Background. A single nucleotide polymorphism in the tumor necrosis factor type II receptor (TNFRII) gene, codon 196, results in the substitution of arginine (R allele) for methionine (M allele). The 196R allele is reportedly associated with an increased susceptibility to autoimmune disease, and donor 196R allele carriage correlates with increased severity of acute graft-versus-host disease (GVHD) after matched unrelated bone marrow transplantation (BMT).
Methods. We investigated the impact of donor and recipient TNFRII genotype on GVHD incidence and severity among 104 adult recipients of myeloablative sibling BMTs.
Results. 196R allele frequency was 0.28 among recipients, donors, and controls. There was an increased incidence of acute GVHD among 196R-positive recipients (odds ratio [OR] 3.6, P =0.05). This association was confirmed in multivariate analysis (relative risk 4, P =0.04), correcting for previously established clinical and genetic risk factors. Donor 196R homozygosity was associated with an increased incidence of extensive chronic GVHD (OR 18.5, P =0.02). This association was also confirmed in multivariate analysis (OR 11, P =0.02). To investigate the functional impact of the TNFRII 196 M/R polymorphism, 79 volunteer blood donors were genotyped at this locus, by polymerase chain reaction and single-strand conformational polymorphism analysis, and plasma soluble TNFRII (sTNFRII) levels were measured by ELISA. Mean plasma sTNFRII levels (pg/mL: ±SEM) were 1224 (±26) and 1063 (±65) for 196M-postive (196 M homozygous or heterozygous) individuals and 196R homozygotes, respectively (P =0.02).
Conclusions. Because sTNFRIIs can act as TNF antagonists, the association between recipient and donor TNFRII 196R allele status and acute or extensive chronic GVHD incidence, respectively, may reflect reduced circulating sTNFRII.
Graft-versus-host disease (GVHD) is the most common severe complication after allogeneic bone marrow transplantation (BMT) (1). Tumor necrosis factor-α (TNF) is a proinflammatory cytokine that has a central role in the pathogenesis of GVHD (2). The actions of TNF are mediated by two receptors: a 55- to 60-kDa type I receptor (TNFRI) and a 75- to 80-kDa type II receptor (TNFRII). TNFRI and TNFRII have been found on most cell types examined to date, with the exception of erythrocytes (3). There are, however, quantitative differences in receptor expression: TNFRII is more abundant on endothelial and hematopoietic cells (3). Distinct cellular responses can be generated by TNF binding at each of these receptors. TNFRI seems to be the primary mediator of TNF-induced cytotoxicity and TNF-induced cell death in nonlymphoid cells (4). Binding at TNFRII evokes apoptosis among CD8+ cells (5) but can also stimulate proliferation of hematopoietic cells, particularly T cells (6). In addition, TNFRII potentiates the effects of TNF at TNFRI (4,7).
The TNFRII gene is located at chromosome position 1p36. Genome-wide scanning highlighted this area as a candidate region for genetic susceptibility to systemic lupus erythematosus (SLE) (8). A single nucleotide polymorphism has subsequently been found in exon 6 at codon 196 (ATG→AGG) (9). This polymorphism results in a nonconservative amino acid substitution [methionine (M)→arginine(R)]. The wild-type allele is denoted 196 M and the polymorphic allele 196R. Two studies, both examining Japanese cohorts, have demonstrated an association between R allele carriage and increased susceptibility to SLE (9,10). Other groups have, however, been unable to confirm these observations (11-13). In a white cohort, 196R allele carriage has been found to associate with an increased susceptibility to rheumatoid arthritis in those with a family history of the disease (14). To date, one study has examined the association between donor and recipient TNFRII 196 genotype and outcome after BMT (15). This Japanese study was undertaken in the matched unrelated donor (MUD) transplant setting and demonstrated that donor 196R allele carriage was associated with a higher cumulative incidence of severe acute GVHD.
The functional significance of the TNFRII 196 polymorphism has not been established, although there is some in vitro evidence that signal transduction by the 196R allele may be more efficient than that by the 196 M allele (10). Two structural considerations may be relevant. First, exon 6 of the gene encodes part of the TNFRII transmembrane domain and in addition codes for the site of proteolytic cleavage, resulting in the generation of soluble TNFRII (sTNFRII) (6). Second, the TNFRII 196 polymorphism is located within one of four cysteine-rich domains that are important for optimal TNF binding (10).
Given the documented associations between the TNFRII 196 R allele and certain inflammatory disorders, we hypothesized that TNFRII 196 R allele carriage by donors or recipients would associate with an increased likelihood of GVHD in matched sibling BMT recipients. We therefore investigated the impact of TNFRII 196 M/R genotype on the incidence and severity of acute and chronic GVHD in a cohort of HLA-identical sibling BMT recipients. In addition, we investigated the effect of TNFRII 196 M/R genotype on sTNFRII levels in a normal control population.