Perforin gene variation influences survival in childhood acute lymphoblastic leukemia

Highlights

• Common perforin gene variants influence overall survival in childhood ALL.

• rs885822 GG genotype was associated with worse outcome, independent of risk group.

• Perforin gene variation may influence mortality in childhood ALL.

Abstract

Although a growing body of data links mutations in the perforin gene with increased susceptibility to hematologic malignancies, no studies discuss their influence on the clinical course of such diseases. The present study examines the impact of perforin gene variation on the clinical outcome in acute lymphoblastic leukemia (ALL) patients. The study enrolled 312 children aged 1–18 years, treated for ALL. PRF1 gene variants were analyzed through direct DNA sequencing. Variation in rs885822 was found to be associated with overall survival: patients carrying the GG genotype demonstrated a significantly increased risk of death compared to those carrying the A allele, independently of ALL risk groups (HR 3.13, 95%CI 1.16–7.8, p = 0.014). The effect was even more pronounced in high-risk ALL patients (p = 0.006). On the other hand, the presence of the rs35947132 minor A allele was slightly protective with regard to overall prognosis (p = 0.047). No differences in relapse-free survival were observed with regard to genotypes. The results of the study may imply that perforin gene variation has a role in modifying mortality in childhood ALL.

Introduction

Perforin is a pore-forming protein stored in the acidic secretory granules of cytotoxic lymphocytes [1]. Perforin-mediated cytotoxicity is crucial in killing transformed cells and cells harboring intracellular pathogens; it is also involved in downmodulation of the immune response by inducing apoptosis of effector lymphocytes and antigen-presenting cells [[2], [3], [4]].

The belief that perforin is critical for immune homeostasis and tumor immune surveillance is supported by the spectrum of pathologies associated with perforin deficiency [5]. Perforin-depleted (Prf1^−/−) mice are highly immunosuppressed and susceptible to diverse intracellular pathogens [6], as well as to transplanted [7], virus-induced [8] and spontaneous malignancies, primarily to aggressive B-cell lymphomas [9]. Perforin has also been shown to play an important role in NK-cell mediated suppression of tumor metastasis [10] and in controlling the growth of carcinogen-induced sarcoma [11]. In humans, biallelic PRF1 gene mutations are well recognized as the cause of 20–50% of familial heamophagocytic lymphohistiocytosis (FHL2) [[12], [13], [14], [15]], a severe hyperinflammatory syndrome with uncontrolled activation of antigen-presenting cells, CD8+ T cells and massive cytokinaemia [16]. Recent studies also describe the presence of perforin-dependent immune surveillance in humans. Carriers of mutant PRF1 were shown to suffer more frequently from relatively early-onset melanoma – a malignancy in which CD8+ T cells may play a role in the prevention of disease progression and metastatis [17]. Both mono- and biallelic PRF1 gene mutations have also been found in a proportion of patients with Hodgkin and non-Hodgkin lymphomas [[18], [19], [20]]. A limited number of studies on acute lymphoblastic leukemia (ALL), the single most common pediatric malignancy [21], have provided contradictory results: the A91V polymorphism was identified as an ALL-predisposing factor in a relatively small group of children [22], but was not confirmed on a larger cohort [23]. It was also suggested that perforin mutation may be more prevalent in ALL with BCR-ABL1 translocation [24].

As perforin plays a pivotal role in maintaining immune homeostasis, not only regarding tumor immune surveillance, but also pathogen defense and immune regulation, the aim of the present study is to examine the impact of perforin gene variation on the clinical outcome in pediatric ALL patients. As such, this is the only study so far to address the role of perforin in the clinical course of ALL.