Glioblastoma multiforme (GBM), usually arising from glial precursor cells or neural stem cells, is the most common and lethal primary brain cancer in adults. It has very limited treatment options and a median life expectancy less than 2 years after diagnosis. Systemic and local immunosuppression induced by GBMs largely contributes to malignancy aggressiveness and resistance to multiple immunotherapies, such as immune checkpoint blockade (ICB) therapy, which is powerful for primary care of other types of solid tumors.
Despite of its huge therapeutic potential, the knowledge regarding how OVM initiates adaptive immunity against gliomas and how the interactions between OVM and our immune system would influence the therapeutic effects of ICB is still lacking. Hence the researchers are seeking to address these two knowledge gaps.
First, they confirmed the efficacy of OVM in reducing glioma progression. The immunocompromised mice were injected intracranially with GBM cell lines (GL261-Luciferase, GL261 and CT2A) to induce a glioma in the brain on day 0 and followed by daily tail intravenous injection of OVM or vehicle from day 5 to day 9. Vehicle includes the buffer solutions that researchers use to deliver OVM but containing no OVM, acting as the control condition. GL261-Luciferase is a cell line where it's infected with lentivirus whose genome was engineered to contain the luciferase gene so that wherever the tumor develops, it would glow. A stronger luminescence intensity (red) indicates the progression of glioma while bluish color indicates little tumor growth. It was found that OVM significantly inhibited the growth of glioma and prolonged the survival of glioma-bearing mice.
Moving on to investigate the immune response, the researchers found that OVM successfully induced immunogenic cell death and reverse the GBM-induced immunosuppression both locally and systemically. Immunogenic cell death is characterized by the release of damage-associated molecular patterns (DAMPs) by tumor cells, which are molecules that normally stay inside the cell and becomes 'danger signals' recognized by immune cells when being released outside, driving adaptive-immunity elimination in tumor microenvironment. They examined the release of DAMPs, revealing significant CRT (externalized calreticulin, a multifunctional protein) exposure and elevated extracellular ATP (adenosine triphosphate, energy source for our cells) in the supernatant collected from glioma cell lines with OVM treatment. This indicates the occurrence of immunogenic cell death induced by OVM.
Additionally, the number of CD4+ and CD8+ T cells increased significantly in peripheral blood of glioma-bearing mice following intravenous OVM treatment. Spleen atrophy and loss of splenic T-cell population were also recovered. Similarly, in the tumor local environment, they also found rapid increase in tumor-specific CD8+ T cells in the spleen. The measurement is achieved by orthotopical implantation of GL261 glioma cells expressing OVA (full-length ovalbumin, processed into SIINFEKL) and H-2Kb-SIINFEKL tetramer that binds to T cell receptors where H-2Kb is the mouse version of MHC class I protein. The recognition of glioma-derived-antigen-MHC complex by T cells allows the accurate tracking of tumor-specific T cells (Hsu et al., 2025). Hence, with OVM infection, both local and systemic immunity are boosted and recovered.
Before diving deeper into the mechanism, the researchers digressed a bit and addressed a main concern about the efficacy of OVM: Spleen is the major body 'filter' consisting of large number of immune cells that's found previously able to eliminate delivered oncolytic viruses and OVM is often 'trapped' inside the spleen of various host animals. Therefore, the researchers removed the spleen (splenectomy) from mice to find out the role of spleen in OVM treatment. To their surprise, opposite to the greater reduction in glioma progression that they have expected, the antitumor activity of OVM treatment was completely abrogated after removal. Splenectomy-OVM mice almost have the same low survival probability as vehicle control and no expansion of T-cell population in the peripheral blood and tumor microenvironment.
Consequently, the researchers tried to find out the specific cell population in the spleen that's mediating the reversal of immunosuppression and antitumor activity. They first employed a broad RNA sequencing and computational screening and found that B cells have the highest abundance and showed strongest predicted interactions with T cells after OVM treatment. To move beyond correlation, a series of validation experiment were conducted: In vitro co-culture experiments demonstrated that B cells from OVM-treated mice significantly enhanced activation of T cells but not other splenic immune populations and this activation is dose-dependent. Further, after blocking the B cells with anti-CD19 antibody, OVM administration failed to prolong the survival of glioma-bearing mice and increase the infiltration of T cell populations in the blood and tumor microenvironment.
