Spacer Length Modification Facilitates Discrimination between Normal and Neoplastic Cells and Provides Clinically Relevant CD37 CAR T Cells.

Despite the remarkable initial efficacy of CD19 chimeric Ag receptor T (CAR-T) cell therapy, a high incidence of relapse has been observed. To further increase treatment efficacy and reduce the rate of escape of Ag-negative cells, we need to develop CAR-T cells that target other Ags. Given its restricted expression pattern, CD37 was considered a preferred novel target for immunotherapy in hematopoietic malignancies. Therefore, we designed a CD37-targeting CAR-T (CD37CAR-T) using the single-chain variable fragment of a humanized anti-CD37 Ab, transmembrane and intracellular domains of CD28, and CD3ζ signaling domains. High levels of CD37 expression were confirmed in B cells from human peripheral blood and bone marrow B cell precursors at late developmental stages; by contrast, more limited expression of CD37 was observed in early precursor B cells. Furthermore, we found that human CD37CAR-T cells with longer spacer lengths exhibited high gene transduction efficacy but reduced capacity to proliferate; this may be due to overactivation and fratricide. Spacer length optimization resulted in a modest transduction efficiency together with robust capacity to proliferate. CD37CAR-T cells with optimized spacer length efficiently targeted various CD37+ human tumor cell lines but had no impact on normal leukocytes both in vitro and in vivo. CD37CAR-T cells effectively eradicated Raji cells in xenograft model. Collectively, these results suggested that spacer-optimized CD37CAR-T cells could target CD37-high neoplastic B cells both in vitro and in vivo, with only limited interactions with their normal leukocyte lineages, thereby providing an additional promising therapeutic intervention for patients with B cell malignancies.

Predictive value of surveillance cultures for bacteremia caused by extended-spectrum beta-lactamase (ESBL)-producing Enterobacterales among patients with hematological diseases.

PURPOSE: Due to the increasing prevalence of extended-spectrum beta-lactamase (ESBL)-producing Enterobacterales, empirical therapies with cefepime or piperacillin/tazobactam for hematology patients with febrile neutropenia have become ineffective. Carbapenems should be administered as soon as possible in such patients with ESBL bacteremia. If the surveillance culture results are consistent with the blood culture findings, the time to adequate treatment initiation can be shortened. METHODS: All consecutive patients with Enterobacterales bacteraemia who were admitted from January 2013 to December 2018 at the hematology wards were enrolled in this study. Surveillance rectal swab and blood culture results were compared. RESULTS: In total, 67 patients with Enterobacterales bacteremia underwent surveillance culture prior to the onset of infection. Regarding the presence or absence of ESBL-producing Enterobacterales, 64 (95.5%) patients had surveillance results concordant with blood culture results. The positive predictive value of surveillance culture for bacteremia caused by ESBL-producing Enterobacterales was 95.0%. Moreover, the negative predictive value of surveillance culture for bacteremia caused by non-ESBL-producing Enterobacterales was 95.7%. CONCLUSION: The concordance rate between the surveillance rectal swab and blood cultures was highly acceptable. Surveillance rectal swab cultures are useful for identifying patients at high risk for ESBL bacteremia.

Composite CD79A/CD40 co-stimulatory endodomain enhances CD19CAR-T cell proliferation and survival.

