Polymorphism in the IFN-γ Gene Is Associated with Severe Acute Graft Versus Host Disease in β Thalassemia Major Patients Undergoing Matched Related Hematopoietic Stem Cell Transplantation (HSCT).

Acute graft versus host disease (aGVHD) is a major cause for morbidity and mortality following allogeneic HSCT (alloHSCT). Polymorphisms in Th2 cytokine genes such as IL-10 have been shown to modulate GVHD. Th1 cytokines, IFN-γ, TNF-α and IL-1β have been implicated in the pathogenesis of aGVHD in mouse models but there is limited data in human HSCT. We have evaluated the prevalence of the following functional polymorphisms in Th1 cytokines (IFN-γ +874, TNF-α −308, IL-1β −511 and +3953), Th2 cytokines (IL-10, IL-6), TGF-β and IL-1Ra in patients with β thalassemia major undergoing matched related alloHSCT and correlated them with the incidence of aGVHD. A total of 129 patients were evaluated. Patients who expired before day 15 (n=9) and for whom appropriate DNA samples were not available (n=18) were excluded. Of the 102 patients who were assessable, 72 (72%) patients received conditioning with Bu (16mg/kg) / Cy (200mg/kg) with anti-thymocyte globulin (ATG) while 30 (28%) patients received Bu (600mg/m2) / Cy (200mg/kg) without ATG. All patients received unmanipulated bone marrow and standard cyclosporine / short-course methotrexate towards prophylaxis against GVHD. Patients who died after HSCT without achieving ANC >500/mm3 were not assessed for aGVHD (n=6). Of the remaining 96 patients, 54 (53%) had aGVHD, 13 (24%) of which were grade III–IV. Apart from the immunogenetic markers mentioned above, the impact of other risk factors for aGVHD such as recipient and donor age, sex mismatch, conditioning regimen, cell dose, ABO compatibility and thalassaemia risk class were also analyzed. Of these, recipient age >10 years and female to male sex-mismatched transplants were found to increase the risk of developing severe aGVHD (grade III–IV). Among the cytokine polymorphisms evaluated, donor IFN-γ (dIFN-γ) +874 T/T genotype, associated with higher levels, was found to significantly increase the risk of developing severe aGVHD (RR= 4.9; p= 0.013; 95% CI 1.39–17.08). These results were also found to be consistent on forward stepwise multivariate analysis. No correlation was found between severe aGVHD and TNF-α, IFN-γ, IL 10 polymorphisms of recipients and IL-1Ra polymorphisms of donor. IFN-γ may facilitate antigen presentation and effector cell recruitment as elucidated in various experimental studies. Therefore, it is possible that dIFN-γ +874 T/T genotype might contribute to increased incidence of severe aGVHD since the effector T cells mediating aGVHD are of donor origin after transplant. Our data shows for the first time that development of severe aGVHD in patients with β thalassemia major undergoing matched related alloHSCT is affected by immunogenetic factors other than HLA.