Expression of murine leukemia virus structural antigens on the surface of chemically induced murine sarcomas

Alien Histocompatibility Determinants on the Cell Surface of Sarcomas Induced by Methylcholanthrene. II. in Vitro Serological Studies

In vitro serological studies were carried out in an attempt to identify the foreign histocompatibility antigens previously detected by transplantation methods on the cell surface of 2 methylcholanthrene-induced BALB/c fibrosarcomas (TZ15 and ST2). The reactivity of the anti-TZ15 and anti-ST2 syngeneic sera and of the C57BL/6J anti-TZ15 and anti-ST2 sera (the latters preabsorbed on normal BALB/c lymphoid cells) was evaluated on normal lymph node cells of C3Hf, C57BL/6J, DBA/2 and AKR strains by the complement-dependent cytotoxicity and on normal fibroblasts of C3Hf and C57BL/6J mice by the isotopic antiglobulin assay. The ability of in vitro-plated TZ15 and ST2 cells to bind BALB/c anti-C3Hf, anti-C57BL/6J, anti-AKR and anti-DBA/2 alloantisera was also examined by the antiglobulin assay. Contrary to the in vivo data, no cross-reactions were found between TZ15 and AKR normal cells, since both syngeneic and allogeneic anti-TZ15 sera were not cytotoxic to C3Hf, C57BL/6J or AKR lymphoid cells nor could BALB/c anti-C3Hf, anti-C57BL/6J or anti-AKR sera bind to TZ15 tumor cells in the antiglobulin assay. Both BALB/c anti-ST2 and C57BL/6J anti-ST2 sera were also ineffective in killing normal C3Hf, C57BL/6J, AKR and DBA/2 lymphoid cells in the complement–dependent cytotoxic assay, whereas a weak but significant binding of the syngeneic anti-ST2 serum to C57BL/6J but not to C3Hf fibroblasts was detected by the antiglobulin test. ST2 but not TZ15 cells were also able to significantly absorb the complement–dependent cytotoxic activity of a BALB/c anti-C57BL/6J but not of a BALB/c anti-C3Hf antiserum. In addition, BALB/c anti-C3Hf, anti-C57BL/6J and anti-AKR sera but not BALB/c anti-DBA/2 serum strongly bound to ST2 cells in the antiglobulin test; this binding activity was absorbed by C3Hf, C57BL/6J, AKR, and NIH but not BALB/c and DBA/2 lymphoid cells. Thus, among the cross-reactions observed in vivo between ST2 and normal cells of C3Hf, DBA/2 and C57BL/6J strains, only C57BL/6J normal antigens were detectable by serology. A new but still undefined system of alien normal antigens shared by C3Hf, AKR, C57BL/6J, NIH lymphoid and ST2 cells was revealed by the BALB/c alloantisera in the antiglobulin assay. The relationship of these findings with those previously obtained in the transplantation study with the same tumors is discussed.

Development and testing of AIDS vaccines

Recent advances in delineating the molecular biology of human immunodeficiency virus type 1 (HIV-1) have led to innovative approaches to development of a vaccine for acquired immunodeficiency syndrome (AIDS). However, the lack of understanding of mechanisms of protective immunity against HIV-1, the magnitude of genetic variation of the virus, and the lack of effective animal models for HIV-1 infection and AIDS have impeded progress. The testing of AIDS vaccines also presents challenges. These include liability concerns over vaccine-related injuries; identification of suitable populations for phase 3 efficacy studies; balancing the ethical obligation to counsel research subjects to avoid high-risk behavior with the necessity to obtain vaccine efficacy data; and the effect of vaccine-induced seroconversion on the recruiting and welfare of trial volunteers. Several candidate AIDS vaccines are nevertheless currently under development, and some are undergoing phase 1 clinical trials. Rapid progress will depend on continued scientific advancement in conjunction with maximum use of resources, open information and reagent exchange, and a spirit of international collaboration.

Detection of immunologically cross-reacting capsid protein of alphaviruses on the surfaces of infected L929 cells

Hyperimmune, but not normal immune, monospecific antiserum made to capsid protein of Sindbis virus (SIN) was found to cause cytolysis equally well of both SIN- and Semliki Forest virus-infected L929 cells in antibody-dependent, complement-mediated cytotoxicity assays. The cell surface reactivity of the hyperimmune antiserum was also demonstrated by solid-phase radioimmune assays with unfixed infected cells or infected cells fixed with low concentrations of glutaraldehyde (0.025%) before reactivity with antisera. Higher concentrations of glutaraldehyde lowered the sensitivity of detection. Purified SIN capsid protein specifically inhibited antibody-dependent, complement-mediated cytotoxicity by the monospecific anti-capsid protein serum on SIN- and Semliki Forest virus-infected target cells. That hyperimmune anti-SIN serum also cross-reacts with capsid protein on the surface of Semliki Forest virus-infected cells was suggested by the fact that capsid protein inhibited cross-cytolysis in the antibody-dependent, complement-mediated cytotoxicity assay. The latter antiserum was collected after repeated injections of purified virions over a 9-month period. The results suggest that hyperimmune monospecific antisera made to SIN capsid protein or hyperimmune antisera to SIN or Semliki Forest virions detect homologous and cross-reacting capsid protein determinants on the surface of infected cells.

