HPV type 39 E6 and E7 genes show genetic variation in central China

The fight against cervical cancer has long focused on the most notorious strains of human papillomavirus, but a new study from central China is turning attention to a less publicized player: HPV type 39. Researchers at Jingzhou Hospital Affiliated to Yangtze University have mapped, for the first time at this level of detail, the genetic variation of the HPV-39 E6 and E7 genes—the two viral workhorses most closely implicated in driving cervical cells toward malignancy—in a region where this particular type circulates at relatively high levels. Their findings, published in Virology Journal, offer a molecular census of a virus that has, until now, been something of a blind spot in regional surveillance efforts, and the results carry implications for everything from vaccine design to the development of immunotherapy targets.

Persistent infection with high-risk human papillomavirus, or HR-HPV, is the central engine of cervical carcinogenesis. Among the dozen or so high-risk types, HPV-16 and HPV-18 dominate the global conversation, and it is against these that prophylactic vaccines were primarily engineered. Yet the distribution of HPV types is strikingly uneven across geography. HPV-39, one of the dozen high-risk types, accounts for a comparatively larger share of infections in central China, a pattern that makes local molecular data not a luxury but a necessity. Without knowing what the virus actually looks like in a given population—which variants of its oncogenes are circulating, and how those variants differ from the reference sequences that diagnostic assays and immunological studies are typically built around—clinicians and researchers are effectively operating with an outdated map.

The research team, led by corresponding author Bing Mei of the hospital’s Department of Laboratory Medicine, approached the problem with a deliberate and technically careful methodology. The investigators began by identifying clinical samples carrying a single HPV-39 infection, as opposed to mixed infections with multiple HPV types, using HPV genotyping before any amplification step. This filtering matters: mixed infections can complicate sequencing results and obscure the true variant composition of a single viral type. Once pure HPV-39-positive samples were secured, the researchers amplified the E6 and E7 genes using polymerase chain reaction and read the resulting sequences by Sanger sequencing, the gold-standard method for confirming the exact nucleotide identity of relatively short DNA fragments.

The sequencing effort produced a rich dataset. Across the E6 and E7 sequences, the team identified a total of 33 single nucleotide variants. Of these, 13 were synonymous mutations—changes in the viral DNA that do not alter the amino acid sequence of the resulting protein—and 20 were non-synonymous mutations, meaning they actually changed the protein-building instructions. Notably, six of the non-synonymous mutations had never been recorded before, making them novel additions to the global catalogue of HPV-39 variation. The distinction between synonymous and non-synonymous changes is more than academic bookkeeping. Synonymous mutations tend to accumulate neutrally, offering a passive record of viral ancestry, whereas non-synonymous changes can reshape protein function, alter how the virus interacts with host cell machinery, or change how the immune system recognizes infected cells.

To place their findings in a broader evolutionary context, the researchers conducted phylogenetic analysis based on the combined E6 and E7 sequences. The picture that emerged was one of relative genetic conservatism: the majority of sequences—56 out of 71—showed similarity to lineage A of HPV-39, suggesting that this lineage is the predominant circulating form in central China. Lineage assignment is a useful epidemiological tool because different lineages of a given HPV type have been associated, in some studies, with different levels of oncogenic risk and different geographic distributions. The dominance of a single lineage in the region provides a baseline against which future shifts in the viral population can be measured.

The team also interrogated the sequences for evidence of selective pressure, asking whether any individual amino acid positions in E6 or E7 showed signs of being actively favored by evolution—changes that would suggest the virus is under pressure to adapt, perhaps in response to host immune defenses. The answer was negative: no positively selected sites were detected in either gene. That finding is consistent with a virus in a relatively stable evolutionary state, at least within this population and timeframe, but it does not mean the virus is standing still. Individual mutations can still matter for immune recognition even in the absence of genome-wide signatures of positive selection.

That is precisely where the study’s immunological analysis becomes compelling. The researchers predicted T-cell epitopes—short stretches of viral protein that, when displayed on the surface of infected cells by human leukocyte antigen (HLA) molecules, can be recognized by cytotoxic T lymphocytes, the immune system’s specialized killers. Substitutions within or near these epitopes can change how well they bind to HLA molecules or how they are recognized by T-cell receptors, potentially allowing infected cells to escape immune surveillance. In the E6 protein, the predicted T-cell epitopes were influenced by non-conservative substitutions at eight positions: H5Y, P7S, T19R, Q26H, E46D, A87G, L102S, and L151P. In E7, eleven positions were implicated: L8V, D14H, D14E, H50Q, D57E, R87Q, Q88E, Q88D, L89V, Q91K, and F93C. Non-conservative substitutions—those that replace one amino acid with another of very different chemical character—are particularly noteworthy because they are more likely to alter protein folding, binding interactions, or antigen presentation than conservative swaps between chemically similar residues.

