Presentation of BK polyomavirus-associated hemorrhagic cystitis after allogeneic hematopoietic cell transplantation

Structural implications of BK polyomavirus sequence variations in the major viral capsid protein Vp1 and large T-antigen: a computational study

BK polyomavirus (BKPyV) is a double-stranded DNA virus causing nephropathy, hemorrhagic cystitis, and urothelial cancer in transplant patients. The BKPyV-encoded capsid protein Vp1 and large T-antigen (LTag) are key targets of neutralizing antibodies and cytotoxic T-cells, respectively. Our single-center data suggested that variability in Vp1 and LTag may contribute to failing BKPyV-specific immune control and impact vaccine design. We, therefore, analyzed all available entries in GenBank (1516 VP1; 742 LTAG) and explored potential structural effects using computational approaches. BKPyV-genotype (gt)1 was found in 71.18% of entries, followed by BKPyV-gt4 (19.26%), BKPyV-gt2 (8.11%), and BKPyV-gt3 (1.45%), but rates differed according to country and specimen type. Vp1-mutations matched a serotype different than the assigned one or were serotype-independent in 43%, 18% affected more than one amino acid. Notable Vp1-mutations altered antibody-binding domains, interactions with sialic acid receptors, or were predicted to change conformation. LTag-sequences were more conserved, with only 16 mutations detectable in more than one entry and without significant effects on LTag-structure or interaction domains. However, LTag changes were predicted to affect HLA-class I presentation of immunodominant 9mers to cytotoxic T-cells. These global data strengthen single center observations and specifically our earlier findings revealing mutant 9mer epitopes conferring immune escape from HLA-I cytotoxic T cells. We conclude that variability of BKPyV-Vp1 and LTag may have important implications for diagnostic assays assessing BKPyV-specific immune control and for vaccine design.

IMPORTANCE

Type and rate of amino acid variations in BKPyV may provide important insights into BKPyV diversity in human populations and an important step toward defining determinants of BKPyV-specific immunity needed to protect vulnerable patients from BKPyV diseases. Our analysis of BKPyV sequences obtained from human specimens reveals an unexpectedly high genetic variability for this double-stranded DNA virus that strongly relies on host cell DNA replication machinery with its proof reading and error correction mechanisms. BKPyV variability and immune escape should be taken into account when designing further approaches to antivirals, monoclonal antibodies, and vaccines for patients at risk of BKPyV diseases.

BK virus-associated hemorrhagic cystitis in pediatric stem cell transplantation: a case report and scoping review

Introduction

BK virus-associated hemorrhagic cystitis (BK-HC) is a debilitating and poorly understood complication of hematopoietic stem cell transplantation (SCT). Hematuria, dysuria, and other symptoms associated with BK-HC are common in the immediate post-SCT period, making BK-HC difficult to distinguish from other conditions presenting with these symptoms. Despite published criteria for diagnosis, the degree to which these criteria are consistently applied to either clinical diagnosis or to studies informing BK-HC management is unclear. We present a case of BK-HC in a pediatric SCT recipient, and discuss the challenges associated with treatment in the absence of rigorous data to inform clinical management.

Methods

We reviewed all cases of BK viruria at our center in patients undergoing SCT between January 2015 and December 2019. We then performed a scoping review of publications in PubMed addressing BK-HC, specifically focusing on how BK-HC was defined. Publications using the keywords "BK polyomavirus" and "hemorrhagic cystitis" were included if they involved a clinical study of SCT recipients and a full-text article was available in English. Case reports were excluded. Analysis focused on whether BK-HC was explicitly defined and whether the definition incorporated elements of diagnostic criteria published by European Conference on Infections in Leukemia (ECIL).

Results

A total of 30 studies published between January 2018 and 30 June 2021 met criteria for review, including 4 clinical trials, 7 prospective observational studies, and 19 retrospective observational studies. Fifteen of these studies included pediatric patients (7 pediatric only, 8 combined adult and pediatric). Of the 30 publications, 19 included a definition of either BK-HC or BK cystitis, with only five using ECIL criteria, all of which were observational studies. Multiple interventions are described for treatment of BK-HC, including cidofovir, leflunomide, quinolones, hyperbaric oxygen, keratinocyte growth factor, and BK-specific cytotoxic T lymphocytes. However, evidence to support efficacy for any of these interventions is lacking.

Discussion

Although BK-HC is a well-known complication of SCT, evidence to support available treatment options is limited. Well-controlled studies that incorporate clear diagnostic criteria are needed to better define the risk factors, natural history, and ideal interventions.

BK Polyomavirus Diversity After Hematopoietic Stem Cell Transplantation

BK polyomavirus (BKPyV) infection is common after hematopoietic stem cell transplantation (HSCT) and is associated with the development of hemorrhagic cystitis (HC). The role that BKPyV plays in the pathogenesis of HC is not well characterized. We investigated the impact of BKPyV diversity on the development of HC using a previously established cohort of pediatric HSCT patients. There were 147 urine samples with quantifiable BKPyV at month 1 after HSCT; 137 (93.2%) were amplified using our in-house polymerase chain reaction approach and sent for next-generation sequencing. Subtype Ia was most frequent (61.3%), followed by subtype Ib1 (31.4%). The median viral load of subtype Ia samples was higher than for subtype Ib1 at month 1. Across the protein coding regions, APOBEC-induced mutations and signature patterns associated with HC were identified. This is the largest sequencing study of a single cohort of HSCT patients, providing a vast resource of sequence data for future analyses.

