Pathogenicity of Avian Polyomaviruses and Prospect of Vaccine Development.

Polyomaviruses are nonenveloped icosahedral viruses with a double-stranded circular DNA containing approximately 5000 bp and 5-6 open reading frames. In contrast to mammalian polyomaviruses (MPVs), avian polyomaviruses (APVs) exhibit high lethality and multipathogenicity, causing severe infections in birds without oncogenicity. APVs are classified into 10 major species: Adélie penguin polyomavirus, budgerigar fledgling disease virus, butcherbird polyomavirus, canary polyomavirus, cormorant polyomavirus, crow polyomavirus, Erythrura gouldiae polyomavirus, finch polyomavirus, goose hemorrhagic polyomavirus, and Hungarian finch polyomavirus under the genus Gammapolyomavirus. This paper briefly reviews the genomic structure and pathogenicity of the 10 species of APV and some of their differences in terms of virulence from MPVs. Each gene's genomic size, number of amino acid residues encoding each gene, and key biologic functions are discussed. The rationale for APV classification from the Polyomavirdae family and phylogenetic analyses among the 10 APVs are also discussed. The clinical symptoms in birds caused by APV infection are summarized. Finally, the strategies for developing an effective vaccine containing essential epitopes for preventing virus infection in birds are discussed. We hope that more effective and safe vaccines with diverse protection will be developed in the future to solve or alleviate the problems of viral infection.

[INTRAVENOUS IMMUNOGLOBULIN TREATMENT TO PREVENT BK NEPHROPATHY IN PEDIATRIC RENAL TRANSPLANT RECIPIENTS WITH BK VIRUS].

AIMS: In this retrospective study we examined the safety and efficacy of high-dose intravenous immunoglobulin (HD-IVIG) therapy in preventing BKVN in pediatric renal transplant recipients with BK-viremia/viruria. BACKGROUND: BK virus nephropathy (BKVN) is diagnosed in 5-16% of pediatric renal transplant recipients and is preceded by BK viremia/viruria. Despite irreversible renal damage associated with BKVN, there is a lack of evidence-based guidelines for preventive measures in patients with BK viremia/viruria. METHODS: All pediatric renal transplant recipients under our care underwent routine testing for urine and blood BK virus, using the polymerase chain reaction (PCR) technique. Patients exhibiting BK-viruria < 107 copies/milliliter (ml) and/or BK-viremia<103 copies/ml without any evidence of BKVN, were managed with 50% dose reduction of the immunosuppressive drug mycophenolate mofetil (MMF). Absence of BK viral load decline within two months from MMF dose reduction was managed with HD-IVIG (at 2 grams/kg body weight). RESULTS: The study included 62 patients over a 6-year period; 31 patients (50%) showed BK-viremia/viruria; 13/31 patients (42%) suffered from significant and persistent BK-viremia/viruria, unresponsive to MMF dose reduction, and were managed with HD-IVIG; 12/13 (92%) showed significant BK viral load reduction within 6 months from HD-IVIG therapy. Except for transient headache, no patient exhibited major adverse effects to HD-IVIG therapy, and none developed overt BKVN during the study period. CONCLUSIONS: Preventive HD-IVIG therapy in pediatric renal transplant recipients with BK viremia/viruria unresponsive to MMF dose reduction is safe and effective in preventing the development of BKVN. Additional large-scale studies are necessary to establish our findings.

Intravenous immunoglobulin as a preventive strategy against BK virus viremia and BKV-associated nephropathy in kidney transplant recipients-Results from a proof-of-concept study.

BK virus (BKV) replication occurs frequently in kidney transplant recipients (KTR), potentially leading to BKV-associated nephropathy (BKVAN) and graft loss. Patients with high titers of BKV-neutralizing antibodies (NAbs) are protected against BKV replication, and intravenous immunoglobulin (IVIg) infusion can increase NAb titers. We investigated whether early IVIg administration prevents BKV replication in patients with low NAb titers (<4 log10 against the BKV-specific genotype). Based on NAb titers on the day of transplantation, KTR followed in the Strasbourg University Hospital (n = 174) were retrospectively divided into the following 3 risk categories for BKV replication: (1) patients with low NAb titers ("high-risk") who received IVIg for the first 3 posttransplant months (n = 44), (2) patients with low NAb titers ("high-risk") who did not undergo IVIg treatment (n = 41), and (3) patients with high NAb titers ("low-risk") who did not receive IVIg (n = 89). At 12 posttransplant months, the incidence of BKV viremia in the high-risk group treated with IVIg (6.8%) was similar to that observed in the low-risk group (10.1%) and markedly lower than that of the untreated high-risk group (36.6%; P < .001). Similar results were observed with regard to BKVAN. We conclude that IVIg may be a valuable strategy for preventing BKV replication.

mSphere of Influence: It's Not Me, It's You-How Donor Factors Influence Kidney Transplant Outcomes.

