Cytogenetic study of spontaneous lympholeukemia in AKR mice in the process of its transplantation to an isogeneic line of animals]

Spontaneous leucosis was cytogenetically studied in subsequent generations (from 1 to 150) of AKR mice. By means of the differential staining technique of chromosomes, large variations in chromosome numbers were found in the karyotypes of leucotic cells of different generations, and the formation of cell clones containing different marker chromosomes as well as the dominance of a hyperdiploid clone with 41-42 chromosomes was revealed. Chromosome analysis of such hyperdiploid cells of the 150th generation has indicated that the supernumerary chromosomes (in 88.0% of cases examined) belong to the smallest chromosomes of the mouse karyogramm (to the 18-19th chromosome pairs or to chromosomes smaller than those of 19th pair). Similar trisomy was also observed in hypodiploid and pseudodiploid leucosis cells. It is suggested that the cell clone with trisomy for the smallest chromosomes is specific to the spontaneous lympholeucosis in AKR mice as well as to the leucosis transplanted to isogenic mice for a number of subsequent generations. Increased rate of hyperdiploid cells was associated with a generalization of leucosis. It was concluded that the development rate and the severity of transplanted lympholeucosis in AKR mice was determined by the domination of the cell clone with trisomy for the 18-19th chromosome pairs in the population of leucotic cells.     

DNA methylation affecting the expression of murine leukemia proviruses.

The endogenous, vertically transmitted proviral DNAs of the ecotropic murine leukemia virus in AKR embryo fibroblasts were found to be hypermethylated relative to exogenous AKR murine leukemia virus proviral DNAs acquired by infection of the same cells. The hypermethylated state of the endogenous AKR murine leukemia virus proviruses in these cells correlated with the failure to express AKR murine leukemia virus and the lack of infectivity of cellular DNA. Induction of the endogenous AKR murine leukemia virus proviruses with the methylation antagonist 5-azacytidine suggested a causal connection between DNA methylation and provirus expression. Also found to be relatively hypermethylated and noninfectious were three of six Moloney murine leukemia virus proviral DNAs in an unusual clone of infected rat cells. Recombinant DNA clones which derived from a methylated, noninfectious Moloney provirus of this cell line were found to be highly active upon transfection, suggesting that a potentially active proviral genome can be rendered inactive by cellular DNA methylation. In contrast, in vitro methylation with the bacterial methylases MHpaII and MHhaI only slightly reduced the infectivity of the biologically active cloned proviral DNA. Recombinant DNA clones which derived from a second Moloney provirus of this cell line were noninfectious. An in vitro recombination method was utilized in mapping studies to show that this lack of infectivity was governed by mechanisms other than methylation.     

Gene expression in chemically transformed mouse embryo cells: selective enhancement of the expression of C type RNA tumor virus genes.

Treatment of a nontumorigenic clone of AKR mouse embryo cells in culture with a variety of polycyclic aromatic hydrocarbons has resulted in the development of derivative clones which are highly tumorigenic and exhibit other characteristics of the transformed phenotype. A 3-methylcholanthrene-transformed derivative clone (clone MCA) has been compared to the parent clone (clone 2B) with respect to the abundance and diversity of polysomal poly(A)-containing mRNA sequences. Hybridization kinetic experiments show that the poly(A)-containing sequences of both clones are organized into indistinguishable abundance classes, and that the vast majority of the sequences are common to both the parent and derivative clones. The levels of two specific messenger RNAs (α- and β-globin mRNA) which characterize highly differentiated mouse erythroid cells were much less than 1 molecule per cell in either cell type. Titration of a balanced complementary DNA probe to AKR murine leukemia virus (AKR-MuLV) 70S RNA with purified polysomal poly(A)-containing RNA from both parent and derivative clones shows that approximately 5000 and 1200 viral 35S RNA equivalents are present in the cytoplasm of growing and resting clone MCA cells, respectively. Rapidly growing clone 2B cells contain less than about 30 viral 35S RNA equivalents per cell. Viral specific sequences therefore correspond to members of the high abundance class of poly(A)-containing RNA sequences in clone MCA cells and to the low abundance class of sequences in clone 2B cells. Within the limits of detection, this large increase in abundance is characteristic only of viral specific RNA sequences.     

