Epidemiological characteristics and outcome of viral respiratory tract infections in the first year after allogeneic hematopoietic cell transplantation

Adverse outcomes of viral respiratory tract infections (RTI) have been reported in recipients of allogeneic hematopoietic cell transplantation. Using a laboratory-developed multiparameter PCR in a consecutive series of 242 patients, we found the highest incidence of viral RTI in the pre-engraftment phase. The occurrence of multiple episodes of viral RTI or viral pneumonia was significantly associated with a higher hazard of non-relapse mortality in the first year after transplantation. We observed a 90-day mortality of 19.7% after viral RTI, which was significantly different between patient groups stratified according to the ISI score.

Alternative genetic alterations of MYC, BCL2, and/or BCL6 in high-grade B-cell lymphoma (HGBL) and diffuse large B-cell lymphoma (DLBCL): Can we identify different prognostic subgroups?

High-grade B-cell lymphoma (HGBL)/diffuse large B-cell lymphoma (DLBCL) with rearrangements (R) in MYC and BCL2 and/or BCL6 are correlated with poor prognosis. Little is known about the impact of other genetic alterations (gain (G) or amplification (A)) of these genes. The aim of the study was to investigate whether we can identify new prognostic subgroups. Fluorescence in situ hybridization (FISH) results from 169 HGBL/DLBCL were retrospectively categorized into: (1) concurrent MYC-R and BCL2-R and/or BCL6-R-samples with MYC-R and BCL2-R (+/- BCL6-R); n = 21, and HGBL/DLBCL with MYC-R and BCL6-R; n = 11; (2) concurrent R and G/A in MYC and BCL2 and/or BCL6 called "alternative HGBL/DLBCL"-samples with (n = 16) or without (n = 6) BCL2 involvement; (3) BCL2 and/or BCL6 alterations without MYC involvement (n = 35); (4) concurrent G/A in MYC and BCL2 and/or BCL6 without R (n = 25); and (5) "No alterations" (n = 55). Patients with HGBL/DLBCL-MYC/BCL2 and "alternative" HGBL/DLBCL (with BCL2 involvement) had significantly worse survival rates compared to the "no alterations" group. G/A of these genes in the absence of rearrangements did not show any prognostic significance. HGBL/DLBCL with MYC-R and BCL6-R without BCL2 involvement showed a better survival rate compared to HGBL/DLBCL-MYC/BCL2. According to immunohistochemistry, "double/triple" expression (DEL/TEL) did not show a significantly worse outcome compared to absent DEL/TEL. This study highlights the continued value of FISH assessment of MYC, BCL2, and BCL6 in the initial evaluation of HGBL/DLBCL with different survival rates between several genetic subgroups.

Breast implant associated EBV-positive Diffuse Large B-cell lymphoma: an underrecognized entity?

Breast-implant associated (BIA) lymphoma is an infrequent type of cancer occurring in the fluid and fibrous capsule around a textured breast implant. Recently, both the 2022 WHO 5th edition classification of Haematological tumours (WHO HAEM5) and 2022 International Consensus Classification of Mature Lymphoid Neoplasms (22ICC), recognized breast implant-associated Anaplastic Large Cell Lymphoma (BIA-ALCL) as a definitive entity, defined as a mature CD30-positive T-cell lymphoma, confined by a fibrous capsule, in a breast implant setting. Only few B-cell lymphomas have been reported in the literature to be associated with breast implants. Here we report two EBV-positive Diffuse Large B-cell lymphomas (EBV + DLBCL) in relation to a breast implant, both expressing CD30 as well as EBV latency type 3. Both lesions were considered as DLBCL associated with chronic inflammation (CI-DLBCL), but one presented as a 7 cm solid mass, while the other presented as a fibrin-associated DLBCL (FA-DLBCL) in an HIV patient. Clinically, both are in complete remission 6 months or longer after capsulectomy and graft removal, without additional chemotherapy.Such cases, characterized by large CD30-positive cells, can easily be misdiagnosed as BIA-ALCL if the cell of origin is not further established. Therefore, a diagnostic panel including lineage-specific B-and T-cell markers and EBER in situ hybridization is essential to recognize this rare entity, to understand lymphomagenesis, to predict outcome and to define clinical approach.

