HLA type-independent method to monitor polyoma BK virus-specific CD4 and CD8 T-cell immunity

The Second International Consensus Guidelines on the Management of BK Polyomavirus in Kidney Transplantation

BK polyomavirus (BKPyV) remains a significant challenge after kidney transplantation. International experts reviewed current evidence and updated recommendations according to Grading of Recommendations, Assessment, Development, and Evaluations (GRADE). Risk factors for BKPyV-DNAemia and biopsy-proven BKPyV-nephropathy include recipient older age, male sex, donor BKPyV-viruria, BKPyV-seropositive donor/-seronegative recipient, tacrolimus, acute rejection, and higher steroid exposure. To facilitate early intervention with limited allograft damage, all kidney transplant recipients should be screened monthly for plasma BKPyV-DNAemia loads until month 9, then every 3 mo until 2 y posttransplant (3 y for children). In resource-limited settings, urine cytology screening at similar time points can exclude BKPyV-nephropathy, and testing for plasma BKPyV-DNAemia when decoy cells are detectable. For patients with BKPyV-DNAemia loads persisting >1000 copies/mL, or exceeding 10 000 copies/mL (or equivalent), or with biopsy-proven BKPyV-nephropathy, immunosuppression should be reduced according to predefined steps targeting antiproliferative drugs, calcineurin inhibitors, or both. In adults without graft dysfunction, kidney allograft biopsy is not required unless the immunological risk is high. For children with persisting BKPyV-DNAemia, allograft biopsy may be considered even without graft dysfunction. Allograft biopsies should be interpreted in the context of all clinical and laboratory findings, including plasma BKPyV-DNAemia. Immunohistochemistry is preferred for diagnosing biopsy-proven BKPyV-nephropathy. Routine screening using the proposed strategies is cost-effective, improves clinical outcomes and quality of life. Kidney retransplantation subsequent to BKPyV-nephropathy is feasible in otherwise eligible recipients if BKPyV-DNAemia is undetectable; routine graft nephrectomy is not recommended. Current studies do not support the usage of leflunomide, cidofovir, quinolones, or IVIGs. Patients considered for experimental treatments (antivirals, vaccines, neutralizing antibodies, and adoptive T cells) should be enrolled in clinical trials.

Epidemiology and Dynamics of BK Polyomavirus Replication after Kidney Transplantation

BACKGROUND/OBJECTIVES

In the absence of an effective antiviral treatment for BK polyomavirus (BKPyV), a better understanding of the epidemiology and time course of BKPyV replication after kidney transplantation is needed to limit the virus's impact on the graft outcome.

METHODS

In a 7-year study, we screened more than 430 kidney transplant recipients and analyzed the time course and virological characteristics of BKPyV replication.

RESULTS

Urinary viral replication was observed in 116 (27%) of the 430 patients, and 90 of the 116 (78%) had viral DNAemia. Thirty-eight patients (8.8%) were presumed to have nephropathy (DNAemia > 4 log10 copies/mL). Of the patients with BKPyV replication, 48%, 60%, 71%, and 80% were first found to be positive one, two, three, and four months post-transplantation. The initial viral load in the urine was below 7 log10 copies/mL in 100% of the patients with viral replication first detected before the first month, and this proportion was 57% when viral replication was first detected after the first month. When the BKPyV replication was first detected in a urine sample at month 3 or later, 81.5% of patients had concomitant BKPyV DNAemia. The predominant viral subtype was Ib2 (60%), and there was no apparent relationship between the subtype and the time course of BKPyV replication.

CONCLUSIONS

Urinary BKPyV replication occurs early after renal transplantation and in most patients will increase to a level requiring therapeutic intervention. Close monitoring for BKPyV in the early post-transplantation period would enable the pre-emptive adjustment of the immunosuppression regimen.

Nutritional characteristics of Stereospermum chelonoides (L.f.) DC., an underutilized edible wild fruit of dietary interest

Malnutrition and hunger is a serious global issue, however, wild fruits possess the potential of combatting it being rich in nutrients. Stereospermum chelonoides (L.f.) DC., commonly known as "Patala" in Ayurvedic text, is a large wild tree bearing edible, yet, underutilized fruits consumed by the locals in Western parts of India and neighboring countries. The present study focuses on the nutritional profile of S. chelonoides fruit along with quantification of bioactive constituents using RP-HPLC-PDA and evaluation of in-vitro anti-oxidant and, anti-microbial activity. The fruit was found rich in nutritional composition having protein (2.41 % ± 0.007), fibre (3.46 % ± 0.02) and carbohydrate (90.19 % ± 1.73) with energy value of 368.2 ± 3.94 Kcal/100g. The elemental analysis of fruit resulted in macronutrients Ca, Mg and Na and micronutrients Fe, Mn, Zn, and Cu in amounts comparable to common marketed fruits. The RP-HPLC-PDA analysis revealed the presence of six phenolic compounds in all 3 extracts made from the fruit in which highest amount are present in hydro-alcoholic extract. All the extracts exhibited potent antioxidant activity evaluated through DPPH assay and oxygen radical absorbing capacity (ORAC), with highest activity in hydro-alcoholic extract. All the analyzed extracts also exhibited potent inhibition, against four human pathogens namely Pseudomonas aeruginosa, Vibrio cholerae, Escherichia coli, and Shigella flexneri. Therefore, it is evident from the study that the fruit of S. chelonoides has immense potential as a nutraceutical supplement and may help in the management of nutrient deficiency and malnutrition among rural and tribal communities.

The effect of BKV reactivation on cytokines behavior in kidney transplanted patients

BACKGROUND

BK virus associated nephropathy (BKVAN) is one of the common causes of graft loss among kidney transplanted recipients (KTRs). The current treatment for BKV nephropathy is decreasing the immunosuppressive regimen in KTRs. Interleukin-27 (IL-27) is a multifunctional cytokine that might be the front-runner of an important pathway in this regard. Therefore, in current study it is tried to evaluate the changes in the expression level of IL-27 and some related molecules, resulting from BKV reactivation in KTR patients.

METHODS

EDTA-treated blood samples were collected from all participants. Patients were divided into two groups, 31 kidney transplant recipients with active and 32 inactive BKV infection, after being monitored by Real time PCR (Taq-Man) in plasma. Total of 30 normal individuals were considered as healthy control group. Real time PCR (SYBR Green) technique is used to determine the expression level of studied genes.

RESULTS

The results of gene expression comparisons showed that the expression level of IL-27, IFN-γ, TNF-α, TNFR2 and IRF7 genes was significantly higher in inactive group in comparison to active group. The expression level of TLR4 was lower in both active and inactive groups in comparison to control group. ROC curve analysis showed that IL-27 and IRF7 are significantly different amongst other studied genes. Finally, the analyses revealed that the expression level of most of the studied genes (except for TNF-α and TLR4) have significant correlation with viral load.

