Sensitivity of Ph 1 + CFU-GM to human recombinant interferon alpha and gamma alone and in combination

A differential sensitivity to recombinant human interferon-alpha 2a between normal and chronic myeloid leukaemic peripheral blood granulocyte-macrophage colony-forming units

The sensitivity to recombinant human interferon-alpha 2a (IFN) of peripheral blood granulocyte-macrophage colony-forming units (PB CFU-GM) from patients with chronic myeloid leukaemia (CML) was studied in a semi-solid clonogenic assay, and compared with normal PB CFU-GM. Like normal PB CFU-GM, the growth of CML PB CFU-GM in vitro was found to be dependent on the plating concentration used. The optimal CFU-GM growth occurred when CML PB mononuclear cells (MNC) were plated at low concentrations in the range of 0.01-0.1 x 10(5)/ml, compared to the range of 0.3-3.0 x 10(5)/ml optimal for CFU-GM growth in normal subjects. The optimal plating concentration for CML PB CFU-GM was similar to that observed in PB collected from patients with ovarian carcinoma during haematological recovery following chemotherapy-induced myelosuppression (recovery phase). The recovery phase PB was used as a source of non-leukaemic cells with a higher incidence of CFU-GM similar to that of CML. IFN produced a dose-related inhibition of CFU-GM growth in normal, recovery phase ovarian carcinoma and CML, PB MNC. The IFN concentration required to inhibit 50% of the CFU-GM in culture (LD50) was found to be significantly influenced by the plating concentration. When cells were cultured at 1.0 x 10(5) MNC/ml the mean LD50 for 7 CML patients was similar to that in normal (n = 5) or recovery phase (n = 5) peripheral blood, 273 i.u./ml, 1047 i.u./ml and 795 i.u./ml, respectively. In contrast when CML cells were cultured at 0.03 x 10(5) MNC/ml the concentration for optimal CML CFU-GM growth, the mean LD50 was significantly lower than that in normal PB and recovery phase PB, 4 i.u./ml, 251 i.u./ml and 78 i.u./ml, respectively (p less than 0.05). This is the first report of a differential sensitivity to IFN between CML and non-CML progenitors using an optimized PB CFU-GM assay system and proposes that further study of the in vitro culture of CML progenitors may increase our understanding of the clinical effects of IFN.

Interferon alfa-2b in acute- and chronic-phase chronic myelogenous leukaemia: initial response and long-term results in 54 patients

Fifty-four patients with Ph1-positive chronic myelogenous leukaemia (CML) (48 with chronic-phase and six acute-phase disease) were treated with interferon alfa-2b subcutaneously (s.c.). The starting dose was 4 million units (MU)/m2 body surface area daily. It was reduced in parallel with serially determined leucocyte counts, and minimal effective doses were given as maintenance after achieving remission. Haematological remissions were induced in 22 of the 48 patients (46%) with chronic-phase disease. Thirteen patients (27%) revealed partial haematological remission and another 13 no response to treatment. No complete remission could be induced, although minor or partial cytogenetic responses were seen in 16 patients (33%). Moreover, a bcr-abl reduction was detected on Southern blot analysis in two patients. In chronic-phase disease, results of treatment were influenced by elapsed time after diagnosis, extent of previous treatment and interferon dosage. No beneficial effects of interferon were detected in the six patients with acute-phase disease. Principal acute side effects were fever and flu-like symptoms at the beginning of the therapy, which usually subsided within 3-7 days. Chronic side effects, especially weakness and neuropathy, were less frequent but more severe and necessitated discontinuation of treatment in 10 patients. In summary, interferon alfa-2b seems to be an effective treatment in early chronic-phase CML. Long-term effects on the course of the disease, however, must be determined.