Diagnostic utility of the lymphoid screening tube supplemented with TRBC1 for the assessment of T-cell clonality

INTRODUCTION

Flow cytometric panels for the investigation of lymphoproliferative disorders, such as the EuroFlow Lymphoid Screening Tube (LST), often fail to demonstrate T-cell clonality, as a suitable clonality marker was unavailable until recently. Aim of this study was to evaluate the added value of supplementing TRBC1, a flow cytometric T-cell clonality marker, to the LST.

METHODS

Flow cytometric analysis was performed on 830 routine samples referred to our lab for suspicion of hematological malignancy. T-cells with monotypic TRBC1-expression were additionally characterized with a 12-color T-cell tube and molecular T-cell receptor gamma gene rearrangement (TRG).

RESULTS

LST analysis revealed 97 (11.7%) samples with the presence of a monotypic T-cell population according to TRBC1, including 21 (2.5%) "high-count" (≥500 cells/μL blood or ≥15% of lymphocytes) and 76 (9.2%) "low-count" (<500 cells/μL blood or <15% of lymphocytes) populations. Clinical symptoms indicative for T-CLPD could be correlated to 11/21 "high-count" and 17/76 "low-count" monotypic T-cell populations. Molecular TRG analysis demonstrated a monoclonal result in 76% (16/21) of "high-count" samples and in 64% (42/66; 10 samples not tested) of "low-count" samples, but also in 9/20 samples with polytypic TRBC1 results.

CONCLUSION

Analysis of an LST tube supplemented with TRBC1 led to the detection of a high number of monotypic T-cell populations. The detection of numerous small monotypic T-cell populations raises the question of their clinical significance. A possible flowchart for assessment of these populations, based on the available literature, is proposed. Molecular TRG analysis is complementary and cannot be omitted from T-cell clonality assessment.

Infectious diarrhea after allogeneic hematopoietic cell transplantation assessed by a multiplex polymerase chain reaction assay

OBJECTIVES

To determine the incidence of infectious diarrhea after allogeneic hematopoietic cell transplantation (HCT) using a multiplex polymerase chain reaction assay and assess risk factors for developing infectious diarrhea.

METHODS

This was a single-center retrospective study of 140 consecutive allogeneic HCT recipients. Infectious diarrhea was assessed using a laboratory-developed multiplex polymerase chain reaction the first year after transplantation.

RESULTS

The incidence rate of infectious diarrhea episodes was 47 per 100 person-years, with the highest rate observed in the pre-engraftment phase. Most episodes were seen as nosocomial infections (38%) and most affected patients (82%) had only one episode of infectious diarrhea. The cumulative incidence of at least one episode of infectious diarrhea was 32% after 1 year. Nonrelapse mortality was higher in transplant recipients with at least one episode of infectious diarrhea (hazard ratio (HR) 2.02, 95% CI = 1.07-3.80). The most frequently observed pathogens were Clostridium difficile, adenovirus, Enteropathogenic Escherichia coli, and Campylobacter jejuni. Patients with acute lower gastrointestinal graft-vs-host disease stage 3 or 4 (HR 3.68, 95% CI = 1.57-8.63) conferred a higher risk for a first infectious diarrhea episode.

CONCLUSION

Infectious diarrhea after allogeneic HCT was seen in about one-third of the patients, mostly as nosocomial infection in the pre-engraftment phase.