CONCLUSIONS

Our findings revealed that IL-27, IFN-γ, TNF-α, TNFR2 and IRF7 expression level is higher in inactive group and TLR4 expression level is lower in patients' groups in comparison to control group. Also, ROC curve analysis showed IL-27 and IRF7 can significantly differentiate studied groups (BKV active vs. inactive). Therefore, these results might help elucidating the pattern in charge of BKV reactivation in kidney transplanted patients.

Innate Immunity Response to BK Virus Infection in Polyomavirus-Associated Nephropathy in Kidney Transplant Recipients

BK polyomavirus (BKV) mainly causes infection in uroepithelial and renal tubular epithelial cells of either immunocompetent or immunocompromised hosts. Despite asymptomatic or mild clinical features in immunocompetent hosts with BK infection, serious complications are frequently found in immunocompromised patients, especially patients with kidney transplantation. Accordingly, BKV-associated nephropathy (BKVN) demonstrates a wide range of clinical manifestations, including ureteric stenosis and hemorrhagic cystitis. In addition, BKV re-infection in post-kidney transplantation is also a main cause of kidney allograft dysfunction and graft loss. Since the direct anti-BKV is unavailable, immune response against BKV infection is the main mechanism for organism control and might be a novel strategy to treat or suppress BKV. As such, the innate immunity, consisting of immune cells and soluble molecules, does not only suppress BKV but also enhances the subsequent adaptive immunity to eradicate the virus. Furthermore, the re-activation of BKV in BKVN of kidney-transplanted recipients seems to be related to the status of innate immunity. Therefore, this review aims to collate the most recent knowledge of innate immune response against BKV and the association between the innate immunity status of kidney-transplanted recipients and BKV re-activation.

BK polyomavirus-pathogen, paradigm and puzzle

BK virus is a polyomavirus with seroprevalence rates of 80% in adults. Infection is usually acquired during childhood, and the virus is benign or pathologic depending on immune status. The virus reactivates in immunodeficiency states, mostly among transplant (either kidney or bone marrow) recipients. There are approximately 15 000 renal transplants every year in the USA, of which 5-10% develop BK polyomavirus nephropathy; 50-80% of patients who develop nephropathy go on to develop graft failure. BK virus is associated with BK polyomavirus nephropathy, ureteral stenosis, late-onset hemorrhagic cystitis, bladder cancer and other nonlytic large T-expressing carcinomas. The renal spectrum begins with viruria and can end with graft failure. The clinical spectrum and outcomes vary among transplant patients. New noninvasive diagnostic methods, such as urinary polyomavirus Haufen detected by electron microscopy, are currently under study. Treatment is primarily directed at decreasing immunosuppression but may be associated with graft rejection. Repeat transplantation is encouraged as long as viral clearance in plasma prior to transplant is accomplished. There remain no definitive data regarding the utility of transplant nephrectomy.

Functional immune monitoring of BK Virus and donor-specific T-cell effector immune responses to guide treatment decision-making after kidney transplantation; an illustrative case report and literature review

Differential diagnosis between Polyoma virus associated-nephropathy (PVAN) and T-cell mediated rejection (TCMR) might be challenging, as respective treatment approaches are totally opposite. Here we report the illustrative case of a kidney transplant recipient with PVAN who developed a persistent acute TCMR after full abrogation of viral infection through immunosuppression modulation. By simultaneous functional immune monitoring of BKV and donor-specific T-cell responses using IFN-γELISPOT assay, we retrospectively demonstrated the predominant effector mechanisms responsible of allograft injury and thus, potential guidance for treatment decision-making. Furthermore, the evidence of an efficient T-cell alloimmunity abrogation accompanied by a sustained anti-viral response after sirolimus addition, promotes the potential benefit of converting patients to an mTOR-based immunosuppression in case of PVAN.

Characterization of aberrant pathways activation and immune microenviroment of BK virus associated nephropathy

In the context of transplantation with the use of immunosuppressive drugs, BK virus infection has become the main cause of BK virus nephropathy(BKVN) in renal transplant recipients(KTRs). More importantly, BKVN may cause further allograft dysfunction and loss. However, the role of the immune microenvironment in the pathogenesis of BKVN remains unknown. Therefore, we collected microarray data of KTRs to elucidate the immune characteristics of BKVN. Via the CIBERSORT, we found that BKVN had relatively more activated memory CD4 T cells. Immunostaining showed that CD4+ and CD8+cells were significantly different between BKVN and stable allografts(STAs). In addition, the expression of immune-related genes(antigen presentation, cytotoxicity, and inflammation) was significantly higher in BKVN than in STAs. The results of gene set enrichment analysis(GSEA) and single-sample GSEA(ssGSEA) indicated that immune cell-,cytokine-,chemokine-, and inflammation-related pathways were significantly activated in BKVN, while metabolism- and renal development-related pathways were significantly downregulated in BKVN. In addition, the immune microenvironments of the peripheral blood in patients with BK viremia(BKV) or transplant kidney biopsy(TKB) with BKVN may be different. Overall, the immune microenvironment may play important roles in the occurrence and development of BKVN and provide a theoretical basis for preventing the occurrence of BKVN and finding novel treatments.

CD4+ T Cell Immune Response to VP1 and VP3 in BK Virus Infected Recipients of Renal Transplantation

OBJECTIVE

To investigate the characteristics of BK virus (BKV) specific cellular immune response in the recipients who have early infection with BKV after renal transplantation.

METHODS

The recipients of renal allografts (n = 30) were divided into groups of BK virus nephropathy (BKVN), viruria, and viremia. The BKV load was observed with real-time fluorescence quantitative polymerase chain reaction in urine and blood every three months. The values of serum creatinine (SCr) were detected. The peripheral blood mononuclear cells (PBMCs) were cultivated with overlapping peptide pool containing BKV structural proteins VP1, VP2, and VP3, and regulatory proteins large tumor antigen (LT-Ag) and small tumor antigen (st-Ag), to stimulate in vitro specific cellular immunoresponse. Flow cytometry was used to measure the proliferation of CD3+/CD4+/CD8+ T and interferon [INF]-γ/interleukin [IL]-2/tumor necrosis factor [TNF]-α T cell subsets.

RESULTS

The BKV infection increased SCr values in recipients of renal transplantation. CD4+ T cells were dominant (>90%) in the in vitro cellular immunoresponse to VP1, VP2, VP3, LT-Ag, and st-Ag. At the presence of viremia and BKVN, IL-2/IFN-γ+/TNF-α+ CD4+ T cells showed significantly decreased in vitro cellular immunoresponse to VP1, VP2, and VP3 (p < 0.05), but insignificantly changed to LT-Ag and st-Ag (p > 0.05). For the cases of viruria and viremia, IL-2/IFN-γ+/TNF-α+ CD4+ T cells showed significantly higher in vitro cellular immunoresponse to VP1, VP2, and VP3 than to LT-Ag and st-Ag (p < 0.05). The immunogenicity of VP1 and VP3 was significantly higher than that of VP2 (p < 0.05).