Association of human T-cell leukaemia/lymphoma virus with the Tac antigen marker for the human T-cell growth factor receptor

Certain adult T-cell lymphoproliferative disorders are associated with human T-cell leukaemia virus (HTLV), a unique human type C retrovirus. (The strains of HTLV used in these studies belong to the subgroup HTLV-I.) HTLV is not an endogenous agent in man, but rather is an acquired virus with T-cell tropism. Neoplastic cells from patients infected with HTLV generally express receptors for T-cell growth factor (TCGF) (interleukin-2), and do not require prior activation with antigens or lectins to undergo TCGF-induced proliferation. Furthermore, neoplastic T-cell lines originating from such patients may constitutively produce TCGF, TCGF receptors and HTLV virions. HTLV is transmissible from cell to cell, and the infection of human T cells in vitro is associated with the expression of TCGF receptors, which can be identified by the monoclonal antibody termed anti-Tac. In our experience to date, T-cell populations that produce HTLV without exception also express epitopes found on TCGF receptors. Recognition of an association between HTLV virions and the Tac antigen would have clinical and theoretical implications. We now present evidence that during the replication or release of HTLV, the virion becomes preferentially associated with the Tac antigen.

Definition of a unique cell surface antigen of mouse leukemia RL male 1 by cell-mediated cytotoxicity

BALB/c x-ray-induced leukemia RL male 1 is strongly immunogenic for (BALB/c x C57BL/6)F1 mice. Transplants of RL male 1 regressed after initial growth, and after tumor regression mice could resist repeated inocula of 10(7) RL male 1 cells. Spleen cells from immunized mice after in vitro stimulation with RL male 1 were cytotoxic for RL male 1 cells in 3-hr 51Cr assays. Pretreatment of immune spleen cells with Thy-1, Lyt-2, or Lyt-3 antisera and complement eliminated cytotoxic activity, indicating that effector cells for RL male 1 lysis are T cells. Tests with other target cells showed little or no cytotoxicity. Analysis of the specificity of T-cell killing of RL male 1 by competitive inhibition assays with unlabeled cells indicated that only RL male 1 could inhibit killing; other BALB/c tumors (13 x-ray or murine leukemia virus-induced leukemias and three myelomas) failed to inhibit lysis of RL male 1. A range of alloantisera and heteroantisera were tested for their capacity to block lytic activity in the absence of added complement. H-2d antisera and Lyt-2 and -3 antisera blocked lysis, the latter at the level of the effector cell. Antisera to other cell surface alloantigens, murine leukemia virus-related antigens, and immunoglobulins did not block RL male 1 lysis. Thus, T cells from mice immunized against RL male 1 recognize an individually distinct or unique antigen that does not appear to be related to any of the serologically defined cell surface determinants of RL male 1. In its restriction to a single leukemia, the RL male 1 antigen resembles the individually distinct antigens of chemically induced tumors and other tumor types of rodents.

Detection of a transformation-related antigen in chemically induced sarcomas and other transformed cells of the mouse

Antisera prepared against BALB/c Meth A sarcoma in syngeneic or compatible F1 mice recognize a protein with an apparent molecular weight of 53,000 in extracts of [35S]methionine-labeled transformed BALB/c cells. This component, designated p53, was not detected in normal adult mouse fibroblasts, lymphoid cells, or hematopoietic cells or in mouse embryo cells or 3T3 cells. An extensive variety of antisera, including alloantisera and heterologous antisera directed against structural antigens of murine leukemia viruses, was tested for reactivity with p53; other than Meth A antisera, only comparably prepared antisera against another BALB/c sarcoma, CMS4, had anti-p53 activity. All transformed mouse cells tested were found to express p53; these tests included chemically induced sarcomas, leukemias, spontaneously transformed fibroblasts, and cells transformed by simian virus 40 and murine sarcoma virus. The presence of p53 in tumors of no known viral etiology indicates coding by resident cellular genes; this does not exclude endogenous viruses as the source of coding sequences or the possibility that transforming viruses code directly for p53.

Antiserum to murine leukemia virus recognizes novel cell surface molecules associated with growth control and transformation

Antiserum directed against murine leukemia virus also reacts with several external proteins present in rat cells transformed by a temperature-sensitive Rous sarcoma virus. Reaction of iodinated cell extracts with anti-MLV (murine leukemia virus) serum revealed the presence of a 200,000 dalton iodinated component detectable also by metabolic labelling with glucosamine only in serum-starved cultures restricted in the expression of transformation. A similar assay with iodinated cells that express the transformed phenotype revealed the preferential recognition of two components with an approximate molecular weight of 100,00 daltons as well as an additional 65,000-dalton external component. Growth of the transformed non-producer NT3-KR cells in the presence of inducers of C-type viruses leads to an increased synthesis of a 100,000-dalton glycoprotein (gp100) recognized by the anti-MLV serum which is also recognized by the antiserum in NRK-MSV-MLV transformed producer cells, in addition to a virus-like glycoprotein of 71,000 dalton (gp71). Absorption of the anti-MLV serum with monolayers of NT3-KR cells eliminated the ability of the serum to recognize the gp100 but not the gp71 from NRK-MSV-MLV-transformed producer cells. The mediation of post-translational changes in growth control is suggested by the transformation-dependent alteration in the molecular weight of the non-virion surface proteins recognized by anti-MLV serum in the rat cells used in this study.