Diana V. Pastrana works in the field of DNA tumor virus biology. In this mSphere of Influence article, she reflects on how the two papers "Donor origin of BKV replication after kidney transplantation" (C. Schmitt, L. Raggub, S. Linnenweber-Held, O. Adams, et al., J Clin Virol 59:120-125, 2014, https://doi.org/10.1016/j.jcv.2013.11.009) and "Neutralizing antibody-mediated response and risk of BK virus-associated nephropathy" (M. Solis, A. Velay, R. Porcher, P. Domingo-Calap, et al., J Am Soc Nephrol 29:326-334, 2018, https://doi.org/10.1681/ASN.2017050532) reminded her of the importance of allowing data, and not adherence to dogma, to drive her research.

HLA-E Polymorphism Determines Susceptibility to BK Virus Nephropathy after Living-Donor Kidney Transplant.

Human leukocyte antigen (HLA)-E is important for the regulation of anti-viral immunity. BK polyomavirus (BKPyV) reactivation after kidney transplant is a serious complication that can result in BKPyV-associated nephropathy (PyVAN) and subsequent allograft loss. To elucidate whether HLA-E polymorphisms influence BKPyV replication and nephropathy, we determined the HLA-E genotype of 278 living donor and recipient pairs. A total of 44 recipients suffered from BKPyV replication, and 11 of these developed PyVAN. Homozygosity of the recipients for the HLA-E*01:01 genotype was associated with the protection against PyVAN after transplant (p = 0.025, OR 0.09, CI [95%] 0.83-4.89). Considering the time course of the occurrence of nephropathy, recipients with PyVAN were more likely to carry the HLA-E*01:03 allelic variant than those without PyVAN (Kaplan-Meier analysis p = 0.03; OR = 4.25; CI (95%) 1.11-16.23). Our findings suggest that a predisposition based on a defined HLA-E genotype is associated with an increased susceptibility to develop PyVAN. Thus, assessing HLA-E polymorphisms may enable physicians to identify patients being at an increased risk of this viral complication.

Intravenous Immunoglobulin Administration Significantly Increases BKPyV Genotype-Specific Neutralizing Antibody Titers in Kidney Transplant Recipients.

BK polyomavirus (BKPyV)-associated nephropathy (BKPyVAN) is one of the major causes of kidney graft dysfunction, and there are no BKPyV-specific antiviral therapies available. BKPyV neutralizing antibodies (NAbs) play key roles in protecting against BKPyV replication and represent a potential therapeutic or preventive strategy. In this study, we evaluated NAb titers in intravenous immunoglobulin (i.v. Ig) preparations and in kidney transplant recipients (KTR) before and after i.v. Ig administration. NAb titers directed against major BKPyV genotypes were measured using a BKPyV pseudovirion system. Thirty-three KTR receiving high (1 g/kg of body weight/day; n = 17) or low (0.4 g/kg/day; n = 16) i.v. Ig doses were included. Median NAb titers in i.v. Ig preparations ranged from 5.9 log10 50% inhibitory concentration (IC50) for genotype I to 4.1 log10 IC50 for genotype IV. A mean of 90% of patients (range, 88% to 100%) displaying low or negative BKPyV NAb titers against genotype I reached 4 log10 IC50 after the first i.v. Ig administration. This value was reached by a mean of 44% (range, 13% to 83%) and 19% (range, 0% to 38%) of patients against genotype II and genotype IV, respectively. The benefit of i.v. Ig administration persisted until the following course of treatment (day 22 ± 7 days) for genotypes I and II, and no cumulative effect was observed through the three doses. Our findings demonstrate that i.v. Ig administration results in a significant increase in BKPyV NAb titers in KTR. These in vitro and in vivo pharmacokinetic data provide the rationale for a proof-of-concept study investigating the efficacy of i.v. Ig for the prevention of BKPyV infection in KTR.