CONCLUSIONS

The BKV infection increases SCr values, and CD4+ T cells are dominant in the in vitro BKV specific cellular immunoresponse in the recipients of renal transplantation. Viremia significantly decreased the immunoresponse to VP1, VP2, and VP3. There is the significantly stronger immunoresponse to VP1 and VP3 when compared with that to VP2, LT-Ag, and st-Ag, suggesting that VP1 and VP3 may be the major targets for the BKV specific immune response.

BK Polyomavirus Immune Response With Stress on BK-Specific T Cells

Polyomavirus-associated nephropathy is a pertinent cause of poor renal allograft survival. Absence of defensive immunity toward BK polyomavirus may favor the occurrence of BK polyomavirus-active infection and influence the progression to polyomavirus-associated nephropathy. Humoral immune responses may offer incomplete protection. In this review, available data on both humoral and cellular immunity were examined, with a concentration on BK polyomavirus-specific T cells; in addition, their roles in BK polyomavirus cellular immune response and immunotherapy were discussed. This traditional narrative review used PubMed and Medline searches for English language reports on BK polyomavirus immune response and BK-specific T cells published between January 1990 and November 2017. The search included the key words BK virus, BK polyomavirus, immune and response, and specific T cells. Monitoring BK polyomavirus-specific T cells has both therapeutic and prognostic value. Innovative cellular immunotherapy approaches, including development of vaccinations and infectious recombinant BK polyomavirus, could further contribute to the prevention of BK polyomavirus infection and related diseases.

Definition and characterization of novel HLA-*A02-restricted CD8+ T cell epitopes derived from JCV polyomavirus with clinical relevance

Human JC and BK polyomaviruses (JCV/BKV) can establish a latent infection without any clinical symptoms in healthy individuals. In immunocompromised hosts infection or reactivation of JCV and BKV can cause lethal progressive multifocal leukoencephalopathy (PML) and hemorrhagic cystitis, respectively. Vaccination with JCV/BKV derived antigen epitope peptides or adoptive transfer of virus-specific T cells would constitute an elegant approach to clear virus-infected cells. Furthermore, donor leukocyte infusion (DLI) is another therapeutic approach which could be helpful for patients with JCV/BKV infections.So far, only few immunodominant T cell epitopes of JCV and BKV have been described and therefore is a fervent need for the definition of novel epitopes. In this study, we identified novel T cell epitopes by screening libraries of overlapping peptides derived from the major capsid protein VP1 of JCV. Virus like particles (VLPs) were used to confirm naturally processing. Two human leucocyte antigen (HLA)-A*02-restricted epitopes were characterized by fine mapping with overlapping peptides and nonamer peptide sequences were identified. Cytokine release profile of the epitope-specific T cells was analyzed by enzyme-linked immunospot (ELISPOT) assays and by flow cytometry. We demonstrated that T cell responses were of polyfunctional nature with the potential of epitope-specific killing and cross-reactivity between JCV and BKV. These novel epitopes might constitute a new potential tool to design effective diagnostic and therapeutic approaches against both polyomaviruses.

BK Polyomavirus: Clinical Aspects, Immune Regulation, and Emerging Therapies. Clin Microbiol Rev. 2017;30:503-528. [PMID: 28298471 DOI: 10.1128/cmr.00074-16]

BK polyomavirus (BKV) causes frequent infections during childhood and establishes persistent infections within renal tubular cells and the uroepithelium, with minimal clinical implications. However, reactivation of BKV in immunocompromised individuals following renal or hematopoietic stem cell transplantation may cause serious complications, including BKV-associated nephropathy (BKVAN), ureteric stenosis, or hemorrhagic cystitis. Implementation of more potent immunosuppression and increased posttransplant surveillance has resulted in a higher incidence of BKVAN. Antiviral immunity plays a crucial role in controlling BKV replication, and our increasing knowledge about host-virus interactions has led to the development of improved diagnostic tools and clinical management strategies. Currently, there are no effective antiviral agents for BKV infection, and the mainstay of managing reactivation is reduction of immunosuppression. Development of immune-based therapies to combat BKV may provide new and exciting opportunities for the successful treatment of BKV-associated complications.

BK polyomavirus: a review of the virology, pathogenesis, clinical and laboratory features, and treatment

BK polyomavirus (BKPyV) is a non-enveloped, circular dsDNA virus with a genome of approximately 5100 base pairs. It can be divided into four major genotypes, but the effects of different genotypes on clinical disease are uncertain. Primary BKPyV infection is generally acquired asymptomatically in childhood. It establishes low-level persistence in many tissues, particularly the genitourinary tract. Reactivation can lead to severe disease including BKPyV-associated nephropathy confirmed by renal biopsy, hemorrhagic cystitis and meningoencephalitis. Nucleic acid amplification testing of blood and urine is the main diagnostic and prognostic test for BKPyV infection. The treatment of BKPyV infection has concentrated on reduction in immunosuppressive therapy. Recent studies suggest that antiviral drugs have demonstrated only modest benefit, but adoptive T-cell therapies offer potential advances.

BK Polyomavirus and the Transplanted Kidney: Immunopathology and Therapeutic Approaches

BK polyomavirus is ubiquitous, with a seropositivity rate of over 75% in the adult population. Primary infection is thought to occur in the respiratory tract, but asymptomatic BK virus latency is established in the urothelium. In immunocompromised host, the virus can reactivate but rarely compromises kidney function except in renal grafts, where it causes a tubulointerstitial inflammatory response similar to acute rejection. Restoring host immunity against the virus is the cornerstone of treatment. This review covers the virus-intrinsic features, the posttransplant microenvironment as well as the host immune factors that underlie the pathophysiology of polyomavirus-associated nephropathy. Current and promising therapeutic approaches to treat or prevent this complication are discussed in relation to the complex immunopathology of this condition.

Antigen-Specificity of T Cell Infiltrates in Biopsies With T Cell-Mediated Rejection and BK Polyomavirus Viremia: Analysis by Next Generation Sequencing

This study interrogates the antigen-specificity of inflammatory infiltrates in renal biopsies with BK polyomavirus (BKPyV) viremia (BKPyVM) with or without allograft nephropathy (BKPyVN). Peripheral blood mononuclear cells (PBMC) from five healthy HLA-A0101 subjects were stimulated by peptides derived from the BKPYV proteome or polymorphic regions of HLA. Next generation sequencing of the T cell-receptor complementary DNA was performed on peptide-stimulated PBMC and 23 biopsies with T cell-mediated rejection (TCMR) or BKPyVN. Biopsies from patients with BKPyVM or BKVPyVN contained 7.7732 times more alloreactive than virus-reactive clones. Biopsies with TCMR also contained BKPyV-specific clones, presumably a manifestation of heterologous immunity. The mean cumulative T cell clonal frequency was 0.1378 for alloreactive clones and 0.0375 for BKPyV-reactive clones. Samples with BKPyVN and TCMR clustered separately in dendrograms of V-family and J-gene utilization patterns. Dendrograms also revealed that V-gene, J-gene, and D-gene usage patterns were a function of HLA type. In conclusion, biopsies with BKPyVN contain abundant allospecific clones that exceed the number of virus-reactive clones. The T cell component of tissue injury in viral nephropathy appears to be mediated primarily by an "innocent bystander" mechanism in which the principal element is secondary T cell influx triggered by both antiviral and anti-HLA immunity.

