Long-term efficacy and safety of tucidinostat in patients with relapsed or refractory peripheral T-cell lymphoma: final analysis of phase IIb results.

Not available.

Impaired humoral immunity following COVID-19 vaccination in HTLV-1 carriers.

BACKGROUND: Whether human T-lymphotropic virus type 1 (HTLV-1) carriers can develop sufficient humoral immunity after coronavirus disease 2019 (COVID-19) vaccination is unknown. METHODS: To investigate humoral immunity after COVID-19 vaccination in HTLV-1 carriers, a multicenter, prospective observational cohort study was conducted at five institutions in southwestern Japan, an endemic area for HTLV-1. HTLV-1 carriers and HTLV-1-negative controls were enrolled for this study from January to December 2022. During this period, the third dose of the COVID-19 vaccine was actively administered. HTLV-1 carriers were enrolled during outpatient visits, while HTLV-1-negative controls included health care workers and patients treated by participating institutions for diabetes, hypertension, or dyslipidemia. The main outcome was the effect of HTLV-1 infection on the plasma anti-COVID-19 spike IgG (IgG-S) titers after the third dose, assessed by multivariate linear regression with other clinical factors. RESULTS: We analyzed 181 cases (90 HTLV-1 carriers, 91 HTLV-1-negative controls) after receiving the third dose. HTLV-1 carriers were older (median age 67.0 vs. 45.0 years, p < 0.001) and more frequently had diabetes, hypertension, or dyslipidemia than did HTLV-1-negative controls (60.0% vs. 27.5%, p < 0.001). After the third dose, the IgG-S titers decreased over time in both carriers and controls. Multivariate linear regression in the entire cohort showed that time since the third dose, age, and HTLV-1 infection negatively influenced IgG-S titers. After adjusting for confounders such as age, or presence of diabetes, hypertension, or dyslipidemia between carriers and controls using the overlap weighting propensity score method, and performing weighted regression analysis in the entire cohort, both time since the third dose and HTLV-1 infection negatively influenced IgG-S titers. CONCLUSIONS: The humoral immunity after the third vaccination dose is impaired in HTLV-1 carriers; thus, customized vaccination schedules may be necessary for them.

Development and evaluation of a rapid one-step high sensitivity real-time quantitative PCR system for minor BCR-ABL (e1a2) test in Philadelphia-positive acute lymphoblastic leukemia (Ph+ ALL).

OBJECTIVE: Minimal residual disease assessment of BCR-ABL messenger ribonucleic acid levels is crucial in Philadelphia chromosome-positive acute lymphoblastic leukemia for prognosis and treatment planning. However, accurately quantifying minor BCR-ABL transcripts, which comprise 70% of Philadelphia chromosome-positive acute lymphoblastic leukemia cases, lacks a national-approved method. METHODS: We developed the "Otsuka" minor BCR-ABLmessenger ribonucleic acid assay kit with exceptional precision (0.00151%). Minor BCR-ABL messenger ribonucleic acid levels were analyzed in 175 adults, 36 children with acute lymphoblastic leukemia and 25 healthy individuals to evaluate the kit's performance. RESULTS: The "Otsuka" kit showed high concordance with a commonly used chimeric gene screening method, indicating reliable detection of positive cases. Quantitative results demonstrated a robust correlation with both a laboratory-developed test and a diagnostic research product. The "Otsuka" kit performs comparably or even surpass to conventional products, providing valuable insights into Philadelphia chromosome-positive acute lymphoblastic leukemia pathology. CONCLUSIONS: The 'Otsuka" minor BCR-ABL messenger ribonucleic acid assay kit exhibits excellent performance in quantifying minor BCR-ABL transcripts in Philadelphia chromosome-positive acute lymphoblastic leukemia patients. Our results align well with established screening methods and show a strong correlation with laboratory-developed tests and diagnostic research products. The "Otsuka" kit holds great promise as a valuable tool for understanding Philadelphia chromosome-positive acute lymphoblastic leukemia pathology and guiding effective treatment strategies.

Integrated genetic and clinical prognostic factors for aggressive adult T-cell leukemia/lymphoma.

