The PTPN22 R620W Polymorphism is Associated With Severe... : Transplantation (original) (raw)
PTPN22 gene encodes a protein tyrosine phosphatase that is expressed in T and B lymphocytes, monocytes, dendritic cells, neutrophils, and natural killer cells. PTPN22 is an important negative regulator of T-cell activation by dephosphorylating and inactivating T-cell receptor (TCR)-associated kinases.
A C/T transition at position 1858 of PTPN22 gene resulting in the amino acid substitution Arg620Trp in the encoded PTPN22 protein has been associated with several autoimmune diseases (type I diabetes, systemic lupus erythematosus, rheumatoid arthritis, and Graves disease) (1).
Because of the role of PTPN22 in immune response and the association of its polymorphism with autoimmune diseases, we hypothesized that C1858T polymorphism of PTPN22 could impact immune reconstitution and graft-versus-host disease (GVHD) after allogeneic hematopoietic stem-cell transplantations (allo-HSCT) whose outcome is essentially impaired by immunological and infectious complications.
MATERIALS AND METHODS
Patients
One hundred ninety-two patients who received a non-T-depleted bone marrow transplant from a human leukocyte antigen (HLA)-identical sibling donor for malignant diseases were included in this analysis. All patients, donors, and transplants characteristics are listed in Table 1. None of these characteristics is statistically different after Bonferroni correction with respect to donor C1858T PTPN22 genotypes. The main outcome complications are listed in Table 2. All donors have signed an informed consent.
Patients and donors characteristics
PTPN22 donor genotype and HSCT outcome
Clinical Endpoint Definitions
Infection Definitions
First episodes of severe bacterial, fungal, and cytomegalovirus (CMV) infections were analyzed up to 180 days after transplantation according to the criteria described by Rocha et al. (2). Briefly, the criteria were for:
Bacterial Infection
We considered severe bacterial infection if they developed sepsis (n=24), pneumonia (n=17), or septic shock (n=5), according to published criteria (2).
Cytomegalovirus Infection
Cytomegalovirus reactivation was defined by a positive antigenemia level (presence of two or more positive nuclei per 200,000 leukocytes). Cytomegalovirus disease was diagnosed according to previously published criteria (2).
Fungal Infection
Candidaemia was defined by one or more positive blood culture for Candida sp. Invasive candidiasis was defined by clinical and radiological signs of fungal infection with one or more positive blood culture for Candida sp. (2).
Acute Graft-Versus-Host Disease
All patients were considered evaluable for acute GVHD at day +1 after transplantation and graded as in Ref. (2).
Chronic Graft-Versus-Host Disease
This was evaluated among patients who survived with sustained engraftment of +100 days after transplantation according to published criteria (2).
Relapse
Thirty-three of 192 (17%) cases have relapsed at the time of the study.
Transplantation-Related Mortality
Fifty-three patients died of transplantation-related complications.
Survival
It was calculated from the time of transplantation to death from any cause.
Gene Polymorphism Typing
The genotyping of the PTPN22 was performed by using a polymerase chain reaction-restriction fragment length polymorphism method as previously described (3).
Statistical Analysis
Differences in categorical variables between two groups were evaluated by chi-square analysis. Bonferroni rule was applied to correct for multiple-comparison. Univariate and multivariate proportional hazard regression models were used to identify independent risk factors of death by means of log-rank tests and Cox proportional hazard models, respectively. The univariate Kaplan–Meier analysis was used to describe risk factors of death. Cumulative incidence using competing risk method as described by Fine and Gray (4) was used for assessment of prognosis factors of GVHD infections, transplantation-related mortality, and relapse with death (without relapse for relapse analysis) as a competing event. Cox regression analysis was also used in multivariate analysis of risk factors of infections. All tests were two-sided, with type I error rate fixed at 0.05. Statistical analyses were performed with SPSS 14 software and “R” packages: “cmprsk” (competing risks) and “coxph” (Cox regression able to maximize a penalized partial likelihood).
RESULTS
Polymorphism Frequency
The donor phenotypic frequencies of C1858T PTPN22 polymorphism are CC=87% (n=167), CT=11.5% (n=22), and TT=1.5% (n=3). The frequencies were not statistically different from those reported in the literature (1,5).
C1858T PTPN22 Polymorphism and Infectious Diseases After Hematopoietic Stem-Cell Transplantations
Data analysis showed that PTPN22 polymorphism was not associated with CMV reactivation (grafts performed between CMV seronegative donors and recipients were excluded). At the opposite, donor CC genotype seemed to be associated with severe bacterial infections compared with CT and TT genotypes (cumulative incidence at day 180: 24% for CC genotype vs. 0% for CT+TT genotypes, _P_=0.003). Forty-six patients presented with severe bacterial infections: 14 were infected with gram-positive bacteria (9 of 14 were staphylococcus), 24 with gram-negative bacteria. For eight patients, the causative agent was not documented (Table 2). In Cox multivariate analysis stratified on acute GVHD, when studying PTPN22 genotype (CC vs. others), chronic GVHD and delay of neutrophil reconstitution (>5×109/L), two factors seemed to be independent risk factors of severe bacterial infections: PTPN22 donor genotype (_P_=0.036, hazard ratio=2.28, 95% confidence interval=1.06–4.90) and chronic GVHD (_P_=0.041, hazard ratio=1.96, 95% Confidence interval=1.03–3.75).
