Rituximab, a chimaeric anti-CD20 monoclonal antibody, in the treatment of hairy cell leukaemia

Refractory and relapsed hairy-cell leukemia (HCL): casting light on promising experimental drugs in clinical trials

INTRODUCTION

Hairy cell leukemia (HCL) is a rare subtype of indolent lymphoid leukemia originating from a mature B lymphocyte. The standard first-line treatment for classic HCL, and HCL variant (HCLv), consists of purine nucleoside analogs (PNA), with or without rituximab. However, almost half of patients relapse and require subsequent therapy.

AREAS COVERED

This article summarizes recent achievements in the treatment of relapsed and refractory HCL. A literature search was conducted of the PubMed and MEDLINE database for articles in English. Publications from 2010 through January 2023 were scrutinized. The search terms used were hairy cell leukemia in conjunction with BRAF inhibitors, Bruton's tyrosine kinase (BTK) inhibitors, CD20 monoclonal antibodies, relapsed, refractory and variant.The growing understanding of HCL biology has allowed the design of several new, chemotherapy-free targeted drugs which have demonstrated encouraging efficacy in early clinical trials.

EXPERT OPINION

Novel drugs will soon be available to assist standard therapy for HCL and HCLv among patients with suboptimal results following PNA treatment. In particular, the BRAF inhibitors vemurafenib and dabrafenib, with or without rituximab, have revolutionized treatment of patients with relapsed or refractory disease.

Treatment of Classic Hairy Cell Leukemia: Targeting Minimal Residual Disease beyond Cladribine

Simple Summary

Standard treatment with purine analogues facilitates a near normal life expectancy in the majority of patients with classic hairy cell leukemia (HCL), a rare chronic B-cell malignancy. However, nearly all patients ultimately relapse and require retreatment, while drug-induced myelotoxicity accumulates predisposing to infectious complications and, possibly, secondary malignancies. Persistence of minimal residual disease (MRD) in a substantial portion of treated patients has become a surrogate for this still limited treatment efficacy. New insights into disease biology initiated design and investigation of several new, chemotherapy-free, targeted drugs with encouraging efficacy in early clinical trials aimed at enhancing eradication of MRD and optimizing drug tolerability. This review provides an update on recent clinical trials investigating treatment strategies beyond purine analogues in HCL and discusses clinically relevant obstacles still to overcome.

Abstract

Classic hairy cell leukemia (HCL) is a rare indolent B-cell lymphoproliferative disorder characterized by profound pancytopenia and frequent infectious complications due to progressive infiltration of the bone marrow and spleen. Lacking effective treatment options, affected patients were confronted with a dismal survival prognosis of less than 5 years when the disease was first described in 1958. Tremendous therapeutic advances were accomplished with the introduction of purine analogues such as cladribine in the 1990s, facilitating a near-normal life expectancy in most HCL patients. Nevertheless, nearly all patients eventually relapse and require successive retreatments, while drug-associated myelotoxicity may accumulate and secondary malignancies may evolve. Detection of minimal residual disease (MRD) in a substantial portion of treated patients has become a surrogate for this still limited treatment efficacy. In the last decade, novel biologic insights such as identification of the driver mutation BRAF V600E have initiated the development and clinical investigation of new, chemotherapy-free, targeted drugs in HCL treatment, with encouraging efficacy in early clinical trials aimed at boosting eradication of MRD while optimizing drug tolerability. This review summarizes current clinical trials investigating treatment strategies beyond purine analogues in HCL and discusses clinically relevant obstacles still to overcome.

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 1^st-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.

Moxetumomab pasudotox in heavily pre-treated patients with relapsed/refractory hairy cell leukemia (HCL): long-term follow-up from the pivotal trial

Background

Moxetumomab pasudotox is a recombinant CD22-targeting immunotoxin. Here, we present the long-term follow-up analysis of the pivotal, multicenter, open-label trial (NCT01829711) of moxetumomab pasudotox in patients with relapsed/refractory (R/R) hairy cell leukemia (HCL).

Methods

Eligible patients had received ≥ 2 prior systemic therapies, including ≥ 2 purine nucleoside analogs (PNAs), or ≥ 1 PNA followed by rituximab or a BRAF inhibitor. Patients received 40 µg/kg moxetumomab pasudotox intravenously on Days 1, 3, and 5 of each 28-day cycle for up to six cycles. Disease response and minimal residual disease (MRD) status were determined by blinded independent central review. The primary endpoint was durable complete response (CR), defined as achieving CR with hematologic remission (HR, blood counts for CR) lasting > 180 days.

Results

Eighty adult patients were treated with moxetumomab pasudotox and 63% completed six cycles. Patients had received a median of three lines of prior systemic therapy; 49% were PNA-refractory, and 38% were unfit for PNA retreatment. At a median follow-up of 24.6 months, the durable CR rate (CR with HR > 180 days) was 36% (29 patients; 95% confidence interval: 26–48%); CR with HR ≥ 360 days was 33%, and overall CR was 41%. Twenty-seven complete responders (82%) were MRD-negative (34% of all patients). CR lasting ≥ 60 months was 61%, and the median progression-free survival without the loss of HR was 71.7 months. Hemolytic uremic and capillary leak syndromes were each reported in ≤ 10% of patients, and ≤ 5% had grade 3–4 events; these events were generally reversible. No treatment-related deaths were reported.

