ISOLATION OF A REOVIRUS FROM A CASE OF BURKITT'S LYMPHOMA

A Role for RNA Viruses in the Pathogenesis of Burkitt's Lymphoma: The Need for Reappraisal

Certain infectious agents are associated with lymphomas, but the strength of the association varies geographically, suggesting that local environmental factors make important contributions to lymphomagenesis. Endemic Burkitt's Lymphoma has well-defined environmental requirements making it particularly suitable for research into local environmental factors. The Epstein-Barr virus and holoendemic Malaria are recognized as important cofactors in endemic Burkitt's Lymphoma and their contributions are discussed. Additionally, infection with Chikungunya Fever, a potentially oncogenic arbovirus, was associated with the onset of endemic Burkitt's Lymphoma in one study and also with space-time case clusters of the lymphoma. Chikungunya Virus has several characteristics typical of oncogenic viruses. The Flavivirus, Hepatitis C, a Class 1 Human Carcinogen, closely related to the arboviruses, Yellow Fever, and Dengue, is also more distantly related to Chikungunya Virus. The mechanisms of oncogenesis believed to operate in Hepatitis C lymphomagenesis are discussed, as is their potential applicability to Chikungunya Virus.

ENZYMATIC ENHANCEMENT OF INFECTIVITY OF REOVIRUS

Spendlove, R. S. (California State Department of Public Health, Berkeley), and F. L. Schaffer. Enzymatic enhancement of infectivity of reovirus. J. Bacteriol. 89:597-602. 1965.-Enhancement of infectivity by chymotrypsin treatment has been demonstrated with all three types of reovirus, although not in all viral preparations. Enzyme treatment did not produce a simultaneous increase in the hemagglutinating activity of reovirus type 1 (the only type tested). The infectivity of reovirus type 1 (Lang strain) was increased by treatment with chymotrypsin, trypsin, papain, and a filtrate from a culture of a Pseudomonas sp. but not by treatment with pepsin. Sedimentation experiments showed that the property of enhanceability was closely associated with the virus particles themselves. Results of studies involving various sequential treatments with chymotrypsin, and with heat in the presence or absence of 2 m MgCl(2), were compatible with the interpretation that inhibited virus is resistant to exposure to a temperature of 56 C in the absence of MgCl(2), whereas activated virus is thermolabile. Activation of reovirus infectivity by heat in the presence of MgCl(2) and by chymotrypsin was not additive.

MORPHOLOGICAL AND BIOLOGICAL STUDIES ON A VIRUS IN CULTURED LYMPHOBLASTS FROM BURKITT'S LYMPHOMA

Lymphoblasts of two tissue culture strains (EB1 and EB2) from different biopsy specimens of Burkitt's lymphoma have been examined in thin sections by electron microscopy, and have each been found to carry a morphologically identical virus. The virus was observed in samples taken over many months, being present in about 1 to 2 per cent of the cells in two forms: Immature particles about 75 mmicro in diameter which were seen in both the nucleus and cytoplasm; and larger mature particles with a diameter of 110 to 115 mmicro, which were either within membrane-bounded cytoplasmic spaces or at the cell surface. There was some indication that the particles matured by budding through the cytoplasmic membranes. Both types of particle occurred in dead degenerating cells or, less frequently, in intact altered cells. The characteristic alterations of the latter included margination of the chromatin, fragmentation of the nuclear envelope, beaded opaque material in the mitochondria, and, with one of the cell strains (EB1), sheaves of altered spindle tubules. All attempts to isolate and identify the virus carried by the two strains of lymphoblasts failed. No pathological effects were caused in 8-day chick embryos inoculated either with whole lymphoblasts or extracts of disrupted lymphoblasts, using the intraallantoic, amniotic, and chorioallantoic routes, and the extraembryonic fluids of such chicks were without haemagglutinating activity for human, chicken, guinea pig, or monkey erythrocytes. Whole lymphoblasts or lymphoblast extracts were likewise without effect when inoculated intraperitoneally into newborn hamsters or two strains of newborn mice. Similar lymphoblast inocula did not cause detectable changes in 9 different test tissue culture systems even after 8 blind passages. The nature of the unknown, unidentified virus in the cultured lymphoblasts from Burkitt's lymphomas is considered and its possible relationship to the cells discussed.