Interaction Between High-Dose Intravenous Busulfan and Post-Transplantation Cyclophosphamide on Hemorrhagic Cystitis After Allogeneic Hematopoietic Cell Transplantation

This study investigates the incidence and predictors of hemorrhagic cystitis (HC) in 960 adults undergoing allo- hematopoietic stem cell transplantation. Two hundred fifty-two (26.5%) patients received myeloablative conditioning regimens, and 81.4% received high-dose intravenous busulfan (HD Bu). Six hundred ninety-five (72.4%) patients received post-transplantation cyclophosphamide (PTCY)-based prophylaxis, and 91.4% additionally received anti-thymocyte globulin (ATG) and Cyclosporine A (CsA) (PTCY-ATG-CsA). Two hundred twenty-eight (23.8%) patients developed HC. The day 100 cumulative incidences of grades 2-4 and 3-4 HC were 11.1% and 4.9%. BK virus was isolated in 58.3% of urinary samples. Using HD BU myeloablative regimens increased the risk for grade 2-4 HC (hazard ratio [HR] = 1.97, P = .035), and HD BU combined with ATG-PTCY-CsA increased this 4 times (HR = 4.06, P < .001) for grade 2-4 HC compared to patients who received neither of these drugs. A significant correlation was documented between grade II-IV acute graft-versus-host disease and grade 2-4 HC (HR = 2.10, P < .001). Moreover, patients with BK-POS grade 2-4 HC had lower 1-year overall survival (HR = 1.51, P = .009) and higher non-relapse mortality (HR = 2.31, P < .001), and patients with BK-NEG grade 2-4 HC had comparable post-transplantation outcomes. In conclusion, intravenous HD Bu was identified as a predictor for grade 2-4 HC. Moreover, when HD Bu was combined with PTCY-ATG-CsA, the risk increased 4-fold. Based on the results provided by this study, preventing the onset of HC, especially in high-risk patients, is mandatory because its presence significantly increases the risk for mortality.

Decreased lymphocyte count before conditioning is associated with BK virus-associated hemorrhagic cystitis after allogeneic hematopoietic stem cell transplantation

BACKGROUND

BK virus-associated hemorrhagic cystitis (BKV-HC) is a serious complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT). It can cause morbidity and may increase treatment-related mortality. Previous studies showed that the occurrence of BKV-HC was related to various factors. However, there are still many controversial factors. It is not clear whether BKV-HC will affect the long-term prognosis of patients.

OBJECTIVE

We aimed to identify risk factors for BKV-HC after allo-HSCT and evaluate the effect of BKV-HC on overall survival (OS) and progression- free survival (PFS) of patients.

STUDY DESIGN

We retrospectively analyzed the clinical data of 93 patients who underwent allo-HSCT. Univariate and multivariate analysis were used to identify risk factors for BKV-HC. The Kaplan-Meier method was used to estimate OS and PFS. A difference was considered statistically significant if P < 0.05.

RESULTS

A total of 24 patients developed BKV-HC. The median occurrence time of BKV-HC was 30 (range:8-89) days after transplantation, and the median duration was 25.5 (range:6-50) days. Multivariate logistic regression analysis indicated that peripheral blood lymphocyte count <1 × 10⁹/L before conditioning (OR = 4.705, P = 0.007) and haploidentical transplantation (OR = 13.161, P = 0.018) were independent risk factors for BKV-HC. The 3-year OS rate was 85.9% (95%CI:62.1%-95.2%) in the BKV-HC group and 73.1% (95%CI: 58.2%-88.0%) in the non-BKV-HC group. There was no significant difference between the two groups (P = 0.516). The 3-year PFS rate was 76.3% (95%CI: 57.9%-94.7%) in the BKV-HC group and 58.1% (95%CI: 39.5%-76.7%) in the non-BKV-HC group. There was no significant difference in the two groups (P = 0.459). The severity of BKV-HC was not related to the OS and PFS of the patients (P value was 0.816 and 0.501, respectively).

CONCLUSION

Haploidentical transplantation and decreased peripheral blood lymphocyte count before conditioning increased the risk of BKV-HC after allo-HSCT. The occurrence of BKV-HC after allo-HSCT and the severity of which did not affect OS and PFS of the patients.

How I prevent viral reactivation in high-risk patients

Preventing viral infections at an early stage is a key strategy for successfully improving transplant outcomes. Preemptive therapy and prophylaxis with antiviral agents have been successfully used to prevent clinically significant viral infections in hematopoietic cell transplant recipients. Major progress has been made over the past decades in preventing viral infections through a better understanding of the biology and risk factors, as well as the introduction of novel antiviral agents and advances in immunotherapy. High-quality evidence exists for the effective prevention of herpes simplex virus, varicella-zoster virus, and cytomegalovirus infection and disease. Few data are available on the effective prevention of human herpesvirus 6, Epstein-Barr virus, adenovirus, and BK virus infections. To highlight the spectrum of clinical practice, here we review high-risk situations that we handle with a high degree of uniformity and cases that feature differences in approaches, reflecting distinct hematopoietic cell transplant practices, such as ex vivo T-cell depletion.

BK Viremia and Changes in Estimated Glomerular Filtration Rate in Children and Young Adults after Hematopoietic Cell Transplantation

Kidney disease in allogeneic hematopoietic cell transplantation (HCT) recipients is associated with increased mortality rates. BK virus (BKV) viremia has been associated with kidney dysfunction in pediatric HCT recipients; however, few studies have investigated longer-term kidney outcomes in association with BKV in this population. Here we assessed the relationship between BK viremia and changes in estimated glomerular filtration rate (eGFR) in children in the first year post-HCT. We selected 136 patients age ≤26 years who underwent HCT in 2007 to 2018 at a single center and had plasma BK viral load data available at 2 time points, weeks 4 to 7 post-HCT and weeks 10 to 13 post-HCT from prospectively collected stored plasma samples. A total of 272 samples were analyzed for BKV using quantitative PCR. We used multivariate linear models to determine the association of BK viremia and change in eGFR by 1 year post-HCT. Forty percent of the patients (54 of 136) had BKV detection in weeks 4 to 7, 13% of whom (7 of 54) had a BK viral load of ≥10,000 copies/mL, and 46% (62 of 136) had BKV detected in weeks 10 to 13, 34% (21 of 62) of whom had a BK viral load of ≥10,000 copies/mL. The mean decline in eGFR was 25.73 mL/min/1.73 m² by 1 year post-HCT. In multivariate models, a BK viral load of ≥10,000 copies/mL during weeks 4 to 7 was associated with a mean decline in eGFR of 30.6 mL/min/1.73 m² (95% confidence interval, -55.94 to -5.17; P = .019) compared with a BK viral load <10,000 copies/mL. In adjusted analyses, a high BK viral load in the blood (≥10,000 copies/mL) was associated with a significant decline in eGFR by 1 year post-HCT.

[Haemorrhagic cystitis following hematopoietic stem cell transplantation: Prophylaxis, diagnosis, and treatment. Guidelines from the SFGM-TC]

Hemorrhagic cystitis (HC) is a common complication after allogeneic hematopoietic cell transplantation (allo-HCT). Its manifestations range from microscopic hematuria without urinary symptoms to extensive and prolonged macroscopic hemorrhage requiring invasive interventions that can often prolong the duration of hospitalization and result in significant morbidity. The early onset of HC is related to allo-HCT conditioning regimen, whereas the late onset form is secondary to viral infection, most commonly due to BK virus. In the framework of the Francophone Society of Bone Marrow Transplantation and Cellular Therapy (SFGM-TC) practice harmonization workshops held in Lille in September 2021, the prophylaxis, the diagnostic approach and the treatments of HC following allografting were reviewed after analysis of published studies.

