Virological characteristics of the SARS-CoV-2 Omicron EG.5.1 variant.

In middle to late 2023, a sublineage of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron XBB, EG.5.1 (a progeny of XBB.1.9.2), is spreading rapidly around the world. We performed multiscale investigations, including phylogenetic analysis, epidemic dynamics modeling, infection experiments using pseudoviruses, clinical isolates, and recombinant viruses in cell cultures and experimental animals, and the use of human sera and antiviral compounds, to reveal the virological features of the newly emerging EG.5.1 variant. Our phylogenetic analysis and epidemic dynamics modeling suggested that two hallmark substitutions of EG.5.1, S:F456L and ORF9b:I5T are critical to its increased viral fitness. Experimental investigations on the growth kinetics, sensitivity to clinically available antivirals, fusogenicity, and pathogenicity of EG.5.1 suggested that the virological features of EG.5.1 are comparable to those of XBB.1.5. However, cryo-electron microscopy revealed structural differences between the spike proteins of EG.5.1 and XBB.1.5. We further assessed the impact of ORF9b:I5T on viral features, but it was almost negligible in our experimental setup. Our multiscale investigations provide knowledge for understanding the evolutionary traits of newly emerging pathogenic viruses, including EG.5.1, in the human population.

A case of successful contribution of therapeutic drug monitoring of valganciclovir as the prophylaxis against cytomegalovirus infection in a lung transplant recipient.

BACKGROUND: Ganciclovir and its prodrug, valganciclovir, are first-line agents for cytomegalovirus infection prophylaxis after lung transplantation. Although valganciclovir prophylaxis is known to result in severe leukopenia as an adverse effect, dosage adjustment based on therapeutic drug monitoring (TDM) of ganciclovir concentration is not generally implemented in clinical practice. CASE PRESENTATION: In this report, we describe the case of a female in her fifties after lung transplantation who successfully maintained valganciclovir prophylaxis under TDM with a minimal occurrence of severe leukopenia. Valganciclovir administration was initiated at a conventional dose of 450 mg/day on postoperative day 43 but was reduced to 450 mg/2 days on postoperative day 69 because of a decrease in white blood cell count and an increase in trough ganciclovir concentration. Subsequently, the valganciclovir dose adjustment was switched from label-indicated renal function-guided dosing to TDM-based dosing, targeting a trough level of 300-800 ng/mL. This target range was determined through deliberations with infectious disease specialists and pharmacists based on previously reported data. The TDM-based dose adjustment successfully prevented cytomegalovirus reactivation without causing significant adverse effects. Valganciclovir prophylaxis was completed on postoperative day 256, and the patient was transferred to another hospital for rehabilitation. CONCLUSIONS: The findings of the present case suggest that TDM-based dosing could be helpful for clinicians in optimizing the prophylactic administration of valganciclovir in patients undergoing lung transplantation.

Clinical characteristics and analysis of prognostic factors in methicillin-resistant Staphylococcus aureus endocarditis: A retrospective multicenter study in Japan.

BACKGROUND: Infective endocarditis (IE) caused by MRSA (methicillin-resistant Staphylococcus aureus) is associated with a high mortality rate. This study aimed to elucidate the characteristics of patients with MRSA-IE in Japan and identify the factors associated with prognosis. METHODS: This retrospective study included patients with a confirmed diagnosis of IE caused by MRSA, between January 2015 and April 2019. RESULTS: A total of 65 patients from 19 centers were included, with a mean age of 67 years and 26 % were female. Fifty percent of the patients with IE were had nosocomial infections and 25 % had prosthetic valve involvement. The most common comorbidities were hemodialysis (20 %) and diabetes (20 %). Congestive heart failure was present in 86 % of patients (NYHA class I, II: 48 %; III, IV: 38 %). The 30-day and in-hospital mortality rates were 29 % and 46 %, respectively. Multi-organ failure was the primary cause of death, accounting for 43 % of all causes of death. Prognostic factors for in-hospital mortality were age, disseminated intravascular coagulation, daptomycin and/or linezolid as initial antibiotic therapy, and surgery. Surgical treatment was associated with a lower mortality rate (odds ratio [OR], 0.026; 95 % confidence interval [CI], 0.002-0.382; p = 0.008 for 30-day mortality and OR, 0.130; 95 % CI; 0.029-0.584; p = 0.008 for in-hospital mortality). CONCLUSION: Mortality due to MRSA-IE remains high. Surgical treatment is a significant prognostic predictor of MRSA-IE.

