Efficacy, pharmacokinetics, and safety of the biosimilar CT-P10 in comparison with rituximab in patients with previously untreated low-tumour-burden follicular lymphoma: a randomised, double-blind, parallel-group, phase 3 trial

BACKGROUND

Studies in patients with rheumatoid arthritis and advanced follicular lymphoma have shown that CT-P10, a rituximab biosimilar, has equivalent or non-inferior efficacy and pharmacokinetics to rituximab. We aimed to assess the therapeutic equivalence of single-agent CT-P10 and rituximab in patients with newly diagnosed low-tumour burden follicular lymphoma.

METHODS

In this ongoing, randomised, double-blind, parallel-group, active-controlled, phase 3 trial, adult patients (≥18 years) with stage II-IV low-tumour-burden follicular lymphoma were randomly assigned (1:1) using an interactive web or voice response system stratified by region, stage, and age to CT-P10 or US-sourced rituximab. Patients received CT-P10 or rituximab (375 mg/m² intravenous) on day 1 of four 7-day cycles (induction period). Patients who had disease control after the induction period continued to a maintenance period of CT-P10 or rituximab administered every 8 weeks for six cycles and, if completed, a second year of maintenance therapy of additional CT-P10 (every 8 weeks for six cycles) was offered. The study was partially unmasked after database lock (Feb 23, 2018) for all data up to 7 months (before cycle 3 of the maintenance period). The primary endpoint was the proportion of patients who achieved an overall response by 7 months in the intention-to-treat population. Efficacy equivalence was shown if the two-sided 90% CIs for the treatment difference in the proportion of responders between CT-P10 and rituximab was within the equivalence margin of 17%. This trial is registered with ClinicalTrials.gov, number NCT02260804.

FINDINGS

Between Nov 9, 2015, and Jan 4, 2018, 402 patients were assessed for eligibility, of whom 258 were randomly assigned: 130 to CT-P10 and 128 to rituximab. 108 (83%) of 130 patients assigned to CT-P10 and 104 (81%) of 128 assigned to rituximab achieved an overall response by month 7 (treatment difference estimate 1·8%; 90% CI -6·43 to 10·20). Therapeutic equivalence was shown (90% CIs were within the prespecified margin of 17%). The most common grade 3 or 4 treatment-emergent adverse events were decreased neutrophil count (two grade 3 in the CT-P10 group) and neutropenia (one in each group); all other grade 3 or 4 treatment-emergent adverse events occurred in one patient each. Six (5%) of 130 patients who received CT-P10 and three (2%) of 128 who received rituximab experienced at least one treatment-emergent serious adverse event.

INTERPRETATION

CT-P10 was equivalent to rituximab in terms of efficacy and was well tolerated. CT-P10 monotherapy is suggested as a new therapeutic option for patients with low-tumour-burden follicular lymphoma.

FUNDING

Celltrion, Inc.

Comparative nonclinical assessments of the proposed biosimilar PF-05280586 and rituximab (MabThera®)

Comparative nonclinical studies were conducted with the proposed biosimilar PF-05280586 and rituximab-EU (MabThera®). In side-by-side analyses, peptide maps and complement-dependent cytotoxicity assay results were similar. Sexually-mature cynomolgus monkeys were administered PF-05280586 or rituximab-EU as a single dose of 0, 2, 10, or 20 mg/kg on day 1 and observed for 92 days (single-dose study) or as 5 weekly injections of 0 or 20 mg/kg and necropsied on day 30, the day after the 5th dose, or on day 121 (repeat-dose study). The pharmacokinetic and pharmacodynamic profiles for both molecules were similar. Marked depletion of peripheral blood B cells 4 days after dosing was followed by near or complete repletion (single-dose study) or partial repletion (repeat-dose study). In the single-dose study, anti-drug antibodies (ADA) were detected by day 29 in all animals administered PF-05280586 or rituximab-EU and persisted through day 85, the last day tested. In the repeat-dose study, ADA were detected on day 121 in 50% of animals administered PF-05280586 or rituximab-EU. Both molecules were well tolerated at all doses. In all endpoints evaluated, PF-05280586 exhibited similarity to rituximab-EU.