In Vitro Generation of BK polyomavirus-specific T cells for adoptive cell therapy in refractory cystitis hemorrhagic patients after hematopoietic stem cell transplantation

Introduction

BKPyV associated hemorrhagic cystitis (BKPyV-HC) is a major and prevalent outcome of hematopoietic stem cell transplantation (HSCT) with no standard treatment option. Adoptive T cell therapy (ACT) against transplant-associated viruses has shown promising potential. We sought to produce virus-specific T cells (VSTs) against BKPyV with the aim of treating refractory HSCT-associated HC.

Methods

Peripheral blood mononuclear cells (PBMC) from healthy donors were isolated by Ficoll-Hypaque density gradient centrifugation. BKPyV-pulsed, monocyte-derived dendritic cells (mo-DCs) and T cells were co-cultured and expanded over 2–3 weeks with the addition of IL-2. The T cells were examined for various functional assays.

Results

Comparison analysis of Carboxyfluorescein diacetate succinimidyl ester (CFSE) indicated that the percentage of proliferated cells were significantly higher in donors (49.62 ± 7.09%) than controls (7.96 ± 4.55%). Furthermore, expanded T cells exhibited specificity to BKPyV antigens by IFN-γ ELISPOT assay. The expanded cells showed cytotoxic function versus human lymphoblastoid cell line (LCL). Final VST products mainly comprised of CD8/CD69 double-positive T cells, which were significantly higher in donors (46.8 ± 7.1%) than controls (16.91 ± 3.40%).

Conclusion

In this study we demonstrated the feasibility of producing functional BKPyV-specific T cells in healthy donors using BKPyV PepMixes. These functional cells were able to proliferate and produce IFN-γ cytokine in response to BKPyV PepMixes. In addition, these T cells had cytotoxic ability against BKPyV antigen-expressing target cells.

Incidence, risk factors and outcome of BK virus hemorrhagic cystitis following allogenic hematopoietic cell transplantation: a retrospective cohort study

BK polyomavirus (BKPyV) can cause hemorrhagic cystitis (HC) after allogeneic hematopoietic cell transplantation (allo-HCT). Recent evaluation of BKPyV HC (BKHC) incidence and risk factors are scarce. We conducted a retrospective single-center study on a recent allo-HCT cohort over 3 years in a referral academic hospital for hematological malignancies. Primary objective was to determine BKHC incidence using competitive risk analysis. Secondary objectives were the identification of HC risk factors using Fine and Gray models and the evaluation of mortality. Among 409 allo-HCT recipients (median age 47 years), 41 developed BKHC after a median delay of 41 [32-55] days. Incidence density of BKHC was 2.4 [1.8-3.1] events per 100 days post-allo-HCT. The proportion of BKHC after adjustment for time-dependent competing risk was 9.5 [9.5-9.6]% at 100 days. BK viremia was detected in 63 versus 20% in tested patients with and without BKHC, respectively. After adjustment for confounders, myeloablative conditioning regimen with and without cyclophosphamide and CMV seropositivity were independently associated with BKHC. Post-transplantation cyclophosphamide was not associated with BKHC. BKHC resolved in 90% of the patients. No difference in mortality was found between patients with or without BKHC. In parallel to the recent evolution of allo-HCT protocols, BKHC remains a frequent complication following allo-HCT.

Risk factors associated with hemorrhagic cystitis after allogeneic hematopoietic stem cell transplantation

Hemorrhagic cystitis (HC) is a common complication of allogeneic hematopoietic stem cell transplantation (HSCT). The incidence is about 7% to 68%, and some patients have to suffer a long period of frequent, urgent, and painful urination, which brings great pain. This study aimed to analyze risk factors of HC and its effect on patient survival. We collected the medical records of 859 patients who underwent HSCT at our hospital between August 2016 and August 2020. Patients with and without HC were matched using propensity score matching at a 1:1 ratio based on sex, age, and diagnosis, and logistic regression analyses were used to identify factors associated with HC. We used Kaplan–Meier curves to analyze the survival rates of patients in the HC and non-HC groups. We also analyzed the relationship between BK viral load and the occurrence of HC using receiver operating characteristic curve (ROC) analysis. After propensity score matching, there were 131 patients each in the HC and non-HC groups. In the HC group, 89 patients (67.9%) had mild HC (stage II°) and 43 (32.1%) had severe HC (stage III–IV). The median interval between stem cell transplantation and HC development was 31 (3–244) days. Univariate analysis indicated that donor age, hematopoietic stem cell source, HLA, acute graft-versus-host disease, busulfan, anti-thymocyte globulin (ATG), total body irradiation, cytomegalovirus (CMV) (urine), and BK polyomavirus (BKV) (urine) were significantly associated with HC. ATG, CMV (urine), and BKV (urine) were independent risk factors for HC based on the multivariate analysis. The Kaplan–Meier survival analysis showed no significant difference between the HC and non-HC groups (P = .14). The 1- and 2-year survival rates in the HC group were 78.4% and 69.6%, respectively, and the corresponding rates in the non-HC group were 84.4% and 80.7%, respectively. ROC analysis indicated that a urine BKV load of 1 × 10⁷ copies/mL was able to stratify the risk of HC. In conclusion, when the BKV load is >1 × 10⁷, we need to be aware of the potential for the development of HC.

Kidney Disease Following Hematopoietic Stem Cell Transplantation

Hematopoietic stem cell transplantation (SCT) provides a curative option for the treatment of several malignancies. Its growing use is associated with an increased burden of kidney disease. Acute kidney injury is usually seen within the first 100 days of transplantation and has an incidence ranging between 12 and 73%, with the highest rate in myeloablative allogeneic SCT. A large subset of patients after SCT develop chronic kidney disease. They can be broadly classified into thrombotic microangiopathy, nephrotic syndrome, and calcineurin toxicity. Dialysis requirement after SCT is associated with mortality exceeding 80%. Given the higher morbidity and mortality related to development kidney disease, nephrologists need to be aware of the various causes and best treatment options.