Complete genome sequence of three Staphylococcus epidermidis strains isolated from patients with skin diseases in Japan.

Staphylococcus epidermidis is a member of the human skin microbiota as a commensal organism but could be an important opportunistic pathogen for immunocompromised individuals. Here, we report the complete genome sequence of three S. epidermidis strains isolated from patients with skin diseases.

Utilizing red blood cell distribution width (RDW) as a reliable biomarker to predict treatment effects after chimeric antigen receptor T cell therapy.

Chimeric antigen receptor T cell (CAR-T) therapy is an effective treatment for B cell malignancies. A certain fraction of patients, however, experience post-CAR-T relapse, and due to the difficulty of precise relapse prediction, biomarkers that can predict the strength and duration of CAR-T efficacy are needed before CAR-T infusion. Therefore, we performed a single-center cohort study including 91 diffuse large B cell lymphoma (DLBCL) patients treated with CAR-T in order to identify such a new prognostic biomarker. After confirming that each of the already reported prognostic parameters (disease status at leukapheresis, primary refractoriness, number of treatment lines, CD3+ cell counts at leukapheresis) has only limited predictive performance, we established a new composite parameter by integrating these four variables, and found that it predicts progression-free survival (PFS) after CAR-T infusion with statistical significance. Moreover, after comprehensive correlation analyses of this new composite parameter with all individual laboratory variables, we determined that the standard deviation of red blood cell distribution width (RDW-SD) at leukapheresis shows significant correlation with the composite parameter and may be a prognostic biomarker (R2 = 0.76, p = 0.02). Validation analysis indicated that a higher RDW-SD is significantly associated with poorer PFS after CAR-T cell therapy (HR, 3.46, P = 0.03). Thus, this study suggests that a single parameter, RDW-SD at leukapheresis, is a novel, useful biomarker that can be obtained early to predict therapeutic effects of CAR-T cell therapy. Post-CAR-T maintenance or re-induction therapies should be adopted for higher risk patients, who may relapse after CAR-T therapy.

Investigation of severe acute respiratory syndrome coronavirus 2 infection status in solid organ transplant recipients treated with tixagevimab/cilgavimab.

INTRODUCTION: Tixagevimab and cilgavimab (T/C) are neutralizing antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that can be used to prevent SARS-CoV-2 infection in solid organ transplant (SOT) recipients. However, their neutralizing activity against recent variants was reduced, raising concerns regarding the emergence of breakthrough coronavirus diseases 2019 (COVID-19). This study aimed to investigate the status of the COVID-19 breakthrough after T/C administration. METHODS: We retrospectively investigated breakthrough COVID-19 in SOT recipients administered T/C at Kyoto University Hospital, Japan, from November 2022 to March 2023. Patients were monitored for 6 months after T/C administration. SARS-CoV-2 infection was diagnosed using polymerase chain reaction or antigen tests. The monthly incidence rates of SARS-CoV-2 infection were calculated using the person-time method. RESULTS: T/C were administered to 67 SOT recipients (liver, 16; lung, 36; and kidney, 15), of whom five were infected with SARS-CoV-2. All five cases were classified as mild, and none of these patients required admission to the intensive care unit (ICU) or died. All infected individuals tested positive for SARS-CoV-2 after March 2023, when T/C-resistant subvariant strains became predominant. The monthly incidence rate of SARS-CoV-2 infection, calculated using the person-time method, suggested an increasing trend. CONCLUSIONS: During the T/C-resistant variant epidemic, SARS-CoV-2 infections were identified even after T/C administration, suggesting that the prophylactic effects of T/C were invalid. Therefore, emerging variants must be carefully monitored and characterized to determine appropriate antiviral strategies, such as the use of suitable neutralizing antibodies.

Longitudinal analysis of genomic mutations in SARS-CoV-2 isolates from persistent COVID-19 patient.

A primary reason for the ongoing spread of coronavirus disease 2019 (COVID-19) is the continuous acquisition of mutations by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, the mechanism of acquiring mutations is not fully understood. In this study, we isolated SARS-CoV-2 from an immunocompromized patient persistently infected with Omicron strain BF.5 for approximately 4 months to analyze its genome and evaluate drug resistance. Although the patient was administered the antiviral drug remdesivir (RDV), there were no acquired mutations in RDV binding site, and all isolates exhibited susceptibility to RDV. Notably, upon analyzing the S protein sequence of the day 119 isolate, we identified mutations acquired by mutant strains emerging from the BF.5 variant, suggesting that viral genome analysis in persistent COVID-19 patients may be useful in predicting viral evolution. These results suggest mutations in SARS-CoV-2 are acquired during long-term viral replication rather than in response to antiviral drugs.

