Rat lymphoid cell lines with human T cell leukemia virus production. I. Biological and serological characterization

Serial transplantation of an HTLV-I-transformed hamster lymphoid cell line into hamsters

A hamster lymphoid cell line, HCT-2, transformed by human T-cell leukemia virus type I (HTLV-I) was serially transplanted for 9 passages in newborn hamsters. A total of 34 newborn hamsters inoculated intraperitoneally (i.p.) with 0.2-2 X 10(7) HCT-2 cells developed fatal lymphomas with dissemination to various organs within 5-10 days. The growth of i.p. inoculated HCT-2 cells was found to be dependent on the age of recipients: all 21 suckling hamsters inoculated when aged 5-10 days succumbed to disseminated lymphomas within 6-7 days, while 4 of 12 older hamsters inoculated at the age of 15-25 days developed less extensive disease with signs of tumor regression. To investigate the effect of immunosuppression on host resistance, 3 adult hamsters treated with anti-thymocyte serum were inoculated i.v. with 2-4 X 10(7) HCT-2 cells; all 3 developed fatal leukemias in 5-7 days. Irrespective of whether HCT-2 cells were inoculated into newborn, suckling, or adult hamsters, histopathological findings were similar, with frequent involvement of liver, spleen, lungs, kidneys, lymph nodes, blood, and bone marrow. Cells harvested from tumors and peripheral blood of some tumor-bearing hamsters could be readily recultured as cell lines. Chromosome analysis and Southern blot hybridization showed that tumors were caused by growth of HCT-2 cells.

Adult T cell leukemia-like disease experimentally induced in rabbits

An HTLV-I-transformed T cell line, obtained from the peripheral blood of a virus-infected (B/J X Chbb:HM) F1 rabbit, was able to kill syngeneic newborn rabbits within 7 days, when inoculated intraperitoneally at a dose of 1 X 10(8) cells. Inoculation of 1 X 10(7) cells killed or rendered moribund 50% of inoculated animals, while surviving animals exhibited cell-mediated cytotoxic activities against the transformed cells. The peripheral blood leukocyte counts increased in all surviving animals, in association with appearance of abnormal lymphocytes with convoluted or lobulated nuclei. Pathological examination of animals that died one week post-inoculation revealed no tumors in the abdominal cavity, but accumulation of ascites containing abnormal lymphocytes. Histological examination showed leukemic infiltration in the liver, lungs, spleen and mesenteric lymph nodes. The same cell line was also able to kill syngeneic adult rabbits in 8-10 days when inoculated intravenously, but not intraperitoneally, at a dose of 1 X 10(8) cells. Leukemic infiltration was observed in the major organs of these animals. Adult animals which were already virus carriers were resistant to this lethal inoculation. This rabbit ATL-like disease may prove to be useful as an experimental model for acute adult T cell leukemia.

Rat lymphoid cell lines with HTLV-I production. III. Transmission of HTLV-I into rats and analysis of cell surface antigens associated with HTLV-I

Newborn WKA rats given a single intraperitoneal injection of MMC treated TARS-1, a rat T cell line producing HTLV-I, were shown to accumulate high titred antibodies specific for HTLV-I. Adult WKA rats rejected TARS-1 transplant with transient appearance of anti-HTLV-I antibodies. However, rats maintained under daily administration of Bredinin, an immunosuppressive drug after TARS-1 transplant showed continuous production of antibodies specific for HTLV-I by aging. Type-C virus particles similar to HTLV-I were demonstrated by electronmicroscopy in the short-term cultured spleen cells of these rats. The evidence indicates that HTLV-I can be transmitted into newborn and immunosuppressed adult rats and they may provide a suitable animal model of ATL and related conditions in man, especially for elucidating the virus-host interactions involved in the leukemogenesis of HTLV-I. By using monoclonal antibodies, cell surface antigens associated with HTLV-I were also analysed.