Murine tumor induction by cytomegalovirus

Cytomegalic inclusion disease can be induced in mice with relative ease. In the study reported here, grandular neoplasms were produced in four mice by means of immunosupression together with large doses of cytomegalovirus. The results of this study suggest that cytomegalovirus may well be an etiologic agent in the formation of salivary gland tumors.

EB virus and the treatment of lymphomas

The high incidence of EB virus infections (and possibly of other viruses) in patients with African lymphoma and, to a lesser extent, in patients with lymphosarcoma in the temperate zones, is thought to be due to its being a passenger virus which persists in the human body and, since it is lymphotropic, presents an opportunistic infection of proliferating lymphoid cells. The thesis is put forward that by entering the cell nucleus, the virus renders malignant lymphoid cells more vulnerable to cytotoxic drugs. Hence a deliberate policy of EB virus inoculation before starting chemotherapy might achieve a more rapid response and longer remissions in indigenous lymphomas of the temperate zones, and might possibly render drug-resistant cases once more drug-sensitive.

Leukemia in animals and man

General comparative aspects of leukemia were reviewed. Leukemia in adult cattle occurs frequently within certain multiple case herds. Cattle in these herds often have persistent lymphocytosis and increased numbers of atypical lymphocytes in blood. Attempts are being made to demonstrate the frequency in which this is a "pre-leukemic" or "perileukemic" condition.With the recognition of viral causative agent(s) in chickens, laboratory rodents and cats, there is increased interest in the leukemia of dogs, cattle and other animals, for the disease in these animals may serve as valuable models in the study and isolation of human leukemogenic agents.Epidemiologic and clinicopathologic aspects of animal leukemias share comparative similarities with themselves and with lymphoreticular neoplasms of man. Causative factor(s) probably act on the host, regardless of species, in a similar fashion. It is not likely, but neither improbable, that leukemia in domesticated animals and leukemia in man share common causal relationships.

The epidemiology of cancer in animals

The principles of epidemiology are applicable to the study of the distribution and determinants of cancer in both human and animal populations. There are many examples of epidemiologic factors (host, environment, agent and time) related to cancer in animals. Certain host characteristics such as age, sex and breed are related to risk of developing cancer. Some environmental influences are illustrated by differences in the geographical distribution of certain types of animal cancer. Aggregations of cancer cases have been reported in herds, families and households. However, the usual distribution of cases in a population does not resemble epidemics typical of infectious diseases. Several factors (radiological, chemical, dietary, parasitic, mechanical, genetic and viral) have been identified as influences that affect the development of animal tumors. Animal species that have been domesticated live longer and consequently malignant disease develops in more of them. Cancer incidence rates now available from data compiled by an animal neoplasm registry in Alameda and Contra Costa counties, California, indicate that some of the frequent sites of cancer in man (skin, breast and the hemic and lymphatic systems) are among the most frequent sites in dogs and cats, man's closest animal associates.

