The generation and specificity of cytotoxic T cells raised against syngeneic tumor cells bearing AKR/Gross murine leukemia virus antigens.

Efforts were made to generate C57BL/6 cytotoxic effector cells to a syngeneic leukemia (E{male}G2) bearing AKR/Gross virus antigens. As we were unable to induce significant cytotoxic activity by immunization with up to 10(8) irradiated E{male}G2 cells, even when cells from such primed animals were subsequently restimulated with E{male}G2 cells in vitro, C57BL/6 mice were immunized with an aliogeneic, virus-producing AKR leukemic cell line (AKR SL3). Peritoneal exudate cells and, to a lesser degree, spleen cells from these mice showed significant lytic activity toward the immunizing allogeneic tumor but not toward E{male}G2. When spleen cells were harvested from animals {approximately equal to}10 d after injection of AKR SL3 and rechallenged in vitro with either E{male}G2 or AKR.H-2(b) SL1, another tumor that displays AKR/Gross virus antigens, then a vigorous cytotoxic response against E{male}G2 and AKR. H-2(b) SL1 was obtained. Effector cells generated by AKR SL3 priming followed by in vitro stimulation with E{male}G2 or AKR.H-2(b) SL1 lysed only cells of H-2(b) haplotype which were strongly positive for the display of serologically detectable AKR/Gross virus antigens. Thus, AKR SL3 cells were not lysed nor were EL4 cells (H-2(b); but only weakly positive for gp70). Cells not bearing the MuLV antigens tested for, such as P815 mastocytoma cells and spleen cell "blasts" from C57BL/6 and CBA (H-2(k)) mice, were also insusceptible to attack. The cytotoxic effector cells induced bore Thy 1.2 alloantigen and were of the Lyt 1+2+ phenotype. Collectively, these findings are consistent with the conclusion that the cytotoxic T cells raised against E{male}G2 are directed against AKR/Gross virus-associated antigens and are H-2 restricted. It will be of interest to determine the relevance of such effector cells to the known resistance of the C57BL/6 mouse to AKR/Gross virus-induced leukemia.

Production of monoclonal antibodies specific for two distinct steric portions of the glycolipid ganglio-N-triosylceramide (asialo GM2).

Two hybrid cell lines were prepared by the fusion of mouse myeloma cells with the spleen cells of BALB/c mice that had been immunized with the glycolipid ganglio-N-triosylceramide (asialo GM2). The specificity of the monoclonal antibodies produced by these hybridomas, one an IgM and the other an IgG3, has been defined by hemagglutination inhibition, complement fixation, and lysis of glycolipid liposomes by antibody and complement. A major determinant recognized by the IgM antibody is the nonreducing terminal N-acetylgalactosamine including the C6 primary hydroxyl group, but excluding the C2-acetamide group of N-acetylgalactosamine, because oxidation with galactose oxidase produced a structure showing only minimal cross-reaction with the IgM but replacement of the N-acetyl group with an N-n-butyryl group produced a glycolipid that reacts with IgM antibody to the same extent as with the unmodified glycoplipd. A major determinant recognized by the IgG3 antibody is the terminal N-acetylgalactosamine including the C2-acetamido group, but excluding the C6 primary hydroxyl group of N-acetylgalactosamine, because replacement of the N-acetyl group with an N-n-butyryl group produced a glycolipid that did not react with the IgG3 antibody; in striking contrast the IgG3 antibody reacted with the C6-oxidized glycolipid as well as with the native glycolipid. Neither antibody reacted significantly with any other natural glycolipids tested including several that are structurally related to asialo GM2 such as ganglioside GM2, ganglio-N-tetraosylceramide (asialo GM1), or ceramide dihexoside. These results indicated that in addition to the fine structure specificity described above both antibodies recognize the nonreducing terminal GalNAc beta 1 leads to 4Gal structure. The strict antigenic specificity of these monoclonal anti-glycolipid antibodies indicates their great potential as specific probes for cell surface studies.

Identification of a human T lymphocyte surface protein associated with the E-rosette receptor.

We describe a new monoclonal murine antibody that reacts with a 50,000-mol wt polypeptide that appears to be present on all E-rosetting cells. We conclude that this antigen is either identical to or closely associated with the E receptor because of (a) the high degree of concordance between E-rosette formation and 9.6 antigen expression, (b) the inhibition of rosette formation by preincubation of cells with 9.6 antibody, and (c) the observed failure of cells lysostripped of 9.6 antigen to form E-rosettes. This last finding suggests cocapping of 9.6 antigen and the E receptor.