Transcription of IL-2 receptor gene is stimulated by ATL-derived factor produced by HTLV-I(+) T cell lines

In HTLV-I transformed T-cell lines established from the patients with adult T-cell leukemia (ATL), there is a constitutive activation of the normal IL-2 receptor (IL-2-R) gene. These cell lines continuously produce an ATL-derived factor (ADF), an IL-2-R inducing factor without IL-2 activity. ADF enhances the expression of the IL-2-R through the augmentation of the IL-2-R mRNA in the HTLV-I(+) T-cell line (ED) as well as the NK cell line cells (YT). In YT cells, the transcriptional initiation of the promoter of the IL-2-R gene was enhanced by ADF but not by IL-2. Production of ADF by HTLV-I(+) T-cell lines may be involved in the abnormal expression of IL-2-Rs on these cells.

Expression of the HT462 antigen on fresh leukemic T cells and on cells of HTLV-I infected lines

We have examined expression of antigens defined by HT462 monoclonal antibody (mAb), together with other HTLV-I related antigens using phorbol 12-myristate 13-acetate treated leukemic mature T cells. Thirteen patients with adult T-cell leukemia (ATL), 3 patients in remission states of ATL and 5 patients with non-ATL were examined. All ATL cells expressed the HT462 antigen, however cells from patients in remission did not express the HT462 antigen. A low percentage of cells from 2 out of 5 patients with non-ATL mature leukemic T cells expressed the HT462 antigen, although these cells did not express other HTLV-I related antigens. Cells of HTLV-I infected human cell lines expressed the HT462 antigen. Three HTLV-I infected rat cell lines (TARS-1, TART-1, TARL-2) did not express the HT462 antigen, although cells of these lines expressed other HTLV-I related antigens. Characterization of the HT462 antigen by strip radioimmunoassay based on western blotting technique using cell lysates of HUT102 cells revealed two additional bands (p68, p35) together with previously reported proteins (gp52, p42). Only p68 was seen in western blots using cell lysates of the rat cell lines. These findings further suggest that the HT462 antigen is a cellular component induced in virus transformed human cells and not a virus encoded protein.

Experimental inoculation of monkeys with autologous lymphoid cell lines immortalized by and producing human T-cell leukemia virus type-I

Cynomolgus monkeys and squirrel monkeys were inoculated with autologous lymphoid cell lines immortalized by and producing human T-cell leukemia virus type-I (HTLV-I) in order to serve as an animal model of adult T-cell leukemia (ATL). The autologous cell lines were established from peripheral blood mononuclear cells (PBMC) from each monkey by co-cultivation with lethally irradiated MT-2 cells producing HTLV-I. All of these cell lines, which had monkey karyotypes, grew continuously without addition of interleukin-2 (IL-2) and expressed virus-specific proteins of HTLV-I and IL-2 receptor. After inoculation with the autologous cell lines, specific antibodies against HTLV-I proteins could be detected in their plasma, and transformed HTLV-I-infected cells could be recovered from their peripheral blood for at least 6 months. However, no signs of ATL have been observed to data, i.e. 2 years after inoculation.

Transformation of hamster spleen lymphocytes by human T-cell leukemia virus type I

Co-cultivation of spleen cells of Syrian golden hamsters with lethally irradiated MT-2 cells harboring human T-cell leukemia virus type I (HTLV-I) resulted in the establishment of lymphoid cell lines, HCT-1 and HCT-2, which exhibited the normal karyotype of golden hamsters. Cells of both the HCT-1 and HCT-2 lines lacked surface immunoglobulins and reacted with a monoclonal antibody (MAb) specific for hamster T cells. Some were positive for OKIa1. None of them expressed HTLV structural antigens (p19 and p24) or virus particles, but they contained HTLV-I proviral DNA monoclonally. By immunochemical analysis of the labelled cell antigens, sera from adult T-cell leukemia (ATL) patients reacted with the two polypeptides, p37 and p40, which may not be viral structural proteins and still remain to be characterized. HCT-1 and HCT-2 cells were transplantable into newborn hamsters, pre-treated with anti-hamster thymocyte serum and non-treated, respectively, producing diffuse malignant lymphoma. These findings indicated that HTLV-I not only immortalized but also transformed hamster T cells non-productively.

p27x-III and p21x-III, proteins encoded by the pX sequence of human T-cell leukemia virus type I