Modeling Immune Response to BK Virus Infection and Donor Kidney in Renal Transplant Recipients

In this paper we develop and validate with bootstrapping techniques a mechanistic mathematical model of immune response to both BK virus infection and a donor kidney based on known and hypothesized mechanisms in the literature. The model presented does not capture all the details of the immune response but possesses key features that describe a very complex immunological process. We then estimate model parameters using a least squares approach with a typical set of available clinical data. Sensitivity analysis combined with asymptotic theory is used to determine the number of parameters that can be reliably estimated given the limited number of observations.

The Loss of BKV-specific Immunity From Pretransplantation to Posttransplantation Identifies Kidney Transplant Recipients at Increased Risk of BKV Replication

Quantification of BKV-load and BKV-specific immunity have been evaluated to monitor BKV-replication and outcomes in kidney transplant recipients (KTRs) with BKV-infection. However, it remains crucial to better understand how immune markers can predict the risk for later infection. We studied all KTRs between 2008 and 2011. Twenty-four KTRs were diagnosed with BKV-replication and a control group of 127 KTRs was used for comparison. Samples were collected before at +1, +2, and +3 months posttransplantation. BKV-specific and alloreactive T cells were measured using an interferon-γ Elispot assay. The extent of immunosuppression was quantified by lymphocyte subpopulations and interferon-gamma levels. KTRs with a loss of BKV-specific T cells directed to Large T-antigen from pretransplantation to posttransplantation were at increased risk of BKV-replication (p < 0.001). In contrast, KTRs with stable/rising BKV-specific T cells were more likely not to develop BKV-replication (p < 0.05). KTRs developing BKV-replication showed significantly lower CD3+, CD4+, CD8+ T cells and interferon-γ levels posttransplantation, but significantly higher alloreactive T cells (p < 0.05). Monitoring pretransplant and posttransplant BKV-specific T cells is suggested a sensitive marker to identify KTRs at increased risk of BKV-replication. Increased susceptibility to immunosuppression predisposes KTRs to a loss of protective BKV-specific immunity that results in impaired virus control and BKV-replication.

A revised strategy for monitoring BKV-specific cellular immunity in kidney transplant patients

Reactivation of Polyomavirus BKV is a severe complication in kidney transplant patients. Current treatment requires close monitoring, and modification of immunosuppressive drugs. As an important additional tool, the monitoring of BKV immunity has been based on detection of cytokine-secreting T cells upon BKV-antigen challenge. However, low frequent BKV-specific T cells are often barely detectable and their roles in BKV clearance remain unclear. Here, we analyzed the effects of immunosuppressive agents on BKV-specific T cells in vitro. Significant reductions in expression of several markers, and reduced killing functions upon treatment with calcineurin but not mTOR inhibitors were detected. However, effects of these drugs on expression of surface markers and GranzymeB were substantially less striking than effects on cytokine expression. Consequently, we applied a novel detection strategy for BKV-specific T cells in immunosuppressed kidney transplant patients using these more robust markers, and showed significantly improved sensitivity compared with the conventional IFNγ-based method. Using this strategy and 17-color flow cytometry, we found BKV-specific helper and cytolytic CD4+ T-cell subsets that differed in their memory phenotype, which corresponded with BKV clearance in kidney transplant patients. Thus, our results offer an improved detection strategy for BKV-specific T cells in kidney transplant patients, and shed light on the contributions of these cells to BKV clearance.

ABO desensitization affects cellular immunity and infection control after renal transplantation

The impact of ABO desensitization on overall immunity, infectious control, and alloreactivity remains unknown. We compared 35 ABO-incompatible kidney transplant recipients (KTRs) to a control of 62 ABO compatible KTRs. Samples were collected before, at +1, +2, +3, +6, and +12 months post-transplantation. CMV-, BKV-specific, and alloreactive T cells were measured using an interferon-γ ELISPOT assay. The extent of immunosuppression was quantified by enumeration of lymphocyte subpopulations and cytokines. No differences were observed for 5-year allograft survival and function between both groups (P > 0.05). However, ABO-incompatible KTRs were more likely to develop CMV infection, BKV-associated nephropathy, and severe sepsis (P = 0.001). Interestingly, ABO-incompatible KTRs with poor HLA-match showed the highest rates of infections and inferior allograft function (P < 0.05). CD3+, CD4+ T-cell counts, interferon-γ and IL-10 levels were lower in ABO-incompatible KTRs early post-transplantation (P < 0.05). Likewise, ABO-incompatible KTRs showed impaired BKV- and CMV-specific T-cell immunity (P < 0.05). ABO-incompatible KTRs showed lower frequencies of alloreactive T cells (P < 0.05). Our data suggest T-cell depletion due to ABO desensitization, which may contribute to the increased risk of T-cell-dependent infections. Elimination of B cells serving as antigen-presenting cells, thereby causing impaired T-cell activation, plays a significant role in both impaired infection control and reduced alloreactive T-cell activation.

Quantitative analysis of BKV-specific CD4+ T cells before and after kidney transplantation

BACKGROUND

BK virus (BKV) is the main infectious cause of renal allograft dysfunction. Although recent studies showed an inverse correlation between BKV-specific T-cell responses and viral load after transplantation, the importance of pre-transplant response in the process of virus reactivation has only been studied once. In this study, we aimed to determine whether pre-transplant CD4+ T-cell response can be used for prediction of BKV reactivation and BKV nephropathy (BKVN), by a method that can practically be used in routine patient monitoring.

METHODS

BKV-specific CD4+ T-cell responses of 31 kidney recipients (all from live donors) were measured by an IFN-γ-enzyme-linked-immunospot (ELISPOT) method using mixture of peptides, at day 0 and +1, +3, and +6 months posttransplant. Additionally, seven other reactivation patients as another group were also analyzed. BKV viral loads in plasma were measured by real-time polymerase chain reaction (PCR). Responses of 10 healthy people were also included as controls in the analysis.

RESULTS

All but one patient and all of the controls had detectable CD4+ T-cell responses. Reactivation occurred in 8 out of 31 patients. There was no significant association between pretransplant BKV-specific CD4+ T-cell responses and BKV reactivation and between BKV DNA levels and CD4+ T-cell responses. In the additional group consisting of reactivation patients, four patients who had BKVN showed negative correlation between BKV-DNA levels and BKV-specific CD4+ T-cell responses (p<0.05). One patient who developed BKVN, however, was not able to mount a similar CD4+ T-cell response to viral reactivation despite immunosuppressive reduction.