Antibody to leukemia virus: widespread occurrence in inbred mice.

Mice from a wide variety of inbred strains produce immunoglobulin G antibody against murine leukemia virus. This is contrary to the common view that the mouse is immunologically tolerant to its endogenous leukemia virus.

Mouse leukemia: therapy with monoclonal antibodies against a thymus differentiation antigen.

Monoclonal antibodies against a thymus cell differentiation antigen (Thy-1.1) were effective in the therapy of a transplanted mouse leukemia. Passive immunization resulted in high titers of cytotoxic antibody in the serum of treated mice and the suppression of metastatic tumor cells. The tumor-suppressive effects of the monoclonal antibodies were amplified by the administration of exogenous complement. This combined antibody and complement therapy resulted in the cure of leukemia in a significant proportion of the treated animals.

Endogenous oncornaviruses in chemically induced transformation. II. Effect of virus production in vivo.

C3H/HeJ and AKR/J mice differed in their susceptibility to 3-methylcholantrhene (MCA)-induced sarcomagenesis (86% incidence of sarcomas in C3H by 18 wk; 5% incidence in AKR by 18 wk) and in the production of endogenous murine leukemia virus (MuLV) (AKR produced greater than 10(5) plaque-forming units/ml tail extract in XC test; C3H did not produce detectable virus.) A genetic corss between C3H and AKR mice was examined to determine the relationship of virus production to oncogenesis by MCA. Mice of the (C3H X AKR)F X C3H backcross were typed for the production of infectious MuLV by tail biospy and then inoculated with MCA. Of the backcross mice, 81% produced high titers of ecotropic MuLV; the remaining 19% did not contain detectable infectious MuLV. The virus-producing and non-virus-producing backcross mice were equally sensitive and highly susceptible to MCA-induced sarcomagenesis. Tumors of all virus-positive mice contained infectious MuLV. Some tumors (54%) of virus-negative mice also contained infectious MuLV; this indicated the induction of endogenous MuLV in the tumors of these mice. We concluded that the overt production of MuLV in mice of this backcross did not function in the sensitivity of the mice to sarcoma induction by MCA. Furthermore, the presence of virus in some chemically induced tumors was due to an induction pehnomenon independent of the primary oncogenic event.

Cell-specific cytotoxicity expressed by a conjugate of ricin and murine monoclonal antibody directed against thy 1.1 antigen.

The isolation and characterization are described of a conjugate between ricin, and a thy 1.1-specific monoclonal IgG2a murine antibody synthesized using N-succinimidyl-3-(2-pyridyldithio)propionate. The conjugate selectively inhibited protein synthesis in Thy 1.1-positive (AKR SL3) mouse leukemia cells compared to Thy 1.2-positive (AKR/Cu SL1) cells.

Cytotoxic activities of monoclonal antibodies against the envelope proteins of murine leukemia virus.

Monoclonal antibodies against the envelope proteins [gp70 and p15(E)] of murine leukemia virus react with the cell surface of virus-infected cells. The specificity and potency of these antibodies exceed those observed with conventional polyvalent antisera. In cytotoxic assays, certain of the monoclonal anti-gp70 antibodies demonstrate 1000-fold differences in their titer on leukemic and normal thymus cells.

Alteration of lymphoid cells in AKR mice by treatment with monoclonal antibody against Thy-1 antigen.

AKR/J mice treated with high levels of monoclonal anti-Thy-1.1 antibody and C' remained healthy without apparent side effects. Examination of the lymphatic organs of these mice demonstrated a selective depletion of T cells in lymph nodes and spleen. Following cessation of treatment of the levels of anti-Thy-1.1 antibody in the circulation fell and the peripheral lymphatic organs gradually became repopulated with T cells. Depletion occurred in lymph nodes whether or not C' was infused along with the antibody. Although the thymocytes of these mice were coated with anti-Thy-1.1 antibody they were not eliminated by the treatment. The elimination of peripheral but not thymic T cells suggests either a thymic barrier to the penetration of cofactors (possibly antibody-dependent effector cells) or that antibody acts by interfering with the normal traffic of peripheral T cells which normally "home" to the lymph nodes and spleen.

Genetic control of natural immunity to ecotropic mouse leukemia viruses: immune response genes.