Human T-cell leukemia virus type I (HTLV-I) is an etiological agent of adult T-cell leukemia and has a unique sequence, pX, that contains four possible open reading frames, I-IV. p40x was previously identified as the gene product of frame IV (x-lor) and was suggested to mediate transcriptional trans-activation of the viral long terminal repeats. We have identified two pX gene products, p27x-III and p21x-III, encoded by frame III, which mostly overlapped frame IV. These proteins were detected with rabbit antiserum against the synthetic peptide predicted from the 3' end of frame III. p27x-III is phosphorylated in cultured cells, and the phosphoprotein (pp27x-III) is localized in nuclei; some pp27x-III was tightly bound to nuclear components. p27x-III was detected in a number of cell lines that express other viral antigens, including a cell line previously reported to express only p40x as a viral protein. The function(s) of p27x-III and p21x-III is not known, but the tight binding of pp27x-III to nuclear components suggests that it is associated with regulation of viral gene expression.

A glycoprotein antigen detected with new monoclonal antibodies on the surface of human lymphocytes infected with human T-cell leukemia virus type-I (HTLV-I)

We have prepared two new mouse monoclonal antibodies (MAbs) named TARM-34 (IgM) and TAG-34 (IgG1), that react with surface antigens of lines of human lymphocytes bearing a human T-cell leukemia virus type-I (HTLV-I). The characters of these antibodies are compared with those of anti-HTLV-1 gp21 MAb (TA-21, IgG1), anti-HTLV-I p19 MAb (GIN-14, IgG1) and human antibodies from patients with adult T-cell leukemia (ATL). An indirect membrane immunofluorescence assay showed that TARM-34, TAG-34 and TA-21 all reacted specifically with cell-surface antigens of HTLV-I-positive T- and B-cell lines and cultured peripheral blood lymphocytes from HTLV-I-infected adults. Radioimmunoassay showed that serum antibodies from the ATL patients interfered with the binding of TA-21 antibody to cells of the HTLV-I-positive T-cell line MT-2, but not with the bindings of TARM-34 and TAG-34 antibodies. TARM-34 and TAG-34 both precipitated a 34-kd glycoprotein (gP34), while TA-21 precipitated gp21 from a lysate of 3H-glucosamine-labelled MT-2 cells. TARM-34 and TAG-34 also precipitated the 34-kd protein from lysates of MT-2 and HUT 102 cells labelled with 125I- or 35S-cysteine. Interestingly, TARM-34 and TAG-34 also precipitated 35-kd protein from a lysate of other HTLV-I-positive cells (F-Taj cell line) derived from an ATL patient. TA-21 precipitated the 21-kd protein from the lysates of 35S-cysteine-labelled HTLV-IMT-2 virions, but TARM-34 and TAG-34 did not precipitate any protein from this lysate. TARM-34 lysed HTLV-I-bearing cells in the presence of rabbit complement. These results indicate that TARM-34 and TAG-34 both recognize a glycoprotein antigen that is expressed on the surface of HTLV-I-infected cells.

Transmission of human T-cell leukemia virus type I to an S+L- cat kidney cell line

The S+L- cat kidney cell line CCC was cocultivated with lethally irradiated human lymphoid cell lines that were producing human T-cell leukemia virus type I (HTLV-I). Eight of nine S+L- CCC sublines that had been cocultivated with nine different HTLV-producing T-cell lines gave positive reactions for HTLV antigens by indirect immunofluorescence assay. One subline CCC/2M was cloned. The percentages of fluorescent cells differed markedly in different sublines and clones. Southern blot hybridization with HTLV probes and electrophoresis of immunoprecipitates indicated that defective HTLVs were often transmitted into S+L- cat cells. S+L- CCC cells were permissive for HTLV and the properties of HTLV-infected cat cells were heterogeneous.