The prognosis of aggressive adult T-cell leukemia/lymphoma (ATL) is poor, and allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a curative treatment. In order to identify favorable prognostic patients after intensive chemotherapy, and who therefore might not require upfront allo-HSCT, we aimed to improve risk stratification of aggressive ATL patients aged <70 years. The clinical risk factors and genetic mutations were incorporated into risk modeling for overall survival (OS). We generated the m7-ATLPI, a clinicogenetic risk model for OS, that included the ATL prognostic index (PI) (ATL-PI) risk category, and non-silent mutations in seven genes, namely TP53, IRF4, RHOA, PRKCB, CARD11, CCR7, and GATA3. In the training cohort of 99 patients, the m7-ATLPI identified a low-, intermediate-, and highrisk group with 2-year OS of 100%, 43%, and 19%, respectively (hazard ratio [HR] =5.46; P<0.0001). The m7-ATLPI achieved superior risk stratification compared to the current ATL-PI (C-index 0.92 vs. 0.85, respectively). In the validation cohort of 84 patients, the m7-ATLPI defined low-, intermediate-, and high-risk groups with a 2-year OS of 81%, 30%, and 0%, respectively (HR=2.33; P=0.0094), and the model again outperformed the ATL-PI (C-index 0.72 vs. 0.70, respectively). The simplified m7-ATLPI, which is easier to use in clinical practice, achieved superior risk stratification compared to the ATLPI, as did the original m7-ATLPI; the simplified version was calculated by summing the following: high-risk ATL-PI category (+10), low-risk ATL-PI category (-4), and non-silent mutations in TP53 (+4), IRF4 (+3), RHOA (+1), PRKCB (+1), CARD11 (+0.5), CCR7 (-2), and GATA3 (-3).

Oral HDAC inhibitor tucidinostat in patients with relapsed or refractory peripheral T-cell lymphoma: phase IIb results.

Tucidinostat (formerly known as chidamide) is an orally available, novel benzamide class of histone deacetylase (HDAC) inhibitor that selectively blocks class I and class IIb HDAC. This multicenter phase IIb study aimed to investigate the efficacy and safety of tucidinostat, 40 mg twice per week (BIW), in patients with relapsed/refractory (R/R) peripheral T-cell lymphoma (PTCL). The primary endpoint was overall response rate (ORR) assessed by an independent overall efficacy review committee. Between March 2017 and March 2019, 55 patients were treated, and 46 and 55 were evaluated for efficacy and safety, respectively. Twenty-one of 46 patients achieved objective responses with an ORR of 46% (95% confidence interval : 30.9-61.0), including five patients with complete response (CR). Responses were observed across various PTCL subtypes. In angioimmunoblastic T-cell lymphoma, there were two CR and five partial responses (PR) among eight patients, achieving an ORR of 88%. The disease control rate (CR + PR + stable disease) was 72% (33/46). The median progression-free survival, duration of response, and overall survival were 5.6 months, 11.5 months, 22.8 months, respectively. The most common adverse events (AE) (all grades) were thrombocytopenia, neutropenia, leukopenia, anemia, and diarrhea. The grade ≥3 AE emerging in ≥20% of patients included thrombocytopenia (51%), neutropenia (36%), lymphopenia (22%), and leukopenia (20%). Importantly, most of the AE were manageable by supportive care and dose modification. In conclusion, the favorable efficacy and safety profiles indicate that tucidinostat could be a new therapeutic option in patients with R/R PTCL (clinicaltrials gov. Identifier: NCT02953652).

A phase I/II study of 10-min dosing of bendamustine hydrochloride (rapid infusion formulation) in patients with previously untreated indolent B-cell non-Hodgkin lymphoma, mantle cell lymphoma, or relapsed/refractory diffuse large B-cell lymphoma in Japan.

PURPOSE: This phase I/II clinical study was conducted to examine the safety, tolerability, pharmacokinetics, and efficacy of 10-min dosing of bendamustine in patients with previously untreated indolent B-cell non-Hodgkin lymphoma (iNHL) or mantle cell lymphoma (MCL) (Group 1) and patients with relapsed/refractory diffuse large B-cell lymphoma (rrDLBCL) (Group 2). METHODS: Rituximab 375 mg/m2 was administered intravenously every 28 days to Group 1 patients on day 1 and every 21 days to Group 2 patients on day 1. Bendamustine 90 mg/m2/day was administered to the former on days 1 and 2; bendamustine 120 mg/m2/day was administered to the latter on days 2 and 3. Each regimen was delivered up to six cycles for both groups. The primary endpoints were safety and tolerability in Groups 1 and 2, respectively. RESULTS: Among 37 enrolled patients, safety was assessed in 36. In Group 1 (n = 30), 27 patients (90%) had follicular lymphoma. Adverse events (AEs) were observed in all 30 patients in Group 1. Dose-limiting toxicities were observed in two of six patients in Group 2. Common AEs included lymphocyte count decreased (86.7%, 100%). In Group 1, overall response and complete response rates were 93.1% (95% confidence interval [CI] 77.2-99.2%) and 75.9% (95% CI 56.5-89.7%), respectively. The Cmax and AUC of bendamustine tended to be higher in Group 2 than in Group 1. CONCLUSIONS: This study showed that bendamustine is safe, well-tolerated and effective for patients with previously untreated iNHL, MCL or rrDLBCL. Pharmacokinetic data were equivalent to those obtained outside of Japan. REGISTRATION NUMBERS: Registration NCT03900377; registered April 3, 2019.

