, longer stretches of DNA reconstructed from the whole microbial community in the same sample. By mapping the VLP sequencing reads back onto those community contigs, researchers can see which pieces of bacterial DNA were packaged into particles. The telltale signature lies in the read coverage patterns: different shapes of coverage along a contig reveal whether the DNA was packaged randomly, from a provirus integrated in a bacterial genome, or through other mechanisms.

The problem, until now, has been that interpreting those coverage patterns required a trained human eye. Every contig had to be inspected and classified manually, a process that could consume hours of expert attention per dataset. For studies involving many samples, or time courses with dozens of conditions, the manual bottleneck rendered transductomics effectively unfeasible at scale. It also introduced a reproducibility concern, since different analysts might classify borderline coverage patterns differently, and even the same analyst might vary from day to day.

TrIdent addresses this bottleneck with a pattern-matching algorithm that automates the classification step entirely. The software systematically compares the read coverage profile of each contig against a library of expected patterns corresponding to distinct packaging mechanisms, assigning each contig to a class that reflects how its DNA was likely mobilized. Because the classification follows explicit, deterministic rules, every run of the tool on the same data produces identical results, a property the manual workflow could never guarantee. The package is platform independent, requires no specialized dependencies beyond the R environment, and is distributed under an open-source GPL-2 license through Bioconductor, making it straightforward for any laboratory to adopt.

Because no equivalent software existed, the development team faced an unusual validation challenge: how do you benchmark an algorithm against a standard that is itself manual? Their solution was to compare TrIdent’s classifications against those of experienced human classifiers. On a previously generated transductomics dataset that had already been carefully classified by hand, TrIdent’s assignments were generally comparable to the manual ones. More rigorously, when the team applied the tool to newly generated transductomics data from the mouse gut microbiota, TrIdent agreed with two independent human classifiers about as much as those two human classifiers agreed with each other. In other words, the algorithm performed at the level of inter-human consistency, the practical ceiling for a task that inherently involves judgment calls.

Speed and reproducibility were equally decisive advantages. TrIdent classified complete transductomics datasets in a fraction of the time required by human classifiers, turning what had been a per-sample slog into a routine computational step. The authors emphasize that this efficiency does not merely save time; it changes the kind of science that becomes possible. Studies that were previously constrained to a handful of samples can now encompass dozens of conditions, time points, and biological replicates, allowing researchers to ask how transduction responds to antibiotics, infection, diet, or other perturbations across entire experiments rather than isolated snapshots.

To demonstrate the tool’s power, the researchers turned TrIdent loose on transductomics datasets generated from murine fecal pellets, including samples collected before and after antibiotic treatment and in a model of Clostridioides difficile infection. The analysis yielded a genuinely surprising biological insight: bacterial DNA associated with two specific bacterial families, the Oscillospiraceae and the Turicibacteraceae, was highly enriched in the DNA packaged by virus-like particles compared with the same families’ abundance in the whole-community metagenomes. Both families are relatively low-abundance members of the murine gut community, yet their DNA appeared disproportionately often inside VLPs. This finding suggests that certain scarce bacteria may be heavily involved in transduction, punching far above their numerical weight in the horizontal movement of genes through the gut ecosystem.

The implications extend well beyond the mouse intestine. Horizontal gene transfer is a central force shaping microbial evolution, and transduction in particular is implicated in the dissemination of antibiotic resistance genes, one of the most pressing public health challenges of the era. A tool that makes transductomics fast, scalable, and reproducible opens the door to systematic surveys of DNA mobilization in soil, ocean, clinical, and human-associated microbiomes. Researchers studying phage therapy, microbiome engineering, or the spread of virulence factors can now incorporate transductomics into standard pipelines without needing a specialist to hand-annotate every contig.

The work was carried out by Jessie L. Maier, Craig Gin, Jorden Rabasco, Yixuan Yang, Avery Bass, Wynter Spencer, Breck A. Duerkop, Benjamin Callahan, and Manuel Kleiner, with teams spanning North Carolina State University and the University of Colorado Anschutz Medical Campus. The research was supported by a seed grant from the North Carolina State University Data Science Academy and by the National Institutes of Health. The authors have released the software with full documentation, and the underlying study is published open access, reflecting a broader movement in microbiology toward transparent, reusable computational methods. As transductomics datasets accumulate across laboratories worldwide, tools like TrIdent are poised to become as indispensable to the field as the sequencing machines that generate the data, turning a once-manual art into an automated science and revealing, contig by contig, the hidden gene highways that connect the microbial world.

