The two murine retroviral restriction genes, Fv-4 and Akvr-1, are very similar in their effects, distributions, ranges of action, and phenotypes. Akvr-1 has been shown to segregate independently in backcrosses with a variety of retroviral restriction loci, including Fv-1, Fv-2, Ril-1, and Ril-2. An allelism test cross of FRG (Fv-4R) X LCRR (Akvr-1R) hybrids mated to AKR mice failed to produce any viremic offspring. These results suggested that Akvr-1R and Fv-4R are alleles of a single locus, Fv-4, on mouse chromosome 12.

A gene named Akvr-1 segregates as a dominant allele in California wild mice (LC). Unlike Fv-1 and Fv-2 restriction alleles, the Akvr-1 confers resistance to replication of all ecotropic (N-, B-, and NB-tropic) murine leukemia viruses (MuLV-E) and prevents endogenous AKR virus-induced lymphoma/leukemia in F1 hybrids of AKR x LC. We have tested fibroblasts and hematopoietic cells from mice of defined Akvr-1 genotypes for in vitro susceptibility to various MuLV infections. Our results indicated a dominant in vitro resistance of exogenously MuLV-E infected cells carrying Akvr-1R allele although resistance was stronger in the homozygous cells than in the heterozygous cells. Moreover, resistance of cells to virus replication was not abrogated by high multiplicities of infection or by growth stimulation of hematopoietic cultures by various T- or B-cell-responsive mitogenic agents.

Amphotropic murine leukemia viruses (MuLV-A) cause mainly lymphoma in newborn inoculated NIH Swiss mice after a long latent period of 6-12 months. Rarely, however, about 1% of the inoculated mice develop hind limb paralysis and progressive central nervous system disease. The biological properties and RNase T1-resistant oligonucleotide fingerprints of the recovered viruses from tissues of both lymphomatous and paralyzed mice inoculated with MuLV-A were analyzed. These results indicate that serial in vivo passages of MuLV-A in NIH Swiss mice lead to generation of new MuLVs of both amphotropic and ecotropic host ranges. The recovered amphotropic viruses are highly lymphomagenic and are recombinants of MuLV-A-specific oligonucleotides and endogenous mouse sequences. The ecotropic viruses fall into two groups: (1) recombinants of MuLV-A genes and NIH Swiss mouse viral or cellular sequences and (2) new ecotropic viruses with oligonucleotide fingerprints not related to any of the known MuLVs. The naturally occurring ecotropic MuLVs of the wild mice produce both lymphoma and paralysis in NIH Swiss mice. The viruses recovered from in vivo passages are mainly of ecotropic host range although dual-tropic virus activity is occasionally seen in the spleens but not in the brains or spinal cords of the lymphomatous or paralyzed mice. Oligonucleotide fingerprinting of the recovered MuLV-Es from paralyzed mice are identical to the input MuLV-Es, indicating that the parental MuLV-E alone, without recombination, is responsible for the paralytic disease.

The feline oncornavirus-associated cell membrane antigen (FOCMA) was defined as a tumor antigen common to cat lymphomas and fibrosarcomas induced by feline leukemia virus (FeLV) and feline sarcoma virus (FeSV), respectively. The antigen was recognized by sera from cats thought to be resistant to leukemogenesis. We report here that a common denominator in the activity of naturally occurring viremic cat antisera to FOCMA is, in fact, their reactivity to FeLV C antigenic determinants. The cat antisera, monoclonal antibodies to FOCMA, and monoclonal antibodies to FeLV C, all reacted in immunofiuorescence assays with FeLV C-infected cells and immunoprecipitated a molecule electrophoretically indistinguishable from envelope glycoprotein of FeLV. Viremic cat antisera to FOCMA bound to budding virus particles of FeLV C-infected cells, even though some of them could not be absorbed by mature virion proteins. Thus, the unusual feature of cat antibodies to FOCMA is their binding to nascent but not to mature virus particles. FOCMA-positive cat lymphomas expressed antigenic determinants of FeLV-C gp70, with or without productive infection. FeLV-negative tumors not expressing FeLV C gp70 were also FOCMA negative. Furthermore, most of the viremic cat sera and the monoclonal antibodies to FOCMA did not react with FeSV-transformed nonproducer cells. The absence of FOCMA from these cells and from FeLV-negative lymphoid tumors and its presence in FeLV-C infected fibroblasts indicated that this antigen is virus encoded and not a cellular tumor-specific antigen.

