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.     

Cladribine in hairy cell leukemia

Cladribine results in prolonged complete remissions in most patients wo have HCL. Several studies have indicated that patients who are in complete remission have survivals that are comparable to those of normal age-matched controls. HCL-related mortality is distinctly uncommon. Nevertheless, it is unlikely that cladribine treatment of HCL is curative because MRD is common in the bone marrows of complete responders. Response criteria for HCL include clinical, hematologic, and morphologic criteria, but do not include flow cytometry, immunohistochemical analysis, or molecular studies. More sensitive techniques have been used by Filleul and colleagues to detect MRD. The used clonoegenic probes from the hypervariable regions of the immunoglobulin heavy-chain gene and performed polymerase chain reactions (PCRs) on bone marrow biopsy specimens, All seven patients who were in morphologic complete remission after a single cladribine infusion were PCR positive. These data indicate that cladribine induces protracted remissions but is not necessarily curative. MRD can be detected in most patients when sensitive techniques are used. Persistence of immunohistochemical MRD may predict detected MRD remains to be studied in a large number of patients. Investigators from the University of Pisa in Italy have used a combination of cladribine and rituximab to eradicate MRD in patients who have HCL. Ten patients received treatment with a standard infusion of cladribine. Two patients achieved a complete remission, 6 patients achieved a partial remission, and 2 patients failed to respond. All were PCR positive for the immunoglobulin heavy-chain (IgH) gene product at the completion of cladribine treatment. All 10 patients had achieved a complete hematologic response 2 months after the completion of ritximab therapy. The curative nature of this treatment will require long-term follow-up. Cladribine represents a major therapeutic advance in the treatment of HCL. The prognosis of patients who have HCL has improved greatly with cladribine therapy. Future strategies should address combination therapy with purine analogs and monclonal antibodies. These strategies should address eradication of MRD in an attempt to develop a potentially curative combination treatment program.     

DNA-abnormality in hairy cell leukemia

Spleen and light density peripheral blood leukocytes of 10 hairy cell leukemia (HCL) patients and total leukocytes of one patient and blood donor cells were stained quantitatively for cellular DNA. The DNA content of single cells was measured by flow cytometry (FC) and compared to the DNA content of sheep cells admixed as an internal control. Eight of eleven patients (72 per cent) showed deviations from blood donor DNA content. Two female patients showed increased cellular DNA content, the six male patients had hypodiploid cells. Chromosomal aberrations are therefore likely to exist in the majority of HCL patients. Separation of HCL cells into sheep erythrocyte rosette and non rosette forming cells revealed similar DNA abnormalities in both cell populations, suggesting that the leukemia encompasses cells with B and with T markers.     

Familial hairy cell leukemia

A mother and son are reported who both developed hairy cell leukemia. The mother aged 74 presented with pancytopenia and responded well to splenectomy. Four years later her son aged 48 presented with pancytopenia; splenectomy was less effective but he improved after treatment with interferon-alpha. Histological examination of the splenic tissue in both cases showed changes characteristic of hairy cell leukemia. This is the third report of this rare disease occurring in family members.     

p53 mutations in hairy cell leukemia.

We have studied the frequency of p53 mutations in genomic DNA extracted from peripheral blood or the spleen of 61 patients with hairy cell leukemia using PCR-SSCP and automated cycle sequencing. We identified exon 5-8 mutations in 17 cases, corresponding to a frequency of 28%. In four cases, mutations were localized in exon 5; one patient with atypical HCL had a mutation in exon 6 at the 3' boundary; five cases showed mutations in exon 7, while exon 8 was found to be mutated in seven cases. The mutations found could be divided into three major categories: structural (n=9), inactivating (n= 6), and neutral (n= 2) mutations. None of the three transitions found occurred at CpG dinucleotides. The rate of p53 mutations found in this large cohort of HCL patients is unexpectedly high as in other non-Hodgkin lymphomas p53 mutations predict for poor treatment outcome. The character of the mutations we have found is entirely different from that described in other hematologic malignancies.     

PRAME expression in hairy cell leukemia

PRAME has been proposed as a useful marker for solid tumors and acute B-cell malignancies. Several studies demonstrate expression in CLL. To further examine its B-cell tumor distribution, we studied PRAME in both CLL and hairy cell leukemia (HCL). While by conventional PCR only 8% of 37 HCL and 27% of 22 CLL patients were positive, nearly all patients and normal donors expressed PRAME by real-time quantitative (TaqMan) PCR. We conclude that HCL and CLL differ in PRAME overexpression, and that basal normal expression of PRAME may limit its usefulness for following patients with minimal residual CLL or HCL.     