Conclusions

Moxetumomab pasudotox resulted in a high rate of durable responses and MRD negativity in heavily pre-treated patients with HCL, with a manageable safety profile. Thus, it represents a new and viable treatment option for patients with R/R HCL, who currently lack adequate therapy.

Trial registration

ClinicalTrials.gov identifier: NCT01829711; first submitted: April 9, 2013. https://clinicaltrials.gov/ct2/show/NCT01829711

Supplementary information

Supplementary information accompanies this paper at 10.1186/s13045-020-01004-y.

The pharmacological management of hairy cell leukemia

INTRODUCTION

Hairy cell leukemia (HCL) is a B-cell lymphoid malignancy that accounts for approximately 2% of all leukemias. Treatment with purine nucleoside analogs (PNA) results in a high response rate and remains the standard of care. Long term follow-up shows that most patients relapse and require retreatment. Newer combination strategies and agents have emerged to try to reduce the relapse rate and to address cases of PNA refractoriness.

AREAS COVERED

The authors reviewed the literature on the pharmacological management of HCL, including recent studies that led to new agents being incorporated into practice.

EXPERT OPINION

Combination of cladribine plus rituximab produces a high rate of measurable residual disease-negative complete remission. In our center, newly diagnosed patients are offered cladribine followed by 8 weekly doses of rituximab in an ongoing phase II trial. Patients in first relapse are also offered this combination if they were initially treated with a single-agent PNA, or if the remission duration was ≥5 years after first-line cladribine plus rituximab. Patients who relapse within 5 years are offered therapy with a novel agent that may include the BRAF inhibitor vemurafenib, alone or in combination with rituximab, dabrafenib in combination with trametinib, the BTK inhibitor ibrutinib, or moxetumomab pasudotox.

Hairy Cell Leukaemia

PURPOSE OF REVIEW

To summarise diagnostic clinical/laboratory findings and highlight differences between classical hairy cell leukaemia (HCLc) and hairy cell leukaemia variant (HCLv). Discussion of prognosis and current treatment indications including novel therapies, linked to understanding of the underlying molecular pathogenesis.

RECENT FINDINGS

Improved understanding of the underlying pathogenesis of HCLc, particularly the causative mutation BRAF V600E, leading to constitutive activation of the MEK/ERK signalling pathway and increased cell proliferation. HCLc is caused by BRAF V600E mutation in most cases. Purine nucleoside analogue (PNA) therapy is the mainstay of treatment, with the addition of rituximab, improving response and minimal residual disease (MRD) clearance. Despite excellent responses to PNAs, many patients will eventually relapse, requiring further therapy. Rarely, patients are refractory to PNA therapy. In relapsed/refractory patients, novel targeted therapies include BRAF inhibitors (BRAFi), anti-CD22 immunoconjugate moxetumomab and Bruton tyrosine kinase inhibitors (BTKi). HCLv has a worse prognosis with median overall survival (OS), only 7-9 years, despite the combination of PNA/rituximab improving front-line response. Moxetumomab or ibrutinib may be a viable treatment but lacks substantial evidence.

Hairy cell leukemia: present and future directions

Hairy cell leukemia (HCL) is an indolent B-cell malignancy, with long-term responses to purine analogs, but with decreasing efficacy and increasing toxicity with repeated courses. Leukemic cells express CD22, CD20, CD25, tartrate-resistant acid phosphatase (TRAP), annexin 1A (Anxa1), and BRAF V600E mutation. HCLv, lacking CD25, Anxa1, TRAP, and BRAF V600E, is more aggressive and less purine analog-sensitive. A molecularly defined IGHV4-34+ variant is also resistant whether HCL or HCLv immunophenotypically. Traces of HCL cells, termed minimal residual disease (MRD), accompany most with complete remission (CR) and may cause relapse. Rituximab has limited single-agent activity, but frequent CR without MRD when combined with purine analog, albeit with chemotherapy toxicities. The anti-CD22 recombinant immunotoxin Moxetumomab Pasudotox can achieve MRD-negative CR in multiply relapsed HCL without chemotherapy toxicities and was FDA approved in 2018 as Lumoxiti. Investigational oral non-chemotherapy options also include Vemurafenib or Dabrafenib/Trametinib targeting BRAF V600E ± MEK, and Ibrutinib targeting Bruton's tyrosine kinase.

Moxetumomab pasudotox in relapsed/refractory hairy cell leukemia. Leukemia. 2018;32:1768-1777. [PMID: 30030507 PMCID: PMC6087717 DOI: 10.1038/s41375-018-0210-1]

This is a pivotal, multicenter, open-label study of moxetumomab pasudotox, a recombinant CD22-targeting immunotoxin, in hairy cell leukemia (HCL), a rare B cell malignancy with high CD22 expression. The study enrolled patients with relapsed/refractory HCL who had ≥2 prior systemic therapies, including ≥1 purine nucleoside analog. Patients received moxetumomab pasudotox 40 µg/kg intravenously on days 1, 3, and 5 every 28 days for ≤6 cycles. Blinded independent central review determined disease response and minimal residual disease (MRD) status. Among 80 patients (79% males; median age, 60.0 years), durable complete response (CR) rate was 30%, CR rate was 41%, and objective response rate (CR and partial response) was 75%; 64 patients (80%) achieved hematologic remission. Among complete responders, 27 (85%) achieved MRD negativity by immunohistochemistry. The most frequent adverse events (AEs) were peripheral edema (39%), nausea (35%), fatigue (34%), and headache (33%). Treatment-related serious AEs of hemolytic uremic syndrome (7.5%) and capillary leak syndrome (5%) were reversible and generally manageable with supportive care and treatment discontinuation (6 patients; 7.5%). Moxetumomab pasudotox treatment achieved a high rate of independently assessed durable response and MRD eradication in heavily pretreated patients with HCL, with acceptable tolerability.