Gardner-Rasheed feline sarcoma virus (GR-FeSV) is an acute transforming retrovirus which encodes a gag-onc polyprotein possessing an associated tyrosine kinase activity. The integrated form of this virus, isolated in the Charon 21A strain of bacteriophage lambda, demonstrated an ability to transform NIH/3T3 cells at high efficiency upon transfection. Foci induced by GR-FeSV DNA contained rescuable sarcoma virus and expressed GR-P70, the major GR-FeSV translational product. The localization of long-terminal repeats within the DNA clone made it possible to establish the length of the GR-FeSV provirus as 4.6 kilobase pairs. The analysis of heteroduplexes formed between lambda feline leukemia virus (FeLV) and lambda GR-FeSV DNAs revealed the presence of a 1,700-base-pair FeLV unrelated segment, designated v-fgr, within the GR-FeSV genome. The size of this region was sufficient to encode a protein of approximately 68,000 daltons and was localized immediately downstream of the FeLV gag gene coding sequences present in GR-FeSV. Thus, it is likely that this 1.7-kilobase-pair stretch encodes the onc moiety of GR-P70. Utilizing probes representing v-fgr, we detected homologous sequences in the DNAs of diverse vertebrate species, implying that v-fgr originated from a well-conserved cellular gene. The number of cellular DNA fragments hybridized by v-fgr-derived probes indicated either that proto-fgr is distributed over a very large region of cellular DNA or represents a family of related genes. By molecular hybridization, v-fgr was not directly related to the onc genes of other known retroviruses having associated tyrosine kinase activity.

We studied the RNA genomes of several wild mouse type C retroviruses by using RNase T1-oligonucleotide fingerprinting. The amphotropic and ecotropic viruses of field strain 1504 produced very similar oligonucleotide fingerprints, but each also had several unique oligonucleotides. All of these unique oligonucleotides were located in the env gene region and were probably responsible for the host range differences between these viruses, as well as the lymphomagenic and paralytogenic properties of the viruses. We obtained similar results with the amphotropic and ecotropic viruses of another field strain (4070), which was isolated from a mouse from a different trapping area. The amphotropic viruses of several field strains (strains 1504, 4070, and 1313) were more closely related than the ecotropic viruses of different strains (strains 1504, 4070, and 4996). These findings suggested that the genetic sequences of the amphotropic viruses are more conserved than those of ecotropic viruses isolated from the same wild mice.

A highly oncogenic retrovirus (strain 10A/1) recovered from NIH Swiss mice inoculated with wild mouse amphotropic virus (strain 1504A) was studied by T1-oligonucleotide fingerprinting of the RNA genome. The virus was found to be an env gene recombinant between the parental 1504A and endogenous AT124 or related xenotropic virogenes of NIH Swiss mice.

We have isolated a highly lymphomagenic wild mouse virus by passage of a weakly oncogenic amphotropic murine leukaemia virus (MuLV‐A) in NIH Swiss mice. This virus is similar in host range, interference and neutralization properties to that of the inoculated amphotropic virus but is distinct from it biochemically and causes lymphomas in 90‐100% of mice within 1‐2 months. Our results indicate that this highly oncogenic virus is a recombinant of wild mouse MuLV‐A and sequences related to env gene region of the endogenous xenotropic virus of NIH Swiss mice.

Natural cell‐mediated cytotoxicity against YAC‐1 targets was measured in splenocytes from leukemiaprone wild mice trapped near Lake Casitas (LC) in southern California. Cytotoxicity was mediated by cells that were non‐adherent to nylon wool, non‐phagocytic and resistant to thy‐1.2 antiserum plus complement. Natural MuLV viremia in LC mice did not impair splenic cytotoxicity against YAC‐1 target cells. Cells infected with amphotropic and ecotropic MuLV of wild mouse origin were not appreciably lysed by LC splenic effectors. Although variable levels of cytotoxicity were detected against YAC‐1 by normal LC spleen cells, consistently low levels of cytotoxicity against allogenic LC lymphoma, sarcoma and carcinoma targets were found using the same splenocytes. These results indicate that LC mice possess splenocytes with the characteristics of natural killer (NK) cells as defined in inbred mice. The resistance of LC‐derived targets to lysis by LC NK cells suggests that NK cells may not be involved in natural tumor immunosurveillance or that the development of spontaneous tumors may involve escape from NK‐mediated effector mechanisms.

