Objectives: The main function of HLA is to present antigens to lymphocytes and to initiate specific immune responses. Autoimmune, viral, allergic, and neurologic diseases have been found to be related to HLA molecules. In renal transplant, the main target of the recipient’s immune system is the HLA molecules on the surface of donor cells. HLA also plays a role in the development of an immune response to viral infections. After renal transplant, BK virus infections may occur due to immunosuppression. Here, we investigated the relationship between HLA and BK virus in renal transplant recipients.
Materials and Methods: This retrospective study investigated HLA-A, HLA-B, and HLA-DR tissue typing before renal transplant. DNA was isolated from whole blood, and tissue typing tests were performed based on polymerase chain reaction. Patients were tested for BK virus posttransplant using DNA isolated from urine and/or plasma samples.
Results: We found HLA-B*13 allele to be a protective factor (P < .049; odds ratio: 0.131; 95% confidence interval, 0.017-1.029) and HLA-DRB1*03 allele to be a possible risk factor (P < .029; odds ratio: 2.521; 95% confidence interval, 1.157-5.490) against BK virus. No significant relationships were found between BK virus and age, sex, donor type, and HLA mismatch.
Conclusions: HLA class I molecules are known to be effective against viruses with the help of cytotoxic T cells. HLA-B*13 alleles within the HLA class I molecules were identified as protective factors against BK virus. HLA class II is associated with CD4-positive T cells that help secrete immune system cytokines, playing a role in stimulating and suppressing the immune system. We demonstrated that HLA-DRB1*03 allele could be a risk factor against BK virus. This allele may be associated with immunomodulatory cytokine secretion of the immune system.
Key words : HLA, Immunosuppression, Renal transplant, Viral infections
Renal transplant is still considered the best treatment modality in patients with end-stage renal disease, as it improves survival and quality of life.1 Numerous studies have identified HLA compliance as a key to improving patient outcomes after renal transplant. HLA antigens are the primary alloantigens recognized by the host immune system in organ transplant compatible with the ABO blood group.2 Graft survival after renal transplant in siblings with full HLA compliance has been considered to last longer than in relatives with less HLA compliance or HLA-matched deceased donors.3 Modern immunosuppressive treatments have improved graft survival after kidney transplant. However, aggressive immunosuppressive therapies can cause increased opportunistic infections such as BK virus (BKV) infections.4
HLA comprises a 3.6-million base-pair genomic region (6p21) located on the short arm of chromosome 6.3 HLA is important in the immune response to viral infections. Viral peptides are presented with HLA class I molecules that are associated with CD8-positive T cells. This presentation is effective in the formation of virus-specific memory T cells. HLA class II molecules are associated with CD4-positive T cells and are effective in effector T-cell formation. Effector T cells make CD8-positive T cells more efficient and stimulate B cells for virus-specific antibody production. Although CD8-positive T cells are effective in the immune response to many virus infections, these cells also affect human BKV infections.5
BK viruses are enveloped, approximately 45 nm in size viruses with a circular double-stranded DNA genome. This genome consists of approximately 5000 base pairs comprising 88% protein and 12% DNA.6
The aim of our study was to investigate the relationship between HLA tissue groups and clinically suspected BKV reactivation in renal transplant recipients.
Materials and Methods
This retrospective study analyzed 232 kidney transplants performed between January 2010 and October 2018 at the Başkent University Dr. Turgut Noyan Medical and Research Center in Turkey. This study was approved by the Baskent University Institutional Review Board (Project no: KA18/296). Clinical characteristics recorded included age, biologic sex, donor type (living/deceased), and HLA mismatch.
HLA-A, HLA-B (class I), and HLA-DRB1 (class II) tissue typing tests were performed before kidney transplant. First, DNA was isolated from patients’ whole blood with EDTA. For DNA isolation, a commercially available kit was used (EZ1 DNA blood 200 μL kit; Qiagen, Hilden, Germany).
Tissue typing tests were performed with the sequence-specific oligonucleotide (SSO) and/or the sequence-specific priming (SSP) method based on polymerase chain reaction. For HLA tissue typing with the SSP method, a commercially available kit was used (A-B-DR SSP Combi Tray; Olerup SSP AB, Stockholm, Switzerland); for HLA tissue typing with the SSO method, another commercially available kit was used (Lifecodes HLA -A, -B, -DRB1 eRES SSO typing kit; Immucor, Dreieich, Germany).
BK virus tests were routinely performed for recipients with suspicion of infection. DNA was isolated from whole blood with EDTA and/or urine sample(s) using a commercially available kit (EZ1 Virus Mini Kit v2.0; Qiagen). For BK virus DNA testing using quantitative real-time polymerase chain reaction, we used a commercially available test from Qiagen. The lowest detection threshold of BKV DNA was < 60 copies/mL.