Adoptively transferred CD19 chimeric antigen receptor (CAR) T cells have led to impressive clinical outcomes in B cell malignancies. Beyond induction of remission, the persistence of CAR-T cells is required to prevent relapse and provide long-term disease control. To improve CAR-T cell function and persistence, we developed a composite co-stimulatory domain of a B cell signaling moiety, CD79A/CD40, to induce a nuclear translocating signal, NF-κB, to synergize with other T cell signals and improve CAR-T cell function. CD79A/CD40 incorporating CD19CAR-T cells (CD19.79a.40z) exhibited higher NF-κB and p38 activity upon CD19 antigen exposure compared with the CD28 or 4-1BB incorporating CD19CAR-T cells (CD19.28z and CD19.BBz). Notably, we found that CD19.79a.40z CAR-T cells continued to suppress CD19+ target cells throughout the co-culture assay, whereas a tendency for tumor growth was observed with CD19.28z CAR-T cells. Moreover, CD19.79a.40z CAR-T cells exhibited robust T cell proliferation after culturing with CD19+ target cells, regardless of exogenous interleukin-2. In terms of in vivo efficiency, CD19.79a.40z demonstrated superior anti-tumor activity and in vivo CAR-T cell proliferation compared with CD19.28z and CD19.BBz CD19CAR-T cells in Raji-inoculated mice. Our data demonstrate that the CD79A/CD40 co-stimulatory domain endows CAR-T cells with enhanced proliferative capacity and improved anti-tumor efficacy in a murine model.

A multicenter phase II study of intrabone single-unit cord blood transplantation without antithymocyte globulin.

To overcome the delayed or failed engraftment after unrelated cord blood transplantation (CBT), we conducted a multicenter phase II study of intrabone single-unit CBT without antithymocyte globulin (ATG) for adult patients with hematological malignancies (UMIN-CTR, UMIN000020997). Sixty-four patients received an intrabone injection of unwashed (n = 61) or washed (n = 3) cord blood after local anesthesia. All injection-related adverse events were mild and resolved spontaneously. Sixty-two patients were evaluable for the efficacy of intrabone CBT of serological HLA-A, -B, and -DR ≥ 4/6 matched cord blood with a median number of 2.57 × 107/kg cryopreserved total nucleated cells. The probability of survival with neutrophil engraftment on day 28 was 77.4% (95% confidence interval, 67.0-85.8%), which exceeded the threshold value. The cumulative incidences of neutrophils ≥ 0.5 × 109/L on day 60 was 80.6% (68.2-88.6%), with a median time to recovery of 21 days after transplantation. The cumulative incidences of platelets ≥ 20 × 109/L and platelets ≥ 50 × 109/L on day 100 were 75.8% (62.6-84.9%) and 72.6% (59.4-82.1%), respectively, with median time to platelets ≥ 20 × 109/L and platelets ≥ 50 × 109/L of 38 and 45 days after transplantation, respectively. The cumulative incidences of grade II-IV and III-IV acute graft-versus-host disease were 29.0% and 6.5%, respectively. All responded to steroid therapy, and secondary treatments were not required. The present study suggests the efficacy of intrabone single-unit CBT without ATG in terms of early engraftment and controllable acute graft-versus-host disease.

[Bacillus cereus bacteremia in patients with hematological disorders].

Bacillus cereus bacteremia is an infectious disease that may sometimes be fatal with a rapid clinical course. We performed a retrospective analysis on 12 patients with Bacillus cereus bacteremia recruited from January 2010 to March 2015. The primary diseases were acute leukemia (n=5), myelodysplastic syndromes (n=3), malignant lymphoma (n=3), and hemophagocytic syndrome (n=1). Neutrophil count at the onset of this bacteremia was less than 500 cells/µl in 9 patients. At the onset of bacteremia, we observed neurological symptoms (n=7), gastrointestinal symptoms (n=6), and findings suspected of infection at the venous catheter insertion site (n=6). Vancomycin was administered to all the patients; 10 patients showed improvement whereas 2 died early after allogeneic hematopoietic stem cell transplantation owing to bacteremia. Three patients had sequelae of central nervous system disorders. Neurological and gastrointestinal symptoms with fever may be predictors for this bacteremia, and early administration of appropriate antibacterial drugs may improve the prognosis. Future research should be aimed toward the identification of the clinical features of poor prognosis and establishment of remedies for Bacillus cereus bacteremia.

The stability of initial tacrolimus concentration following allogeneic hematopoietic stem cell transplantation reduces the risk of acute GVHD.

