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The oncostatic effect of polyinosinic-polycytidylic acid (poly IC) on several varieties of tumors has been reported previously (Levy et al., 1969) and we have observed its effect on Walker’s tumor. A number of clinical trials have been conducted (De Vita et al., 1970; Krakoff et al., 1970) but they merely confirmed tolerance to the product and did not yield therapeutical results. Although the mechanism of the oncostatic action exerted by polynucleotides on experimental tumors is not precisely defined, it is thought that it is probably multiple, for poly IC is cytotoxic (Braun, personal communication), is an inducer of interferon (Field et al., 1967), is an adjuvant of immunity, as reported by Braun et al. (1968), and as observed by us by studying its effect on the multiplication of cells capable of forming antibodies in mice immunized with sheep red blood cells (Hayat and Mathe, in preparation). From this last-mentioned type of study, we have deduced the hypothesis according to which poly IC could have an action on acute leukemia only when the number of tumor cells is not very high. In fact, we have shown (Mathe, 1968; Mathe et al., 1969) that the adjuvants of immunity in the animal exert a detectable oncostatic action only when the number of cancer cells is low. |