Fludarabine therapy in hairy cell leukemia

This study evaluated the efficacy of fludarabine, a new adenine nucleoside analogue, in typical and variant forms of hairy cell leukemia (HCL). Two patients with HCL and one patient with a variant form of HCL (HCL-variant) with resistant or progressive disease with prior treatments were studied. Fludarabine (30 mg/m2) was administered intravenously over 30 minutes daily for 5 days every month. Two patients (one with HCL and one with HCL-variant) achieved partial responses; the third patient had a minor response. This is the first report of encouraging activity of fludarabine in typical and variant forms of HCL. Further experience with fludarabine in these disorders is indicated.     

Second malignancies in hairy cell leukemia

Among 172 patients with hairy cell leukemia (HCL) seen at the University of Chicago over a 10-year period, 15 were found to have a second malignancy. Neoplasia of the skin was noted most frequently; there were three cases of basal cell carcinoma, one case of anaplastic squamous cell carcinoma, and one case of malignant melanoma. This was followed in frequency by three cases of carcinoma of the lung. The clinical characteristics of these 15 patients did not differ from those of the general population of patients with HCL. A variety of second hematologic malignant disorders and solid tumors were identified. In one case, the second neoplasm occurred before the diagnosis of HCL; six were diagnosed concurrently; and eight followed the diagnosis of HCL. Since HCL is a well-defined clinicopathologic entity, patients with HCL who exhibit unusual features of the disease should be investigated further for the presence of second malignancies.     

Bone marrow in hairy cell leukemia

HCL is a well-recognized entity among the lymphoproliferative disorders. With better appreciation of the wide variability in its clinical and hematologic manifestations, some authors have proposed several subtypes of HCL such as leukopenic and nonleukopenic subtypes and subtypes with and without massive splenomegaly. As opposed to such a clinical and hematologic variability, the pathology of HCL in the spleen and bone marrow is consistent and highly characteristic. Since the spleen becomes available for pathologic examination only after therapeutic splenectomy, the bone marrow pathology often plays the most important role in the differential diagnosis of HCL. It is characterized by focal or diffuse mononuclear cell infiltration with a wide spacing between individual nuclei in most patients and by a severely hypocellular marrow with individual hairy cells infiltrating between the marrow fat cells in the remaining minority of patients. The bone marrow biopsy also serves as one of the criteria in selecting the therapeutic modality as well as monitoring the therapeutic effect. Further, new insights into the pathogenesis of HCL are emerging from recent studies of the bone marrow microenvironment.     

Genetics of hairy cell leukemia

Hairy cell leukemia (HCL) is a chronic B-cell lymphoproliferative disorder characterized by cytopenias, splenomegaly, and bone marrow fibrosis associated with an infiltrate of B-lymphocytes. Although in the majority of cases diagnosis and treatment of the disease is relatively straightforward, there is a lack of clinical and molecular data on its genetic mechanisms. Recent advances in gene expression profiling have identified a number of proteins that are specific to the HCL phenotype. However, these data are only the first step in identifying the genetic event responsible for development of the disease. Because of the success of purine analog therapy in treating the disease, there has so far been little interest within the scientific community in gaining a greater understanding of the genetics that drive the neoplastic clone in this strikingly homogeneous and well characterized clinical entity. This review describes the epidemiological genetic and molecular events associated with HCL.     

Ultrastructural characteristics of the spleen in hairy cell leukemia.

Eighteen spleens derived from patients with hairy cell leukemia (HCL) were analyzed by correlative scanning and transmission electron microscopy. In 15 of the cases, the white pulp areas were markedly decreased or absent when compared to normal spleens, although few hairy cells were observed within this region. In only one case did the white pulp appear normal. In all HCL cases, hairy cells were observed within normal, dilated, and abnormal sinuses. The abnormal sinuses contained hairy cells of typical morphology attached to other hairy cells, to endothelial lining, and to erythrocytes. The degree of sinus filling by hairy cells varied from loosely- to tightly-packed. Endothelial cells exhibiting degenerative changes, such as swelling with smooth surfaces and dilated intercellular spaces, were frequently seen. These results indicate that in addition to the previously described overcrowding of the spleen by hairy cells, the splenic tissue itself is considerably altered and sometimes severely damaged in patients with HCL.     

Cell-surface characteristics of hairy cell leukemia in seven patients.

