Clinico-pathological and Immunophenotype Analysis of Hairy Cell Leukemia Cases – A Single Institute Experience

Background: Hairy cell leukemia is a mature lymphoid B cell disorder, characterized by hairy cells, a specific genetic profile, different clinical course and the need for an appropriate treatment. It is seen primarily in elderly, characterized by a triad of splenomegaly, pancytopenia and monocytopenia. Aim: To evaluate clinicopathologically and with immunophenotyping hairy cell leukemia cases received at our institute in conjunction with similar studies. Material and methods: This is a retrospective study which included 7 cases over a period of 3 years (2019-2021) confirmed on morphology and flow cytometry. Results: The study revealed 7 cases which showed patients with age ranging from 34-65 years. M:F ratio was 6:1. Two cases were covid positive (28.5%). Most of the cases presented with fever, weakness (28.5%). Splenomegaly was seen in three of the cases (42.6%). Laboratory investigations revealed anemia in 71% cases, leucopenia in 56.8%, lymphocytic prominence in 100% and pancytopenia in 14.2%. One patient presented with leukocystosis (14.2%). Marrow was hemodiluted and aparticulate in 3(42.6%) cases. Hairy cells were seen on morphology of peripheral smear and marrow aspirate. On flow cytometry, CD5 negative in all cases (100%), CD10 positive in 2(28.5%) and CD23 in 2 cases (28.5%). Few cases confirmed BRAF v600e mutations. Conclusion: Unusual findings like leukocytosis, absence of spleen, presence of lymphadenopathy can be present in hairy cell leukemia. Classical fried egg appearance in trephine biopsy may not be afeature in all the cases. CD123 is expressed in covid patients unlike other studies and further research is needed to establish the loss of CD123 in covid patients.

Clinicopathological spectrum of hairy-cell leukemia: A single-center study with brief review of Indian literature

Objective: The presence of specific chemotherapeutic protocols for hairy cell leukemia (HCL) makes it essential to discriminate this entity from other lymphoproliferative disorders. Hence, awareness of the variations in clinical presentations and immunophenotypic aberrancies is requisite to ensure diagnostic accuracy. Materials and Methods: A retrospective study was carried out to analyze the clinical-pathological profile of patients with HCL diagnosed over a period of 81 months (2010–September 2017) in our institute. Flow cytometry was performed in all the patients, and further, BRAFV600E mutation analysis was performed by real-time polymerase chain reaction in a limited number of samples. Result: A total of 353 lymphoproliferative disorders were assessed during the period, of which 16 (4.5%) were diagnosed as HCL, which included 15 cases of classical HCL and single case of HCL-v. Striking male predominance was noted with a median age of 52 (range 22–90 years). 47% patients presented with pancytopenia, while 20% cases had leukocytosis. Three patients presented with bleeding diathesis in the form of melena and purpuric spots. The absence of splenomegaly was observed in 20% patients (4/15) while 2 (13.3%) cases had lymphadenopathy. Hypocellular marrow was observed in 13% cases. Bright expression of CD20/CD22 along with CD25/CD103/CD123/CD11c was noted in all the patients of classical HCL. Aberrant expression of CD23 and CD5 was seen in 33% ( n =5) and 6.7% ( n =1) cases respectively. CD200 was positive in all the 5/15 cases tested. The case of HCL–v presented with very high leukocyte count and exhibited a CD103/CD11c+ and CD123/CD25- profile. BRAFV600E, mutation was present in all the four patients tested who included patients with a hypocellular marrow and absent splenomegaly. Conclusion: HCL has characteristic profiles, yet it may exhibit unusual clinical and immunophenotypic presentations. Perspicacious use of flow cytometry and BRAFV600E mutation analysis will aid in the diagnosis in unprecedented cases

Outcome of hairy cell leukemia patients treated with cladribine - a 10-year single-center experience in Pakistan

ABSTRACT Introduction and objective: Hairy cell leukemia is an uncommon, indolent B-cell lymphoproliferative disorder. Therapy with cladribine (2-chlorodeoxyadenosine) is able to induce complete remission (CR) in the majority of patients after a single course of treatment. We report the outcomes of patients treated at Aga Khan University Hospital, Karachi, Pakistan. Methods: This was a retrospective review. Medical records of patients were used to collect data. Results: A total of 21 patients with hairy cell leukemia were treated with cladribine. All patients achieved an initial CR. Four patients (19%) required hospitalization and therapy for neutropenic fever. Six patients (29%) relapsed at a median of 48 months. All 6 patients were treated for relapse, out of which 4 achieved CR, 1 had partial response and 1 had refractory disease. The overall survival rate was 90.5%, with a median follow-up of 35 months. Conclusion: A single course of cladribine is able to induce CR in a vast majority of patients. Unfortunately, relapse is not uncommon. Patients who relapse can be successfully retreated with cladribine. Cladribine has impressive efficacy and a favorable acute and long-term toxicity profile when administered to patients with HCL.