Host cell range of adult T-cell leukemia virus. I. Viral infectivity and binding to various cells as detected by flow cytometry

Adult T-cell leukemia virus is the member of a human type-C retrovirus family (HTLV) found to be associated with adult T-cell leukemia (ATL) in Japan. In our study, HTLV was isolated from the MT-2 cell line, purified on sucrose gradient and labelled with fluorescein-isothiocyanate (FITC-HTLV). The protein pattern of the virus was determined by SDS-gel electrophoresis and assured by Western blotting using ATL patient serum. Fresh human lymphocytes, separated B and T cells, mouse and rabbit lymphocytes, mouse fibroblasts, and 13 different tumor cell lines were tested in parallel for binding of FITC-HTLV and infectability by the virus. Virus binding to cell receptors was assayed by flow cytometry. Successful infection was monitored by following the expression of HTLV-determined antigen (HTLA). Most of the cells bound FITC-HTLV at levels ranging from 5% to 130% of the MT-2 cell binding. Only fresh human T, mouse and rabbit lymphocytes were infectable by cell-free virus preparations. The results demonstrate that HTLV receptors are present on different types of cells of both human and animal origin, and that infection by the virus is restricted to fewer host cells but not limited to a specific class of human lymphocytes.

Expression of the pX gene of HTLV-I: general splicing mechanism in the HTLV family

Human T-cell leukemia virus type I (HTLV-I) is an etiological agent of adult T-cell leukemia. A viral gene pX encodes for p40X and it has been proposed that this protein trans-activates the viral long terminal repeat and possibly some cellular genes; this activation may be associated with T-cell transformation. The mechanism of pX gene expression and the primary structure of p40X are now reported. Two-step splicing generates the 2.1-kilobase pX mRNA; the initiator methionine for env becomes part of the pX protein. These splicing signals are conserved among all members of the HTLV family except for the acquired immune deficiency syndrome-associated viruses.

HTLV in Sweden: antibodies to HTLV I antigens in experimental monkeys and their caretakers

252 monkeys kept at 4 different Swedish universities and laboratories for experimentation were screened for antibodies to HTLV I associated antigens by means of a sensitive membrane antigen enzyme immunoassay (MA-ELISA). 17/185 Macaca fascicularis, 1/56 M. mulatta, 0/1 Cercopithecus aetiops and 0/10 Saimirii squiureus had antibodies. All of 11 MA-ELISA positive animals which were subjected to further testing were also positive in a competition assay for anti-HTLV p19 antibodies and in an anti-whole virion enzyme immunoassay. One colony of 32 M. fascicularis monkeys from the Philippines contained 7 antibody-positive animals. Except for one M. fascicularis which suffered from a chronic dermal lesion, major disease was not observed in any of the antibody-positive animals. None of 28 animal caretakers or experimenters, of which several had been repeatedly exposed to blood from antibody-positive animals, had antibodies measurable by the MA-ELISA. The contagiosity for humans of the majority of the antibody-positive monkeys thus appears to be relatively low. We conclude that the presence in Sweden of HTLV I antibody-positive animals probably does not constitute a great health risk. However, we consider it appropriate that antibody-positive animals should be handled with special care.

Rat lymphoid cell lines producing human T cell leukemia virus. II. Constitutive expression of rat interleukin 2 receptor

Three rat lymphoid cell lines (TARS-1, TARL-2, and TART-1) (12) transformed by human T cell leukemia/lymphoma virus I (HTLV-I) had rearrangement of the beta chain gene of the T cell antigen receptor, and had integrated proviral DNA from HTLV-I in their genomes. As is the case with adult T cell leukemia (ATL)-derived human T cell lines transformed by HTLV-I, these rat cell lines unequivocally expressed interleukin 2 (IL-2) receptor, as determined by radiolabeled IL-2 binding. By Scatchard plot analysis, one of the cell lines, TART-1, proved to have high affinity receptors (Ka = 1.3 X 10(11)/M and 8.8 X 10(9)/M). Rat IL-2 receptor, not human IL-2 receptor, was expressed on HTLV+ rat cell lines, as demonstrated by the fact that they expressed antigens reactive with monoclonal antibodies (ART-18) against rat IL-2 receptor, but not with anti-Tac antibodies. The collective evidence indicates that the endogenous IL-2 receptor gene is activated in human and rat lymphoid cell lines with HTLV-I production. The mechanism of abnormal IL-2 receptor expression in HTLV infection is discussed.

