Alpha Peled

Erythropoietin induces tumor regression and antitumor immune responses in murine myeloma models

Recombinant human erythropoietin (rHuEpo) has been used successfully in the treatment of cancer-related anemia. Clinical observations with several patients with multiple-myeloma treated with rHuEpo has shown, in addition to the improved quality of life, a longer survival than expected, considering the poor prognostic features of these patients. Based on these observations, we evaluated the potential biological effects of rHuEpo on the course of tumor progression by using murine myeloma models (MOPC-315-IgAλ2 and 5T33 MM-IgG2b). Here we report that daily treatment of MOPC-315 tumor-bearing mice with rHuEpo for several weeks induced complete tumor regression in 30–60% of mice. All regressors that were rechallenged with tumor cells rejected tumor growth, and this resistance was tumor specific. The Epo-triggered therapeutic effect was shown to be attributed to a T cell-mediated mechanism. Serum Ig analysis indicated a reduction in MOPC-315 λ light chain in regressor mice. Intradermal inoculation of 5T33 MM tumor cells followed by Epo treatment induced tumor regression in 60% of mice. The common clinical manifestation of myeloma bone disease in patients with multiple-myeloma was established in these myeloma models. Epo administration to these tumor-bearing mice markedly prolonged their survival and reduced mortality. Therefore, erythropoietin seems to act as an antitumor therapeutic agent in addition to its red blood cell-stimulating activity.

Induction of Leukemia in Mice by Irradiation and Radiation Leukemia Virus Variants

Publisher Summary This chapter reviews the experimental data concerning pathways involved in the development of leukemias in the C57BL strain induced by exposure to fractionated whole-body irradiation or by inoculating one of the different radiation leukemia virus variants available. In the absence of cofactors, these virus variants differ in their leukemogenic potential. The target organ for the overt development of most spontaneous or induced murine lymphoid leukemias is the thymus. The thymus is considered by many investigators because of the site of neoplastic transformation and proliferation. Potential leukemic cells are identified in the bone marrow of most mice treated with leukemogenic agents irrespective of the ultimate overt leukemia development expressed mostly in the thymus. The development pathways during leukemogenesis involve two fundamental phases preceding the overt expression of a tumor: (1) the transformation of normal stem cells or prothymocytes into preleukemic cells and (2) the differentiation and proliferation of the transformed cells into autonomously growing malignant cells. The leukemogenic potential of the different leukemogenic agents is determined by different tumor cell-host relationships. The presence of an intact thymus leads to the establishment and proliferation of preleukemic cells induced by the radiation leukemia virus (RadLV) variants.

Dietary fish oil suppresses tumor growth and metastasis of Lewis Lung Carcinoma in mice

Abstract In this study we examined the influence of different polyunsaturated fatty acid (PUFA) diets on the tumor growth and metastatic dissemination of the well-characterized Lewis Lung Carcinoma (3LL) in C57BL 6J mice. The tumor-bearing mice were fed ad libitum with three different diets of 5% oil; either soybean oil (SO), which is rich in omega-6 (ω-6); perilla oil (PO), which is rich in omega-3 (ω-3) 18:3; and fish oil (FO), which is rich in ω-3, 20:5 and 22:6 PUFA. A significantly slower growth of primary tumor, lower mortality rate, and lower metastatic spread were observed in mice fed FO. This trend was also observed in mice fed first with SO and after tumor inoculation transferred to the FO diet. Indomethacin reduced significantly the metastasis growth in the SO-fed group, and exerted only a small effect in the FO and PO fed counterparts, suggesting that eicosanoid derivatives of ω-6 fatty acids support the process of tumor growth. In addition, the long chain PUFA of fish oil, which are sensitive to oxidation, could act as targets for membrane perforation and eventual elimination of the proliferating tumor cells.

