Characterization of B-cell receptor clonality and immunoglobulin gene usage at multiple time points during active SARS-CoV-2 infection.

Although monoclonal antibodies to the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) are known, B-cell receptor repertoire and its change in patients during coronavirus disease-2019 (COVID-19) progression is underreported. We aimed to study this molecularly. We used immunoglobulin heavy chain (IGH) variable region (IGHV) spectratyping and next-generation sequencing of peripheral blood B-cell genomic DNA collected at multiple time points during disease evolution to study B-cell response to SARS-CoV-2 infection in 14 individuals with acute COVID-19. We found a broad distribution of responding B-cell clones. The IGH gene usage was not significantly skewed but frequencies of individual IGH genes changed repeatedly. We found predominant usage of unmutated and low mutation-loaded IGHV rearrangements characterizing naïve and extrafollicular B cells among the majority of expanded peripheral B-cell clonal lineages at most tested time points in most patients. IGH rearrangement usage showed no apparent relation to anti-SARS-CoV-2 antibody titers. Some patients demonstrated mono/oligoclonal populations carrying highly mutated IGHV rearrangements indicating antigen experience at some of the time points tested, including even before anti-SARS-CoV-2 antibodies were detected. We present evidence demonstrating that the B-cell response to SARS-CoV-2 is individual and includes different lineages of B cells at various time points during COVID-19 progression.

COVID-19 in patients with classic and variant hairy cell leukemia.

Hairy cell leukemia (HCL), similar to its variant HCLv, is a B-cell malignancy associated with decreased humoral immunity. We prospectively monitored the largest cohort of patients with HCL/HCLv to date (n = 503) for COVID-19 by symptoms, antibody, and polymerase chain reaction (PCR) and/or antigen positivity. Fifty percent (253 of 503) of the patients with HCL/HCLv (238 HCL and 15 HCLv) had evidence of COVID-19, with 210 (83%) testing positive by PCR or rapid-antigen test. Of the 43 patients without positive tests, all had nucleocapsid antibodies indicating COVID-19 exposure, 7 recalled no symptoms, and 36 had mild symptoms. Of the 210 who tested positive, 23, 46, 129, and 12 cases occurred in 2020, 2021, 2022, and 2023, respectively. Among them, 175 began treatment for HCL/HCLv 0.4 to 429 (median, 66) months before, and 132 had their last dose of anti-CD20 monoclonal antibody 0.2 to 229 (median, 63) months before. Two patients died, including a young woman who began rituximab 2 months after first-line cladribine before vaccine availability. Nearly all patients with HCL/HCLv recovered uneventfully from COVID-19 including those without vaccination or those with significant immunosuppression and recent treatment. However, decreased normal B cells from HCL or treatment was associated with lower spike antibody levels as a response to COVID-19 (P = .0094) and longer recovery time (P = .0036). Thus, in a large cohort of patients with HCL/HCLv and in the first to determine relationships between COVID-19 outcome and immune markers, mortality was relatively low (∼1%), sequelae were uncommon, and recovery from COVID-19 was longer if normal B cells were low after recent treatment. The trials are registered at www.clinicaltrials.gov as #NCT01087333 and #NCT04362865.

Dabrafenib plus trametinib in patients with relapsed/refractory BRAF V600E mutation-positive hairy cell leukemia.

