Single-cell lineage tracing approaches to track kidney cell development and maintenance.

The kidney is a complex organ consisting of various cell types. Previous studies have aimed to elucidate the cellular relationships among these cell types in developing and mature kidneys using Cre-loxP-based lineage tracing. However, this methodology falls short of fully capturing the heterogeneous nature of the kidney, making it less than ideal for comprehensively tracing cellular progression during kidney development and maintenance. Recent technological advancements in single-cell genomics have revolutionized lineage tracing methods. Single-cell lineage tracing enables the simultaneous tracing of multiple cell types within complex tissues and their transcriptomic profiles, thereby allowing the reconstruction of their lineage tree with cell state information. Although single-cell lineage tracing has been successfully applied to investigate cellular hierarchies in various organs and tissues, its application in kidney research is currently lacking. This review comprehensively consolidates the single-cell lineage tracing methods, divided into 4 categories (clustered regularly interspaced short palindromic repeat [CRISPR]/CRISPR-associated protein 9 [Cas9]-based, transposon-based, Polylox-based, and native barcoding methods), and outlines their technical advantages and disadvantages. Furthermore, we propose potential future research topics in kidney research that could benefit from single-cell lineage tracing and suggest suitable technical strategies to apply to these topics.

Clinical significance of urinary inflammatory biomarkers in patients with IgA nephropathy.

BACKGROUND: IgA nephropathy (IgAN) is the most common type of primary glomerulonephritis, although the definitive markers are unknown. We aimed to investigate the clinical significance of urinary cytokines in patients with IgAN. METHODS: From 2009 to 2018, the patients were divided into three groups: IgAN (n = 191), disease control (n = 53), and normal control (n = 76). We used a multiplex enzyme-linked immunosorbent assay to measure 16 selected urinary inflammatory cytokines, evaluated the correlation between clinical and pathological features following regression analysis on progression. RESULTS: The IgAN group exhibited significantly different levels of urinary cytokines compared to the normal control and disease control groups. Urinary levels of B-cell-activating factor, vascular endothelial growth factor receptor-2, monocyte chemoattractant protein-1, C-X-C motif chemokine 10, C-X-C motif ligand 16, epidermal growth factor (EGF), endocan, endostatin, growth/differentiation factor-15 (GDF-15), interleukin-6 (IL-6), mannose-binding lectin, transferrin receptor, and kidney injury molecule-1 were significantly correlated with both the estimated glomerular filtration rate and urine protein-creatinine ratio. In a multivariate Cox regression analysis, urinary EGF (hazard ratio [HR] 0.40, 95% confidence interval [CI] 0.17-0.95, P = 0.04), GDF-15 (HR 2.45, 95% CI 1.01-5.94, P = 0.048), and IL-6 (HR 3.02, 95% CI 1.05-8.64, P = 0.04) were associated with progression in IgAN. CONCLUSIONS: Urinary inflammatory biomarkers may serve as alternative predictive biomarkers in patients with IgAN. Further studies are needed to elucidate the physiological mechanisms and confirm the results.

Urine Exosomal bkv-miR-B1-5p and BK Virus Nephropathy in Kidney Transplant Recipients.

BACKGROUND: Urine exosomal bkv-miR-B1-5p is associated with BK virus (BKV) nephropathy (BKVN); however, its posttransplantation changes and predictability for BKVN have not been determined in kidney transplant recipients (KTRs). METHODS: Urine exosomal bkv-miR-B1-5p and urine and plasma BKV DNA were measured at 2 weeks and 3, 6, and 12 months posttransplant in 83 KTRs stratified into biopsy-proven or presumptive BKVN, BKV viruria, and no evidence of BKV reactivation. Joint model, multivariable Cox model and receiver operating characteristic curve (ROC) were used to investigate the association of each assay with the following events: a composite of biopsy-proven or presumptive BKVN, and biopsy-proven BKVN. RESULTS: Urine exosomal bkv-miR-B1-5p and urine and plasma BKV DNA showed similar posttransplant time-course changes. Joint models incorporating serial values demonstrated significant associations of all assays with the events, and Cox analyses using single time point values at 2 weeks posttransplant showed that only urine exosomal bkv-miR-B1-5p was significantly associated with the events, although it did not outperform urine BKV DNA in ROC analyses. CONCLUSIONS: Urine exosomal bkv-miR-B1-5p was associated with BKVN as were urine and plasma BKV DNA loads on serial follow-up, and might have potential as a predictive marker for BKVN during the early posttransplant period. CLINICAL TRIALS REGISTRATION: Clinical Research Information Service (https://cris.nih.go.kr/cris/), KCT0001010.