Tumor-associated antigens of chemically-induced murine tumors; the emergence of MuLV and fetal antigens after serial passage in culture

Using radioiodinated Staphylococcus aureus protein A [125I]SPA to measure syngeneic, allogeneic and heterogeneic IgG bound to murine tumor cells, we performed a serological analysis of surface antigens of 8 solid tumors and 2 leukemias of BALB/c mice (3 chemically-induced colon carcinomas, 3 chemically-induced sarcomas, 1 murine leukemia virus (MuLV) induced leukemia, 1 irradiation induced leukemia, 1 spontaneous melanoma and 1 spontaneous sarcoma). We were able to detect and distinguish between at least five separate antigenic specificities on these tumors. Unique tumor-associated antigens were found on 3 of the tumors, MuLV related antigens on 8 tumors, fetal antigens on 7 tumors and two distinct common antigens on 7 tumors (common antigen 1 (CA-1) on 5 tumors and common antigen 2 (CA-2) on 2 tumors). Neither of the common antigens was found to be sarcoma, carcinoma or tissue-tupe specific. A number of tumors which did not originally express either MuLV or fetal antigens in primary cultures expressed these antigens after several serial passages in vitro.

Production of xenoantiserum to a chemically induced murine tumor: analysis of tumor specificity in different immune tests

The method of in vivo absorption of xenoantisera raised against murine chemically-induced tumors has been used to obtain specific anti-tumor sera. To assess if the tumor specificity was maintained under different experimental conditions, the sera were employed in in vitro tests based on different immunologic reactions. In vivo absorption results in the production of xenoantisera which are highly specific for the immunizing tumor and that lack antibody activity toward histocompatibility and organ specific antigens and endogenous virus antigens. Thus, in vivo absorbed antisera appear to be valuable reagents for the immunochemical characterization of chemically-induced tumors.

Expression of oncofetal antigens on murine sarcomas characterized for expression of endogenous MuLV

A rabbit antiserum raised by repeated immunization with BALB/c fetuses obtained at 10-14 days of gestation was used to search for oncofetal antigens (OFA) in murine sarcomas which had previously been characterized for the expression of endogenous murine leukemia virus (MuLV). Iodinated protein A from staphylococcus aureus (IPA) was used to quantitate binding of the antiserum to cultured tumor or fetal cells or to saline extracts of tumors and fetuses. Use of the "antigen" extracts facilitated the assay: the extracts bound to plastic and served as targets for the binding assay, eliminating the need to establish tumors in culture. After absorbtion in vitro and in vivo with adult tissues the rabbit antiserum bound to day 10-14 fetal cells and extract but not to endogenous MuLV (BALB virus 1). The antiserum bound equally well to MuLV-negative and MuLV-positive sublines of MCA-induced sarcomas 1420 and 1414 but not to Moloney sarcoma cells and MCA-induced sarcoma 1386. Thus, the absorbed antiserum detects a class of common cross-reacting antigens which are serologically distinct from MuLV-associated antigens.

Surface expression of murine leukemia virus structural polypeptides on host cells and the virion

The expression of murine leukemia virus structural polypeptides on the surface of cells producing exogenous Friend leukemia virus, endogenous ecotropic AKR and xenotropic BALB/c virus was investigated. Antisera to Friend virus gp71, p30, p15E, p12 and p10 were employed in a complement-dependent chromium release assay and to immunoprecipitate lactoperoxidase iodinated surface polypeptides prior to analysis in polyacrylamide gel electrophoresis. With the latter technique gag-gene encoded proteins and their precursors were not discovered on the viral and cellular surface membranes. Only env-gene encoded polypeptides gp85, gp71, and p15E were detectable. p15E is embedded into the lipid membrane. gp85 is formed by disulfide linkage of p15E to surface-exposed gp71. The ratio of gp71 to gp85 is variable and apparently determined by the host cell. Antibodies of strong cytotoxicity are those against type- and group-specific epitopes of gp71 as well as type-specific epitopes of p12.

Relationship of tumor-specific transplantation antigens to the histocompatibility complex: dissociation of in vitro alloantigen expression and in vivo alloimmunity from tumor-specific transplantation antigen strength

The studies reported here explore the relationship between tumor-specific transplantation antigens (TSTA) and (1) the expression of serologically defined specificities, and (2) the immunogenicity of H-2K- or H-2D-determined alloantigens on methylcholanthrene (MCA)-induced murine fibrosarcomas. Expression of H-2K and H-2D serologically-detected private specificities on groups of tumors raised in B10.A, B10.BR or B10.D2 strains varied greatly among tumors. No regular reciprocal or direct relationship to tumor TSTA strength was found. Each tumor, however, expressed H-2K or H-2D alloantigens stably as determined by direct cytotoxicity or absorption techniques. Even those tumors expressing little or no detectable alloantigen by serologic analysis were immunogenic in H-2K or H-2D incompatible congeneic hosts. This was assayed in terms of capacity to evoke primary or secondary tumor resistance, and to induce allo-antibody toward private H-2K or H-2D end specificities. An exception was that B10.BR tumors failed to induce anti-H-2Dk antibody despite strong surface alloantigen expression. While TSTA strength did not correlate with serologically detected alloantigen expression, TSTA strength did tend to correlate inversely with capacity to resist primary growth in the H-2K different host, and directly with resistance in the H-2D different host.