Leukemia prevention and long-term survival of AKR mice transplanted with MHC-matched or MHC-mismatched bone marrow

The current studies were designed to evaluate the effectiveness of marrow transplantation within and outside the major histocompatibility complex (MHC) on the long-term survival and occurrence of spontaneous leukemia in AKR mice. AKR mice, which were lethally irradiated and received MHC-matched marrow from CBA/J mice (CBA----AKR), never developed leukemia and were alive and remained healthy for up to 280 days post-transplant. These long-term surviving chimeras possessed substantial immune vigor when both cell-mediated and humoral responses were tested. Lethally irradiated AKR mice, which had received MHC-mismatched marrow (anti-Thy-1.2 treated or nontreated) from C57BL/6J mice (B6----AKR), never developed leukemia and survived up to 170 days post-transplant. However, both groups of these chimeras began dying 180 to 270 days post-transplant due to a disease process which could not be readily identified. Histological analysis of B6----AKR chimeras revealed severe lymphoid cell depletion in thymus and spleen; however, none of these chimeras exhibited classical features of acute graft versus host disease. Concanavalin A mitogenesis, primary antibody responses to sheep red blood cells and the production of interleukin 2 (IL-2) were suppressed in B6----AKR chimeras. IL-2 treatment of B6----AKR chimeras was shown to partially correct these deficiencies without stimulating mixed lymphocyte responsiveness to donor or host lymphocytes. These studies indicate that the use of MHC-mismatched marrow for the prevention of spontaneous AKR leukemia may rely on augmentative IL-2 therapy for complete immune reconstitution of leukemia-free chimeras.     

Resistance to cell-mediated cytotoxicity is correlated with reduction of H-2K gene products in AKR leukemia

AKR leukemia cell lines differing in the amount of H-2K and H-2D antigens expressed on the cell surface were used to assess cell-mediated immune responses in syngeneic mice against Gross/AKR murine leukemia virus (MuLV)-induced tumors. Leukemic cells with reduced expression of H-2K^k antigens were inactive as inducers of Gross-MuLV/H-2^k-specific cytotoxic T lymphocytes (CTL) and resistant to lysis by CTL raised against H-2K^k positive AKR leukemia cells. H-2K^k positive leukemias induced cytotoxic effectors, which upon restimulation in vitro, lysed the stimulating and other H-2K^k positive leukemia cells. In antibody inhibition experiments, T-cell-mediated cytotoxicity to these leukemias could only be inhibited by antisera and monoclonal antibodies specific for the H-2K^k antigens. Due to this specific role of H-2K^k antigens in T-cell cytotoxicity to Gross/AKR MuLV-induced tumors, reduced expression of H-2K^k antigens on spontaneous AKR leukemic cells could have important implications for surveillance of these neoplastic cells.Abbreviations used in this paper CTL cytotoxic T lymphocytes - MuLV murine leukemia virus     

Characterization of alloimmunization-induced T lymphocytes reactive against AKR leukemia in vitro and correlation with graft-vs-leukemia activity in vivo

We have reported that immunization of H-2k mice with lymphoid cells from various allogeneic strains induced a population of cells that could eliminate first-passage spontaneous AKR leukemia from the spleens of immuno-suppressed AKR (H-2k) hosts. In the present study, we examined the nature of the cells responsible for this graft-vs-leukemia (GVL) reaction and compared them to cytolytic cells detected in vitro. Spleen cells from alloimmunized CBA/J (H-2k) mice were selectively depleted of various subpopulations by treatment with antibody and complement (C), then tested in vivo for GVL reactivity. Cell suspensions depleted of Thy-1.2+, Lyt-1+, or Lyt-2+ lymphocytes had no significant GVL reactivity, whereas suspensions depleted of NK-1.2+ cells retained GVL reactivity. The GVL-reactive cells persisted in H-2-compatible donor mice for up to 56 days. Lyt-1+2+ lymphocytes that were cytotoxic for cultured AKR leukemia cells in vitro could be detected in the spleens of alloimmunized H-2-compatible mice after expansion of the cells in T cell growth factor. Using quantitative limiting dilution cytotoxicity assays, we found that the frequency of leukemia-reactive cytotoxic lymphocytes (CL) in the spleen showed a direct correlation with the GVL efficacy of the cells in vivo. Alloimmunization was essential for induction of the GVL-reactive cell population. CL in alloimmunized mice consisted of heterogeneous cytotoxic specificities; i.e., some CL were leukemia-specific, others lysed only nonleukemic AKR target cells, and a third group mediated killing of both leukemic and nonleukemic target cells. The CL appeared to be H-2 restricted and specific for non-H-2 antigens shared by the AKR leukemia and the alloimmunizing cells.     