How I manage patients with hairy cell leukaemia

Patients with hairy cell leukaemia (HCL) have highly favourable outcomes after purine analogue therapy. However, most patients subsequently relapse and require re-treatment. A minority of patients develop purine analogue-refractory disease. Targeted therapies have improved outcomes for such patients. Recently, the BRAF V600E mutation was identified in most patients with classical HCL, resulting in constitutive mitogen-activated protein kinase pathway activation; impressive responses are achieved in heavily pre-treated patients with BRAF inhibition. The CD22-targeted immunoconjugate moxetumomab pasudotox and BTK inhibitor ibrutinib also achieve responses in relapsed and refractory patients. HCL variant and the IGHV4-34 molecular variant of HCL lack BRAF mutation and have inferior outcomes with standard purine analogue therapy. The addition of rituximab to purine analogues achieves very high rates of minimal residual disease-negative complete remission and improves outcomes for patients with HCL variant. Given the rarity of HCL, optimal integration of novel therapies into treatment algorithms will require well-designed, collaborative studies.

Long-term treatment of hairy cell leukemia with interferon-α: still a viable therapeutic option

Classic hairy cell leukemia (HCL) is a rare indolent B‑cell-lymphoproliferative disorder, first described as a distinct disease entity in 1958. After more than two decades without effective chemotherapeutic options and a dismal prognosis of less than 5 years, only the introduction of interferon‑α (IFN‑α) allowed for response rates between 80–90 % and survival improvement. Nowadays, however, patients are rarely treated with IFN-α as purine analogues were found to be highly effective in HCL facilitating a near normal life span in most cases. Moreover, novel therapeutic tools for patients with relapsed or refractory disease after purine analogues have emerged such as rituximab and, more recently, vemurafenib. In the absence of long-term safety data for these novel agents, however, IFN-α may still represent a viable therapeutic option when the profound immunosuppressive side effects of purine analogues are to be avoided. We herein report a HCL patient, who has received multiple lines of therapy, including pentostatin, cladribine, and a total of 164 months of treatment with IFN‑α yielding long-term disease control. Our case illustrates that long-term administration of IFN-α with adequate dose-adjustments according to toxicity and disease activity is feasible in HCL and may still be a viable therapeutic option when purine analogues are considered unsuitable.

Chemoimmunotherapy for hairy cell leukemia

Success in the treatment of patients with hairy cell leukemia (HCL) over the last several decades is largely due to the high efficacy of the nucleoside analogs, cladribine and pentostatin. However, the relapse-free survival curves have not shown a plateau and many patients treated with these agents will eventually relapse. Although better understanding of the pathogenic mechanisms in HCL have led to effective and novel options for the treatment of relapse, long term durability of the responses obtained with these agents still remains unclear. Combination of nucleoside analogs with monoclonal antibodies such as rituximab has been shown to be safe and effective and has the potential to supersede the nucleoside analogs as the frontline strategy. Such chemo-immunotherapy approaches are under further investigation and will have to be assessed with socioeconomic considerations in mind. Other novel monoclonal antibodies, approved for the treatment of other lymphoid neoplasms, may also be considered for future studies of chemo-immunotherapy.

Hairy cell leukemia-new genes, new targets

Hairy cell leukemia (HCL), a B cell malignancy comprising 2 % of all leukemias, has become quite exciting recently with regard to the development of new targets for therapy. This review will focus on advancements made within the past 1-2 years in targeted therapy for this disease. These advances may be grouped into two very difference categories, namely targeting of CD22 with the recombinant immunotoxin moxetumomab pasudotox, and targeting of the mutated BRAF component of the MAP kinase pathway. Moxetumomab pasudotox in phase I testing was recently reported to be associated with an overall response rate of 86 % and a complete remission (CR) rate of 46 % in 28 patients with relapsed and refractory HCL. Many of the CRs are without minimal residual disease (MRD). Severe or dose limiting toxicity was not observed on this trial, but a completely reversible and largely asymptomatic form of grade 2 hemolytic uremic syndrome occurred in two patients during retreatment. This agent has commenced phase III multicenter testing to validate its phase I results. An extensive number of studies have documented the V600E mutation in nearly all HCL patients, but not in similar hematologic malignancies. The thymidine kinase inhibitor vemurafenib, which inhibits the V600E mutant of BRAF, was reported to induce a CR in multiply relapsed and refractory HCL, with nearly complete clearing of MRD. One additional partial and one additional complete remission were subsequently reported.