B-tropic oncornavirus production by BALB/c methylcholanthrene-induced sarcoma cells

Six oncogenic cell lines were established from primary sarcomas that had been induced in thymectomized, aged, BALB/cSt mice by the injection of 3-methylcholanthrene. Of these lines, three produced B-tropic murine leukemia virus (MuLV), i.e. MuLV that would patently infect fibroblasts of BALB/c origin but not those from NIH Swiss mice. One of these lines, M-138, produced large quantities of virus, permitting the isolation of milligram quantities of B-tropic MuLV. Neonatal BALB/c mice injected with the M-138 MuLV developed high plasma levels of the species-specific virion antigen p30, but during 9 months of observation failed to manifest clinical signs of leukemia. Plasma p30 levels of NIH Swiss mice (non-permissive host) that were inoculated also as neonates with the same virus preparation, remained undetectable by radioimmunoassay. Xenotropic MuLV, i.e. that which infects cells of species other than the species of origin, was released by one of the three remaining cell lines. Two of the six original lines have remained free of detectable oncornavirus production. Our results suggest that cell lines that are stable sources of large quantities of B-tropic MuLV may be easily obtainable by the described manipulations. Equally important, however, is the fact that these data re-emphasize the danger that is inherent in assuming that a cell line is virus-free simply because it was isolated from a chemical carcinogen-induced neoplasm

Antibody response of mice to chemically induced tumors

BALB/c mice immunized with syngeneic methylcholanthrene-induced fibrosarcomas did not have antibodies against the unique tumor-specific transplantation antigens, even though they were capable of rejecting a lethal dose of tumor cells. Endogenous murine leukemia virus antigens expressed by certain of the tumors did, however, elicit high titers of antibodies, accounting for serological crossreactions that occurred between those tumors.

Assembly of type C oncornaviruses: a model

The salient features of this model for oncornavirus assembly are that uncleaved precursor molecules to the internal virus polypeptides possess specific recognition sites both for viral envelope constituents already inserted in the cell membrane and for the viral RNA. After orderly alignment of these components at the budding site, virus maturation proceeds through specific proteolytic cleavage of the precursor components and association of the resultant molecules into the characteristic type C virion substructures revealed by electron microscopy.

Cell surface antigens of chemically induced sarcomas of the mouse. I. Murine leukemia virus-related antigens and alloantigens on cultured fibroblasts and sarcoma cells: description of a unique antigen on BALB/c Meth A sarcoma

As background for a serological definition of the unique antigens of chemically induced sarcomas, we have typed a series of fibroblast and sarcoma cell lines of BALB/c and C57BL/6 origin by cytoxicity and absorption tests for murine leukemia virus (MuLV)-related cell surface antigens and known alloantigens. 7 of the 17 cultured lines expressed the range of cell surface antigens associated with MuLV (GIX, GCSA, gp70, p30), and this was invariably associated with MuLV production. In nonproducer lines of C57BL/6 (but not BALB/c) origin, a MuLV-gp70-like molecule was found on the surface of fibroblasts and sarcoma cells. The alloantigenic phenotype of these MuLV+ and MuLV- cell lines was H-2D+, H-2K+, Thy-1.2+ or -, PC.1+ or -, Lyt-1.2-, Lyt-2.2-, Ia.7-, and TL.2-. A unique antigen was defined on the BALB/c ascites sarcoma Meth A with antisera prepared in BALB/c or (BALB/c X C57BL/6)F1 mice. Tissue culture lines derived from this tumor were MuLV-, which facilitated serological study of the antigen. Absorption analysis indicated that the antigen was restricted to Meth A; it could not be detected in normal or fetal BALB/c tissue MuLV+ or MuLV- fibroblast lines, 12 syngeneic or allogeneic sarcomas, or normal lymphoid cells from 13 different inbred mouse strains.

Immunologic recognition of influenza virus-infected cells. II. Expression of influenza A matrix protein on the infected cell surface and its role in recognition by cross-reactive cytotoxic T cells

Two distinct subpopulations of cytotoxic T cells are generated in the primary or secondary response of mice to type A influenza viruses. One subpopulation is specific for the immunizing virus strain. The other subpopulation shows a high degree of cross-reactivity for heterologous type A virus of a different subtype. This report examines the possibility that distinct influenza virus antigens, expressed on the surface of the infected cell, are recognized by the different subpopulations of influenza-specific cytotoxic T cells. Data are presented which demonstrate that influenza A matrix protein, an internal virion antigen, is detectable on the surface of target cells infected with influenza A viruses of different subtypes. Since this viral antigen is type specific, i.e., serologically cross-reactive among all type A influenza viruses, it could serve as the target for cross-reactive cytotoxic T cells. To further examine the specificity of the two cytotoxic T-cell subpopulations, experiments were carried out by using the inhibitor of glycoprotein synthesis - 2-Deoxy-D-Glucose 2-DG. These experiments examine first the effect of 2-DG on the expression of influenza matrix protein and viral glycoprotein on the infected cell surface and second, the susceptibility of 2-DG-treated target cells to lysis by cytotoxic T cells. 2-DG inhibits the expression of the viral hemagglutinin glycoprotein on the cell surface but does not inhibit the expression of the nonglycosylated matrix protein. Furthermore, inhibition of glycoprotein synthesis in infected target cells abrogates the reactivity of infected target cells to lysis by virus strain-specific but not cross- reactive cytotoxic T cells. These findings suggest that the influenza glycoproteins (hemagglutinin and/or neuraminidase) and the nonglycosylated matrix protein are the targets for the virus strain- specific and cross-reactive cytotoxic T cells, respectively. These results are discussed in the light of available information on influenza virus structure and the biology of influenza infection and in terms of current models for cytotoxic T-cell recognition of virus-infected cells.

