Effects of hyperthermia on the production and activity of primary and secondary cytolytic T-lymphocytes in vitro.

We studied the effects of hyperthermia (up to 43°)on the cytolytic activity (''Cr release assay) and differentia tion of primary and secondary cytolytic T-lymphocytes (CTL) in vitro. Mixed-leukocyte cultures were established from splenic leukocytes of C57BL/6 mice and DBA/2 stimulator lymphocytes, and the CTL formed on Day 4 (primary) or on Day 21, 3 days after restimulation of the cultures with alloantigen (secondary), were assayed against P815 mastocytoma cells. Hyperthermia (43°) caused a marked decrease in cytolytic activity, the re sponse curves for primary and secondary CTL being characterized by an initial shoulder followed by an expo nential curve with an increment of dose needed to reduce activity to 37% of a starting value of 4 or 2 min, respec tively. Some of the damage was repaired when the cells were incubated at 20°or 37°for several hr (peak = 4 hr), and neither suppression of protein synthesis nor damage to membrane lipids seemed to be the causative mecha nism. Heat also affected the differentiation of precursor cells into CTL. In both short-term mixed-leukocyte cul tures stimulated with 2-mercaptoethanol and long-term mixed-leukocyte cultures stimulated with alloantigen, heating to 43°before stimulation caused a 2to 3-fold increase in subsequent CTL formation with short heating times, followed by a severe decrease with longer heating times. The results demonstrate that both primary and secondary CTL, as well as the cells Involved in their differentiation in this system, are quite sensitive to tem peratures in the range that is proposed for use in tumor therapy.