BRAF V600E is the key oncogenic driver mutation in hairy cell leukemia (HCL). We report the efficacy and safety of dabrafenib plus trametinib in patients with relapsed/refractory BRAF V600E mutation-positive HCL. This open-label, phase 2 study enrolled patients with BRAF V600E mutation-positive HCL refractory to first-line treatment with a purine analog or relapsed after ≥2 prior lines of treatment. Patients received dabrafenib 150 mg twice daily plus trametinib 2 mg once daily until disease progression, unacceptable toxicity, or death. The primary endpoint was investigator-assessed objective response rate (ORR) per criteria adapted from National Comprehensive Cancer Network-Consensus Resolution guidelines. Secondary endpoints included duration of response (DOR), progression-free survival (PFS), overall survival (OS), and safety. Fifty-five patients with BRAF V600E mutation-positive HCL were enrolled. The investigator-assessed ORR was 89.0% (95% confidence interval, 77.8%-95.9%); 65.5% of patients had a complete response (without minimal residual disease [MRD]: 9.1% [negative immunohistochemistry of bone marrow {BM} biopsy], 12.7% [negative BM aspirate flow cytometry {FC}], 16.4% [negative immunohistochemistry and/or FC results]; with MRD, 49.1%), and 23.6% had a partial response. The 24-month DOR was 97.7% with 24-month PFS and OS rates of 94.4% and 94.5%, respectively. The most common treatment-related adverse events were pyrexia (58.2%), chills (47.3%), and hyperglycemia (40.0%). Dabrafenib plus trametinib demonstrated durable responses with a manageable safety profile consistent with previous observations in other indications and should be considered as a rituximab-free therapeutic option for patients with relapsed/refractory BRAF V600E mutation-positive HCL. This trial is registered at www.clinicaltrials.gov as #NCT02034110.

Genetic regulation of OAS1 nonsense-mediated decay underlies association with COVID-19 hospitalization in patients of European and African ancestries.

The chr12q24.13 locus encoding OAS1-OAS3 antiviral proteins has been associated with coronavirus disease 2019 (COVID-19) susceptibility. Here, we report genetic, functional and clinical insights into this locus in relation to COVID-19 severity. In our analysis of patients of European (n = 2,249) and African (n = 835) ancestries with hospitalized versus nonhospitalized COVID-19, the risk of hospitalized disease was associated with a common OAS1 haplotype, which was also associated with reduced severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) clearance in a clinical trial with pegIFN-λ1. Bioinformatic analyses and in vitro studies reveal the functional contribution of two associated OAS1 exonic variants comprising the risk haplotype. Derived human-specific alleles rs10774671-A and rs1131454 -A decrease OAS1 protein abundance through allele-specific regulation of splicing and nonsense-mediated decay (NMD). We conclude that decreased OAS1 expression due to a common haplotype contributes to COVID-19 severity. Our results provide insight into molecular mechanisms through which early treatment with interferons could accelerate SARS-CoV-2 clearance and mitigate against severe COVID-19.

Diagnosis and treatment of hairy cell leukemia as the COVID-19 pandemic continues.

Hairy cell leukemia (HCL) is an indolent B-cell malignancy, usually driven by the BRAF V600E mutation. For 30 years, untreated and relapsed HCL was successfully treated with purine analogs, but minimal residual disease (MRD) remained in most patients, eventually causing relapse. Repeated purine analogs achieve decreasing efficacy and increasing toxicity, particularly to normal T-cells. MRD-free complete remissions (CRs) are more common using rituximab with purine analogs in both 1st-line and relapsed settings. BRAF inhibitors and Ibrutinib can achieve remission, but due to persistence of MRD, must be used chronically to prevent relapse. BRAF inhibition combined with Rituximab can achieve high MRD-free CR rates. Anti-CD22 recombinant immunotoxin moxetumomab pasudotox is FDA-approved in the relapsed setting and is unique in achieving high MRD-free CR rates as a single-agent. Avoiding chemotherapy and rituximab may be important in ensuring both recovery from COVID-19 and successful COVID-19 vaccination, an area of continued investigation.

Long term follow-up of a phase II study of cladribine with concurrent rituximab with hairy cell leukemia variant.

