Methylation in the Promoter Region and Expression of FOX-P3 Correlate with Graft Versus Host Disease, Relapse and Survival after Allogeneic Stem Cell Transplantation

Introduction: Methylation of CpG dinucleotides is a fundamental mechanism of epigenetic regulation in eukaryotic genomes that controls the expression of certain genes. FOX-P3 is a member of the forkhead/winged-helix family of transcriptional regulators which expression is constitutive in regulatory T lymphocytes CD4/CD25 (Treg). Recent evidence suggests that human effector T cells express FOX-P3, albeit transiently and with significantly lower levels. Therefore, FOX-P3 mehtylation within the promoter region and gene expression could play a role in allogeneic stem cell transplantation (alloSCT).

Objective: To analyze the association between the mehtylation status and the levels of expression of FOX-P3 with the dynamics of chimerism and the development of complications after alloSCT.

Patients and methods: The degree of methylation was quantified in a 600 pb CpG island within the regulatory sequence of FOX-P3 by quantitative methylation-specific real time-PCR from 32 peripheral blood (PB) samples obtained within the first month post-alloSCT. Moreover, the expression level of FOX-P3 mRNA was analyzed by real-time quantitative PCR in 18 patients from which RNA samples were available. Results were analyzed using Fisher’s exact test due to the reduced sample size.

Results: A statistically significant association (Table 1) was observed between a higher degree of methylation in the FOX-P3 promoter and a lower incidence of acute graft versus host disease (GVHD) grades II-IV (35.3% vs a 88.9% in low methylation patients; p=0.014). Moreover, patients with higher degree of methylation showed significantly higher incidence of disease relapse (41.2% vs a 0% in low methylation patients; p=0.05). The observation of a high degree of methylation would reflect a lower amount of FOX-P3 expressing cells, both Treg and effector cells. Since Treg comprises a minority population, such observation would result from relative low levels of effector T cells, which would explain the lower graft-versus-host and graft-versus-leukemia effect observed in high mehtylation group. Surprisingly, when FOX-P3 mRNA levels were analyzed, an association with statistical significance between a higher methylation status and a higher expression of FOX-P3 (90% vs 55.8%; p=0.047) was observed. It has been shown that FOX-P3 is mainly produced by Treg while effector T cells produce very low amounts of FOX-P3 mRNA. In this sense, a higher amount of Treg cells produces high FOX-P3 mRNA levels and reduces the number of effector T cells, resulting in a higher methylation status in PB samples, in which most cells would have methylated FOX-P3. Low FOX-P3 expression would, in turn, indicate a lower amount of Treg to suppress the immune activation, resulting in higher amount of effector T cells and therefore would be associated with a lower methylation. Additionally, a significant association between higher FOX-P3 expression and lower incidence of death (7.7% vs 80%; p=0.007) was observed. Moreover, the main cause of death (3/4) in the group with lower expression of FOX-P3 was acute GVHD. The lower amount of effector T cells in PB samples with high FOX-P3 expression would protect from the development of GVHD.

Conclusions: Both FOX-P3 mRNA expression and promoter methylation are of prognostic value for the development of complications post-SCT. These determinations would favor an early establishment of the immunotherapeutic options for an improved management of transplanted patients.

Table 1. Association between FOX-P3 promoter methylation and mRNA expression with chimerism and complications post-SCT.

MC, mixed chimerism; PB, peripheral blood; Fail/Reject., graft failure/rejection. p, Fisher`s Test.