CONCLUSION

Even though our cohort is small, our results may suggest that pre-transplant measurement of BKV specific CD4+ T-cell response may not be necessary, and that post-transplant monitoring, particularly during reactivation, may be more helpful in the management of the infection.

Characterization of urinary CD4⁺ and CD8⁺ T cells in kidney transplantation patients with polyomavirus BK infection and allograft rejection

BACKGROUND AND OBJECTIVES

The objective of this study was to characterize CD4(+) and CD8(+) T-cell populations in blood and urine of renal transplant patients with BK virus (BKV) infection or allograft rejection.

MATERIALS AND METHODS

Percentages and absolute numbers of CD4(+) and CD8(+) effector memory T-cell subtype (TEM ) and terminal differentiated T cells (TTD ) in renal transplant patients with BKV infection (n = 14), with an episode of allograft rejection (n = 9), and in uncomplicated renal transplant patients with a stable kidney function (n = 12) were measured and compared using 4-color fluorescence-activated cell sorting. Results were correlated with the number of CD4(+) and CD8(+) T cells in renal biopsies.

RESULTS

In patients with allograft rejection, the number of urinary CD4(+) TEM and CD8(+) TEM cells was significantly increased compared to patients with BKV infection or patients without complications. Positive correlation was found between the number of CD4(+) and CD8(+) cells in the renal biopsies and the number of CD4(+) and CD8(+) cells in urine. In patients with rejection, after 2 months of immunosuppressive therapy, a reduction in urinary CD8(+) TEM cells was found.

CONCLUSIONS

CD4(+) TEM and CD8(+) TEM cells in urine could be a marker to distinguish allograft rejection from BKV-associated nephropathy and to monitor therapy effectiveness in renal transplant patients with allograft rejection.

Cellular immunotherapy for patients with reactivation of JC and BK polyomaviruses after transplantation

Immunosuppression of patients after hematopoietic stem cell or kidney transplantation potentially leads to reactivation of JC and BK polyomaviruses. In hematopoietic stem cell transplantation, the reactivation rate of BKV can be up to 60%, resulting in severe complications of the urogenital tract, particularly hemorrhagic cystitis and renal dysfunction. After kidney transplantation, BKV reactivation can cause a loss of the graft. JCV can cause progressive multifocal leukoencephalopathy, a lethal disease. Adoptive transfer of donor-derived polyomavirus-specific T cells is an attractive and promising treatment that restores virus-specific cellular immunity. Pioneering work in the early 1990s on the reconstitution of cellular immunity against cytomegalovirus and recent development in the field of monitoring and isolation of antigen-specific T cells paved the way toward a personalized T-cell therapy. Multimer technology and magnetic beads are available to produce untouched T cells in a single-step, good manufacturing practice-compliant procedure. Another exciting aspect of T-cell therapy against polyomaviruses is the fact that both JCV and BKV can be targeted simultaneously because of their high sequence homology. Finally, "designer T cells" can be redirected to recognize polyomavirus antigens with high-affinity T-cell receptors. This review summarizes the state-of-the art technologies and gives an outlook of future developments in the field.

Genomics of BK viremia in kidney transplant recipients. Transplantation. 2014;97:451-456. [PMID: 24310299 DOI: 10.1097/01.tp.0000437432.35227.3e]

BACKGROUND

This study aimed to investigate global gene expression profiles of BK viremia and nephropathy (BKVN) samples using microarrays to investigate the immunologic response to BK virus.

METHODS

Patients were monitored for BK viremia in the blood monthly for 6 months, then at 9 and 12 months after kidney transplantation. BKVN and normal transplant kidney biopsy samples, and whole blood samples of patients with and without BK viremia were analyzed by Affymetrix Human Gene 1.0 ST Arrays.

RESULTS

During a mean follow-up of 917±325 days, 61 of the 289 patients (21%) developed BK viremia at a median 149 (27, 1,113) days after transplantation with a median peak PCR titers of 35,900 (1,000, 2,677,000). The only significant risk factor for development of BK viremia was induction with anti-thymocyte globulin (P=0.03). Only four patients developed BKVN (1.3%). Pathogenesis-based transcript analysis revealed a significant increased expression of interferon-gamma and rejection induced (GRIT), quantitative cytotoxic T-cell (QCAT), quantitative constitutive and alternate macrophage, B-cell and natural killer cell-associated transcripts (NKAT), indicating an active inflammatory immune response in BKVN biopsies (n=3) compared to normal transplant kidney biopsies with (n=3) and without BK viremia (n=11). The whole blood gene expression profiles of 19 BK viremia patients revealed significant increased expression of GRIT, QCAT, and NKAT compared to 14 patients without viremia.

CONCLUSIONS

The results showed increased activity of cytotoxic T cells and natural killer cells in BKVN and viremia samples resembling acute rejection and suggested the involvement of both adaptive and innate immunity.

TCR repertoire analysis by next generation sequencing allows complex differential diagnosis of T cell-related pathology

Clonotype analysis is essential for complete characterization of antigen-specific T cells. Moreover, knowledge on clonal identity allows tracking of antigen-specific T cells in whole blood and tissue infiltrates and can provide information on antigenic specificity. Here, we developed a next generation sequencing (NGS)-based platform for the highly quantitative clonotype characterization of T cells and determined requirements for the unbiased characterization of the input material (DNA, RNA, ex vivo derived or cell culture expanded T cells). Thereafter we performed T cell receptor (TCR) repertoire analysis of various specimens in clinical settings including cytomegalovirus (CMV), polyomavirus BK (BKV) reactivation and acute cellular allograft rejection. Our results revealed dynamic nature of virus-specific T cell clonotypes; CMV reactivation was linked to appearance of new highly abundant antigen-specific clonalities. Moreover, analysis of clonotype overlap between BKV-, alloantigen-specific T cell-, kidney allograft- and urine-derived lymphocytes provided hints for the differential diagnosis of allograft dysfunction and enabled appropriate therapy adjustment. We believe that the established approach will provide insights into the regulation of virus-specific/anti-tumor immunity and has high diagnostic potential in the clinical routine.

HLA-A2, HLA-B44 and HLA-DR15 are associated with lower risk of BK viremia

BACKGROUND

Human leucocyte antigens (HLAs) modulate immunity to polyomavirus BK (BKV). Identification of HLAs that alter the course of infection will facilitate risk stratification, and customization of pre-emptive intervention strategies.

METHODS

We performed a retrospective cohort study with 998 kidney transplant patients with BKV infection status confirmed by polymerase chain reaction (PCR). Clinical parameters and donor-recipient matching for specific HLAs were examined in relation to occurrence of viremia. An emphasis was placed on donor-recipient matching rather than the actual frequency of specific HLA-alleles, since a successful immune response requires sharing of HLAs between a virus-infected target cell and the anti-viral effector cell.