Influence of T-lymphocyte deprivation on the antileukemic effect of bacillus calmette-guérin in vivo

Summary The effect in AKR mice of T-lymphocyte deprivation in vivo, obtained by adult thymectomy plus/minus whole-body irradiation and bone-marrow reconstitution, was studied in the growth of grafted leukemia cells obtained from spontaneous AKR leukemia. Both thymectomized mice and mice subjected to thymectomy, whole-body irradiation, and bone-marrow reconstitution (B) had a lower take-frequency of graft leukemia than conventional mice. Growth of graft leukemia was inhibited by BCG treatment both in thymectomized mice and in B mice. Concomitant with the increased inhibition of leukemia growth, an increased incidence of wasting-like disease was observed. In vitro cytotoxicity studies revealed that spleen lymphoid cells from nonleukemic mice were cytotoxic to AKR leukemia cells, to nonmalignant AKR fibroblasts, and to other nonmalignant cells with H-2^k haplotype. The activity of this self-directed cytotoxicity was most marked in AKR mice with wasting-like disease. The presence of autocytotoxic cells was frequently associated with a positive direct Coombs' test. Immunofluorescence studies showed, further, that the cytotoxic activity was independent of retrovirus antigens as tested by indirect immunofluorescence with anti-MuLV antibodies. Adult thymectomy of AKR mice confers an increased antitumoral immune potential, but also an increased risk of development of serious autoimmune disease.     

Host Effect on Arbovirus Replication: Appearance of Defective Interfering Particles in Murine Cells

Serial passage of Semliki Forest virus (SFV) in chicken embryo cells had little effect on SFV yield; however, high multiplicity infection of murine cells with one of the late passage pools (passage 9 SFV) resulted in a virus yield 10- to 20-fold lower than that obtained with earlier passage virus and 80-fold lower than the corresponding yield in chicken cells. This effect was accompanied by a striking decrease in the levels of 42S and 26S RNA and by increased proportions of a small single-stranded viral RNA (molecular weight, 9 x 10(5)) and of a low-molecular-weight replicative form. There was also a reduction in the number of specific membranous structures previously associated with the group A arbovirus replication complex. These results suggested that passage 9 SFV contained defective interfering particles which were detected more readily after one passage in a murine indicator host cell. Identical results were obtained with two different murine cell lines: one a leukemia virus-free clone of AKR cells and the other JLS-V9 cells chronically infected with Rauscher leukemia virus. Host production of RNA tumor virus particles apparently did not affect arbovirus replication.     

Genes controlling receptors for ecotropic and xenotropic type C virus in Mus cervicolor and Mus musculus.

Gene loci controlling cell surface receptors for murine leukemia virus were studied by using murine X Chinese hamster hybrid cells. Hybrids which exclusively segregate murine chromosomes were made by fusing Mus cervicolor and Mus musculus lymphocytes to hamster fibroblasts. Sensitivity to Moloney murine leukemia virus infecotion and specific binding of the envelope glycoprotein of Rauscher murine leukemia virus (gp70) cosegregate and isozyme analysis show an association with chromosome 5 in both species. With the possible exception of one clone, no evidence was found for a proviral integration site independent of chromosome 5. Evidence is presented for additional unlinked ectropic and xenotropic receptors independent of chromosome 5.     