Hairy cell leukemia variant (HCLv) responds poorly to purine analogue monotherapy. Rituximab concurrent with cladribine (CDAR) improves response rates, but long-term outcomes are unknown. We report final results of a phase 2 study of CDAR for patients with HCLv. Twenty patients with 0 to 1 prior courses of cladribine and/or rituximab, including 8 who were previously untreated, received cladribine 0.15 mg/kg on days 1 to 5 with 8 weekly rituximab doses of 375 mg/m2 beginning day 1. Patients received a second rituximab course ≥6 months after cladribine, if and when minimal residual disease (MRD) was detected in blood. The complete remission (CR) rate from CDAR was 95% (95% confidence interval, 75-100). Sixteen (80%) of 20 patients (95% confidence interval, 56-94) became MRD negative according to bone marrow at 6 months. The median duration of MRD-negative CR was 70.1 months, and 7 of 16 are still MRD negative up to 120 months. With a median follow-up of 69.7 months, 11 patients received delayed rituximab, and the 5-year progression-free survival (PFS) and overall survival (OS) were 63.3% and 73.9%, respectively. Five patients with TP53 mutations had shorter PFS (median, 36.4 months vs unreached; P = .0024) and OS (median, 52.4 months vs unreached; P = .032). MRD-negative CR at 6 months was significantly associated with longer PFS (unreached vs 17.4 months; P < .0001) and OS (unreached vs 38.2 months; P < .0001). Lack of MRD in blood at 6 months was also predictive of longer PFS and OS (P < .0001). After progression following CDAR, median OS was 29.7 months. CDAR is effective in HCLv, with better outcomes in patients who achieve MRD-negative CR. This trial is registered at www.clinicaltrials.gov as #NCT00923013.

Genetic regulation of OAS1 nonsense-mediated decay underlies association with risk of severe COVID-19.

Genomic regions have been associated with COVID-19 susceptibility and outcomes, including the chr12q24.13 locus encoding antiviral proteins OAS1-3. Here, we report genetic, functional, and clinical insights into genetic associations within this locus. In Europeans, the risk of hospitalized vs. non-hospitalized COVID-19 was associated with a single 19Kb-haplotype comprised of 76 OAS1 variants included in a 95% credible set within a large genomic fragment introgressed from Neandertals. The risk haplotype was also associated with impaired spontaneous but not treatment-induced SARS-CoV-2 clearance in a clinical trial with pegIFN-λ1. We demonstrate that two exonic variants, rs10774671 and rs1131454, affect splicing and nonsense-mediated decay of OAS1 . We suggest that genetically-regulated loss of OAS1 expression contributes to impaired spontaneous clearance of SARS-CoV-2 and elevated risk of hospitalization for COVID-19. Our results provide the rationale for further clinical studies using interferons to compensate for impaired spontaneous SARS-CoV-2 clearance, particularly in carriers of the OAS1 risk haplotypes.

Expression of the muscle-associated gene MYF6 in hairy cell leukemia.

Hairy cell leukemia (HCL) is a purine analog-responsive B-cell malignancy containing the BRAF V600E mutation, expressing CD22, CD11c, CD103, tartrate resistant acid phosphatase (TRAP) CD25, CD123, and annexin 1A. BRAF V600E and the latter 4 markers are usually absent in the more aggressive and chemoresistant variant HCLv. To evaluate differences between HCL and HCLv, expression microarrays comparing HCL with HCLv were performed for 24694 genes using 47323 probes. Microarray data from 35 HCL and 27 HCLv purified samples showed the greatest HCL-HCLv difference in the muscle-associated gene MYF6, expressed by its 2 probes 18.5- and 10.8-fold higher in HCL than HCLv (p<0.0001). By real-time quantitative PCR (RQ-PCR), 100% of 152 classic HCL samples were MYF6-positive, vs 5 (6%) of 90 blood donors. MYF6-expression was also detected in 18 (35%) of 51 with HCLv, 11 (92%) of 12 with HCL expressing unmutated IGHV4-34, 35 (73%) of 48 with chronic lymphocytic leukemia (CLL), and 1 (8%) of 12 with mantle cell lymphoma. Hypomethylation status of MYF6 supported expression in HCL more than HCLv. Posttreatment blood samples becoming negative by flow cytometry remained MYF6+ by RQ-PCR in 42 (48%) of 87 HCL patients, and MYF6 RQ-PCR could detect 1 HCL in 105 normal cells. MYF6, universally expressed in HCL and in most CLL samples, may be a useful biomarker for these leukemias. Further studies are underway to determine the role of MYF6 in HCL.

