[Adult T-cell leukemia virus--introduction--]

Attempts were made to find a putative virus causally related to ATL. A retrovirus was demonstrated in a T-cell line originating from leukemic cells of a patient with adult T-cell leukemia (ATL) in and subsequent virological and serological studies suggested that the virus be etiologically related to ATL. This retrovirus was named adult T-cell leukemia virus (ATLV). This article reports the general properties of ATLV and the possible etiological relation of ATLV to ATL.

An association of carcinogenesis and decrease of cellular NAD concentration

It is postulated that a decrease in nicotinamide adenine dinucleotide (NAD) concentration has a primary association with carcinogenesis. The following observations are presented as evidence: (1) NAD and adenosine triphosphate (ATP) concentrations are lower in cancer cells; (2) chemical carcinogens and radiation can cause a lowering of NAD concentration in precancerous cells: (3) biosynthesis of NAD in Ehrlich ascites tumor cells is altered; and (4) NAD is involved in regulating deoxyribonucleic acid (DNA) synthesis. The lowering of NAD concentration would lead to the expression of oncogene and/or virogene according to the protovirus hypothesis, and the cellular characteristics of cancer cells can also be explained through the lowering of cellular NAD concentration. Experimental approaches are also proposed.

An investigation into the susceptibility of cattle to bovine leukosis virus following inoculation by various routes

The effect of different routes of inoculation on the incubation period, as indicated by the detection of antibody and by the detection of bovine leukosis virus (BLV) in lymphocytes, were compared. None of the 12-month-old steers exposed to BLV by the oral route developed BLV infection. Intratracheal, subcutaneous and intradermal inoculations were found to be particularly effective in establishing BLV infection, which was detected three to four weeks after inoculation. In the majority of animals, serum antibody and virus were detected at the same time. One out of four in-oestrus heifers inoculated via the uterus with mixtures of BLV infected lymphocytes and semen became infected. It appears that there is an inhibitory factor in fresh semen that prevents BLV infection from becoming established. Viral antigen was detected earlier in BLV infected lymphocytes using the cocultivation method than by electron microscopy to demonstrate BLV particles in mitogen stimulated lymphocytes.

Biological characteristics of type C viruses isolated from different Friend erythroleukaemic cells

We have examined the expression of type C RNA viruses in different Friend erythroleukaemic cell types, distinguished on the basis of increasingly malignant characteristics, which arise during the ageing of mice inoculated with the polycythaemic Friend virus complex. Most early appearing Friend cells (type I) expressed ecotropic virus, but cells of later malignant types showed decreased and variable expression. In general, the more malignant cells released less ecotropic virus. Xenotropic virus was detected in low numbers from type I, II, and IV cells. Two viruses were cloned from type II tumour cells: a xenotropic virus (II clone 1) and an N-tropic ecotropic virus (II clone 2). No pathogenic activity was found when II clone 1 was inoculated into newborn and adult DBA/2J and NIH/Swiss mice observed for up to 20 months, whereas II clone 2 caused a rapid anaemic erythroleukaemia in both N- and B-type newborn mouse strains. It caused a similar form of leukaemia in susceptible N-type adult mice, but at a lower frequency and with a longer latency (usually greater than 5 months). This finding demonstrated a lack of NB restriction in newborn mice. The virus was much less active in DBA/2J mice from which it had been originally cloned; it also appeared to cause lymphoma or to shorten the latency of spontaneous lymphoma in DBA/2J mice.

Viruses as environmental carcinogens: an agricultural perspective

Under natural circumstances tumor viruses can be considered as risk factors which in themselves are neither necessary nor sufficient to produce cancer; they may do so, however, if provided with suitable genetic and environmental conditions. It follows that a reduction in amount of virus or other environmental cofactors may prevent the associated tumors. In this paper we will consider four major families of viruses associated with cancer in animals and man, and will highlight the exogenous cofactors and related preventive measures. We will mention those agricultural practices that have resulted in significant economic loss from virus induced cancer in farm and domestic animals and will summarize some of the occupational hazards from environmental agents other than tumor viruses.

Tissue connections in a transplantable virus-producing sebaceous adenoma of the mouse

In this study a transplantable sebaceous adenoma is presented, which maintained its histological structure with similarities to normal sebaceous glands over a long series of transplantations. From the periphery toward the center a basal lamina, an outer layer of undifferenciated stem cells, loosely connected secreting tissue, a tightly packed zone of close cell attachment, and finally a central sebaceous zone can be distinguished. Special reference is made to the belt-like region around the zone of cell lysis and sebum accumulation, which forms a barrier to the surrounding tissue by means of numerous cell adhesions in the form of desmosomes. Relatively few virus particles of the retrovirus group, particularly type A particles, were found in any of the examined tumors.

Origin of malignant adenocarcinoma cell line induced by retrovirus-like particles from DMBA rat mammary tumors

Intraperitoneal inoculation of neonate Sprague Dawley rats with cell-free extracts containing retrovirus-like particles from DMBA-induced rat mammary tumors resulted in a fivefold increase of benign mammary neoplasias in the survivor animals, in comparison to the spontaneous tumor incidence rate. In addition, four animals developed metastasizing abdominal adenocarcinomas. The ascitic cells of one of the abdominal tumors were established as a permanent tissue culture line (HH-1). After subsequent animal passage, cells of the permanent line HH-9 clone 14 showed increased malignancy manifested by the number of takes per animals injected, and by the number of remote metastases observed.