[Model studies on virus-induced tumors and their immunological treatment (author's transl)]

After a review of the general biological properties of C-type oncorna viruses, results are presented on the structure of an exogenous murine leukemia virus (FLV) and on the serobiological properties of its structural proteins. Our findings suggested a major role of the viral surface glycoprotein gp71 in immunological defense mechanisms. This was confirmed by vaccination experiments with isolated gp71 in mice. The induced immunity was highly specific and not operative against endogenous murine C-viruses belonging to other serotypes. Surprisingly the latter were found to be activated by the vaccination with gp71 of FLV. In heterologous animal species isolated FLV-gp71 induced the formation of broadly reacting antibodies. They were found to be effective in the therapy of infections with FLV in mice as well as with feline leukaemia virus in cats. Most impressive results were obtained with an antiserum prepared against feline leukaemia virus in a goat. This serum completely suppressed sarcomas induced by infection with feline sarcoma virus.

Expression of alien H-2 specificities of a chemically induced BALB/c fibrosarcoma

The presence of alien histocompatibility antigens on the cell surface of the 3-methylcholanthrene-induced BALB/c (H-2d) fibrosarcoma C-1, was investigated by serological and transplantation studied. Absorption experiments with monospecific alloantisera showed that C-1 cells expressed their original private (H-2.4 and 31) and public (H-2.3, 8, 28, and 35) specificities. C-1 cells were also able to absorb monospecific antisera directed to the private specificity H-2.23 of the H-2k haplotype, as well as antisera to the public specificities H-2.1, 5, 11 11 and 25 (H-2k and in part H-2q, H-2a and H-2b haplotypes), which are absent from H-2d normal cells. Conversely, other alien specificities (H-2.2, 17, 30, 32, and 33) were not detected on C-1 cells. The C-1 cells were also unable to absorb the activity of an anti-Ia serum (1-28) directed to 1a.1, 2 and 19 (lak) specificities. Transplantation studies showed that resistance against the challenge of C-1 cells could be induced in syngeneic BALB/c mice by preimmunization with normal tissues from C3Hf and AKR (H-2k), A (H-2a) and C57BL/6J (H-2b) strains (expressing all or some of the extra H-2 antigens of the tumor) whereas no protection was obtained with DBA/2 (H-2d) or with W/Fu rat tissues. The anti-tumor activity could be passively transferred by BALB/c lymphoid cells immune to normal C3Hf, AKR, A, and NIH (H-2q) tissues, but no protection was achieved with lymphoid cells immune to DBA/2 or to W/Fu normal rat tissues. These data indicate that foreign H-2 antigens are expressed on C-1 tumor and that they might function as tumor-associated transplantation antigen which was shown to be present and individually distinct on this sarcoma by appropriate in vivo tests.

Solubilized TSTA and the major viral structural proteins, gp70 and p30, in the immune response to murine leukemias induced by Friend and Rauscher virus

Antigens present in gp70 and p30 purified from Rauscher virus, were tested for immunogenicity in various assays measuring the anti-tumor immune response against lymphocytic leukemias of Friend (FBL-3) or Rauscher (RBL-5) virus origin. p30 had no effect on in vitro cytotoxicity against tumor cell targets mediated by either an anti RBL-5 serum or lymphocytes from animals immunized with FBL-3 cells. gp70 had had no effect on serum-mediated cytotoxicity but used at high concentrations it inhibited cell-mediated cytotoxicity. When used to immunize mice directly against subsequent challenge with the RBL-5 and FBL-3 leukemias, p30 had no discernible effect, while gp70 afforded partial protection against RBL-5 but only at high concentrations. Cell-free preparations of tumor membranes containing negligible amounts of gp70 were antigenically superior to gp70 in both the in vitro and in vivo assays. It is concluded that antigens on these purified proteins that are also expressed on tumor cells are not major targets of the anti-tumor immune response in this system.

Multiple foreign non-H-2 determinants on the surface of a chemically-induced murine sarcoma

By immunizing BALF/c (H-2d) mice against normal tissues from C57BL/6J (H-2d), C3Hf (H-2k) and DBA/2 (H-2d), but not from AKR (H-2k) strains, resistance was induced to the subsequent challenge of the 'syngeneic' methyl-cholanthrene-induced BALB/c sarcoma ST5; lymph node cells from alloimmune BALB/c mice were also able to exert a parallel cytotoxic effect against in vitro cultured ST5 cells. The involvement of foreign H-2 specificities in the observed cross-reactions was ruled out by absorption of H-2 monospecific sera and by the interallelic combinations used, thus suggesting that non-H-2 histocompatibility antigens were responsible for the above findings. By using the indirect isotopic antiglobulin assay, BALF/c anti-C57BL/6J and anti-C3Hf polyspecific sera were found to bind specifically to cultured ST5 cells. C57BL/6J and C3Hf, but not DBA/2, lymph node cells were able to absorb the anti-ST5 activity of the anti-C57BL/6J serum. These results indicated that ST5 cells expressed on their surface at least two different sets of foreign non-H-2 antigens: one shared by C57BL/6J and C3Hf tissues, and detected by both cell-mediated and serological techniques; the other one belonging to DBA/2 tissues, and revealed mainly at the cell-mediated level.