Randomized Phase II Study of First-Line Cladribine With Concurrent or Delayed Rituximab in Patients With Hairy Cell Leukemia.

PURPOSE: Single-agent purine analog, usually cladribine, has been the standard first-line therapy of hairy cell leukemia (HCL) for 30 years. High complete remission (CR) rates often include minimal residual disease (MRD), leading to relapse and repeated treatments. Rituximab can clear MRD, but long-term results are unknown and optimal timing of rituximab undefined. PATIENTS AND METHODS: Patients were randomly assigned to first-line cladribine 0.15 mg/kg intravenously days 1-5 with 8 weekly doses of rituximab 375 mg/m2 begun either day 1 (concurrent, CDAR) or ≥ 6 months later (delayed) after detection of MRD in blood. MRD tests included blood and bone marrow (BM) flow cytometry, and BM immunohistochemistry. RESULTS: Sixty-eight patients with purine analog-naïve classic HCL were randomly assigned 1:1 to concurrent versus delayed arms. At 6 months after CDAR versus cladribine monotherapy, CR rates were 100% versus 88% (P = .11), MRD-free CR rates 97% versus 24% (P < .0001, primary end point), and blood MRD-free rates 100% versus 50% (P < .0001), respectively. At 96 months median follow-up, 94% versus 12% remained MRD free. Compared with CDAR, delayed rituximab after cladribine achieved lower rate (67% of 21 evaluable patients; P = .0034) and durability (P = .0081, hazard radio favoring CDAR, 0.094) of MRD-free CR. Nevertheless, 12 patients in the delayed arm remained MRD free when restaged 6-104 (median, 78) months after last delayed rituximab treatment. Compared with cladribine monotherapy, CDAR led to brief grade 3/4 thrombocytopenia (59% v 9%; P < .0001) and platelet transfusions without bleeding (35% v 0%; P = .0002), but higher neutrophil (P = .017) and platelet (P = .0015) counts at 4 weeks. CONCLUSION: Achieving MRD-free CR of HCL after first-line cladribine is greatly enhanced by concurrent rituximab and less so by delayed rituximab. Longer follow-up will determine if MRD-free survival leads to less need for additional therapy or cure of HCL.

Differential Expression of CD43, CD81, and CD200 in Classic Versus Variant Hairy Cell Leukemia.

BACKGROUND: Hairy cell leukemia (HCL) and hairy cell leukemia variant (HCLv) are rare diseases with overlapping clinicopathological features. Features distinguishing HCL from HCLv include expression of CD25, CD123, CD200, annexin-A1, and the presence of BRAF V600E mutation. HCLv typically lacks these markers, but they may occur in a subgroup of HCL patients with an aggressive clinical course. We examined CD43, CD81, CD79b, and CD200 expression in HCL and HCLv. METHODS: Multiparametric flow cytometry (FCM) was performed on blood from 59 HCL and 15 HCLv patients for protocol entry. Mean fluorescent intensity (MFI) of CD43, CD79b, CD81, and CD200 was determined (for CD200, n = 17 and 7, respectively). RESULTS: Median MFI of HCL vs HCLv was 545 vs 272 for CD43, 602 vs 2,450 for CD81, 4,962 vs 1,969 for CD79b, and 11,652 vs 1,405 for CD200, respectively. Analysis of the median differences, HCL minus HCLv (and their 95% confidence intervals and P-values) indicated that CD43 MFI (estimated median difference (95% CI): 212 [72-413; P = 0.0027) and CD200 MFI (9,883 [3,514-13,434]; P < 0.0001) were higher in HCL than in HCLv, while CD81 MFI (-1,858 [-2,604 to -1,365]; P < 0.0001) was lower in HCL than in HCLv. CD79b MFI HCL median was more than double that of HCLv, but the observed difference (1,571 [-739 to 4,417]) was consistent with the null hypothesis of no difference (P = 0.13). CONCLUSIONS: CD200, CD43, and CD81 are likely differentially expressed between HCL and HCLv, reflecting their differing disease biology. Inclusion of these markers in FCM is potentially informative. © 2019 International Clinical Cytometry Society.