First-line treatment (Tx) with subcutaneous (SC) epcoritamab (epco) + R-CHOP in patients (pts) with high-risk diffuse large B-cell lymphoma (DLBCL): Phase 1/2 data update

7523

Background: Outcomes of pts with newly diagnosed DLBCL with high/poor risk according to the revised International Prognostic Index (IPI) treated with immunochemotherapy (IC) remain suboptimal, with a 4-year survival rate of 55% (Sehn et al, Blood 2007). SC epco is a well-tolerated bispecific antibody with single-agent activity in the relapsed/refractory (R/R) aggressive B-cell NHL setting. The mechanism of action and safety profile of epco are distinct from IC, and epco is well suited for use in combinations and in earlier lines of therapy. Addition of a novel agent to standard of care IC may overcome the adverse prognosis of high-risk pts. Presented here are updated results of epco + rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) in previously untreated DLBCL pts with IPI 3–5 (EPCORE NHL-2 arm 1; NCT04663347). Methods: Adults with previously untreated CD20+ DLBCL and IPI ≥3 received SC epco (every week, cycle [C] 1–4; every 3 weeks, C5–6) + R-CHOP for 6 cycles (21 d) followed by single-agent epco every 4 weeks up to 1 y (in cycles of 28 d). To mitigate CRS, epco step-up dosing and corticosteroid prophylaxis were required. Response was assessed by PET-CT with contrast per Lugano 2014 criteria. Results: As of Dec 1, 2021, 33 pts (median age, 66 y; range, 19–82) received epco + R-CHOP (epco 24 mg, n = 4; 48 mg, n = 29). Median time from diagnosis to first dose was 25 d (range, 5–70). All pts had IPI ≥3 and ≥24% had double- or triple-hit DLBCL. Median follow-up was 3 mo (range, 0–9.7); median number of total cycles initiated was 5 (1–13). Overall, 94% of pts (31/33) remained on Tx. Tx-emergent adverse events (TEAEs) in ≥30% of pts were neutropenia (48%; febrile neutropenia in 9% of all pts), CRS (45%), infections (42%), anemia (39%), injection-site reactions (36%), nausea (33%), constipation (30%), and pyrexia (30%). No TEAEs led to epco discontinuation. AEs of special interest included CRS (42% grade [G] 1/2, 3% G3) and ICANS (3% G2); 1 pt had tumor lysis syndrome (3% G3). Most CRS events occurred in C1 and resolved after a median of 2 days (1–11); 4 pts with CRS received tocilizumab. No fatal TEAEs were reported. In efficacy-evaluable pts, the overall response rate (ORR) was 96% (24/25); 68% (17/25) had complete metabolic response (CMR). For the 10 pts who received 6 cycles of R-CHOP and had a subsequent response assessment, the ORR and CMR rate were 100% and 90%, respectively. As of the data cutoff, all of these 10 pts remained in response, with the longest duration of response 7.1+ mo and ongoing. Updated data will be presented. Conclusions: Epco is the first SC bispecific antibody assessed in combination with standard of care in previously untreated DLBCL. The safety profile of epco + R-CHOP is manageable. CRS events were mostly of low grade and did not lead to Tx discontinuation. ORR and CMR rate were high with no relapses as of the data cutoff date. Clinical trial information: NCT04663347.

Phase 3 randomized study of loncastuximab tesirine in combination with rituximab (Lonca-R) versus immunochemotherapy in patients with R/R DLBCL (LOTIS-5)