Among the immunological findings, one result stands out. The team identified a predicted candidate T-cell epitope spanning residues 70 to 78 of the E6 protein, with the amino acid sequence KFYAKIREL, restricted by the HLA-C*06:02 molecule. This is the kind of precise, actionable information that underpins the design of therapeutic vaccines and adoptive T-cell therapies, which aim to train or harness a patient’s own immune system to recognize and destroy virus-infected or tumor cells. An epitope’s restriction by a specific HLA allele is critical, because HLA genes are extraordinarily polymorphic—each person carries a different combination of HLA alleles, and an epitope that is well-presented by one HLA molecule may be invisible to another. Identifying epitopes restricted by common HLA alleles in a given population is a prerequisite for developing immunotherapies that can work broadly.

The E6 and E7 proteins themselves deserve a moment of technical explanation, because their biology is central to why this study matters. In the life cycle of high-risk HPV, E6 and E7 are the two principal oncoproteins. E6 recruits a cellular complex that tags the tumor suppressor protein p53 for degradation, effectively silencing one of the cell’s most important safeguards against cancer. E7 binds to the retinoblastoma protein (pRb), releasing transcription factors that push the cell into the DNA synthesis phase of the cell cycle, creating the cellular environment the virus needs to replicate its genome. When HPV infection persists and its DNA integrates into the host genome, the expression of E6 and E7 becomes dysregulated, and their oncogenic activities accumulate. These proteins are also major targets of immune recognition, which is why sequence variation in their genes can have cascading consequences for both cancer biology and immunology.

The regional context of this work gives it particular weight. Central China has been the site of several earlier studies of HPV genetic variability, including analyses of HPV-16 E6 and E7 published in 2023 and HPV-18 E6, E7, and L1 published in 2024, as well as an examination of HPV-39 variability in Southwest China in 2021. But HPV-39 data specific to central China remained thin. By filling that gap, the Jingzhou team contributes a piece to a larger puzzle: understanding how HPV genetic diversity is distributed across populations, and whether regionally specific variants might affect the performance of HPV screening tests, which often rely on probe-based detection of particular sequence regions. Sequence variation in a probe-binding site can, in principle, reduce assay sensitivity, so cataloguing circulating variants is a practical safeguard for diagnostic reliability.

The study was supported by a key research and development plan project of Hubei Province, and it was conducted under the approval of the Ethics Committee of Jingzhou Hospital Affiliated to Yangtze University, with informed consent obtained from all participants and privacy protections in place before sample collection. The work reflects the broader push toward open-access sharing of research, with the article published under a Creative Commons license that allows free reading and distribution with attribution.

Looking ahead, the researchers position their dataset as a foundation for future investigations into HPV-39 evolution and host immune interactions. The six novel non-synonymous mutations they describe may merit functional characterization—laboratory studies that test whether these changes alter E6 or E7 protein activity, transform cell behavior in culture, or affect the binding of viral proteins to host factors. The T-cell epitope predictions, meanwhile, invite immunological validation: laboratory assays could confirm whether the KFYAKIREL epitope is genuinely presented by HLA-C*06:02 and recognized by T cells, and whether the other identified substitutions measurably reduce immune recognition. The authors also caution, implicitly, that the database of HPV-39 sequences remains sparse compared with the resources available for HPV-16 and HPV-18, so every additional regional dataset helps refine the global picture.

For a virus that infects millions and contributes to hundreds of thousands of cervical cancer deaths worldwide each year, HPV-39 has lived in the shadow of its more famous relatives. This study does not claim to overturn any paradigm, but it does something quieter and arguably more durable: it replaces guesswork with sequence data for a region where the virus matters, it documents variations that could influence immune escape, and it hands vaccine developers a concrete candidate epitope to investigate. In molecular epidemiology, that combination of surveillance, mechanism, and forward-looking application is the standard against which useful research is measured—and on that measure, this work earns its place in the growing literature on HPV diversity in China.

The broader message for public health is also worth underscoring. As cervical cancer screening and vaccination programs expand globally, understanding the genetic makeup of circulating HPV types becomes part of ensuring those programs work as intended. Variants that alter diagnostic targets, change immunodominant epitopes, or signal shifts in viral lineage composition could all influence the long-term effectiveness of prevention and treatment strategies. Studies like this one, grounded in careful sequencing of clinical samples and rigorous bioinformatic analysis, provide the granular molecular data that population-level policy ultimately depends on. The authors’ catalog of 33 variants, their lineage assignments, and their epitope predictions will now become part of the reference landscape that other researchers in China and beyond can build upon as the effort to eliminate cervical cancer enters its most demanding phase.