Hairy cell leukemia: short review, today's recommendations and outlook

Hairy cell leukemia (HCL) is part of the low-grade non-Hodgkin lymphoma family and represents approximately 2% of all leukemias. Treatment with splenectomy and interferon-α historically belonged to the first steps of therapeutic options, achieving partial responses/remissions (PR) in most cases with a median survival between 4 and 6 years in the 1980s. The introduction of the purine analogs (PA) pentostatin and cladribine made HCL a well-treatable disease: overall complete response rates (CRR) range from 76 to 98%, with a median disease-free survival (DFS) of 16 years a normal lifespan can be reached and HCL-related deaths are rare. However, insufficient response to PA with poorer prognosis and relapse rates of 30–40% after 5–10 years of follow-up may require alternative strategies. Minimal residual disease can be detected by additional examinations of bone marrow specimens after treatment with PA. The use of immunotherapeutic monoclonal antibodies (mAB) like rituximab as a single agent or in combination with a PA or more recently clinical trials with recombinant immunotoxins (RIT) show promising results to restrict these problems. Recently, the identification of the possible disease-defining BRAF V600E mutation may allow the development of new therapeutic targets.

Hairy cell leukemia - immunotargets and therapies

Hairy cell leukemia (HCL) is an indolent low-grade B-cell lymphoproliferative disorder that is reasonably sensitive to standard first-line purine analog therapy. However, in many cases, repeat relapses occur, requiring multiple courses of purine analog therapy, promoting eventual drug resistance. This, coupled with the concerning side effects of repeated purine analog exposure, has prompted the search for alternative targets and therapies that may provide deeper remissions. Novel strategies employing immune-mediated targeting via monoclonal antibody therapies and recombinant immunotoxins appear promising in HCL and are currently under investigation. More recently, the concept of targeted kinase inhibition using small-molecule inhibitors in HCL has emerged as another potentially viable option. As a deeper understanding of the aberrant molecular pathways contributing to the pathogenesis of HCL develops, the landscape of management for HCL, particularly in the relapse setting, may change significantly in the future as a result of these promising immunotargets and therapies.

Multiply relapsing hairy cell leukemia responsive to repeated courses of rituximab: A case report

While cladribine is a highly effective therapy for patients with symptomatic hairy cell leukemia (HCL), up to 37% of patients ultimately relapse and incompletely responding patients relapse more frequently. Rituximab is a monoclonal antibody against CD20 that has been shown to be effective in patients with relapsed HCL. We present an unusual case of successful multiple re-treatments with rituximab in a patient with heavily pre-treated HCL and briefly review the relevant literature.

My treatment approach to hairy cell leukemia

Hairy cell leukemia (HCL) is a rare chronic lymphoproliferative disorder characterized by circulating B cells with cytoplasmic projections, pancytopenia, splenomegaly, and a typical flow cytometry pattern. Recently, the BRAF V600E mutation was uniformly identified in one HCL series, which may provide insights into the pathogenic mechanisms. The disease course is usually indolent but inexorably progressive. Patients require treatment when they have significant cytopenia or occasionally recurrent infections from immunocompromise. In the mid-1980s, interferon replaced splenectomy as the initial treatment. A few years later, 2 purine nucleoside analogs, cladribine and pentostatin, showed promising activity in HCL. Complete response rates approached 95% with cladribine given as a single 7-day intravenous infusion. Newer methods of cladribine administration and modified dosing schedules have since been studied. Pentostatin response rates are comparable. We generally prefer cladribine because of its ease of administration, single infusion schema, and favorable toxicity profile. Since the introduction of these drugs, which have never been randomly compared, long-term follow-up studies have confirmed impressive and durable response durations. However, roughly 40% of patients with HCL eventually relapse. In this setting, patients can be re-treated with purine analogs. Rituximab also has a reasonable response rate in relapsed HCL; it can be given as a single agent sequentially after purine nucleosides or concurrently. Immunotoxins have robust responses but remain in development. Targeting the BRAF pathway will be an exciting future area of research. Many patients have minimal residual disease after initial treatment, but the clinical significance of this remains unknown.

Infectious complications in hairy cell leukemia

The natural history of hairy cell leukemia (HCL) includes frequent and potentially life-threatening infections. Prior to the development of effective therapy, the incidence in patients followed for several years was as high as 60%, with infection as a prime cause of death in patients. Studies of the immune system of patients with HCL identified several potential reasons, including profound neutropenia and monocytopenia. In addition, treatment including chemotherapy and splenectomy further compromised the immune system. The success of new therapies has changed the frequency and severity of infections in patients with HCL. During the initial phase of treatment, however, infection risk remains high, with incidence ranging from 30 to 50%. Attempts to ameliorate the risk with growth factors in conjunction with treatment have not been successful, but lower doses of drugs and/or combination therapy have been tried with reported success. In the majority of patients, successful therapy results in normalization of the neutrophil count and marked reduction in the severity and frequency of infections. Interestingly, after purine nucleoside treatment, there is profound depression of CD4+ cells without development of the opportunistic infections seen with patients with human immunodeficiency virus (HIV). Studies to reduce morbidity and mortality should focus on initial induction regimens, as well as confirming the long-term benefit of treatment on risk of infection.