In order to validate this finding in vivo, researchers targeted the Major Histocompatibility Complex class I (MHC-I), a critical component of the structural interface between B and T cells. B cells communicate and 'educate' T cells by presenting a fragment of tumor on MHC-I to activate them, which process is known as antigen presentation. Blocking MHC-I with a specific antibody completely abolished B-cell-induced CD8+ T cell proliferation and activation. Collectively, these results confirm that the direct physical interface is crucial for immunity restoration by OVM treatment. Later the researchers identified the specific subset of B cells that's responsible for this interaction to be Bst2+ B cells by computational screening and in-vivo evidence: Bst+B cells significantly prolonged the survival of B-cell-deficient, GL261-OVA-bearing mice after OVM stimulation while Bst2-B cells and B cells from vehicle control group did not.
To test the synergy between ICB and OVM therapy, immunocompromised mice was injected intracranially on day 0 and from day 5 to day 9, the mice is divided into different groups and treated daily intravenously with different combinations of immune checkpoint protein antibodies, including isotype antibody as control, PD-1 and PD-L1 antibodies, with or without OVM. The researchers revealed that, comparing with other 5 combinations, OVM treatment and PD-1 inhibitor together yielded the greatest recruitment of CD8+ T cells into tumor microenvironment, suppression of intracranial glioma growth as well as restoration of splenic size and weight. Systematically, massive expansions of effector (activated) CD8+ and CD4+ T cells in peripheral bloodstream are also observed. Therefore, OVM synergizes with PD-1 inhibitors for glioma treatment by simultaneously reshaping systemic immunity and the local immune environment in the brain.
Citations:
For images:
https://www.cancerresearch.org/immunotherapy-by-treatment-types/oncolytic-virus-therapy
https://www.nature.com/articles/s41592-020-01031-0
https://www.cancer.gov/about-cancer/treatment/types/immunotherapy/checkpoint-inhibitors
For academic literature:
the primary article:
Han, Yu, et al. “Oncolytic Virus M1 Reinvigorates CD8+ T-Cell Immunity against Glioblastoma through B-Cell-Dependent Antigen Cross-Presentation in the Spleen.” Cellular & Molecular Immunology, 4 Mar. 2026, www.nature.com/articles/s41423-026-01396-w/figures/8, https://doi.org/10.1038/s41423-026-01396-w. Accessed 26 Mar. 2026.
Others:
National Cancer Institute. “Https://Www.cancer.gov/Publications/Dictionaries/Cancer-Terms/Def/Blood-Brain-Barrier.” Www.cancer.gov, 2 Feb. 2011, www.cancer.gov/publications/dictionaries/cancer-terms/def/blood-brain-barrier.
Hsu, Chung-Yao, et al. “Polymerised Superparamagnetic Antigen Presenting Cell Lymphocyte Capture for Enriching Tumour Reactive T-Cells and Neoantigen Identification.” Nature Communications, vol. 16, no. 1, 2 June 2025, www.nature.com/articles/s41467-025-60321-3, https://doi.org/10.1038/s41467-025-60321-3. Accessed 26 Mar. 2026.
“Up Close: How Immune Checkpoint Inhibitors Revolutionize Cancer Treatment | What’s up at Upstate | SUNY Upstate.” Www.upstate.edu, www.upstate.edu/whatsup/2023/100523-up-close-how-immune.php.
Zhang, Haipeng, et al. Naturally Existing Oncolytic Virus M1 Is Nonpathogenic for the Nonhuman Primates after Multiple Rounds of Repeated Intravenous Injections. Vol. 27, no. 9, 1 Sept. 2016, pp. 700–711, https://doi.org/10.1089/hum.2016.038. Accessed 1 Aug. 2023.
“Defined Immune Response Tracking in Mice: OVA MHC Tetramers – Caltag Medsystems.” Caltagmedsystems.co.uk, Mar. 2024, www.caltagmedsystems.co.uk/information/defined-immune-response-tracking-in-mice-ova-mhc-tetramers/. Accessed 29 Apr. 2026.
“Oncolytic Virus Therapy and Its Side Effects.” Cancer.org, 2023, www.cancer.org/cancer/managing-cancer/treatment-types/immunotherapy/oncolytic-virus-therapy.html.