I. Prevention of spontaneous AKR T cell lymphomagenesis by 24-666, a virus isolated from an AKR B cell lymphoma

Injection of a nonlymphomagenic ecotropic virus 24-666 isolated from a B cell lymphoma of AKR origin into young AKR mice (1-60 days old) inhibited spontaneous T cell lymphoma development. The reduction in T cell lymphoma incidence (16/106-15%) was accompanied with the appearance of B cell lymphomas (16/106-34%) in older mice (500 days mean latency). Infection of newborn to 60-day-old AKR mice with 24-666 prevented changes in thymus subpopulations and expression of MuLV-related cell surface antigens, normally observed in the thymus of 5- to 6-month-old AKR mice prior to lymphoma development. Thymuses of 24-666-infected 9- to 12-month-old mice lacked recombinant dual tropic virus (DTV) expression and retained the thymus pattern of 2-month-old AKR mice. At 12 months after 24-666 administration a striking decrease in Thy1.1 level and in the CD4+ CD8+ population and an increase in CD4- CD8- cells and in mu+ B cells, predominantly Ly1+, were observed. The presence of B cells in these thymuses was also reflected in the high response of thymocytes to LPS blastogenesis accompanied by a decreased response to PHA. Although T cell lymphoma development was markedly reduced by 24-666 administration, the establishment of potential lymphoma cells (PLC) was not affected. Transfer of lymphoid cells from 12-month-old grossly normal 24-666-infected mice to the appropriate recipients resulted in a high incidence (64-80%) of B cell lymphoma development. Thus, 24-666 seems to act through interference with the establishment of DTV in the thymus, thereby preventing PLC promotion to overt T cell lymphomas. Lack of the favorable microenvironment for PLC development in the T cell pathway enables PLC development in the B cell pathway in older mice.

H-2I-linked control of immunological resistance to viral leukemogenesis as a response to preleukemic cells

The mechanism of resistance to leukemogenesis by two radiation leukemia virus variants, A-RadLV and D-RadLV, was investigated. Resistance to these viruses is linked toH-2I in both B10.S and C57BL/10 mice. The resistance of virus-infected mice to transplantation of syngeneic, A- or D-RadLV-induced lymphoma cells was similar to their resistance to leukemogenesis by the same viruses. This resistance could be transferred by lymphoid cells from immune donors to normal recipients, and it was specific for RadLV lymphomas. Virus-primed (responder x sensitive)F1 hybrids rejected only resistant-type parental lymphoma cells. Hence, it appears thatH-2I-linked resistance to RadLV leukemogenesis is regulated byIr genes. Resistant mice immunized by A- or D-RadLV rejected syngeneic lymphoma cells, irrespective of whether they were sensitive or resistant to the RadLV variant used for the induction of the lymphoma cells. It follows that resistant and sensitive type lymphomas are antigenically similar for the effector mechanism, and that theIr genes may be expressed in the sensitization phase of the reaction. In virus-infected mice which are resistant to A- or D-RadLV we were able to demonstrate the presence of preleukemic lymphocytes. Normal mice could be immunized by these preleukemic cells against lymphoma challenge. These data are interpreted to suggest that mice havingH-2I-linked resistance to RadLV infection may be sensitized by their preleukemic cells, and that these preleukemic cells are then arrested in their development as a result of the immune response.

Variations in surface charge distribution of leukemic and non-leukemic transformed cells

The surface negative charge distribution of fresh leukemic cells from patients with acute leukemia was examined with cationized ferritin (CF), an electron dense label of anionic sites and compared with leukemic cells from phase-cycle fractionated populations of a human leukemic cell line K-562. Normal-untreated and phytohemagglutinin (PHA)-transformed lymphocytes were also tested. A CF-induced redistribution of anionic sites into clusters and patches within a wide range of variations in density was observed electron microscopically both in fresh acute leukemic cells and in unseparated cells of the K-562 line. Cells of the G0/G1 fraction from a phase-cycle separated K-562 population exhibit a higher density of CF label per unit length of membrane as compared with the G2 + M cell fraction. PHA-benign transformed normal lymphocytes exhibit an even and continuous CF labeling, similar to that of normal-untreated lymphocytes. An attempt was made to correlate the CF-induced charge redistribution with the rate of agglutination with the cationic Poly-L-lysine. Our observations indicate that the CF ligand does induce an anionic site redistribution, varying in density, both in fresh leukemic cells and in cells from a K-562 line, and does not in normal untreated and PHA-benign transformed lymphocytes. The particular pattern of anionic site redistribution observed in leukemic cells of this study is apparently phase-cycle dependent.