Oral histone deacetylase inhibitor HBI-8000 (tucidinostat) in Japanese patients with relapsed or refractory non-Hodgkin's lymphoma: phase I safety and efficacy.

OBJECTIVE: HBI-8000 (tucidinostat) is a novel, oral histone deacetylase inhibitor that selectivity inhibits Class I (histone deacetylase 1, 2, 3) and Class II (histone deacetylase 10) with direct anti-tumor activity through various mechanisms of action, including epigenetic reprogramming and immunomodulation. It has been approved in China for the treatment of relapsed or refractory peripheral T-cell lymphoma. METHODS: This multicenter, prospective phase I dose-escalation trial evaluating the safety of twice weekly HBI-8000 was conducted in Japan. Eligible patients had non-Hodgkin's lymphoma and no available standard therapy. The primary endpoint was maximum tolerated dose; secondary endpoints included anti-tumor activity, safety and pharmacokinetics. RESULTS: Fourteen patients were enrolled in the study. Twelve patients were assessed for dose-limiting toxicity: six patients in the 30 mg BIW cohort had no dose-limiting toxicitys; two of six patients in the 40 mg BIW cohort had asymptomatic dose-limiting toxicitys. Treatment was well tolerated; adverse events were predominantly mild to moderate hematologic toxicities and were managed with dose modification and supportive care. Thirteen patients were included in the efficacy analysis. Objective response was seen in five of seven patients in the 40 mg BIW cohort; three partial responders had adult T-cell leukemia-lymphoma. In the 30 mg BIW cohort, three of six patients had stable disease after the first cycle. CONCLUSIONS: Treatment with HBI-8000 30 and 40 mg BIW were well-tolerated and safe, with hematological toxicities as expected from other studies of histone deacetylase inhibitor. The maximum tolerated dose and recommended dosage for phase II studies of HBI-8000 is 40 mg BIW. Preliminary efficacy results are encouraging.

Genomic determinants impacting the clinical outcome of mogamulizumab treatment for adult T-cell leukemia/lymphoma.

In order to identify genomic biomarkers for the outcome of mogamulizumab-containing treatment, an integrated molecular analysis of adult T-cell leukemia/lymphoma (ATL) was conducted on 64 mogamulizumab-naïve patients. Among driver genes, CCR4 and CCR7 alterations were observed in 22% and 11% of the patients, respectively, both consisting of single nucleotide variants (SNV)/insertion-deletions (indels) in the C-terminus. Patients with CCR4 alterations or without CCR7 alterations exhibited a more favorable clinical response (complete response [CR] rate 93%, 13/14; P=0.024, and CR rate 71%, 40/56; P=0.036, respectively). Additionally, TP53, CD28, and CD274 alterations were identified in 35%, 16%, and 10% of the patients, respectively. TP53 alterations included SNV/indels or copy number variations (CNV) such as homozygous deletion; CD28 alterations included SNV, CNV such as amplification, or fusion; CD274 alterations included CNV such as amplification, or structural variants. Univariate analysis revealed that TP53, CD28 or CD274 alterations were associated with worse overall survival (OS) (hazard ratio [HR]: 2.330, 95% confidence interval [CI]: 1.183-4.589; HR: 3.191, 95% CI: 1.287- 7.911; HR: 3.301, 95% CI: 1.130-9.641, respectively) but that CCR4 alterations were associated with better OS (HR: 0.286, 95% CI: 0.087-0.933). Multivariate analysis indicated that in addition to performance status, TP53, CCR4 or CD274 alterations (HR: 2.467, 95% CI: 1.197-5.085; HR: 0.155, 95% CI: 0.031-0.778; HR: 14.393, 95% CI: 2.437-85.005, respectively) were independently and significantly associated with OS. The present study contributes to the establishment of precision medicine using mogamulizumab in ATL patients.

