Although several major immunologic hurdles need to be overcome, the pig is currently considered the most likely source animal of cells, tissues and organs for transplantation into humans. Concerns have been raised with regard to the potential for the transfer of infectious agents with the transplanted organ to the human recipient. This risk is perceived to be increased as it is likely that the patient will be iatrogenically immunocompromised and the organ-source pig may be genetically engineered in such a way to render its organs particularly susceptible to infection with human viruses. Furthermore, the risk may not be restricted to the recipient, but may have consequences for the health of others in the community. The identification of porcine endogenous retroviruses and of hitherto unknown viruses have given rise to the most concern. We document here the agents we believe should be excluded from the organ-source pigs. We discuss the likelihood of achieving this aim and outline the potential means by which it may best be achieved.

Neutralizing and nonneutralizing monoclonal antibodies to the peplomer glycoprotein and nucleocapsid protein of a mouse hepatitis virus (MHV), MHV-NuU, protected mice against lethal MHV-2 challenge. Histopathologically, livers of mice receiving protective antibodies showed some focal necrotic lesions with remarkable cellular infitration instead of fulminant hepatitis caused by MHV-2. Mouse hepatitis virus (MHV) is a member of the coronavirus group producing both acute and chronic diseases in various species of animals (15, 17, 25). Most MHV strains have been shown to have the nucleocapsid protein (NP) and the minor (El) and major (E2) envelope glycoproteins (18, 19). El is probably of the viral matrix, whereas E2 forms the peplomers that have important roles in attachment to host cells (18, 19). We described previously the production of monoclonal antibodies (MAbs) to low-virulence MHV-NuU, an isolate from a wasted nude mouse (7), and their specificity for viral polypeptides (10). Those MAbs were shown to be crossreactive in vitro with other strains of MHV including the highly hepatitogenic strain MHV-2 (6, 11, 12). This paper describes protective effects of MAbs against E2 as well as NP of MHV-NuU in highly virulent MHV-2 infection in mice.

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The matrix (M) genes of Yamagata-1 strain subacute sclerosing panencephalitis virus passaged in African green monkey kidney cells and human neuroblastoma cells displayed strikingly nonrandom sequence divergence. The genes of both substrains shared a large number of uridine (U) to cytidine (C) transitions, but the latter contained numerous additional U to C changes in a localized region. Over 90% of the additional mutations were identical to the hypermutated nucleotides in the M gene found in a measles inclusion body encephalitis case. The nonrandom nature, the apparent host dependency, and the abrupt boundaries of these mutations suggest that these mutations might be caused by an extrinsic biased mutational activity rather than intrinsic polymerase errors. This mutational activity might account for the extraordinarily high C to U ratios in the non-protein-coding regions of both the M and fusion genes of wild-type measles virus.

SUMMARYTwenty-four monoclonal antibodies (MAbs) against rinderpest virus (RPV) were established and characterized by several serological tests. Of the 24 MAbs, 10 recognized the nucleoprotein (NP), six the phosphoprotein (P), four the haemagglutinin (H), and two the fusion (F) protein as determined by radioimmunoprecipitation assay. The specificities of the remaining two MAbs could not be determined. From a competitive binding assay using MAbs against each structural protein, at least five, four and two separate antigenic sites were identified on the NP, P and H proteins, respectively. MAbs against the H protein neutralized the infectivity of the virus, but those against the F protein were only neutralizing in the presence of guinea-pig complement. The reactivities of each of the MAbs for other strains of morbillivirus were tested using an indirect immunofluorescent antibody assay. The MAbs against four out of five antigenic sites on the NP showed cross-reactivity amongst all the strains of morbillivirus tested whereas the fifth antibody reacted only with RPV. Of the antibodies specific for the P protein, the antibody against one site was cross-reactive with all the strains of RPV, measles virus (MV) and canine distemper virus (CDV), the antibody against another site was reactive with RPV and MV but not with CDV, and the antibodies against the other two sites were specific for RPV.