Blocking one protein makes invisible HPV cancers suddenly vulnerable to immunotherapy

HPV-positive head and neck cancers have a trick that has baffled oncologists for years. They strip away the molecular markers - called MHC-I molecules - that cells use to flag themselves as damaged or infected. Without those markers, immune cells patrol right past the tumor without recognizing anything is wrong. The cancer hides in plain sight. Immunotherapy drugs that work well against other cancers fail here, because you cannot unleash the immune system against a target it cannot see.

A team at Henry Ford Health and Michigan State University Health Sciences has now identified exactly how the trick works - and demonstrated, in experimental models, that reversing it can turn previously untreatable tumors into targets the immune system destroys on its own.

MARCHF8: the protein that shreds the warning flags

The research, published in Proceedings of the National Academy of Sciences (PNAS), pins the immune evasion mechanism on a single protein: MARCHF8. Human papillomavirus co-opts this protein - a ubiquitin ligase involved in normal protein regulation - to dismantle MHC-I molecules before they reach the cell surface. It is an elegantly destructive hijacking. The virus does not merely block the signal. It uses the cell's own machinery to destroy the signal before it can form.

Without MHC-I molecules on the cell surface, CD8+ T cells and natural killer cells - the immune system's primary tumor-killing forces - have nothing to respond to. The tumor microenvironment stays immunologically "cold." No immune cells infiltrate. No attack is mounted. The cancer grows undisturbed.

Researchers had known for years that HPV-positive cancers lacked MHC-I expression. But the field had only fragments of the explanation. How exactly was HPV suppressing these molecules? Through what pathway? At what step? Dohun Pyeon, a professor in the Department of Microbiology, Genetics, and Immunology at MSU and the study's lead investigator, described the MARCHF8 discovery as the central piece of a puzzle that had remained frustratingly incomplete.

Cold tumors turned hot

The results were stark. When the researchers knocked out MARCHF8 in experimental models, the immune response came back fast. CD8+ T cells and natural killer cells rapidly infiltrated the tumor microenvironment - an area they had previously ignored entirely. Tumors shrank. In combination with standard immunotherapy drugs - checkpoint inhibitors that are already FDA-approved - the approach worked even on tumors that had resisted every prior treatment.

"The most exciting part is that our discovery worked on tumors that were previously impossible to treat," Pyeon said. The phrasing is worth noting: not difficult to treat, but impossible. These are the cancers oncologists call "cold" - tumors where the immune system shows essentially no activity at all. Turning a cold tumor hot is one of the central unsolved challenges in cancer immunology. The MARCHF8 knockout achieved it decisively in the models tested.

Mohamed Khalil, a research assistant professor and the paper's first author, detailed the immune landscape changes. Knocking out MARCHF8 did not merely restore MHC-I expression on the cell surface. It activated T cells and enhanced infiltration by T cells, natural killer cells, and macrophages into the tumor microenvironment. The immune system did not just notice the tumor. It mounted a coordinated, multi-cell-type attack - the kind of robust anti-tumor response that oncologists aim for but rarely achieve in these cancer types.

Mapping the immune rewiring at single-cell resolution

To understand precisely how the immune landscape changed after MARCHF8 removal, the team collaborated with Qing-Sheng Mi, a physician-researcher and vice chair for research in MSU's Department of Dermatology, who also directs the Center for Cutaneous Biology and Immunology and the immunology program at the Henry Ford Cancer Institute.

Mi used single-cell RNA-sequencing to map the tumor microenvironment at a resolution that bulk sequencing methods cannot achieve. Rather than measuring average gene expression across thousands of cells, the technique profiles each cell individually, revealing not just which immune cell types are present but what they are doing - what genes they are expressing, what signals they are sending, and how they are interacting with neighboring cells.

"We showed knocking out MARCHF8 fundamentally rewires immune cell crosstalk - dramatically boosting the cytotoxic activity of CD8+ T cells and NK cells," Mi said. The word "rewires" is apt. The change was not incremental but structural, altering the functional relationships between immune cell populations and transforming a suppressive microenvironment into an active one.

An epidemic scale problem

The clinical urgency behind this work is substantial and growing. HPV-positive head and neck cancers have increased at what researchers describe as epidemic rates in the United States over the past several decades, particularly oropharyngeal cancers affecting the back of the throat, the base of the tongue, and the tonsils. This rise has occurred even as HPV vaccination campaigns have expanded - a reminder that vaccination prevents future infections but does nothing for the millions of people already carrying the virus.

Many HPV-positive head and neck cancers respond reasonably well to radiation and chemotherapy, and survival rates for this subtype are generally better than for HPV-negative head and neck cancers. But a subset resists standard treatment. For that subset, the therapeutic landscape has been grim. Checkpoint inhibitor immunotherapy, which has transformed outcomes in melanoma, lung cancer, and several other tumor types, has shown limited effectiveness in HPV-positive tumors precisely because the cancers lack the MHC-I molecules that the whole immunotherapy paradigm depends on.

The MARCHF8 finding offers a potential two-step solution: restore the immune target first by blocking MARCHF8, then apply checkpoint inhibitor immunotherapy to unleash the immune response. The combination produced results in the experimental models that neither strategy achieved alone.

From genetic knockout to a drug: the translational gap

The study used genetic knockout to remove MARCHF8 - a powerful research tool but not something that can be directly administered to a patient. Gene editing a protein out of a patient's tumor cells is, for now, not a viable clinical strategy. The team's stated goal is to develop a small-molecule drug that blocks MARCHF8 activity in humans, which would allow the approach to be combined with existing, already-approved immunotherapy regimens.

That is a significant translational step, and the timeline is uncertain. Drug development from target identification to clinical use typically takes a decade or more, and the majority of promising targets never yield viable drugs. MARCHF8 is a ubiquitin ligase with normal biological functions beyond cancer - it participates in protein quality control pathways throughout the body. Blocking it systemically could have unintended effects that the tumor-focused experiments did not reveal. The specificity, toxicity profile, and therapeutic window of any future MARCHF8 inhibitor will need careful preclinical and clinical evaluation.

The work has also been conducted entirely in experimental models, not in human patients. Preclinical cancer immunology has an uneven track record of predicting clinical outcomes. Immune responses that look dramatic in mice sometimes translate poorly to the more complex, heterogeneous, and often immunosuppressed environment of human tumors. These caveats are standard for preclinical cancer research, but they are important ones to keep firmly in view.

The team plans next to investigate how different immune cell types - particularly natural killer cells, which appeared to play a larger role than previously understood - contribute to tumor clearance once MHC-I markers are restored. Understanding the full choreography of immune cell cooperation could inform how combination therapies are designed.

Last year, the researchers received a $3 million grant from the National Institute of Dental and Craniofacial Research to continue this work. Additional funding came from an MSU Foundation Strategic Partnership grant and the Henry Ford + MSU Cancer Seed Funding Program.