BACKGROUND: Early tacrolimus (TAC) concentrations correlate with the risk of acute graft-versus-host disease (aGVHD); however, whether the variability of early TAC concentrations after allo-HSCT governs the occurrence of aGVHD remains unknown. Here, we evaluate the correlation between the intrapatient variability (IPV) of initial TAC concentrations and the development of aGVHD. METHODS: We retrospectively assessed 202 patients who underwent allo-HSCT and received standard GVHD prophylaxis by continuous intravenous (iv) infusion of TAC and iv methotrexate. IPV was calculated by using the % coefficient of variation in the initial 4 weeks. RESULTS: With median follow-up duration of 20.7 months, 24 patients were diagnosed with grades II-IV aGVHD. Overall survival (OS) and relapse at 12 months after allo-HSCT were 70.6% (95% confidence interval [CI], 63.7%-76.4%) and 18.9% (95% CI, 13.0%-24.4%), respectively. When IPV was categorized into two groups (high: ≥9.5%; low: <9.5%), the cumulative incidence of grades II-IV aGVHD was greater in the IPV-high group at week 3 (odds ratio: 4.15; 95% CI, 1.37%-12.6%, P = .01). No significant differences were observed in OS and relapse between the two groups. CONCLUSION: We concluded that adjusting early TAC concentration stable may reduce aGVHD after allo-HSCT without affecting the relapse rate.

[Leukemic pulmonary infiltration diagnosed by sputum Giemsa-staining].

A 54-year-old man with acute myeloid leukemia (AML) underwent allogeneic bone marrow transplantation from a human leukocyte antigen-matched unrelated donor in nonremission status. Bone marrow aspiration performed on day 14 showed that the patient had achieved complete remission; however, he relapsed on day 28. The patient developed a wet cough, and chest computed tomography performed on day 27 revealed pneumonia. Because pneumonia developed along with the leukemic relapse, we suspected that it was due to pulmonary leukemic infiltration (PLI). Giemsa-stained sputum showed some blast cells and fluorescence in situ hybridization indicated that the patient had monosomy 7, which was also detected in bone marrow blasts. Though we prescribed hydroxycarbamide and decreased tacrolimus rapidly, AML progressed and led to the patient's death on day 45. Histopathological findings of the autopsy performed the next day showed diffuse alveolar damage in both lungs. The blast cells were packed in blood vessels of alveolar septa and were also seen in alveoli. PLI was diagnosed pathologically. In conclusion, our case demonstrates that Giemsa stain of sputum is useful in quick diagnosis of PLI without invasive examination.

Quantitative Assessment of T Cell Clonotypes in Human Acute Graft-versus-Host Disease Tissues.

Owing to the difficulty in isolating T cells from human biopsy samples, the characteristics of T cells that are infiltratinghuman acute graft-versus-host disease (GVHD) tissues remain largely uninvestigated. In the present study, TCR-ß deep sequencing of various GVHD tissue samples and concurrent peripheral blood obtained from transplant recipients was performed in combination with functional assays of tissue-infiltrating T cell clones. The T cell repertoire was more skewed in GVHD tissues than in the peripheral blood. The frequent clonotypes differed from tissue to tissue in the same patient, and the frequent clonotypes in the same tissue differed from patient to patient. Two T cell clones were successfully isolated from GVHD skin of a patient. In a cytotoxicity assay, both Tcell clones lysed patient peripheral blood mononuclear cells, but not donor-derived Epstein-Barr virus-transformed lymphoblastoid cells. Their clonotypes were identical to the most and second most frequent T cell clonotypes in the original GVHD skin and accounted for almost all of the skin-infiltrating T cells. These results suggest that human acute GVHD may result from only a few different alloreactive cytotoxic T cell clones, which differ from tissue to tissue and from patient to patient. The characterization of T cells infiltrating human GVHD tissues should be further investigated.

Higher Peak Tacrolimus Concentrations after Allogeneic Hematopoietic Stem Cell Transplantation Increase the Risk of Endothelial Cell Damage Complications.

