[Elimination of suppressor macrophages in tumor-bearing mice by 6-mercaptopurine and its therapeutic contribution].

6-Mercaptopurine inhibited suppressor macrophages and induced antitumor monocytes in L1210-bearing mice. Although these antitumor monocytes did not neutralize L1210, they augmented the antitumor response in L1210 vaccine-primed recipient mice against a subsequent inoculation of live L1210. These results led to the trial of a novel immunochemotherapy regimen in which L1210 vaccine and 6-mercaptopurine in combination produced a synergistic therapeutic effect. In contrast, cyclophosphamide did not inhibit suppressor macrophages, nor did it induce antitumor monocytes in L1210-bearing mice. Consequently, the combination of L1210 vaccine and cyclophosphamide did not produce any further improvement in therapy. These results showed that modulation of macrophages and monocytes was associated with immunotherapeutic effect.