Heterogeneity of germinal center B cells: New insights from single-cell studies

Upon antigen exposure, activated B cells in antigen-draining lymphoid organs form microanatomical structures, called germinal centers (GCs), where affinity maturation occurs. Within the GC microenvironment, GC B cells undergo proliferation and B cell receptor (BCR) genes somatic hypermutation in the dark zone (DZ), and affinity-based selection in the light zone (LZ). In the current paradigm of GC dynamics, high-affinity LZ B cells may be selected by cognate T- follicular helper cells to either differentiate into plasma cells or memory B cells, or re-enter the DZ and initiate a new round of proliferation and BCR diversification, before migrating back to the LZ. Given the diversity of cell states and potential cell fates that GC B cells may adopt, the two-state DZ-LZ paradigm has been challenged by studies that explored GC B-cell heterogeneity with a variety of single-cell technologies. Here, we review studies and single-cell technologies which have allowed to refine the working model of GC B-cell cellular and molecular heterogeneity during affinity maturation. This review also covers the use of single-cell quantitative data for mathematical modeling of GC reactions, and the application of single-cell genomics to the study of GC-derived malignancies.     

Double-intensive therapy in high-risk multiple myeloma.

A high remission rate is achieved with high-dose melphalan (HDM) in multiple myeloma (MM), and autologous transplantation of hematopoietic stem cells allows a prompt hematologic recovery after high-dose therapy. We treated 97 patients with high-risk MM (group 1:44 advanced MM including 14 primary resistances and 30 relapses; group 2: 53 newly diagnosed MM) with a first course of HDM. For responding patients a second course of high-dose therapy with hematopoietic stem cell support was proposed. After the first HDM, the overall response and complete remission rates were 71% and 25% with no significant difference between the two groups. The median durations of neutropenia and thrombocytopenia were significantly longer in group 1 (29.5 days and 32 days, respectively) than in group 2 (23 days and 17 days, respectively). This severe myelosuppression led to eight toxic deaths and the fact that only 38 of the 69 responders could proceed to the second course (three allogenic and 35 autologous transplantations). Among the 35 patients undergoing autologous transplantation (10 in group 1, 25 in group 2), 31 received their marrow unpurged collected after the first HDM, and four received peripheral blood stem cells. The median durations of neutropenia and thrombocytopenia after autologous transplantation were 24 days and 49 days, respectively. Two toxic deaths and nine prolonged thrombocytopenias were observed. The median survival for the 97 patients was 24 months (17 months in group 1, 37 months in group 2) and the median duration of response was 20 months. The only parameters that have a significant impact on the survival are the age (+/- 50 years) and the response to HDM. The median survival of the 35 patients undergoing autologous transplantation is 41 months, but the median duration of remission is 28 months with no plateau of the remission duration curve. Patients responding to HDM may have prolonged survival, but even a second course of high-dose therapy probably cannot eradicate the malignant clone.     

Rituximab (anti-CD20 monoclonal antibody) as single first-line therapy for patients with follicular lymphoma with a low tumor burden: clinical and molecular evaluation

The clinical activity of rituximab, a chimeric monoclonal antibodywhich binds to the CD20 antigen, was evaluated as a single first-linetherapy for patients with follicular non-Hodgkin lymphoma (NHL). Fiftypatients with follicular CD20⁺ NHL and a low tumor burdenwere analyzed for clinical and molecular responses. They received 4 weekly infusions of rituximab at a dose of 375 mg/m². Theresponse rate a month after treatment (day 50) was 36 of 49 (73%),with 10 patients in complete remission, 3 patients in completeremission/unconfirmed, and 23 patients in partial remission. Tenpatients had stable disease, and the disease progressed in 3 patients. One of 13 (8%) patients in complete remission, 9 of 23 (39%) patients in partial remission, and 5 of 10 (50%) patients withstable disease exhibited disease progression during the first year.Within the study population, 32 patients were initially informative forpolymerase chain reaction (PCR) data on bcl-2-J_H rearrangement. On day 50, 17 of 30 patients (57%) were negative forbcl-2-J_H rearrangement in peripheral blood, and 9 of 29 (31%) were negative in bone marrow; a significant association wasobserved between molecular and clinical responses(P < .0001). At month 12, 16 of 26 patients (62%) werePCR negative in peripheral blood. These results indicate that earlymolecular responses can be sustained for up to 12 months and that thisresponse is highly correlated with progression-free survival. Rituximabhas a high clinical activity and a low toxicity and induces a highcomplete molecular response rate in patients with follicular lymphomaand a low tumor burden.     