Noninfectious transplantation-related complications (TRCs) such as graft-versus-host disease (GVHD) and endothelial cell damage (TRC-EC) are critical after allogeneic hematopoietic stem cell transplantation. Tacrolimus (TAC) is used to control GVHD. Hypertension and renal failure are common adverse events after TAC treatment. Higher blood concentrations of TAC would be expected to reduce the risk of GVHD but may increase TRC-EC. TRC-EC often develops in patients with GVHD; thus, it is difficult to clinically determine the proper intensity of immunosuppression. We therefore evaluated the impact of weekly mean/peak TAC blood concentrations (PTCs) on TRC-EC occurrence and prognosis. Patients (N = 295) who received TAC as a GVHD prophylaxis at our institute from 2009 to 2016 were eligible for this retrospective study. Forty-three patients were diagnosed with TRC-EC: 8 with sinusoidal obstructive syndrome, 28 with transplant-associated microangiopathy, and 7 with idiopathic pneumonia syndrome. The cumulative incidence of TRC-EC at 12 months was 13.8% (95% confidence interval [CI] 10.1% to 18.1%). After multivariate analysis high PTCs during days 22 to 28 (hazard ratio [HR] 2.47; 95% CI, 1.37 to 4.45; P < .01) and grades II to IV acute GVHD (HR, 5.61; 95% CI, 2.99 to 10.53; P < .01) were associated with TRC-EC occurrence. The probability of overall survival (OS) at 12 months was 67.7% (95% CI, 61.7% to 73.0%). After multivariate analysis TRC-EC diagnosis (HR, 2.47, 95% CI, 1.59 to 3.83; P < .01) and high-risk disease (HR, 1.75; 95% CI, 1.17 to 2.61; P < .01) were significantly associated with poor OS. In conclusion, higher PTC during days 22 to 28 increased the risk of TRC-EC. TRC-EC development was associated with poor OS.

[Mesenchymal stem cell therapy in hematopoietic stem cell transplantation].

Mesenchymal stem cells (MSCs) have received considerable attention in allogeneic hematopoietic cell transplantation because of their abilities to modulate immune responses and promote hematopoiesis. Because MSCs are capable of producing several cytokines and growth factors, they have been widely used in the treatment of graft-versus-host disease (GVHD). A number of clinical trials have demonstrated the safety and efficacy of MSC therapy for acute GVHD. Moreover, in Japan, allogeneic bone marrow-derived MSC product, TEMCELL®, was approved as a regenerative medicine for acute GVHD. Besides, MSCs can also produce bone marrow stroma and promote hematopoiesis, the co-transplantation of hematopoietic stem cells and MSCs have been efficiently performed in cord blood transplantation and HLA-mismatched transplantation to enhance engraftment and prevent GVHD. In this review, we provide an overview of clinical trials using MSCs in allogeneic hematopoietic cell transplantation and discuss the possibilities and optimization of MSC therapy.

Phase II study of intrabone single unit cord blood transplantation for hematological malignancies.

The outcomes of cord blood transplantation with non-irradiated reduced-intensity conditioning for hematological malignancies need to be improved because of graft failure and delayed engraftment. Intrabone infusion of cord blood cells has the potential to resolve the problems. In this phase II study, 21 adult patients with hematological malignancy received intrabone transplantation of serological HLA-A, B, and DR ≥4/6 matched single cord blood with a median number of cryopreserved total nucleated cells of 2.7 × 107 /kg (range, 2.0-4.9 × 107 /kg) following non-irradiated fludarabine-based reduced-intensity conditioning. Short-term methotrexate and tacrolimus were given as graft-versus-host disease prophylaxis, and granulocyte colony-stimulating factor was given after transplantation. No severe adverse events related to intrabone injection were observed. The cumulative incidences of neutrophils ≥0.5 × 109 /L, reticulocytes ≥1%, and platelets ≥20 × 109 /L recoveries were 76.2%, 71.4%, and 76.2%, respectively, with median time to recoveries of 17, 28, and 32 days after transplantation, respectively. The probability of survival with neutrophil engraftment on day 60 was 71.4%, and overall survival at 1 year after transplantation was 52.4%. The incidences of grade II-IV and III-IV acute graft-versus-host disease were 44% and 19%, respectively, with no cases of chronic graft-versus-host disease. The present study showed the safety of direct intrabone infusion of cord blood. Further analysis is required to confirm the efficacy of intrabone single cord blood transplantation with non-irradiated reduced-intensity conditioning for adult patients with hematological malignancy. This study was registered with UMIN-CTR, number 000000865.