Cellular immune response induced by the radiation leukemia virus (RadLV)

Abstract Studies on the cellular basis involved in the build up of immunity in C57BL/6 mice inoculated intrathymically with the radiation leukemia virus (RadLV) have been carried out. The virus inoculated C57BL/6 mice were resistant to isotransplantation of leukemic cells for two months after immunization. Lymphoid cells from immune mice present in the thymus, lymph nodes, spleen and peritoneal exudate were found to cause tumor growth retardation. RadLV inoculated C57BL/6 mice performed transplantation resistance only to leukemic cells induced by RadLV (127 LC), but not to radiation induced leukemias (XRL-1, XRL-2, XRL-3), to EL4 or to any other syngeneic tumors tested. The immunological specificity of the lymphoid cells taken from immunized mice (with RadLV) was tested in vivo and in vitro against leukemic cells induced in C57BL/6 mice by various agents (RadLV, chemical carcinogens and X-rays) and were found to be highly specific for the presence of RadLV associated antigen(s) on their cell surface. A cytostatic effect rather than a cytolytic effect was demonstrated, when effector:leukemic cell interaction was tested in vitro. The cytostasis assay was performed on syngeneic leukemic cells (induced by RadLV) in suspension at various leukemic: effector cell ratios. A specific reaction occurred mainly at the ratio of 1:80.

Changes of H-2 antigen expression on thymocytes during leukemia development by radiation leukemia virus.

The expression of antigens encoded by the K and D region genes of the major histocompatibility complex on thymocytes of BL/6 mice infected with Radiation Leukemia Virus (RadLV) variants, A-RadLV to which they are sensitive or D-RadLV to which they are resistant, was investigated. Reduced thymus cellularity due to the thymolytic effect of both RadLV variants (30-40% cell reduction within 24 h after intrathymic virus injection) was accompanied with elevated H-2 expression on thymocytes. A high density of H-2D and to a lesser degree increased expression of H-2K were observed following infection with both virus variants. This elevated H-2 expression was maintained transiently for 6-7 weeks in the resistant situation and persisted in the sensitive situation until overt leukemia developed. The occurrence of A-RadLV transformed cells in 75% of the tested thymuses within 10 days after infection (vs 16% in D-RadLV treated mice) and their further expansion until overt leukemia developed could explain the continued expression of elevated H-2 expression on thymocytes in the sensitive situation. The majority (85%) of the primary A-RadLV induced leukemias tested expressed more H-2D/H-2K gene products than normal thymocytes. We conclude that leukemia development due to RadLV infection is not associated with the reduction or disappearance of H-2D/H-2K gene products.

II. Prevention of spontaneous AKR T cell lymphomagenesis by elimination of potential lymphoma cells with antibody to specific gp 71 determinants

AKR mice, highly susceptible to spontaneous T cell lymphomagenesis, were protected from developing the disease by a course of daily treatment with antibody 18-5 to gp 71 determinants (administered from birth to 10 days). Potential lymphoma cells (PLC) identified among bone marrow cells of untreated AKR mice since birth (using the transplantation bioassay method) were eliminated following treatment with antibody 18-5. Namely, transplantation of bone marrow cells and thymocytes of 250-day-old untreated AKR mice into (AKR/J x DBA/2)F1 and/or AKR recipients yielded 86-93% T cell lymphoma of AKR origin at a short mean latent period of 38-42 days. In contrast, transfer of lymphoid cells from 18-5-treated mice at a matching age caused only 7-13% T cell lymphoma of AKR origin. The accelerating effect of MCF 247 on lymphoma development in untreated AKR mice was not effective in 18-5-treated mice, probably due to lack of PLC that are promoted by MCF 247 to overt T cell lymphoma. The characteristic changes in thymus subpopulations preceding lymphoma development and coinciding with PLC identification in the thymus of untreated mice was prevented by 18-5. It is suggested that prevention of lymphoma development in AKR mice by passive antiviral immunotherapy involves elimination of PLC representing the initial tumorigenic phase in AKR lymphomagenesis.

EVALUATION OF IMMUNE MEMORY OF HUMAN LYMPHOCYTES ENGRAFTED IN SCID MICE

Peripheral blood lymphocytes (PBL) isolated from 17 healthy subjects were engrafted i.p. each to an individual SCID mouse. After 48 hours the mice were tested for skin response to the common recall antigen PPD at various sites on the body periphery. In 8 of them PPD elicited a distinct positive skin reaction only at the abdomen. This procedure could provide a basis for detection of specific cellular immune response such as in autoimmune diseases.