Subject of Research: Automated transductomics analysis of virus-like particle mediated DNA mobilization in microbiomes

Article Title: TrIdent—an R package to automate transductomics analysis of virus-like particle mediated DNA mobilization

Article References: Maier, J. L., Gin, C., Rabasco, J., Yang, Y., Bass, A., Spencer, W., Duerkop, B. A., Callahan, B., & Kleiner, M. (2026). TrIdent—an R package to automate transductomics analysis of virus-like particle mediated DNA mobilization. Microbiome. https://doi.org/10.1186/s40168-026-02546-y

Image Credits: AI Generated

DOI: 10.1186/s40168-026-02546-y

Keywords: transduction, horizontal gene transfer, transductomics, virus-like particles, R package, microbiome, metagenomics, gut microbiota, DNA mobilization, pattern-matching, bioinformatics, antibiotic resistance

Standard organoid culture media typically include a basal formulation such as DMEM/F12 supplemented with factors that promote neural differentiation, including N2 and B27 supplements, and often retinoic acid at later stages to encourage photoreceptor maturation. Variations among laboratories in the choice of basal medium, the concentration of supplements, the presence or absence of serum components, and the timing of factor additions have long been recognized as sources of heterogeneity, but the systematic consequences of these choices for downstream applications have been less thoroughly characterized. The finding that media alter both adeno-associated virus transduction and retinal ganglion cell survival suggests that seemingly minor formulation differences can propagate into functional outcomes that matter enormously for translational work.

Adeno-associated virus vectors are the leading platform for retinal gene therapy, with approved products demonstrating that subretinal or intravitreal delivery can produce durable clinical benefit in inherited retinal degenerations. The success of AAV-mediated gene transfer depends on a cascade of events: vector particles must reach the target cells, bind to cell surface receptors, undergo endocytosis, traffic through the cytoplasm, enter the nucleus, uncoat, and convert their single-stranded genome into a transcriptionally competent double-stranded form. Each step can be influenced by the physiological state of the target cell, including membrane composition, endosomal trafficking dynamics, proteasome activity, and the expression of factors that second-strand synthesis. If culture media shift cells into states that favor or hinder any of these steps, then organoid-based assessments of vector tropism and potency will yield results that are artifacts of the culture condition rather than faithful predictions of clinical behavior.

This consideration is particularly acute because organoids are increasingly used as preclinical screening platforms for vector engineering. Researchers seeking capsids with improved photoreceptor tropism, or with the ability to penetrate the inner limiting membrane after intravitreal injection, frequently validate their designs in retinal organoids before advancing to animal studies. A capsid that appears highly efficient in organoids maintained in one medium might underperform in organoids maintained in another, not because the capsid has changed but because the cellular context has. Standardizing media composition, or at minimum reporting it comprehensively and testing key findings across multiple formulations, would strengthen the predictive value of such screens and reduce the risk of pursuing vector designs whose apparent advantages do not survive a change of culture conditions.

The effects on retinal ganglion cell survival are equally consequential. Retinal ganglion cells are the projection neurons of the visual system, conveying visual information from the retina to the brain through the optic nerve, and their degeneration underlies glaucoma and other optic neuropathies. In organoid culture, ganglion cells are notoriously fragile; they are among the first cell types generated, they reside in the innermost layer of the tissue, and they depend on trophic support that is difficult to reproduce in a dish. Their progressive loss during long-term organoid culture is a well-documented limitation, and it complicates any effort to model ganglion cell diseases or to test neuroprotective strategies. If specific medium components can substantially extend ganglion cell survival, this opens two important avenues: first, the creation of longer-lived organoid models in which disease-relevant cell types remain available for study; and second, the identification of the trophic factors and metabolic conditions that ganglion cells require, which may themselves point toward therapeutic targets.

The mechanistic links between medium composition and cell survival likely involve several intersecting pathways. Oxidative stress is a prominent candidate, since retinal neurons are metabolically demanding and vulnerable to reactive oxygen species, and the antioxidant capacity of medium supplements such as those in B27 varies with formulation and with the degradation of components over time in culture. Energy metabolism is another: the retina is among the most oxygen-consuming tissues in the body, and photoreceptors in particular rely on aerobic glycolysis, a metabolic mode whose support depends on glucose and pyruvate availability in the medium. Growth factor signaling, including pathways involving BDNF, CNTF, GDNF, and insulin-like growth factors, also modulates ganglion cell survival, and the presence, stability, and concentration of such factors differ across media formulations. Even the buffering system and the resulting pH stability can influence neuronal health, as can osmolarity and the accumulation of metabolic waste products between medium changes.

For AAV transduction specifically, medium composition might act through effects on the cell surface. The glycocalyx, the dense layer of sugars coating the plasma membrane, provides attachment points that many AAV seruses exploit, and its composition is sensitive to culture conditions, including the availability of specific sugars and the activity of glycosyltransferases. Heparan sulfate proteoglycans serve as primary attachment receptors for several AAV serotypes, and sialic acid residues are critical for others. Media that alter glycosaminoglycan synthesis or sialylation could therefore change the efficiency of the initial binding step. Downstream, intracellular trafficking depends on the cytoskeleton and on endosomal pH, both of which can be modulated by medium components such as ammonium chloride accumulation, chloroquine-like compounds, or simply the energetic state of the cell. These mechanisms offer plausible, testable explanations for how the same vector applied to the same organoid type can perform differently across media.