Efficacy of Annexin A1 Immunostaining in Bone Marrow for the Diagnosis of Hairy Cell Leukemia

Splenic B-cell lymphomas (SBCLs) show characteristically pronounced splenomegaly without significant lymphadenopathy. Distinguishing hairy cell leukemia (HCL) from other SBCLs (splenic marginal zone lymphoma [SMZL], variant HCL [v-HCL], and splenic diffuse red pulp small B-cell lymphoma [SDRPL]) is essential to determine suitable treatments and prognoses. With advances in diagnostic modalities and therapies, splenectomy is not commonly performed, and thus diagnosis of HCL must be based on the results obtained using blood and bone marrow samples. Annexin A1 is known as the most specific marker for HCL. There has yet been no report of the assessment of annexin A1 immunostaining from Korea. In this study we analyzed samples from 13 Korean patients with SBCLs (three HCL, three v-HCL, six SMZL, and one SDRPL) from May 2001 to December 2016. Immunohistochemical analyses for annexin A1 and CD20 were performed using bone marrow sections; molecular analyses for detection of the BRAF V600E mutation were also performed. All HCL patients showed positive results for annexin A1 immunostaining and the presence of the BRAF V600E mutation, and negative results for other SBCLs. Our results confirmed the high specificity of annexin A1 and the BRAF V600E mutation as HCL markers. Molecular analysis requires expensive equipment and substantial manpower. Annexin A1 is a better alternative as an HCL marker than the BRAF V600E mutation in terms of cost-effectiveness.

“Hairiness” is a Facsimile of Reorganized Cytoskeletons: A Cytopathic Effect of Coxiella burnetii

In 1993, I reported that Coxiella burnetii transforms human B cells into hairy cells (cbHCs), the first hairy cell reported outside of hairy cell leukemia (HCL). Over last few decades, advances in molecular biology have provided evidence supporting that C. burnetii induces hairiness and inhibits the apoptosis of host cells. The present review summarizes new information in support of cbHC. C. burnetii was shown to induce reorganization of the cytoskeleton and to inhibit apoptosis in host cells. Peritoneal B1a cells were found to be permissive for virulent C. burnetii Nine Mile phase I (NMI) strains in mice. C. burnetii severely impaired E-cad expression in circulating cells of Q fever patients. B-cell non-Hodgkin lymphoma was linked to C. burnetii. Mutation of BRAF V600E was pronounced in HCL, but “hairiness” was not linked to the mutation. Risk factors shared among coxiellosis and HCL in humans and animals were reported in patients with Q-fever. Accordingly, I propose that C. burnetii induces reorganization of the cytoskeleton and inhibits apoptosis as cytopathic effects that are not target cell specific. The observed hairiness in cbHC appears to be a fixed image of dynamic nature, and hairy cells in HCL are distinct among lymphoid cells in circulation. As the cytoskeleton plays key roles in maintaining cell structural integrity in health and disease, the pathophysiology of similar cytopathic effects should be addressed in other diseases, such as myopathies, B-cell dyscrasias, and autoimmune syndromes.

BRAFV600E mutation in hairy cell leukemia: A single-center experience

Background: BRAFV600E mutation has been reported as a unique genetic lesion of hairy cell leukemia (HCL), a subset of which lacks this lesion and shows adverse outcomes. Aims: To determine the prevalence of BRAFV600E in HCL from our center and derive clinicopathological correlation, if any. Materials and Methods: A 9-year retrospective analysis of 46 consecutive cases of HCL diagnosed on morphology and immunophenotyping was done. Stained smears were used as samples for amplification refractory mutation system polymerase-chain reaction using fluorescent primers for mutation detection. Results: BRAFV600E mutation was detected in 41/46 patients (89.1%) while absent in control samples of chronic lymphocytic leukemia. Cases mimicking HCL-variant clinically or immunophenotypically too showed the presence of this mutation. HCL with mutated BRAF presented at a younger age. No statistical difference in blood counts, tumor load, and immunophenotype patterns existed among BRAF mutated and unmutated group. Nine patients (45%) with mutated BRAF had residual disease following treatment with cladribine. Conclusion: BRAFV600E mutation analysis has a definitive role in the diagnosis of HCL.