Generation of antibody-based therapeutics targeting the Idiotype of B-cell Malignancies.

BACKGROUND: A feature of many B-cell tumors is a surface-expressed immunoglobulin (sIg). The complementarity determiningregions (CDRs)of the sIg, termed the 'idiotype', are unique to each tumor. We report on a phage selection strategy to generate anti-idiotype therapeutics that react with sIg CDR3 sequences: the MEC1 B-cell tumor line was used as proof of concept. METHODS: To create a mimetic of the MEC1 idiotype, CDR3 sequences from heavy and light chains of the sIg were grafted into a scFv framework scaffold. Using the Tomlinson I phage library of human scFvs, we enriched for binders to MEC1 CDR3 sequences over unrelated CDR3 sequences. RESULTS: By ELISA we identified 10 binder phage. Of these, five were sequenced, found to be unique and characterized further. By flow cytometry each of the five phage bound to MEC1 cells, albeit with different patterns of reactivity. To establish specificity of binding and utility, the scFv sequences from two of these binders (phage 1, and 7) were converted into antibody-toxin fusion proteins (immunotoxins) and also cloned into a human IgG1 expression vector. Binder-1 and -7 immunotoxins exhibited specific killing of MEC1 cells with little toxicity for non-target B-cell lines. The full-length antibody recreated from the binder-1 scFv so exhibited specific binding. CONCLUSION: Our results establish the utility of using engrafted CDR3 sequences for selecting phage that recognize the idiotype of B-cell tumors.

Update on hairy cell leukemia.

Hairy cell leukemia (HCL) is a chronic B-cell malignancy with multiple treatment options, including several that are investigational. Patients present with pancytopenia and splenomegaly, owing to the infiltration of leukemic cells expressing CD22, CD25, CD20, CD103, tartrate-resistant acid phosphatase (TRAP), annexin A1 (ANXA1), and the BRAF V600E mutation. A variant lacking CD25, ANXA1, TRAP, and the BRAF V600E mutation, called HCLv, is more aggressive and is classified as a separate disease. A molecularly defined variant expressing unmutated immunoglobulin heavy variable 4-34 (IGHV4-34) is also aggressive, lacks the BRAF V600E mutation, and has a phenotype of HCL or HCLv. The standard first-line treatment, which has remained unchanged for the past 25 to 30 years, is single-agent therapy with a purine analogue, either cladribine or pentostatin. This approach produces a high rate of complete remission. Residual traces of HCL cells, referred to as minimal residual disease, are present in most patients and cause frequent relapse. Repeated treatment with a purine analogue can restore remission, but at decreasing rates and with increasing cumulative toxicity. Rituximab has limited activity as a single agent but achieves high complete remission rates without minimal residual disease when combined with purine analogues, albeit with chemotherapy-associated toxicity. Investigational nonchemotherapy options include moxetumomab pasudotox, which targets CD22; vemurafenib or dabrafenib, each of which targets the BRAF V600E protein; trametinib, which targets mitogen-activated protein kinase enzyme (MEK); and ibrutinib, which targets Bruton tyrosine kinase (BTK).

Impact of telomere length on survival in classic and variant hairy cell leukemia.