An evaluation of the potential for drug-drug interactions between bendamustine and rituximab in indolent non-Hodgkin lymphoma and mantle cell lymphoma

Purpose

Bendamustine plus rituximab has been reported to be effective in treating lymphoid malignancies. This analysis investigated the potential for drug–drug interactions between the drugs in patients with indolent non-Hodgkin lymphoma or mantle cell lymphoma.

Methods

Data were derived from a bendamustine–rituximab combination therapy study, a bendamustine monotherapy study, and published literature on rituximab monotherapy and combination therapy. Analysis of the potential for rituximab to affect bendamustine systemic exposure included comparing bendamustine concentration–time profile following monotherapy to that following combination therapy and comparing model-predicted Bayesian bendamustine clearance in the presence and absence of rituximab. Analysis of the potential for bendamustine to affect rituximab systemic exposure included plotting observed minimum, median, and maximum serum rituximab concentrations at the end of rituximab infusion (EOI) and 24 h and 7 days post-infusion in patients receiving combination therapy versus concentrations reported in literature following rituximab monotherapy.

Results

The established population pharmacokinetic model following bendamustine monotherapy was evaluated to determine its applicability to combination therapy for the purpose of confirming lack of pharmacokinetic interaction. The model adequately described the bendamustine concentration–time profile following monotherapy and combination therapy in adults. There was no statistically significant difference in estimated bendamustine clearance either alone or in combination. Also, rituximab concentrations from EOI to 24 h and 7 days demonstrated a pattern of decline similar to that seen in rituximab studies without bendamustine, suggesting that bendamustine does not affect the rituximab clearance rate.

Conclusions

Neither bendamustine nor rituximab appears to affect systemic exposure of the other drug when coadministered.

Evaluation of 89Zr-rituximab tracer by Cerenkov luminescence imaging and correlation with PET in a humanized transgenic mouse model to image NHL

PURPOSE

This research aimed to study the use of Cerenkov luminescence imaging (CLI) for non-Hodgkin's lymphoma (NHL) using 89Zr-rituximab positron emission tomography (PET) tracer with a humanized transgenic mouse model that expresses human CD20 and the correlation of CLI with PET.

PROCEDURES

Zr-rituximab (2.6 MBq) was tail vein-injected into transgenic mice that express the human CD20 on their B cells (huCD20TM). One group (n=3) received 2 mg/kg pre-dose (blocking) of cold rituximab 2 h prior to tracer; a second group (n=3) had no pre-dose (non-blocking). CLI was performed using a cooled charge-coupled device optical imager. We also performed PET imaging and ex vivo studies in order to confirm the in vivo CLI results. At each time point (4, 24, 48, 72, and 96 h), two groups of mice were imaged in vivo and ex vivo with CLI and PET, and at 96 h, organs were measured by gamma counter.

RESULTS

huCD20 transgenic mice injected with 89Zr-rituximab demonstrated a high-contrast CLI image compared to mice blocked with a cold dose. At various time points of 4-96 h post-radiotracer injection, the in vivo CLI signal intensity showed specific uptake in the spleen where B cells reside and, hence, the huCD20 biomarker is present at very high levels. The time-activity curve of dose decay-corrected CLI intensity and percent injected dose per gram of tissue of PET uptake in the spleen were increased over the time period (4-96 h). At 96 h, the 89Zr-rituximab uptake ratio (non-blocking vs blocking) counted (mean±standard deviation) for the spleen was 1.5±0.6 for CLI and 1.9±0.3 for PET. Furthermore, spleen uptake measurements (non-blocking and blocking of all time points) of CLI vs PET showed good correlation (R2=0.85 and slope=0.576), which also confirmed the corresponding correlations parameter value (R2=0.834 and slope=0.47) obtained for ex vivo measurements.

CONCLUSIONS

CLI and PET of huCD20 transgenic mice injected with 89Zr-rituximab demonstrated that the tracer was able to target huCD20-expressing B cells. The in vivo and ex vivo tracer uptake corresponding to the CLI radiance intensity from the spleen is in good agreement with PET. In this report, we have validated the use of CLI with PET for NHL imaging in huCD20TM.