Modern strategies for hairy cell leukemia

Enormous progress in the treatment of hairy cell leukemia over the last five decades has emerged as a result of organized clinical investigations. Although interferon represented one of the initial major therapeutic advances in the management of this disease in 1984, the subsequent introduction of purine nucleoside analogs (pentostatin and cladribine) changed the natural history of this rare disease by achieving a high rate of complete and durable remissions. The disease-free survival after effective therapy has not reached a plateau, suggesting control but not cure of the disease. Identification of minimal residual disease in patients achieving a complete hematologic remission provides insight into the potential source for predicting eventual relapse. Modern strategies of targeted therapies directed against immunophenotypic markers on the leukemic cells provide hope that improved long-term control of the disease is possible. Combined chemoimmunotherapy may hold the highest promise for disease eradication, but the optimal strategy for using this approach is under active investigation. Despite the perception by hematologists that this disease has already been conquered, there are critically important unanswered questions that remain. Investigation of the bone marrow microenvironment and its impact on minimal residual disease may ultimately prevent relapse. Consideration of the median age of patients at diagnosis combined with a substantial relapse rate mandates continued pursuit of improved therapy. The ultimate goal will be to achieve cure rather than simple control of the disease.

Hairy-cell leukemia variant: recent view on diagnosis, biology and treatment

Hairy-cell leukemia variant (HCl-V) is a district clinico-pathological entity with intermediate features between classical HCl (HCl-C) and B-cell prolymphocytic leukemia. HCl-V is now included in the World Health Organization (WHO) classification as a provisional entity. It is an uncommon disorder accounting for approximately 0.4% of chronic lymphoid malignancies and 10% of all HCl cases. In contrast to HCl-C, HCl-V is a more aggressive disease and according to the new WHO classification it is no longer considered to be biologically related to HCl-C. Patients with HCl-V have an elevated white blood count, easy-to-aspirate bone marrow and weak reactivity to tartrate - resistant acid phosphatase (TRAP). Immunophenotypically, HCl-V cells are positive for CD103 and CD11c and negative for CD25. The HCl-V cells express also the B-cell antigens, CD19, CD20 and CD22. The HCl-V patients have frequently an unmutated Ig gene configuration. Currently, the principles of therapy for this rare disease derive from uncontrolled single institutional studies, or even single case reports. In contrast to HCl-C, the HCl-V response to purine nucleoside analogs (PNA) is limited to partial responses in approximately 50% of patients. However, complete responses were observed in patients treated with rituximab and anti-CD22 immunotoxins. In Japan, a distinct subtype of HCl known as HCl-Japanese variant (HCl-JV) has been identified. As with HCl-V, patients with HCl-JV have leukocytosis, weak TRAP activity in leukemic cells, and lack of CD25 antigen. In this review, the biology, diagnostic criteria, and current therapeutic options in HCl-V and HCl-JV are presented.

Approach to the patient after relapse of hairy cell leukemia

The current hairy cell leukemia (HCL) treatment is excellent, but evidence of cure with purine analogs cladribine and pentostatin, is lacking. Significant long-term immune suppression, particularly to CD4+ T-cells, and declining complete remission rates with each course, make the identification of new therapies an important goal. The anti-CD20 monoclonal antibody (Mab) rituximab displays significant activity, and, while causing prolonged normal B-cell depletion, spares T-cells. Recombinant immunotoxins, containing an Fv fragment of a Mab fused to truncated Pseudomonas exotoxin, have shown efficacy in HCL resistant to both purine analogs and rituximab. LMB-2 targets CD25 and can induce remission providing the HCL cells are CD25+. All HCL cells display CD22. Recombinant anti-CD22 immunotoxin BL22, targeting CD22, has shown significant efficacy in phase I and II testing, and avoids prolonged suppression of both normal B- and T-cells. An improved high-affinity version of BL22, termed HA22, is currently undergoing phase I testing.

Importance of minimal residual disease in hairy cell leukemia: monoclonal antibodies as a therapeutic strategy

With the use of nucleoside analogs as frontline therapy, the prognosis of hairy cell leukemia (HCL) has improved dramatically. Unfortunately, disease recurrence remains problematic. Eradication of minimal residual disease (MRD) persisting after therapy may further improve outcome. The evolution of available techniques used to assess MRD, and the potential incorporation of novel agents such as monoclonal antibodies (MoAbs) into the treatment armamentarium for HCL mandate that MRD analyses be performed concurrently with routine assessments of disease status. Herein, the available data regarding the prevalence and clinical relevance of MRD after therapy for HCL is reviewed.

Hairy cell leukemia

Progress in the treatment of patients with hairy cell leukemia (HCL) has led to a significant change in the natural history of the disease. With current regimens, the majority of patients achieve a complete remission, and their survival curves are similar to those for appropriate age-matched individuals without the disease. At the same time, new technologies are allowing better understanding of the molecular mechanisms responsible for the pathogenesis of this and other indolent lymphoid neoplasms. Several studies using modern techniques with different sensitivities have demonstrated the persistence of minimal residual disease (MRD) after therapy with nucleoside analogues in majority of patients. However, it is not clear whether such MRD would invariably lead to leukemia recurrence or what level of MRD can predict relapse. The role of monoclonal antibodies, naked or conjugated with toxins, in the management of HCL and their ability to eradicate MRD is under investigation. Whether such strategies of chemoimmunotherapy would lead to further improvements in the outcome of patients with HCL needs to be further investigated.

Phase II trial of recombinant immunotoxin RFB4(dsFv)-PE38 (BL22) in patients with hairy cell leukemia

PURPOSE

To conduct a phase II trial in chemoresistant hairy cell leukemia (HCL) with BL22, a recombinant anti-CD22 immunotoxin which showed phase I activity in HCL.