Antimicrobial therapy and outcome of methicillin-resistant Staphylococcus aureus endocarditis: A retrospective multicenter study in Japan.

BACKGROUND: MRSA (methicillin-resistant Staphylococcus aureus)-infective endocarditis (IE) is associated with high morbidity and mortality. This study aimed to assess data from patients with MRSA-IE across multiple facilities in Japan, with a specific focus on antimicrobial therapy and prognosis. METHODS: This retrospective study enrolled patients with a confirmed diagnosis of IE attributed to MRSA, spanning the period from January 2015 to April 2019. RESULTS: Sixty-four patients from 19 centers were included, with a median age of 67 years. The overall mortality rate was 28.1% at 30 days, with an in-hospital mortality of 45.3%. The most frequently chosen initial anti-MRSA agents were glycopeptide in 67.2% of cases. Daptomycin and linezolid were selected as initial therapy in 23.4% and 17.2% of cases, respectively. Approximately 40% of all patients underwent medication changes due to difficulty in controlling infection or drug-related side effects. Significant prognostic factors by multivariable analysis were DIC for 30-day mortality and surgical treatment for 30-day and in-hospital mortality. For vancomycin as initial monotherapy, there was a trend toward a worse prognosis for 30-day and in-hospital mortality (OR, 6.29; 95%CI, 1.00-39.65; p = 0.050, OR, 3.61; 95%CI, 0.93-14.00; p = 0.064). Regarding the choice of initial antibiotic therapy, statistical analysis did not show significant differences in prognosis. CONCLUSION: Glycopeptide and daptomycin were the preferred antibiotics for the initial therapy of MRSA-IE. Antimicrobial regimens were changed for various reasons. Prognosis was not significantly affected by choice of antibiotic therapy (glycopeptide, daptomycin, linezolid), but further studies are needed to determine which antimicrobials are optimal as first-line agents.

Autochthonous Cryptococcus gattii genotype VGIIb infection in a Japanese patient with anti-granulocyte-macrophage colony-stimulating factor antibodies.

A 31-year-old Japanese man presented with cerebral and pulmonary cryptococcosis. Cryptococcus gattii (C. gattii) genotype VGIIb was detected in the patient's sputum and cerebrospinal fluid specimens. The serum levels of anti-granulocyte-macrophage colony-stimulating factor (GM-CSF) antibodies were elevated in this patient, which has been associated with pulmonary alveolar proteinosis and is considered a risk factor for C. gattii infection. After undergoing >12 months of antifungal treatments, the patient showed improvements in symptoms and findings on brain and lung imaging. Several Japanese patients who develop C. gattii infection have also been reported; however, most of these patients have been infected outside Japan, as C. gattii infection is rare in Japan. Only one patient with C. gattii genotype VGIIb infection has been reported in Japan, and it is believed that this patient contracted the infection in China. In the present case, our patient has never been outside Japan, indicating that the infection originated in Japan. Our findings suggest that C. gattii might be spreading in Japan. Therefore, patients with positive serum anti-GM-CSF antibodies should be thoroughly monitored for C. gattii infection, even those living in Japan.

Micro-patterned culture of iPSC-derived alveolar and airway cells distinguishes SARS-CoV-2 variants.

The emergence of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) variants necessitated a rapid evaluation system for their pathogenesis. Lung epithelial cells are their entry points; however, in addition to their limited source, the culture of human alveolar epithelial cells is especially complicated. Induced pluripotent stem cells (iPSCs) are an alternative source of human primary stem cells. Here, we report a model for distinguishing SARS-CoV-2 variants at high resolution, using separately induced iPSC-derived alveolar and airway cells in micro-patterned culture plates. The position-specific signals induced the apical-out alveolar type 2 and multiciliated airway cells at the periphery and center of the colonies, respectively. The infection studies in each lineage enabled profiling of the pathogenesis of SARS-CoV-2 variants: infection efficiency, tropism to alveolar and airway lineages, and their responses. These results indicate that this culture system is suitable for predicting the pathogenesis of emergent SARS-CoV-2 variants.

Comparison of the safety and cost-effectiveness of nebulized liposomal amphotericin B and amphotericin B deoxycholate for antifungal prophylaxis after lung transplantation.