Alternating bortezomib-dexamethasone and lenalidomide-dexamethasone in patients with newly diagnosed multiple myeloma aged over 75 years.

More than 40% of Japanese patients with multiple myeloma (MM) are over 75 years of age at diagnosis. Regardless of the treatment benefits, complications and relapses obstruct long-term survival. We conducted a phase II, open-label, single-arm, multicenter clinical trial to assess the efficacy and safety of alternating bortezomib-dexamethasone (Bd) and lenalidomide-dexamethasone (Ld) (Bd/Ld) treatment in MM patients aged over 75 years (MARBLE trial). Patients received Bd therapy from days 1 to 35 and Ld therapy from days 36 to 63. For Bd therapy, patients were administered bortezomib 1.3 mg/m2 and oral dexamethasone 20 mg on days 1, 8, 15, and 22. For Ld therapy, they were administered lenalidomide 15 mg from days 36 to 56 and dexamethasone 10 mg on days 36, 43, 50, and 57. They underwent six treatment cycles in total, each consisting of a 63-day regimen. In total, 10 patients were enrolled, with a median age of 81 years. Efficacy was not evaluated because the patients were fewer than planned. The overall response rate was 80.0% and complete response rate 40.0%. Seventy percent of patients completed the study treatment. Progression-free survival and overall survival at 2 years were 40.0% and 80.0%, respectively. Adverse events of grade 3 or higher, including anemia, decreased lymphocyte count, neutropenia, and hypokalemia, were observed in eight patients. Alternating chemotherapy with Bd/Ld might be feasible, but its efficacy should be verified further.

Bendamustine plus rituximab in Japanese patients with relapsed or refractory diffuse large B-cell lymphoma.

This single-arm phase 3 study was conducted to confirm the results of our phase 2 study of bendamustine (B)-rituximab (R) in patients with relapsed/refractory diffuse large B cell lymphoma (rrDLBCL). The primary endpoint was overall response rate (ORR). Autologous stem cell transplantation-ineligible rrDLBCL patients with ≤ 2 prior chemotherapy regimens received R 375 mg/m2 IV on day 1 and B 120 mg/m2/day IV on days 2 and 3 every 21 days up to 6 cycles. Thirty-eight patients with a median age of 74 years (range, 43-86) received BR. The ORR and complete response rates were 76.3% and 47.4%, respectively. With a median follow-up of 19.5 months including long-term follow-up, median progression-free survival was 11.9 months. Median OS was 29.2 months. Discontinuation of treatment due to Gr3-5 TEAE was observed among 13 of 38 patients (34.2%). One patient with cytomegalovirus enterocolitis died during follow-up. This BR regimen was confirmed to be effective and tolerable in studied patients. ClinicalTrials.gov Identifier: NCT03372837 registered on 14 December 2017, NCT04354402 registered on 21 April, 2020.

Clinical significance of the immunoglobulin G heavy-chain repertoire in peripheral blood mononuclear cells of adult T-cell leukaemia-lymphoma patients receiving mogamulizumab.

'Monitoring of immune responses following mogamulizumab-containing treatment in patients with adult T-cell leukaemia-lymphoma (ATL)' (MIMOGA) is a multicentre prospective clinical study (UMIN000008696). In the MIMOGA study, we found that a lower percentage of CD2- CD19+ B cells in peripheral blood mononuclear cells (PBMC) was a significant unfavourable prognostic factor for overall survival (OS). Accordingly, we then analysed the immunoglobulin G (IgG) heavy-chain repertoire in PBMC by high-throughput sequencing. Of the 101 patients enrolled in the MIMOGA study, for 81 a sufficient amount of PBMC RNA was available for repertoire sequencing analysis. Peripheral IgG B cells in patients with ATL had a restricted repertoire relative to those in healthy individuals. There was a significant positive correlation between the Shannon-Weaver diversity index (SWDI) for the IgG repertoire and proportions of B cells in the PBMC of the patients. Multivariate analysis identified two variables significantly affecting OS: a higher serum soluble interleukin-2 receptor level, and a lower SWDI for the IgG repertoire [hazard ratio, 2·124; 95% confidence interval, 1·114-4·049; n = 44]. The present study documents the importance of humoral immune responses in patients receiving mogamulizumab-containing treatment. Further investigation of strategies to enhance humoral immune responses in patients with ATL is warranted.