Gross-virus-induced lymphoma in the rat. IV. Cytotoxic cells in normal rats

Lymphoid cells from normal W/Fu rats are cytotoxic in vitro for syngeneic Gross-virus-induced lymphoma cells in a 4 1/2 h 51Cr release test, and protect against tumour growth in vivo when adoptively transferred to syngeneic recipient rats. Cytotoxicity by normal lymphoid cells was greater with in vitro rather than in vivo passaged target cells, and was increased by preincubation of the lymphoid cells at 37 degrees C for 3 h in vitro before their addition to the target cells. Cytotoxic activity, which was localized predominantly in the spleen, was absent at birth but increased until adulthood with some decline in older age. Histocompatibility at the major Ag-B locus was not required for the killer cell--target cell interaction; normal spleen cells of many Ag-B genotypes were cytotoxic for W/FuG-1 target cells, although BDIX and (BDIX X W/Fu)F1 were less active and BN were inactive. The specificity of cytotoxicity was studied by the techniques of direct lysis, competitive inhibition or adsorption to cellular monolayers, using a variety of cell lines. Selectively of lysis or binding was observed and was restricted to rat target cells releasing exogenous or endogenous C-type viruses.

Natural anti-tumor serum reactivity in BALB/c mice. I. Characterization and interference with tumor growth

A natural cytotoxic reactivity directed against syngeneic or allogeneic tumor cells was demonstrated in serum of BALB/c mice by an in vitro cytotoxicity test using rabbit serum as the source of complement. The reactivity, studied on syngeneic fibrosarcoma cells, was found to be minimal in mice less than 10 weeks old and to increase progressively with age. T-deprivation determined an increase of reactivity in young mice to levels reached spontaneously only by the serum of 40-week-old mice. The BALB/c serum also revealed natural anti-thymus antibodies. Non-identity between anti-tumor and anti-thymus antibodies was demonstrated by direct cytotoxicity and absorption tests. An inoculum of syngeneic fibrosarcoma cells increased the level of anti-tumor serum reactivity in both normal and T-deprived young mice. The natural anti-tumor cytotoxicity revelaed in vitro seemed to exert a specific in vivo protection as suggested by the indirect correlation found between the level of the natural anti-tumor reactivity and the grwoth of a transplanted fibrosarcoma.

Interspecies determinants of Friend leukemia virus antigens involved in cytolysis of virus-pfoducing cells

The cytolytic reactivity of a complex goat anti-feline leukemia virus (FeLV) antiserum for mouse cells (Eveline) releasing large quantities of Friend leukemia virus (FLV) was analyzed by the sensitive [14C]nicotinamide release microcytotoxicity assay. Whereas this interspecies killing reactivity could be blocked by absorption of the goat anti-FeLV serum with a preparation of disrupted FLV, absorption with purified FLV gp71, the major envelope glycoprotein, had no effect. Subsequent serum absorptions with the individual FLV structural polypeptides revealed that the lysis of the Eveline cells by the goat anti-FeLV serum is mediated by antibodies recognizing the interspecies determinant of p30, the major internal capsid protein. The expression of this internal viral component at the surface of virus-producing cells is discussed further. The results also demonstrated that removal of approximately 70% of the carbohydrate portion of gp71 with a preparation of glycosidases did not affect the integrity of its interspecies determinant; these results are in agreement with an earlier study (Bolgnesi et al., 1975) that examined primarily the group- and type-specific sites.

Contained indirect viable-cell membrane immunofluorescence microassay for surface antigen analysis of cells infected with hazardous viruses

A microtechnique for an indirect viable-cell membrane immunofluorescence titration assay was developed using Friend murine leukemia virus (F-MuLV)-producing cells and monospecific rabbit antisera to F-MuLV structural antigens. The assay was sensitive and displayed little variation within or between assays. Since moderate-risk tumor viruses, such as recently discovered primate oncornaviruses or feline leukemia virus (FeLV), may be hazardous to laboratory personnel, the assay was adapted for containment of cells infected with such viruses. Cells producing gibbon ape lymphoma virus or FeLV were grown in class III containment cabinets and transferred in sealed flasks to a class II laminar-flow cabinet, where the assay was performed. This micromethod not only conserved reagents but also minimized the numbers of moderate-risk tumor virus-infected cells handled at one time. Centrifugation was contained using custom-made devices shown to form a gas-tight seal over microtiter plates. Interspecies reactivity of monospecific rabbit antisera against F-MuLV structural antigen gp71, but not against p12, was demonstrated for surface antigens on FeLV-producing cells.

