The Genotype of the Donor for the (GT)_n Polymorphism in the Promoter/Enhancer of the FOXP3 Gene Influences Graft Versus Host Disease without Affecting Graft Versus Leukemia Effect After Myeloablative HLA-Identical Allogeneic Stem Cell Transplantation

The FOXP3 gene encodes for a protein (Foxp3) involved in the development and functional activity of regulatory T cells (CD4+/CD25+/Foxp3+, Tregs) which exert regulatory and suppressive roles over the immune system. After allogeneic stem cell transplantation (allo-SCT), Tregs are known to mitigate graft versus host disease (GVHD) while maintaining a graft versus leukemia effect (GVL). Allele (GT)₁₅ for the functional (GT)_n polymorphism in the promoter/enhancer of the FOXP3 gene is associated with a higher expression of FOXP3 and production of a greater amount of Tregs. However, its impact in the allo-SCT setting has not been analyzed.

To analyze the impact of the (GT)_n polymorphism in the promoter/enhancer of the FOXP3 gene on the development of complications and ultimately on the success of conventional HLA-identical allo-SCT.

The study includes 33 patients with hematological malignancies, treated with myeloablative HLA-identical peripheral blood allo-SCT (Table 1). Diagnosis, classification and grading of GVHD were made by clinical criteria and confirmed when necessary by pathological examination of histological samples from gut, skin, liver or lung, according to international consensus criteria. Donor and recipient genomic DNA was purified from EDTA anticoagulated peripheral blood before allo-SCT and using QIAamp Blood DNA extraction kit (Qiagen). Genotyping of the (GT)_n microsatellite polymorphism in the FOXP3 gene was performed by a fluorescence-based short tandem repeat-polymerase chain reaction (STR-PCR) method (GeneAmp 7900; Applied Biosystems) and sized by capillary electrophoresis (POP7 - ABI PRISM 3130 xL Genetic Analyzer; Applied Biosystems) followed by fragment analysis (GeneMapper 4.0 Software; Applied Biosystems) as previously described [Bassuny WM, et al. Immunogenetics. 2003;55 :149–56].

The median follow-up time for the cohort was 34 months (range 9.5–110). Allelic frequencies observed were similar to those previously reported (50.5% (GT)₁₅, 41% (GT)₁₆ and 7% (GT)₁₇; no (GT)₁₄ or (GT)₁₈ alleles were found). Patients transplanted from donors harboring allele (GT)₁₅ showed a lower incidence of grades II-IV acute GVHD (29% vs 67%; p =0.049). These patients also showed a trend to a lower incidence of severe (grades III-IV) GVHD (12% vs 33%; p =0.167) as well as chronic GVHD (75% vs 100%; p =0.143; Table 1, Figure 1). No statistically differences were found between patients transplanted from (GT)₁₅ and non-(GT)₁₅ donors in terms of relapse rate (38% vs 33%; p =0.825; Table 1) or cumulative incidence of relapse (CIR at 2 years 35.3% vs 37.5%, Figure 2). Finally, survival analysis did not show statistically significant differences between the two groups of patients in terms of median event (relapse) free survival (EFS, 15.6 months vs 4.5 months, p =0.686) or overall survival (OS, 29 months vs not reached, p =0.610).

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Tregs are known to modulate the allotolerance-alloreactivity balance between donor and recipient in the allo-SCT setting, mitigating GVHD while preserving the anti-tumor effect (GVL) of the donor graft. In the present study, the presence of allele (GT)₁₅ in the donor, which promotes a higher expression of FOXP3 and greater amount of Tregs, affected allo-SCT outcome by decreasing grades II-IV acute GVHD and chronic GVHD, without affecting GVL (no differences in CIR and OS). Analysis of this polymorphism can help in appropriate donor selection and, more importantly, drive a tailored management of patients submitted to allo-SCT.

No relevant conflicts of interest to declare.