H-2-specific antibodies induced by injection of syngeneic leukemia cells

AKR/J mice immunized with several syngeneic leukemia cells contained antibodies in their sera which reacted with certain AKR leukemia cell lines, depending on their H-2 expression, and precipitated H-2K antigens from lysates of leukemia cells. Precipitation of H-2K was not due to virus-specific antibodies: it could not be blocked by prior absorption with H-2-negative leukemias, but was blocked by certain allogeneic lymphocytes. Tumor-specific H-2K antibodies did not react with H-2K from normal AKR lymphocytes either on the cell surface or after detergent solubilization; however, they did react with H-2K from mitogen-activated AKR and BALB.K lymphoblasts. Since both these latter cells were also lysed by AKR-Gross/MuLV-specific and H-2K^k-restricted cytotoxic T lymphocytes, we consider the possibility that antibodies detecting conformational alterations induced in H-2K^k molecules by viral association may be present in syngeneic AKR antileukemia sera.Abbreviations used in this paper GCSA Gross-virus-induced cell-surface antigen - MCF mink cell focus-forming virus - MuLV murine leukemia virus - Th T helper     

AKR.H-2b lymphocytes inhibit the secondary in vitro cytotoxic T-lymphocyte response of primed responder cells to AKR/Gross murine leukemia virus-induced tumor cell stimulation.

We have previously shown that AKR.H-2b congenic mice, though carrying the responder H-2b major histocompatibility complex haplotype, are unable to generate secondary cytolytic T-lymphocyte (CTL) responses specific for AKR/Gross murine leukemia virus (MuLV). Our published work has shown that this nonresponsive state is specific and not due to clonal deletion or irreversible functional inactivation of antiviral CTL precursors. In the present study, an alternative mechanism based on the presence of inhibitory AKR.H-2b cells was examined. Irradiated or mitomycin C-treated AKR.H-2b spleen cells function as in vitro stimulator cells in the generation of C57BL/6 (B6) anti-AKR/Gross virus CTL, consistent with their expression of viral antigens. In contrast, untreated viable AKR.H-2b spleen cells functioned very poorly as stimulators in vitro. Viable AKR.H-2b spleen cells were also able to cause dramatic (up to > or = 25-fold) inhibition of antiviral CTL responses stimulated in vitro by standard AKR/Gross MuLV-induced tumor cells. This inhibition was specific: AKR.H-2b modulator spleen cells did not inhibit allogeneic major histocompatibility complex-specific CTL production, even when a concurrent antiviral CTL response in the same culture well was inhibited by the modulator cells. These results and those of experiments in which either semipermeable membranes were used to separate AKR.H-2b modulator spleen cells from AKR/Gross MuLV-primed responder cells or the direct transfer of supernatants from wells where inhibition was demonstrated to wells where there was antiviral CTL responsiveness argued against a role for soluble factors as the cause of the inhibition. Rather, the inhibition was dependent on direct contact of AKR.H-2b cells in a dose-dependent manner with the responder cell population. Inhibition was shown not to be due to the ability of AKR.H-2b cells to function as unlabeled competitive target cells. Exogenous interleukin-2 added at the onset of the in vitro CTL-generating cultures partially restored the antiviral response that was decreased by AKR.H-2b spleen cells. Positive and negative cell selection studies and the development of inhibitory cell lines indicated that B lymphocytes and both CD4- CD8+ and CD4+ CD8- T lymphocytes from AKR.H-2b mice could inhibit the generation of AKR/Gross virus-specific CTL in vitro. AKR.H-2b macrophages were shown not to be required to demonstrate AKR/Gross MuLV-specific inhibition, however, confirming that the inhibition by T-cell (or B-cell)-depleted spleen populations was dependent on the enriched B-cell (T-cell) population per se.(ABSTRACT TRUNCATED AT 250 WORDS)     

AKR leukemogenesis: identification and biological significance of thymic lymphoma receptors for AKR retroviruses.