Specificity of serum from rodents immune to Moloney C-type virus-induced tumours

When cells are infected by C-type viruses such as Moloney sarcoma/leukaemia virus, new antigens appear on the cell membrane. Mice and rats will respond immunologically to the antigen(s). It was uncertain whether the antigens were related to the viral structural proteins or to non-virion, tumour-specific surface antigens (TSSA) or both. In an 125I-antiglobulin binding assay, Moloney virus completely blocked the binding of mouse and rat sera to virus shedding target cells, thus suggesting that mice and rats recognise only viral proteins. Mice responded to type-specific and rats mainly to group-specific determinants on the virus. Individual Moloney viral proteins were prepared using the guanidine HCl method and were used to block the binding of the rat anti-Moloney immune serum to Moloney virus shedding target cells. By this method, it was demonstrated that the rat serum contains specificities for the viral proteins gp70 and p30, but it was not possible to detect any antibodies directed towards non-virion or TSSA-like molecules.

Serologically detectable specific and cross-reactive antigens on the membrane of a polyoma virus-induced murine tumor

With the aid of an assay measuring complement-dependent cytotoxocity mediated by syngeneic antibodies, we performed a serological analysis of surface antigens of a polyoma-virus-induced murine tumor (SEYF-a). In vivo propagated SEYF-a ascites tumor cells expressed a specific membrane antigen in addition to various other cross-reacting antigens. Among these we could identify at least four separate specificities. Two of these were present on MuLV-induced lymphoma cells, the first on Moloney-virus-induced YAC cells and the second on Gross-virus-induced GHA cells. The third cross-reacting antigen was detected on EL-4 cells. At least one additional specificity was present on two methylcholantthrene-induced murine sarcomas. Normal syngeneic lymphoid cells were insensitive to cytotoxicity mediated by the anti-tumor antisera. Quantitative and perhaps also qualitative differences between that antigenic expression of in vivo propagated on cultured SEYF-a cells were indicated. These studies show that hyperimmune sera produced in syngeneic mice against transplanted tumors may contain a considerable number of antibody specificities, only some of which are specific for the tumor. Furthermore, the results also suggest that polyoma-virus-induced tumors may possess individually distinct antigenic specificities, over and above the known cross-reacting TSTA or TSSA type antigen.

Characterization of the type and group specificities of the immune response in mice to murine leukemia viruses

Normal sera from a variety of strains of inbred mice have precipitating antibodies to murine type C viruses that are detected by radioimmune precipitation assays. The results demonostrate that this humoral immune response is primarily directed against the AKR strain of murine leukemia virus (MuLV) proteins gp71, gp43, and p15(E). These sera also react with Friend- or Rauscher-MuLV in radioimmune precipitation assays. This reaction is not due to a separate immune response, but rather is primarily a consequence of the cross-reactivity of antibodies to the AKR strain of MuLV p15(E) with the p15(E) of these viruses. These data, using autogenous immune sera, emphasize the serological differences of the virion glycoproteins and the serological similarity of the p15(E) virion component of the viruses. Furthermore, based on the serological reactivities to the glycoproteins, the results suggest that the AKR strain of MuLV is endogenous to and expressed in mice, but that the Friend-Moloney-Rauscher virus group is not.

Purification and serological characterization of the major envelope glycoprotein from AKR murine leukemia virus and its reactivity with autogenous immune sera from mice

The major envelope glycoprotein (gp71) from AKR murine leukemia virus (MuLV) was purified and its serological reactivity with heterologous and autogenous immune mouse sera was examined. Homologous and interspecies competition radioimmunoassays using antisera to Rauscher-MulV gp69/71 or Friend-MuLV gp71 or antisera to feline leukemia virus to precipitate 125I-labeled gp71 from various MuLV showed that distinct differences exist between Rauscher- or Friend-MuLV and AKR-MuLV glycoproteins. Characteristically the AKR-MuLV gp71, in contrast to FLV or RLV gp71, does not compete fully in homologous or interspecies radioimmunoassays with iodinated Friend of Rauscher glycoproteins. Purified 125I-labeled AKR-MuLV gp71, in contrast to the Rauscher- or Friend-MuLV glycoproteins, reacts with normal (autogenous immune) mouse sera in direct radioimmune precipitation assays. Competition experiments further demonstrate that this is a predominant immunological reactivity of normal mouse sera which had previously been detected by radioimmune precipitation assay against intact virions.

Detection of private and common tumor-associated antigens in murine sarcomas induced by different chemical carcinogens

Two fibrosarcomas of similar histological type, induced in C3Hf mice by either methylcholanthrene or 3,4-benz(a)pyrene, were shown to have individually unique tumor-rejection antigens in classical transplantation-type experiments. By contrast, sera of autochthonous mice, which resisted only transplants of the immunizing sarcoma, were found to contain complement-dependent cytotoxic antibodies, specific for both sarcomas, in vitro. The existence of individually unique as well as common tumor-associated antigens in chemically-induced murine sarcomas is suggested. The private "tumor transplantation-type" antigens elicited tumor rejection responses in vivo. The common tumor-associated antigens, although immunogenic in autochthonous hosts, inducing the production of tumor-specific antibodies, failed to induce transplantation cross-resistance in vivo. This study supports the contention that, in carcinogen-induced murine tumors, and perhaps in human neoplasms as well the evaluation of humoral (and cell-mediated) immune responses in vitro may not reflect tumor rejection-type immune responses in vivo.