Midbody plays an active role in fibroblast-myofibroblast transition by mediating TGF-ß signaling.

The transition of fibroblasts into myofibroblasts is a crucial step in kidney fibrosis. However, the biological processes involved in this transdifferentiation are incompletely understood. In this study, we discovered that the midbody plays a role in the fibroblast-myofibroblast transition by mediating TGF-ß/Smad signaling. Combining bulk RNA-seq, histology, and the western blot of unilateral ureteral obstruction kidneys, we demonstrated that the pathway related to microtubules is implicated in kidney fibrosis, and the blocking of microtubule dynamics by colchicine improved kidney fibrosis. Subsequently, to explore microtubule-based organelles in detail, we cultured NRK-49F (rat kidney fibroblast cell line) and HKC-8 (human proximal tubule cell line) under transforming growth factor-ß1 (TGF-ß1) stimulation, which caused deciliation in both cell lines during epithelial-mesenchymal and fibroblast-myofibroblast transition. We identified another microtubule-based organelle, the midbody, whose formation is promoted by TGF-ß1 in fibroblasts as a result of proliferation in contrast to tubular cells. Notably, TGF-ß receptors were present in the midbody of both cell lines. In TGF-ß1-treated fibroblasts, colchicine or Hedgehog pathway inhibitor 4 impaired the midbody formation, and attenuated the upregulation of canonical TGF-ß/Smad signaling and α-SMA expression. These findings offer novel insight into the midbody as an active organelle involved in fibroblast-myofibroblast transition by mediating TGF-ß/Smad signaling, which could be a potential therapeutic target.

Risk of malignancy in kidney transplant recipients: a nationwide population-based cohort study.

BACKGROUND: Post-transplant malignancy is major morbidity complicated in kidney transplantation (KT). In Korea, a few studies have investigated the sex- and age-dependent risk for post-transplant malignancy among KT recipients on a large scale. METHODS: We utilized a national health insurance database in Korea to investigate the relative risk of post-transplant malignancy in 12,634 KT recipients between 2007 and 2017. The same number of patients with acute appendicitis was included as a control group. The relative risk of malignancy was estimated using a multivariable-adjusted Cox model, and interaction analysis was performed to investigate age- and sex-predominant patterns. RESULTS: KT recipients had an overall 1.8-fold higher risk for post-transplant malignancy with an increased risk for 14 of 29 cancer types, among which Kaposi's sarcoma, non-Hodgkin's lymphoma, kidney, uterus, and bladder/urinary tract cancers were most prominent. Although the overall risk for post-transplant malignancy was similar between male and female KT recipients, head and neck cancer had a higher risk among male KT recipients, whereas non-Hodgkin's lymphoma and bladder/urinary tract cancer had a higher risk among female KT recipients. Overall, the young (< 50 years) KT recipients had a higher risk for post-transplant malignancy than older ones (≥ 50 years), whose pattern was most prominent in non-Hodgkin's lymphoma. In contrast, breast and nonmelanoma skin cancer showed a higher risk among older KT recipients. CONCLUSION: KT recipients had an increased risk for a wide range of cancer types, some of which showed differential risk patterns with age and sex. Our result suggests that focused screening for predominant post-transplant malignancies may be an effective strategy for selected KT recipients.

Urinary chemokine C-X-C motif ligand 16 and endostatin as predictors of tubulointerstitial fibrosis in patients with advanced diabetic kidney disease.