Feline sarcoma virus induced in vitro progression from premalignant to neoplastic transformation of human diploid cells

Human diploid cells morphologically transformed by feline sarcoma virus were serially propagated under selective cell culture conditions. When injected into nude mice prior to passage in soft agar (0.35%), morphologically transformed cells did not produce tumors. However, when propagated under selective cell culture conditions, transformed cells grew in soft agar and, when injected subcutaneously into the subcapsular region of the n mu/n mu mice, produced neoplastic nodules histopathologically interpreted as fibromas. Karyological examination of cell populations grown out from the tumors confirmed that the tumors were composed of human cells. Examination of electron micrographs of the excised tumor tissue revealed the presence of budding virus particles. Tumor cells isolated from nude mice and morphologically transformed cells both contained the feline oncornavirus-associatied cell membrane antigen. It was concluded that expression of feline oncornavirus-associated cell membrane antigen is associated with an early stage of feline retrovirus-induced carcinogenesis, namely focus formation. In addition, it was shown that FeLV-FeSV can induce morphological transformation in human cells in vitro and that there is a requirement for the cells to passage through soft agar before subsequent tumor formation (neoplastic transformation) can be demonstrated.

Oncogenicity of gibbon type-C myelogenous leukemia virus

Young gibbons that were experimentally inoculated with cell-free gibbon ape leukemia virus (GaLV) and developed peristent viremia subsequently developed chronic granulocytic leukemia (CGL) with associated multifocal bone lesions and metastases. An 8-month-old gibbon inoculated with 10(5) tissue culture infectious virus (TCIV) developed acute myeloproliferative disease with associated bone lesions after a latency of 5 months, while a 9-month-old gibbon inoculated with 10(3) TCIV developed CGL after and 11-month latency. The clinical symptoms associated with the onset of leukemia were an increased number of leukocytes which were predominantly mature granulocytes, development of anemia, and multifocal bone lesions. Terminally, the animals had elevated immature granulocytes in the blood, cellular bone marrow with a predominant number of immature granulocytes, and hepatosplenomegaly. The gibbon with CGL had metastatic growth in the spleen and lung. Two 14-month-old gibbons that were inoculated with 10(3) TCIV and developed persistent neutralizing antibody to the virus infection remained free of hematopoietic disease, as did uninoculated animals. The fact that only animals with persistent viremia developed leukemia supports the oncogenicity of GaLV in gibbons.

Lymphomagenicity of recombinant mink cell focus-inducing murine leukemia viruses

Recombinant mink cell focus-inducing (MCF) murine leukemic viruses, as well as ecotropic and xenotropic viruses, were tested for ability to accelerate or cause development of lymphoma in AKR and other strains of mice. Of the three classes of virus isolated from AKR, only the MCF viruses were able to accelerate development of AKR lymphoma. This fully supports the idea that the MCF viruses are the proximal cause of spontaneous AKR lymphoma. MCF lymphomagenicity was strain specific, however, in that AKR MCF viruses did not induce lymphomas in many murine strains; they were moderately lymphomagenic in C3H/Bi mice and in National Institutes of Health Swiss partially congenic for Akv-1 or Akv-2. In contrast, MCF viruses from nonthymic hematopoietic neoplasms of C3H/Fg, BALB/c, or mice partially congenic for ecotropic virus loci (Akv-1, Akv-2, Fgv-1, C58v-1, and C58v-2) were not able to accelerate or cause lymphomia in AKR or any other mouse strain tested, including some of the strains of origin. MCF lymphomagenicity correlated with thymic origin in the virus and with ability to replicate in the thymus.

Avian retroviruses that cause carcinoma and leukemia: identification of nucleotide sequences associated with pathogenicity

Avian myelocytomatosis virus (MC29V) is a retrovirus that transforms both fibroblasts and macrophages in culture and induces myelocytomatosis, carcinomas, and sarcomas in birds. Previous work identified a sequence of about 1,500 nucleotides (here denoted onc(MCV)) that apparently derived from a normal cellular sequence and that may encode the oncogenic capacity of MC29V. In an effort to further implicate onc(MCV) in tumorigenesis, we used molecular hybridization to examine the distribution of nucleotide sequences related to onc(MCV) among the genomes of various avian retroviruses. In addition, we characterized further the genetic composition of the remainder of the MC29V genome. Our work exploited the availability of radioactive DNAs (cDNA's) complementary to onc(MCV) (cDNA(MCV)) or to specific portions of the genome of avian sarcoma virus (ASV). We showed that genomic RNAs of avian erythroblastosis virus (AEV) and avian myeloblastosis virus (AMV) could not hybridize appreciably with cDNA(MCV). By contrast, cDNA(MCV) hybridized extensively (about 75%) and with essentially complete fidelity to the genome of Mill Hill 2 virus (MH2V), whose pathogenicity is very similar to that of MC29V, but different from that of AEV or AMV. Hybridization with the ASV cDNA's demonstrated that the MC29V genome includes about half of the ASV envelope protein gene and that the remainder of the MC29V genome is closely related to nucleotide sequences that are shared among the genomes of many avian leukosis and sarcoma viruses. We conclude that onc(MCV) probably specifies the unique set of pathogenicities displayed by MC29V and MH2V, whereas the oncogenic potentials of AEV and AMV are presumably encoded by a distinct nucleotide sequence unrelated to onc(MCV). The genomes of ASV, MC29V, and other avian oncoviruses thus share a set of common sequences, but apparently owe their various oncogenic potentials to unrelated transforming genes.