Introduction: In liver transplantation (LT), de novo donor-specific antibody (dnDSA) formation is one of the factors that can affect long-term prognosis after transplantation, and it is very important to predict its risk. Recently, follicular helper T (Tfh) cells, a subtype of CD4+ T cells, were reported to play an important role in dnDSA formation after solid organ transplantation. Genetic polymorphisms are one of the determinants of humoral response, and the candidate gene approach is an effective way to identify genetic risk factors for complex diseases such as dnDSA formation. Given the growing recognition of the importance of Tfh cells in generating a strong humoral immune response, it is reasonable to hypothesize that single nucleotide polymorphisms (SNPs) in Tfh cells related molecules are associated with dnDSA formation after LT. Therefore, in this study, six single nucleotide polymorphisms (SNPs) within six genes (BCL6, CXCR5, CXCL13, ICOS, CD40L, and IL21) were selected and analyzed to determine if Tfh cell-related polymorphisms contribute to dnDSA formation after LT.
Methods: A total of 60 patients underwent living-donor LT at the Hiroshima University Hospital between January 2010 and July 2022 were included. Clinical data, including patient characteristics and perioperative variables, were collected. Anti-HLA antibodies of all recipients were analyzed before transplantation and monitored annually post-transplantation. Mean fluorescence intensity values above 1,000 for DSAs against HLA-A, -B, -C, -DRB1, and -DQB1 at the 4-digit level were considered positive. Six Tfh-related SNPs (rs1056932 in BCL6, rs3922 in CXCR5, rs355687 in CXCL13, rs1126535 in ICOS, rs440425 in CD40L, and rs907715 in IL21) were detected by TaqMan SNP genotyping.
Results: Among the 60 LT recipients, 13 developed dnDSAs during the observation period. Statistically significant differences in baseline characteristics between patients with and without dnDSA formation were not observed except for ABO compatibility and HLA-DQ allele mismatch. Among the six Tfh-related SNPs, no SNPs were associated with significantly higher de novo DSA positivity, but AA genotype of rs10569322 in BCL6 and TT genotype of rs907715 in IL21 tended to have higher DSA positivity. To clarify whether any cumulative effect of SNPs associated with dnDSA formation exist, the patients were classified into two groups based on their BCL6 and IL21 SNP genotypes. Patients harboring the AA genotype of rs10569322 and TT genotype of rs907715 (group1) had higher rates of dnDSA formation than patients with all other genotypes (group2) (42.3% vs 15.2%, p=0.03).
Conclusions: Our findings indicate that genetic polymorphisms in Tfh cell-related molecules can be  predisposing factors for dnDSA formation after LT. A rigorously designed, large-scale prospective study is essential to further validate these results.