Immunological evidence of an early seroconversion to oncogenic Merkel cell polyomavirus in healthy children and young adults

Understanding Merkel Cell Carcinoma: Pathogenic Signaling, Extracellular Matrix Dynamics, and Novel Treatment Approaches

Merkel cell carcinoma (MCC) is a rare but aggressive neuroendocrine skin cancer, driven by either Merkel cell polyomavirus (MCPyV) integration or ultraviolet (UV)-induced mutations. In MCPyV-positive tumors, viral T antigens inactivate tumor suppressors pRb and p53, while virus-negative MCCs harbor UV-induced mutations that activate similar oncogenic pathways. Key signaling cascades, including PI3K/AKT/mTOR and MAPK, support tumor proliferation, survival, and resistance to apoptosis. Histologically, MCC consists of small round blue cells with neuroendocrine features, high mitotic rate, and necrosis. The tumor microenvironment (TME) plays a central role in disease progression and immune escape. It comprises a mix of tumor-associated macrophages, regulatory and cytotoxic T cells, and elevated expression of immune checkpoint molecules such as PD-L1, contributing to an immunosuppressive niche. The extracellular matrix (ECM) within the TME is rich in proteoglycans, collagens, and matrix metalloproteinases (MMPs), facilitating tumor cell adhesion, invasion, and interaction with stromal and immune cells. ECM remodeling and integrin-mediated signaling further promote immune evasion and therapy resistance. Although immune checkpoint inhibitors targeting PD-1/PD-L1 have shown promise in treating MCC, resistance remains a major hurdle. Therapeutic strategies that concurrently target the TME-through inhibition of ECM components, MMPs, or integrin signaling-may enhance immune responses and improve clinical outcomes.

Serum antibodies against mimotopes of Merkel cell polyomavirus oncoproteins detected by a novel immunoassay in healthy individuals and Merkel cell carcinoma patients

Merkel cell polyomavirus (MCPyV) is the foremost causative factor of Merkel cell carcinoma (MCC), a rare yet highly aggressive skin cancer. Although the evaluation of circulating IgG antibodies against Merkel cell polyomavirus (MCPyV) LT/sT oncoproteins is clinically useful for MCC diagnosis/prognosis, a limited number of assays for identifying such antibodies have been developed. Herein, a novel indirect immunoassay with synthetic epitopes/mimotopes of MCPyV oncoproteins was computationally designed and experimentally validated on control sera and sera from healthy individuals and MCC patients. Upon computational design of five synthetic peptides, the performance of the immunoassay in detecting anti-oncoprotein IgGs in MCPyV-positive and -negative control sera was evaluated. The immunoassay was afterwards extended on sera from healthy individuals, and, for longitudinal analysis, MCC patients. Performance properties such as sensitivity and specificity and positive/negative predictive values were adequate. Receiver-operating characteristic (ROC) curves indicated that the areas under the curves (AUCs) were within the low/moderately accurate ranges. Immunoassay was repeatable, reproducible and accurate. As expected, the serum anti-oncoprotein IgG prevalence in healthy individuals was low (2%-5%). Anti-oncoprotein IgGs slightly increased when MCC patients experienced partial tumour remission and/or stable disease, compared to baseline. Our data indicate that the newly developed immunoassay is reliable for detecting circulating anti-oncoprotein IgGs both in healthy individuals and MCC patients.

Prevalence of IgG antibodies against Malawi polyomavirus in patients with autoimmune diseases and lymphoproliferative disorders subjected to bone marrow transplantation

Introduction

Human polyomaviruses (HPyVs) cause persistent/latent infections in a large fraction of the population. HPyV infections may cause severe diseases in immunocompromised patients. Malawi polyomavirus (MWPyV) is the 10th discovered human polyomavirus (HPyV 10). MWPyV was found in stool samples of healthy children. So far, the few investigations carried out on HPyV 10 did not find an association with human disease.

Methods

In this study, to verify the putative association between MWPyV and human diseases, MWPyV seroprevalence was investigated in patients affected by i) lymphoproliferative disorders (LPDs) and ii) immune system disorders, i.e., autoimmune diseases (ADs), and in iii) healthy subjects. An indirect ELISA, employing virus-like particles (VLPs) to detect serum IgG antibodies against MWPyV/HPyV 10, was carried out. The study also revealed the prevalence of another polyomavirus, Merkel cell polyomavirus (MCPyV).

Results

Sera from patients with distinct autoimmune diseases (n = 44; mean age 20 years) had a prevalence of MWPyV antibodies of 68%, while in patients with lymphoproliferative disorders (n = 15; mean age 14 years), subjected to bone marrow transplantation, the prevalence was 47%. In healthy subjects (n = 66; mean age 13 years), the prevalence of MWPyV antibodies was 67%. Our immunological investigation indicates that MWPyV/HPyV 10 seroconversion occurs early in life and MWPyV/HPyV 10 appears to be another polyomavirus ubiquitous in the human population. A significantly lower MWPyV antibody reactivity together with a lower immunological profile was detected in the sera of LPD patients compared with HS2 (*p < 0.05) (Fisher's exact test). LPD and AD patients have a similar MCPyV seroprevalence compared with healthy subjects.

Discussion

MWPyV seroprevalence indicates that this HPyV is not associated with lymphoproliferative and autoimmune diseases. However, the ability to produce high levels of antibodies against MWPyV appears to be impaired in patients with lymphoproliferative disorders. Immunological investigations indicate that MWPyV seroconversion occurs early in life. MCPyV appears to be a ubiquitous polyomavirus, like other HPyVs, in the human population.