Whole-genome landscape of adult T-cell leukemia/lymphoma.

Adult T-cell leukemia/lymphoma (ATL) is an aggressive neoplasm immunophenotypically resembling regulatory T cells, associated with human T-cell leukemia virus type-1. Here, we performed whole-genome sequencing (WGS) of 150 ATL cases to reveal the overarching landscape of genetic alterations in ATL. We discovered frequent (33%) loss-of-function alterations preferentially targeting the CIC long isoform, which were overlooked by previous exome-centric studies of various cancer types. Long but not short isoform-specific inactivation of Cic selectively increased CD4+CD25+Foxp3+ T cells in vivo. We also found recurrent (13%) 3'-truncations of REL, which induce transcriptional upregulation and generate gain-of-function proteins. More importantly, REL truncations are also common in diffuse large B-cell lymphoma, especially in germinal center B-cell-like subtype (12%). In the non-coding genome, we identified recurrent mutations in regulatory elements, particularly splice sites, of several driver genes. In addition, we characterized the different mutational processes operative in clustered hypermutation sites within and outside immunoglobulin/T-cell receptor genes and identified the mutational enrichment at the binding sites of host and viral transcription factors, suggesting their activities in ATL. By combining the analyses for coding and noncoding mutations, structural variations, and copy number alterations, we discovered 56 recurrently altered driver genes, including 11 novel ones. Finally, ATL cases were classified into 2 molecular groups with distinct clinical and genetic characteristics based on the driver alteration profile. Our findings not only help to improve diagnostic and therapeutic strategies in ATL, but also provide insights into T-cell biology and have implications for genome-wide cancer driver discovery.

Identification of TCR repertoires in functionally competent cytotoxic T cells cross-reactive to SARS-CoV-2.

SARS-CoV-2-specific CD8+ T cells are scarce but detectable in unexposed healthy donors (UHDs). It remains unclear whether pre-existing human coronavirus (HCoV)-specific CD8+ T cells are converted to functionally competent T cells cross-reactive to SARS-CoV-2. Here, we identified the HLA-A24-high binding, immunodominant epitopes in SARS-CoV-2 spike region that can be recognized by seasonal coronavirus-specific CD8+ T cells from HLA-A24+ UHDs. Cross-reactive CD8+ T cells were clearly reduced in patients with hematological malignancy, who are usually immunosuppressed, compared to those in UHDs. Furthermore, we showed that CD8+ T cells in response to a selected dominant epitope display multifunctionality and cross-functionality across HCoVs in HLA-A24+ donors. Cross-reactivity of T-cell receptors isolated from them exhibited selective diversity at the single-cell level. Taken together, when stimulated well by immunodominant epitopes, selective pre-existing CD8+ T cells with high functional avidity may be cross-reactive against SARS-CoV-2.

Efficacy of Intravenous Itraconazole Versus Liposomal Amphotericin B as Empirical Antifungal Therapy in Hematological Malignancy with Persistent Fever and Neutropenia: Study Protocol for a Multicenter, Prospective, Randomized Non-inferiority Trial.

Febrile neutropenia, a serious complication that can occur during the treatment of hematological malignancies, can sometimes be fatal owing to fungal infection. Prospective randomized trials indicated the utility of liposomal amphotericin B or caspofungin as an empirical antifungal therapy. Itraconazole, a broad-spectrum tri azole antifungal agent, is poorly absorbed in the intestines after oral absorption and makes it difficult to achieve a stable serum drug concentration. Therefore, an intravenous formulation might offer a potentially safer and more effective alternative. To compare the efficacy and safety of empirical antifungal therapy, patients will be randomly assigned to either the liposomal amphotericin B 3.0 mg/kg once daily group or the intravenous itraconazole 200 mg dose group with five stratification factors (disease risk, previous antifungal prophylaxis, age, sex, and institute). The primary endpoint will be overall favorable response, comprising five secondary endpoints: successful treatment of baseline infection by the end of the treatment; absence of breakthrough infection; no discontinuation of the antifungal treatment due to drug-related toxicity; fever resolution during neutropenia; and 7-day survival after termination of the antifungal treatment. The target sample size of 850 subjects is sufficient to prove the non inferiority of itraconazole compared with liposomal amphotericin B, with a non-inferiority margin of 10%, one sided significance level of 5%, and power of 90%.

Gilteritinib versus chemotherapy in Japanese patients with FLT3-mutated relapsed/refractory acute myeloid leukemia.

