Groundbreaking research challenges decades of scientific thinking about Epidermodysplasia Verruciformis
Epidermodysplasia verruciformis (EV) is a rare, inherited skin disorder that reads like something from a medical mystery novel. Individuals with this condition develop widespread skin lesions and have an unusual susceptibility to specific types of human papillomavirus (HPV), particularly betapapillomaviruses (βHPV). What makes EV particularly fascinating is that while these patients struggle with persistent HPV infections that often lead to skin cancer in sun-exposed areas, they typically control other viral infections without difficulty—creating a puzzle that has intrigued scientists for decades.
EV patients show specific susceptibility to βHPV but handle other viral infections normally, pointing to a targeted immune deficiency rather than a general one.
For years, the prevailing theory suggested that EV resulted from mutations in genes that provide keratinocyte-intrinsic immunity—a specialized defense system within skin cells that specifically targets βHPV. The prime suspects were mutations in either the TMC6 (EVER1) or TMC8 (EVER2) genes, which form a protein complex in the endoplasmic reticulum with CIB1. This complex was hypothesized to act as a restriction factor in keratinocytes specifically for βHPV infection.
However, recent groundbreaking research using a mouse model has turned this theory on its head, suggesting that the story is far more complex—and interesting—than previously imagined.
Epidermodysplasia verruciformis follows an autosomal recessive inheritance pattern, meaning an individual must inherit two defective copies of the gene—one from each parent—to develop the condition. The condition is primarily linked to biallelic loss-of-function mutations in:
Forms part of the heterotrimeric complex in the endoplasmic reticulum. Mutations disrupt normal function.
Partners with TMC6 in the protein complex. Loss-of-function mutations lead to EV phenotype.
Completes the heterotrimeric complex. Mutations in some cases also lead to EV.
These three proteins form a heterotrimeric complex in the endoplasmic reticulum, though their exact function remains unknown. What makes the situation more complex is that this protein complex is present not only in keratinocytes but also in lymphocytes—a clue that perhaps the immune system plays a larger role than previously appreciated.
Human papillomaviruses don't infect laboratory animals, creating a significant obstacle for research. This barrier was overcome when scientists discovered the murine papillomavirus MmuPV1, which was first isolated from immunodeficient mice with extensive skin warts.
This virus shares important characteristics with βHPV:
The murine papillomavirus that enabled researchers to study EV mechanisms in a mouse model.
Researchers developed an innovative model using FVB mice genetically engineered to lack Tmc6 or Tmc8—the mouse equivalents of the human TMC6 and TMC8 genes. This model provided the perfect opportunity to investigate whether these genes function as intracellular restriction factors or if a different mechanism explains the unusual susceptibility to papillomaviruses in EV.
To unravel the mystery of EV, researchers designed a meticulous experiment comparing how MmuPV1 infection progresses in different mouse models:
The study included three groups of FVB mice: Tmc6⁻/⁻, Tmc8⁻/⁻, and wildtype (with normal Tmc6/Tmc8 genes)
All mice were challenged with MmuPV1 either vaginally (females) or on the tail (males)
Viral activity was assessed at multiple time points, starting at day 16 post-infection and continuing for several weeks
Age-matched nude mice (with compromised immune systems) served as positive controls, while unchallenged mice served as negative controls
Researchers used qRT-PCR to measure viral transcript levels and flow cytometry to characterize immune cell populations
The findings challenged decades of scientific thinking:
Initial infection rates were similar across all groups—Tmc6⁻/⁻, Tmc8⁻/⁻, and wildtype mice showed comparable levels of viral transcripts at day 16 post-challenge. This was the first surprise: if Tmc6/8 were true restriction factors, their absence should have led to immediately higher infection rates.
The critical difference emerged over time: wildtype mice showed significantly better viral clearance compared to both knockout strains. This persistence of infection in the Tmc6⁻/⁻ and Tmc8⁻/⁻ mice pointed toward a problem with viral control rather than initial infection.
