Children’s Hospital of Philadelphia study uncovers missing RNA fragments as potential key to targeted immunotherapy for pediatric brain tumors

Children’s Hospital of Philadelphia (CHOP) has identified a promising therapeutic vulnerability in pediatric high-grade gliomas that could open the door to a new generation of targeted immunotherapies for hard-to-treat brain tumors. The preclinical study, published in Cell Reports, found that certain microexons—tiny fragments of messenger RNA—are consistently absent in tumor cells but present in healthy brain tissue, altering protein structures in a way that could be exploited to improve the selectivity and safety of cancer treatments.

Pediatric high-grade gliomas are among the most aggressive brain cancers, carrying poor prognoses despite decades of research. Standard treatments, including surgery, radiation, and chemotherapy, often fail to halt disease progression, and five-year survival rates remain dismally low. Although adoptive immunotherapies such as CAR-T cells have shown success in blood cancers, they face a fundamental challenge in brain tumors: the surface proteins on cancerous neurons are strikingly similar to those on healthy neurons, making it difficult to selectively destroy tumor cells without harming critical brain tissue.

This study’s findings could represent a shift in that paradigm, adding a new layer of precision targeting by exploiting differences in RNA splicing patterns between healthy and malignant cells.

How microexon skipping shapes tumor-specific targets

RNA splicing is a biological process in which a single gene can generate multiple proteins by rearranging exons—the coding sequences in messenger RNA—in different combinations. While this mechanism allows for complexity in protein production, aberrant splicing can create cancer-specific protein variants that are absent in normal cells.

The CHOP team’s research zeroed in on “microexons,” extremely short exons that had been overlooked in prior RNA sequencing studies of pediatric high-grade gliomas. These microexons, despite their small size, can significantly influence the structure and function of proteins.

Through deeper sequencing analysis, the scientists discovered that many microexons are skipped in tumor cells, particularly in genes encoding neuronal cell adhesion molecules. One protein, NRCAM (neuronal cell adhesion molecule), emerged as a central player. Healthy neurons require full-length NRCAM to form synapses—close contact points essential for brain function. In contrast, tumor cells consistently skipped two key microexons, producing a truncated NRCAM protein with a structure distinct from the normal version.

According to the researchers, this altered NRCAM variant appears to play a role in tumor invasiveness. In laboratory experiments, glioma cells expressing the truncated protein demonstrated enhanced migration and invasive capabilities. When tested in preclinical mouse models, tumors expressing this altered NRCAM grew more aggressively, underscoring its functional relevance.

From molecular insight to potential immunotherapy

Recognizing the glioma-specific NRCAM variant as a potential therapeutic target, the CHOP team developed a mouse monoclonal antibody designed to bind specifically to the altered protein structure created by microexon skipping.

“When mixed with glioma cells, the antibody worked like a highlighter, ‘painting’ glioma cells and marking them for killing by T cells armed with an immune receptor for mouse antibodies,” said senior author Dr. Andrei Thomas-Tikhonenko, chief of the Division of Cancer Pathobiology at CHOP and Professor of Pathology and Laboratory Medicine at the Perelman School of Medicine, University of Pennsylvania.

This antibody-based approach forms the basis for two possible therapeutic strategies. The first involves developing immune receptors that recognize and bind to the glioma-specific NRCAM variant, enabling targeted destruction by engineered immune cells. The second is designing traditional CAR-T cell therapies tuned to this unique protein configuration, ensuring that healthy brain cells remain untouched.

Lead author Dr. Priyanka Sehgal, a research scientist in the Thomas-Tikhonenko laboratory, emphasized that this discovery could influence strategies beyond brain tumors. “This could also change the way we find new targets in other solid tumors,” she said, noting that aberrant microexon splicing may be a broader phenomenon in cancer biology.

Sector context: advancing solid tumor immunotherapy

The potential impact of CHOP’s discovery extends beyond pediatric oncology. Solid tumors—particularly those in the brain—have historically proven difficult to treat with immunotherapy due to their complex microenvironments, heterogeneity, and proximity to vital structures.

Over the past decade, the biotech sector has invested heavily in improving CAR-T and other adoptive cell therapies for solid tumors, with global funding for oncology cell therapy surpassing $15 billion in 2024. Yet, clinical successes remain limited, in part because tumor-specific targets are rare.

By identifying structural protein differences driven by microexon skipping, the CHOP study adds a new category of potential targets for pharmaceutical development. If the NRCAM variant can be validated in other tumor types—such as glioblastoma multiforme and neuroendocrine cancers, as the researchers suggest—it could stimulate new licensing opportunities, biotech-pharma partnerships, and a wave of early-stage clinical trials focused on splicing-derived targets.

Funding landscape and collaborative ecosystem

This work was supported primarily by the CureSearch for Children’s Cancer Foundation Acceleration Initiative, alongside multiple National Institutes of Health (NIH) grants, including U01 CA232563 and R03 CA293992. Additional funding came from the National Science Foundation Graduate Research Fellowship Program, the Cancer Research Society’s Next Generation of Scientists Award, and philanthropic contributions from the Chad Tough Foundation and the Mildred L. Roeckle Endowed Chair in Pathology at CHOP.

The research also leveraged resources from the Children’s Brain Tumor Network, a multi-institutional data and biospecimen consortium. Such cross-institutional collaborations are increasingly vital for rare pediatric cancer research, where patient sample sizes are limited and multi-site data pooling accelerates discovery.

Early market and expert sentiment

While the findings are still in the preclinical phase, oncology researchers and biotech analysts are watching closely. Precision immunotherapy startups have seen strong venture capital interest when presenting compelling tumor-specific antigen data. Investors view CHOP’s NRCAM variant discovery as a potentially patent-protectable platform technology with applications in multiple cancer indications.

From a pharmaceutical development perspective, the approach aligns with a growing shift toward “neoantigen-mimicking” therapies—targeting tumor-specific protein structures that arise from unique genetic or splicing events. Analysts note that therapies leveraging such targets could reduce the risk of severe off-tumor toxicity, a major hurdle in past solid tumor CAR-T trials.

Next steps toward clinical translation

The CHOP team plans to continue preclinical validation of their monoclonal antibody and to optimize CAR-T constructs that can selectively recognize the glioma-specific NRCAM variant. Parallel studies will explore whether similar microexon skipping patterns exist in adult glioblastomas, medulloblastomas, and certain neuroendocrine tumors.

If successful, these studies could lead to a first-in-human clinical trial in pediatric patients within the next five to seven years. Given the rarity of pediatric high-grade gliomas, such a trial would likely require international collaboration and could follow the regulatory pathways established for other orphan drug-designated immunotherapies.

A potential blueprint for new cancer target discovery

Beyond its immediate therapeutic implications, this research could influence how the oncology community approaches target discovery in solid tumors. By integrating microexon detection into RNA sequencing pipelines, scientists may uncover previously invisible vulnerabilities in cancers once considered “undruggable.”

As Dr. Thomas-Tikhonenko noted, “While microexons may be small, the effects they have on the overall protein structure are quite profound.” That insight could catalyze a new class of precision oncology therapeutics, rooted not in the wholesale differences between cancer and normal cells, but in the subtle molecular edits that make tumors unique.