INTRODUCTION: Fungal infection after lung transplantation can lead to poor clinical outcome, for which lung transplant recipients require prophylaxis. One of the antifungal agents used after lung transplantation is nebulized amphotericin B (AMB). Nebulized AMB causes adverse events such as dyspnea and airway irritation, and long-term use leads to high economic costs. So far, prophylactic regimens employing AMB deoxycholate (AMB-d) and liposomal AMB (L-AMB) have been developed. This study compared the efficacy, safety, and cost of AMB-d and L-AMB. PATIENTS AND METHODS: Patients who underwent lung transplantation at Kyoto University Hospital from January 2021 to May 2023 were included in this study. Thirty-three patients received nebulized AMB-d, whereas 29 received nebulized L-AMB. RESULTS: Both regimens maintained comparable prophylactic efficacy regarding the development of fungal infection in the AMB-d and L-AMB groups (3.0% vs. 3.4%, P = 0.877). Patients treated with nebulized L-AMB experienced fewer respiratory-related adverse reactions than those treated with nebulized AMB-d (6.9% vs. 30.3%, P < 0.05), leading to a longer treatment duration with L-AMB than with AMB-d. Additionally, the daily cost of administering L-AMB was lower than that of administering AMB-d (3609 Japanese yen vs. 1792.3 Japanese yen, P < 0.05). DISCUSSION: These results suggest that nebulized L-AMB is safer and more cost-effective than nebulized AMB-d, with comparable efficacy.

Development and evaluation of three automated media pooling and molecular diagnostic systems for the detection of SARS-CoV-2.

Pooled testing combined with molecular diagnostics for the detection of SARS-CoV-2 is a promising method that can increase testing capacities and save costs. However, pooled testing is also associated with the risks of decreased test sensitivity and specificity. To perform reliable pooled testing, we developed and validated three automated media pooling and molecular diagnostic systems. These pooling systems (geneLEAD-PS, Panther-PS, and Biomek-PS) comprised existing automated molecular detection platforms, corresponding automated media pooling devices, and laboratory information management systems. Analytical sensitivity analysis and mock sample evaluation were performed, and the obtained data were used to determine the sizes of the pool for the validation study. In the validation study, a total of 2,448, 3,228, and 6,420 upper respiratory samples were used for geneLEAD-PS, Panther-PS, and Biomek-PS, respectively, and the diagnostic performances were compared with the reference RT‒PCR assay. A pool size of 6 for geneLEAD-PS and a pool size of 4 for Panther-PS and Biomek-PS were selected for the validation studies. All three systems showed high positive percent agreement values of ≥90.5% and negative percent agreement values of ≥99.8% for any specimen type. Pooled testing resulted in a 65%-71% reduction in cost per sample. The testing capacities of geneLEAD-PS, Panther-PS, and Biomek-PS were 144 samples in 3 hours, 384 samples in 5.5 hours, and 376 samples in 4 hours, respectively. The developed pooling systems showed robust diagnostic performances and will increase the testing capacities of molecular diagnostic tests while saving costs and may contribute to infection control of COVID-19.IMPORTANCEDuring the COVID-19 pandemic, there have been surges in demand for accurate molecular diagnostic testing and laboratory supply shortages. Pooled testing combined with highly sensitive molecular testing, which entails mixing multiple samples as a single sample, is a promising approach to increase testing capacities while reducing the use of consumables. However, pooled testing is associated with risks that compromise diagnostic performance, such as false negatives due to dilution of positive samples or false positives due to cross-contamination. To perform reliable pooled testing, three different pooling systems (an automated pooling device, an automated molecular detection platform, and a laboratory information management system) were developed to accurately interpret pooled testing results. These three systems were validated using multiple clinical samples and showed high concordance with individual testing. The developed pooling systems will contribute to increasing reliable molecular testing capacities while using fewer consumables and saving costs.

Clinical Impact of Cytokine Release Syndrome on Prolonged Hematotoxicity after Chimeric Antigen Receptor T Cell Therapy: KyoTox A-Score, a Novel Prediction Model.