We have previously demonstrated that in vitro cell lines of mouse thymic lymphomas express surface receptors specific for the retrovirus that induced them. This study extends these observations to an analysis of receptor-bearing cells in the preleukemic and leukemic phases of spontaneous AKR thymic lymphomagenesis. AKR mice regularly begin expressing N-tropic retroviruses (as assayed on NIH fibroblasts by the XC plaque assay) in several tissues early in life; thymic lymphocytes also express these viruses, but are not autonomously transformed. Later thymic lymphomas emerge which are capable of metastasizing in the host of origin or transplanting leukemias into syngeneic hosts. Just prior to the appearance of thymic lymphomas, these mice also begin producing xenotropic retroviruses [as assayed in xenogeneic (For example, mink) fibroblasts], and concomitant with the appearance of the leukemias is the appearance of "recombinant" retroviruses which cause mink fibroblast foci (MCF); these viruses express elements of both N- and X-tropic virus envelopes and N-tropic viral gene products in their cores. Spontaneous AKR leukemias also produce other retroviruses which do not cause XC plaques or mink fibroblast foci; these are called SL viruses. The subject of this study was to test whether in vivo thymocytes in the preleukemic and leukemic periods also bear receptors specific for N-tropic, recombinant MCF and SL AKR retroviruses. We demonstrated that each spontaneous thymic lymphoma does bear receptors that bind viruses produced by the lymphomas and MCF-247 to a high degree and that bind N-ecotropic AKR retroviruses less well. Thymic lymphocytes predominating in the preleukemic period do not express detectable levels of receptors for either of the viruses. In some mice, receptor-positive cells co-exist with receptor-negative cells; only the receptor-positive cells are capable of transplanting leukemia to syngeneic hosts. We conclude that the presence of specific cell surface receptors for lymphoma cell-produced and recombinant AKR retroviruses is a marker for leukemia in these hosts.     

Elimination of leukemia in the absence of lethal graft-versus-host disease after allogenic bone marrow transplantation

Donor T cells are able to effect a graft-vs-leukemia (GVL) response but also induce graft-vs-host disease (GVHD) after allogeneic bone marrow transplantation. We used an AKR leukemia murine transplant model, analogous to human acute lymphoblastic leukemia, in which donor T cells expressed a thymidine kinase suicide gene, to test whether separation of GVL and graft-vs-host (GVH) responses was feasible by selectively eliminating alloactivated donor T cells at defined time points posttransplant. Under experimental conditions where untreated mice could not be cured of disease without dying from GVHD, mice transplanted with thymidine kinase-positive T cells and subsequently administered ganciclovir (GCV) could eliminate leukemia without lethal GVHD. Timing of GCV administration, donor T cell dose, and preexisting leukemia burden were observed to be critical variables. Eradication of leukemia without lethal GVHD in GCV-treated mice implied that the kinetics of GVL and GVH responses were asynchronous and could therefore be temporally dissociated by timely GCV administration. That this strategy was feasible in a murine leukemia model in which GVHD and GVL reactivity are tightly linked suggests that this approach may be relevant to the treatment of selected human leukemias where similar constraints exist. This strategy represents an alternative approach to separating GVL and GVH reactivity and challenges the current paradigm that separation of these responses is dependent upon the administration of donor T cells with restricted specificity for leukemia as opposed to host Ags.     

Immunoadjuvant treatment of primary grafted and spontaneous AKR-leukemia. I. Treatment efficiency correlated to autoimmune reactivity.

Young AKR mice grafted i.v. with 10(1) or 10(3) cells from spontaneous AKR thymomas were treated with repeated i.v. injections of BCG or subcutaneous injections of irradiated AKR thymoma cells. BCG often cured mice from graft leukemia, whereas the effect of irradiated thymoma cells was less effective. Mice that did not develop graft-leukemia after graft of 10(1) leukemia cells and BCG treatment showed a spontaneous leukemia in 30% of the cases later. Ninety percent of nongrafted mice developed spontaneous leukemia whether BCG-treated or not. General immune reactivity as assessed in individual mice by T and B lymphocyte mitogen tests as well as the hemolytic plaque-forming cell assay had no clear correlation to the effects of immune adjuvants in respect to survival. In contrast, occurrence of self-directed immune reactions were clearly correlated to survival and cure of grafted and BCG-treated mice as revealed by assays both in vitro and in vivo. However, 13 to 25% of the mice apparently cured of leukemia developed a wasting-like syndrome that sometimes terminated in death. The immplications of self-directed immune reactions as mediators of the anti-neoplastic effects of immunoadjuvants.     

Resistance to transplantation of spontaneous AKR lymphoma cells by substrains of AKR mice. In vivo resistance and generation of an H-2 restricted CML response.

