Esther F. Hays

A lipid mobilizing factor in serum of tumor-bearing mice.

There is considerable evidence that the growing tumor requires a source of unsaturated fatty acids, but the nature of this source and the mechanism of mobilizing the fatty acids from it are obscure. These experiments make use of AKR mice with implanted adipose tisue labeled with 1-14C linoleic acid. With this experimental animal, it has been found that: (a) in the normal, fed mouse, fat is mobilized slowly and appears largely as respiratory CO2, following oxidation, (b) in the normal, fasted mouse, fat is mobilized rapidly and appears largely as respiratory CO2; (c) in the tumor-bearing, fed mouse, fat is mobilized rapidly and appears largely in the tumor; and (d) the serum from tumor-bearin mice, when injected into normal mice, produces an immediate massive fat mobilization that does not respond to feeding, whereas the serum from normal, fed mice does not. It is concluded that a mobilizing factor of unknown nature is present in the serum of tumor-bearing AKR mice.

Differential tropism of HIV-1 isolates for distinct thymocyte subsets in vitro.

ObjectiveUnderstanding the interaction between HIV and developing thymocytes is crucial in determining how HIV infection perturbs the immune system. We determined which thymocyte subsets can harbor and express HIV. DesignHIV expression in mature and immature thymocytes obtained from surgical specimens from non-infected children was determined after in vitro infection with the syncytium-inducing, cytopathic NL4–3 and the non-syncytium-inducing, relatively noncytopathic JR-CSF isolates. MethodsIntracellular staining for the HIV p24gag antigen was combined with cell surface phenotyping to determine thymocyte subsets expressing HIV. Infection was quantitated by polymerase chain reaction on sorted subsets. ResultsNL4–3 replicated faster and to higher titers and caused a more severe decrease of all CD4-bearing thymocytes than did JR-CSF. In addition, both immature CD1+ and mature CD1− thymocytes expressed NL4–3, whereas only mature CD1 -cells expressed JR-CSF. The tropism of NL4–3 for these immature cells suggests a mechanism for a more profound impact on T-cell maturation than that seen with JR-CSF. We also found that thymocytes lacking cell surface CD4 (CD4-CD8− and CD4-CD8+ subsets) expressed virus with either isolate late in infection, when viral levels were high. The CD4-CD8− cells expressing HIV were mature CD3bright T-cell receptor (TCR)α/βbright cells. ConclusionsThese results show that NL4–3 can be expressed by thymocytes at immature and mature stages of differentiation and cause severe loss of CD4+ cells. Thus, tropism of a virus for immature cells can affect the capability of the thymus to produce new T lymphocytes leading to a greater impact on development and functions of the immune system. It is proposed that this in vitro model can be used to study pathogenic mechanisms in the thymus.

In vitro studies of HIV-1 expression in thymocytes from infants and children.

ObjectiveTo determine whether thymocytes from infants and young children can be infected with and their maturation capability altered by HIV-1, and to examine the effects of interleukin (IL)-2 and IL-4 on this process. DesignSerum-free culture medium was used so that cytokine effects could be studied under defined conditions. The primary virus isolates HIV-1JR-CSF and HIV-1JR-FL were used because their effects should most closely resemble those of viruses which might be found in an infected child. MethodsThymocytes from infants and young children were infected with virus and cultured in serum-free medium with the cytokines IL-2 and IL-4 alone or in combination. HIV-1 expression was measured after 12 days by p24 levels in culture supernatants. Thymocyte maturation was determined by changes in surface phenotype, as measured by flow cytometry. ResultsHIV-1 expression by thymocytes, which increased with time of culture, occurred when thymocytes were cultured with each cytokine. p24 levels were slightly increased when cultured with IL-2, compared with IL-4. Virus expression was remarkably increased when the cytokines were combined in culture. This expression was synergistic rather than additive. The synergy, evident in mature, but not immature thymocytes, was demonstrated with both pharmacologie and physiologic concentrations of cytokines. T-cells from peripheral blood cultured under the same conditions demonstrated lower virus expression in the presence of cytokines and synergy was not shown. Cytokine-induced thymocyte maturation and thymocyte survival in vitro was unimpaired by infection with HIV-1. ConclusionsThese findings indicate that the cytokines IL-2 and IL-4, which are normally present in the thymic environment, can synergize to promote HIV-1 expression by thymocytes infected in vitro. This occurs without impairing the maturation induced by these cytokines. Thus, the mature thymocyte may provide a continuous supply of virus-expressing T-cells to the peripheral blood and lymphoid tissues of the infected child.

Oncornaviruses produced by murine leukemia cells in culture.

Abstract Leukemia cells from mice of the AKR and C58 strains produced leukemia viruses (MuLV) in culture that failed to induce syncytia in the XC plaque assay (XC − ), were poorly infectious for mouse embryo fibroblasts, and yielded low levels of infectious progeny upon the establishment of infection. In host range analysis the majority of these viruses were N-ecotropic, although one leukemia cell line also produced xenotropic MuLV. Viral isolates from five different leukemia cell lines were oncogenic upon inoculation into newborn AKR mice. In contrast, viruses that occurred in high titer in the tissues and sera of normal AKR mice were not oncogenic in vivo and in culture they efficiently induced (with N-ecotropism) syncytia in the XC plaque assay (XC + ). These findings demonstrate that the transforming agent for spontaneous leukemogenesis differs in biological properties from the endogenous MuLV that is commonly observed in mice of high leukemic strains.

