Because of the high homology that exists between the DNA of SV40 and the DNA of the JC or BK viruses, the identity of the band obtained by PCR and visualized by ethidium bromide staining was confirmed by both Southern blot hybridization and DNA sequencing. The results of these analyses confirmed that authentic SV40 was amplified from these tumors. All of the positive samples were further analyzed with the primers R1/R2 for the SV40 regulatory region (Table 1). All of the lymphomas in the nonimmunocompromised group tested negative. In the immunocompromised group, one specimen from posttransplant lymphoproliferative disorders and one AIDS lymphoma also tested positive for the SV40 regulatory region. The other specimens from immunocompromised individuals that had tested positive with the primers SV5/SV6 tested negative with primers for the regulatory region (Table 1, and Fig 2, bottom, B). Primers for the RB-pocket binding domain are more sensitive than primers for other regions of the SV40 genome. Therefore, the positivity for the regulatory region in these two specimens suggested that a larger percentage of the cells contained SV40. It should be noted, however, that one additional specimen from an immunocompromised individual (sample 7, Fig 2, bottom, B) tested positive for the regulatory region and negative with primers for the RB-pocket of Tag. This unusual result could be related to deletions or mutations that occasionally occur in the Tag DNA sequence in some human tumors.
In parallel, we tested 12 mesothelioma samples for SV40. Eight of 12 mesotheliomas tested positive with the primers SV5/SV6 for the RB-pocket binding domain of Tag (Fig. 3, top, A). The same samples tested positive for the regulatory region and the origin of replication of the SV40 virus (primers R1 and R2) (Fig. 3, bottom, B). Click Here
Figure 3. Top, A: Southern blot hybridization of the PCR products obtained from mesothelioma DNA samples using the SV5/SV6 set of primers. Bottom, B: Southern blot hybridization of the PCR products obtained from mesothelioma DNA samples using the R1/R2 set of primers. Samples 1, 3-6, 8, 11, and 12 are positive with both sets of primers. ( —) = H2O, negative control; ( + ) = SV40 DNA, positive control.