The effects of interferon-alpha on the proliferation of CML progenitor cells in vitro are not related to the precise position of the M-BCR breakpoint

We investigated the effects of brief (2 h) and continuous exposure to recombinant interferon-alpha (2a) (rIFN-alpha) on the proliferation of primitive (blast colony-forming cells, Bl-CFC) and committed myeloid progenitor cells (BFU-E and GM-CFC) derived from blood and bone marrow of patients with chronic myeloid leukaemia (CML) and normal subjects. In all three clonogenic assays, rIFN-alpha suppressed colony formation in a dose-dependent manner. No differences were detected in the proliferation of CML or normal Bl-CFC and GM-CFC exposed to rIFN-alpha. Erythroid colony formation by normal, but not by CML BFU-E, was inhibited by relatively low concentrations (100 U/ml) of rIFN-alpha. However, in patients whose blood or marrow contained a mixture of Philadelphia chromosome (Ph)-positive and Ph-negative BFU-E, cytogenetic analysis of individual erythroid colonies showed no differential inhibition by rIFN-alpha. We found no difference in the sensitivity to rIFN-alpha of GM-CFC from patients whose leukaemic cells expressed BCR/ABL mRNA with the b2a2 junction and that of GM-CFC from patients with the b3a2 mRNA. We conclude that (1) rIFN-alpha does not have a significant leukaemia-specific effect on the progenitor cells detected in these assays, and (2) the sensitivity of CML GM-CFC to rIFN-alpha is independent of the type of BCR/ABL message present in the cells. The clinical efficacy of rIFN-alpha could be due to selective toxicity to cells not assayed in this study, to effects on accessory cells or to alterations induced in progenitor cell/stromal cell interactions.

Sensitivity of chronic myeloid leukemia hemopoietic progenitors to PTT-119 in combination with human recombinant interferon alpha and gamma

PTT-119, a new synthetic alkylating compound, has shown a marked "in vitro" inhibitory effect on chronic myeloid leukemia (CML) granulo-monocytic precursors (CFU-GM) at doses greater than 5 micrograms/ml. Based on previous experiences of synergistic associations between alkylating drugs and biological modifiers, we tested the effects of low doses of PTT-119 (from 0.1 to 1 microgram/ml) in concert with alpha, gamma, or alpha + gamma interferons and compared to IFNs alone, in order to investigate an alternative choice for treatment of CML patients in chronic phase. Our results showed a significantly higher CFU-GM cloning inhibition after addition of 100 or 1,000 U/ml of alpha IFN to 0.1 microgram/ml PTT-119 (from 39.6% +/- 26.6 SD to 80.7% +/- 10 SD and 91.5% +/- 8 SD, respectively), while gamma IFN resulted in only a slight increase in colony growth inhibition when compared to the drug used alone. The association of alpha plus gamma IFN coupled with PTT-119 treatment did not significantly improve the results observed after exposure of leukemic progenitors to PTT-119 and alpha IFN alone. We conclude that a combined treatment with PTT-119 and IFN is probably worth testing both for purging methods before autologous bone marrow transplantation and for in vivo administration in chronic myeloid leukemia.

Treatment of Ph+ chronic myeloid leukemia by gamma interferon

The clinical, hematologic and cytogenetic effects of human recombinant gamma interferon (IFN) were investigated in 14 patients with Ph+ chronic myeloid leukemia (CML). Gamma-IFN was given at a daily dosage of 0.50 mg (= 10 x 10(6) U)/m2 from the 3rd week of treatment on, but the dosage had to be reduced to 0.25 mg/m2 in 10 cases and to 0.35 mg/m2 in 2 cases, because of the severity and persistence of side effects (mainly fever, fatigue, headache and pain). Only 2 patients tolerated the full dosage. The overall response rate was 64% (1 complete and 8 partial hematologic responses). Only patients in stable chronic phase responded. Two out of two patients in unstable chronic phase and two out of two patients in accelerated phase failed to respond. Eight out of nine responding patients remained in remission throughout the duration of treatment (30 to 35 weeks). No karyotypic conversion was detected. These data show that gamma IFN alone is effective in Ph+ CML, but that side effects can limit substantially the dosage and duration of treatment.