Considering fungal infections, donor CC genotype of C1858T PTPN22 also seemed to be a risk factor (cumulative incidence at day 180: 12% for CC vs. 0% for CT+TT genotypes, _P_=0.04) although not statistically significant in a multivariate analysis including the previously mentioned factors.
Looking for an association with the other endpoints of the study, no association was observed between donor PTPN22 polymorphism and severe acute GVHD, chronic GVHD, relapse, and transplantation-related mortality.
A significant association was found between survival and donor PTPN22 genotype at 30 months (63% for CC vs. 83% for CT+TT genotypes, _P_=0.03), but this result was not confirmed in a multivariate analysis including sex matching, donor or recipient CMV serology, severity of the disease, and age of recipient.
No other association with any endpoint of the study has been found by multivariate analysis when considering the recipient PTPN22 genotype.
DISCUSSION
This study showed a strong association between donor 1858T PTPN22 polymorphism and the protection against severe bacterial infections after non-T-cell depleted bone marrow transplantation from an HLA identical sibling donor.
Active natural and acquired immune responses participate to the response to bacterial infections. Natural immune mechanisms such as dendritic cells, natural killer cells, macrophages, and neutrophils have an important role in the control of bacterial infections as well as the acquired immune response through helper T cells and humoral responses.
PTPN22 is a tyrosine phosphatase involved in limiting the adaptative response to antigen by dephosphorylating and inactivating TCR-associated kinases and their substrates. In lymphocytes, PTPN22 physically associates with the Csk kinase, an important suppressor of the Src family kinases that mediate TCR signaling. PTPN22 inhibits activation of T cells in a synergistic manner with Csk (6,7).
It has been shown that substituting of Arginin 620 (encoded by 1858C allele) by a tryptophan residue (encoded by 1858T allele) in the PTPN22 protein disrupts the formation of the complex between PTPN22 and Csk (3), suggesting that Csk tyrosine kinase activity and the inhibition of T-cell activation could be impaired. However, despite not binding Csk, PTPN22 Trp620 is a more potent inhibitor of TCR signaling (8). It is therefore still difficult to draw any conclusion about functional consequences of PTPN22 C1858T polymorphism.
In addition, the function of PTPN22 is not restricted to T cells because PTPN22 may be expressed in all hematopoietic tissues and in normal human peripheral blood monocyte cells, especially in natural killer cells and neutrophils (5).
Actually, we did not find an impact on the occurrence of acute GVHD but conversely on susceptibility to severe bacterial infections. This reflects the extreme complexity of alloreactivity in the GVHD process in humans (9).
Two recent studies have shown that C1858T PTPN22 polymorphism could influence immune response against infectious diseases: the 1858T allele was suggested to be a protective factor against Mycobacterium tuberculosis (10), and the same allele to be a risk factor of invasive pneumococcal disease and gram-positive thoracic empyema (11). Chapman et al. studied nonimmunocompromised patients suffering from pneumococcal infections and gram-positive empyema (82.8% streptococcus and 11.7% staphylococcus), whereas we exclusively studied immunodepressed patients, 63% of them suffering from gram-negative infections. In fact, Chapman et al. clearly showed an association of 1858T allele of PTPN22 with pneumococcal and streptococcal infections but not with gram-negative infections. The natural and acquired immune defenses against bacteria are greatly impaired after HSCT. The acquired immune response is particularly durably affected. Our observation linking PTPN22 C1858T polymorphism and severe infections early after transplant is suggestive of a role through the function of neutrophils or other cells from the myeloid lineage in an ongoing process of hematological reconstitution. Therefore, the differences in the impact of C1858T PTPN22 polymorphism observed in Chapman study compared with ours could be explained by differences in the type of bacterial infections and also in the host immune status.
We focused this study on bone marrow transplantation, excluding transplantations with peripheral blood stem cells that have a different pattern of immune reconstitution. Myeloid recovery is more rapid and the rate of severe infections lower (12) in this graft setting where these data would need to be evaluated specifically.
In total, these results further illustrate the importance of defining genetic susceptibility to infectious complications, especially in allo-HSCT in the context of an ongoing immune recovery. From a practical point of view, this could help to better define patients at risk of severe bacterial infections, who could benefit from a reinforced antimicrobial prophylaxis.
REFERENCES
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11. Chapman SJ, Khor CC, Vannberg FO, et al. PTPN22 and invasive bacterial disease. Nat Genet 2006; 38: 499.
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Keywords:
Hematopoietic stem-cell transplantation; PTPN22 polymorphism; Bacterial infection
© 2008 Lippincott Williams & Wilkins, Inc.