Fludarabine and Rituximab in Relapsed or Refractory Hairy Cell Leukmia Variant: A Case Report and Review of Literature / 고신대학교의과대학학술지

Hairy cell leukemia (HCL) is a rare chronic B cell leukemia morphologically characterized by cells with an abundant cytoplasm and hair-like projections that can be found in the peripheral blood and bone marrow. The treatment for HCL is splenectomy or chemotherapy with the purine analogs pentostatin and cladribine. However, patients continue to relapse. Retreatment with the same or alternate purine analogs produces lower response rates and a shorter duration of response. Fludarabine is another purine analog widely used in treating indolent lymphoid cancers, often in combination with rituximab. Here, we report a case of HCL variant in a 60-year-old man who experienced multiple relapses after splenectomy and retreatment with cladribine. The patient was then treated with fludarabine and rituximab combination chemotherapy. After the treatment, he achieved complete remission that continued for 35 months.

V-raf murine sarcoma viral oncogene homolog B (BRAF) mutations in hairy cell leukaemia.

Introduction: Hairy cell leukemia (HCL) is a B-cell non-Hodgkin lymphoma with distinct clinical, morphological and immunophenotypic features; however, there are many other B-cell lymphomas, which closely mimic HCL. Accurate diagnosis of HCL is important as treatment with 2-chloro-2’-deoxyadenosine (cladribine) is associated with >80% chance of complete cure. The recent description of BRAF p.V600E mutations in almost all HCL cases in various studies has not only improved the pathogenetic understanding of this entity but also increased the diagnostic accuracy of this disorder. Aim: The aim of the study was to standardize a molecular test for diagnosis of HCL and compare with standard established morphological, cytochemical and immunophenotypic parameters for HCL diagnosis. Materials and Methods: The incidence of this mutation was sought in 20 patients with either classical HCL or HCL variant (HCLv) by Sanger sequencing and allele-specifi c polymerase chain reaction. BRAF p.V600E mutation was present in all HCL cases and absent in the only HCLv case. Results: A high degree of correlation was noted between the presence of BRAF p.V600E and established diagnostic criteria in 20/20 patients with HCL/ HCLv. Our data supports the observation that this mutation is present in all cases of HCL and is absent in HCLv. Hence, detection of the BRAF p. V600E mutation can be a useful adjunct in the diagnostic algorithm.

Hairy cell leukemia: a rare case report.

Hairy cell leukemia (HCL) is a rare chronic B-cell leukemia accounting for 2% of all the leukemias and occurs more frequently in the elderly males. The etiology is unknown but possible relationships to radiation exposure, exposure to benzene, to farm animals and to commercial herbicides and pesticides have been identified. Familial predisposition among first degree relatives has been noted. It is characterized by distinctive cytoplasmic “hair like” projections on the cell surface of lymphoid cells, pancytopenia and splenomegaly. We report a rare case of 29 year old female, farm labourer presenting with fever, fatigue and weakness for 1 month. On examination the patient had hepatomegaly, massive splenomegaly and inguinal lymphadenopathy. After peripheral smear examination diagnosis of HCL was made which was confirmed by bone marrow aspiration examination, bone marrow biopsy and immunohistochemistry (IHC).

Clinico-pathological profile of Hairy cell leukemia: Critical insights gained at a tertiary care cancer hospital.

Context: Hairy cell leukemia (HCL) is a rare, low grade, B-cell neoplasm with a characteristic morphologic and immunophenotypic profile. It has to be distinguished from chronic lymphoproliferative disorders because of different treatment protocol and clinical course. Aims: To evaluate clinicopathological features including immunophenotypic analysis of cases diagnosed as HCL. Materials and Methods: The present study included 28 cases diagnosed over a period of nine years (2002-2010). Clinical presentation, complete blood count, bone marrow aspirate, and flow cytometric analysis of cases were reviewed. Treatment and follow-up details (ranging from 3-90 months) were noted. Results: This study revealed 28 cases (referrals-7, indoor-21), aged 26-69 years with a median age of 47 years, with a male predominance (M:F=6:1). The presenting complaints were weakness (80%) followed by fever (56%) and abdominal pain. Physical examination revealed splenomegaly in most patients (92%) and hepatomegaly in a minority (28%). The common laboratory features were anemia in 23 cases, pancytopenia in 14 cases, while two patients had leukocytosis and three patients had normal WBC count. Dry tap was observed in 84% of the cases where hairy cells constituted 16-97% of non-erythroid nucleated cells. Tartarte resistant acid phosphate staining was positive in all the eight cases where it was done. CD5 was negative in all the cases, while CD10 was expressed in three cases (13%) and CD23 in five cases (19%). Conclusions: Though pancytopenia is common, occasional patient can present with normal blood counts or leukocytosis. Few unusual findings include presence of lymphadenopathy, absence of palpable splenomegaly, and expression of CD23 and CD10 by the leukemic cells.

