AAV Gene Therapy in Cancer: Insights from the AACR Annual Meeting 2025

Cancer’s persistent grip as a major cause of illness and death worldwide underscores the limitations of current treatments, including chemotherapy, targeted therapy, immunotherapy, cell therapy, surgery, and radiotherapy, particularly when facing metastatic and recurrent disease. In response to these challenges, gene therapy has emerged as a promising and innovative approach, aiming to address the fundamental genetic defects that drive cancer development and progression. Within the realm of gene therapy, recombinant adeno-associated viruses (rAAVs) are garnering increasing attention due to their unique and advantageous characteristics.

The Appeal of AAV Vectors in Cancer Therapy

Several key features distinguish AAVs as particularly well-suited vectors for cancer gene therapy:

• Low Immunogenicity: Compared to other viral delivery systems, AAVs are less likely to trigger strong immune responses, potentially allowing for repeated or sustained therapeutic gene expression.
• Versatile Targeting: The existence of multiple AAV serotypes and the ability to engineer their capsids provide a remarkable capacity to target a wide array of tissues and specific tumor types with enhanced precision.
• Sustained Gene Expression: AAVs can mediate long-lasting expression of the delivered therapeutic gene, which is particularly advantageous for addressing chronic diseases like cancer where continuous intervention may be required.
• Established Safety Profile: AAVs have demonstrated a strong safety record in clinical gene therapy applications for various non-cancerous conditions, providing a foundation of confidence for their use in oncology.

Diverse Mechanisms of AAV-Based Cancer Therapy

Leveraging these properties, researchers are engineering AAVs to deliver therapeutic genes to tumors through a variety of compelling strategies:

• Direct Tumor Suppression: This involves the delivery of genes that can directly inhibit tumor growth.

  • Restoring Growth Control: Introducing tumor suppressor genes, such as p53 or PTEN, can reinstate normal cellular growth regulation within cancer cells.
  • Inducing Cell Death: Delivering “suicide genes,” like HSV-TK, can make cancer cells susceptible to specific prodrugs, leading to their targeted destruction.

• Immunomodulation: AAVs can be harnessed to stimulate the body’s own anti-cancer defenses.

  • Boosting Anti-tumor Immunity: Delivery of cytokines (e.g., IL-12) or immune checkpoint modulators (e.g., anti-PD-1 antibodies) can enhance the activity of immune cells against tumors.
  • Enhancing Cancer Vaccines: AAVs can be employed to express tumor-specific antigens, thereby improving the effectiveness of cancer vaccine strategies.

• Tumor Microenvironment Modulation: Targeting the supportive environment surrounding tumors offers another therapeutic avenue.

  • Inhibiting Growth and Metastasis: AAVs can deliver genes that disrupt the stromal or vascular components of the tumor microenvironment, hindering tumor growth and spread.

• Combination Therapies: Recognizing the complexity of cancer, AAV-based gene therapies are being investigated in conjunction with conventional treatments.

  • Enhancing Efficacy and Overcoming Resistance: Combining AAVs with chemotherapy, immunotherapy, or radiotherapy holds the potential to improve treatment outcomes and overcome drug resistance mechanisms.

Promising Preclinical and Emerging Clinical Evidence

Compelling evidence from preclinical studies has demonstrated the potential of AAV-mediated gene delivery to significantly reduce tumor growth and burden in various cancer models, including ovarian carcinoma, hepatocellular carcinoma, and triple-negative breast cancer. Notably, combination regimens involving AAVs and standard therapies have shown particular promise in overcoming drug resistance and targeting the challenges of metastatic disease. While clinical translation of these approaches is still in its early phases, with the majority of data currently derived from animal models, the established safety profile and inherent versatility of AAVs provide an encouraging outlook for future clinical trials in cancer.

The American Association for Cancer Research (AACR) Annual Meeting

AACR, the world’s oldest and largest professional organization dedicated to advancing cancer research, recently convened its Annual Meeting 2025 from April 25 to 30 at McCormick Place in Chicago, Illinois. This premier international event brought together over twenty thousand researchers, clinicians, and advocates to discuss the latest groundbreaking discoveries in the field. Highlighting the growing interest in AAV-based cancer therapies, we have identified three noteworthy posters presented at this year’s conference.

   1. Gene Therapy Targets Choroid Plexus to Combat Chemotherapy-Related Cognitive Decline

A poster by Ahram Jang et al. from Boston Children’s Hospital and Beth Israel Deaconess Medical Center has revealed promising approaches to addressing chemotherapy-related cognitive impairment through gene therapy targeting the choroid plexus (ChP). The research explores how the choroid plexus and cerebrospinal fluid (CSF) system can be leveraged to protect brain function during cancer treatment.