BACKGROUND: Interstitial fibrosis and tubular atrophy (IFTA) is a well-recognized risk factor for poor renal outcome in patients with diabetic kidney disease (DKD). However, a noninvasive biomarker for IFTA is currently lacking. The purpose of this study was to identify urinary markers of IFTA and to determine their clinical relevance as predictors of renal prognosis. METHODS: Seventy patients with biopsy-proven isolated DKD were enrolled in this study. We measured multiple urinary inflammatory cytokines and chemokines by multiplex enzyme-linked immunosorbent assay in these patients and evaluated their association with various pathologic features and renal outcomes. RESULTS: Patients enrolled in this study exhibited advanced DKD at the time of renal biopsy, characterized by moderate to severe renal dysfunction [mean estimated glomerular filtration rate (eGFR) 36.1 mL/min/1.73 m2] and heavy proteinuria (mean urinary protein:creatinine ratio 7.8 g/g creatinine). Clinicopathologic analysis revealed that higher IFTA scores were associated with worse baseline eGFR (P < 0.001) and poor renal outcome (P = 0.002), whereas glomerular injury scores were not. Among measured urinary inflammatory markers, C-X-C motif ligand 16 (CXCL16) and endostatin showed strong correlations with IFTA scores (P = 0.001 and P < 0.001, respectively), and patients with higher levels of urinary CXCL16 and/or endostatin experienced significantly rapid renal progression compared with other patients (P < 0.001). Finally, increased urinary CXCL16 and endostatin were independent risk factors for poor renal outcome after multivariate adjustments (95% confidence interval 1.070-3.455, P = 0.029). CONCLUSIONS: Urinary CXCL16 and endostatin could reflect the degree of IFTA and serve as biomarkers of renal outcome in patients with advanced DKD.

Associations between Cell-Free Mitochondrial DNA and Inflammation, and Their Clinical Implications for Patients on Hemodialysis: A Prospective Multicenter Cohort Study.

BACKGROUND: Cell-free mitochondrial DNA (cf-mtDNA) has recently been in the spotlight as an endogenously produced danger molecule that can potentially elicit inflammation. However, its clinical and prognostic implications are uncertain in patients undergoing hemodialysis. METHODS: We examined the association of baseline cf-mtDNA categorized as tertiles with health-related quality of life (HRQOL), inflammatory cytokines, and mortality in a multicenter prospective cohort of 334 patients on hemodialysis. To better understand cf-mtDNA-mediated inflammation, we measured cytokine production after in vitro stimulation of bone marrow-derived macrophages (BMDMs) with mtDNA. RESULTS: The higher cf-mtDNA tertile had a longer dialysis vintage, a greater comorbidity burden, and increased levels of inflammatory markers, including high-sensitivity-C-reactive protein, tumor necrosis factor-alpha, CXCL16, and osteoprotegerin. In particular, mtDNA augmented inflammatory cytokine release from BMDMs by lipopolysaccharide, the levels of which are reported to be increased in hemodialysis patients. Although the patients with higher levels of cf-mtDNA generally had lower (poorer) scores for HRQOL, cf-mtDNA was not associated with all-cause mortality in hemodialysis patients. CONCLUSION: cf-mtDNA was correlated with poor clinical status and modestly associated with impaired quality of life in patients on hemodialysis. In proinflammatory milieu in end-stage renal disease, these associations may be attributed to the boosting effects of cf-mtDNA on inflammation.

A Cell-Penetrating Peptide That Blocks Toll-Like Receptor Signaling Protects Kidneys against Ischemia-Reperfusion Injury.

Renal ischemia-reperfusion injury (IRI) is involved in the majority of clinical conditions that manifest as renal function deterioration; however, specific treatment for this type of injury is still far from clinical use. Since Toll-like receptor (TLR)-mediated signaling is a key mediator of IRI, we examined the effect of a multiple-TLR-blocking peptide named TLR-inhibitory peptide 1 (TIP1), which exerts the strongest action on TLR4, on renal IRI. We subjected C57BL/6 mice to 23 min of renal pedicle clamping preceded by intraperitoneal injection with a vehicle or TIP1. Sham control mice underwent flank incision only. Mouse kidneys were harvested after 24 h of reperfusion for histology, western blot, RT-PCR, and flow cytometry analysis. Pretreatment with TIP1 lowered the magnitude of elevated plasma creatinine levels and attenuated tubular injury. TIP1 treatment also reduced mRNA expression of inflammatory cytokines and decreased apoptotic cells and oxidative stress in post-ischemic kidneys. In kidneys pretreated with TIP1, the infiltration of macrophages and T helper 17 cells was less abundant than those in the IRI only group. These results suggest that TIP1 has a potential beneficial effect in attenuating the degree of kidney damage induced by IRI.

Uric acid and inflammation in kidney disease.

