title: Effector cells of low-dose IL-2 immunotherapy in tumor bearing mice: tumor cell killing by CD8+ cytotoxic T lymphocytes and macrophages.
abstract: The presence and cytotoxicity of tumor infiltrating cells is described in mice during effective immunotherapy with interleukin 2 (IL-2). DBA/2 mice were inoculated i.p. with 2 x 10(4) tumor cells on day 0 and treated with daily i.p. injections with 20,000 units IL-2 on days 10-14. Mice bearing a large syngeneic i.p. tumor burden (SL2 lymphoma, P815 mastocytoma, L5178Y lymphoma, or L1210 lymphoma) could be cured by i.p. immunotherapy with these low doses of IL-2. In the peritoneal cavity of these mice an infiltrate of mononuclear cells was present. Similar numbers of lymphocytes (10(6)-10(7)) and macrophages (+/- 10(7)) were present in control tumor bearing mice and IL-2 treated tumor bearing mice. The ratio of CD4+/CD8+ T lymphocytes in the peritoneal cavity of mice rejecting the SL2 tumor was smaller than 0.5, whereas this ratio is about 2 in naive mice. In the spleens of IL-2 treated tumor bearing mice only a minor decrease of CD4+/CD8+ ratio was observed from 2.1-2.4 to 0.9-1.9. T cells isolated from the peritoneal cavity of mice inoculated with SL2 tumor cells and treated with IL-2, were highly cytotoxic to SL2 cells: at E:T ratio 2:1 the cytotoxicity index was 37 +/- 3. This cytotoxicity was specific and mediated by CD8+ T lymphocytes. Macrophages that were present in the peritoneal cavity of mice treated with IL-2 were also highly cytotoxic. The C.I. of these cells was 63-76% at E:T ratio 1:1. Cytotoxic macrophages were also present in untreated tumor bearing mice. The i.p. injections of IL-2 (20,000 units/day) caused a four-fold increase in the local NK-activity in the peritoneal cavity in naive mice. These IL-2 injections did not generate LAK-activity in vivo. Specificity of the in vivo tumor rejection was tested by injection SL 2 i.p. on day 0 and P815 i.p. on day 10, or vice versa, followed by IL-2 treatment. Only the tumor cells that were injected on day 0 were rejected. These in vivo experiments point to specific tumor rejection. In conclusion, both cytotoxic macrophages and CTL's are present in a sufficient number and with sufficient cytotoxicity to explain the killing of tumor cells in the peritoneal cavity. The CTL-activity seems of decisive importance for tumor rejection as this is induced by IL-2.
authors: Department of Pathology, University Hospital Utrecht, The Netherlands.
authors: R A
authors: RA
authors: Maas
authors: P A
authors: PA
authors: Roest
authors: M J
authors: MJ
authors: Becker
authors: I S
authors: IS
authors: Weimar
authors: H F
authors: HF
authors: Dullens
authors: W
authors: W
authors: Den Otter
mesh_terms: D000818:Animals; D016827:CD8 Antigens; D002460:Cell Line; D003602:Cytotoxicity, Immunologic; D004195:Disease Models, Animal; D004306:Dose-Response Relationship, Immunologic; D007376:Interleukin-2 / Q000627:therapeutic use*; D007958:Leukocyte Count; D008223:Lymphoma / Q000628:therapy*; D008264:Macrophages / Q000276:immunology*; D012515:Mast-Cell Sarcoma / Q000628:therapy*; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D010534:Peritoneal Neoplasms / Q000473:pathology / Q000628:therapy*; D016176:T-Lymphocyte Subsets / Q000276:immunology*; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*
chemical_list: D016827:CD8 Antigens; D007376:Interleukin-2