Congenital infections with reovirus

Congenital reovirus, type 2 infections were produced after intraperitoneal inoculations of brood mothers on the 1st, 3rd, 6th, 10th, and 15th day of gestation. The offspring presented with a varied syndrome. About a quarter of a total of over 200 mice showed symptoms within the first 14 days of life; namely, lassitude, retarded growth, and roughening of fur. Some died, apparently of respiratory or renal failure. Post mortem examination showed marked interstitial pneumonia and subcortical renal tubular necrosis. Reovirus was isolated in high titer from the kidney and lungs as well as from blood, hearts, hind limbs, and brains in lesser titer. At 3 wk of age over 50 apparently well mice were sacrificed, and virologic, serologic, and pathologic study was done. High titers of virus were again found in the kidney, lung, blood, brain, heart, and skeletal muscle, but all tissues appeared normal histologically. Type-specific serum antibody titers in these mice were approximately those of their mothers. Another half of these mice showed decreased spontaneous activity and growth retardation which appeared between the 15th and 36th days of life. Three of these mice with late illnesses had marked proptosis and conjunctivitis. A subepidermal conjunctival and extraocular muscle lymphocytic infiltrate was observed on section, and reovirus was isolated from these eyes in tissue culture. Again blood, brain, kidney, liver, spleen, myocardium, and skeletal muscle were studied, and were found to be normal histologically and not to contain reovirus. Finally, the rest of the mice remain well to date. At 3 months of age, 10 of them were sacrificed. All had lost their maternal antibody and contained no reovirus, type 2 hemagglutinating inhibiting antibodies. No developmental abnormalities were observed. These data suggest that prolonged reovirus infections may be established by means of congenital inoculation of the developing fetus. Tolerant infection with immune paralysis seems to have been established.

Further isolations of reovirus type 3 from cases of Burkitt's lymphoma

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Immunofluorescence in cells derived from Burkitt's lymphoma

Henle, Gertrude (Children's Hospital of Philadelphia, Philadelphia, Pa.), and Werner Henle. Immunofluorescence in cells derived from Burkitt's lymphoma. J. Bacteriol. 91:1248-1256. 1966.-Indirect immunofluorescence tests led to the brilliant staining of a small proportion of the cells in five different cultures derived from Burkitt's (African) lymphomas. The reaction was not restricted to the 17 sera from cases of this disease but extended to many sera from American individuals, whether healthy donors or patients suffering from a variety of illnesses. The incidence of positive sera increased with age from about 30% in childhood to > 90% in adults. Fluorescein-isothiocyanate-conjugated human gamma-globulins were suitable for direct staining of the same proportion of cells. The stained cells appeared to be in varying stages of degeneration, but cultural conditions leading to an increase in the cellular death rates failed to result in a rise in fluorescent cells. Several observations suggest that the stainable cells might be those which are seen to harbor virus particles under the electron microscope. Two cell lines derived from leukemic patients in this country also contained a small fraction of stainable cells but two others, and numerous primary human leukocyte cultures, gave consistently negative results. Attempts to relate the staining to known viral antigens have failed to implicate herpes simplex, varicella, cytomegalo, and reo viruses types 1, 2, and 3. The nature of the virus carried by the lymphoma cells as well as of the staining reactions remains to be determined.

VIRUSES AND CANCER

The answer to the important question, "Do viruses play a role in human cancer?" is still unknown. Although many scientists think that they may play a role, straightforward attempts to isolate human tumor viruses in animals or in tissue cultures have failed. Possibly the most sensitive test object, newborn human infants, of course cannot be used as test objects, and this may explain the failure to isolate human tumor viruses. At present, it would appear that the best means of tackling the problem of viral-induced carcinogenesis is to study the basic characteristics of known tumor viruses and the basic aspects of their interactions with cells. Both RNA-containing and DNA-containing viruses, two obviously different classes of virus, can cause cancer and therefore both classes must be studied in order to obtain a complete picture of the role of viruses in causing cancer in animals and cell transformation in vitro. Such basic studies already have yielded information of great importance to general biology.A number of exciting developments have occurred in the area of virus-induced cancer. One of these is the oncogenic capacity in hamsters of certain human adenoviruses, and an intensive probe of their possible role in human cancer is in progress. Another is the detection by electron microscopy of virus-like particles in the tissues and serum of patients with leukemia. Rigid criteria have been suggested to establish etiologic significance of viruses recovered from human cancer tissues and of the virus-like particles observed by electron microscopy in serum or malignant tissues from cancer patients. If viruses are eventually found to play a role in human cancer, then perhaps the disease can be prevented by vaccines and treated with antiviral substances.