The broader lesson resonates with a recurring theme in stem cell biology: the environment is part of the experiment. Organoids are often described as miniaturized versions of human tissues, but they are better understood as products of a continuous dialogue between intrinsic developmental programs and the culture environment. Small differences in oxygen tension, media exchange schedules, matrix composition, and the physical handling of cultures have all been shown to affect organoid morphology and cell type composition. The present findings add media formulation to this list in a way that directly touches two of the most translationally important readouts: gene delivery efficiency and survival of a clinically critical neuron.

From a practical standpoint, laboratories working with retinal organoids for gene therapy applications should consider several measures. Detailed documentation of medium composition, including lot numbers of supplements whose activity varies between batches, would improve reproducibility across the field. Cross-validation of key results in at least two distinct media formulations would reveal whether findings are robust or condition-dependent. Where possible, matching the metabolic and trophic environment of the organoid to the physiological state of the target tissue in vivo would improve the clinical relevance of preclinical testing. For ganglion cell studies specifically, optimizing media for survival may need to be balanced against the goal of photoreceptor maturation, since conditions that favor one cell class may not favor another, and the developmental timing of these requirements may differ.

There are also implications for disease modeling. Many inherited retinal diseases are cell-type specific, and the value of an organoid model depends on maintaining the relevant cells in a state that resembles their in vivo counterpart. Ganglion cell loss in culture has limited the use of organoids for modeling optic neuropathies such as those caused by mutations in OPA1 or other genes affecting mitochondrial function. If optimized media extend ganglion cell survival substantially, models of these diseases become feasible, enabling the study of pathogenesis in a human developmental context and the screening of candidate neuroprotective compounds. Similarly, for glaucoma research, where the interplay between elevated intraocular pressure, axonal transport disruption, and somal survival is difficult to disentangle in animal models, longer-lived organoid systems with robust ganglion cell populations would provide a complementary human platform.

The intersection with AAV biology deserves particular attention as the gene therapy field matures. Dose-limiting toxicity, immune responses, and the challenge of achieving pan-retinal transduction after intravitreal delivery remain central obstacles. Organoids offer a human-relevant system in which to evaluate candidate capsids, promoters, and expression cassettes, but their utility depends on the transduction results reflecting what would occur in a patient retina. The finding that media promote or suppress transduction suggests that part of the variability reported across organoid studies of AAV tropism may be attributable to culture conditions rather than to genuine differences in vector performance. Disentangling these variables will require systematic comparisons in which identical vectors are applied to organoids raised in parallel under different media conditions, with careful quantification of both transduction efficiency and the cell-type composition of the tissues.

It is also worth considering how these findings fit into the larger regulatory and manufacturing landscape. As retinal organoids move toward use in potency assays and release testing for cell and gene therapy products, the dependence of their properties on media composition becomes a matter of product consistency. Regulatory frameworks emphasize the characterization of critical quality attributes, and for organoid-based assays, the culture medium is arguably a critical reagent whose composition must be controlled with the same rigor as the biological material itself. Manufacturers of media and supplements may need to provide more detailed specifications, and users may need to implement qualification procedures for each new lot, particularly for supplements such as B27 whose complex composition includes components with variable biological activity.

Looking forward, the systematic mapping of how individual medium components affect retinal organoid physiology could yield a design framework for culture conditions tailored to specific applications: media optimized for photoreceptor maturation for studies of inherited photoreceptor degenerations, media optimized for ganglion cell survival for optic neuropathy models, and media that support efficient AAV transduction for vector validation studies. Such an approach would treat the medium as an engineering variable rather than a fixed convention, transforming a source of uncontrolled variability into a tool for shaping organoid properties. The present work, by demonstrating that culture media alter both AAV transduction and retinal ganglion cell survival in retinal organoids, provides both a caution about the interpretation of existing organoid studies and a constructive starting point for this more deliberate approach to organoid culture design.

Subject of Research: Culture media alter retinal organoid physiology promoting AAV transduction and retinal ganglion cell survival

Article Title: Culture media alter retinal organoid physiology promoting AAV transduction and retinal ganglion cell survival

Article References: O’Hara-Wright, M., Lim, B. Y., M. Mangala, M., Kaiser, V., Wong, E., Aubin, D., Nemeruck, V., Reynisson, H., Doroudian, F., Chan, O. P. Y., Aryamanesh, N., A. Paulo, J., Palomba, S., Mirzaei, M., Ginn, S. L., & Gonzalez-Cordero, A. (2026). Culture media alter retinal organoid physiology promoting AAV transduction and retinal ganglion cell survival. Gene Therapy. https://doi.org/10.1038/s41434-026-00642-0

Image Credits: AI Generated

DOI: 10.1038/s41434-026-00642-0

Keywords: Culture, media, alter, retinal, organoid, physiology, promoting, transduction, ganglion, cell, survival, scientific research