RESULTS

Using multivariate statistics, low risk of BK viremia was associated with matching of HLA-A2 [hazard ratio (HR) 0.51, 95% confidence interval (CI) 0.28-0.85], HLA-B44 (HR 0.31, 95% CI 0.076-0.85) and HLA-DR15 (HR 0.35, 95% CI 0.084-0.93) (P < 0.05), whereas high risk of viremia was associated with male gender (HR 2.38, 95% CI 1.46-4.09, P < 0.001).

CONCLUSIONS

HLAs that associated with a lower predisposition to the development of BK viremia have been identified. Evaluation of donor-recipient mismatching for these HLAs could potentially be used to (i) fine tune virus screening strategies for BKV in individual patients and (ii) facilitate discovery of major histocompatibility complex (MHC) class I and II binding peptides that can elicit clinically meaningful BKV-specific immunity.

HLA-A2, HLA-B44 and HLA-DR15 are associated with lower risk of BK viremia

BACKGROUND

Human leucocyte antigens (HLAs) modulate immunity to polyomavirus BK (BKV). Identification of HLAs that alter the course of infection will facilitate risk stratification, and customization of pre-emptive intervention strategies.

METHODS

We performed a retrospective cohort study with 998 kidney transplant patients with BKV infection status confirmed by polymerase chain reaction (PCR). Clinical parameters and donor-recipient matching for specific HLAs were examined in relation to occurrence of viremia. An emphasis was placed on donor-recipient matching rather than the actual frequency of specific HLA-alleles, since a successful immune response requires sharing of HLAs between a virus-infected target cell and the anti-viral effector cell.

RESULTS

Using multivariate statistics, low risk of BK viremia was associated with matching of HLA-A2 [hazard ratio (HR) 0.51, 95% confidence interval (CI) 0.28-0.85], HLA-B44 (HR 0.31, 95% CI 0.076-0.85) and HLA-DR15 (HR 0.35, 95% CI 0.084-0.93) (P < 0.05), whereas high risk of viremia was associated with male gender (HR 2.38, 95% CI 1.46-4.09, P < 0.001).

CONCLUSIONS

HLAs that associated with a lower predisposition to the development of BK viremia have been identified. Evaluation of donor-recipient mismatching for these HLAs could potentially be used to (i) fine tune virus screening strategies for BKV in individual patients and (ii) facilitate discovery of major histocompatibility complex (MHC) class I and II binding peptides that can elicit clinically meaningful BKV-specific immunity.

Predominance of TH2 cells and plasma cells in polyoma virus nephropathy: a role for humoral immunity?

The differential diagnosis of T cell-mediated rejection (TCMR) and BK-virus nephropathy (BKVN) in renal transplant biopsies is notoriously difficult. Therefore, attempts were made to differentiate between the two by characterizing the immune cell infiltrate. Using immunohistochemistry, the distribution of immune cell (sub)populations such as CD4(+) T helper (TH), TH1, TH2, CD8(+) cytotoxic T cells, regulatory T cells, B cells, plasma cells and follicular dendritic cells was determined in a total of 38 renal biopsy specimens. In addition, the expression of the HLA class I antigen presentation machinery (APM) components was investigated. In general, the frequency of T cells was higher than B cells, and TH cells outnumbered cytotoxic T cells with a predominance of TH2 over TH1 cells. In BKVN, a significantly higher number of plasma cells was observed (P = .028), and interstitial fibrosis and tubular atrophy was more pronounced in BKVN (P = .007) compared to TCMR. The expression of components of the HLA class I APM was not affected by the infection with BK virus compared to TCMR. These findings indicate a TH2 shift in renal transplants in the context of alloreactive and virus-induced inflammation maybe as a consequence of immunosuppression, which usually targets T cell reaction. The predominance of plasma cells might underline an important role of humoral immunity in BKVN. Moreover, BK virus does not seem to modulate the expression of HLA class I APM as a strategy of immune evasion.

Novel approach for improved assessment of phenotypic and functional characteristics of BKV-specific T-cell immunity. Transplantation. 2011;92:1269-1277. [PMID: 22124284 DOI: 10.1097/tp.0b013e318234e0e5]

BACKGROUND

BKV-associated nephropathy represents a serious complication of the posttransplant period in kidney transplant recipients. Monitoring BKV-specific immunity is of a special importance for estimation of clinical course in patients with BKV reactivation. Our recent data demonstrated that all five BKV antigens are immunogenic and elicit T-cell responses varying within patients. Therefore, all five BKV proteins should be evaluated for the assessment of BKV-specific immunity. However, analysis of five proteins performed separately is time- and cost-intensive and requires large amount of blood.

METHODS

Using novel approach of a mixture of overlapping peptide pools encompassing all five BKV antigens (viral protein [VP] 1, VP2, VP3, large tumor antigen, and small tumor antigen) and multiparameter flow cytometry, we evaluate BKV-specific T cells in patients with a previous/present severe long-lasting or transient BKV reactivation. Patients without BKV reactivation were used as control.

RESULTS

In this study, we show that using mixture of overlapping peptide pool results in the magnitude of CD4- and CD8-positive BKV-specific T-cell response, which is significantly higher compared with any frequencies detected by previously used single BKV antigen stimulation. Of interest, patients with a history of rapid BKV clearance had significantly higher frequency of multifunctional interferon gamma-γ/interleukin (IL)-2/tumor necrosis factor-α and IL-2/tumor necrosis factor-α CD4-positive T cells, suggesting protective potential of polyfunctional T cells. Furthermore, we did not find IL-17-producing BKV-specific memory T cells in patients recovered from BKV reactivation.

CONCLUSIONS

Here, we established a fast and sensitive approach allowing the most comprehensive assessment of the total BKV immunity performed to date and offer a new platform for further prospective studies.

BK virus-specific immunity kinetics: a predictor of recovery from polyomavirus BK-associated nephropathy

Impaired BKV-specific immunity is associated with development of BKV-associated nephropathy. Suitable immunological parameters to identify patients at risk, however, are still debated. We monitored 18 kidney-transplant recipients through the course of self-limited BKV-reactivation (n = 11) and BKV-associated nephropathy (n = 7). BKV-specific cellular immunity directed to nonstructural small and Large T-antigen, and structural VP1-3 was analyzed in an interferon-γ Elispot assay. BKV-specific IgM and IgG were measured using an enzyme-linked immunosorbent assay simultaneously. BKV-specific cellular immunity directed to five BKV-proteins increased significantly from diagnosis to resolution of BKV-reactivation (p < 0.001). Patients with self-limited BKV-reactivation developed BKV-specific T cells without therapeutic interventions, and cleared BKV-reactivation within a median period of 1 month. Patients with BKV-associated nephropathy, however, showed BKV-specific T cells after a median period of 5 months after therapeutic interventions only, and cleared BKV-reactivation after a median period of 8 months. Anti-structural T cells were detected earlier than anti-nonstructural T cells, which coincided with BKV-clearance. Patients with BKV-associated nephropathy showed the highest frequencies of BKV-specific T cells at recovery, the highest increase in BKV-specific IgG and persistence of increased IgM levels (p < 0.05). Our results suggest prognostic values of BKV-specific immune monitoring to identify those patients at risk of BKV-associated nephropathy and to aid in the management of therapeutic interventions.