Do Antithymocyte Globulin-Free Acute Rejection Therapies Increase the Risk of Polyoma Nephropathy in Renal Transplant Recipients?

INTRODUCTION: BK virus nephropathy is a serious complication that can lead to allograft kidney loss. Excessive immunosuppression increases the risk. We aimed to evaluate whether there is an increased risk of BK viremia and nephropathy in patients who underwent high-dose immunosuppression because of the development of acute rejection in the early period after kidney transplantation. METHODS: This retrospective cohort study was performed between April 2015 and March 2016. Twenty-nine patients who had biopsy-proven acute rejection in the first 3 months were evaluated for BK viremia and nephropathy. Thirty patients who had transplantations at the same period were the control group. Plasma BK-DNA values were examined at 1, 2, 3, 6, 9, and 12 months after the rejection treatment and at 3, 6, 9, and 12 months in the control group. Presence of polyoma nephropathy was examined with surveillance biopsies at the 6 and 12 months. RESULTS: Acute rejection treatment was started on the 12th day after transplantation (2-37 days). Seventeen cellular rejections and 12 humoral rejections were reported by biopsy. Two of the 12 humoral rejections were suspicious. Only pulse steroid (PS) (n = 18); PS, plasmapheresis, and intravenous immunoglobulin (n = 8); PS and intravenous immunoglobulin (n = 2); and PS and plasmapheresis (n = 1) treatments were performed. In 21 patients in the rejection group and 25 patients in the control group, BK-DNA was not positive at all. Two patients had graft loss at 11 and 36 months in the rejection group. Graft losses were secondary to rejection. CONCLUSIONS: Treatment with antithymocyte globulin-free regimens after acute rejection episodes did not lead to an increase in BK viremia.

Ciprofloxacin for BK viremia prophylaxis in kidney transplant recipients: Results of a prospective, double-blind, randomized, placebo-controlled trial.

In kidney transplantation, BK virus infection has historically resulted in high rates of graft dysfunction and graft loss. Unlike other opportunistic infections, no therapies have been shown to prevent BK. The purpose of the current study was to evaluate the safety and efficacy of ciprofloxacin for the prevention of BK viremia in kidney transplant recipients. Two hundred kidney transplant recipients were enrolled in a prospective, randomized, double-blind, placebo-controlled trial comparing a 3-month course of ciprofloxacin (n = 133) vs placebo (n = 67) for the prevention of BK viremia. The primary endpoint of BK viremia at month 6 posttransplant occurred in 25 (18.8%) patients in the ciprofloxacin group and 5 (7.5%) in the placebo group (P = .03). Higher rates of BK viremia (23.3% vs 11.9%; P = .06) and BK nephropathy (5.8% vs 1.5%; P = .26) remained at 12 months in the ciprofloxacin group. Ciprofloxacin use was associated with a significantly higher rate of fluoroquinolone-resistant gram-negative infections (83.3% vs 50%; P = .04). A 3-month course of ciprofloxacin was ineffective at preventing BK viremia in kidney transplant recipients and was associated with an increased risk of fluoroquinolone-resistant infections. Clinical trial registration number: NCT01789203.

Metagenomic Virome Sequencing in Living Donor and Recipient Kidney Transplant Pairs Revealed JC Polyomavirus Transmission.

BACKGROUND: Before kidney transplantation, donors and recipients are routinely screened for viral pathogens using specific tests. Little is known about unrecognized viruses of the urinary tract that potentially result in transmission. Using an open metagenomic approach, we aimed to comprehensively assess virus transmission in living-donor kidney transplantation. METHODS: Living kidney donors and their corresponding recipients were enrolled at the time of transplantation. Follow-up study visits for recipients were scheduled 4-6 weeks and 1 year thereafter. At each visit, plasma and urine samples were collected and transplant recipients were evaluated for signs of infection or other transplant-related complications. For metagenomic analysis, samples were enriched for viruses, amplified by anchored random polymerase chain reaction (PCR), and sequenced using high-throughput metagenomic sequencing. Viruses detected by sequencing were confirmed using real-time PCR. RESULTS: We analyzed a total of 30 living kidney donor and recipient pairs, with a follow-up of at least 1 year. In addition to viruses commonly detected during routine post-transplant virus monitoring, metagenomic sequencing detected JC polyomavirus (JCPyV) in the urine of 7 donors and their corresponding recipients. Phylogenetic analysis confirmed infection with the donor strain in 6 cases, suggesting transmission from the transplant donor to the recipient, despite recipient seropositivity for JCPyV at the time of transplantation. CONCLUSIONS: Metagenomic sequencing identified frequent transmission of JCPyV from kidney transplant donors to recipients. Considering the high incidence rate, future studies within larger cohorts are needed to define the relevance of JCPyV infection and the donor's virome for transplant outcomes.