Subcutaneous versus intravenous administration of rituximab: pharmacokinetics, CD20 target coverage and B-cell depletion in cynomolgus monkeys

The CD20-specific monoclonal antibody rituximab (MabThera^®, Rituxan^®) is widely used as the backbone of treatment for patients with hematologic disorders. Intravenous administration of rituximab is associated with infusion times of 4–6 hours, and can be associated with infusion-related reactions. Subcutaneous administration of rituximab may reduce this and facilitate administration without infusion-related reactions. We sought to determine the feasibility of achieving equivalent efficacy (measured by endogenous B-cell depletion) and long-term durability of CD20 target coverage for subcutaneously administered rituximab compared with intravenous dosing. In these preclinical studies, male cynomolgus monkeys were treated with either intravenous rituximab or novel subcutaneous formulation of rituximab containing human recombinant DNA-derived hyaluronidase enzyme. Peripheral blood samples were analyzed for serum rituximab concentrations, peripheral B-cell depletion, and CD20 target coverage, including subset analysis according to CD21+ status. Distal lymph node B-cell depletion and CD20 target coverage were also measured. Initial peak serum concentrations of rituximab were significantly higher following intravenous administration than subcutaneous. However, the mean serum rituximab trough concentrations were comparable at 2 and 7 days post-first dose and 9 and 14 days post-second dose. Efficacy of B-cell depletion in both peripheral blood and distal lymph nodes was comparable for both methods. In lymph nodes, 9 days after the second dose with subcutaneous and intravenous rituximab, B-cell levels were decreased by 57% and 42% respectively. Similarly, levels of peripheral blood B cells were depleted by >94% for both subcutaneous and intravenous dosing at all time points. Long-term recovery of free unbound surface CD20 levels was similar, and the duration of B-cell depletion was equally sustained over 2 months for both methods. These results demonstrate that, despite initial peak serum drug level differences, subcutaneous rituximab has similar durability, pharmacodynamics, and efficacy compared with intravenous rituximab.

Safety and clinical activity of a combination therapy comprising two antibody-based targeting agents for the treatment of non-Hodgkin lymphoma: results of a phase I/II study evaluating the immunoconjugate inotuzumab ozogamicin with rituximab

PURPOSE

Inotuzumab ozogamicin (INO) is an antibody-targeted chemotherapy agent composed of a humanized anti-CD22 antibody conjugated to calicheamicin, a potent cytotoxic agent. We performed a phase I/II study to determine the maximum-tolerated dose (MTD), safety, efficacy, and pharmacokinetics of INO plus rituximab (R-INO) for treatment of relapsed/refractory CD20(+)/CD22(+) B-cell non-Hodgkin lymphoma (NHL).

PATIENTS AND METHODS

A dose-escalation phase to determine the MTD of R-INO was followed by an expanded cohort to further evaluate the efficacy and safety at the MTD. Patients with relapsed follicular lymphoma (FL), relapsed diffuse large B-cell lymphoma (DLBCL), or refractory aggressive NHL received R-INO every 4 weeks for up to eight cycles.

RESULTS

In all, 118 patients received one or more cycles of R-INO (median, four cycles). Most common grade 3 to 4 adverse events were thrombocytopenia (31%) and neutropenia (22%). Common low-grade toxicities included hyperbilirubinemia (25%) and increased AST (36%). The MTD of INO in combination with rituximab (375 mg/m(2)) was confirmed to be the same as that for single-agent INO (1.8 mg/m(2)). Treatment at the MTD yielded objective response rates of 87%, 74%, and 20% for relapsed FL (n = 39), relapsed DLBCL (n = 42), and refractory aggressive NHL (n = 30), respectively. The 2-year progression-free survival (PFS) rate was 68% (median, not reached) for FL and 42% (median, 17.1 months) for relapsed DLBCL.

CONCLUSION

R-INO demonstrated high response rates and long PFS in patients with relapsed FL or DLBCL. This and the manageable toxicity profile suggest that R-INO may be a promising option for CD20(+)/CD22(+) B-cell NHL.