Understanding the Choroid Plexus-CSF System

The choroid plexus is a specialized tissue located within each of the brain’s ventricles, consisting of epithelial cells surrounding a core of capillaries and connective tissue. This structure performs the critical function of producing and secreting most of the cerebrospinal fluid in the central nervous system. The choroid plexus epithelium forms the blood-CSF barrier through tight junctions between cells, carefully regulating what substances can enter the CSF from the bloodstream.

CSF serves multiple essential functions:

• Providing protective buoyancy for the brain
• Facilitating the removal of metabolic waste through the glymphatic system
• Regulating the exchange of biomolecules between the blood and brain

Chemotherapy’s Impact on Brain Function

According to the research presented, methotrexate (MTX), a commonly used chemotherapy drug, induces significant oxidative stress in the choroid plexus. The poster demonstrates through multiple experiments that:

1. MTX treatment metabolically alters CSF in mice
2. MTX increases oxidative damage specifically in the hippocampus, a brain region critical for learning and memory
3. The drug reduces antioxidant activity in the CSF
4. MTX induces reactive oxygen species (ROS) production and impairs mitochondrial function

These findings help explain the mechanism behind the cognitive impairment many cancer patients experience during and after chemotherapy, often referred to as “chemo brain.”

 Innovative Gene Therapy Approach

The researchers developed a novel therapeutic strategy targeting the choroid plexus with SOD3 (superoxide dismutase 3) gene therapy. They detailed an experimental approach where AAV is used to deliver the SOD3 gene specifically to the choroid plexus. This gene therapy strategy aims to boost antioxidant capacity in the CSF and protect neuronal tissues from MTX-induced oxidative stress. The use of AAV as a vector is central to the study’s methodology.

Their data shows:

1. ChP-SOD3 augmentation successfully alters markers of oxidative stress in CSF.
2. This gene therapy approach rescues oxidative stress against MTX in the hippocampus.
3. The treatment effectively replenishes the protective capacity of mouse CSF (Figure 1).

Figure 1. Supplemental ChP-SOD3 expression mitigates MTX-induced oxidative stress in the CSF and the hippocampus.

Some of their findings were also published in Neuron, 2022. What makes this approach particularly promising is that the choroid plexus can be harnessed for therapeutic gene delivery to broadly influence CNS redox state. By targeting the choroid plexus rather than attempting to treat the entire brain, the researchers have found a more efficient delivery method for neuroprotective factors.

Clinical Relevance

The poster highlights that CNS lymphoma patients treated with MTX have decreased CSF antioxidant levels, suggesting these findings have direct clinical relevance. This research opens new possibilities for protecting cancer patients from cognitive side effects of treatment without compromising the anti-cancer efficacy of chemotherapy.

Conclusions

The research presents three key points:

1. MTX induces oxidative stress in the choroid plexus.

2. Choroid plexus-targeted SOD3 gene therapy effectively replenishes the protective capacity of mouse CSF.

3. The choroid plexus can be harnessed for therapeutic gene delivery to broadly influence CNS redox state.

This research underscores the dynamic interplay between the choroid plexus, cerebrospinal fluid, and the brain’s health, particularly in the context of toxic insults like chemotherapy. The development of ChP-targeted AAV gene therapies holds significant promise for mitigating the debilitating cognitive side effects of cancer treatment and improving the lives of cancer survivors.

   2. AAV-Delivered PTEN-Long Reprograms Tumor Microenvironment and Shrinks Mouse Tumors

In a study presented by Tiphaine Martin and Jia Xu et al., at the Icahn School of Medicine at Mount Sinai, a secreted form of the tumor suppressor PTEN — known as PTEN-Long — has been shown to suppress tumor growth and stimulate anti-tumor immunity by reshaping the tumor microenvironment. Importantly, the team leveraged AAV vectors to deliver PTEN-Long systemically, demonstrating effective tumor regression in mouse models.

PTEN-Long: A Soluble Tumor Suppressor with Systemic Impact

PTEN is a well-characterized phosphatase that inhibits the PI3K/AKT signaling pathway, a key driver of cell survival and growth in many cancers. Unlike canonical PTEN, PTEN-Long is a secreted isoform capable of entering other cells, but its functional role has remained poorly defined — until now.

Using both genetic overexpression models and AAV-mediated delivery of PTEN-Long, the researchers discovered that secreted PTEN-Long not only reduced PI3K signaling but also drastically altered the tumor immune landscape.

Key Findings: Tumor Regression and Immune Activation

• Growth Suppression: Mice overexpressing PTEN-Long or receiving AAV-PTEN-Long injections exhibited significant tumor growth retardation.
• PI3K Pathway Inhibition: PTEN-Long reduced downstream pAKT levels and glucose uptake in tumors.
• Immune Remodeling: Tumors treated with AAV-PTEN-Long showed:

  • Increased MHC-II and CD86 expression in myeloid cells.
  • Reduced PD-L1 expression in cancer cells.
  • Enhanced infiltration of cytotoxic CD8+ T cells and NK cells.
  • Expansion of antigen-presenting cells, especially macrophages and dendritic cells.