BKV Related Hemorrhagic Cystitis-An Insight into Risk Factors and Later Complications-An Analysis on Behalf of Polish Adult Leukemia Group

Simple Summary

Despite noticeable progress in allogeneic hematopoietic stem cell transplantation, potential viral reactivations are still one of the most challenging complications. The aim of our study was to identify predictive and risk factors associated with the occurrence of the BK virus related hemorrhagic cystitis following hematopoietic stem cell transplantation. Furthermore, we investigated the impact of various factors on the clinical course of patients after hematopoietic stem cell transplantation. We confirmed that >0.75 × 10³ BK virus copies/mL in serum at day +21 after allogeneic hematopoietic stem cell transplantation has a strong predictive ability for hemorrhagic cystitis. Thus, we believe that our findings could be helpful in establishing the predictive validity of the BK viral load measurement in polyomavirus BK-associated hemorrhagic cystitis and survival.

Abstract

BK virus reactivation increases the likelihood of hemorrhagic cystitis (HC) after allogeneic hematopoietic stem cell transplant (HCT). In this study, we aimed to identify predictive and risk factors associated with the increased occurrence of this condition following HCT. On a group of 124 patients aged ≤71 years old (median 40 years) who underwent HCT, we analyzed sex, age, time from diagnosis to transplantation, type of conditioning, donor’s relationship, age, and sex, the impact of immunosuppression with different drugs, and acute and chronic GVHD, BK viremia and viruria as potential factors increasing the risk of BK-related HC after HCT. HC occurred among 24 patients (24/124; 29.2%). A significant correlation was observed between HC incidences after HCT, BK viremia and viruria, and acute GVHD occurrence. Furthermore, the level of BKV DNA in serum at day +21 (>0.75 × 10³) significantly impacted the patients’ survival time. According to our results, the likelihood ratio of BKV-DNA on day +21 in serum is 6.25, indicating that this diagnostic test has the potential to be utilized in a clinical setting. These findings may be used as a voice in the discussion on implementing an optimal preemptive treatment in BKV reactivation after allogeneic HCT.

Hemorrhagic cystitis in allogeneic stem cell transplantation: a role for age and prostatic hyperplasia

PURPOSE

Hemorrhagic cystitis (HC) is a frequent complication of allogeneic hematopoietic stem-cell transplantation (HSCT). HC worsens transplant outcomes and patient wellbeing in terms of pain, hospitalization, and need for supportive care. A deeper understanding of the risk factors of HC may lead to more intensive prevention in high-risk patients.

METHODS

In this report, we analyzed 237 consecutive patients who received HSCT with the aim of identifying possible risk factors for HC and their consequences, with a particular focus on transplant- and gender-related risk factors.

RESULTS

HC occurred in 17% of patients, with a higher incidence in males (21% vs 11%, p = 0.03). Risk factors identified for HC included age over 55 years, male recipient, HLA mismatch, reduced intensity conditioning, and cyclophosphamide-based graft-versus-host disease (GVHD) prophylaxis. Increased HC was seen in patients with grade II-IV acute GVHD and detectable BKV and JCV viruria. In a multivariate model, increased age remained significant (p = 0.013). Patients with HC had longer hospitalizations and increased non-relapse mortality (NRM). Among male recipients, independent risk factors for HC included age (p = 0.016) and prostate volume (p = 0.016). Prostatic hyperplasia (volume more than 40 cm³) occurred in 33% of male patients, of which 32% developed HC (compared with 16% of patients without prostatic hyperplasia; p = 0.032).

CONCLUSIONS

Age is the most important risk factor for HC. Additional potential risk factors include cyclophosphamide-based GVHD prophylaxis and HLA mismatch. Among male recipients, prostatic hyperplasia is an additional independent risk factor. As HC is common and associated with prolonged hospitalization, more intensive prophylactic strategies should be considered in high-risk patients.

BK polyomavirus hemorrhagic cystitis in hematopoietic cell transplant recipients

Introduction:

BK polyomavirus-associated hemorrhagic cystitis (BKPyV-HC) is a well-recognized infective complication of hematopoietic cell transplant (HCT) with increased organ dysfunction and mortality. This study was performed to describe the local incidence, risk factors, and outcomes of BKPyV infection.

Methods:

This retrospective case–control study was conducted between 2007 and 2016 from a tertiary hospital in South India. We identified HCT recipients diagnosed with BKPyV-HC and compared them with recipients over the same period who did not develop BK virus infection matched for age, sex, diagnosis, and donor type. We collected data from central electronic medical records and databases maintained in the departments of hematology and virology.

Results:

Over the study period, 1276 transplants were performed, of which 262 patients (20.5%) developed HC and 105 (8.2%) were BKPyV-positive. Grade 3 HC was most commonly (57.1%) seen, and the median time to develop BKPyV-HC was 35 (range 0–858) days. Survival was significantly lower in the cases (42.9% vs. 61%, P < 0.05). On univariate analysis, the protective effect of nonmyeloablative conditioning (P = 0.04), residual disease at the time of transplant in malignant conditions (P = 0.001), lower CD34 dose (P = 0.006), presence of acute graft versus host disease (GVHD, P < 0.001), reactivation of cytomegalovirus infection (P < 0.001), and presence of bacterial urinary tract infection (UTI) (P < 0.001) were significant factors. Multivariate logistic regression confirmed the presence of acute GVHD (P = 0.041), bacterial UTI (P < 0.001), and residual disease (P = 0.009) at HCT as significant risk factors for BKPyV-HC.

Conclusions:

Our study affirms the homogeneity of BKPyV-HC disease in low- and middle-income HCT settings with prior reports and the need for therapeutic strategies to reduce its resultant mortality.

Beyond antivirals: virus-specific T-cell immunotherapy for BK virus haemorrhagic cystitis and JC virus progressive multifocal leukoencephalopathy

PURPOSE OF REVIEW

The clinical manifestations of the polyomaviruses BK and JC in immunocompromised patients include BK virus (BKV) induced haemorrhagic cystitis and nephropathy, and JC virus (JCV) associated progressive multifocal leukoencephalopathy (PML) and are typically a consequence of impaired adaptive immunity in the host. To date, little clinical success has been achieved with antiviral agents or other drug therapies to treat these conditions. Here we review the methods and outcomes of the most recent clinical studies utilising adoptive immunotherapy with BK and/or JC virus-specific T-cells (VST) as either prophylaxis or treatment alternatives.