Elimination of BK viremia in renal transplant recipients by optimization of immunosuppressive medications without precipitating acute rejection.

BK Polyomavirus-associated nephropathy (BKVAN) has been recognized as an increasing threat in renal transplant patients (RTP) for more than a decade. Reduction in immunosuppression is the mainstay of treatment through various options of treatment has been suggested. Published reports on these protocols have shown mixed results, and no randomized controlled trials have compared one strategy with another. In this context, we hypothesize that the appearance of BKV in the blood compels one to optimize the immunosuppression with possible long-term beneficial effects. We conducted a retrospective study among the RTP being followed up by the Renal Medicine Department at Royal Hospital who tested positive for BKV-polymerase chain reaction and whose immunosuppression was altered with a final aim to get rid of BK viremia, yet avoiding acute rejection. Results were analyzed by the clinical and statistical approach. Extensive literature review was carried out to look into the prevalence, prognosis, and treatment of BKVAN. In all the patients in whom BKV was detected alteration in immunosuppression resulted in eliminating the virus without precipitating acute rejection. The study shows that in the exercise of eliminating BKV by alteration of immunosuppression, we have "tailored" the immunosuppression in each particular RTPs, without precipitating acute rejection.

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.

BK virus-induced renal allograft nephropathy.

BK virus nephropathy (BKVN) is a serious opportunistic infection threatening renal function especially during the first year after transplantation. Its incidence is now on the rise and is closely related to the level of the recipient's immune system inhibition. This is more intensive with current trends in transplantation medicine, where more potent immunosuppressive protocols are used and more aggressive antirejection therapy is applied. In the absence of BK virus (BKV) specific therapy and limited treatment options for advanced BKVN, active screening of BKV replication and subsequent preemptive adjustment of immunosuppression are essential measures to prevent BKVN. However, it remains unclear how to modify immunosuppressive protocols as well as how to address initial stages of BKV replication. This comprehensive review summarizes the currently applied and not completely uniform procedures for the detection, prophylaxis and therapy of BKV replication and BKVN. The pitfalls brought by reduced immunosuppression, as a typical response to a significant viral replication or a developed BKVN, are also mentioned, particularly in the form of graft rejection. The paper also outlines the authors' experiences, and lists currently ongoing studies on the subject. The perspectives of new, especially immune-based, procedures in the treatment of complications associated with BKV infections are highlighted. Different views on the management of patients indicated for kidney re-transplantation whose previous graft failed because of BKVN are also discussed.

Conversion from tacrolimus-mycophenolate mofetil to tacrolimus-mTOR immunosuppression after kidney-pancreas transplantation reduces the incidence of both BK and CMV viremia.

BACKGROUND: We sought to determine whether conversion from tacrolimus/mycophenolate mofetil (TAC-MMF) into tacrolimus/mTOR inhibitor (TAC-mTOR) immunosuppression would reduce the incidences of BK and CMV viremia after kidney/pancreas (KP) transplantation. METHODS: In this single-center review, the TAC-mTOR cohort (n = 39) was converted at 1 month post-transplant to an mTOR inhibitor and reduced-dose tacrolimus. Outcomes were compared to a cohort of KP recipients (n = 40) maintained on TAC-MMF. RESULTS: At 3 years post-transplant, KP survivals and incidences of kidney/pancreas rejection were equivalent between mTOR and MMF-treated cohorts. (P = ns). BK viremia-free survival was better for the mTOR vs MMF-treated group (P = .004). In multivariate analysis, MMF vs mTOR immunosuppression was an independent risk factor for BK viremia (hazard ratio 12.27, P = .02). Similarly, mTOR-treated recipients displayed better CMV infection-free survival compared to the MMF-treated cohort (P = .01). MMF vs mTOR immunosuppression (hazard ratio 18.77, P = .001) and older recipient age (hazard ratio 1.13 per year, P = .006) were independent risk factors for CMV viremia. Mean estimated GFR and HgbA1c levels were equivalent between groups at 1, 2, and 3 years post-transplantation. CONCLUSION: Conversion from TAC/MMF into TAC/mTOR immunosuppression after KP transplantation reduced the incidences of BK and CMV viremia with an equivalent risk of acute rejection and similar renal/pancreas function.

