Chronic Myeloid Leukemia Patients in Prolonged Remission following Interferon-α Monotherapy Have Distinct Cytokine and Oligoclonal Lymphocyte Profile

Anna Kreutzman,Satu Mustjoki,Edgar Faber,Peter Rohon,Veli Kairisto,Karel Indrak,Kimmo Porkka,Marjatta Sinisalo,Marjatta Sinisalo,Vesa Juvonen,Emília Flochová,Jukka Vakkila,Petteri Arstila,Jaroslava Voglová,Paul Proost

doi:10.1371/journal.pone.0023022

Abstract

Before the era of tyrosine kinase inhibitors (TKIs), interferon-alpha (IFN-α) was the treatment of choice in chronic myeloid leukemia (CML). Curiously, some IFN-α treated patients were able to discontinue therapy without disease progression. The aim of this project was to study the immunomodulatory effects of IFN-α in CML patients in prolonged remission and isolate biological markers predicting response. Due to rarity of patients on IFN-α monotherapy, a relatively small cohort of patients still on treatment (IFN-ON, n = 10, median therapy duration 11.8 years) or had discontinued IFN-α therapy but remained in remission for >2 years (IFN-OFF, n = 9) were studied. The lymphocyte immunophenotype was analyzed with a comprehensive flow cytometry panel and plasma cytokine levels were measured with multiplex bead-based assay. In addition, the clonality status of different lymphocyte subpopulations was analyzed by TCR γ/δ rearrangement assay. Median NK-cell absolute number and proportion from lymphocytes in blood was higher in IFN-OFF patients as compared to IFN-ON patients or controls (0.42, 0.19, 0.21×109/L; 26%, 12%, 11%, respectively, p<0.001). The proportion of CD8+ T-cells was significantly increased in both patient groups and a larger proportion of T-cells expressed CD45RO. Most (95%) patients had significant numbers of oligoclonal lymphocytes characterized by T-cell receptor γ/δ rearrangements. Strikingly, in the majority of patients (79%) a distinct clonal Vγ9 gene rearrangement was observed residing in γδ+ T-cell population. Similar unique clonality pattern was not observed in TKI treated CML patients. Plasma eotaxin and MCP-1 cytokines were significantly increased in IFN-OFF patients. Despite the limited number of patients, our data indicates that IFN-α treated CML patients in remission have increased numbers of NK-cells and clonal γδ+ T-cells and a unique plasma cytokine profile. These factors may relate to anti-leukemic effects of IFN-α in this specific group of patients and account for prolonged therapy responses even after drug discontinuation.

Highlights

The Philadelphia chromosome (Ph) resulting from the reciprocal translocation between chromosomes 9 and 22 is the hallmark of chronic myeloid leukemia (CML)
The interferon alpha (IFN-a) dose differed markedly between patients ranging from 1.5 million units (MU) twice weekly to 3 MU daily mirroring well the real clinical situation as the tolerated and effective dose of IFN-a varies greatly between individual patients. 85% of patients (11 of 13) from whom data was available belonged to low Sokal risk group and 15% to intermediate risk group
IFN-a therapy (IFN-ON) were divided in 2 groups based on the absolute NK-cell count in the peripheral blood

Summary

Introduction

The Philadelphia chromosome (Ph) resulting from the reciprocal translocation between chromosomes 9 and 22 is the hallmark of chronic myeloid leukemia (CML). The discovery of tyrosine kinase inhibitors (TKIs) has dramatically improved the survival of CML patients [2,3,4]. They are not considered to be curative since they do not eliminate all Ph+ cells and discontinuation of the therapy often leads to disease relapse [5]. Before the TKI therapy era, interferon alpha (IFN-a) was the treatment of choice in CML [6]. Studies evaluating the successful treatment discontinuation in CML have suggested that IFN-a therapy may improve the possibility to stop TKI therapy [5,12]. The mechanism of action of IFN-a therapy is incompletely understood; the drug exerts both direct cytostatic and immunomodulatory effects on leukemic cells

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