http://www.retroconference.org/2 011/Abstracts/40987.htm Session 43-Themed Discussion TD: XMRV: New Findings and Controversies Wednesday, 1-2 pm; Room 302-304 Paper # 217 Presence of XMRV Sequences in B Cells Are Restricted by APOBEC Jorge Carrillo1, J Blanco1, E Garcia1, J Arreal2, B Clotet1, and C Cabrera1 1Fndn irsiCaixa, Barcelona, Spain and 2Hosp Univ Germans Trias i Pujol, Barcelona, Spain Background: A link between xenotropic murine leukemia virus-related virus (XMRV) infection and different human diseases, such as chronic fatigue syndrome (CFS) and prostate cancer, has been recently established. Given that this retrovirus can infect different tissues and cell types both in vivo and in vitro, including cells from the immune system, the identification of the cellular compartment(s) where XMRV can establish a reservoir may be useful to understand the pathology associated with this virus. Methods: In order to determine the presence of XMRV in B lymphocytes, we have screened EBV-transformed B-cell lines available in our laboratory. The origin of these cell lines include CFS patients (n = 11; fulfilling both Fukuda and Canadian criteria), HIV+ individuals (n = 4), prostate cancer patients (n = 1), and healthy donors (n = 5). DNA was extracted from cellular dry pellets and several XMRV genes were amplified by either real-time PCR (pol) or nested PCR (gag and env). Results: We detected 7 positive samples from 14 individuals tested by RT-PCR (4 CFS, 2 donors, and 1 HIV+ individual). env amplification identified 4 positive samples out of 21 individuals tested (3 CFS-affected individuals and 1 healthy donor), whereas gag amplification showed only 3 positive samples (1 CFS-affected individual, 1 healthy donor, and one HIV+ patient). To confirm the presence of XMRV we performed sequence analyses of gag and env amplicons. The 3 gag sequences available showed a 100% homology with XMRV gag published sequences, including the XMRV characteristic 24nt deletion which is not found in any known exogenous murine leukemia virus. Furthermore, env sequences were also homologous to previously described XMRV sequences, showing none or low variability. Interestingly, most of the observed changes corresponded to multiple G to A mutations that were accumulated in 1 positive sample, resulting in a truncated env protein and suggesting that APOBEC-related restrictions operate in vivo during XMRV infection. Conclusions: Despite the discrepancies observed in the different PCR approaches, our data provide evidence that EBV-transformed B-cell lines harbor XMRV-specific sequences, although the establishment of this infection could be modulated by the innate restriction factor APOBEC 3G . Our data suggest that, in vivo, B cells may represent a reservoir for XMRV contributing to its potential pathogenesis.