Asymptomatic hyperuricemia is frequently observed in patients with kidney disease. Although a substantial number of epidemiologic studies have suggested that an elevated uric acid level plays a causative role in the development and progression of kidney disease, whether hyperuricemia is simply a result of decreased renal excretion of uric acid or is a contributor to kidney disease remains a matter of debate. Over the last two decades, multiple experimental studies have expanded the knowledge of the biological effects of uric acid beyond its role in gout. In particular, uric acid induces immune system activation and alters the characteristics of resident kidney cells, such as tubular epithelial cells, endothelial cells, and vascular smooth muscle cells, toward a proinflammatory and profibrotic state. These findings have led to an increased awareness of uric acid as a potential and modifiable risk factor in kidney disease. Here, we discuss the effects of uric acid on the immune system and subsequently review the effects of uric acid on the kidneys mainly in the context of inflammation.

Gait speed and handgrip strength as predictors of all-cause mortality and cardiovascular events in hemodialysis patients.

BACKGROUND: Low physical performance in patients undergoing maintenance hemodialysis is associated with a high mortality rate. We investigated the clinical relevance of gait speed and handgrip strength, the two most commonly used methods of assessing physical performance. METHODS: We obtained data regarding gait speed and handgrip strength from 277 hemodialysis patients and evaluated their relationships with baseline parameters, mental health, plasma inflammatory markers, and major adverse clinical outcomes. Low physical performance was defined by the recommendations suggested by the Asian Working Group on Sarcopenia. RESULTS: The prevalence of low gait speed and handgrip strength was 28.2 and 44.8%, respectively. Old age, low serum albumin levels, high comorbidity index score, and impaired cognitive functions were associated with low physical performance. Patients with isolated low gait speed exhibited a general trend for worse quality of life than those with isolated low handgrip strength. Gait speed and handgrip strength showed very weak correlations with different determining factors (older age, the presence of diabetes, and lower serum albumin level for low gait speed, and lower body mass index and the presence of previous cardiovascular events for low handgrip strength). Patients with low gait speed and handgrip strength had elevated levels of plasma endocan and matrix metalloproteinase-7 and the highest risks for all-cause mortality and cardiovascular events among the groups (adjusted hazard ratio of 2.72, p = 0.024). Elderly patients with low gait speed and handgrip strength were at the highest risk for poor clinical outcomes. CONCLUSION: Gait speed and handgrip strength reflected distinctive aspects of patient characteristics and the use of both factors improved the prediction of adverse clinical outcomes in hemodialysis patients. Gait speed seems to be a better indicator of poor patient outcomes than is handgrip strength.

Sex-related differences in the intratubular renin-angiotensin system in two-kidney, one-clip hypertensive rats.

The intratubular renin-angiotensin system (RAS) is thought to play an essential role in hypertensive renal disease, but information regarding sex-related differences in this system is limited. The present study investigated sex differences in the intratubular RAS in two-kidney, one-clip (2K1C) rats. A 2.5-mm clip was placed on the left renal artery of Sprague-Dawley rats, and rats were euthanized 3 or 5 wk after the operation. Systolic blood pressure increased in 2K1C rats in both sexes but was significantly higher in male rats than in female rats, and an antihypertensive effect was not observed in 2K1C ovariectomized (OVX) female rats. Compared with male 2K1C rats, intratubular angiotensin-converting enzyme (ACE) and ANG II were repressed, and intratubular ACE2, angiotensin (1-7), and Mas receptor were increased in both kidneys in female 2K1C rats 5 wk after surgery. Comparison with male and female rats and intratubular mRNA levels of ACE and ANG II type 1 receptor were augmented in OVX female rats, regardless of the clipping surgery 3 wk postoperation. ANG II type 2 receptor was upregulated in female rats with or without OVX; thus, the ANG II type 1-to-type 2 receptor ratio was higher in male rats than in female rats. In conclusion, female rats were protected from hypertensive renal and cardiac injury after renal artery clipping. An increase in the intratubular nonclassic RAS [ACE2/angiotensin (1-7)/Mas receptor] and a decrease in the ANG II type 1-to-type 2 receptor ratio could limit the adverse effects of the classic RAS during renovascular hypertension in female rats, and estrogen is suggested to play a primary role in the regulation of intratubular RAS components.

Hypocomplementemic Urticarial Vasculitis Syndrome with Membranous Nephropathy: Case Report.