Prolonged hematotoxicity is the most common long-term adverse event in chimeric antigen receptor T cell therapy (CAR-T). To evaluate the impact on prolonged cytopenia of inflammatory status after CAR T infusion, we performed a single-center retrospective study and analyzed patients with B cell lymphomas after CAR-T. Among 90 patients analyzed at 90 days after infusion, the cumulative incidence was 57.5% for prolonged neutropenia, 36.7% for anemia, and 49.8% for thrombocytopenia. Patients who experienced cytokine release syndrome (CRS) had significantly higher incidence and longer duration of prolonged cytopenia. In addition, we found that among patients with grade 1 CRS, those with a longer duration of CRS-related symptoms (>5 days; grade 1b in modified CRS grading [m-CRS]) had a significantly higher incidence and longer duration of prolonged cytopenia than those whose CRS-related symptoms resolved within 5 days (grade 1a m-CRS). Multivariate analysis revealed that a higher m-CRS grade (grade 1b or 2; hazard ratio [HR], 2.42), higher peak CRP (≥10 mg/dL; HR, 1.66), longer duration of elevated CRP (≥10 days; HR, 1.83), and a decrease in serum inorganic phosphorus concentration (≥30% from baseline; HR, 1.95) were associated with significantly higher cumulative incidence of prolonged neutropenia, as well as anemia and thrombocytopenia. Using these factors, we developed a new predictive scoring model for prolonged hematotoxicity, the KyoTox a-score, which can successfully stratify the incidence and duration of cytopenia independent of the existing model, CAR-HEMATOTOX, which is based on laboratory data at lymphodepletion. Thus, this newly developed post-CAR-T inflammation-dependent score is accurate and useful for predicting prolonged hematotoxicity.

SARS-CoV-2-induced disruption of a vascular bed in a microphysiological system caused by type-I interferon from bronchial organoids.

Blood vessels show various COVID-19-related conditions including thrombosis and cytokine propagation. Existing in vitro blood vessel models cannot represent the consequent changes in the vascular structure or determine the initial infection site, making it difficult to evaluate how epithelial and endothelial tissues are damaged. Here, we developed a microphysiological system (MPS) that co-culture the bronchial organoids and the vascular bed to analyze infection site and interactions. In this system, virus-infected organoids caused damage in vascular structure. However, vasculature was not damaged or infected when the virus was directly introduced to vascular bed. The knockout of interferon-related genes and inhibition of the JAK/STAT pathway reduced the vascular damage, indicating the protective effect of interferon response suppression. The results demonstrate selective infection of bronchial epithelial cells and vascular damage by cytokines and also indicate the applicability of MPS to investigate how the infection influences vascular structure and functions.

Impact of perioperative airway pathogens on living-donor lobar lung transplantation outcomes.

PURPOSE: To elucidate the clinical impact of pathogenic organism (PO) positivity early after transplantation, we evaluated the impact of perioperative airway POs on outcomes after living-donor lobar lung transplantation (LDLLT), where the graft airway is supposed to be sterile from a healthy donor. METHOD: A retrospective review of 67 adult LDLLT procedures involving 132 living donors was performed. Presence of POs in the recipients' airways was evaluated preoperatively and postoperatively in intensive-care units. RESULTS: POs were detected preoperatively in 13 (19.4%) recipients. No POs were isolated from the donor airways at transplantation. POs were detected in 39 (58.2%) recipients postoperatively; most were different from the POs isolated preoperatively. Postoperative PO isolation was not associated with short-term outcomes other than prolonged postoperative ventilation. The 5-year overall survival was significantly better in the PO-negative group than in the PO-positive group (89.1% vs. 63.7%, P = 0.014). In the multivariate analysis, advanced age (hazard ratio [HR]: 1.041 per 1-year increase, P = 0.033) and posttransplant PO positivity in the airway (HR: 3.684, P = 0.019) significantly affected the survival. CONCLUSIONS: The airways of the living-donor grafts were microbiologically sterile. PO positivity in the airway early after transplantation negatively impacted long-term outcomes.

A population-based study of the trend in SARS-CoV-2 diagnostic modalities from the beginning of the pandemic to the Omicron surge in Kyoto City, Kyoto, Japan.

