Plasma samples from ten patients with prostate cancer do not contain infectious XMRV or related retroviruses and can neutralize XMRV only partially if at all.

*Patient identifiers shown in bold indicate patients who had previously tested positive for XMRV. See Discussion for details.†Nucleotides at position 1385 of the RNase L coding regions of both patient alleles are shown. A G1385A transition at position 1385 results in a glutamine instead of arginine at amino acid position 462 (R462Q) of RNase L, which has been associated with higher XMRV infection rates in homozygous R462Q patients in some studies [1].‡The virus neutralization assay was performed by incubating XMRV-pseudotype LAPSN vector (harvested from human cells infected with XMRV and the LAPSN vector) with plasma samples at the indicated dilutions, or with phosphate-buffered saline as a no plasma control, for 30 min at room temperature. The remaining LAPSN virus was measured by infection of HTX human fibrosarcoma cells and staining for foci of AP+ cells two days later. Plasma heat inactivation was performed at 56°C for 30 min. All dilutions were performed using phosphate-buffered saline.