AL amyloid imaging and therapy with a monoclonal antibody to a cryptic epitope on amyloid fibrils

The monoclonal antibody 2A4 binds an epitope derived from a cleavage site of serum amyloid protein A (sAA) containing a -Glu-Asp- amino acid pairing. In addition to its reactivity with sAA amyloid deposits, the antibody was also found to bind amyloid fibrils composed of immunoglobulin light chains. The antibody binds to synthetic fibrils and human light chain (AL) amyloid extracts with high affinity even in the presence of soluble light chain proteins. Immunohistochemistry with biotinylated 2A4 demonstrated positive reaction with ALκ and ALλ human amyloid deposits in various organs. Surface plasmon resonance analyses using synthetic AL fibrils as a substrate revealed that 2A4 bound with a K_D of ∼10 nM. Binding was inhibited in the presence of the –Glu-Asp- containing immunogen peptide. Radiolabeled 2A4 specifically localized with human AL amyloid extracts implanted in mice (amyloidomas) as evidenced by single photon emission (SPECT) imaging. Furthermore, co-localization of the radiolabeled mAb with amyloid was shown in biodistribution and micro-autoradiography studies. Treatment with 2A4 expedited regression of ALκ amyloidomas in mice, likely mediated by the action of macrophages and neutrophils, relative to animals that received a control antibody. These data indicate that the 2A4 mAb might be of interest for potential imaging and immunotherapy in patients with AL amyloidosis.

Mechanism-based approach to the economic evaluation of pharmaceuticals: pharmacokinetic/pharmacodynamic/pharmacoeconomic analysis of rituximab for follicular lymphoma

BACKGROUND AND OBJECTIVES

Economic value is an important consideration during all phases of the drug development process. We previously published an article in PharmacoEconomics in which we described a mechanism-based economic modelling approach that incorporates data obtained during phase II clinical studies on the relationships between dose, exposure and response. We now describe case studies of rituximab for the treatment of follicular non-Hodgkin's lymphoma based on this methodology.

METHODS

We utilized a population pharmacokinetic and pharmacodynamic model linking serum rituximab concentration to progression-free survival, to simulate the effectiveness of rituximab in various clinical contexts. These served as inputs to economic models of follicular lymphoma, based on National Institute for Health and Clinical Excellence (NICE) appraisals, to assess the cost effectiveness of rituximab. Our results were compared with trial-based estimates from the NICE appraisals. In a further analysis, we simulated the results of an ongoing trial to generate predictions of cost effectiveness.

RESULTS

Our analyses suggest an acceptable degree of concordance between simulation- and trial-based estimates of cost effectiveness. For first-line and maintenance therapy, deviations of £2,099 and £1,355 per QALY, respectively, from trial-based incremental cost-effectiveness ratio estimates of £8,290 and £7,721 per QALY gained would not affect reimbursement decisions. The probability of rituximab-containing regimens being cost effective at £20,000 and £30,000 per QALY thresholds was 1 for both first-line and maintenance therapy in both simulated and trial-based analyses.

CONCLUSIONS

Our analyses demonstrate the feasibility of mechanism-based economic analyses, which may have applications during drug development to the following: (i) directing future research based on the cost of reducing uncertainty; (ii) assessing subgroups, dosing schedules and protocol deviations; and (iii) informing strategic research and development and pricing decisions.

Model-based design of rituximab dosage optimization in follicular non-Hodgkin's lymphoma

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

The concentration-effect relationship of rituximab in follicular lymphoma (FL) was previously described using pharmacokinetic-pharmacodynamic (PK-PD) modelling. The influence of genetic polymorphism of FCGR3A on rituximab efficacy in FL patients was included in this PK-PD model. Previous studies suggest that increasing the dose of rituximab and/or the number of infusions may lead to a better clinical response in FL.

WHAT THIS STUDY ADDS

The previously validated PK-PD model can be used to design an optimized rituximab dose regimen in FL patients. Clinical trial simulation shows the potential clinical benefits of changes in rituximab dose. Optimization of the rituximab dose regimen cannot compensate for the lower response of FCGR3A-158F carriers compared with that of FCGR3A-158VV patients. AIMS Rituximab has dramatically improved the survival of patients with non-Hodgkin's lymphoma (NHL). However, studies have suggested that the dose regimen currently used (i.e. 375 mg m(-2) ) could be optimized. The aims of this study were to quantify the benefits of the new dose regimen for rituximab in follicular NHL (FL) patients using a previously validated PK-PD model and to design clinical trials investigating optimization of rituximab dosage.