BACKGROUND: The coronavirus disease 2019 (COVID-19) presents critical diagnostic challenges for managing the pandemic. We investigated the 30-month changes in COVID-19 testing modalities and functional testing sites from the early period of the pandemic to the most recent Omicron surge in 2022 in Kyoto City, Japan. METHODS: This is a retrospective-observational study using a local anonymized population database that included patients' demographic and clinical information, testing methods and facilities from January 2020 to June 2022, a total of 30 months. We computed the distribution of symptomatic presentation, testing methods, and testing facilities among cases. Differences over time were tested using chi-square tests of independence. RESULTS: During the study period, 133,115 confirmed COVID-19 cases were reported, of which 90.9% were symptomatic. Although nucleic acid amplification testing occupied 68.9% of all testing, the ratio of lateral flow devices (LFDs) rapidly increased in 2022. As the pandemic continued, the testing capability was shifted from COVID-19 designated facilities to general practitioners, who became the leading testing providers (57.3% of 99,945 tests in 2022). CONCLUSIONS: There was a dynamic shift in testing modality during the first 30 months of the pandemic in Kyoto City. General practitioners increased their role substantially as the use of LFDs spread dramatically in 2022. By comprehending and documenting the evolution of testing methods and testing locations, it is anticipated that this will contribute to the establishment of an even more efficient testing infrastructure for the next pandemic.

Development and evaluation of the automated multipurpose molecular testing system PCRpack for high-throughput SARS-CoV-2 testing.

IMPORTANCE: Accurate and fast molecular testing is important for the diagnosis and control of COVID-19. During patient surges in the COVID-19 pandemic, laboratories were challenged by a higher demand for molecular testing under skilled staff shortages. We developed an automated multipurpose molecular testing system, named PCRpack, for the rapid, high-throughput testing of infectious pathogens, including SARS-CoV-2. The system is provided in an all-in-one package, including a liquid handling instrument, a laboratory information management system, and other materials needed for testing operation; is highly customizable; and is easily implemented. PCRpack showed robust liquid handling performance, high clinical diagnostic performance, a shorter turn-around time with minimal hands-on time, and a high testing capacity. These features contribute to the rapid implementation of the high-performance and high-throughput molecular testing environment at any phase of the pandemic caused by SARS-CoV-2 or future emerging pathogens.

Novel intrathoracic irrigation using ultrafine ozone bubbles in a rat empyema model.

Dissolved ozone is generally used for sanitization, but it has not been used for thoracic cavity sanitization because of its short half-life (< 20 min) and possible toxicity. We developed a novel solution containing ultrafine ozone bubbles (ozone-UFB) with a fivefold longer half-life than non-UFB ozone. Using an in vitro model, Staphylococcus aureus colonies were counted after exposure to ozone-UFB or non-UFB ozone at the same ozone concentration (0.4 mg/L). The colony count was significantly lower in the ozone-UFB group than in the non-UFB ozone group (p = 0.034). The effect of repeated pleural irrigation using ozone-UFB and saline was compared in a rat empyema model of S. aureus infection. The bacterial count in the pleural effusion was decreased by at least fivefold following intrathoracic lavage with ozone-UFB (3 mg/L). To examine the safety of ozone-UFB for intrathoracic use, ozone-UFB with a higher ozone concentration (10 mg/L) was injected into the thoracic cavities of normal rats. The treatment did not result in any specific pleural damage or elevated serum interleukin-6 concentrations. The findings highlighted the efficacy and safety of ozone-UFB for intrathoracic sanitization, but further studies are needed to determine the optimal therapeutic ozone concentration with appropriate safety margins.

Risk analysis of fluctuating hypercalcemia after leukapheresis in cellular therapy.

Optimized management of citrate-induced hypocalcemia is required to provide safe leukapheresis. We prospectively analyzed subjects who underwent leukapheresis for cytotherapy, and evaluated serum ionized (iCa) concentrations before, at the end of, and 1 h after leukapheresis. During leukapheresis, calcium gluconate solution was continuously supplemented intravenously with hourly measurement of iCa. 76 patients including 49 lymphapheresis for chimeric antigen receptor T-cell therapy and 27 stem cell collections were enrolled. Median processing blood volume was 10 L (range, 6-15 L). Fluctuating hypercalcemia, in which the iCa concentration rose above its upper limit 1 h after leukapheresis, was observed in 58 subjects (76.3%). Multivariate analysis revealed that higher ratios of processing blood volume to body weight, more rapid calcium supplementation, and lower iCa concentration at the end of leukapheresis significantly increased elevation of serum iCa concentration by 1 h after leukapheresis. Based on multivariate analyses, we developed a formula and a diagram that accurately estimates serum iCa concentration 1 h post-leukapheresis. This suggests optimal targets for iCa concentration and calcium supplementation rates. In cases with high ratios of processing blood volume to body weight, slowing the rate of blood processing, rather than increasing calcium supplementation should safely alleviate hypocalcemia during leukapheresis without inducing hypercalcemia thereafter.