BK Virus in Kidney Transplant Recipients: The Influence of Immunosuppression

The incidence of BK virus infection in kidney transplant recipients has increased over recent decades, coincident with the use of more potent immunosuppression. More importantly, posttransplant BK virus replication has emerged as an important cause of graft damage and subsequent graft loss. Immunosuppression has been accepted as a major risk for BK virus replication. However, the specific contribution of individual immunosuppressive medications to this risk has not been well established. The purpose of this paper is to provide an overview of the recent literature on the influence of the various immunosuppressant drugs and drug combinations on posttransplant BK virus replication. Evidence supporting the various immunosuppression reduction strategies utilised in the management of BK virus will also be briefly discussed.

BK polyomavirus infection and nephropathy: the virus-immune system interplay. Nat Rev Nephrol. 2011;7:399-406. [PMID: 21610680 DOI: 10.1038/nrneph.2011.59]

Reactivation of latent BK polyomavirus (BKV) infection continues to be a major challenge in renal graft recipients. Progression of BKV infection to BKV-associated nephropathy (BKVAN) leads to graft loss in up to 60% of affected patients. Interestingly, although >80% of healthy adults are seropositive for BKV, BKVAN occurs almost exclusively in transplanted kidneys, which raises questions about its underlying pathogenetic mechanisms. Intragraft inflammation and an insufficient antiviral immune response seem to be the most important risk factors. Early studies revealed an association between the rate of recovery of BKV-specific cellular immunity (which shows high interindividual variation) and BK viral clearance, which determines the clinical course of BKV infection. In patients with prompt recovery of BKV-specific T cells, BKV infection can be controlled at the early reactivation stage and does not progress to BKVAN. By contrast, in patients with persistent BKV reactivation caused by insufficient BKV-specific immunity, continued viral replication and inflammation ultimately lead to graft injury and/or BKVAN. As the chronic course of BKV infection can be prevented in most patients by prompt restoration of BKV-specific immunity, frequent monitoring of BK viral load and targeted, timely modification or reduction of immunosuppression is strongly recommended for affected patients.

BK-VP3 as a new target of cellular immunity in BK virus infection. Transplantation. 2011;91:100-107. [PMID: 21452414 DOI: 10.1097/tp.0b013e3181fe1335]

BACKGROUND

Polyomavirus BK virus (BKV) infection represents a serious complication leading to BKV-associated nephropathy (BKVAN) and subsequent kidney graft loss in up to 10% of transplant patients. Cellular immunity is known to play a crucial role in the control of BKV replication. However, the knowledge on the BKV-T-cell response is limited: only two (VP1 and large T antigen) of six known BKV proteins were evaluated for their antigenicity so far.

METHODS

By using 10-color flow cytometry and newly created overlapping peptide pools of five BKV antigens (VP1, VP2, VP3, large T antigen, and small t antigen), we performed cross-sectional phenotypic and functional analysis of BKV-specific T cells in kidney transplant patients with a history of BKVAN. Patients with clinically unapparent BKV infection (history of transient/no BKV reactivation) were used as control group.

RESULTS

Our data demonstrate for the first time the antigenic properties of all five evaluated proteins with VP3 as a new important target of cellular immunity. Further, we found a correlation between the severity of the previous BKV infection and the magnitude of memory CD4+ T-cell response. Thus, compared with the control group, patients with a history of BKVAN demonstrated significantly higher frequencies of interferon-γ- and interleukin-2-producing effector memory CD4+ T cells. In the control group, more patients with detectable interferon-γ+/interleukin-2+/tumor necrosis factor+ triple producers were found, suggesting possibly a protective function of these multifunctional T cells.

CONCLUSIONS

In conclusion, our study results suggest an implementation of new targets for monitoring of BKV immunity. Further studies are required to evaluate the protective function of the found BKV-specific T-cell subsets.

Intravenous immunoglobulin as rescue therapy for BK virus nephropathy

BKVN has emerged as an important cause of pediatric renal allograft nephropathy, with significant graft dysfunction in majority of the cases. Reduced immunosuppression and cidofovir therapy are the most commonly used therapeutic options for the treatment of BKVN in these patients. Recently, a preliminary study in adult renal allograft recipients with BKVN showed a therapeutic response to a combined approach of immunosuppression reduction and IVIg administration. A therapeutic benefit of IVIg without another concomitant treatment intervention has not been evaluated. We report stabilization of renal functions, histological resolution of BKVN and significant reduction in BK viremia in pediatric renal transplant with the use of IVIg, after an inadequate response to immunosuppression reduction and cidofovir therapy. In addition, we review the current literature on the use of cidofovir in pediatric renal transplant patients with BKVN and the potential of IVIg use in this condition.

Clonotype analysis of cytomegalovirus-specific cytotoxic T lymphocytes

Cytotoxic T lymphocytes (CTL) control the replication of human cytomegalovirus (CMV). Previous studies assessed the clonotypic composition of CTL specific for individual immunodominant peptides within a certain HLA context. Such an approach has inherent limitations and may not assess the true clonal CTL response in vivo. Here, the clonotypic composition of CMV-specific CTL was determined in HLA-A2, CMV-seropositive kidney transplant recipients and healthy blood donors after stimulation of peripheral blood mononuclear cells with either a pp65 whole-peptide pool or a single immunodominant peptide. Even after stimulation with the whole peptide pool, CMV-specific CTL remained monoclonal or oligoclonal. Regarding intraindividual variation, the CDR3 motifs of the dominant clones were identical to those observed in CTL generated by the single immunodominant peptide. Sequencing of the CDR3 regions demonstrated significant interindividual variation; however, structural homology was observed for immunodominant clonotypes in three individuals. In conclusion, the highly focused T cell receptor repertoire found after stimulation with either a single immunodominant peptide or a peptide pool demonstrates a pivotal role for immunodominant epitopes in the generation of a clonal repertoire. These results provide new insights into the regulation of CMV clonal dominance and may contribute to the design and monitoring of adoptive immunotherapy.

Recovery of BK virus large T-antigen-specific cellular immune response correlates with resolution of bk virus nephritis. Transplantation. 2008;85:185-192. [PMID: 18212622 DOI: 10.1097/tp.0b013e31815fef56]

BACKGROUND

BK virus (BKV) infection of kidney transplant patients is an increasing problem and is thought to be secondary to potent immunosuppressive therapy. BKV infection progresses to BKV nephritis (BKVN) in approximately 8% of transplants and in half of these cases the graft is lost.

METHODS

We used an interferon-gamma enzyme-linked immunosorbent spot (ELISPOT) assay to measure the cellular immune response to peptides encoding BKV large T antigen. Eight kidney transplant patients with BKVN were tested at the time of diagnosis of BKVN and then after resolution of active BKV infection.