Further investigation revealed immune abnormalities in the knockout mice: they exhibited partial CD8 T cell deficits and elevated Treg cells. While their CD8 T cells could produce interferon-γ and surface CD25 normally upon stimulation, fewer of them were dividing compared to wildtype cells.
Most intriguingly, these immune defects appeared specific to papillomavirus control—the knockout mice handled vaccinia virus infection normally and generated appropriate neutralizing antibodies.
| Time Point | Tmc6⁻/⁻ Mice | Tmc8⁻/⁻ Mice | Wildtype Mice |
|---|---|---|---|
| Day 16 | High | High | High |
| Week 6 | High | High | Moderate-Low |
| Parameter | Tmc6⁻/⁻ / Tmc8⁻/⁻ Mice | Wildtype Mice |
|---|---|---|
| CD8 T cell function | Partial deficit | Normal |
| Treg levels | Elevated | Normal |
| Response to vaccinia virus | Normal | Normal |
| Antiviral antibodies | Normal production | Normal production |
| Feature | Typical EV | Atypical EV |
|---|---|---|
| Cause | TMC6/TMC8/CIB1 mutations | Immunodeficiency, AIDS, immunosuppressive drugs |
| Primary defect | Subtle T cell dysfunction | Broad immune deficit |
| Response to other infections | Normal | Compromised |
| Reagent/Material | Function in EV Research |
|---|---|
| Tmc6⁻/⁻ and Tmc8⁻/⁻ FVB mice | Model typical EV genetic background |
| MmuPV1 virus | Infection challenge to study βHPV-like pathogenesis |
| qRT-PCR assays | Quantify viral transcript levels |
| Flow cytometry | Analyze immune cell populations and function |
| Vaccinia virus | Test specificity of immune defects |
| Anti-CD3/CD28 antibodies | Stimulate T cells to assess functionality |
Creating knockout mice with specific gene deletions to study gene function.
Using qRT-PCR and flow cytometry to measure viral and immune parameters.
Testing immune responses with specific viral infections.
"This research has fundamentally shifted our understanding of epidermodysplasia verruciformis. The evidence strongly suggests that EV is not primarily a disorder of keratinocyte-intrinsic immunity but rather a subtle cellular immune deficiency that specifically compromises control of papillomavirus infections."
The Tmc6/Tmc8 complex appears to play a role in optimal CD8 T cell function, particularly against papillomaviruses. When this complex is disrupted, the immune system can still handle most viral challenges but fails to effectively control βHPV infections, allowing them to persist and eventually lead to skin cancer in combination with UV exposure.
This new understanding has important implications for treatment. If EV involves immune dysfunction rather than just a skin cell defect, interventions that enhance immune control of papillomaviruses might benefit patients. The research team explored this possibility by testing whether adoptive transfer of splenocytes from vaccinated wildtype mice could reduce viral loads in infected knockout mice. Interestingly, these transfers didn't significantly impact viral transcript levels, suggesting that simply providing immune cells isn't sufficient—the complex itself likely plays a specific role in anti-papillomavirus immunity that isn't easily replaced.
The story of how a mouse papillomavirus helped rewrite our understanding of a rare human genetic disorder exemplifies the power of animal models in biomedical research. What began as a straightforward hypothesis—that EV genes provide intrinsic immunity in skin cells—evolved into a more nuanced understanding of immune specialization against specific viral threats.
This research not only advances our knowledge of EV but also sheds light on the broader question of why our immune systems seem to have particular vulnerabilities to certain pathogens despite general competence against others. As we continue to unravel these mysteries, we move closer to developing targeted therapies that could help those living with this challenging condition—proving that even the rarest disorders can provide profound insights into human biology.
This article was based on recent research published in PLOS Pathogens (January 2025) examining MmuPV1 infection in Tmc6/Ever1 or Tmc8/Ever2 deficient FVB mice as a model for βHPV in epidermodysplasia verruciformis.