Urticarial vasculitis is a rare disorder that principally manifests with recurrent urticarial, sometimes hemorrhagic, skin lesions and/or angioedema. Its clinical presentation is not always limited to cutaneous lesions and it can potentially affect other organs, such as the joints, lungs, kidneys, and eyes. Systemic involvement can either be present at the onset of disease or develop over time. In cases with systemic manifestations, urticarial vasculitis is more likely to be associated with a low complement level. We present the case of a teenage boy with hypocomplementemic urticarial vasculitis syndrome (HUVS) that occurred shortly following swine-origin influenza A virus infection in 2009. Afterwards, HUVS was systemically complicated with myositis and membranous nephropathy that developed several months and about 2 years after its onset, respectively. A combination of glucocorticoid and immunosuppressive agents has been used to effectively control disease activity.

BK virus-associated nephropathy with hydronephrosis in a patient with AIDS: a case report and literature review.

BK virus is ubiquitous worldwide, with infection usually occurring in early childhood. BK virus replicates prolifically under immunosuppressive conditions, causing inflammation along the genitourinary tract and progressing clinically to hemorrhagic cystitis, ureteral stenosis, and tubulointerstitial nephritis. Most BK virusassociated nephropathy occurs in renal allograft patients after kidney transplantation, although some case reports have described BK virus-associated nephropathy in the native kidney, particularly in patients with human immunodeficiency virus infection. Here we present the case of a 49-year-old male with acquired immunodeficiency syndrome (AIDS) and renal dysfunction with hydronephrosis. The renal biopsy showed tubulointerstitial nephritis with lymphoplasmacytic infiltrates and intranuclear inclusions in the tubular epithelium, which are typical findings for BK virus-associated nephropathy. In addition, immunohistochemical staining revealed that the SV40 large T antigen exhibited a nuclear localization in tubular cells. To the best of our knowledge, this is the first case report of BK virus-associated nephropathy combined with hydronephrosis that was diagnosed by biopsy in a patient with AIDS.

High physical activity alleviates the adverse effect of higher sedentary time on the incidence of chronic kidney disease.

BACKGROUND: Low physical activity (PA) increases the prevalence of chronic kidney disease (CKD). This study aimed to investigate the effects of PA and sedentary time (ST) on the changes in renal function and the development of CKD in the middle-aged Korean population. METHODS: From the Korean Genome and Epidemiology Study Database, 7988 participants in their 40s and 60s were identified and stratified by (1) PA: high-PA (>24 MET-h/day), moderate-PA (9-24 MET-h/day) and low-PA (<9 MET-h/day); and (2) ST: high-ST (>6 h/day), moderate-ST (3-6 h/day) and low-ST (<3 h/day). Incident CKD was defined as estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m2 following the Chronic Kidney Disease Epidemiology Collaboration equation. RESULTS: The mean age of the participants was 52.0 years. The overall incidence of CKD was 16.8 per 1000 person-years over a median of 12 years. The lower the PA and the higher the ST, the lower the baseline eGFR. Relative to the high-PA, the coefficients of the annual eGFR decline were -0.12 (95% confidence interval [CI]: -0.26 to 0.001, P = 0.081) and -0.13 (95% CI: -0.27 to 0.01, P = 0.078) in the moderate- and low-PA groups, respectively. Similarly, relative to the low-ST, the coefficients of annual eGFR decline were -0.07 (59% CI: -0.19 to 0.05, P = 0.236) and -0.14 (95% CI: -0.28 to -0.01, P = 0.039) in the moderate- and high-ST groups, respectively. Incident CKD was higher with lower PA (hazard ratio: high-PA 1.00, moderate-PA 1.13 [1.00, 1.28, P = 0.056] and low-PA 1.25 [1.11, 1.24, P < 0.001]) and higher ST (hazard ratio: low-ST 1.00, moderate-ST 1.04 [0.94, 1.16, P = 0.440] and high-ST 1.19 [1.05, 1.34, P = 0.007]). The high-PA reduced the risk for the CKD development irrespective of the amount of ST. CONCLUSIONS: Low-PA and high-ST are risk factors for the development of CKD in the middle-aged Korean population. High-PA recovers high-ST, inducing a harmful effect on the occurrence of CKD.

Discordant renal progression of Fabry disease in male monozygotic twins: a case report.

