CTLA-4 Polymorphisms: Influence on Transplant-Related Mortality and Survival in Children Undergoing Allogeneic Hematopoietic Stem Cell Transplantation

Background: Allogeneic hematopoietic stem cell transplantation (HSCT) is a curative approach for a variety of hematologic diseases but is still associated with substantial morbidity and mortality. Transplant-related mortality (TRM) after HSCT depends mainly on the toxicity of the conditioning regimen, infections, and graft-versus-host disease (GVHD). Polymorphisms at major histocompatibility complex MHC) have been proven to be critical for successful allogeneic HSCT. Polymorphisms at non-MHC loci have been associated with HSCT outcome as well. Cytotoxic T-lymphocyte antigen-4 (CTLA-4) is an inhibitory molecule that down-regulates T-cell activation. The purpose of this study was to identify an association between CTLA-4 single nucleotide polymorphisms (SNPs) and TRM in children undergoing allogeneic HSCT.

Methods: 153 donors and 153 children (median age, 11 years) with acute lymphoblastic leukemia (n=90), acute myeloid leukemia (n=58) or juvenile myelomonocytic leukemia (n=5) who underwent allogeneic HSCT in a single center were genotyped of CTLA-4 gene for rs3087243 (CT60 A/G), rs231775 (+49 A/G) and rs4553808 using TaqMan real-time polymerase chain reaction. 49 children were transplanted in first, 40 children in second and 15 in third complete remissions. 49 patients did not reach complete remission at the time of transplantation. The donor was HLA-matched unrelated in 59% of transplants and HLA-identical related in 41% of transplants. Conditioning regimen was myeloablative in all cases and based on total body irradiation in 52% of transplants or busulfan in 44% of transplants. Two forms of post-transplant immunosuppression predominated, cyclosporine A and methotrexate in 64% of transplants and cyclosporine A alone in 25% of transplants.

Results: We observed a significant association between the donor´s CTLA-4 genotype of rs3087243 and TRM in children undergoing allogeneic HSCT. Genotype AG of CTLA-4 rs3087243 SNP was found in 78 donors (51%), GG in 44 donors (29%), and 31 donors were homozygous for AA (20%). 30 patients died of transplant-related causes. 16 patients died of multi-organ failure, 7 of infection, 3 of acute GVHD, 2 of chronic GVHD, and 2 of hepatic sinusoidal obstruction syndrome. Interestingly, we observed a significantly reduced TRM in children who were transplanted from a donor with the CTLA-4 genotype GG in comparison to genotype AG or AA of rs3087243 (9% versus 19% versus 36%, p=0.013). In addition, we found significant differences of event-free survival (EFS) depending on the donor´s genotype. The EFS was 64%, 46% or 32% if the patient was transplanted from a donor with CTLA-4 genotype GG, AG or AA of rs3087243, respectively (p=0.043). In multivariate analysis, CTLA-4 genotype of rs3087243 was an independent risk factor for TRM (0.021). The CTLA-4 genotypes, in either donors or recipients, had no significant impact on relapse rate, acute and chronic graft-versus host disease.

Conclusions: This study provides the first evidence that the CTLA-4 polymorphisms are significant risk factors for TRM and survival in children undergoing allogeneic HSCT and should be evaluated in further trials.