The presence and location of DNA sequences related to the U3 and U5 portions of the infectious exogenous feline leukemia virus (FeLV) long terminal repeat (LTR) in various cat DNAs have been determined by hybridization experiments. In uninfected cat DNAs, the U5 LTR segment from the Gardner-Arnstein strain B virus is present at approximately 150 copies per cell. This level is approximately 10-fold greater than that of endogenous internal FeLV sequences. The U5 sequences differ in copy number and, to some extent, in location from one animal to another. For any one animal, the sequence organization of the U5 segments is the same among different tissues, showing that the pattern is inherited through the germ line. Most importantly, the viral U3 LTR probe hybridizes only very weakly with uninfected cat DNAs. Both the U3 and the U5 regions of the LTR from the Gardner-Arnstein strain of virus cross-hybridize with DNA derived from four other infectious FeLVs representing A, B, and C subtypes. Thus, the C3 region may be used as a probe for studying the number and location of exogenously acquired FeLV proviruses in infected cat tissues. In some cases exogenously acquired proviruses are present in unique sites in the genome of virus-positive cat lymphosarcomas, indicating a monoclonal origin for the tumor. In other tumors, the proviral sequences are randomly distributed over many sites. Lymphosarcomas of virus-negative cats have no exogenous U3 sequences despite epidemiological evidence of an association of virus-negative leukemia with exposure to FeLV.

Growth characteristics and susceptibility to viral transformation were compared in cultured skin fibroblasts from patients with Gardner's syndrome (GS), those with familial polyposis coli (FP), asymptomatic family members, and unrelated controls. Compared to cells from unrelated controls, cells from 4 of 5 GS patients were transformed by Kirsten murine sarcoma virus at 100- to 1,000-fold increased efficiency. The transformation efficiencies of fibroblasts from 2 of 3 FP patients were 10- to 100-fold greater than those of unrelated controls. However, because the fibroblasts from some of the young asymptomatic GS and FP family members also transformed at higher efficiency than did cells from unrelated controls, long-term observation of these families is required. This would determine whether or not these members develop clinical manifestations of GS or FP and thus establish the specificitiy of this assay for detection of individuals bearing the mutant gene. Compared to fibroblasts from unrelated controls, GS and FP fibroblasts showed a twofold to threefold increased saturation density and plating efficiency, but this difference was not noted with fibroblasts from most of the asymptomatic family members.

A strain of feline leukemia virus (FeLV), subgroup A, was isolated in early subpassage of a testicular fibroblast culture obtained from a captive Asian leopard cat. Neither FeLV nor RD-114 virus was recovered from cultured tissues of 15 other animals, representing eight species of wild Felidae.

Growth characteristics and susceptibility to viral transformation were compared in cultured skin fibroblasts from patients with Gardner's syndrome (GS), those with familial polyposis coli (FP), asymptomatic family members, and unrelated controls. Compared to cells from unrelated controls, cells from 4 of 5 GS patients were transformed by Kirsten murine sarcoma virus at 100- to 1,000-fold increased efficiency. The transformation efficiencies of fibroblasts from 2 of 3 FP patients were 10- to 100-fold greater than those of unrelated controls. However, because the fibroblasts from some of the young asymptomatic GS and FP family members also transformed at higher efficiency than did cells from unrelated controls, long-term observation of these families is required. This would determine whether or not these members develop clinical manifestations of GS or FP and thus establish the specificitiy of this assay for detection of individuals bearing the mutant gene. Compared to fibroblasts from unrelated controls, GS and FP fibroblasts showed a twofold to threefold increased saturation density and plating efficiency, but this difference was not noted with fibroblasts from most of the asymptomatic family members.

We describe a restriction gene (Akvr-1, for AKR virus restriction) that is polymorphic for two alleles, Akvr-1R (restrictive) and Akvr-1r (susceptible), in a feral population of mice (Mus) musculus domesticus) at a squab farm near Lake Casitas (LC) in southern California. Akvr-1k is a dominant allele that exhibits 100% penetrance in prevention of viremia of AKR endogenous retrovirus and of virus-mediated lymphoma in LC (Akvr-1RR) X AKR F1 hybrids. The restriction phenotype segregates as a single Mendelian locus in backcrosses to AKR mice. Akvr-1R likewise is effective in restriction of NB-tropic Moloney murine leukemia virus-induced viremia and NB-tropic Friend virus-induced splenomegaly but fails to restrict expression or pathogenesis of LC-derived amphotropic retrovirus. Pleiotropic restriction of AKR, Friend, and Moloney ecotropic viruses, but not of amphotropic virus, suggests that the viral targets of Akvr-1 in the three ecotropic viruses are similar to each other and distinct from the target in the LC-amphotropic virus. The relationship of Akvr-1 to previously reported murine restriction loci Fv-1, Fv-2, and Fv-4 is discussed.