TPS7591

Background: Patients (pts) with refractory or relapsed (R/R) diffuse large B-cell lymphoma (DLBCL) have poor outcomes with standard treatment. Loncastuximab tesirine (loncastuximab tesirine-lpyl; Lonca), an antibody-drug conjugate (ADC) comprising a humanized anti-CD19 monoclonal antibody conjugated to a pyrrolobenzodiazepine dimer toxin, is approved in R/R DLBCL based on data from the phase 2 LOTIS-2 trial (Caimi et al. Lancet Oncol 2021). Rituximab (R) is part of standard immunochemotherapy for DLBCL, both as frontline therapy and in subsequent treatments. Preclinical evidence suggests that the addition of rituximab to anti-CD19 ADC therapy may result in prolonged tumor control (Ryan et al. Blood 2017). LOTIS-5 aims to evaluate Lonca-R vs. standard immunochemotherapy of R + gemcitabine + oxaliplatin (R-GemOx) in pts with R/R DLBCL. Methods: This is a phase 3 randomized open-label, two-part, two-arm multicenter study of Lonca-R in pts with R/R DLBCL (NCT04384484). A review of safety data from the nonrandomized safety run-in (Part 1), comparing the safety of Lonca-R to previous Lonca safety data, was completed in January 2022. The trial is now continuing to the randomized phase (Part 2). In Part 2, approximately 330 pts will be randomized 1:1 to receive Lonca-R or R-GemOx. The primary objective of the study is to evaluate the efficacy of Lonca-R versus R-GemOx. The primary endpoint is progression-free survival by independent central review (ICR). Secondary endpoints include overall survival, overall response rate (by ICR using 2014 Lugano classification), complete response rate by ICR, duration of response by ICR, frequency and severity of adverse events, changes from baseline in safety laboratory and clinical variables, concentration and pharmacokinetic parameters of Lonca (conjugated and total antibody and unconjugated warhead), immunogenicity, and changes in patient-reported outcomes. The time to event endpoints will be analyzed based on the intent-to-treat population using a stratified log-rank test. The dosing regimen for Lonca-R: Lonca at 0.15 mg/kg + rituximab at 375 mg/m2 every 3 weeks (Q3W) for 2 cycles and then Lonca at 0.075 mg/kg + rituximab at 375 mg/m2 Q3W for up to 6 cycles. The dose regimen of R-GemOx: rituximab at 375 mg/m2, gemcitabine at 1000 mg/m2 Gem, and oxaliplatin at 100 mg/m2 every 2 weeks for up to 8 cycles. Key inclusion criteria include age ≥18 years, pathologic diagnosis of DLBCL (including pts with DLBCL transformed from indolent lymphoma) or high-grade B-cell lymphoma with MYC and BCL2 and/or BCL6 rearrangements, ≥1 line of prior systemic therapy, not being a candidate for stem cell transplantation, and measurable disease per the 2014 Lugano classification. The randomized part of LOTIS-5 commenced in January 2022, and recruitment is ongoing. Funding: ADC Therapeutics SA; medical writing: CiTRUS Health Group. Clinical trial information: NCT04384484.

Lenalidomide maintenance for diffuse large B-cell lymphoma patients responding to R-CHOP: quality of life, dosing, and safety results from the randomised controlled REMARC study

Lenalidomide maintenance therapy prolonged progression‐free survival (PFS) versus placebo in elderly patients with diffuse large B‐cell lymphoma (DLBCL) responding to induction chemotherapy in the phase 3 REMARC study. This subpopulation analysis assessed the impact of lenalidomide maintenance and treatment‐emergent adverse events (TEAEs) on health‐related quality of life (HRQOL). Global health status (GHS), and physical functioning and fatigue subscales were evaluated in patients who completed the European Organisation for Research and Treatment of Cancer quality‐of‐life questionnaire‐C30 v3.0. The impact of TEAEs classified post hoc as subjective (patients can feel) or observable (only measurable by physicians) on dose reductions and discontinuations was assessed. Among 457 patients (lenalidomide, n = 229; placebo, n = 228), mean (standard deviation) GHS was similar between treatment arms [68·2 (20·7) Versus 72·0 (17·8)] at randomisation and remained similar during maintenance. Patients receiving lenalidomide experienced no meaningful changes in GHS, physical functioning, or fatigue. Observable TEAEs were more common (81·1% Versus 66·3%) and more likely to lead to dose reductions, than subjective TEAEs in both arms. PFS was superior in the lenalidomide arm regardless of dose reduction. Lenalidomide maintenance prolonged PFS and did not negatively impact HRQOL in patients with DLBCL despite TEAEs being more common, when compared with placebo.