RECENT FINDINGS

In the last 12-18 months, several clinical trials have been published in the post-haemopoietic stem cell transplant (HSCT) setting showing good clinical success with the use of VST for treatment of BK viremia ± haemorrhagic cystitis. Between 82 and 100% clinical response has been observed in haemorrhagic cystitis using either third-party or donor-derived VST. The therapy was well tolerated with few cases of graft versus host disease in HSCT recipients, but immune mediated renal allograft loss was observed in one renal transplant recipient. Studies using BKV/JCV VST to treat PML are hindered by few patients who are sufficiently stable to receive VST. In a condition that otherwise carries such poor prognosis, VST were associated with clearance of JC virus, clinical and radiological improvement in some patients. Immune reconstitution inflammatory syndrome was a noted adverse event.

SUMMARY

Restoration of BK and JC virus immunity using VST immunotherapy has shown good clinical outcomes in BKV associated infections. Further evaluation with the administration of VST earlier in the course of disease is warranted for the treatment of BKV associated nephropathy in renal allograft and in JCV PML. In both indications, larger cohorts and standardisation of dosing and outcome measures would be of benefit.

A cluster of BK polyomavirus-associated hemorrhagic cystitis after allogeneic hematopoietic stem cell transplantation

BACKGROUND

BK polyomavirus (BKV) can cause hemorrhagic cystitis (HC) in immunocompromised patients after hematopoietic stem cell transplantation (HSCT). It remains unclear whether nosocomial BKV infections occur. During a 9-month period, an increase in BKV-associated HC (BKV-HC) cases was observed at our institution.

AIM

The BKV-HC cluster population was compared with populations of HSCT patients from before and after the BKV-HC cluster to evaluate whether nosocomial BKV transmission had occurred.

METHODS

A retrospective analysis was carried out to assess the risk of patients developing BKV-HC after HSCT. The background data of the cluster patients were compared with those of the patients who underwent HSCT before or after the cluster, and the collected BKV isolates were serotyped.

RESULTS

BKV-HC involving grade ≥2 hematuria occurred in six of 15 HSCT recipients during a 9-month period. The incidence of BKV-HC was significantly higher in this period than in the other periods (p = 0.0014). There were no significant differences in the patients' background data between the cluster and non-cluster periods, including in terms of risk factors for BKV-HC. Serotype analyses of BKV revealed that the BKV detected in the urine samples from four of the six BKV-HC patients belonged to subtype Ic. The gene sequences of these four BKV exhibited >99.5% homology.

CONCLUSION

Our study suggests that nosocomial BKV infections may occur after HSCT. Although many cases of BKV-HC are caused by the reactivation of a latent virus, it is necessary to employ appropriate hygiene measures when cases of BKV-HC occur.

Evaluation and Management of Genitourinary Emergencies in Patients with Cancer

Background

Genitourinary emergencies in cancer patients are common. Most cancer treatments are administered in the outpatient setting, and patients with complications often visit the emergency department. However, there is no recent emergency medicine literature review focusing on genitourinary emergencies in the oncologic population. Objective of the review. To increase awareness of common genitourinary emergencies in patients with cancer and enable the prompt recognition and appropriate management of these conditions. Discussion. Genitourinary emergencies in patients with cancer require a multidisciplinary approach to treatment. The most common genitourinary emergencies in patients with cancer are related to infection, obstructive uropathy, hemorrhagic cystitis, and complications associated with urinary diversions. The treatment approach in patients with infections, including viral infections, is similar to those without cancer. Understanding the changes in the anatomy of patients with urinary diversions or fistulas can help with the management of genitourinary emergencies.

Conclusions

Familiarization with the uniqueness of genitourinary emergencies in patients with cancer is important for emergency physicians.

Use of high-dose mesna and hyperhydration leads to lower incidence of hemorrhagic cystitis after posttransplant cyclophosphamide-based allogeneic transplantation

Currently, there is no consensus on best practices to prevent hemorrhagic cystitis (HC) in patients receiving posttransplant cyclophosphamide (PTCy). We retrospectively reviewed 194 patients undergoing their first hematopoietic cell transplant (HCT) who received PTCy from 2014 to 2018 to describe the incidence and severity of HC, identify potential risk factors, and impact of HC on HCT outcomes. Standard HC prophylaxis was hyperhydration with forced diuresis and mesna at 320% the daily dose of PTCy. Incidence of HC was 31.4% at day +100 of HCT. Median onset of HC was 12 days with 11.5% grade 3 HC and no Grade 4 HC. Patients with chemical HC experienced earlier onset (7 days vs. 34 days, p < 0.001) with a shorter median resolution time (5 days vs. 14 days, p = 0.001) when compared to BK-associated HC. In multivariate analysis, age above 60 years (HR 4.16, p = 0.006) and myeloablative conditioning (HR 2.44, p = 0.054) were associated with higher risk for HC, but overall, HC did not affect nonrelapse mortality or overall survival. In conclusion, hyperhydration with forced diuresis combined with aggressive mesna dosing is an effective strategy in preventing severe PTCy-associated HC, subsequently preventing any negative impact on transplant outcome.

Economic and Clinical Burden of Virus-Associated Hemorrhagic Cystitis in Patients Following Allogeneic Hematopoietic Stem Cell Transplantation in the United States

