In vivo natural antitumor resistance against murine EL-4 lymphoma cells in lethally irradiated syngeneic C57Bl/6 mice

Splenic cytotoxic cells recognize surface HSP70 on culture-adapted EL-4 mouse lymphoma cells

Heat shock proteins (HSPs) are intracellular proteins which function as molecular chaperones. At the same time, translocation of HSPs to the cell surface has been observed in stressed, infected and transformed cells. It seems plausible that surface HSPs may represent molecular targets for recognition and elimination of 'altered' cells by cytotoxic lymphocytes. Previously we demonstrated that EL-4 mouse lymphoma cells growing in vitro express HSPs on their plasma membrane. In this study, we tested the hypothesis that surface HSPs present on EL-4 cells may mediate their recognition and killing by cytotoxic lymphocytes. We have found that susceptibility of culture-adapted EL-4 cells to in vitro lysis by syngeneic and allogeneic splenocytes correlated with the expression of HSP70 on EL-4 cells. Moreover, cytotoxicity was blocked by pretreatment of EL-4 target cells with anti-HSP70 antibody, whereas antibodies to MHC class I molecules and Thy1 did not have such effect. Cytotoxicity against EL-4 lymphoma was not MHC class I-restricted, and was not decreased after depletion of CD8(+) cells from the effector cell population. We conclude that in vitro killing of EL-4 cells is mediated, at least in part, by NK cells via recognition of HSPs present on the surface of tumor cells. Thus, cytotoxic response against EL-4 lymphoma should serve as a good model to study the role of HSPs in anti-tumor immunity.

Immunochemotherapy of advanced colorectal cancer with alpha-interferon and 5-fluorouracil. 1. Toxicological studies

Twelve patients with advanced colorectal cancer were subjected to alternating cycles of treatment with low immunomodulating doses of recombinant alpha-interferon (alpha IFN) + 5-fluorouracil (5FU) or with 5FU alone. Hematological, biochemical and physical evaluation of the patients showed that alpha IFN + 5FU cycles were well tolerated like 5FU alone, except for modest and transient fever following alpha IFN administration. At hematological nadir (day 15-18 of each cycle) lymphocytopenia and granulocytopenia were more pronounced during alpha IFN + 5FU than 5FU cycles. No difference was found for platelet nadir. At the beginning of each cycle complete leukocyte recovery was observed in all cases. Platelet recovery was also complete, although counts were higher after alpha IFN + 5FU than after 5FU alone. Clinical results showed 1 complete remission, 1 partial remission, 5 stable disease and 5 progressive disease. These data point out that low doses of alpha IFN can be safely associated with 5FU. However further studies are required to establish the possible therapeutic value of alpha IFN-mediated immunomodulation for immunochemotherapy of colorectal cancer.

Natural resistance in mice against Friend leukemia cells. II. Studies with in vivo passaged interferon-sensitive and interferon-resistant cell clones

Experiments were designed to test the presence of antitumor natural resistance (NR) in DBA/2 mice against highly oncogenic in vivo passaged histocompatible Friend leukemia cells (FLC-V). NR was measured in vivo as rapid clearance of radiolabeled cells from different organs or as growth inhibition in lethally irradiated mice. Interferon-sensitive (745) or interferon-resistant (3C18) lines were used. Organ clearance studies showed that young recipients eliminate cells more rapidly than old mice. Moreover, depressive (e.g., cyclophosphamide or carrageenen) or enhancing (e.g., poly (I:C) or Friend leukemia virus infection) agents of NR function modulate accordingly leukemia cell clearance. Similar results were obtained testing tumor growth in lethally irradiated hosts, although modulating agents were substantially less effective in this system. Both FLC-745-V and FLC-3C18-V lines were equally susceptible to NR. Therefore, these data provide further support to the hypothesis that exogenous IFN capable of suppressing the growth of both lines could act via enhancement of the NR function.