Functional activation of the long terminal repeat of human T-cell leukemia virus type I by a trans-acting factor

Promoter function for gene expression of the long terminal repeat (LTR) of human T-cell leukemia virus type I (HTLV-I) was studied by constructing plasmids containing the LTR sequence. The gene encoding chloramphenicol acetyltransferase (CATase) was linked to an HTLV-I LTR sequence (pLTR-CAT) by replacing the simian virus 40 promoter in plasmid pSV2-CAT with the LTR sequence. The transient CATase activities of cells transfected with the plasmids were compared. The results are summarized as follows: The HTLV LTR was active even in an epithelial cell line, with efficiency similar to that of the simian virus 40 promoter. pLTR-CAT expressed high CATase activity, 40-200 times that expressed by pSV2-CAT, in HTLV-I-infected T-cell lines, such as the human cell lines MT-2 and HUT-102, or in HTLV-I-infected rat cell lines. This enhanced activity of the LTR seems to be associated with HTLV gene expression, since only low activity of pLTR-CAT was observed in the HTLV-infected cell line MT-1, in which only a small percent of cells express viral antigens. In HTLV-infected rat cell lines, the pX-encoded protein p40x was the only viral protein detected. Thus, we suggest that p40x is the factor associated directly or indirectly with the enhanced activity of the LTR.

Isolation of simian retroviruses closely related to human T-cell leukemia virus by establishment of lymphoid cell lines from various non-human primates

Simian retroviruses closely related to human T-cell leukemia virus (HTLV) were isolated by establishing virus-producing lymphoid cell lines from 7 species of non-human primates. By co-cultivation with human umbilical cord-blood cells and/or in the presence of interleukin-2, lymphoid cell lines were successfully established from the chimpanzee. African green monkey, pig-tailed macaque, red-faced macaque, Formosan monkey, Japanese monkey and bonnet monkey that had antibodies against HTLV antigens. These cell lines reacted with human sera of ATL patients and monoclonal antibodies against p19 and p24 of HTLV antigens. Cellular DNAs contained the provirus sequences homologous to HTLV-I by Southern blot hybridization. Moreover, they produced extracellular type-C virus particles and RNA-dependent DNA polymerase. All of these lymphoid line cells had Tac antigen, interleukin-2 receptor, and those of chimpanzee and red-faced macaque had helper/induced T-cell markers, while those derived from African green monkey had suppressor/cytotoxic T-cell markers. Furthermore, simian HTLV-related viruses of pig-tailed macaque, red-faced macaque and Japanese monkey were transmitted to human lymphocytes on co-cultivation.

Infectious transmission of human T-cell leukemia virus to rabbits

A rabbit lymphoid cell line (Ra-1) was established by co-cultivation with a human T-cell line (MT-2) carrying human T-cell leukemia virus (HTLV). The Ra-1 cell line is chromosomally male and is persistently infected with HTLV. Ra-1 cells, with or without mitomycin C treatment, were inoculated intravenously (i.v.) into 3 female rabbits. All 3 animals responded with the production of antibodies to HTLV antigens. Lymphocytes from one of these seroconverters were cultured in the presence of T-cell growth factor (TCGF) and HTLV particles were detected in the TCGF-grown lymphocytes which were chromosomally female. Co-cultivation of lymphocytes from the 2 other seroconverters with lymphocytes from 2 anti-HTLV-negative healthy men gave rise to the establishment of an HTLV-producing T-cell line derived from each individual. Blood transfusion from one of the HTLV-infected rabbits into 2 female rabbits also resulted in the seroconversion of both recipients. An HTLV-carrying lymphoid cell line (Ra-2) was established from one of the transfusion-related seroconverters. The Ra-2 cell line was initially TCGF-dependent but later became TCGF-independent. There results indicate that HTLV can be transmitted to rabbits. These animals may provide a suitable model system for studying the mode of transmission and pathogenicity of HTLV.