Prognostic utility of pre-transplantation [18F] fluorodeoxyglucose positron emission tomography/computed tomography in patients with diffuse large B-cell lymphoma who underwent rituximab,dexamethasone, high-dose cytarabine,carboplatin salvage chemotherapy

We analysed the outcomes of 62 patients with refractory/relapsed diffuse large B-cell lymphoma (rrDLBCL) who had pre-transplantation fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) after R-DHAC (rituximab, dexamethasone, high-dose cytarabine, carboplatin) salvage chemotherapy, and were evaluated using Deauville criteria and total lesion glycolysis (TLG). A positive pre-transplantation PET/CT with Deauville score of 5 was associated with shorter progression-free survival (PFS) (P = 0·01), while a Deauville score of 4 was not predictive of outcome. Only pre-transplant TLG was significantly associated with both PFS (P = 0·005) and overall survival (P = 0·03). TLG deserves to be further investigated in prospective studies.     

Outcome of conditioning intensity in acute myeloid leukemia with monosomal karyotype in patients over 45 year‐old: A study from the acute leukemia working party (ALWP) of the European group of blood and marrow transplantation (EBMT)

Acute myeloid leukemia with monosomal karyotype (MK AML) carries a very poor prognosis, even after allogeneic stem cell transplantation (SCT). However, SCT remains the only curative option in this high‐risk population. Because myeloablative conditioning regimen (MAC) is associated with less relapse, we hypothesized that more intensive conditioning regimen might be beneficial for MK AML patients. We reviewed 303 patients over age 45 diagnosed with either de novo or secondary MK AML. One hundred and five patients received a MAC and 198 a reduced‐intensity conditioning (RIC). The median age at SCT was 57‐year‐old, significantly lower in the MAC (53‐year‐old) than in the RIC group (59‐year‐old). The median follow‐up was 42 months (range, 3 ? 156 months). The 3‐year overall survival (OS), leukemia‐free survival (LFS), and relapse rate (RR) were not significantly different between both groups with overall values of 34%, 29%, and 51%, respectively. On the contrary, the 3‐year nonrelapse mortality (NRM) was significantly higher in MAC recipients (28%) compared with RIC patients (16%, P = 0.004). The incidence of Grades II to IV acute graft‐versus‐host disease (GvHD) was significantly higher after a MAC (30.5%) than after a RIC (19.3%, P = 0.02). That of chronic GvHD was comparable between both groups (35%) and did not impact on LFS. Interestingly, within our MK AML cohort, hypodiploidy was significantly associated with worse outcomes. Due to reduced toxicity and comparable OS, LFS, and RR, RIC appears as a good transplant option in the very high‐risk population, including older patients, diagnosed with MK AML. Am. J. Hematol. 90:719–724, 2015. © 2015 Wiley Periodicals, Inc.     

Total body irradiation–high-dose cytosine arabinoside and melphalan followed by allogeneic bone marrow transplantation from HLA-identical siblings in the treatment of children with acute lymphoblastic leukaemia after relapse while receiving chemotherapy: a Société Française de Greffe de Moelle study

