Leukemic cell lysis by activated human macrophages: significance of membrane-associated tumor necrosis factor

Possible role of immune surveillance at the initial phase of metastasis produced by B16BL6 melanoma cells

The relationship among the real-time trafficking of lung metastatic B16BL6 cells, metastatic potential, and the injected number of the cells was examined, since the smaller the number of tumor cells injected, the more clearly the immune defense may be observed. When 1x10(6) or 1x10(5) B16BL6 cells were injected into mice via the tail vein, both numbers of cells accumulated in the lung at a similar rate: there was an approximately 10-fold difference in the number of accumulated cells between the two doses. Elimination from the lung was not dependent on the cell number but on the proportion of accumulated cells. However, the injection of 1x10(4) cells resulted in lung accumulation less than one-tenth of that obtained with 1x10(5) cell injection. Metastasis was observed when 1x10(5) or 1x10(6) B16BL6 cells were injected, but not after injection of 1x10(4) cells. To clarify the roles of the immune defense system at the initial phase of metastasis, we challenged macrophage-depleted mice with 1x10(4) tumor cells. Treatment of mice with 2-chloroadenosine prior to the tumor cell challenge cancelled the suppression of not only metastasis but also the lung accumulation. Furthermore, the administration of 2-chloroadenosine following the tumor cell challenge had little effect on the metastatic potential. These results suggest that the immune surveillance whose action was obvious at the low dose of challenged tumor cells functions strongly at the initial phase but not at the advanced stages of the metastatic process, and that macrophages play an important role in the suppression of metastasis.

The expression of co-stimulatory molecules and their relationship to the prognosis of human acute myeloid leukaemia: poor prognosis of B7-2-positive leukaemia

We examined the expression of co-stimulatory molecules on leukaemic cells of 52 adult patients with acute myeloid leukaemia (AML) (34 men and 18 women) and analysed the relationship between these expressions and the patient's prognosis. B7-1 was not expressed in any of the 23 patients investigated, whereas B7-2 was expressed in 26/52 patients (50.0%). B7-2 was expressed in all AML patients with monocytic morphology (M4 or M5) and in 16/42 cases without monocytic morphology. CD54 was expressed in 28/ 37 patients examined (75.7%), and CD58 was expressed in all of the AML patients except one (M 7). The overall survival of the 26 B7-2-positive leukaemia patients (1-24 months, median survival 11.5 months) was significantly shorter than that of the 26 B7-2-negative leukaemia patients (1-71+ months, median 35.1 months) (P=0.0080). In addition, the B7-2-positive patients exhibited significantly shorter disease-free survival periods compared to the B7-2-negative patients (P=0.021). There was no significant difference in age, sex, haematological data and complete remission rate between the B7-2-positive and B7-2-negative patients. Our results indicated that B7-2 is one of the most crucial factors in the prognosis of adult acute leukaemia and can be expected to have an important role in tumour immunity.

Inhibition by sphingosine of leukemic cell killing by human monocytes activated with interleukin-2: a possible role of protein kinase C

Sphingosine and its analogs, which inhibit protein kinase C (PKC), are known to be potent inducers of apoptosis in tumor cells. However, we were concerned that sphingosine might also interfere with anti-tumor cells of the immune system. Therefore, we evaluated the effect of sphingosine on activation of human monocytes by interleukin-2 (IL-2) for killing of leukemic cells. Monocytes, purified by elutriation and adherence, were activated with IL-2 or interferon-gamma (IFN-gamma) in the presence or absence of sphingosine or another inhibitor for 18 h. Then the monocytes were washed and the culture medium was replaced with fresh medium to remove the sphingosine. HL- 60 and K562 leukemic cells were added to the monocyte cultures. Over the next 48 h, the cytotoxic activity of the monocytes towards the leukemic cells was assessed by means of an 111-indium-releasing assay. IL-2-activated monocytes lysed 48 +/- 3% of HL-60 cells and 44 +/- 3% of K562 cells. Sphingosine, dihydrosphingosine, N,N-dimethylsphingosine, and the PKC inhibitor H7 inhibited the activation of monocytes by IL-2, blocking cytotoxic activity against the leukemic cells by approximately 75%. These inhibitors were not toxic to monocytes at the concentrations used. In a PKC assay, sphingosine and H7 inhibited PKC activity in IL-2-treated monocytes. Thus, sphingosines, by inhibiting PKC activity, inhibited activation of monocytes by IL-2, which inhibited the killing of leukemic cells.

Potentiation of antitumor effects of tumor necrosis factor alpha and interferon gamma by macrophage-colony-stimulating factor in a MmB16 melanoma model in mice

The efficacy of systemic infusion of recombinant human macrophage-colony-stimulating factor (M-CSF) in combination with local treatment with human recombinant tumor necrosis factor (TNF) alpha and mouse recombinant interferon (IFN) gamma was studied in vivo on a subclone of B16 melanoma (MmB16) in mice. Short-term intravenous administration of M-CSF at a dose of 10(6) units daily had no antitumor effect in vivo. Similarly, local treatment of tumor with TNF alpha (5 micrograms daily) did not produce any therapeutic effect. However, simultaneous administration of the same dose of TNF alpha with IFN gamma (1000 units daily) resulted in a synergistic effects manifested by the retardation of tumor growth. Addition of systemic infusion of M-CSF to the local therapy with TNF alpha and IFN gamma induced further augmentation of antitumor efficacy and delayed progression of MmB16 melanoma. The strengthened antitumor effect of combination therapy including M-CSF, TNF alpha and IFN gamma was most probably due to the increased release of monocytes from the bone marrow, their recruitment into the site of tumor growth and subsequent local stimulation of their antitumor activity.

Combination of immunotherapy with cyclophosphamide/actinomycin D chemotherapy potentiates antileukemic effect and reduces toxicity in a L1210 leukemia model in mice

The therapeutic effects of the combination of chemotherapy (cyclophosphamide and actinomycin D) and immunotherapy (TNF-alpha and macrophages) were evaluated on L1210 leukemia in mice. When given as single agents, both cyclophosphamide (CY), administered intraperitoneally 2 days after subcutaneous inoculation of leukemic cells, and actinomycin D (Act D), injected intratumorally (i.t.) 4 days following injection of leukemic cells, exerted therapeutic effects and prolonged mice survival. Unexpectedly, combination of CY and Act D did not result in prolongation of mice survival, due mainly to substantial cumulative toxic effects that led to death in several cases. Immunotherapy with TNF-alpha and M phi, injected i.t. on day 4 following inoculation of leukemic cells, did not give significant therapeutic effect, either when used alone or when used in conjunction. However, combination of chemotherapy and immunotherapy, including all four agents, produced a beneficial effect resulting in significant prolongation of the survival of leukemia-bearing mice. This study indicates the potential of appropriate combinations of cytotoxic drugs with immunotherapy against neoplasia.