Relationships between membrane antigens of human leukemic cells and oncogenic RNA virus structural components

Leukemic cells from all human chronic granulocytic leukemia (CGL) and some acute myelomonocytic leukemia (AMML) donors are lysed by rabbit antisera to a purified glycoprotein of Friend murine leukemia virus (FLV gp71) in a microcytotoxicity assay. These antisera are not cytotoxic to cells from patients with acute myelocytic leukemia (AML), acute lymphocytic leukemia (ALL), chronic lymphocytic leukemia (CLL), or to peripheral blood lymphocytes from normal donors. A goat antiserum to gradient purified FLV in addition to reacting with cells from CGL and AMML donors also reacted with cells from AML patients and some ALL donors. However, this antiserum failed to react with cells from CLL patients. Peripheral blood and bone marrow leukocytes prepared from leukemic patients in clinical remission failed to react with antisera to FLV and FLV gp71. Absorption experiments demonstrated that the antigen on CGL cells which is reacting with the antiserum to FLV gp71 is also present on normal human platelets and neutrophils. Similar absorption studies showed that the antigen on AML cells detected by the FLV antiserum is not present on normal leukocytes and platelets and appears to be related to the major internal p30 antigens of mammalian RNA tumor viruses. Another antigenic relationship between oncornaviruses and membrane antigens of human leukemia cells was shown by the ability of FLV antigens to absorb the cytotoxic reactivity of nonhuman primate antisera detecting human leukemia-associated antigens. FLV and FLV gp71 antigens were able to absorb all cytotoxic activity of monkey and chimpanzee antisera to human myeloid leukemia antigens when these antisera were tested with CGL cells. These two approaches to an analysis of cross-reactivity indicate that the antigenic determinant(s) detected by the cytotoxic reactions of the FLV gp71 antiserum with human CGL cells is different from the determinant on FLV gp71 which is responsible for the inhibition of the reactivity of simian antisera with CGL cells. Since the goat and rabbit antisera to FLV and FLV gp71 are able to distinguish AML from CGL cells by direct cytotoxicity testing and absorption, they may be valuable reagents for the serological diagnosis of myeloid leukemia. In addition, since peripheral blood cells from AML and CGL patients in clinical remission were seronegative, the antisera may be valuable as management aids. The data in this report indicates that whatever the mechanism of leukemogenesis is in man, cells from CGL and AML patients possess certain membrane antigens which cross-react with FLV structural components such as p30 and gp71.

Alien histocompatibility determinants on the cell surface of sarcomas induced by methylcholanthrene. I. In vivo studies

Groups of BALB/c mice were immunized to normal tissues (skin and/or liver plus kidney) of C3Hf, C57Bl/6, DBA/2 and AKR strains and challenged with either of two syngeneic 3-methylcholanthrene-induced immunogenic sarcomas, ST2 and TZ15, or with a "spontaneous" non-immunogenic BALB/c sarcoma, B2. It was found that anti-C3Hf and anti-DBA/2 immune mice were significantly protected against the growth of ST2, whereas anti-AKR immune mice rejected TZ15; no protection was elicited by immunizing with normal tissues of any strain against B2, which lacked individual tumor-associated transplantation antigens (TATA). The reciprocal experiment, i.e. the immunization of BALB/c mice with tumor cells and challenge with skin grafts of different strains, was also carried out with ST2 and TZ15. Accelerated rejection of all the various allogeneic skins was observed in anti-ST2 immune mice and of AKR and C3Hf skin in anti-TZ15 immune animals. In addition the Winn test demonstrated that lymph-node cells of BALB/c mice immune to C3Hf or DBA/2 tissues were specifically inhibitory for ST2, and that lymph-node cells immune to AKR tissues protected against TZ15. In a further experiment both ST2 and TZ15 tumors were left to grow in (C3Hf X BALB/c)F1, (C57Bl/6 X BALB/c)F1, (BALB/c X DBA/2)F1 and (BALB/c X AKR)F1 mice; the tumors were then excised and the "immune" mice challenged with the related tumor to measure their immune response in comparison with that elicited by the same procedure in BALB/c mice. ST2 was highly immunogenic in syngeneic BALB/c mice and in all the hybrid combinations except (C3Hf X BALB/c)F1 mice, where it completely lost its immunogenicity; TZ15 showed a certain loss of immunogenic strength in (BALB/c X AKR)F1 hybrids. It was concluded that TATA of ST2 contain antigenic determinants expressed on the normal cells of C3Hf and DBA/2 strains, and that TATA of TZ15 are likely to share antigens with AKR normal tissues.

Mitosis is required for production of murine leukemia virus and structural proteins during de novo infection

Cloned 3T3FL cells were synchronized in G1 phase of the cell cycle by deprivation of multiplication stimulatory activity of serum and were then infected with Moloney leukemia virus. Eclipse period of virus could be made to vary from less than 10 to 34 h. All virus release was completely dependent and occurred immediately after the first mitosis following serum reconstitution. Virus yield was not affected by the time of virus inoculation as related to the cell DNA synthetic phase. Colchicine arrested the cells in mitosis and prevented the formation of infectious virus. Viral proteins p10, p30, and gp71 were assayed in cell lysates during the growth curve of virus in synchronized cells. The group-specific determinants of each protein were measured in a competition radioimmunoassay. None of the virus proteins appeared during the eclipse period of the virus. All three proteins appeared simultaneously, coincident with mitosis, and continued to rise during the G1 phase. The absolute quantities of each protein were proportional to the amount of Moloney leukemia virus produced. The relative amounts of some of the viral proteins in the cell did not correspond to their content in purified virions suggesting several possible mechanisms of control.