PATIENTS AND METHODS

Eligible patients had relapsed/refractory HCL and needed treatment based on blood counts. Patients were stratified into three groups: response to cladribine less than 1 year, those with a response lasting 1 to 4 years, or no response and uncontrolled infection. Patients received BL22 40 microg/kg every other day for three doses on cycle 1. Those achieving hematologic remission (HR), defined as neutrophils > or = 1,500/mm(3), hemoglobin > or = 11 g/dL, and platelets > or = 100,000/mm(3), were observed. Patients without HR were re-treated at 30 microg/kg every other day for three doses every 4 weeks beginning at least 8 weeks after cycle 1.

RESULTS

Thirty-six patients were enrolled including 26, nine, and one in groups 1 to 3. The response after one cycle (CR, 25%; PR, 25%) improved when 56% were re-treated (CR, 47%; PR, 25%). CR rate was similar in groups 1 and 2 (P = .7). Twenty-two with baseline spleen height lower than 200 mm had higher CR (64% v 21%; P = .019) and OR rates (95% v 36%; P = .0002) compared to 14 with spleens either absent or higher than 200 mm. The only serious toxicity was reversible grade 3 hemolytic uremic syndrome, not requiring plasmapheresis, in two patients (6%). High neutralizing antibodies were observed in four patients (11%) and prevented re-treatment.

CONCLUSION

BL22 activity in HCL is confirmed. Best responses to BL22 after cladribine failure are achieved before the patients develop massive splenomegaly or undergo splenectomy.

Hairy cell leukemia: current concepts

Hairy cell Leukemia (HCL) is a chronic lymphoproliferative disorder that was characterized in the late 1950s. HCL is defined, according to the WHO classification, as a mature (peripheral) B-cell neoplasm (1). HCL accounts for between 2-3% of all leukemia cases, with about 600 new cases diagnosed in the U.S. each year (1). HCL occurs more commonly in males, with an overall male to female ratio of approximately 4:1. The median age of onset is 52 years. This disease is seen more commonly in Caucasians and appears to be especially frequent in Ashkenazi Jewish males, with rare occurrence in persons of Asian and African descents (1). Hairy cells are distinct, clonal B cells arrested at a late stage of maturation. They are small B lymphoid cells that possess oval nuclei and abundant cytoplasm with characteristic micro-filamentous ("hairy") projections. They strongly express CD103, CD22, and CD11c (2). These cells typically infiltrate the bone marrow, the spleen, and to a lesser extent the liver, lymph nodes, and skin. Many patients present with splenomegaly and pancytopenia. Other clinical manifestations include recurrent opportunistic infections and vasculitis. Historically, HCL was considered uniformly fatal (2). However, recent treatment advances, using purine analogues such as Cladribine and Pentostatin, led to a significant improvement in prognosis with achievement of high response rates and durable remissions (2).

Emerging drugs for rarer chronic lymphoid leukemias

BACKGROUND

Rarer indolent lymphoid leukemias include well defined mature B-cell and T-cell neoplasm with widely varying natural history and specific morphological, immunophenotypic and molecular characteristics. Among these are prolymphocytic leukemia (PLL), hairy cell leukemia (HCL) and its variants, large granular lymphocyte leukemia (LGLL) and adult T-cell leukemia/lymphoma (ATLL).

OBJECTIVE

To present current therapies and emerging drugs potentially useful in the treatment of rarer chronic lymphoid leukemias.

METHODS

After searching MEDLINE, PubMed and the Current Contents database, and conference proceedings from the previous 3 years of the American Society of Hematology (ASH), the European Society of Hematology (EHA) and the American Society of Clinical Oncology (ASCO) were searched manually; articles written in English and additional relevant publications were then selected.

RESULTS/CONCLUSION

New drugs including monoclonal antibodies (mAbs), new purine analogs, small molecules targeting specific molecular targets and other agents are included. Future research should focus on the novel therapeutic strategies based on the molecular pathogenic mechanisms and the development of new targeted therapies for each distinct chronic lymphoid leukemia.

2-CdA in the treatment of hairy cell leukemia: a review of long-term follow-up

Hairy cell leukemia is a rare, indolent, chronic lymphoproliferative disorder characterized by the proliferation of a malignant B-cell clone with irregular cytoplasmic projections. Treatment with purine analogs such as 2-chlorodeoxyadenosine (2-CdA) is associated with excellent remission rates and long-term survival. Although the majority of patients achieve a complete remission (CR), most have minimal residual disease detected by sensitive methods. Despite the long term disease-free survival, approximately 36% of patients relapse and many require further therapy. Repeat administration of 2-CdA is very effective in achieving a second CR. Recently, new agents such rituximab and BL22 were shown to be effective in the treatment of relapsed and refractory disease.

The role of rituximab in combination with pentostatin or cladribine for the treatment of recurrent/refractory hairy cell leukemia

BACKGROUND

The purine analogs pentostatin and cladribine have revolutionized the treatment of hairy cell leukemia (HCL) with overall responses in greater than 85% of patients and a median progression-free survival of up to 15 years. They continue to be effective at second- and even third-line therapy; however, alternative treatments are needed for patients who are or have become refractory to these agents or whose remissions are shorter with each course of therapy.

