In vitro arming and blocking activity of sera from BALB/c mice bearing a spontaneous transplantable adenocarcinoma.

The kinetics of the immune response of BALB/c mice to a syngeneic spontaneous adenocarcinoma (ADK-1t) were analyzed in vitro during the various stages of tumor growth. Cell-mediated cytotoxicity, as measured by a colony inhibition assay, was first detected 5 days after tumor inoculation, reached a peak at about 13 days, and then declined to low but significant levels by day 21. A peak of complement-dependent serum cytotoxicity was observed at 10 days when the tumor size was about 5 mm. Moreover, sera from animals bearing tumors of 1.5–10 mm dia were able to arm lymphocytes from normal BALB/c mice and enhance the cytotoxic activity of lymphocytes from tumor-bearing mice. On the other hand, no blocking activity was observed when the ADK-1t target cells were preincubated with the same sera. When cytotoxic lymphocytes were pretreated with sera from mice bearing tumors larger than 10 mm in size, inhibition of cell-mediated cytotoxicity was observed. These findings show that the interaction of serum factors on cellular reactivity is of a complex, evolving nature, directly related to the tumor size.