Immortalization of peripheral blood lymphocytes of cats by human T-cell leukemia virus

Peripheral blood lymphocytes of domestic cats were co-cultivated with lethally irradiated MT-2 cells, which produced human T-cell leukemia virus type 1 (HTLV-I). Two cat lymphoid cell lines, CaL-1 and CaL-2, established and maintained without exogenously added T-cell growth factor, were characterized after more than 6 months of cultivation. These cells grew in suspension, had a chromosome number of 38 and lacked cytoplasmic and surface immunoglobulins. CaL-2 cells formed E-rosettes. Both cell lines harbored HTLV genomes but not human Alu family sequences, which are highly repetitious in the human genome, suggesting that transfer of human DNA fragments was not necessary for their immortalization or transformation. HTLV antigens were detected in CaL-1 and CaL-2 cells by indirect immunofluorescence assay. CaL-1 and CaL-2 cells both expressed viral proteins with apparent molecular weights of 53 kd, 24 kd and 19 kd, and CaL-2 cells also expressed 28 kd and 20 kd proteins. Reverse transcriptase activity was detected in culture fluid of CaL-2 cells, but not of CaL-1 cells. CaL-2 cells but not CaL-1 cells had syncytium-induced activity. These findings indicated that lymphocytes of cats, especially T lymphocytes, were susceptible to infection with HTLV and to immortalization by HTLV.

Envelope proteins of human T-cell leukemia virus: expression in Escherichia coli and its application to studies of env gene functions

The DNA fragments of the 5' and 3' halves of the putative env gene predicted from the DNA sequence of human T-cell leukemia virus (HTLV) provirus were inserted into expression vectors pORF2 and pORF1, respectively, and two hybrid proteins composed of env polypeptides and beta-galactosidase were efficiently produced in Escherichia coli. The hybrid proteins containing the NH2-terminal (EH9) and COOH-terminal (EA1) halves were both immunologically reactive with sera from adult T-cell leukemia patients, demonstrating the utility of the hybrid proteins for diagnosis of HTLV infection. Rabbit antisera against these hybrid proteins detected the two glycoproteins gp62 and gp46, which were previously identified as HTLV env gene products. With these rabbit antisera, two properties of the env gene products were studied. (i) The antisera inhibited syncytia formation of cat S+L- cells induced by HTLV, suggesting that one or both of the env gene products of HTLV, gp62 and gp46, are involved in induction of cell fusion. (ii) The env product gp62 or gp46 or both products are exposed on the surface of HTLV-infected cells and might modulate the proliferation of HTLV-infected T cells in the host because the antisera against the hybrid proteins were cytotoxic on HTLV-producing cell lines. The latter conclusion also is supported by the fact that adult T-cell leukemia patients and healthy HTLV carriers have antibodies to the env gene products.

Establishment of retrovirus-, Epstein-Barr virus-positive B-lymphoblastoid cell lines derived from individuals at risk for acquired immune deficiency syndrome (AIDS)

Peripheral blood lymphocytes from male individuals at risk for AIDS were cultured in the presence of interleukin-2. Approximately 90% of cultures originating from pre-AIDS and AIDS patients were retrovirus-positive as detected by the reverse transcriptase (RT) assay and confirmed by electron microscopy. Prolonged incubation of the retrovirus-positive cells resulted in the establishment of several interleukin-2-independent B-lymphoblastoid cell lines. These cells were positive for Epstein-Barr virus (EBV)-specific antigens and contained EBV particles. When irradiated cells from the new lines were cocultivated with an RT-negative T-cell line CEM, an efficient transmission of retrovirus was detected. The supernatants from cocultivated cells had 5-10 fold higher levels of RT activity as compared with the supernatant from the cell line alone. Type-C retroviral particles and budding structures similar to those of human T cell leukemia virus type III (HTLV-III) and lymphadenopathy-associated virus (LAV) were found by electron microscopy. HTLV-III/LAV-specific polypeptides were detected by immunoprecipitation with sera from lymphadenopathy and AIDS patients, but not with sera from healthy individuals. Our data suggest that EBV-infected B lymphocytes from individuals at risk for AIDS may serve as a biological reservoir for the AIDS-associated retrovirus.