Lack of Transmission of Mouse Minute Virus (MMV) from In Vitro-Produced Embryos to Recipients and Pups Due to the Presence of Cumulus Cells During the In Vitro Fertilization Process

Abstract

The risk of transmission of mouse minute virus (MMV) to recipients of murine embryos arising from in vitro fertilization (IVF) of cumulus-enclosed oocytes (CEOs) or without cumulus cells (CDOs) in the presence of MMV-exposed (10(4) TCID(50) [mean tissue culture infective dose]/ml MMVp [prototype strain of MMV]) spermatozoa was evaluated. Also, the time after embryo transfer to detection of MMV antibody and the presence of MMV DNA in the mesenteric lymph nodes of recipients and pups were investigated. All mice were MMV free, but two seropositive recipients and four seropositive pups were found in the group with CDOs. With regard to the CEOs, two of 11 holding drops and five of 11 groups of embryos were MMV positive using PCR, while neither holding drops nor embryos carried infectious MMVp, as evidenced by the in vitro infectivity assay. From IVF with CDOs, five of 14 holding drops and four of nine groups of embryos were MMV positive, while one of 14 holding drops and no embryos carried infectious MMVp. When 10(5) cumulus cells were analyzed 5 h after exposure to 10(4) TCID(50)/ml MMVp, cells had an average titer of 10(4) TCID(50)/ml MMVp. The present data show that, in contrast to CDOs, 2-cell embryos from CEOs did not transmit infectious MMVp to the holding drops and to recipients. This observation is due to the presence of cumulus cells during the IVF process that reduce entry of MMV into the zona pellucida and absorb some of the virus. These data further confirm the efficacy of the IVF procedure in producing embryos that are free of infectious virus, leading to virus-free seronegative recipients and rederived pups.