Genetic Variation in the Effector Pathways of Cytotoxic T Lymphocytes Influences Alloimmune Reactivities Following Allogeneic Hematopoietic Stem Cell Transplantation

Disease relapse, major infection and graft-versus-host disease (GVHD) are the leading causes of death following allogeneic hematopoietic stem cell transplantation (allo-HSCT). Donor T lymphocytes play a critical role in alloimmune recognition and their ability to detect non-self-antigens can lead to GVHD or contribute to prevention of relapse and infection. Three effector pathways have been described for T-cell cytotoxicity: granzyme B/perforin, Fas/Fas ligand (FasL) and secreted molecules such as tumor necrosis factor (TNF)-alpha. Granzyme B is a proapoptotic serine protease. Fas is widely expressed in immunocompetent cells and non-lymphoid tissues. FasL is mainly expressed on activated cytotoxic T lymphocytes (CTLs). When CTLs recognize target cells, they become activated and express FasL which induces apoptosis of target cells. The Fas gene has been found to be silenced in many tumor types. The importance of those effector pathways for the development of acute GVHD (aGVHD) has been well established. In our previous study, we have reported donor and/or recipient TNF-alpha gene polymorphism influenced on the risk of aGVHD. Recently several important polymorphisms have been identified in granzyme B, Fas, and FasL genes and reported to be relevant to allograft rejection in solid organ transplant patients. However, such information is less available in allo-HSCT. This present study was designed to investigate the influence of donor and recipient genetic variations of effector pathway molecules on the abilities of T-cell alloimmune responses including GVHD, cytomegalovirus (CMV) infection within 100 days and disease relapse following allo-HSCT. Methods: The entire study population consisted of 138 pairs of recipients and their unrelated donors, who underwent HSCT in our Center from January 2001 to March 2009. Genomic DNA was extracted from peripheral blood samples obtained from recipients and donors before transplantation. Five single nucleotide polymorphisms (SNPs) including granzyme B +55(A/G), -295(C/T), Fas -1377(G/A), -670(T/C) and FasL -844 (T/C) were analyzed. Results: (1) Patients receiving stem cells from a donor with granzyme B +55 AA genotype developed aGVHD more frequently than those with mutated allele (AG or GG), which has been reported to be associated with low-producing of granzyme B by CTLs and incapable of inducing apoptosis. Multivariate analysis confirmed that donor with the granzyme B +55 AA genotype was an independent risk factor for aGVHD (RR=1.545, 95%CI: 1.012–2.357, P=0.044). (2) Donor with FasL -844 TT genotype, a genotype reported to a reduction in the expression of FasL on T cells, conferred protection against the risk of aGVHD (RR=2.981, 95% CI: 1.320–6.736, P=0.009), however was an independent risk factor for early CMV infection (RR: 3.658, 95% CI: 1.534–8.722, P=0.003). Patients experiencing aGVHD have a higher risk of developing early CMV infection (RR=1.931, 95% CI: 1.242–3.003, P=0.003), early CMV infection also was a significant factor impacting aGVHD (RR=1.630, 95%CI: 1.294–2.053, P<0.001). (3) Recipient with Fas -670 C- allele positive, a mutated allele with higher Fas expression, was associated with a significantly lower risk of relapse (RR=3.453, 95% CI: 1.699–7.091, P=0.001) as well as superior overall survival (84.2% vs 21.2%, P<0.001) in patients with acute myeloid leukemia (AML), but not in patients with other myelogenous or lymphoid malignancies. The polymorphic sites granzyme B -295(C/T), Fas -1377(G/A), did not correlate with the T-cell alloimmune reactivities. Conclusions: Genetic variation, other than HLA polymorphism, regulating the immune response may influence outcomes of patients undergoing allo-HSCT. Transplant patients would thus benefit from accurate risk assessment and individualization of immunosuppressive therapy, taking into account donor and recipient genetic data, as well as other risk factors. This study is the first report of relationship between donor or recipient genetic variations of effector pathway molecules and the abilities of T-cell alloimmune responses. According to our results, special targeting granzyme B and Fas/FasL pathways may be a promising therapeutic strategy in patients with aGVHD, CMV infection and leukemia relapse after allo-HSCT at least in AML patients harboring Fas -670 wild-type genotype.

No relevant conflicts of interest to declare.