TARP is an immunotherapeutic target in acute myeloid leukemia expressed in the leukemic stem cell compartment

Immunotherapeutic strategies targeting the rare leukemic stem cell compartment might provide salvage to the high relapse rates currently observed in acute myeloid leukemia (AML). We applied gene expression profiling for comparison of leukemic blasts and leukemic stem cells with their normal counterparts. Here, we show that the T-cell receptor γ chain alternate reading frame protein (TARP) is over-expressed in de novo pediatric (n=13) and adult (n=17) AML sorted leukemic stem cells and blasts compared to hematopoietic stem cells and normal myeloblasts (15 healthy controls). Moreover, TARP expression was significantly associated with a fms-like tyrosine kinase receptor-3 internal tandem duplication in pediatric AML. TARP overexpression was confirmed in AML cell lines (n=9), and was found to be absent in B-cell acute lymphocytic leukemia (n=5) and chronic myeloid leukemia (n=1). Sequencing revealed that both a classical TARP transcript, as described in breast and prostate adenocarcinoma, and an AML-specific alternative TARP transcript, were present. Protein expression levels mostly matched transcript levels. TARP was shown to reside in the cytoplasmic compartment and showed sporadic endoplasmic reticulum co-localization. TARP-T-cell receptor engineered cytotoxic T-cells in vitro killed AML cell lines and patient leukemic cells co-expressing TARP and HLA-A*0201. In conclusion, TARP qualifies as a relevant target for immunotherapeutic T-cell therapy in AML.

Obinutuzumab combined with lenalidomide for relapsed or refractory follicular B-cell lymphoma (GALEN): a multicentre, single-arm, phase 2 study

BACKGROUND

Lenalidomide plus rituximab is approved to treat patients with relapsed or refractory follicular lymphoma. Obinutuzumab has been shown to enhance antibody-dependent cellular cytotoxicity, phagocytosis, and direct B-cell killing better than rituximab. Our aim was to determine the activity and safety of lenalidomide plus obinutuzumab in previously treated patients with relapsed or refractory follicular lymphoma.

METHODS

In this multicentre, single-arm, phase 2 study, patients were enrolled from 24 Lymphoma Academic Research Organisation centres in France. Eligible patients (age ≥18 years) had histologically confirmed CD20-positive relapsed or refractory follicular lymphoma of WHO grade 1, 2, or 3a; an ECOG performance status of 0-2; and received at least one previous rituximab-containing therapy. Patients received oral lenalidomide (20 mg) plus intravenously infused obinutuzumab as induction therapy (1000 mg; six 28-day cycles), 1-year maintenance with lenalidomide (10 mg; 12 28-day cycles; days 2-22) plus obinutuzumab (1000 mg; alternate cycles), and 1-year maintenance with obinutuzumab (1000 mg; six 56-day cycles; day 1). The primary endpoint was the proportion of patients who achieved an overall response at induction end as per investigator assessment using the 1999 international working group criteria. The secondary endpoints were event-free survival, progression-free survival, overall survival, and safety. Analyses were per-protocol; the efficacy population included all patients who received at least one dose of both obinutuzumab and lenalidomide, and the safety population included all patients who received one dose of either investigational drug. The study is registered with ClinicalTrials.gov, number NCT01582776, and is ongoing but closed to accrual.

FINDINGS

Between June 11, 2014, and Dec 18, 2015, 89 patients were recruited and 86 patients were evaluable for efficacy and 88 for safety. Median follow-up was 2·6 years (IQR 2·2-2·8). 68 (79%) of 86 evaluable patients (95% CI 69-87) achieved an overall response at induction end, meeting the prespecified primary endpoint. At 2 years, event-free survival was 62% (95% CI 51-72), progression-free survival 65% (95% CI 54-74), duration of response 70% (95% CI 57-79), and overall survival 87% (95% CI 78-93). Complete response was achieved by 33 (38%, 95% CI 28-50) of 86 patients at induction end, and the proportion of patients achieving a best overall response was 70 (81%, 95% CI 72-89) and 72 (84%, 74-91) of 86 patients during induction and treatment, respectively. The most common adverse events were asthenia (n=54, 61%), neutropenia (n=38, 43%), bronchitis (n=36, 41%), diarrhoea (n=35, 40%), and muscle spasms (n=34, 39%). Neutropenia was the most common toxicity of grade 3 or more; four (5%) patients had febrile neutropenia. 57 serious adverse events were reported in 30 (34%) of 88 patients. The most common serious adverse events were basal cell carcinoma (n=5, 6%), febrile neutropenia (n=4, 5%), and infusion-related reaction (n=3, 3%). One patient died due to treatment-related febrile neutropenia.