Humoral immune response to ectropic leukemia viruses in AKR and C57BL/6 mice was controlled by a gene that mapped in linkage group IX. Mice of the AKR strain had an immune nonresponsive allele of this gene, whereas mice of the C57BL/6 strain had an immune responsive allele. Antibody against murine leukemia virus (MuLV) reacted primarily with p15 protein of the viral envelope. It was concluded that the failure to find antibody production in AKR mice was the result of a genetic immunological defect, rather than the result of immunological tolerance that was induced by the persistent viremia of endogenous MuLV.

Cell surface antigens associated with murine leukemia virus: definition of the GL and GT antigenic systems.

Two new serological specificities were identified on the surface of murine leukemia virus (MuLV)-infected cells by direct and absorption immunofluorescence tests. Both antigens were detected with antisera prepared in rats that were growing transplants of syngenic MuLV-induced leukemias. Antigen G(L) was defined with the AKR leukemia K36 as the test cell; antigen G(T) was defined with the W/Fu leukemia C58(NT)D as the test cell. G(L) and G(T) antigens were serologically and genetically independent of the MuLV-induced Gross and G(IX) cell-surface antigens. G(L) and G(T) antigens were found in normal lymphoid cells of mice from high-leukemic strains, but not in lymphoid tissues of mice from most low-leukemic strains. Tumors and leukemias of mice of low-leukemic strains often were G(L) and G(T) positive. Similarly, infection of normal cells with MuLV resulted in expression of G(L) and G(T). With ferritin-labeled antibody the G(L) and G(T) antigens were observed on virus-free segments of the cell surface. Genetically, G(L) and G(T) antigens were each controlled by two dominant unlinked genes in AKR mice; these same antigens were each controlled by three or more dominant unlinked genes in C58 mice. Penetrance of G(L) and G(T) regulatory genes was dependent upon the Fv-1 genotype of the host. Expression of G(L) antigen was closely associated with virus production, whereas expression of G(T) antigen was less closely associated.

Identification of the Gross cell surface antigen associated with murine leukemia virus-infected cells.

The Gross cell surface antigen (GCSA) is produced by cells that are either exogenously infected with murine leukemia virus (MuLV) or are expressing endogenous MuLV genomes. In immune precipitation assays, GCSA was resolved into two serologically distinct 85,000- and 95,000-dalton viral proteins. These antigenic components are glycosylated forms of the polyprotein precursors of the MuLV internal structural proteins.

Anomalous reactions of mouse alloantisera with cultured tumor cells. II. Cytotoxicity is caused by antibodies to leukemia viruses.

Certain alloantisera prepared in mice against H-2 region membrane antigens were found to be unexpectedly cytotoxic for murine sarcoma and leukemia cells in culture. This anomalous cytotoxicity was shown to be the result of antibody in these alloantisera directed against the p15 and gp70 envelope proteins of Mu LV which were present on the surface of the tumor target cells. Sera from aged unimmunized mice of strains used for the preparation of alloantisera also contained antibodies against MuLV protein p15 and gp70 that were cytotoxic for sarcoma and leukemia cells, which indicates that these antibodies occurred naturally in mice. These results independently confirm earlier findings of the widespread occurrence in mouse serum of antibodies reactive with MuLV. The presence of antibody against MuLV in mouse serum which can cause cytotoxic reactions with tumor cells points to the fact that particular caution should be used during the typing of murine sarcomas or leukemias for cell surface antigens, since mouse antisera may yield cytotoxicity (or other serologic reactions) based on anti-MuLV specificities, rather than on anticipated antigens.

Endogenous ecotropic mouse type C viruses deficient in replication and production of XC plaques.

Endogenous ecotropic type C viruses were induced by iodedeoxyuridine from nontransformed and chemically or spontaneously transformed clones of the C3H/10T1/2 cell line. Viruses produced by cells of certain transformed clones were N-tropic and formed large XC plaques. In contrast, viruses produced by nontransformed C3H/10T1/2 cells were not detectable in the XC plaque test. These XC- viruses infected mouse cells with high efficiency, as shown by the induction of murine leukemia virus group-specific antigens in infected cells, but virus production, as determined by DNA polymerase-containing particles, was extremely low. Upon growth in certain mouse cells these replication-deficient, XC(-) viruses converted to type C viruses that were similar in XC assays to N-tropic AKR virus (XC+).