BALB/C mice injected with LSTRA leukemic cell line are cured by in vivo treatment with IL-2 + GM-CSF

Typhonium flagelliforme inhibits the proliferation of murine leukemia WEHI-3 cells in vitro and induces apoptosis in vivo

Typhonium flagelliforme (TF) is a tropical plant, traditionally used by the ethnic population of Malaysia for the cure of various cancers. This plant had shown to induce antiproliferative effect as well as apoptosis in cancer cells. However, there is no available information to address that TF affects murine leukemia cells in vitro and in vivo. Here, we investigated in vitro and in vivo effects of TF on murine leukemia WEHI-3 cells. It was found that the growth of leukemia cells in vitro was inhibited by the various extracts of TF. Among these fractions, the dichloromethane (DCM) tuber extracts of TF showed the lowest IC(50) (24.0 ± 5.2 μg/ml) and had demonstrated apoptogenic effect when observed under fluorescent microscope. We investigated the in vivo effects of DCM tuber extracts of TF on murine leukemia cells, and the results showed that the counts of immature granulocytes and monocytes were significantly decreased in peripheral blood of BALB/c leukemia mice after the oral administration of DCM tuber extracts of TF for 28 days with three doses (200, 400 and 800 mg/kg). These results were confirmed by observing the spleen histopathology and morphology of enlarged spleen and liver in leukemia mice when compared with the control. Furthermore, the cell death mechanism in the spleen tissue of treated mice was found via apoptosis.

Arsenic trioxide enhances the cytotoxic effect of thalidomide in a KG-1a human acute mylogenous leukemia cell line

Studies have shown that thalidomide exerts modest activity as a single agent in the therapy of acute myeloid leukemia (AML). The present investigation was conducted to test the hypothesis that the cytotoxic effect of thalidomide is enhanced when properly combined with other chemotherapeutic agents. The human AML cell line KG-1a was used in this study. Cells were cultured for 48 h in the presence or absence of thalidomide, arsenic trioxide and a combination of the two substances. Results obtained indicate that thalidomide at concentrations of 1, 2 and 5 mg/l produced a dose-dependent cytotoxic effect and at 5 mg/ml resulted in late apoptosis in 49.39% of the total cell population (as compared to 5.35% in the control cells). When the cells were incubated with arsenic trioxide alone (4 µM), late apoptosis was detected in 16.97% of the total cell population. However, when cells were incubated with a combination of thalidomide (5 mg/l) and arsenic trioxide (4 µM), late apoptosis was noted to be 80.6% in the total cell population. This percentage of late apoptosis was statistically significant from that observed when cells were incubated with thalidomide alone. These findings clearly indicate that arsenic trioxide enhances the cytotoxic effects of thalidomide.

Autologous control of a highly malignant syngeneic CRNK-16 leukemia in the rat: a role for NK cells

It is unclear whether autologous immunity could be recruited to restrict the progression of leukemia. Patients harboring leukemia commonly display suppressed cell mediated immunity, which may contribute to their inability to control the disease. Immune response against leukemia is evident in allogeneic HLA-mismatched bone marrow transplantation, implicating the involvement of NK cells. This graft-versus-leukemia (GVL) activity suggests that, if not suppressed, an autologous NK cell response could potentially control acute leukemia that had down-regulated HLA expression. In the current study we assessed the role of non-suppressed autologous NK cells in controlling a syngeneic highly malignant leukemia, the CRNK-16 line, that constitute a major cause of natural death in aged F344 rats. A minuscule dose of 60 CRNK-16 leukemia cells per rat was sufficient to induce 50% mortality rates, and animals that survived this challenge did not show improved survival upon a second challenge. The CRNK-16 line was found to exhibit low levels of MHC-I, and selective in vivo depletion of NK cells nullified in vitro NK activity against the CRNK-16 line and reduced survival rates from this leukemia. In vivo activation of NK cells, employing low doses of poly I-C or IL-12, increased in vitro NK activity against the leukemia and dramatically improved survival rates when treatment was initiated before, but not after leukemia inoculation. These results indicate the ability of competent autologous NK cells to restrict highly malignant non-immunogenic leukemia. Thereby, this model presents an opportunity to study specific in vivo NK-leukemia interactions.

Vaccination with leukemia cells expressing cell-surface-associated GM-CSF blocks leukemia induction in immunocompetent mice

The fundamental basis for immunotherapy of leukemia is that leukemic cells express specific antigens that are not expressed by normal hematopoietic cells. However, the host immune system appears to be tolerant to leukemia cells. To overcome this tolerance, we vaccinated immunocompetent mice with murine leukemia cells (WEHI-3B and BCR-ABL+ 32D cells) transduced with a specifically constructed transmembrane form of granulocyte-macrophage colony-stimulating factor (tmGM-CSF). The transduced cells expressed tmGM-CSF on the cell-surface. To determine whether tmGM-CSF-expressing WEHI-3B leukemia cells would prevent leukemia formation as a vaccine, immunocompetent mice (BALB/c and C3H/HEJ) were immunized with lethally irradiated murine leukemia cells expressing cell-surface tmGM-CSF before challenging mice with murine leukemia cells. Two immunocompetent mouse models were investigated, either WEHI-3B cells in BALB/c mice or BCR-ABL+ 32D cells in C3H/HEJ mouse. The results showed that 100% of WEHI-3B/tmGM-CSF-vaccinated BALB/c mice and about 65% of 32D+ BCR-ABL/tmGM-CSF-vaccinated C3H/HEJ mice were protected from leukemia after leukemia cell challenge, whereas all non-vaccinated mice succumbed to leukemia. Spleen and marrow cell suspensions from vaccinated mice challenged with WEHI-3B cells lacked detectable GFP+ WEHI-3B cells at 82 days post-challenge. A significant delay of death was observed in C3H/HEJ mice challenged with the very aggressive DA-1 cell line expressing BCR-ABL. Vaccination of mice with WEHI-3B/CD40L cells protected 80% of the mice from the WEHI-3B challenge. Notably, 60% of the WEHI-3B/BALB/c mice were also protected from leukemia when WEHI-3B/tmGM-CSF vaccination was carried out after the leukemia challenge. In order to determine whether cellular immunity is involved in this vaccine-mediated protection, either CD4+ or CD8+ T cells were depleted from mice after the WEHI-3B/tmGM-CSF vaccination. The results indicate that CD8+ T-cells mediated the protective immune response provided by the irradiated tmGM-CSF-expressing WEHI-3B cells. In addition, vaccination of nude mice did not provide protection from WEHI-3B leukemia induction. Importantly, 80% of non-vaccinated mice were also protected from a WEHI-3B cell challenge after receiving spleen cells from vaccinated mice 1 day before challenge with leukemia cells. These results indicate that overexpression of tmGM-CSF on the leukemia cell-surface can enhance the recognition of leukemic cells by CD8+ T cells, and can either prevent or significantly delay leukemia induction. These findings suggest that injection of irradiated leukemia cells expressing cell-surface-bound GM-CSF has the potential as an immunological approach to treat leukemia.