We investigated the use of a new conditioning regimen followed by allogeneic bone marrow transplantation (BMT) for treating children with acute lymphoblastic leukaemia (ALL) after relapse within 6 months of the completion of therapy. One hundred and sixteen children with acute lymphoblastic leukaemia in second or subsequent complete remission (CR) underwent allogeneic bone marrow transplantation from HLA-identical siblings after a preparative regimen comprising total body irradiation (TBI), high-dose cytosine arabinoside and melphalan (TAM regimen). The Kaplan-Meier product-limit estimate (mean ± SE) of disease-free survival (DFS) at 7 years was 59.5 ± 9% (95% confidence interval). The estimated chance of relapse was 22.5 ± 15% with a median follow-up of 88.5 months (range 51–132). 26 patients (22.4%) died with no evidence of recurrent leukaemia, mainly from interstitial pneumonitis, veno-occlusive disease or acute graft-versus-host disease (GVHD). Three factors significantly affected DFS: acute GVHD, site of relapse and, for children in second remission after a marrow relapse, the disease status at the time of transplantation. The DFS were 59.02 ± 12.6%, 37.5 ± 19.8% and 77.4 ± 15% among patients in CR2 after a marrow relapse, in CR3 or in untreated partial marrow relapse, and in CR2 after an isolated CNS relapse, respectively. The lowest DFS was seen in children with acute GVHD grades 3–4. Two significant factors were associated with relapse: the marrow status at the time of transplantation and chronic GVHD. The relapse rate was lower among children in CR2 or with chronic GVHD. We conclude that transplantation after the TAM regimen is an effective therapy for this population with acceptable toxicity, particularly for children in second remission after a very early marrow relapse, or those with early isolated CNS involvement.     

Long-term follow-up of high-dose treatment with autologous haematopoietic progenitor cell support in 693 patients with follicular lymphoma: an EBMT registry study.

To evaluate the outcome of a large series of patients who received high-dose treatment (HDT) for follicular lymphoma (FL), 693 patients undergoing HDT (total-body irradiation (TBI)-containing regimen: 58%; autologous bone marrow (BM)/peripheral blood progenitor cells (PBPCs): 378/285 patients) were included in the study. A total of 375 patients (54%) developed recurrent lymphoma, 10-year progression-free survival (PFS) being 31%. On multivariate analysis, younger age (P=0.003) and HDT in first complete remission (CR1) (P<0.001) correlated with longer PFS. With a median follow-up of 10.3 years, 330 patients died. Ten-year overall survival (OS) from HDT was 52%. Shorter OS was associated on multivariate analysis with older age (P<0.001), chemoresistant disease (P<0.001), BM+PBPC as source of stem cells (P=0.007) and TBI-containing regimens (P=0.004). Thirty-nine patients developed secondary myelodysplastic syndrome/acute myeloid leukaemia (MDS/AML), in 34 cases having received TBI as the conditioning regimen. The 5-year non-relapse mortality (NRM) was 9%. On multivariate analysis, older age (P<0.001), refractory disease (P<0.001) and TBI (P=0.04) were associated with a higher NRM. This long follow-up study shows a plateau in the PFS curve, suggesting that a selected group of patients might be cured with HDT. On the downside, TBI-containing regimens are associated with a negative impact on survival.     

Effect of cell determinant (CD)34+ cell dose on the cost and consequences of peripheral blood stem cell transplantation for non-Hodgkin's lymphoma patients in front-line therapy

The aim of this study was to assess the effect of cell determinant (CD)34+ cell dose on the cost and consequences of peripheral blood stem cell transplantation for non-Hodgkin's lymphoma (NHL) patients in front-line therapy. Resource utilisation, length of aplasia, overall (OS) and event-free survival (EFS) were assessed for 63 patients. Economic data were calculated taking into account harvest, hospitalisation, blood product requirements and drugs required until discharge. The point of view of the Hospital Institution was chosen. A significantly earlier haematopoietic engraftment was achieved in patients with a count of more than 5×10⁶ CD34+/kg. There were no differences for OS and EFS. A high CD34+ cell content resulted in a total cost saving of $4210. This was principally related to a significant reduction in the length of hospitalisation (−$3010) and platelet and red blood cell transfusions (−$815), although the latter was not significant. Several sensitivity analyses showed the robustness of our results. A CD34+ cell dose higher than 5×10⁶/kg appeared to be optimal for clinical and economic considerations in NHL patients undergoing transplantation in front-line therapy.