INTERPRETATION

Our data shows that lenalidomide plus obinutuzumab is active in previously treated patients with relapsed or refractory follicular lymphoma, including those with early relapse, and has a manageable safety profile. Randomised trials of new immunomodulatory regimens, such as GALEN or using GALEN as a backbone, versus lenalidomide plus rituximab, are warranted.

FUNDING

Lymphoma Academic Research Organisation, and Celgene and Roche.

A new transcript in the TCRB locus unveils the human ortholog of the mouse pre-Dß1 promoter

Introduction

While most transcripts arising from the human T Cell Receptor locus reflect fully rearranged genes, several germline transcripts have been identified. We describe a new germline transcript arising from the human TCRB locus.

Methods

cDNA sequencing, promoter, and gene expression analyses were used to characterize the new transcript.

Results

The new germline transcript encoded by the human TCRB locus consists of a new exon of 103 bp, which we named TRBX1 (X1), spliced with the first exon of gene segments Cß1 or Cß2. X1 is located upstream of gene segment Dß1 and is therefore deleted from a V‐DJ rearranged TCRB locus. The X1‐Cß transcripts do not appear to code for a protein. We define their transcription start and minimal promoter. These transcripts are found in populations of mature T lymphocytes from blood or tissues and in T cell clones with a monoallelic TCRB rearrangement. In immature thymocytes, they are already detectable in CD1a⁻CD34⁺CD4⁻CD8⁻ cells, therefore before completion of the TCRB rearrangements.

Conclusions

The X1 promoter appears to be the ortholog of the mouse pre‐Dß1 promoter (PDß1). Like PDß1, its activation is regulated by Eß in T cells and might facilitate the TCRB rearrangement process by contributing to the accessibility of the Dß1 locus.

Humanized Mice to Study Human T Cell Development

While in vitro models exist to study human T cell development, they still lack the precise environmental stimuli, such as the exact combination and levels of cytokines and chemokines, that are present in vivo. Moreover, studying the homing of hematopoietic stem (HSC) and progenitor (HPC) cells to the thymus can only be done using in vivo models. Although species-specific differences exist, "humanized" models are generated to circumvent these issues. In this chapter, we focus on the humanized mouse models that can be used to study early T cell development. Models that study solely mature T cells, such as the SCID-PBL (Tary-Lehmann et al., Immunol Today 16:529-533) are therefore not discussed here, but have recently been reviewed (Shultz et al., Nat Rev Immunol 12:786-798).

Colistin and neurotoxicity: recommendations for optimal use in cystic fibrosis patients

Case description The use of i.v. colistin reappeared recently for the treatment of multidrug-resistant Gram negative organisms in the intensive care and cystic fibrosis (CF) setting. According to the latest pharmacokinetic data, a loading dose and high antibiotic doses are given. Two cases of adverse events (paraesthesias, bad taste) were observed immediately after the start of infusion of a high dose of i.v. colistin in adult CF patients at the Ghent University Hospital. Conclusion Recommendations for optimal administration of i.v. colistin in adult CF patients are scarce. This article highlights the importance of mode of administration to avoid toxicity and relates it to recent pharmacokinetic/-dynamic literature.

Can immunotherapy specifically target acute myeloid leukemic stem cells?