RESULTS

When total spot counts from all peptide pools were combined, the mean ELISPOT signal per 10,000 cells at the time of BKVN diagnosis was 23.1 (range 3.4-59.7), with a median of 21.8. This increased to 70.2 (range 5.4-189.4) with a median of 37.0 (P=0.1216) after resolution of active BKV infection. To further increase specificity of response, we counted the number of peptide pools with ELISPOT activity of greater than 10 spots per well after subtraction of background. The mean number of pools fitting this criteria at the time of BKVN diagnosis was 2.1 (range 0-8) with a median of 1.5; this increased to 8 (range 1-18) and a median of 6.5 after recovery (P=0.0338).

CONCLUSION

This demonstrates that recovery of cellular immune response to large T antigen corresponds with resolution of active BKV infection. This may prove useful in monitoring patients' cellular immunity and recovery from active BKV infection when treated with reduction in immunosuppressive therapy.

Functional characterization of BK virus-specific CD4+ T cells with cytotoxic potential in seropositive adults

BK polyomavirus (BKV) reactivation is associated with a failure of T cell immunity in kidney transplant patients, and may lead to BKV-associated nephropathy (BKVN) and loss of the allograft. BKV reactivation in hematopoietic stem cell transplant recipients is associated with hemorrhagic cystitis. We have investigated T cell responses to overlapping peptide mixtures corresponding to the whole BKV major T antigen (TAg) and major capsid protein (VP1) in peripheral blood mononuclear cell samples from a cohort of healthy BKV-seropositive subjects. The majority of these individuals possessed populations of both CD8(+) and CD4(+) T cells specific for these BKV antigens. After expansion in culture, the majority of the BKV-specific CD4(+) T cells, in addition to expressing CD40L (CD154), secreted both interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha, contained both granzyme A and granzyme B, and degranulated/mobilized CD107 in response to antigen-specific stimulation. These T cells thus represent potentially functional BKV-specific cytotoxic CD4(+) T lymphocytes. Secretion of both TNF-alpha and IFN-gamma by CD154(+)CD4(+) T cells on BKV-specific stimulation was associated with higher levels of granzyme B and a higher proportion of degranulating cells compared with CD154(+)CD4(+) T cells producing only IFN-gamma or neither cytokine. These healthy subjects also harbored populations of functional CD8(+) T cells specific for one or more of three newly defined HLA-A 02-restricted cytotoxic T lymphocyte epitopes within the BKV TAg as well as two HLA-A 02-restricted epitopes within the BKV VP1 we have previously described. The BKV-specific CD4(+) T cells characterized in this study may play a part in maintaining persistent memory T cell responses to the virus and thus contribute to the immune control of BKV in healthy individuals.

Prospective monitoring of polyomavirus BK replication and impact of pre-emptive intervention in pediatric kidney recipients

Polyoma BK virus (BKV)-associated nephropathy (PVAN) is a relevant cause of poor renal allograft survival. In a prospective analysis, we monitored BKV DNA in blood and urine samples from 62 consecutive pediatric kidney recipients. In patients with BKV replication, we analyzed the impact of reduction of maintenance immunosuppression on viral load kinetics and PVAN in patients with BKV replication. BKV-specific immunity was concomitantly evaluated on blood samples of viremic patients, by measuring the frequency of BKV-specific interferon-gamma-producing and cytotoxic T cells, and BKV IgG antibody levels. At a median follow-up of 24 months, BK viruria was observed in 39 of 62 patients, while BK viremia developed in 13 patients (21%). In all viremic patients, immunosuppression reduction resulted in the clearance of viremia, and prevented development of PVAN, without increasing the rate of acute rejection or causing graft dysfunction. As a consequence of immunosuppression adjustment, an expansion of BKV-specific cellular immunity was observed that coincided with viral clearance. We conclude that treating pediatric kidney transplant patients pre-emptively with immunosuppression reduction guided by BKV DNA in blood is safe and effective to prevent onset of PVAN. BKV-specific cellular immunity may be useful to guide this intervention.

BK virus nephropathy and kidney transplantation

Nephropathy from BK virus (BKV) infection is an evolving challenge in kidney transplant recipients. It is the consequence of modern potent immunosuppression aimed at reducing acute rejection and improving allograft survival. Untreated BKV infections lead to kidney allograft dysfunction or loss. Decreased immunosuppression is the principle treatment but predisposes to acute and chronic rejection. Screening protocols for early detection and prevention of symptomatic BKV nephropathy have improved outcomes. Although no approved antiviral drug is available, leflunomide, cidofovir, quinolones, and intravenous Ig have been used. Retransplantation after BKV nephropathy has been successful.

Polyomavirus BK-specific cellular immune response to VP1 and large T-antigen in kidney transplant recipients

Polyomavirus BK (BKV) is the primary cause of polyomavirus-associated nephropathy (PVAN) in kidney transplant (KT) recipients. Using ELISpot assays, we compared the frequency of interferon-gamma (IFN-gamma) secreting peripheral blood mononuclear cells (PBMC) after stimulation with overlapping peptide pools covering BKV large T-antigen (LT) and VP1 capsid proteins (VP1). In 10 healthy donors, LT and VP1 responses were low with median 24 (range 15-95) and 25 (7-113) spot-forming units/10(6) PBMC (SFU), respectively. In 42 KT patients with current or recent plasma BKV loads, median LT and VP1 responses of 29 (0-524) and 114 (0-1432) SFU were detected, respectively. In KT patients with decreasing or past plasma BKV loads, significantly higher median BKV-specific IFN-gamma responses were detected compared to KT patients with increasing or persisting BKV loads [LT: 78 (8-524) vs. 22 (0-120) SFU, p=0.003; VP1: 285 (45-1432) vs. 53 (0-423) SFU, p=0.001, respectively]. VP1-specific IFN-gamma responses were higher and more likely to involve CD4(+) T cells, while CD8(+) T cells were more frequently directed against LT. Stimulation with JCV-specific VP1 and LT peptides indicated only low-level cross-recognition. The data suggest that control of BKV replication is correlated with differentiated expansion of BKV-specific cellular immune responses.

Immune responses to BK and JC viruses in immunocompromised patients

BK virus (BKV) and JC virus (JCV) are ubiquitous human polyomaviruses that establish persistent asymptomatic infections in immunocompetent individuals, but in a minority of immunocompromised patients, reactivate and cause clinical disease. BKV is associated with BKV nephropathy (BKVN) in kidney transplant recipients and JCV is the etiologic agent of progressive multifocal leukoencephalopathy (PML) in AIDS patients. Humoral responses do not appear adequate to protect against reactivation or disease, and both BKVN and PML appear to be due to a failure of cellular immune responses to control the virus. Among the goals of current research is the identification of the functional correlates of cellular immune protection against these viruses in immunocompetent individuals. Such insights may help identify the small subset of patients at risk of BKV and JCV reactivation, aid clinical management and permit the development of immunotherapeutic approaches.