Background: Fabry disease (FD) is a rare X-linked lysosomal storage disease caused by mutations in the GLA gene that encodes α-galactosidase A (α-GAL). Clinical phenotypes tend to vary in monozygotic female twins because mutations are located on the X-chromosome, whereas similar phenotypes are found in male monozygotic twins. Here we report the case of male monozygotic twins with FD presenting with distinguishable renal phenotypes. Case: A 49-year-old male patient who visited the hospital with proteinuria 14 years prior was readmitted for the same issue. His monozygotic twin brother had started hemodialysis 6 months prior due to renal failure of unknown origin. The patient's renal function was within the normal range, while his spot urine protein-to-creatinine ratio was 557 mg/g. Echocardiography revealed left ventricular hypertrophy (LVH). The findings of a renal biopsy were consistent with FD. Genetic testing identified a c.656T>C mutation in the GLA gene, and α-GAL activity was significantly decreased. Genetic screening of his family clarified that his mother, older sister, twin brother, and his daughter had the same genetic mutations. The patient received enzyme replacement therapy 34 times. Subsequently, migalastat was initiated that continues today. Renal function and proteinuria remain stable, and the LVH has mildly improved. Conclusion: This is the first case of male monozygotic twins expressing different progressions of FD. Our findings demonstrate the possibility that environmental or epigenetic factors may critically influence genotype-phenotype discordance.

Correction: Kim et al. The Medium Cut-Off Membrane Does Not Lower Protein-Bound Uremic Toxins. Toxins 2022, 14, 779.

In the original publication [...].

Clinical significance of urinary exosomal microRNAs in patients with IgA nephropathy.

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. The clinical relevance of 11 urinary exosomal microRNAs (miRNAs) was evaluated in patients with IgAN. From January 2009 to November 2018, IgAN (n = 93), disease control (n = 11), and normal control (n = 19) groups were enrolled. We evaluated the expression levels of urinary exosomal miRNAs at the baseline and their relationship with clinical and pathologic features. This study aimed to discriminate statistically powerful urinary exosomal miRNAs for the prognosis of IgAN. Urinary miRNA levels of miR-16-5p, miR-29a-3p, miR-124-3p, miR-126-3p, miR-199a-3p, miR-199b-5p, and miR-335-3p showed significant correlation with both estimated glomerular filtration rate (eGFR) and urine protein-to-creatinine ratio (uPCR). In univariate regression analysis, age, body mass index, hypertension, eGFR, uPCR, Oxford classification E, and three miRNAs (miR-16-5p, miR-199a-3p, and miR-335-3p) were associated with disease progression in patients with IgAN. The area under the curve (AUC) of miR-199a-3p was high enough (0.749) without any other clinical or pathologic factors, considering that the AUC of the International IgAN Risk Prediction Tool was 0.853. Urinary exosomal miRNAs may serve as alternative prognostic biomarkers of IgAN with further research.

Comparison of Humoral Response between Third and Fourth Doses of COVID-19 Vaccine in Hemodialysis Patients.

Dialysis patients are more likely to die or become hospitalized from coronavirus disease 2019 (COVID-19). Currently, only a few studies have evaluated the efficacy of a fourth booster vaccination in hemodialysis (HD) patients and there is not enough evidence to recommend for or against a fourth booster vaccination. This study compared the humoral response and disease severity of patients on HD who received either three or four doses of COVID-19 vaccine. A total of 88 patients were enrolled. Humoral response to vaccination was measured by quantifying immunoglobulin G levels against the receptor binding domain of SARS-CoV-2 (anti-RBD IgG) at five different times and plaque reduction neutralization tests (PRNT) at two different times after vaccination over a period of 18 months. Antibody levels were measured at approximately two-month intervals after the first and second dose, then four months after the third dose, and then one to six months after the fourth dose of vaccine. PRNT was performed two months after the second and four months after the third dose of vaccine. We classified patients into four groups according to the number of vaccine doses and presence of COVID-19 infection. Severe infection was defined as hospital admission for greater than or equal to two weeks or death. There was no difference in antibody levels between naïve and infected patients except after a fourth vaccination, which was effective for increasing antibodies in infection-naïve patients. Age, sex, body mass index (BMI), dialysis vintage, and presence of diabetes mellitus (DM) did not show a significant correlation with antibody levels. Four patients who experienced severe COVID-19 disease tended to have lower antibody levels prior to infection. A fourth dose of SARS-CoV-2 vaccine significantly elevated antibodies in infection-naïve HD patients and may be beneficial for HD patients who have not been previously infected with SARS-CoV-2 for protection against severe infection.