Characterization of a lipid mobilizing factor from tumors

Many observations have indicated that a growing tumor is able to derive the fatty acids necessary for membrane formation from the host tissues. It seems evident that in mammals, at least, the major source of rapidly available fatty acid must be adipose tissue and many observations of tumor-bearing animals and human cancer patients have revealed a picture of fat depletion with advanced malignancies but the mechanism of this type of mobilization of fatty acids has remained obscure. 1-6 The present experiments make use of AKR mice with implanted adipose tissue labeled with [1-14C]linoleic acid to address this question.

Effect of hypertransfusion on granulopoiesis in bone marrow depression. Studies in the irradiated mouse.

The response of granulopoietic activity in bone marrow depression to a reduction in the demand for erythropoiesis has been examined by means of hypertransfusing C57B mice which had been exposed to sublethal whole body irradiation. Multiple intraperitoneal injections of 0.5 ml packed red cells from irradiated donors were employed to maintain the haematocrit sufficiently above the normal range to produce significant suppression of erythropoietic activity for the duration of the bone marrow depression. This was associated with elevation above control values of 32‐102% in the blood granulocyte count, 22‐78% in total cells of the granulocytic series per femur, and up to 44% in total agar colony forming units per femur. Restoration of essentially normal values occurred 13 d after irradiation in contrast to 17‐18 d in controls. Single transfusions which produced less suppression of erythroblast numbers per femur resulted in an intermediate degree of improvement in these parameters. Such changes in the granulocyte compartment indicate improved granulopoietic capacity in the hypertransfused group. It is suggested that this effect reflects increased production of granulocyte progenitors due to the reduction in competing demands on the compromised multipotential stem cell compartment for progenitors of the erythroid series. The findings raise the possibility that hypertransfusion might be capable of producing a beneficial effect on granulopoiesis in human bone marrow depression.

Immunologic effects of human thymic stromal grafts and cell lines

These experiments report a method of preparing stromal remnants from human thymus. The remnants were composed of epithelial cells, fibroblasts, and macrophages. They were grafted under the renal capsule of nude mice. Some of the grafts were reconstituted with lymphocytes to obtain the microscopic morphology of the thymus. The mice with reconstituted grafts survived in a conventional environment, had increased numbers of T cells in their spleen, and showed improvement of T-cell mediated immunologic function. This was measured by a positive allogeneic effect, a mixed lymphocyte reaction, and cell-mediated lysis. In vitro cell lines were established from thymic remnants of two separate individuals. These lines grew as attached monolayers. One of them was composed of fibroblasts. The other had an epithelial morphology. This epithelial cell line (HT-7) was shown to produce factors which promoted thymocyte differentiation in vitro.

Thymic stroma in AKR mice: its function and virus production.

This study reports experiments with thymic stromal remnants in AKR mice, a strain with a high natural incidence of thymic lymphoma. A method has been developed in which thymic stromal cells which survive a 4-week culture period, 1 week at 24 degrees C and 3 weeks at 37 degrees C are suitable for grafting. Most thymic lymphocytes die under these conditions. Stromal remnants were studied by culturing and grafting under the kidney capsule of 2-month-old syngeneic mice. Their in vitro morphology and virus production, their ability to reconstitute a new thymus from host progenitors and their eventual lymphoma development was evaluated. The stromal remnants were from: 1- and 3-month-old normal mice; 6-10-month-old normal mice; 21-28-day-old animals treated with the lymphomagenic virus, SL3-3, at 3 days of age. Our data show that thymic stromal function as measured by lymphoid reconstitution of thymic stromal grafts of AKR mice is not impaired with age or by the presence of oncogenic virus. Oncogenic viruses are found in the thymic stroma of old mice and in thymic stroma of young virus-treated mice. Oncogenic viruses are not found in thymic stroma of young normal mice. Lymphoma can develop in the grafted stromal remnants expressing lymphomagenic virus.

Differences in lymphomagenic properties of AKR mouse retroviruses

Long-term studies on lymphomagenicity of several AKR mouse retroviruses have shown that the biologically cloned ecotropic SL3-3c virus is the most lymphomagenic of all viruses tested. This fact was demonstrated by lymphomagenicity in five mouse strains SJL, C3Hf/Bi, C3H/HeJ, CBA/H, and NFS, and lymphoma acceleration in AKR mice. The incidence was higher and latent periods shorter than that found with the other retroviruses tested (SL3-1c, SL3-2c, MCFc, and GMuLVc). In addition, it was the only retrovirus found to be highly oncogenic in the C3H/HeJ and CBA/H strains. Lack of lymphomagenicity of MCFc in CBA/H strain was shown to be due to a block in viral replication. Addition of nononcogenic Akv ecotropic virus did not affect this lack of oncogenicity. The lymphomas developing in CBA/H and SJL mice after neonatal inoculation of SL3-3c virus only produced lymphomagenic ecotropic virus. Thus, SL3-3c lymphomagenesis is most likely due solely to the action of that virus. These studies indicate that pure ecotropic AKR viruses can be highly leukemogenic.

Bone marrow progenitor cells of akr mice give rise to thymic lymphoma cells.

Abstract Bone marrow cells from one-month-old AKR mice give rise to thymic lymphomas when grafted into (AKR × DBA/2)F 1 , hybrid mice. This finding implicates a bone marrow progenitor as a “target cell” for the age-related development of thymic lymphomas in AKR mice.