Relato de caso de leucemia de células pilosas / Case report of hairy cell leukemia

A leucemia de células pilosas (LCP) é um tipo raro de linfoma não Hodgkin de células B. O quadro clínico inclui esplenomegalia, pancitopenia e linfocitose. Estudos de carcinogênese da doença revelam sua associação a agentes químicos agrícolas. O objetivo deste estudo foi o relato de um caso de paciente com LCP, masculino, tratorista, com pancitopenia, lesões de pele, sem esplenomegalia e com marcadores positivos para linfócitos B (CD19, CD20, CD22, CD79b, CD23, Lambda, imunoglobulina M [IgM], CD25 e CD103). Embora a LCP seja uma doença rara, a demora em seu diagnóstico pode levar a sérias complicações e à morte do paciente antes do diagnóstico.

Hairy cell leukemia (HCL) is a rare type of B-cell non-Hodgkin's lymphoma. The clinical symptoms include splenomegaly, pancytopenia, and lymphocytosis. Studies on its carcinogenesis reveal association with exposure to agricultural chemical agents. The objective of this study was to report the case of a male patient, tractor operator, diagnosed with HCL, pancytopenia, cutaneous lesions, without splenomegaly and positive markers for B-cell lymphocytes (CD19, CD20, CD22, CD79b, CD23, Lambda, immunoglobulin M [IgM], CD25 and CD103). Although HCL is a rare disease, late diagnosis may ultimately lead to severe complications and patient's death.

Leucemia de células pilosas: relato de caso / Hairy cell leukaemia: case report

JUSTIFICATIVA E OBJETIVOS: Leucemia de células pilosas é uma doença linfoproliferativa rara caracterizada pelo achado de esplenomegalia, pancitopenia, associado à linfocitose relativa e monocitopenia. Pode mimetizar ou coexistir com outras doenças hematológicas clonais e tem sido associado a desordens auto-imunes e, por isso, deve ser considerado como alternativa no diagnóstico diferencial de alguns processos patológicos. O objetivo desse estudo foi relatar o caso de um paciente portador de leucemia de células pilosas com marcador para linfócitos B positivos, que iniciou quadro clínico com pneumonia, revendo aspectos relacionados à essa doença. RELATO DO CASO: Paciente do sexo masculino, 73 anos, com esplenomegalia sem linfadenopatia, com ascite e pneumonia. Sua leucometria na admissão era normal e não havia relato de linfócitos atípicos no hemograma. Evoluiu, após um mês de internação, com pancitopenia progressiva grave. Realizada biópsia de medula óssea e análise de sangue periférico com microscopia de linfócitos grandes com citoplasma proeminente simulando pêlos. A análise imuno-histoquímica mostrou positividade para CD20 e DBA44, definindo o diagnóstico de leucemia de células pilosas. CONCLUSÃO: Embora a leucemia de células pilosas seja um diagnóstico raro deve ser pensado no diagnóstico diferencial de outras alterações linfoproliferativas. O atraso em seu diagnóstico pode levar a sérias complicações infecciosas e culminar com a morte do paciente, antes mesmo de sua definição. O fármaco de primeira linha é a cladribina, com poucos casos resistentes, devendo ser avaliada, individualmente, a persistência de doença após o tratamento.

BACKGROUND AND OBJECTIVES: Hairy cell leukemia is a rare linfoproliferative disorder characterized by the aspects of splenomegaly and pancytopenia associated with a relatively linfocitosis and monocytopenia. It can mimic or coexist with other clonal hematologic disorders and has been associated with autoimmune diseases and for that has to be considered in the differential diagnosis of some pathologic process. The objectives of this study are to report the case of a hairy cell leukemia patient with B positive lymphocyte marker that initiated his condition with pneumonia and to review the aspects related to this disease. CASE REPORT: Male patient, 73 year-old with splenomegaly and ascitis without linfadenopathy cursing with pneumonia. His white blood count was normal at admission and there was no sign of abnormality with his lymphocytes. He developed in a period of one month a severe progressive pancytopenia. After bone marrow biopsy and peripheric blood analysis it could be found microscopic lymphocytes bigger with a hairy-simulating cytoplasm. The imunohistoquimic analysis showed positively for CD20 and DBA44 ensuring the diagnosis of hairy cell leukemia. CONCLUSION: Although hairy cell leukemia is a rare disease it should be thought along other llinfoproliferatives disorders for the differential diagnosis in some cases. The delay in its diagnosis can lead to serious infectious complications and may terminate in patient death before even its discrimination. Claribin is the first line drug with a few resistance cases. The persistence of the disease must be evaluated individually after treatment.