Hemorrhagic cystitis (HC) caused by viral infections such as BK virus, cytomegalovirus, and/or adenovirus after allogeneic hematopoietic stem cell transplantation (allo-HCT) causes morbidity and mortality, affects quality of life, and poses a substantial burden to the health care system. At present, HC management is purely supportive, as there are no approved or recommended antivirals for virus-associated HC. The objective of this retrospective observational study was to compare the economic burden, health resource utilization (HRU), and clinical outcomes among allo-HCT recipients with virus-associated HC to those without virus-associated HC using a large US claims database. Claims data obtained from the Decision Resources Group Real-World Evidence Data Repository were used to identify patients with first (index) allo-HCT procedure from January 1, 2012, through December 31, 2017. Outcomes were examined 1 year after allo-HCT and included total health care reimbursements, HRU, and clinical outcomes for allo-HCT patients with virus-associated HC versus those without. Further, a generalized linear model was used to determine adjusted reimbursements stratified by the presence or absence of any acute or chronic graft-versus-host disease (GVHD) after adjusting for age, health plan, underlying disease, stem cell source, number of comorbidities, baseline reimbursements, and follow-up time. Of 13,363 allo-HCT recipients, 759 (5.7%) patients met the prespecified criteria for virus-associated HC. Total unadjusted mean reimbursement was $632,870 for patients with virus-associated HC and $340,469 for patients without virus-associated HC. In a multivariable model, after adjusting for confounders, the adjusted reimbursements were significantly higher for virus-associated HC patients with and without GVHD compared to patients without virus-associated HC (P < .0001). Patients with virus-associated HC stayed 7.9 additional days in the hospital (P < .0001) and 6.1 additional days (P = .0009) in the intensive care unit (ICU) for the index hospitalization, as compared to patients without virus-associated HC. The hospital readmission rate was higher for allo-HCT patients with versus without virus-associated HC (P < .0001), resulting in 12.9 more days in the hospital (P < .0001) and 7.3 more days in the ICU (P < .0001) after the index hospitalization. Among patients with GVHD, those with virus-associated HC had significantly higher all-cause mortality as compared to those without virus-associated HC (23.2% versus 18.4%; P = .0035). In an adjusted analysis, patients with virus-associated HC had a significantly higher risk of mortality, regardless of the presence of GVHD. When stratified by GVHD, there were no significant differences in the baseline risk for renal impairment; virus-associated HC was associated with increased risk for renal impairment in the follow-up period in patients with or without GVHD (P < .0001 for both). After allo-HCT, patients with virus-associated HC have significantly higher health care reimbursements and HRU, with worse clinical outcomes, including renal impairment, irrespective of the presence of GVHD and significantly higher all-cause mortality in the presence of GVHD. Our results highlight the unmet clinical need for effective strategies to prevent and treat virus-associated HC in HCT recipients that may also reduce costs among these patients.

BK virus-specific T-cell immune reconstitution after allogeneic hematopoietic cell transplantation

Clinical disease caused by BK virus reactivation is a frequent complication of allogeneic hematopoietic cell transplantation (HCT). Because of the lack of effective antiviral agents, BK virus-specific T cells are emerging as a potential therapy for BK virus disease, but the immune response to BK virus after allogeneic HCT has not been well characterized. Our study describes reconstitution of BK virus-specific T-cell immunity in 77 adult patients after HCT. All patients had urinary symptoms, and urine was tested for BK virus replication; 33 patients were positive for BK virus (cases), and 44 were negative (controls). In BK virus cases, the median time to first positive test was 75 days (range, 2-511). BK virus cases had lower CD4 T-cell counts 3 to 9 months after transplant, but CD8 T-cell counts were similar in cases and controls. BK virus-specific T cells were identified by cytokine flow cytometry in cryopreserved samples collected prospectively. BK virus-specific CD4 T cells producing T helper 1 (Th1) cytokines recovered quickly after HCT. BK virus-specific T cells were detected more frequently in patients with BK virus reactivation at most time points, and CD4 T cells producing Th1 cytokines were more frequent than BK virus-specific cytolytic CD8 T cells. Early detection of interferon-γ+ and cytolytic BK virus-specific CD4 T cells was associated with lower rates of hematuria among cases. Overall, our study describes recovery of BK virus-specific T cells after HCT and the distinct roles for BK virus-specific T cells in the development and resolution of clinical symptoms.

Virus-specific T-cell therapy to treat BK polyomavirus infection in bone marrow and solid organ transplant recipients

BK polyomavirus (BKPyV) infection is a major complication of hematopoietic stem cell transplant (HSCT) and solid organ transplant (SOT). Treatment options are limited, poorly effective, and have significant toxicities. Cellular therapy using T cells directed against BKPyV is an emerging therapy, and we report efficacy in controlling BKPyV-associated disease in highly immunocompromised patients. Virus-specific T cells (VSTs) against BKPyV were manufactured using either blood from the patient's stem cell donor (donor-derived VSTs) or from unrelated donors (third-party VSTs). VSTs were used to treat BKPyV in 38 HSCT recipients and 3 SOT recipients between June 2017 and December 2019. Overall response rate was 86% in patients treated for BK viremia, 100% in patients treated for hemorrhagic cystitis, and 87% in patients treated for both BK viremia and hemorrhagic cystitis. No infusional toxicity, de novo graft-versus-host disease, or rejection of the organ occurred attributable to the VST infusion. BKPyV-specific immune responses were demonstrated by interferon-γ production by peripheral blood mononuclear cells postinfusion in response to BKPyV antigens. VSTs are a safe and potentially effective strategy to treat BKPyV and associated symptoms in recipients of HSCT and SOT. Cellular therapy should be considered for all patients with BKPyV and underlying immune suppression at risk of complications. This trial was registered at www.clinicaltrials.gov as #NCT02532452.

Antivirals against human polyomaviruses: Leaving no stone unturned

Human polyomaviruses (HPyVs) encompass more than 10 species infecting 30%-90% of the human population without significant illness. Proven HPyV diseases with documented histopathology affect primarily immunocompromised hosts with manifestations in brain, skin and renourinary tract such as polyomavirus-associated nephropathy (PyVAN), polyomavirus-associated haemorrhagic cystitis (PyVHC), polyomavirus-associated urothelial cancer (PyVUC), progressive multifocal leukoencephalopathy (PML), Merkel cell carcinoma (MCC), Trichodysplasia spinulosa (TS) and pruritic hyperproliferative keratinopathy. Although virus-specific immune control is the eventual goal of therapy and lasting cure, antiviral treatments are urgently needed in order to reduce or prevent HPyV diseases and thereby bridging the time needed to establish virus-specific immunity. However, the small dsDNA genome of only 5 kb of the non-enveloped HPyVs only encodes 5-7 viral proteins. Thus, HPyV replication relies heavily on host cell factors, thereby limiting both, number and type of specific virus-encoded antiviral targets. Lack of cost-effective high-throughput screening systems and relevant small animal models complicates the preclinical development. Current clinical studies are limited by small case numbers, poorly efficacious compounds and absence of proper randomized trial design. Here, we review preclinical and clinical studies that evaluated small molecules with presumed antiviral activity against HPyVs and provide an outlook regarding potential new antiviral strategies.