High leukemia incidence AKR/J (H-2k, Thy 1.1) and AKR/Cu (H-2k, Thy 1.2) substrains of AKR mice reject the reciprocal strains spontaneously arising lymphoma cells. In the course of rejection, splenic precursor cells are generated which, upon secondary stimulation in vitro, result in specific cytotoxic T-cells. The antigenic component of AKR cells resulting in this secondary CML response resides on both lymphoma and normal T- and B-cells, and is distinct from the Thy antigen. Primed AKR/J lymphocytes will respond to and only lyse immunogens and targets homologous at the K- and-or D-end of the MHC, while primed AKR/Cu cells require homology at the D-end of the MHC.     

Expression of CTL-defined, AKR/Gross retrovirus-associated tumor antigens by normal spleen cells: control by Fv-1, H-2, and proviral genes and effect on antiviral CTL generation

In previous studies we have characterized H-2-restricted cytolytic T lymphocytes (CTL) type specific for Gross cell surface antigen-positive tumor cells induced by AKR/Gross leukemia viruses. The generation of such CTL was shown to be controlled by at least three genetic loci including H-2 and Fv-1. The Fv-1n phenotype was able to negate positive immune response gene effects of the H-2b haplotype. Fv-1n-mediated inhibition appeared to operated by allowing the early expression by normal cells of N-ecotropic leukemia virus-related antigens recognized by the antiviral CTL, perhaps via tolerance induction. In the present study, the expression of CTL-defined viral antigens by normal cells is further considered. Possible gene dosage effects by H-2 as well as Fv-1 and the other virus-related (V) genes, including proviral structural loci, were examined by comparison of a panel of congenic and F1 mice. These experiments indicated that the quantitative level of expression of CTL-defined viral antigens was primarily controlled by the Fv-1 genotype. Gene dosage effects were also observed for the V genes and, in some situations, for H-2. The importance of the early display of viral antigens by normal cells was underscored by the inability of those mice to generate specific antiviral CTL responses. Even strains expressing low levels of viral antigens, such as responder X nonresponder (AKR.H-2b:Fv-1b X AKR.H-2b)F1 mice, failed to respond. These results are discussed with respect to the inability of mice of the AKR background to respond with specific antiviral CTL generation and in light of their high incidence of spontaneous leukemia.     

Viral proteins expressed on the surface of murine leukemia cells.

Leukemic cells of AKR mice contain as constituents of their membranes the murine leukemia virus envelope protein gp70 and the precursor polyprotein of the viral internal (core) structural proteins. Both gp70 and the core polyprotein are represented on the cell surface as glycoproteins, as evidenced by incorporation of [3H]glucosamine into their structure and the binding of these proteins to lectins. The glycosylated core polyprotein exists in at least two serologically distinguishable forms: the 95,000-dalton polyprotein reacts with antisera prepared against the viral proteins p30, p12, and p10, whereas the 85,000-dalton polyprotein reacts with antisera prepared against the viral proteins p30 and p12, but not p10. Additional heterogeneity in these cell surface polyproteins has been observed wtih leukemias induced by exogenous leukemia viruses. Spontaneous leukemia cells of AKR mice invariably express gp70 and the core polyprotein on their cell surface; normal thymocytes of young AKR mice express gp70, but not the core polyprotein on their surface.     

Immunologic characteristics in relation to high and low leukemogenic activity of radiation leukemia virus variants. I. Cellular analysis of immunosuppression.

Infection of adult C57BL/6 mice with variants of the radiation leukemia virus resulted in variable leukemia incidence. One variant, designated D-RadLV, induced lymphatic leukemia in 0 to 25% of mice after virus inoculation directly into the thymus of young adult mice. The leukemia incidence could be increased to 80 to 100% by host exposure to x-rays. The second variant, A-RadLV, induced lymphatic leukemia in 80 to 100% of similarly inoculated mice without the need for additional radiation treatment. Adult mice were inoculated with D-radLV or A-RadLV. Both variants reduced the immune response to sheep erythrocytes whereas only D-RadLV had an immunosuppressive effect after immunization with a thymus-independent immunogen polyvinyl-pyrrolidone (PVP). Results of transfer experiments indicated that the immunosuppressive effects were expressed at the immunocompetent cell level. Thymus-derived cells were affected by A-RadLV since their immunocompetent function was impaired, whereas D-RadLV affected the marrow cell population of immunocytes. Exposure of D-RadLV-inoculated mice to x-rays induced functional impairment of both thymus and marrow cells. Since the radiation leukemia virus induces "T" lymphatic leukemia it could be proposed that the initial tropism of the virus to thymocytes would lead to high leukemia induction potential, whereas virus tropism to bone marrow cells would yield a low leukemia incidence. The coleukemogenic effect of x-rays could perhaps be related with its capacity to alter and introduce a change in virus-lymphoid cells interaction.     