BACKGROUND: Until recently, no effective targeted therapies for FLT3-mutated (FLT3mut+) relapsed/refractory (R/R) acute myeloid leukemia (AML) were available in Japan. The FLT3 inhibitor, gilteritinib, was approved in Japan for patients with FLT3mut+ R/R AML based on the phase 3 ADMIRAL trial, which demonstrated the superiority of gilteritinib over salvage chemotherapy (SC) with respect to overall survival (OS; median OS, 9.3 vs 5.6 months, respectively; hazard ratio, 0.64 [95% confidence interval 0.49, 0.83]; P < 0.001). METHODS: We evaluated the Japanese subgroup (n = 48) of the ADMIRAL trial, which included 33 patients randomized to 120-mg/day gilteritinib and 15 randomized to SC. RESULTS: Median OS was 14.3 months in the gilteritinib arm and 9.6 months in the SC arm. The complete remission/complete remission with partial hematologic recovery rate was higher in the gilteritinib arm (48.5%) than in the SC arm (13.3%). After adjustment for drug exposure, fewer adverse events (AEs) occurred in the gilteritinib arm than in the SC arm. Common grade ≥ 3 AEs related to gilteritinib were febrile neutropenia (36%), decreased platelet count (27%), and anemia (24%). CONCLUSION: Findings in Japanese patients are consistent with those of the overall ADMIRAL study population.

Feasibility of an intensified myeloablative conditioning regimen consisting of busulfan, fludarabine, cytarabine, and total body irradiation before single cord blood transplantation in elderly patients.

The optimal conditioning regimen for stem cell transplantation in elderly patients remains to be established. We developed a novel preparative regimen using fludarabine 180 mg/m2, intravenous busulfan 12.8 mg/m2, cytarabine 8 g/m2, and 4-Gy total body irradiation before cord blood transplantation (CBT) in patients older than 55 years with various hematological malignancies. All but one patient received graft-versus-host disease (GVHD) prophylaxis consisting of cyclosporine (CsA) and short-term methotrexate (sMTX). Thirty-three patients were included in this study, with a median age of 64 years (range 56-70). The disease risk index was high or very high in 67% of patients, and 73% had a disease status other than complete remission. The probabilities of overall survival and disease-free survival at 3 years were 60 and 57%, respectively. The cumulative incidences of relapse and non-relapse mortality at 3 years were 18 and 25%, respectively. Regimen-related toxicities were generally tolerable. Disease-free survivors (n = 20) stopped immunosuppressants at a median of 7.4 months (range 2.6-25.0), in all cases by the time of the last follow-up. In conclusion, this highly myeloablative conditioning regimen resulted in a high probability of disease-free, GVHD-free, immunosuppressant-free survival after single CBT.(190 words).

A multicenter non-randomized, uncontrolled single arm trial for evaluation of the efficacy and the safety of the treatment with favipiravir for patients with severe fever with thrombocytopenia syndrome.

Severe fever with thrombocytopenia syndrome (SFTS) is a bunyavirus infection with high mortality. Favipiravir has shown effectiveness in preventing and treating SFTS virus (SFTSV) infection in animal models. A multicenter non-randomized, uncontrolled single arm trial was conducted to collect data on the safety and the effectiveness of favipiravir in treatment of SFTS patients. All participants received favipiravir orally (first-day loading dose of 1800 mg twice a day followed by 800 mg twice a day for 7-14 days in total). SFTSV RT-PCR and biochemistry tests were performed at designated time points. Outcomes were 28-day mortality, clinical improvement, viral load evolution, and adverse events (AEs). Twenty-six patients were enrolled, of whom 23 were analyzed. Four of these 23 patients died of multi-organ failure within one week (28-day mortality rate: 17.3%). Oral favipiravir was well tolerated in the surviving patients. AEs (abnormal hepatic function and insomnia) occurred in about 20% of the patients. Clinical symptoms improved in all patients who survived from a median of day 2 to day10. SFTSV RNA levels in the patients who died were significantly higher than those in the survivors (p = 0.0029). No viral genomes were detectable in the surviving patients a median of 8 days after favipiravir administration. The 28-day mortality rate in this study was lower than those of the previous studies in Japan. The high frequency of hepatic dysfunction as an AE was observed. However, it was unclear whether this was merely a side effect of favipiravir, because liver disorders are commonly seen in SFTS patients. The results of this trial support the effectiveness of favipiravir for patients with SFTS.