Immune Genes Shape How a Transplant Menace Is Seen in Peru

Human cytomegalovirus is one of the most successful pathogens ever to colonize our species, infecting the majority of adults worldwide and persisting for life inside cells of the immune system. For most healthy carriers it is a silent passenger, but for kidney transplant recipients it can become a dangerous opportunist. Immunosuppressive drugs that keep the body from rejecting a donor organ simultaneously blunt the antiviral defenses that normally hold cytomegalovirus in check, and reactivation of the virus after transplantation is associated with graft injury, systemic illness, and even death. A new study from Peru now adds a crucial piece to the puzzle of why some patients mount effective responses to the virus while others do not, pointing to the inherited diversity of human leukocyte antigen genes as a decisive factor in how the immune system actually sees the pathogen.

The research, published in PLOS One by a team led by Mirella Dara Moreno Rosado, focused on a population that has long been underrepresented in immunogenetic studies: South Americans. Although the seroprevalence of human cytomegalovirus in Peru exceeds ninety percent, the influence of local human leukocyte antigen diversity on immune recognition of the virus had never been systematically explored in the region. This gap matters because the human leukocyte antigen molecules, which display fragments of viral proteins on the surface of infected cells for inspection by T lymphocytes, vary enormously between human populations. Alleles that are common in Europe or East Asia may be rare in the Andes, and each variant presents a different repertoire of viral peptide fragments.

To map this landscape, the researchers performed high-resolution genotyping of six human leukocyte antigen loci, spanning the classical class I genes A, B, and C and the class II genes DRB1, DQA1, and DQB1, in 562 kidney transplant candidates and their related donors. This cohort size is substantial for a single-country immunogenetic survey and reflects the practical clinical context in which cytomegalovirus matters most. The team identified sixteen common class I and ten common class II allele groups, defined as those occurring at a frequency of at least five percent in the population. Because full four-digit resolution data were not available for every group, the researchers assigned four-digit proxies based on local prevalence, a pragmatic strategy that allowed downstream prediction of peptide binding with alleles that best represent the Peruvian repertoire.

A striking finding emerged when the Peruvian alleles were compared with databases covering the rest of South America: ninety-two percent of the four-digit proxies identified in Peru are already widely distributed across the continent, suggesting a broadly shared immunogenetic foundation among South American populations. One variant, however, stood out. The class I allele C*15:12 appeared to be a potentially endemic Peruvian variant, rarely reported elsewhere. Alleles of this kind are of particular interest to transplant medicine because donor-recipient matching at the human leukocyte antigen loci, and the viral peptides those loci present, can influence both rejection risk and antiviral immunity. A locally enriched allele could therefore shape regional patterns of cytomegalovirus disease in ways invisible to studies conducted on other continents.

With the allele inventory in hand, the team turned to the virus itself. Rather than surveying the entire viral proteome, they concentrated on three antigens that dominate the immune response to cytomegalovirus: the 65-kilodalton phosphoprotein known as pp65, the immediate early protein 1, and the envelope glycoprotein B. The pp65 protein is the principal target of cytotoxic T lymphocytes during natural infection and forms the backbone of current cellular immunotherapy strategies. Immediate early protein 1 drives viral replication programs and is a second major T-cell target, while glycoprotein B sits on the viral surface, elicits antibody responses, and is the antigen used in the licensed vaccine candidate that has advanced furthest in clinical testing. Linear T-cell epitopes within these three proteins were predicted using high-performance algorithms that estimate how strongly each human leukocyte antigen variant binds candidate peptide fragments.

The computational screen produced a rich catalog: 954 candidate class I epitopes across the three immunodominant antigens for the common Peruvian alleles. Among these, 169 corresponded to epitopes already documented in the Immune Epitope Database, meaning they had been experimentally described in previous studies and carry established credentials as targets of human T-cell recognition. The authors highlight this subset as having particular potential for immunotherapy, because previously reported epitopes that also bind strongly to locally common alleles could be translated more rapidly into monitoring panels or therapeutic peptide pools for South American patients than entirely novel predictions with no experimental track record.

To go beyond simple lists of predicted binders, the researchers introduced a quantitative metric they call the Predicted Strong Binder Density, or PSBD. This measure captures, for each human leukocyte antigen variant, the density of antigenic peptides that are predicted to bind with high affinity, effectively summarizing the antigen-presentation capacity of an allele across a viral antigen. The PSBD analysis revealed distinct predicted antigen-presentation profiles across the common variants identified in the cohort. In practical terms, two patients carrying different common alleles would be expected to display substantially different fragments of pp65, immediate early protein 1, or glycoprotein B on their infected cells, and therefore to direct their T-cell responses against different parts of the virus.

This kind of allelic variation has real clinical consequences. Immune monitoring of transplant recipients increasingly relies on measuring T-cell reactivity to defined cytomegalovirus peptide pools, and most commercially available assays were calibrated on epitopes recognized through alleles common in European and North American populations. If a Peruvian patient’s dominant class I molecules present a different set of viral fragments, standard monitoring panels may underestimate that patient’s antiviral immunity or miss responses entirely. Conversely, therapeutic T-cell products generated from donors with mismatched allele distributions may target peptides that the recipient’s cells cannot present. The Peruvian epitope catalog offers a foundation for regionally tailored versions of both approaches.

The study also fills a more fundamental gap in global immunology. Human leukocyte antigen diversity has been shaped over millennia by pathogen pressure, migration, and population admixture, and indigenous and mixed South American populations carry combinations of alleles that are uncommon in the reference datasets that dominate the immunoinformatics literature. Documenting which alleles are common in Peru, and which viral peptides they can present, corrects a systematic blind spot. The finding that most Peruvian proxies are shared across South America is encouraging, because it suggests that a single regional epitope framework could serve multiple countries rather than requiring nation-by-nation catalogs.

The authors are careful to frame their results as predictions that now require experimental validation. Binding algorithms, however sophisticated, do not guarantee that a predicted epitope will be naturally processed from viral proteins, transported to the cell surface, or recognized by T cells, and immunogenicity can only be confirmed in the laboratory and the clinic. They call for experimental testing of the high-confidence candidates and for association studies linking specific human leukocyte antigen alleles to cytomegalovirus outcomes after transplantation. If those steps succeed, the predicted antigen-presentation profiles defined here could guide immune monitoring and future immunotherapeutic applications across South American populations, turning a long-standing data gap into a foundation for precision medicine in one of the regions where the virus imposes its heaviest burden on transplant patients.

Subject of Research: HLA-driven variability in T-cell recognition of human cytomegalovirus epitopes in a Peruvian kidney transplant cohort

Article Title: HLA-driven variability in human cytomegalovirus immune recognition: Epitope predictions from a kidney transplant Cohort

Article References: Moreno Rosado, M. D., Chavez-Arias, T., Marín-Sánchez, O., Juarez Zevallos, R. J., Murillo Carrasco, A. G., Ortiz Rojas, C. A., Ita-Balta, Y., & Chacón Villanueva, R. D. (2026). HLA-driven variability in human cytomegalovirus immune recognition: Epitope predictions from a kidney transplant Cohort. PLOS One, 21(10), e0360632. https://doi.org/10.1371/journal.pone.0360632

Image Credits: AI Generated

DOI: 10.1371/journal.pone.0360632

Keywords: human cytomegalovirus, HLA, epitope prediction, kidney transplantation, pp65, IE1, glycoprotein B, MHC peptide binding, Peru, immunogenetics, immune monitoring, immunotherapy