Effect of immunosuppression or immunostimulation on the growth rate of a lymphoid and of a myeloid leukemia in mice

Summary The influence of immunosuppression or immunostimulation on the growth rate of a lymphatic and of a myeloid murine leukemia has been investigated in syngeneic host-tumour relation. Immunosuppression by chemotherapy or X-rays, induced before transplantation of leukemia cells, did not change the survival time of the animals. Treatment with the immunosuppressive drug cortisone which is not cytostatic for these leukemias, if instituted after the transplantation of malignant cells, enhanced the growth rate of the lymphatic leukemia. Nonspecific stimulation with Corynebacterium parvum induced resistance to a graft of lymphatic leukemia in a majority of the mice, but only slowed the growth rate of myeloid leukemia, without preventing death. Immunosuppressive treatment, given before C. parvum, completely blocked the induction of resistance, and if given after C. parvum, abolished the established resistance to lymphatic leukemia. Thus, the danger of immunosuppression accompanying chemotherapy may lie in its abrogating the protective effects of nonspecific immunostimulation.Abbreviations PFC = plaque-forming-cell - SRBC = sheep red blood cell - cort. = cortisone - cyclo. = cyclophosphamide - L-asp. = L-asparaginase - mtx. = methotrexate - ara C = cytosine arabinoside - C.p. = Corynebacterium parvum     

Genetic control of the induction of cytolytic T lymphocyte responses to AKR/Gross viral leukemias. II. Negative control by the Fv-1 locus in AKR mice of responder H-2b haplotype

To assess whether the presence of a responder H-2b haplotype would be sufficient to allow mice of nonresponder "high leukemic" phenotype to generate syngeneic anti-AKR/Gross virus cytolytic T lymphocytes (CTL), the AKR.H-2b strain was examined. Although capable of mounting vigorous apparent anti-minor histocompatibility-specific CTL responses, AKR.H-2b mice failed to produce anti-viral CTL after a variety of stimulation protocols. In contrast, the "doubly congenic" AKR.H-2b:Fv-1b strain was able to respond with substantial levels of H-2-restricted anti-AKR/Gross virus CTL activity. These results indicated that Fv-1n alleles could exert negative epistatic control over responder H-2b-encoded gene(s). Because the B6.Fv-1n congenic was also able to generate anti-viral CTL indistinguishable from the prototype B6 strain, however, it was apparent that other genes of AKR background were required for the Fv-1n-mediated inhibition in AKR.H-2b mice. The mechanism by which Fv-1 intereacted with other genes to override positive H-2b control appeared to be related to the expression of the CTL-defined, virus-associated antigens by normal AKR.H-2b cells. Thus, AKR.H-2b spleen cells but not thymus cells were able to stimulate the production of B6 anti-AKR/Gross virus CTL and were recognized as target cells by such anti-viral CTL. In contrast, both spleen cells and thymocytes from AKR.H-2b:Fv-1b mice were negative when tested as stimulator or target cells in these assays. In addition, AKR.H-2b but not AKR.H-2b:Fv-1b spleen cells were shown to display serologically defined gp70 determinants and the Gross cell surface antigen. Taking these data together, it appeared that the inhibition of anti-viral CTL responsiveness might be due to tolerance induced by the cell surface expression of virus-associated antigens by normal AKR.H-2b cells. Widespread display of viral antigens, in turn, may have been due to the permissive effects of Fv-1n on the spread of the early arising N-ecotropic, endogenous AKR leukemia virus controlled by other background genes. In this context, the implications of the multi-gene control of anti-AKR/Gross virus CTL production are discussed with respect to the induction of spontaneous leukemia in the high incidence AKR strain.