Telomeres, which protect the ends of chromosomes, are shortened in several hematologic malignancies, often with adverse prognostic implications, but their effect on prognosis of classic and variant hairy cell leukemia (HCL and HCLv) has not been reported. HCL/HCLv genomic DNA from 46 patients was studied by PCR to determine the ratio of telomere to single copy gene number (T/S). T/S was unrelated to diagnosis of HCL or HCLv (p=0.27), but shorter T/S was associated with unmutated immunoglobulin rearrangements (p=0.033) and age above the median at diagnosis (p=0.017). Low T/S was associated with shorter overall survival from diagnosis (OS), particularly T/S <0.655 (p=0.0064, adjusted p=0.019). Shorter OS was also associated with presence of unmutated (p<0.0001) or IGHV4-34+ (p<0.0001) rearrangements, or increasing age (p=0.0002). Multivariable analysis with Cox modeling showed that short T/S along with either unmutated or IGHV4-34+ rearrangements remained associated with reduced OS (p=0.0071, p=0.0024, respectively) after age adjustment. While T/S is relatively long in HCL and the disease usually indolent with excellent survival, shortened telomeres in HCL/HCLv are associated with decreased survival. Shortened T/S could represent a risk factor needing further investigation/intervention to determine if non-chemotherapy treatment options, in addition to or instead of chemotherapy, might be particularly useful.

Class II human leucocyte antigen DRB1*11 in hairy cell leukaemia patients with and without haemolytic uraemic syndrome.

Frequencies of human leucocyte antigens (HLA) were determined in 287 classic hairy cell leukaemia (HCL) patients. With respect to both population (n = 287) and allele (2n = 574) frequency respectively, the most common HLA class I and II antigens expressed were HLA-A*02 (49·1% and 28·6%), HLA-B*07 (21·3% and 11·1%), HLA-C*07 (46·7 and 28·2%), HLA-DQB1*03 (62·7% and 37·3%), HLA-DRB1*11 (30·0% and 16·0%) and HLA-DRB4*01 (45·3% and 29·6%). In comparing 6-14 databases of control Caucasians to 267 Caucasian HCL patients, only HLA-DRB1*11 was consistently over-represented in HCL, 31·1% of patients vs. 17-19·9% of controls (P = 0·0055 to <0·0001) and 16·5% of alleles vs. 6·5-12·3% of control alleles (P = 0·022 to <0·0001). HLA-DRB1*11 is a known risk factor for acquired thrombotic microangiopathy. Anti-CD22 recombinant immunotoxin BL22 in HCL was associated with a 12% incidence of completely reversible grade 3-4 haemolytic uraemic syndrome (HUS), mainly during the second or third retreatment cycle. Of 49 HCL patients receiving ≥2 cycles of BL22, 7 (14%) had HUS and HLA-DRB1*11 was expressed in 71% of 7 with HUS compared with only 21% of 42 without (P = 0·015). These data suggest that DBR1*11 may be a marker for increased susceptibility to HCL and, among HCL patients, could be a risk factor for BL22-induced HUS.

The bruton tyrosine kinase inhibitor ibrutinib (PCI-32765) blocks hairy cell leukaemia survival, proliferation and B cell receptor signalling: a new therapeutic approach.

B cell receptor (BCR) signalling plays a critical role in the progression of several B-cell malignancies, but its role in hairy cell leukaemia (HCL) is ambiguous. Bruton tyrosine kinase (BTK), a key player in BCR signalling, as well as B cell migration and adhesion, can be targeted with ibrutinib, a selective, irreversible BTK inhibitor. We analysed BTK expression and function in HCL and analysed the effects of ibrutinib on HCL cells. We demonstrated uniform BTK protein expression in HCL cells. Ibrutinib significantly inhibited HCL proliferation and cell cycle progression. Accordingly, ibrutinib also reduced HCL cell survival after BCR triggering with anti-immunoglobulins and abrogated the activation of kinases downstream of the BCR (PI3K and MAPK). Ibrutinib also inhibited BCR-dependent secretion of the chemokines CCL3 and CCL4 by HCL cells. Interestingly, ibrutinib inhibited also CXCL12-induced signalling, a key pathway for bone marrow homing. Collectively, our data support the clinical development of ibrutinib in patients with HCL.

High prevalence of MAP2K1 mutations in variant and IGHV4-34-expressing hairy-cell leukemias.