METHODS

The authors conducted a retrospective review of 8 patients who received pentostatin or cladribine combined concurrently (n = 6 patients) or sequentially (n = 2 patients) with rituximab at second-line therapy (n = 3 patients) and at subsequent lines of therapy (n = 5 patients). Results from a previously reported database of 219 patients with HCL (73 patients who received second-line therapy and 20 patients who received third-line therapy) were used as a historic control group against which to measure benefit.

RESULTS

All 8 patients responded to therapy, with 7 complete responses (CRs) (87.5%) and minimal toxicity. All patients who had CRs were negative for minimal residual disease (MRD). At a median follow-up of 29 months (range, 5-39 months) 1 patient developed recurrent disease, and the estimated 2-year recurrence rate was 20% (0% after second-line therapy and 25% after subsequent lines of therapy). In the historic control group, the CR rates were 70% after second-line therapy and 45% after third-line therapy, and the recurrence rates at 2 years were 15% and 33%, respectively.

CONCLUSIONS

The combination of purine analogs with rituximab was safe and effective for patients with recurrent and/or refractory HCL, and the current results suggested an added benefit compared with standard treatment.

BL22 and lymphoid malignancies

BL22 is a recombinant immunotoxin containing a truncated form of the bacterial toxin Pseudomonas exotoxin A attached to an Fv fragment of an anti-CD22 monoclonal antibody. Its mechanism of action involves binding to CD22, being internalized into the target cell by endocytosis, being processed to generate a free toxin fragment which is translocated into the cytoplasm, and finally induction of cell death by catalytic inactivation of elongation factor 2. In phase-I testing BL22 was very active in chemoresistant hairy-cell leukemia (HCL), with 19 (61%) of 31 patients achieving complete remission (CR). The low blood counts (cytopenias) which are characteristic of HCL improved in all complete and partial responders. Dose-limiting toxicity in HCL was due to a reversible hemolytic uremic syndrome (HUS), observed only during cycles 2 or 3. Already under way are a phase-II trial in HCL and phase-I trials in chronic lymphocytic leukemia (CLL) and acute lymphocytic leukemia (ALL) administering BL22 in a modified protocol in an effort to prevent HUS.

Monoclonal antibody therapy for hairy cell leukemia

The use of MoAb therapy for the treatment of HCL offers great promise and potential for improving progression-free survival. Rituximab has activity in the setting of previously treated HCL and the ability to eradicate MRD after 2-CdA given as frontline therapy. Alemtuzumab, epratuzumab, Hu-Max-CD20, and other candidate MoAb's should be studied in HCL. Appropriate pharmacologic investigation, use of antigen modulation, and assessments of soluble antigen levels should be considered with future clinical trial s of MoAb's in HCL to optimize therapeutic strategies.

Hairy cell leukemia: towards a curative strategy

Although not all patients who have HCL require therapy at diagnosis, most eventually need treatment. Historically, splenectomy and interferon-alpha resulted in hematologic responses; however, responses tend to be short. The introduction of purine analogs dramatically changed the prognosis for most patients who hae HCL. It is now considered standard of care to use a purine analog, such as 2-CdA or 2'-DCF, as first-line therapy. This approach results in a high CR rate and prolong DFS. Although both agents yield the same rates of CR and survival, 2-CdA seems easier to administer and my be associated with less toxicity. Despite the excellent results with purine analogs, most patients have MRD detected by sensitive techniques; 30% to 40% of patients eventually relapse and most require further therapy. A repeat course of 2-CdA (or 2'-DCF) will result in CR in approximately 70% of patients. For patients who have relapsed or refractory disease, monoclonal antibody-based therapies are emerging options. Rituximab and BL22 are highly active in this setting. Until BL22 becomes widely available, rituximab is a reasonable choice for salvage therapy; however, the dosing schedule needs to be denied further. The roles of rituximab and BL22 as initial therapy for patients who have previously untreated HCL have not been investigated. Fig. 1 is a suggested algorithm for the treatment of HCL. With the introduction of effective new agents, further studies will determine whether the now achievable prolonged survival will translate into cure.

Hairy cell leukemia

Hairy cell leukemia is a rare B-cell neoplasm. When treated with either pentostatin or cladribine, complete and durable remissions can be secured and life expectancy for most patients is normal. A small minority of patients require alternative treatment with monoclonal antibodies or immunotoxins. Patients who attain a complete response to first-line treatment have the best prognosis.

Characterization of T-cell repertoire in hairy cell leukemia patients before and after recombinant immunotoxin BL22 therapy

We previously reported that hairy cell leukemia (HCL) patients have high percentages of CD56+/CD57+/CD3+ large granular lymphocytes consistent with cytotoxic T-lymphocytes (CTLs), and other investigators have reported skewing of the T-cell repertoire. In previous studies of up to seven HCL patients, many of the 22 established T-cell receptor (TCR) beta variable region (TRBV) families showed mono- or oligoclonal restriction. To determine whether percentages of CTLs are correlated with TRBV clonal excess, we studied 20 HCL patients with flow cytometry, PCR of TCR gamma and TRBV regions, and fractional gel electrophoresis of PCR-amplified TRBV CDR3 domains (CDR3 spectratyping). Increased percentages of CD3+/CD8+/CD57+ CTLs correlated with more mono/oligoclonal and fewer polyclonal TRBV families (r=0.53; P=0.016). Age correlated with number of mono/oligoclonal TRBV families (r=0.51; P=0.022). Time since last purine analog therapy correlated with number of polyclonal TRBV families (r=0.46; P=0.040), but treatment with the anti-CD22 recombinant immunotoxin BL22 was not related to clonal excess. We conclude that abnormalities in the T-cell repertoire in HCL patients may represent deficient immunity, and may be exacerbated by purine analogs. Increased CD3+/CD57+ T-cells may be a useful marker of abnormal TRBV repertoire in HCL patients, and might prove useful in deciding whether patients should receive biologic antibody-based treatment rather than repeated courses of purine analog for relapsed disease.

