Viral sequences have been detected in human brain tissue corroborating the hypothesis that JCPyV could be involved in the development of human brain tumors (Ahye et al. 2020). In our study, qPCR showed that PXA, a rare brain tumor with histopathological features resembling PML, harbored JCPyV DNA. To define JCPyV as infectious agent associated with brain cancer, JCPyV DNA positivity alone is not sufficiently specific to establish its etiological role. For this reason, in this study the expression of the LTAg and VP1 at the DNA and RNA level was investigated.

In 1998, Boldorini et al. identified JCPyV LTAg and VP1 DNA sequences, but not virus particles in the brain tissue of a 9-year-old boy with PXA (Boldorini et al. 1998). In our case, we detected DNA sequences and transcripts, corresponding to the 5ʹ end but not the 3ʹ end of the LTAg gene and VP1 was undetectable both at DNA and RNA level.

During viral replication, JCPyV displays an orderly gene expression cascade in which LTAg transcript is expressed first followed by the expression of the VP1 gene. Loss of the viral replication capacity is a common feature of virus-associated tumors. In this case, the hampered viral replication could explain the expression of LTAg but not VP1 gene.

Since NCCR and miRNA could represent independent modalities of regulating JCPyV replication at the transcriptional and post-transcriptional levels, in this study, NCCR architecture and miRNA expression were investigated.

We detected a NCCR with archetype architecture and the absence of miR-J1-5p expression. Since JCPyV miRNA-5p has been proposed to act as an important safeguard, reducing LTAg expression during viral persistence, in our study we could speculate that the absence of JCPyV-miRNA expression and the detection of LTAg contribute to a persistence state rather than a viral reactivation.

We failed to detect p53 at the DNA, RNA, and protein level in our tumor specimen. As previously described, the C-terminal region of LTAg can interact with p53 (Zheng et al. 2022) although inactivation of p53 is not absolutely required for polyomaviruses to induce cancer as shown for MCPyV and MCC. In fact, the LTAg expressed in MCPyV-positive MCC lacks the p53 binding domain but retains the Rb domain (DeCaprio 2021), as observed in our case. Therefore, further studies are required to establish whether the genesis of PXA could depend on the transformation capacity of LTAg by Rb sequestration, as demonstrated in the MCC. Additional studies are required (i) to establish whether full-length or C-terminal truncated LTAg is expressed; (ii) to establish whether the truncation is the result of a deletion in the LTAg gene rather than nonsense mutation (as is the case in the LTAG gene of MCPyV-positive MCCs); and (iii) to explain the lack of p53 DNA detection in the tumor.