To understand the genetic mechanisms driving variant and IGHV4-34-expressing hairy-cell leukemias, we performed whole-exome sequencing of leukemia samples from ten affected individuals, including six with matched normal samples. We identified activating mutations in the MAP2K1 gene (encoding MEK1) in 5 of these 10 samples and in 10 of 21 samples in a validation set (overall frequency of 15/31), suggesting potential new strategies for treating individuals with these diseases.

Cladribine with immediate rituximab for the treatment of patients with variant hairy cell leukemia.

PURPOSE: In contrast with the classic form, variant hairy cell leukemia (HCLv) responds poorly to single-agent purine analogs, expresses unmutated BRAF, has shorter overall survival, and lacks effective standard therapy. No treatment has achieved a high complete remission (CR) rate even in small series, and of 39 reported cases from six studies, overall response rate after cladribine was 44% with 8% CRs. Rituximab has been found to increase the sensitivity of malignant cells to cladribine, suggesting that combination with cladribine might improve response in HCLv. To test this hypothesis, patients with HCLv were treated with simultaneous cladribine and rituximab. EXPERIMENTAL DESIGN: Patients with HCLv with 0 to 1 prior courses of cladribine received cladribine 0.15 mg/kg for days 1 to 5, with eight weekly doses of rituximab 375 mg/m(2) beginning day 1. Restaging was performed, and minimal residual disease (MRD) in blood and marrow was quantified using PCR, immunohistochemistry, and flow cytometry. RESULTS: By 6 months, 9 (90%) of 10 patients achieved CR, compared with 3 (8%) of 39 reported cases treated with cladribine alone (P < 0.0001). Of the 9 CRs, 8 remain free of MRD at 12 to 48 (median 27) months of follow-up. No dose-limiting toxicities were observed when beginning cladribine and rituximab on the same day, although most patients required short-term steroids to prevent and treat rituximab infusion reactions. Cytopenias in CRs resolved in 7 to 211 (median 34) days without major infections. CONCLUSION: Although cladribine alone lacks effectiveness for early or relapsed HCLv, cladribine with immediate rituximab achieves CRs without MRD and is feasible to administer.

Bendamustine and rituximab in relapsed and refractory hairy cell leukemia.

PURPOSE: To determine tolerability and for the first time explore efficacy of bendamustine-rituximab (BR) in multiply relapsed/refractory hairy cell leukemia (HCL), using two different dose levels of bendamustine. EXPERIMENTAL DESIGN: Patients with HCL with ≥2 prior therapies requiring treatment received rituximab 375 mg/m(2) days 1 and 15 plus bendamustine 70 (n = 6) or 90 (n = 6) mg/m(2), days 1 and 2, for six cycles at 4-week intervals. RESULTS: At 70 and 90 mg/m(2)/dose of bendamustine, overall response rate was 100%, with three (50%) and four (67%) complete remissions (CR) in each respective group. Minimal residual disease (MRD) was absent in 67% and 100% of CRs, respectively. All six without MRD remain in CR at 30 to 35 (median, 31) months of follow-up. Soluble CD22 and CD25 levels decreased with all responses, with median values decreasing from 17.7 and 42 ng/mL at baseline to undetectable and 2 ng/mL after CR, respectively (P < 0.001). Of 12 patients receiving 72 cycles of BR, the most common toxicities were hematologic, including thrombocytopenia (83%), lymphopenia (75%), leukopenia (58%), and neutropenia (42%). Grade III and IV hematologic toxicity included lymphopenia and thrombocytopenia (each 75%), leukopenia (58%), and neutropenia (25%). No significant dose-related differences were detected in response or toxicity. CONCLUSION: BR has significant activity in HCL. Bendamustine at either 70 or 90 mg/m(2)/dose was highly effective in multiply relapsed/refractory HCL and could be considered for achieving durable CRs without MRD in patients after failure of standard therapies. As it was not dose-limiting, 90 mg/m(2)/dose was chosen for future testing.