The Genotype of T-Cell Costimulatory Molecule Is Associated with Relapse Incidence In Patients with Acute Myeloid Leukemia After Allogeneic Hematopoietic Cell Transplantation

Disease relapse is one of 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 graft-versus-host disease (GVHD) or contribute to relapse prevention through recognition and elimination of minimal residual disease. CD28 is the primary T-cell costimulatory molecule constitutively expressed on the majority of T cells. Upon interaction with its ligands B7, CD28 transduces a signal that enhances the activation and proliferation of T cells. Another member of the CD28 family is inducible co-stimulator (ICOS). Although not constitutively expressed, ICOS is rapidly upregulated on T lymphocytes upon activation. Cytotoxic T-lymphocyte antigen 4 (CTLA-4), a homologous molecule of CD28, is a key factor in regulating and maintaining self-tolerance, providing a negative signal to T cells. Although several single-nucleotide polymorphisms (SNPs) within those costimulatory molecule genes have been identified to be associated with the risk of autoimmune disease, their association with outcome after allo-HSCT has yet to be explored. This present study was designed to investigate the influence of CD28, ICOS and CTLA-4 genes polymorphisms on the outcome of patients with acute myeloid leukemia (AML) after allo-HSCT.

The entire study population consisted of 86 consecutive AML patients and their donors who were transplanted from 2001 to 2009 in our Unit. Genomic DNA was extracted from peripheral blood samples obtained from recipients and donors before transplantation. Five SNPs of CD28 -594(A/G), ICOS -693(G/A) and CTLA-4 -1722(A/G), +49(A/G) and CT60(A/G) were analyzed.

(1) The media age of the patients was 27 years (range, 12–49 years). At the time of transplantation, 70 patients were in first complete remission (CR), 10 patients in second CR, 3 patients in third CR and 3 patients in progressive status. 33 patients underwent HLA-matched sibling HSCT and 53 patients underwent unrelated HSCT. All patients received myeloablative conditioning based on busulfan/cyclophosphamide (BuCy) without total body irradiation (TBI). The GVHD prophylaxis is consisted of cyclosporin A, a short-term methotrexate and mycophenolate mofetil. (2) Only one patient experienced engraftment failure. 18(20.9%), 20(23.3%) and 3(3.5%) patients respectively developed grade I, II and severe acute GVHD (aGVHD). 16(18.6%) and 15(17.4%) patients developed limited and extensive chronic GVHD (cGVHD). (3) 17 patients (19.8%) experienced relapse, the media time was 15.6 months after allo-HSCT (range, 2–24 months). (4) Patients receiving stem cells from a donor with AA genotype in position +49 or CT60 of CTLA-4 gene relapsed more frequently than those with AG/GG genotypes (for +49: 50% vs 14.1%, P=0.012; for CT60: 80% vs 16%, P<0.0001). (5) Patients receiving stem cells from a donor with CD28 -594 AA genotype had a lower incidence of relapse than those with other genotypes (0 vs 25%, P=0.04), due to a higher incidence of aGVHD (83.3% vs 38.2%, P=0.004). (6) In multivariate analysis, donor with CTLA-4 CT60 AA genotype (RR=13.411, 95%CI: 3.808–47.233, P<0.0001), and absence of cGVHD (RR=2.12, 95%CI: 1.112–4.042, P=0.022) were found to significantly contribute to the risk of relapse after allo-HSCT. Furthermore, patients receiving CTLA-4 CT60 AA genotype donor had worse overall survival at 7 years (20% vs 77.8%, RR=10, 95%CI: 3.761–16.239, P<0.0001). The polymorphic sites CTLA-4 -1722 and ICOS -693 did not correlate with the risk of relapse. Nor did patient 5 polymorphic sites genotype.

These results, which is the first report of T-cell costimulatory molecule genes polymorphic features with the risk of leukemia relapse in AML patients after allo-HSCT, suggest an interaction between donor CTLA-4 CT60 AA genotype and the risk of relapse. The CTLA-4 CT60 AA genotype has been reported to increase the production of soluble form of CTLA-4, suggesting that increased expression of CTLA-4 would be associated with a decrease ability of the immune system to detect and eliminate tumor associated antigens. According to our results, anti-CTLA-4 antibodies may be a promising therapeutic strategy in leukemia relapse after allo-HSCT at least in patients receiving CTLA-4 CT60 AA genotype donor.

No relevant conflicts of interest to declare.