Retroviral immunotoxin gene therapy of acute myelogenous leukemia in mice using cytotoxic T cells transduced with an interleukin 4/diphtheria toxin gene

The potential benefit of immunotoxin (TT) for cancer therapy has mostly bee n limited by the fact that only a small portion of injected dose ever reach es the cancer target. Thus, we set out to determine whether antigen-specifi c CTLs would be suitable vehicles to deliver IT to the site of cancer cells in vivo, A retroviral vector was constructed for gene therapy with (interl eukin 4) IL-4 positioned downstream of its 20-amino-acid leader sequence th at permitted cotranslational protein synthesis of IT along with truncated d iphtheria toxin (DT), IL-4 was chosen as a ligand based on the expression o f IL-4 receptor (IL-4R) on most acute myeloid leukemia cases. The first-tim e expression and secretion of a cytokine/DT fusion toxin was accomplished i n mammalian NIH.3T3 cells, and then a retroviral vector was assembled, The retroviral IT was used to transiently transduce T15, a CD8(+) CTL T cell Li ne that specifically recognized C1498 (a lethal murine acute myeloid leukem ia cell line), Transduced T15 T cells expressed intracellular DT and IL-4 a s determined by immunofluorescence, Secreted IT supernatants collected from T15 had enzymatic activity and killed IL-4R(+) C1498 cells, but not IL-4R( -) EL4 cells. Intravenous injection of transduced T15, but not nontransduce d T15, into mice with sc, tumors significantly inhibited tumor growth, In c ontrast, systemic therapy with a bacterial preparation of the same IL-4 IT given at its maximum tolerated dose did not protect. Retroviral IT-treated mice showed no sign of the renal or hepatic toxicity that is common to this class of IT,Together, these data indicate that retroviral TT may solve pro blems relating to systemic IT therapy by delivering reagent more directly t o the site of cancer in vivo and may impart new anticancer defense mechanis ms to antigen-specific T cells.