Target antigen density governs the efficacy of anti-CD20-CD28-CD3 ζ chimeric antigen receptor-modified effector CD8+ T cells.

The effectiveness of chimeric Ag receptor (CAR)-transduced T (CAR-T) cells has been attributed to supraphysiological signaling through CARs. Second- and later-generation CARs simultaneously transmit costimulatory signals with CD3ζ signals upon ligation, but may lead to severe adverse effects owing to the recognition of minimal Ag expression outside the target tumor. Currently, the threshold target Ag density for CAR-T cell lysis and further activation, including cytokine production, has not yet been investigated in detail. Therefore, we determined the threshold target Ag density required to induce CAR-T cell responses using novel anti-CD20 CAR-T cells with a CD28 intracellular domain and a CD20-transduced CEM cell model. The newly developed CD20CAR-T cells demonstrated Ag-specific lysis and cytokine secretion, which was a reasonable level as a second-generation CAR. For lytic activity, the threshold Ag density was determined to be ∼200 molecules per target cell, whereas the Ag density required for cytokine production of CAR-T cells was ∼10-fold higher, at a few thousand per target cell. CD20CAR-T cells responded efficiently to CD20-downregulated lymphoma and leukemia targets, including rituximab- or ofatumumab-refractory primary chronic lymphocytic leukemia cells. Despite the potential influence of the structure, localization, and binding affinity of the CAR/Ag, the threshold determined may be used for target Ag selection. An Ag density below the threshold may not result in adverse effects, whereas that above the threshold may be sufficient for practical effectiveness. CD20CAR-T cells also demonstrated significant lytic activity against CD20-downregulated tumor cells and may exhibit effectiveness for CD20-positive lymphoid malignancies.

Malignant lymphoma with cardiac involvement.

Malignant lymphoma with cardiac involvement is difficult to diagnose and treatment selection decisions can be challenging, because patients usually present with atypical disease involvement and the incidence is low. Herein, we describe the clinical characteristics and courses of three non-Hodgkin lymphoma patients showing cardiac involvement. All three patients were male, ages 32, 74 and 64 years. All three patients had presented with cardiac involvement mainly in the right heart system. We promptly performed needle biopsies for patients 1 and 3, and open-heart biopsy for patient 2, which showed PMBL for patient 1, DLBCL for patients 2 and 3. Since we were concerned regarding possible transient exacerbation of heart failure or the occurrence of fatal arrhythmia, we chose to start with relatively low dose chemotherapeutic interventions or pre-phase steroid therapy. After one course of chemotherapy or pre-phase steroid therapy, symptoms associated with heart failure almost completely subsided, and we further administered full-dose chemotherapy thereafter, resulting in complete responses in 2 cases. This case series demonstrates that malignant lymphoma with cardiac involvement is a treatable disease, despite widespread involvement. Furthermore, rapid and appropriate diagnostic imaging and biopsy are important when this disease is suspected.

[Clinical Analysis of Combination Chemotherapy Using High Dose Methotrexate, Rituximab, and Vincristine with or without Procarbazine for Elderly Patients with Diffuse Large B-Cell Lymphoma of the Central Nervous System].