Minimal residual disease in hairy cell leukemia patients assessed by clone-specific polymerase chain reaction

Cladribine induces long-term complete remission in hairy cell leukemia (HCL) patients but does not clear minimal residual disease (MRD) according to high-sensitivity PCR assays. To quantify MRD in patients after anti-CD22 recombinant immunotoxin BL22 and other agents, we used a relative quantitative PCR (RQ-PCR) assay using a primer and probe, both patient specific for the immunoglobulin heavy chain rearrangement. Using this method, we were able to detect one Bonna 12 HCL cell in either 10(6) Jurkat cells or in 10(6) normal mononuclear cells. We studied 84 samples from 10 patients, taken before or after treatment with BL22 and other agents. Patient-specific RQ-PCR was much more sensitive than flow cytometry, which in turn was (as recently reported) more sensitive than PCR using consensus primers. RQ-PCR was positive in 62 of 62 (100%) flow-positive samples in 10 patients and in 20 of 22 (91%) flow-negative samples in six patients. The relative level of MRD as quantified by RQ-PCR correlated with disease status and remission. Thus, patient-specific RQ-PCR is the most sensitive test for MRD in HCL patients and could be used to determine maximal response in patients obtaining multiple cycles of nonmyelotoxic biological treatment for this disease.

Current treatment options in hairy cell leukemia and hairy cell leukemia variant

Hairy cell leukemia (HCL) is a chronic B-cell lymphoproliferative disorder characterized by splenomegaly, pancytopenia and circulating lymphocytes displaying prominent cytoplasmic projections. HCL has usually an indolent course and the patients with asymptomatic disease do not require therapy. Treatment of progressive symptomatic HCL includes a variety of pharmacological approaches such as interferon-alpha (IFN-alpha), pentostatin (DCF) and cladribine (2-CdA), which have significantly improved the disease prognosis. 2-CdA and DCF seem to induce a similar high response rate and a long overall survival. They are also active in relapsed patients. More recently high activity of anti-CD20 monoclonal antibody (rituximab) and anti-CD25 (LMB-2) and anti-CD22 (BL-22) immunotoxins have increased the number of therapeutic options for HCL. Splenectomy may be still indicated in patients with massive, symptomatic splenomegaly or results in severe cytopenia. IFN-alpha may have a place in patients with very severe cytopenia, in HCL in pregnancy and in patients who have failed prior therapy with purine nucleoside analogs. HCL variant (HCL-V) is a distinct clinico-pathological entity which seems to be resistant to IFN-alpha and purine nucleoside analogs - DCF and 2-CdA. However, preliminary observations suggest that monoclonal antibodies - rituximab and BL-22 immunotoxin are highly active in this disorder even refractory to 2-CdA. In this review current therapeutic strategies in HCL and HCL-V are presented.

A quantitative exploration of surface antigen expression in common B-cell malignancies using flow cytometry

The use of flow cytometry to diagnose hematological malignancies has become routine due to its ability to often differentiate between morphologically similar diseases based on antigens expressed on the surface of malignant cells. In an attempt to expand on the utility of flow cytometry in the study of B-cell malignancies we have used the most reliable quantitative methodology, QIFI (quantitative indirect immunofluorescence assay), to study the expression of CD5, CD10, CD11c, CD19, CD20, CD22, CD23, and CD79b in 384 cases of several common B-lineage malignancies, including: B-ALL, CLL, SLL, hairy cell leukemia, diffuse large B-cell lymphoma, and follicular lymphoma. The impetus behind this extensive, single institution study of surface antigens was two-fold: evaluating similarities and differences of antigen expression between B-cell neoplasms and finding additional clinical utility for the quantitative flow cytometric data generated. Our results show that each distinct malignant histology has its own quantitative pattern of surface antigen expression. In most cases, these quantitative patterns do not increase the ability of flow cytometry to distinguish between them. However, a high expression of specific antigens on a given B-cell malignancy may potentially identify optimal therapeutic targets for current and/or future monoclonal antibody-based therapies.

Efficacité du rituximab dans la leucémie à tricholeucocytes

INTRODUCTION

Rituximab is an alternative treatment for hairy cell leukemia, when the standard treatments are unavailable.

CASE

An 82-year-old woman was diagnosed with hairy cell leukemia. The severity of her neutropenia ruled out purine analogs, while heart disease and age both contraindicated use of interferon. Rituximab, in four weekly treatments, was effective from the first treatment and the positive response was sustained thereafter.

DISCUSSION

Rituximab may be used to treat hairy cell leukemia, especially for patients refractory to purine analogs or after relapse or in the case of severe neutropenia, when interferon is contraindicated.