[Studies on the possible causes of decreasing NK cell activity in tumor-bearing mice. I. The number of NK cells in the spleens of tumor-bearing mice is higher than that in normal mice].

In studies of viral immunotherapy of cancer, we found that NK cell activity in tumor-bearing mice was usually below the normal level, a universal phenomenon in tumor-bearing animals and patients. Our data show that the depressed NK cell activity in tumor-bearing mice was not due to a decrease of NK cell number. The percentage of NK cells in the spleens of tumor-bearing mice was much higher than that in normal mice. Using morphological and 3H-TdR uptake methods, we found that there were many NK blast cells in the spleens of tumor-bearing mice, and blastogenesis was sustained up to the day of death.