Accumulating evidence supports the role of leukemic stem cells (LSCs) in the high relapse rate of acute myeloid leukemia (AML) patients. The clinical relevance of LSCs, which were originally characterized in xenograft models, has recently been confirmed by the finding that stem cell-like gene expression signatures can predict the clinical outcome of AML patients. The targeted elimination of LSCs might hence constitute an efficient therapeutic approach to AML. Here, we review immunotherapeutic strategies that target LSC-associated antigens, including T cell-mediated and monoclonal antibody-based regimens. Attention is given to the issue of antigen specificity because this is relevant to the therapeutic window and determines the superiority of LSC-targeting immunotherapy.

Specific Notch receptor-ligand interactions control human TCR-αβ/γδ development by inducing differential Notch signal strength

Jagged2 preferentially signals through Notch3 to promote γδ T cell development.

In humans, high Notch activation promotes γδ T cell development, whereas lower levels promote αβ-lineage differentiation. How these different Notch signals are generated has remained unclear. We show that differential Notch receptor–ligand interactions mediate this process. Whereas Delta-like 4 supports both TCR-αβ and -γδ development, Jagged1 induces mainly αβ-lineage differentiation. In contrast, Jagged2-mediated Notch activation primarily results in γδ T cell development and represses αβ-lineage differentiation by inhibiting TCR-β formation. Consistently, TCR-αβ T cell development is rescued through transduction of a TCR-β transgene. Jagged2 induces the strongest Notch signal through interactions with both Notch1 and Notch3, whereas Delta-like 4 primarily binds Notch1. In agreement, Notch3 is a stronger Notch activator and only supports γδ T cell development, whereas Notch1 is a weaker activator supporting both TCR-αβ and -γδ development. Fetal thymus organ cultures in JAG2-deficient thymic lobes or with Notch3-blocking antibodies confirm the importance of Jagged2/Notch3 signaling in human TCR-γδ differentiation. Our findings reveal that differential Notch receptor–ligand interactions mediate human TCR-αβ and -γδ T cell differentiation and provide a mechanistic insight into the high Notch dependency of human γδ T cell development.

Notch Induces T Cell Receptor γδ Thymocytes to Differentiate along a Bipotent CD4 CD8 Double Positive Pathway (111.6)

It is well documented that in wildtype mice TCRγδ+ cells differentiate along a double negative (DN) pathway whereas TCRαβ+ cells differentiate along the double positive (DP) pathway, suggesting that the TCR itself induces lineage differentiation. Under experimental conditions and in genetically modified mice, however, evidence was presented suggesting that rather than TCR itself, TCR signal strength and notch determine lineage choice. In the human thymus, a “chimeric” DP TCRγδ+ cell population is present and constitutes a sizeable fraction of the γδ population. We asked the question whether these cells belong to the αβ or γδ lineage or whether these cells are bipotent. We found that TCRγδ DP cells are bipotent cells since strong TCR signals induces differentiation to TCRγδ cells, whereas Notch activation induces TCRαβ lineage differentiation. We furthermore could show that Notch signaling diverts TCRγδ DN cells to the DP pathway and induces strong proliferation. In line with these findings, TCRγδ+ acute lymphoblastic leukemias (ALL) with activating Notch1 mutations follow the DP differentiation pathway, whereas the DN ALL cells are devoid of these activating Notch1 mutations. We were able to confirm that also in vivo TCRγδ DP have rearranged TCRβ chains, actively rearrange the TCRα locus and delete the TCRδ locus (αβ lineage). Using TCRα rearrangements as a lineage marker, we could show that a subpopulation of mature TCRγδ cells is derived from DP cells.