Surface marker studies were performed on "hairy cells" from 7 patients with hairy cell leukemia (HCL). Using sensitive analytic techniques including specific antisera and Fluorescence Activated Cell Sorter (FACS-1), further definition of the abnormal cell was achieved. Four different antisera were used in infestigating the cell surface characteristics of these patients: anti-p23,30, an antiserum reactive with B cells and a subset of monocytes, anti-311, which reacts only with T cells, pepsin digested anti-F(ab')2 which reacts with B cells only and pepsin digested anti-lysozyme reactive with monocytes and myeloid cells, but not with B or T cells. In all cases strong reactivity was observed with anti-p23,30 and anti-F(ab')2, but no reactivity with anti-311. Five out of the seven cases were reactive with anti-lysozyme in a pattern similar to normal monocytes. Furthermore, when cells were separated according to binding to anti-p23,30, anti-F(ab')2 and anti-lysozyme and in two cases, according to cell size, the majority of reactivity and large cells were "hairy" when examined under microscopy. In contrast, the small and nonreactive (dull cells) appeared as normal mature lymphocytes. Thus, our data supports the view that HCL cells bear in most cases B cell and monocytic membrane markers.     

Therapy results in hairy cell leukemia]

20 patients with hairy cell leukemia were treated between 1966 and 1978. All modalities of treatment for lymphoproliferative disorders have been used in at least some patients. Besides prednisone, vincristine, cyclophosphamide and their combinations as well as irradiation of enlarged spleens, cell depletion was achieved by splenectomy and leukapheresis. Cytostatics had no beneficial effect. Cytostatic therapy exposed some patients to the hazards of severe infections. On the contrary splenectomy lead to the improvement of some blood parameters. Leukapheresis seemed to work nearly identically. The survival of the splenectomized patients was longer than of controls. Because of the variability of the duration of the disease no definite statement could be made concerning the survival of both groups. 12 patients died during the observation period. Splenectomy was followed by one death, 11 patients died of septicemia.     

Action of interferons in hairy cell leukemia

We have investigated the direct effects of interferon (IFN) on hairy cells (HCs) isolated from patients with hairy cell leukemia using one- and two-dimensional gel electrophoresis. We have previously characterized the induction of synthesis of 10-16 specific proteins by IFN-alpha 2b in HCs, as analyzed by one-dimensional electrophoresis. By two-dimensional electrophoresis, we have now confirmed this induction and shown that the synthesis of the same number of specific proteins is down-regulated in HCs exposed to IFN-alpha 2b. When compared to HCs, fewer proteins are induced by IFN-alpha 2b in other normal, or neoplastic, lymphoid cells. We also report that protein induction occurs in HCs exposed in vivo to IFN-alpha 2b. We have demonstrated the presence of tubuloreticular structures in the cytoplasm of HCs exposed to IFN-alpha 2b in vitro, using transmission electron microscopy. We now report that these too are seen in HCs exposed to IFN in vivo during therapy. We investigated the effects of IFN-gamma on HCs and found that it also induces specific proteins. The pattern of induced proteins is distinctly different after IFN-gamma exposure in vitro. The fact that such induction occurs suggests that HCs possess also a receptor for IFN-gamma. These results demonstrate that there are direct effects of IFN-alpha on HCs and that such direct effects might be important in the antitumor activity of IFN-alpha in hairy cell leukemia.     

Relationship between human T cell leukemia virus-II and atypical hairy cell leukemia: a serologic study of hairy cell leukemia patients

Human T cell leukemia virus (HTLV-II) is an infrequently encountered human T cell leukemia virus first isolated from a patient with atypical hairy cell leukemia. Recently, we identified a second patient infected with HTLV-II who had a similar clinical syndrome of atypical hairy cell leukemia associated with peripheral T cell lymphocytosis. HTLV-II was detected by molecular hybridization studies, and more recently, by electron microscopy, in cell lines derived from the patient. Both patients came from the Los Angeles area and had spent several years in Alaska. As opposed to our two patients, 21 patients with more typical cases of hairy cell leukemia were seronegative for HTLV-II. Two additional cases of unusual T cell malignancy linked to HTLV-II have been described by other investigators and bear limited similarity to our index cases. Further studies are necessary to define the spectrum of malignancies linked to HTLV-II and to identify infected individuals for prospective study.     

Flow analysis of hairy cell leukemia

Cellular DNA content, Coulter volume and light scatter were measured in cell suspensions from spleens or peripheral blood in 6 patients with hairy cell leukemia. In 2 of 6 cases, the DNA distribution obtained by flow microfluorometry demonstrated an abnormal cellular DNA content of the G₀?G₁ cells. This abnormality was confirmed by mixing the patients' cells with normal blood mononuclear cells. This is the first report of cellular DNA abnormalities in hairy cell leukemia demonstrated by flow microfluorometry. A relatively low number of cells were observed in the S phase of the cell cycle in all cases. On Coulter analysis, “hairy” cells displayed a modal volume 2 to 3 times larger than that of non-malignant lymphoid populations. Differences between “hairy” cell populations and normal lymphoid cells were also noted using light scatter measurements of ethanol-fixed cells, but they were less marked than those observed by Coulter analysis.