Cytogenetic remissions induced by interferon α and imatinib mesylate are immunologically distinct in chronic myeloid leukemia

Immunological status of chronic myelogenous leukemia patients with complete cytogenetic response after treatment

BACKGROUND

The aim of this study was to compare the T lymphocyte subsets of chronic myelogenous leukemia (CML) patients who had a complete cytogenetic response (CCyR) after treatment with imatinib (IM) or homoharringtonine (HHT).

METHODS

T and Th lymphocyte subsets in CCyR patients treated with HHT (n = 15) or IM (n = 16) were assayed with flow cytometry.

RESULTS

It was found that there were no differences in T lymphocyte subset proportions at the time of achieving CCyR0 and also no difference in the CD8+T cell proportions at the 12th month after CCyR (CCyR12), between the 2 groups. The values of CD3+T, CD4+T, CD8+T, CD4+T/CD8+T, Th1 and Th2 cells were 54.21% ± 6.12% vs. 44.32% ± 4.85%, 29.83% ± 5.53% vs. 22.27% ± 3.22%, 24.66 ± 4.91 vs. 25.41% ± 5.72% , 1.11 ± 0.23 vs. 0.92 ± 0.19, 10.23% ± 4.24% vs. 8.34% ± 3.45% and 11.12% ± 3.91% vs. 13.67% ± 4.78%, respectively in the HHT group and IM group at CCyR12, which meant that the proportions of CD3+T, CD4+T and Th1 cells and the ratio of CD4+T to CD8+T cells were higher and the CD8+T and Th2 cell proportions were lower in the HHT group than in the IM group.

CONCLUSIONS

HHT has a weaker immunodepression effect on T lymphocyte subsets compared with IM.

Imatinib mesylate directly impairs class switch recombination through down-regulation of AID: its potential efficacy as an AID suppressor

Activation-induced cytidine deaminase (AID) is essential for class switch recombination and somatic hypermutation. Its deregulated expression acts as a genomic mutator that can contribute to the development of various malignancies. During treatment with imatinib mesylate (IM), patients with chronic myeloid leukemia often develop hypogammaglobulinemia, the mechanism of which has not yet been clarified. Here, we provide evidence that class switch recombination on B-cell activation is apparently inhibited by IM through down-regulation of AID. Furthermore, expression of E2A, a key transcription factor for AID induction, was markedly suppressed by IM. These results elucidate not only the underlying mechanism of IM-induced hypogammaglobulinemia but also its potential efficacy as an AID suppressor.

Combination of pegylated IFN-α2b with imatinib increases molecular response rates in patients with low- or intermediate-risk chronic myeloid leukemia

Biologic and clinical observations suggest that combining imatinib with IFN-α may improve treatment outcome in chronic myeloid leukemia (CML). We randomized newly diagnosed chronic-phase CML patients with a low or intermediate Sokal risk score and in imatinib-induced complete hematologic remission either to receive a combination of pegylated IFN-α2b (Peg-IFN-α2b) 50 μg weekly and imatinib 400 mg daily (n = 56) or to receive imatinib 400 mg daily monotherapy (n = 56). The primary endpoint was the major molecular response (MMR) rate at 12 months after randomization. In both arms, 4 patients (7%) discontinued imatinib treatment (1 because of blastic transformation in imatinib arm). In addition, in the combination arm, 34 patients (61%) discontinued Peg-IFN-α2b, most because of toxicity. The MMR rate at 12 months was significantly higher in the imatinib plus Peg-IFN-α2b arm (82%) compared with the imatinib monotherapy arm (54%; intention-to-treat, P = .002). The MMR rate increased with the duration of Peg-IFN-α2b treatment (< 12-week MMR rate 67%, > 12-week MMR rate 91%). Thus, the addition of even relatively short periods of Peg-IFN-α2b to imatinib markedly increased the MMR rate at 12 months of therapy. Lower doses of Peg-IFN-α2b may enhance tolerability while retaining efficacy and could be considered in future protocols with curative intent.

PR1-specific T cells are associated with unmaintained cytogenetic remission of chronic myelogenous leukemia after interferon withdrawal

Background

Interferon-α (IFN) induces complete cytogenetic remission (CCR) in 20–25% CML patients and in a small minority of patients; CCR persists after IFN is stopped. IFN induces CCR in part by increasing cytotoxic T lymphocytes (CTL) specific for PR1, the HLA-A2-restricted 9-mer peptide from proteinase 3 and neutrophil elastase, but it is unknown how CCR persists after IFN is stopped.

Principal Findings

We reasoned that PR1-CTL persist and mediate CML-specific immunity in patients that maintain CCR after IFN withdrawal. We found that PR1-CTL were increased in peripheral blood of 7/7 HLA-A2+ patients during unmaintained CCR from 3 to 88 months after IFN withdrawal, as compared to no detectable PR1-CTL in 2/2 IFN-treated CML patients not in CCR. Unprimed PR1-CTL secreted IFNγ and were predominantly CD45RA±CD28+CCR7+CD57-, consistent with functional naïve and central memory (CM) T cells. Similarly, following stimulation, proliferation occurred predominantly in CM PR1-CTL, consistent with long-term immunity sustained by self-renewing CM T cells. PR1-CTL were functionally anergic in one patient 6 months prior to cytogenetic relapse at 26 months after IFN withdrawal, and in three relapsed patients PR1-CTL were undetectable but re-emerged 3–6 months after starting imatinib.

Conclusion

These data support the hypothesis that IFN elicits CML-specific CM CTL that may contribute to continuous CCR after IFN withdrawal and suggest a role for T cell immune therapy with or without tyrosine kinase inhibitors as a strategy to prolong CR in CML.