Impact of a functional polymorphism in the IL12B promoter region on survival in patients with malignant melanoma

Abstract

8001 Background: Interleukin-12 (IL-12), a heterodimeric cytokine, is important in the generation of a Th1-biased immune response. Several polymorphisms have been described in IL12B, the gene encoding the p40 subunit of IL-12. A bi-allelic polymorphism within the IL12B promoter region has been reported to show association with diseases as diverse as severe childhood asthma and fatal cerebral malaria. Methods: In order to define the molecular basis for these disease associations we investigated the secretion of IL-12 by human monocyte-derived dendritic cells. The amount of IL-12p40 and p70 produced by DCs from normal blood donors was determined following CD40L activation. Subsequently, we therefore sought to investigate the frequency of IL12B genotypes and their impact on the outcome of patients with malignant melanoma. Genomic DNA was isolated from 75 normal blood donors and 80 melanoma cell lines and used for genotyping the IL12B polymorphism. Corresponding clinical data were retrieved from the in-house melanoma database. Results: Allele frequency for IL12Bpro-1 is 0.45 and for IL12Bpro-2 0.55. Homozygotes for the IL12B promoter polymorphism showed a 10-fold difference in median p70 secretion in response to CD40 ligation. Remarkably, this difference resulted from the inability of most allele 1 homozygotes to secrete heterodimeric IL-12. In contrast, most of the donors homozygous for allele 2 had detectable secretion. Distribution of genotypes in melanoma patients was not significantly different from normal blood donors. Kaplan-Meier survival analysis showed significantly decreased survival of patients homozygous for the longer allele, previously defined as being associated with decreased IL-12 secretion (log-rank p=0.015). Subgroup analysis indicated that this survival advantage was seen exclusively in female patients. Conclusions: The recently described IL12B promoter polymorphism is highly correlated with secretion of bioactive IL-12 and has a significant impact on the clinical course of disease in patients with melanoma and may therefore be useful for prognostic stratification. No significant financial relationships to disclose.