We studied the clinical effects of high-dose methotrexate(HD-MTX)combined with rituximab and vincristine in 5 elderly patients, aged 65-83 years, with diffuse large B-cell lymphoma of the central nervous system(DLBCL CNS). Patients aged 65- 71 years were given 3.0 g/m2 of HD-MTX, while patients aged 75-83 years were given 1.5 g/m2 of the drug. All patients showed responses; 1 CR and 1 PR in MTX 3.0 g/m2 group, and 2 CRs and 1 PR in MTX 1.5 g/m2 group.

Asciminib in Patients With CML-CP Previously Treated With ≥ 2 Tyrosine Kinase Inhibitors: 96-Week Results From the Japanese Subgroup Analysis of the ASCEMBL Study.

Asciminib is a first-in-class BCR::ABL1 inhibitor that Specifically Targets the ABL1 Myristoyl Pocket (STAMP). It is approved worldwide and in Japan for chronic myeloid leukemia in chronic phase (CML-CP) with resistance or intolerance to previous tyrosine kinase inhibitor (TKI) therapy. In the Phase 3 ASCEMBL study, patients with CML-CP who received ≥ 2 prior ATP-competitive TKIs were randomized (2:1) to asciminib 40 mg twice-daily or bosutinib 500 mg once-daily. Here, we report the 96-week results of the subgroup analysis of Japanese patients (asciminib, n = 13; bosutinib, n = 3) in the ASCEMBL study. The MMR rate at Week 96 was 46.2% in asciminib-treated patients, increasing from Weeks 24 and 48. Patients who achieved MMR at Week 24 remained in MMR up to the Week 96 cutoff. While a high proportion of patients treated with asciminib remained on treatment at cutoff, none randomized to bosutinib were on treatment at Week 96. Despite the longer duration of exposure to asciminib, its safety and tolerability continued to be favorable with no new or worsening safety findings. Overall, the efficacy and safety outcomes in the Japanese subgroup were comparable with the ASCEMBL global study population, which supports the use of asciminib in Japanese patients with previously treated CML-CP.

Asciminib vs bosutinib in CML patients pretreated with ≥2 tyrosine kinase inhibitors: Results from the Japanese subgroup analysis of ASCEMBL study.

Asciminib, a first-in-class, allosteric inhibitor of BCR-ABL1 that acts by STAMP (Specifically Targeting the ABL Myristoyl Pocket), is a novel therapeutic option for patients with chronic myeloid leukemia (CML). In the global, phase 3, open-label ASCEMBL study in patients with CML in chronic phase (CML-CP) pretreated with ≥2 tyrosine kinase inhibitors (TKIs) (NCT03106779), asciminib (40 mg twice-daily) demonstrated significant superiority over the ATP-competitive TKI bosutinib (500 mg once daily) for the primary endpoint of major molecular response (MMR; BCR::ABL1 transcript levels on the international scale [BCR::ABL1IS ] ≤0.1%) at week 24. Here, we report results from a descriptive subgroup analysis of Japanese patients enrolled in ASCEMBL study (data cut-off: May 25, 2020). Overall, 16 Japanese patients were randomized (asciminib, n = 13; bosutinib, n = 3). At week 24, the MMR rate with asciminib was 30.8% (4/13; 95% confidence interval [CI], 9.09-61.43). BCR::ABL1IS ≤1% and complete cytogenic response (CCyR) at week 24 were 61.5% (8/13 patients) and 50.0% (4/8 patients), respectively. In the bosutinib group, no patient achieved MMR, CCyR, or BCR::ABL1IS ≤1%, but results were limited by the low number of patients. The safety profile of asciminib was comparable to that previously observed in the overall study population. Findings from this Japanese subgroup analysis of the ASCEMBL study support the use of asciminib for the treatment of Japanese patients with CML-CP previously treated with ≥2 TKIs. ClinicalTrials.gov Identifier: NCT03106779.

Antibody response after third dose of COVID-19 mRNA vaccination in allogeneic hematopoietic stem cell transplant recipients is comparable to that in healthy counterparts.