Risk factors of BK viral hemorrhagic cystitis in allogenic hematopoietic stem cell transplantation

Reactivation of BK virus (BKV) can occur during intensive immunosuppression such as in allogenic hematopoietic stem cell transplant (AHSCT) recipients for whom a systematic PCR urine test for BKV will be positive in 50% to 100% of patients. Only 5% to 40% will develop BKV hemorrhagic cystitis (HC). Thus, BKV PCR testing is useful to confirm a diagnosis of BKV-HC but not to predict its occurrence. The aim of this retrospective study was to ascertain the risk factors of developing BKV HC, mostly in patients receiving posttransplant cyclophosphamide. The study looked at data from Grenoble Alpes University Hospital included in the national retrospective register ProMISe, administered by the "Société Francophone de Greffe de Moelle et de Thérapie Cellulaire". Urine BKV PCR was performed when patients presented grade ≥ 2 hematuria with clinical symptoms of cystitis. BKV-HC was defined as an association of clinical symptoms of cystitis, grade ≥ 2 hematuria and BKV viruria > 7 log₁₀ copies/ml. From January 2014 to January 2018, 168 AHSCTs were considered for analysis, of which 43 (25.6%) developed BKV-HC and 44.9% of the subgroup that received posttransplant cyclophosphamide. After logistic regression, the risk factors associated with BKV-HC were reduced to posttransplantation exposure to cyclophosphamide (OR 4.25, [1.66; 10.87], P = .02), age < 40 y (OR 3.85 [1.51; 9.80], P = .005) and corticosteroid therapy (OR 3.86, [1.59; 9.36], P = .003). Exposure to cyclophosphamide, younger age (<40) and corticosteroid therapy are potential risk factors for BKV-HC.

Evaluation of a Next-Generation Sequencing Metagenomics Assay to Detect and Quantify DNA Viruses in Plasma from Transplant Recipients

Viral infections are major causes of morbidity and mortality in solid-organ and hematopoietic stem cell transplant recipients. This study evaluated the performance of the Galileo Pathogen Solution metagenomics Next-Generation sequencing assay to detect and quantify 11 DNA viruses (cytomegalovirus, Epstein-Barr virus, BK virus, human adenovirus, JC virus, herpes simplex virus 1 and 2, varicella zoster virus, human herpesvirus 6A and 6B, and parvovirus B19) and to qualitatively detect torque teno virus. DNA extracted from 47 plasma samples of viremic transplant recipients were subjected to DNA library preparation with pathogen enrichment/human background depletion, sequencing, and automated data analysis. The viral loads were determined with the Galileo assay using a standard curve generated from a calibration panel. All of the samples tested had a 100% agreement with the real-time quantitative PCR (qPCR) assays in detecting the primary virus targets and the majority of the quantified samples had a viral load difference within 0.46 log₁₀ IU/mL or copies/mL. The mean difference for cytomegalovirus between the Galileo and qPCR assays was 0.21 log₁₀ IU/mL (SD, ±0.43 log₁₀ IU/mL). The mean difference for BK virus between the Galileo and qPCR assays was 0.17 log₁₀ cp/mL (SD, ±0.67 log₁₀ cp/mL). Additionally, 75 co-infections were detected in 31 samples by the Galileo assay. The study findings show that the Galileo assay can simultaneously detect and quantify multiple viruses in transplant recipients with results that are comparable with standard-of-care qPCR assays.

Management of BK virus-associated haemorrhagic cystitis in allogeneic stem cell transplant recipients

BK virus (BKV)-related haemorrhagic cystitis (HC) is an important cause of morbidity following allogeneic haematopoietic stem cell transplantation (HSCT). The various risk factors include high-level BKV viruria and/or viremia, myeloablative conditioning, acute graft versus host disease (GVHD), cytomegalovirus viremia, and unrelated or HLA-mismatched donor. The presence of high plasma BK viral load and cytopenias have been implicated as important predictors for protracted disease course. These patients frequently require hospitalisation which may extend for several weeks. Supportive measures in the form of analgesics, intravenous hydration, bladder irrigation, and transfusion support remain the mainstay of management. Various drugs have been used with limited success in this setting. These include antiviral drugs, fluoroquinolones, leflunomide, growth factors, clotting factors, estrogens, and prostaglandins. The role of adoptive cellular immunotherapy has also been explored but lacks clinical validation. The strategies aimed at expediting urothelial repair like hyperbaric oxygen therapy (HBOT), intravesical fibrin glue and platelet-rich plasma (PRP) are emerging. Some patients with severe disease do require surgical intervention to relieve urinary obstruction. The frequent co-occurrence of acute GVHD and CMV disease further complicates the management in such patients. There is an unmet need for effective and evidence-based options for the prevention and management of this disease. Due to lack of robust data supported by randomised trials, the acceptability of the available guidelines to simplify the treatment is expected to be low. Despite the availability of various treatment options, the management of BKV-related HC in day-to-day practice continues to be a challenge. The aim of this article is to put forward an up-to-date review of the preventive and therapeutic strategies for BKV-related HC.

Variations in BK Polyomavirus Immunodominant Large Tumor Antigen-Specific 9mer CD8 T-Cell Epitopes Predict Altered HLA-Presentation and Immune Failure

Failing BK polyomavirus (BKPyV)-specific immune control is underlying onset and duration of BKPyV-replication and disease. We focused on BKPyV-specific CD8 T-cells as key effectors and characterized immunodominant 9mer epitopes in the viral large tumor-antigen (LTag). We investigated the variation of LTag-epitopes and their predicted effects on HLA-class 1 binding and T-cell activation. Available BKPyV sequences in the NCBI-nucleotide (N = 3263), and the NCBI protein database (N = 4189) were extracted (1368 sequences) and analyzed for non-synonymous aa-exchanges in LTag. Variant 9mer-epitopes were assessed for predicted changes in HLA-A and HLA-B-binding compared to immunodominant 9mer reference. We identified 159 non-synonymous aa-exchanges in immunodominant LTag-9mer T-cell epitopes reflecting different BKPyV-genotypes as well as genotype-independent variants altering HLA-A/HLA-B-binding scores. Decreased binding scores for HLA-A/HLA-B were found in 27/159 (17%). This included the immunodominant LPLMRKAYL affecting HLA-B*07:02-, HLA-B*08:01- and HLA-B*51:01-presentation. In two healthy BKPyV-seropositive HLA-B*07:02 blood donors, variant LSLMRKAYL showed reduced CD8 T-cell responses compared to LPLMRKAYL. Thus, despite LTag being highly conserved, aa-exchanges occur in immunodominant CD8 T-cell epitopes of BKPyV-genotypes as well as of genotypes -independent variants, which may contribute to genotype-dependent and genotype-independent failure of cellular immune control over BKPyV-replication. The data warrant epidemiological and immunological investigations in carefully designed clinical studies.

