In vitro IL-12 treatment of peripheral blood mononuclear cells from patients with leukemia or myelodysplastic syndromes: increase in cytotoxicity andreduction in WT1 gene expression

Interleukin-12 (IL-12) has potent antitumor activities. We examined whether IL-12 enhanced the cytotoxicity of peripheral blood mononuclear cells (PBM NC) and decreased leukemia cells in 30 patients with leukemia or myelodyspl astic syndromes (MDS): 12 acute myeloid leukemia (AML) (five in complete re mission (CR) and seven in non-CR); six chronic myeloid leukemia (CML); and 12 MDS (three refractory anemia (RA), eight RA with excess of blasts and on e chronic myelomonocytic leukemia). PBMNC from patients and five healthy vo lunteers were cultured at 5x10(5)/ml parallel with or without 100 units/ml of IL-12 for 3 days. Cytotoxicity of PBMNC against K562 cells was assessed by flow cytometry. To quantify the amount of leukemia cells, WT1 mRNA was m easured by competitive reverse transcription polymerase chain reaction (RT- PCR), since WT1 mRNA is considered as a marker of minimal residual disease (MRD) in leukemia or MDS. The cytotoxicity of non-IL-12-treated PBMNC of 30 patients was 13.4 +/- 9.3% at the effector to target (E:T) ratio of 20:1, and significantly lower than that of normal subjects (25.7 +/- 8.4%). The c ytotoxicity increased to 30.6 +/- 17.9% in the IL-12-treated PBMNC. WT1 mRN A in PBMNC of five healthy volunteers was less than 10(3) copies/mu g of to tal RNA. Following the 3-day IL-12 treatment, mean WT1 mRNA of PBMNC was re duced from 10(4.8) to 10(4.2) copies/mu g of total RNA in six CML patients, from 10(5.4) to 104.8 copies/mu g in 12 MDS patients and from 10(5.0) to 1 0(4.2) copies/mu g in five AML patients in CR, but not reduced in five of s even AML in non-CR. These results showed that IL-12 significantly enhanced PBMNC cytotoxicity and decreased the quantity of leukemia cells in PBMNC of most patients with MDS, CML and AML in CR. IL-12 might be of considerable benefit in the elimination of MRD in patients with hematological malignanci es.