To determine the efficacy of SARS-CoV-2 mRNA vaccination for allogeneic hematopoietic stem cell transplantation (allo-HSCT) recipients, we measured antibody titer serially in 92 allo-HSCT patients. Among the evaluable 87 patients, median age at vaccination was 53 years (range, 18-75). The average time between allo-HSCT and vaccination was 3.3 years (range, 0.5-15.7). One month after the second dose, 70 patients (80.5%) had a positive response, whereas 17 patients (19.5%) had a negative response (< 20 U/mL). Only patients older than 44 years had a negative response. Low IgM level was the only significant predictor of vaccine failure in elderly patients. When antibody response before and after the third vaccination was examined in 47 patients, antibodies increased significantly from a median of 18.3 U/mL to 312.6 U/mL (P < 0.01). The median antibody titer after the third vaccination of healthy individuals (n = 203) was 426.4 U/mL, which was comparable to that of patients (P = 0.2). The antibody titer after the third mRNA vaccination increased even in patients whose first two mRNA vaccinations failed. These findings suggest that allo-HSCT recipients should receive the mRNA vaccine regularly.

Development of quantitative RT-PCR assays for detection of three classes of HHV-6B gene transcripts.

The monitoring of active human herpesvirus 6 (HHV-6) B infection is important for distinguishing between the reactivation and latent state of the virus. The aim of this present study is to develop a quantitative reverse transcription polymerase chain reaction (RT-PCR) assay for diagnosis of active viral infection. Primers and probes for in house quantitative RT-PCR methods were designed to detect the three kinetic classes of HHV-6B mRNAs (U90, U12, U100). Stored PBMCs samples collected from 10 patients with exanthem subitum (primary HHV-6B infection) and 15 hematopoietic stem cell transplant recipients with HHV-6B reactivation were used to evaluate reliability for testing clinical samples. Excellent linearity was obtained with high correlation efficiency between the diluted RNA (1-100 ng/reaction) and C(t) value of each gene transcript. The U90 and U12 gene transcripts were detected in all of the peripheral blood mononuclear cells (PBMCs) samples collected in acute period of primary HHV-6B infection. Only one convalescent PBMCs sample was positive for the U90 gene transcript. Additionally, the reliability of HHV-6B quantitative RT-PCRs for diagnosis of viral reactivation in hematopoietic transplant recipients was evaluated. Relative to virus culture, U90 quantitative RT-PCR demonstrated the highest assay sensitivity, specificity, positive predictive value, and negative predictive value. Thus, this method could be a rapid and lower cost alternative to virus culture, which is difficult to perform generally, for identifying active HHV-6B infection.

Downregulation of HLA class II is associated with relapse after allogeneic stem cell transplantation and alters recognition by antigen-specific T cells.

Genomic deletion of donor-patient-mismatched HLA alleles in leukemic cells is a major cause of relapse after allogeneic hematopoietic stem cell transplantation (HSCT). Mismatched HLA is frequently lost as an individual allele or a whole region in HLA-class I, however, it is downregulated in HLA-class II. We hypothesized that there might be a difference in T cell recognition capacity against epitopes associated with HLA-class I and HLA-class II and consequently such allogeneic immune pressure induced HLA alterations in leukemic cells. To investigate this, we conducted in vitro experiments with T cell receptor-transduced T (TCR-T) cells. The cytotoxic activity of NY-ESO-1-specific TCR-T cells exhibited similarly against K562 cells with low HLA-A*02:01 expression. However, we demonstrated that the cytokine production against low HLA-DPB1*05:01 expression line decreased gradually from the HLA expression level approximately 2-log lower than normal expressors. Using sort-purified leukemia cells before and after HSCT, we applied the next-generation sequencing, and revealed that there were several marked downregulations of HLA-class II alleles which demonstrated consistently low expression from pre-transplantation. The marked downregulation of HLA-class II may lead to decreased antigen recognition ability of antigen-specific T cells and may be one of immune evasion mechanism associated with HLA-class II downregulation.