COVID-19 inflammation results in urine cytokine elevation and causes COVID-19 associated cystitis (CAC)

Coronavirus disease 2019 (COVID-19) causes a wide range of symptoms, including several unexpected symptoms such as loss of taste, skin changes, and eye problems. We recently observed patients with documented COVID-19 develop de novo severe genitourinary symptoms, most notably urinary frequency of ≥ 13 episodes/24 h and nocturia ≥ 4 episodes/night. We call these associated urinary symptoms COVID-19 associate cystitis (CAC). COVID-19 severity is associated with inflammation. We collected urine samples from COVID-19 patients, including patients with CAC, and found elevation of proinflammatory cytokines also in the urine. It has been previously shown that patients with urinary incontinence and ulcerative interstitial cystitis/bladder pain syndrome have elevated urinary inflammatory cytokines compared to normal controls. We therefore hypothesize that CAC, with presentation of de novo severe urinary symptoms, can occur in COVID-19 and is caused by increased inflammatory cytokines that are released into the urine and/or expressed in the bladder.

The most important implications of our hypothesis are: 1) Physician caring for COVID-19 patients should be aware of COVID-19 associate cystitis (CAC); 2) De novo urinary symptoms should be included in the symptom complex associated with COVID-19; and 3) COVID-19 inflammation may result in bladder dysfunction.

Harnessing T Cells to Control Infections After Allogeneic Hematopoietic Stem Cell Transplantation

Dramatic progress in the outcome of allogeneic hematopoietic stem cell transplantation (allo-HSCT) from alternative sources in pediatric patients has been registered over the past decade, providing a chance to cure children and adolescents in need of a transplant. Despite these advances, transplant-related mortality due to infectious complications remains a major problem, principally reflecting the inability of the depressed host immune system to limit infection replication and dissemination. In addition, development of multiple infections, a common occurrence after high-risk allo-HSCT, has important implications for overall survival. Prophylactic and preemptive pharmacotherapy is limited by toxicity and, to some extent, by lack of efficacy in breakthrough infections. T-cell reconstitution is a key requirement for effective infection control after HSCT. Consequently, T-cell immunotherapeutic strategies to boost pathogen-specific immunity may complement or represent an alternative to drug treatments. Pioneering proof of principle studies demonstrated that the administration of donor-derived T cells directed to human herpesviruses, on the basis of viral DNA monitoring, could effectively restore specific immunity and confer protection against viral infections. Since then, the field has evolved with implementation of techniques able to hasten production, allow for selection of specific cell subsets, and target multiple pathogens. This review provides a brief overview of current cellular therapeutic strategies to prevent or treat pathogen-related complications after HSCT, research carried out to increase efficacy and safety, including T-cell production for treatment of infections in patients with virus-naïve donors, results from clinical trials, and future developments to widen adoptive T-cell therapy access in the HSCT setting.

Treatment protocols for BK virus associated hemorrhagic cystitis after hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation (HSCT) represents a vital curative choice for many disease. However its outcome can be hampered by a variety of transplant associated complications. Hemorrhagic cystitis (HC) considered as one of the major difficulties after HSCT. HC symptoms comprise hematuria, dysuria, burning during urination, urinary frequency, urgency and incontinency, abdominal or suprapubic pain, urinary obstruction, and renal or bladder damage. There are a lot of causes for HC development. BK virus reactivation is one of the major causes of HC after HSCT. There is still no standard and approved treatment protocol for BK virus associated HC (BKV-HC). Treatment of HC is according to the local standard operating procedures, depending on the cause and severity. In this study we will review the current treatments available for this disease. We have divided the therapeutic procedures into 5 categories including conservative therapy, complimentary options, surgical procedures, pharmacological treatments and adoptive cell therapy. We believe that comparing the advantages and disadvantages of different therapies make it easier to choose the best treatment protocol. In addition, we had a greater focus on adoptive cell therapy, because it is a relatively new introduced method and might be a logical alternative to conventional treatments for refractory patients. In total, no definitive recommendation is possible for current available treatments because these procedures have only been utilized sporadically in a limit number of patients. Furthermore, a number of treatment options are only experimental and definitely need more effort.

Development and validation of a risk assessment tool for BKPyV Replication in allogeneic stem cell transplant recipients

BACKGROUND

BK polymavirus (BKPyV), a member of the family Polyomaviridae, is associated with increased morbidity and mortality in allogeneic stem cell transplant recipients.

METHODS

In our previous retrospective study of 2477 stem cell transplant patients, BKPyV replication independently predicted chronic kidney disease and poor survival. In this study, using the same cohort, we derived and validated a risk grading system to identify patients at risk of BKPyV replication after transplantation in a user-friendly modality. We used 3 baseline variables (conditioning regimen, HLA match status, and underlying cancer diagnosis) that significantly predicted BKPyV replication in our initial study in a subdistribution hazard model with death as a competing risk. We also developed a nomogram of the hazard model as a visual aid. The AUC of the ROC of the risk-score-only model was 0.65. We further stratified the patients on the basis of risk score into low-, moderate-, and high-risk groups.

RESULTS

The total risk score was significantly associated with BKPyV replication (P < .0001). At 30 days after transplantation, the low-risk (score ≤ 0) patients had a 9% chance of developing symptomatic BKPyV replication, while the high-risk (score ≥ 8) of the population had 56% of developing BKPyV replication. We validated the risk score using a separate cohort of 1478 patients. The AUC of the ROC of the risk-score-only model was 0.59. Both the total risk score and 3-level risk variable were significantly associated with BKPyV replication in this cohort (P < .0001).

CONCLUSIONS

This grading system for the risk of symptomatic BKPyV replication may help in early monitoring and intervention to prevent BKPyV-associated morbidity, mortality, and kidney function decline.

BK virus infection in allogeneic hematopoietic cell transplantation: An update on pathogenesis, immune responses, diagnosis and treatments

In hematopoietic cell transplantation (HCT) patients, BK polyomavirus (BKPyV) infection results in significant morbidity mainly due to hemorrhagic cystitis (HC). Despite increased knowledge acquired over recent decades, no treatment has shown effectiveness in the management of organ damage in HCT allografts. This review summarizes the current knowledge on BKPyV, from the virus constitution to the pathophysiology and immune-related mechanisms. We next focus on BKPyV-induced HC in HCT to discuss the benefit of monitoring BKPyV viruria and viremia in the management of patients. At last, we review currently used therapeutics, along with future promising therapies to propose clinical and practical guidelines and further interesting research areas.