ECIL guidelines for the prevention, diagnosis and treatment of BK polyomavirus-associated haemorrhagic cystitis in haematopoietic stem cell transplant recipients.

OBJECTIVES: To define guidelines for BK polyomavirus (BKPyV)-associated haemorrhagic cystitis (BKPyV-HC) after paediatric and adult HSCT. METHODS: Review of English literature and evidence-based recommendations by expert consensus. RESULTS: BKPyV-HC occurs in 8%-25% of paediatric and 7%-54% of adult recipients undergoing allogeneic HSCT. Diagnosis requires the triad of cystitis, macro-haematuria and high urine BKPyV loads >7 log10 copies/mL, and exclusion of other relevant aetiologies. BKPyV viraemia is frequent and may serve as a more specific semiquantitative follow-up marker. No randomized controlled trials are available to inform antiviral prophylaxis or treatment. However, hyper-hydration and/or bladder irrigation showed limited prophylactic value. Fluoroquinolones are not effective for prophylaxis or treatment, but rather increase antibiotic resistance. Hyperbaric oxygen or fibrin glue is marginally effective based on small case series from correspondingly equipped centres. Although cidofovir has been reported to improve and/or reduce BKPyV viraemia or viruria, the current data do not support its regular use. CONCLUSIONS: BKPyV-HC remains a disabling unmet clinical need in HSCT that requires novel approaches supported by proper clinical trials.

Biopsy-Proven BK Virus-Associated Nephropathy: Clinico-Pathologic Correlations.

OBJECTIVES: Our objective was to study the clinico-pathologic correlations in BK virus nephropathy. MATERIALS AND METHODS: We conducted a retrospective study of all patients with biopsy-proven polyoma (BK) virus infection. We compared their survival and renal outcomes versus BK virus-negative patients with biopsy-proven graft rejection. Histopathologic characterization by a blinded nephropathologist was performed. RESULTS: BK nephropathy was found in 10 patients biopsied for graft dysfunction. All virus-positive patients received antithymocyte globulin induction therapy compared with only 59.3% of the BK-negative group (P = .06). The percentage of patients in the BK-negative group who received acyclovir was significantly higher than that in the BK-positive group (P = .01). After a mean observation period of 6.8 ± 3.2 years, 70% of the BK group had functioning grafts compared with 68% in the BK-negative group (P = .9) with similar 3-year graft survival in the 2 groups (80% and 90%; P = .8). Within the BK group, graft survival was better in the older group (P = .005) and in those with deceased donor kidney grafts (P = .016). Patients in the BK-negative group were heavier (mean weight of 64.3 ± 12.1 vs 46.7 ± 20.6 kg; P = .003). None of the histopathologic features studied had any effect on renal prognosis. CONCLUSIONS: The risk factors for developing BK nephropathy were use of antithymocyte globulin, lower weight, and not using acyclovir as early prophylaxis. Within the BK nephropathy group, better graft survival was observed in deceased donor kidney recipients and in older patients. The viral load and polyoma virus nephropathy stage did not affect graft survival in this small sample study.

BK and Other Polyomaviruses in Kidney Transplantation.

For more than 40 years, polyomaviruses (BK virus and JC virus) have been known to cause disease in human beings. Recently, 11 new polyomaviruses were discovered. However, the majority of these viruses are rare in renal transplant recipients and BK and JC viruses remain the most important polyomaviruses to impact this population. BK virus presents as BK virus nephropathy and has, in rare instances, been associated with hemorrhagic cystitis or ureteral strictures. JC virus can cause progressive multifocal leukoencephalopathy or nephropathy in this population as well, but is uncommon. Antiviral prophylactic and therapeutic interventions for these diseases are lacking to date, although reduction of immunosuppression has been associated with success in treating both BK virus nephropathy and JC virus-induced disease. Risk factors are not well defined and vary across studies. However, the cumulative degree of immunosuppression is regarded universally as an important contributor to BK virus replication. For these reasons, it is recommended to screen all renal transplant recipients prospectively for BK virus infection. Multicenter trials using standardized BK and JC virus screening methods are necessary to define risk factors better, and to determine the effect of prophylaxis and treatments for these polyomaviruses affecting renal transplant recipients.