Data were analyzed by chi-square method using SPSS software (SPSS: An IBM Company, version 17.0, IBM Corporation, Armonk, NY, USA). P < .05 was considered significant; 95% confidence intervals (95% CI) and odds ratios (OR) were reported.
Clinical characteristics of the study population are presented in Table 1. Prevalence of BKV was found in 37.1% (n = 86/232) of renal transplant recipients. No significant relationship was found between BKV and age, biologic sex, donor type, and HLA mismatch.
No significant relationship was shown between HLA-A alleles and BKV. When HLA-B alleles and BKV were compared, results for HLA-B*13 were statistically significant (P < .049; OR: 0.131; 95% CI, 0.017-1.029) (Table 2); HLA-B*13 may be a protective factor. When HLA-DRB1 alleles and BKV were compared, results for HLA-DRB1*03 were statistically significant (P < .029; OR: 2.521; 95% CI, 1.157-5.490) (Table 3). HLA-DRB1*03 could be a risk factor.
When BKV reactivation was examined according to patient sex, no statistically significant relationship was found between male (35.53%) and female (40%) recipients. Similar results were shown by Li and associates7 and Hässig and associates.4 However, Masutani and colleagues5 reported that male sex could be a significant (P < .001) risk factor. However, these differences may related to the study group, the number of patients included in the study, and the treatment protocol.
In deceased-donor transplant, immunosuppressive treatment is planned differently due to prolonged cold ischemia of the organ and generally low HLA compliance. Reactivation of BKV is dependent on immunosuppression; therefore, it is natural to expect BKV after deceased-donor transplant. Studies have reported that deceased-donor transplants have more complications, although not statistically significant in terms of BKV.4,5,8 Similarly, in our study, although not statistically significant, BKV infection was more common in deceased-donor versus living-donor transplant.
Our study group consisted of 175 adults and 57 children. Our center has performed the most pediatric patient transplants in the region. In our study, we observed no significant difference between pediatric and adult transplant recipients with regard to BKV infection. Other studies have also not found significant differences between adult and pediatric age groups.4,8-10
The most important factor in organ transplant is that the transplanted organ is not perceived as foreign by the recipient and rejected. Low HLA tissue mismatch between the recipient and donor reduces the risk of rejection. Two patients in our study who were BKV positive had 0/6 HLA mismatches. As HLA mismatch decreased, we noticed an increase in BKV positivity. Although there are publications that support this result,4,9 other studies have not reported a statistical difference between HLA-incompatible transplants and HLA fully compatible or semicompatible transplants and BKV infection.10 However, these studies that investigated the relationship between HLA mismatches and BKV aimed to reveal the relationship between the presence of cellular and humoral rejection after transplant. In our study, we aimed to investigate the relationship between HLA allele frequency and BKV reactivation regardless of the presence of rejection.
Class I HLA molecules are known to be effective against viruses with the help of the cytotoxic CD8-positive T cells. In our study, we determined that the HLA-B*13 allele within the HLA class I molecule is a protective factor (P < .049; OR: 0.131; 95% CI, 0.017-1.029), which supports this information.
HLA class II molecules are associated with CD4-positive T cells that help by secreting immune system cytokines. CD4-positive T cells play a role in both stimulating and suppressing the immune system. In our study, the HLA-DRB1*03 allele was found to be a risk factor (P < .029; OR: 2.521; 95% CI, 1.157-5.490) for BKV. This suggests that the immune response may be suppressive to the BKV response in renal transplant patients with the HLA-DRB1*03 allele.
There are few studies that have investigated the relationship between HLA alleles and BKV in renal transplant patients. Our results showed that the HLA-B*13 allele may be protective against BKV reactivation and that the HLA-DRB1*03 allele may be a risk factor in renal transplant patients. Further randomized studies with larger sample sizes will increase our knowledge on this issue.
Volume : 18
Issue : 1
Pages : 51 - 54
DOI : 10.6002/ect.TOND-TDTD2019.O24
From the 1Department of Medical Biology, Baskent University, Ankara; the
Typing and Transplantation Laboratory, Baskent University, Adana; the
3Department of Immunology, Baskent University, Ankara; and the 4Department of
Medical Microbiology, Baskent University, Adana, Turkey
Acknowledgements: This study was supported by the Baskent University Research Fund. The authors have no conflicts of interest to declare.
Corresponding author: Miray Kavuzlu, Başkent Üniversitesi Dr. Turgut Noyan Uygulama ve Araştırma Merkezi Dadaloğlu Mah. 2591 Sok. 4/A 01240 Yüreğir / Adana, Turkey
Table 1. Clinical Characteristics of Patients Positive and Negative for BK Virus
Table 2. The Most Common HLA-B Antigens and BK Virus Results
Table 3. The Most Common HLA-DRB1 Antigens and BK Virus Results