METHODS

A PK-PD model was used to predict progression-free survival (PFS) of FL patients treated by rituximab alone in asymptomatic FL, and those treated by rituximab combined with chemotherapy (R-CHOP) in relapsed/resistant FL. This model accounts for the influence of a polymorphism in FCGR3A, the gene encoding the FcγRIIIa receptor, on clinical efficacy. Several induction and maintenance dose regimens using rituximab alone or in combination with conventional chemotherapy (CHOP) were tested. The benefits of rituximab dose adjustment for F carriers were investigated. The numbers of subjects required for the design of two-armed clinical trials were calculated using model-predicted PFS at a power of 80%.

RESULTS

The model predicted a potential benefit of 1500 mg m(-2) maintenance doses of rituximab for both rituximab monotherapy and R-CHOP. The model shows that the PFS of FCGR3A-F carriers remains lower than that of homozygous FCGR3A-VV patients, even with markedly increased rituximab doses.

CONCLUSION

Our results suggest a benefit of increasing doses of rituximab in FL, both during induction and maintenance. These results need to be confirmed in controlled clinical trials.

Stable IgG-like bispecific antibodies directed toward the type I insulin-like growth factor receptor demonstrate enhanced ligand blockade and anti-tumor activity

Bispecific antibodies (BsAbs) target multiple epitopes on the same molecular target or different targets. Although interest in BsAbs has persisted for decades, production of stable and active BsAbs has hindered their clinical evaluation. Here, we describe the production and characterization of tetravalent IgG-like BsAbs that combine the activities of allosteric and competitive inhibitors of the type-I insulin-like growth factor receptor (IGF-1R). The BsAbs, which were engineered for thermal stability, express well, demonstrate favorable biophysical properties, and recognize both epitopes on IGF-1R. Only one BsAb with a unique geometry, denoted BIIB4-5scFv, was capable of engaging all four of its binding arms simultaneously. All the BsAbs (especially BIIB4-5scFv) demonstrated enhanced ligand blocking over the single monoclonal antibodies (mAbs), particularly at high ligand concentrations. The pharmacokinetic profiles of two IgG-like BsAbs were tested in nude mice and shown to be comparable with that of the parental mAbs. The BsAbs, especially BIIB4-5scFv, demonstrated an improved ability to reduce the growth of multiple tumor cell lines and to inhibit ligand-induced IGF-1R signaling in tumor cells over the parental mAbs. BIIB4-5scFv also led to superior tumor growth inhibition over its parental mAbs in vivo. In summary, BsAbs that bridge multiple inhibitory mechanisms against a single target may generally represent a more effective strategy for intervention in oncology or other indications compared with traditional mAb therapy.

CD20 antigen imaging with ¹²⁴I-rituximab PET/CT in patients with rheumatoid arthritis

INTRODUCTION

Visualization of the CD20-antigen expression could provide a tool to localize sites of inflammation and could be of additive value in the diagnosis, and subsequently, in the treatment follow-up of patients with rheumatoid arthritis. In this study, an anti-CD20 monoclonal antibody, rituximab (Mabthera®), was radiolabeled with ¹²⁴Iodine. We report the first results of I¹²⁴-rituximab PET/CT in patients with rheumatoid arthritis.

METHODS

Eligible patients received 50 MBq ¹²⁴I-rituximab. Wholebody PET/CT imaging was performed at 10 min, 24 h, 48 h and 72-96 h post injection. Images were evaluated primarily on a visual basis and were correlated with disease activity as determined by physical examination and clinical measures.

RESULTS

Joints with visually detectable targeting of ¹²⁴I-rituximab were observed in 4 out of 5 evaluable patients. Only the images at 24 h and later showed accumulation in joints, indicating that the visualized signal represented active targeting of rituximab to the CD20 antigen. Several images showed CD20 positive B-cell infiltration in joints which were clinically normal, while a few clinically diagnosed arthritis localizations were not visualized. This discrepancy suggests that infiltration of CD20 positive B-cells in synovium is a phenomenon that is at least partially independent of clinical inflammation. The level of uptake in joints was generally low, representing less than 0.5% of the injected dose.

CONCLUSION

We have shown the feasibility of CD20 antigen imaging using ¹²⁴I-rituximab in patients with rheumatoid arthritis. Further research is needed to elucidate the clinical significance of demonstrated B-cell infiltration in rheumatic joints.