1,25 Dihydroxyvitamin D circulating levels, calcitriol administration, and incidence of acute rejection, CMV infection, and polyoma virus infection in renal transplant recipients.

Observation that 1,25-Dihydroxyvitamin-D3 has an immunomodulatory effect on innate and adaptive immunity raises the possible effect on clinical graft outcome. Aim of this study was to evaluate the correlation of biopsy-proven acute rejection, CMV infection, BKV infection, with 1,25-Dihydroxyvitamin-D3 deficiency and the benefit of calcitriol supplementation before and during the transplantation. Risk factors and kidney graft function were also evaluated. All RTRs received induction therapy with basiliximab, cyclosporine, mycophenolic acid, and steroids. During the first year, the incidence of BPAR (4% vs 11%, P=.04), CMV infection (3% vs 9%, P=.04), and BKV infection (6% vs 19%, P=.04) was significantly lower in users compared to controls. By multivariate Cox regression analysis, 1,25-Dihydroxyvitamin-D3 deficiency and no calcitriol exposure were independent risk factors for BPAR (HR=4.30, P<.005 and HR=3.25, P<.05), for CMV infection (HR=2.33, P<.05 and HR=2.31, P=.001), and for BKV infection (HR=2.41, P<.05 and HR=2.45, P=.001). After one year, users had a better renal function: eGFR was 62.5±6.7 mL/min vs 51.4±7.6 mL/min (P<.05). Only one user developed polyomavirus-associated nephropathy vs 15 controls. Two users lost their graft vs 11 controls. 1,25(OH)2-D3 deficiency circulating levels increased the risk of BPAR, CMV infection, BKV infection after kidney transplantation. Administration of calcitriol is a way to obtain adequate 1,25(OH)2-D3 circulating levels.

Strategies to prevent BK virus infection in kidney transplant recipients.

PURPOSE OF REVIEW: Despite improvements in posttransplant care, BK virus (BKV) remains one of the most challenging posttransplant infections in kidney transplant recipients with high rates of allograft failure. In the absence of well tolerated and efficacious viral specific therapeutics, treatment is primarily focused on reduction of immunosuppression, which poses a risk of rejection and fails to lead to viral clearance in a number of patients. RECENT FINDINGS: Recent work has turned toward preventive therapies analogous to those used for other infections like cytomegalovirus. These efforts have focused on the use of quinolone antibiotic prophylaxis to prevent BKV infection and pretransplant vaccination to boost humoral and cellular immunity. SUMMARY: Despite promising in-vitro and observational data, quinolone antibiotic prophylaxis has not been effective in preventing BKV infection in prospective studies. However, prophylaxis with newer less toxic viral specific agents such as brincidofovir - the lipid oral formulation of cidofovir - may yet prove effective. Strategies focused on eliciting a humoral immune response to recombinant virus-like particles or using adoptive transfer of BKV-specific T cells have also shown significant potential to prevent BKV infection in organ transplant recipients.

Scaffolded Antigens in Yeast Cell Particle Vaccines Provide Protection against Systemic Polyoma Virus Infection.

Background. U65, a self-aggregating peptide scaffold, traps fused protein antigens in yeast cells. Conversion to Yeast Cell Particle (YCP) vaccines by partial removal of surface mannoproteins exposes ß-glucan, mediating efficient uptake by antigen-presenting cells (APCs). YCP vaccines are inexpensive, capable of rapid large-scale production and have potential for both parenteral and oral use. Results. YCP processing by alkaline hydrolysis exposes up to 20% of the glucan but converts scaffolded antigen and internal yeast proteins into a common aggregate, preventing selective yeast protein removal. For U65-green fluorescent protein (GFP) or U65-Apolipoprotein A1 (ApoA1) subcutaneous vaccines, maximal IgG responses in mice required 10% glucan exposure. IgG responses to yeast proteins were 5-fold lower. Proteolytic mannoprotein removal produced YCPs with only 6% glucan exposure, insufficiently porous for selective removal of even native yeast proteins. Vaccine efficacy was reduced 10-fold. Current YCP formulations, therefore, are not suitable for human use but have considerable potential for use in feed animal vaccines. Significantly, a YCP vaccine expressing a GFP fusion to VP1, the murine polyoma virus major capsid protein, after either oral or subcutaneous administration, protected mice against an intraperitoneal polyoma virus challenge, reducing viral DNA levels in spleen and liver by >98%.