title: Inhibition of CTL induction by rapamycin: IL-2 rescues granzyme B and perforin expression but only partially restores cytotoxic activity.
abstract: Rapamycin (RAP) is a potent inhibitor of CTL induction. Since RAP is known to block IL-2 signaling through the IL-2R, we hypothesized that RAP may interfere with CTL generation by inhibiting IL-2-induced expression of granzyme (Gzm) B, perforin, and/or Fas ligand (FasL). MHC-unrestricted mouse CTL induced in vitro with anti-CD3 mAb in the presence of RAP (1 ng/ml) exhibited dramatically reduced cellular proliferation and cytotoxicity against P815 tumor target cells. Gzm B mRNA expression and enzymatic activity in RAP-treated CTL were greatly reduced compared with those in control CTL. Perforin mRNA expression was also reduced by RAP. In contrast, RAP failed to inhibit FasL mRNA expression. RAP, therefore, inhibits induction of the perforin/Gzm B cytolytic pathway but spares Fas/FasL-mediated cytotoxicity. To determine whether RAP exerts a total blockade of the IL-2R signaling pathway, we induced CTL in the presence of both RAP and exogenous rIL-2 (100 U/ml). Under these conditions, Gzm B and perforin mRNA and protein expression as well as cellular proliferation were restored to at least control levels. Surprisingly, inhibition of cytotoxicity was only partially alleviated when CTL were induced in the presence of RAP plus rIL-2, even though CTL conjugated normally with target cells and had an intact granule secretory pathway. We conclude that 1) the inhibitory effect of RAP at the level of the IL-2R is incomplete; and 2) the suppressive effect of RAP on CTL induction is only partly due to inhibition of Gzm B and perforin gene expression.
authors.affiliation: Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada.
authors.forename: A P
authors.initials: AP
authors.lastname: Makrigiannis
authors.forename: D W
authors.initials: DW
authors.lastname: Hoskin
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D017252:CD3 Complex / Q000276:immunology; D002478:Cells, Cultured; D003602:Cytotoxicity, Immunologic / Q000187:drug effects* / Q000235:genetics; D005786:Gene Expression Regulation / Q000187:drug effects / Q000276:immunology; D053804:Granzymes; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D007376:Interleukin-2 / Q000494:pharmacology*; D008213:Lymphocyte Activation / Q000187:drug effects* / Q000235:genetics; D018655:Lymphocyte Count / Q000187:drug effects; D008285:Major Histocompatibility Complex / Q000187:drug effects / Q000276:immunology; D008297:Male; D008562:Membrane Glycoproteins / Q000096:biosynthesis* / Q000187:drug effects / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D054353:Perforin; D011090:Polyenes / Q000494:pharmacology*; D052899:Pore Forming Cytotoxic Proteins; D011994:Recombinant Proteins / Q000494:pharmacology; D012697:Serine Endopeptidases / Q000096:biosynthesis* / Q000187:drug effects / Q000235:genetics; D020123:Sirolimus; D013602:T-Lymphocytes, Cytotoxic / Q000187:drug effects* / Q000201:enzymology / Q000276:immunology
chemical_list: D000911:Antibodies, Monoclonal; D017252:CD3 Complex; D007166:Immunosuppressive Agents; D007376:Interleukin-2; D008562:Membrane Glycoproteins; D011090:Polyenes; D052899:Pore Forming Cytotoxic Proteins; D011994:Recombinant Proteins; D054353:Perforin; D053804:Granzymes; C509214:Gzmb protein, mouse; D012697:Serine Endopeptidases; D020123:Sirolimus