The pharmacokinetics of ¹²⁴I-rituximab in patients with rheumatoid arthritis

Rheumatoid arthritis is a destructive inflammatory joint disorder. Pre- and mature B-cells, characterized by CD20 antigen expression, play an important role in the inflammatory process. Rituximab, a chimeric monoclonal antibody against the CD20 antigen, has been approved since 2006 for the treatment of patients with rheumatoid arthritis. However, not all patients benefit from this treatment. Persistent activity of the disease has been reported despite treatment with rituximab. Imaging of radiolabeled rituximab can be used to monitor the biodistribution of rituximab, and potentially to predict the efficacy of the treatment. In this study, rituximab was radiolabeled with ¹²⁴Iodine for positron emission tomography (PET) imaging. The aim of this study was to investigate the pharmacokinetics and biodistribution of ¹²⁴I-rituximab in patients with rheumatoid arthritis, to establish the optimal procedure for PET imaging. Eligible patients received 50 MBq ¹²⁴I-rituximab, corresponding to approximately 1.5 mg rituximab. Wholebody PET/CT imaging was performed at 10 min, 24 hrs, and 48 hrs post injection. The total body activity, radioactivity in whole blood, and rituximab serum levels were determined. ¹²⁴I-rituximab has favorable pharmacokinetics for targeting of (pathological) B cells and imaging over several days, but only after pre-treatment with unlabeled rituximab. In addition, protection of the thyroid is recommended to prevent uptake of released ¹²⁴I.

[In vivo imaging analysis of biodistribution of FITC-labeled Rituximab in lymphoma-bearing nude mice]

OBJECTIVE

To conduct an in vivo optical imaging analysis of the biodistribution of antibody Rituximab in lymphoma tumor-bearing nude mice.

METHODS

Laser scanning confocal microscope and flow cytometry were employed to determine the affinity of FITC-labeled Rituximab (FITC-Rituximab) with human lymphoma Raji cells. And the in vivo optical imaging system was used to analyze the biodistribution of FITC-Rituximab in lymphoma-transplanted xenograft nude mice.

RESULTS

The results of flow cytometry and laser scanning confocal microscope demonstrated that FITC-Rituximab had remarkable affinity with lymphoma Raji cells and was mainly bound at cell membrane. The results of in vivo imaging analysis suggested that FITC-Rituximab could specifically accumulated at peritumor tissue less than 1 h, then penetrated into the interior of tumor and concentrated in 3-4 h. And the specific concentration of FITC-Rituximab could still been observed more than 8-10 h whereas there was no apparent fluorescence at other tissues. Furthermore, the results observed from a two-flank tumor xenograft model showed that FITC-Rituximab possessed specific binding affinity for CD20-overexpressed lymphoma.

CONCLUSION

The in vivo optical imaging system can accurately monitor the distribution of FITC-Rituximab in tumor-bearing nude mice. And this technique has a reference value and significance for a real-time analysis of tumor-targeting capability of antibody drugs.

Rituximab pharmacokinetics during the management of acute idiopathic thrombotic thrombocytopenic purpura

BACKGROUND

Increasingly, patients with acute, idiopathic, antibody mediated thrombotic thrombocytopenic purpura (TTP) are being treated with rituximab to achieve a durable remission, however, there is the potential that it is removed by plasma exchange (PEX).

OBJECTIVES

To look at the pharmacokinetics and pharmacodynamics of rituximab in patients with acute idiopathic TTP undergoing PEX.

PATIENTS AND METHODS

Patients who received rituximab for acute idiopathic TTP (group 1, n = 30) and a control group (group 2, n = 3) of TTP patients in remission receiving rituximab electively as maintenance were included. Rituximab levels were measured before/after each infusion, before/after PEX and in follow-up. ADAMTS-13 activity, anti-ADAMTS-13 IgG and CD19% were measured to assess response.

RESULTS

The median number of PEX to remission after rituximab was 10 (range 4-25). In group 1 there was no significant incremental rise in the peak serum rituximab level until dose 4. Trough levels were lower in patients who had had PEX since their last rituximab infusion. In the control group, there was an incremental rise in the peak serum rituximab level and all patients had detectable trough levels. The median fall in rituximab per PEX was 65%. All patients achieved CD19 < 1%. In group 1, the median time to undetectable rituximab was 5 months (range 0-12 months) and to B cell return was 7 months (range 3-24 months). ADAMTS-13 increased and anti-ADAMTS-13 fell after therapy. There were three deaths and two relapses in group 1. Relapse was not temporally related to B cell return.