RHAMM/HMMR (CD168) is not an ideal target antigen for immunotherapy of acute myeloid leukemia

BACKGROUND

Criteria for good candidate antigens for immunotherapy of acute myeloid leukemia are high expression on leukemic stem cells in the majority of patients with acute myeloid leukemia and low or no expression in vital tissues. It was shown in vaccination trials that Receptor for Hyaluronic Acid Mediated Motility (RHAMM/HMMR) generates cellular immune responses in patients with acute myeloid leukemia and that these responses correlate with clinical benefit. It is not clear however whether this response actually targets the leukemic stem cell, especially since it was reported that RHAMM is expressed maximally during the G2/M phase of the cell cycle. In addition, tumor specificity of RHAMM expression remains relatively unexplored.

DESIGN AND METHODS

Blood, leukapheresis and bone marrow samples were collected from both acute myeloid leukemia patients and healthy controls. RHAMM expression was assessed at protein and mRNA levels on various sorted populations, either fresh or after manipulation.

RESULTS

High levels of RHAMM were expressed by CD34(+)CD38(+) and CD34(-) acute myeloid leukemia blasts. However, only baseline expression of RHAMM was measured in CD34(+)CD38(-) leukemic stem cells, and was not different from that in CD34(+)CD38(-) hematopoietic stem cells from healthy controls. RHAMM was significantly up-regulated in CD34(+) cells from healthy donors during in vitro expansion and during in vivo engraftment. Finally, we demonstrated an explicit increase in the expression level of RHAMM after in vitro activation of T cells.

CONCLUSIONS

RHAMM does not fulfill the criteria of an ideal target antigen for immunotherapy of acute myeloid leukemia. RHAMM expression in leukemic stem cells does not differ significantly from the expression in hematopoietic stem cells from healthy controls. RHAMM expression in proliferating CD34+ cells of healthy donors and activated T cells further compromises RHAMM-specific T-cell-mediated immunotherapy.

Notch induces human T-cell receptor γδ+ thymocytes to differentiate along a parallel, highly proliferative and bipotent CD4 CD8 double-positive pathway

In wild-type mice, T-cell receptor (TCR) γδ(+) cells differentiate along a CD4 CD8 double-negative (DN) pathway whereas TCRαβ(+) cells differentiate along the double-positive (DP) pathway. In the human postnatal thymus (PNT), DN, DP and single-positive (SP) TCRγδ(+) populations are present. Here, the precursor-progeny relationship of the various PNT TCRγδ(+) populations was studied and the role of the DP TCRγδ(+) population during T-cell differentiation was elucidated. We demonstrate that human TCRγδ(+) cells differentiate along two pathways downstream from an immature CD1(+) DN TCRγδ(+) precursor: a Notch-independent DN pathway generating mature DN and CD8αα SP TCRγδ(+) cells, and a Notch-dependent, highly proliferative DP pathway generating immature CD4 SP and subsequently DP TCRγδ(+) populations. DP TCRγδ(+) cells are actively rearranging the TCRα locus, and differentiate to TCR(-) DP cells, to CD8αβ SP TCRγδ(+) cells and to TCRαβ(+) cells. Finally, we show that the γδ subset of T-cell acute lymphoblastic leukemias (T-ALL) consists mainly of CD4 SP or DP phenotypes carrying significantly more activating Notch mutations than DN T-ALL. The latter suggests that activating Notch mutations in TCRγδ(+) thymocytes induce proliferation and differentiation along the DP pathway in vivo.

In vitro generation of immune cells from pluripotent stem cells

Stem cell transplant recipients and acquired or inherited immune-deficiency patients could benefit from the infusion of B, T and/or NK cells. These lymphoid cells can be generated in vitro from bone marrow derived CD34+CD45+ hematopoietic stem cells (HSC). The number of cells that can be obtained in this way is limited especially in the adult. An alternative source may therefore constitute human pluripotent stem cells (PSC) such as embryonic (hESC) or induced pluripotent stem cells (hiPSC). Here, we focus on present knowledge on the generation of lymphoid cells from hESC. The two main obstacles for the generation of clinically relevant immune cells are the failure to generate from hESC long-term repopulating HSC which could be kept in culture for prolonged time; and insufficient knowledge of the selection process which generates mature T cells from CD4 CD8 double positive (DP) precursors in vitro.