clinical effect of human fibroblast interferon on malignant cancer 2 immunological study of the patients under treatment several immunological studies were performed in patients with various malignant diseases under treatment of human fibroblast interferon hfif lymphocyte natural killer nk activity against culture cell lines was measured before and at various time after hfif treatment the majority of patients reached the highest level of nk activity at 1824 hours mostly at 24 hours after initiating hfif in one group of patients thereafter nk activity remained the highest level during hfif treatment and in another group of patients nk activity declined even with daily infusion of hfif but usually remained above pretreatment level there seemed to be no correlation between nk activity and clinical activity in contrast to nk activity against culture cell lines an increase in lymphocyte cytotoxic activity against autologous tumor cells was not observed following hfif treatment mixed lymphocyte tumor cell reaction performed in 6 patients showed that a slight increase of 3hthymidine uptake was seen in one patient but the rest of them had no change in vitro sensitization to assess the in vitro generation of cytotoxic cells were negative in all 6 patients lymphocyte blastogenic responses to nonspecific mitogens showed no significant change delayed type hypersensitivity reaction to recall antigens was increased in about half of the patients after hfif treatment