Mechanism: Tumor–Immune Crosstalk via Soluble PTEN-Long

Single-cell transcriptomic analysis revealed that PTEN-Long activates antigen presentation pathways, reduces tumor cell immune evasion, and facilitates immune-stimulatory crosstalk between tumor-associated myeloid cells and effector lymphocytes. The result is a shift from a suppressive to an inflammatory tumor microenvironment.

AAV Gene Therapy as a Delivery Platform

The use of AAV to express PTEN-Long in vivo was pivotal. Liver-directed AAV injection led to systemic secretion of PTEN-Long, which was taken up by distant tumors (Figure 2). This gene therapy approach bypassed the need to directly modify tumor cells and proved sufficient to reprogram tumor behavior and trigger immune rejection.

Figure 2.AAV-mediated treatment with PTEN-Long expression in mouse models.

Conclusion: PTEN-Long as an Immune-Modulating Therapeutic

This study highlights the dual tumor-intrinsic and immune-modulating activity of PTEN-Long, suggesting that it could represent a novel immunotherapeutic strategy for cancer. By simultaneously targeting tumor cell signaling pathways and modulating the tumor microenvironment to favor anti-tumor immunity, this approach holds the potential to overcome some of the limitations of current immunotherapies. The ability to deliver PTEN-Long systemically via an AAV vector offers a potential advantage for treating metastatic disease and solid tumors.

   3.Novel AAV-Mediated Virotherapy Targets Tumor Microenvironment in Triple-Negative Breast Cancer

A poster presented by Md. Manirujjaman et al., from LSU Health New Orleans and collaborating institutions details a promising AAV-mediated virotherapy approach for targeting the tumor microenvironment (TME) in triple-negative breast cancer (TNBC) – a notoriously aggressive and therapy-resistant subtype of breast cancer. The approach uses a soluble AAV/TGFβRD virotherapy to modulate immunosuppressive signaling and improve the efficacy of conventional chemotherapy.

Overcoming the Immunosuppressive Barrier in TNBC

TNBC’s aggressive growth and poor response to therapy have been linked to its heavily immunosuppressive microenvironment, often driven by TGF-β signaling. To counteract this, the team developed an AAV vector encoding a soluble TGFβ receptor domain (TGFβRD) that sequesters extracellular TGF-β, preventing it from engaging cellular receptors and promoting immune suppression.

The AAV/TGFβRD therapy was shown to:

• Transduce both mouse and human TNBC cells, including the aggressive 4T1 and MDA-MB-231 lines.
• Significantly reduce tumor growth in syngeneic TNBC mouse models.
• Increase infiltration of macrophages, dendritic cells, and CD8+ T cells, while decreasing T regulatory cells (Tregs), as demonstrated by NanoString and flow cytometry data.
• Enhance the therapeutic response when combined with chemotherapy (Paclitaxel).

Synergistic Effects with Chemotherapy

In vivo studies showed that mice treated with the AAV/TGFβRD construct — especially in combination with Paclitaxel — had significantly lower tumor volume, reduced tumor weight, and decreased metastatic burden compared to control groups.

Histological analysis confirmed these findings, showing reduced tumor cell proliferation and a more immune-activated microenvironment.

Mechanistic Insights from Transcriptomics

RNA-seq and NanoString analyses revealed upregulation of immune-activating pathways and downregulation of TGF-β and tumor growth-associated signaling. The treatment increased cytokine/chemokine signaling, suggesting enhanced antigen presentation and immune cross-talk within the tumor bed.

Gene ontology (GO) enrichment analyses also pointed to activation of pathways involved in innate immune signaling, pathogen response, and cellular adhesion.

Translational Potential

This study provides strong preclinical evidence that AAV-based soluble TGFβ receptor virotherapy can reprogram the TNBC tumor microenvironment to be more permissive to immune activation and therapeutic intervention. When paired with chemotherapy, this dual approach appears to significantly improve anti-tumor outcomes.

Summary

The insights gleaned from these AACR abstracts reinforce the substantial promise of AAV-mediated gene therapy in oncology, especially when integrated into combination regimens with existing treatments. AAV’s inherent safety profile, adaptability, and capacity for sustained gene expression position it as an asset in tackling the genetic complexities and resistance mechanisms inherent in cancer. Future breakthroughs in capsid engineering, vector and promoter design, and immune evasion strategies will be pivotal in fully realizing its therapeutic potential in the fight against cancer.

Reference:

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2. Santiago-Ortiz JL et al. Adeno-associated virus (AAV) vectors in cancer gene therapy. J Control Release.2016;240:287-301.
3. Luo J et al. Adeno-associated virus-mediated cancer gene therapy: current status. Cancer Lett.2015;356
4. Jang A et al. Choroid plexus-CSF targeted antioxidant therapy protects the brain from toxicity of cancer chemotherapy. 2022;110(20):3288-3301.