A Case of Hairy Cell Leukemia, Variant / 대한혈액학회지

Hairy cell leukemia-variant (HCL-variant) is a rare B-cell disorder of hairy cell leukemia cases. The main features are splenomegaly, lymphocytosis and cytopenias without monocytopenia. Diagnosis is based on the distinctive hairy cell morphology and immunophenotype. Cells from hairy cell leukemia (HCL) and HCL-variant have a distinct immunophenotype which is of a mature but not terminally differentiated activated B-cell. We experienced a case of HCL- variant in a 50-year-old man with marked splenomegaly and skin eruptions. Peripheral blood smear showed abnormal lymphoid cells with cytoplasmic projections. The bone marrow was easily aspirated and showed hypercellularity and diffuse interstitial infiltration of hairy cells. Tartrate-resistant acid phosphatase (TRAP) reactivity was negative in the hairy cells. Immunophenotyping results of lymphoid cells were CD2 (-), CD3 (-), CD5 (-), CD7 (-), CD10 (-), CD19 (++), CD20 (+++), sKappa (-), sLambda (+), CD23 (-), CD25 (-), FMC7 (+) and CD103 (++).

A Case of Complete Remission of Hairy Cell Leukemia by 2-Chlorodeoxyadenosine / 영남의대학술지

Hairy cell leukemia (HCL) is an uncommon chronic B-cell lymphoproliferative disorder that is characterized by cytopenia, splenomegaly, and mononuclear cells displaying cytoplasmic projections. We experienced a case of hairy cell leukemia that developed in a 38-year-old man. He showed marked splenomegaly without palpable lymphoadenopathy. A complete blood cell count revealed leukopenia (3300/microliter with 63% of lymphocyte) and the peripheral blood smear showed abnormal lymphoid cells with cytoplasmic projections. The bone marrow smear revealed abnormal lymphocytes and severe myelofibrosis. Tartrate-resistant acid phosphatase reactivity was strongly positive in the hairy cells. The immunophenotyping results of lymphoid cells were CD5 (-), CD10 (-), CD19 (+), CD25 (+), CD103 (+), CD20 (+), lambda (+). The patient was treated with 2-Chlorodeoxyadenosine at a daily dose of 0.1mg/Kg by a continuous intravenous infusion for 7 days. The patient achieved complete remission.

Report of 3 Cases of Hairy Cell Leukemia Treated with 2-Chlorodeoxyadenosine / 대한혈액학회지

Hairy cell leukemia (HCL) is an uncommon chronic B-cell lymphoproliferative disorder characterized by cytopenia, splenomegaly and mononuclear cells displaying cytoplasmic projections. Diagnosis is based on the distinctive hairy cell morphology and immunological profile. In the last 10 to 15 years the prognosis of patients with HCL has improved considerably following the use of purine analogues such as deoxycoformycin and 2-chlorodeoxyadenosine (2-CdA). We report 3 patients with HCL who were treated with 2-CdA at a daily dosage of 0.1mg/kg by continuous intravenous infusion for 7 days. After 1 or 2 courses of treatment, all patients achieved complete remission and are still alive in disease-free status.

Atypical Hairy Cell Leukemia / 대한혈액학회지

We experienced a case of atypical hairy cell leukemia in a 42-year-old woman. She showed marked splenomegaly without palpable lymphadenopathy. Complete blood cell count revealed leukocytosis at 44,000/micro L with lymphocytes 74% and peripheral blood smear showed abnormal lymphoid cells with cytoplasmic projections. The bone marrow was easily aspirated and also revealed the abnormal lymphocytes in up to 95%. Tartrate-resistant acid phosphatase reactivity was negative in the hairy cells. Immunophenotyping results of lymphoid cells were CD5(-), CD7(-), CD10(-), CD19(+), and HLA-DR(+). She was treated with an adenosine analogue, fludarabine at a daily dose of 30mg/m2 for 5 consecutive days, every four weeks. Immediately after treatment, the size of the spleen was normalized. Correct diagnosis was difficult due to insufficient laboratory and pathologic data. The differential diagnosis of mature B-cell neoplasms with cytoplasmic projections in patients with splenomegaly includes hairy cell leukemia and splenic lymphoma with villous lymphocytes. We herein described the present case with a brief review of the literature.

A Case of Hairy Cell Leukemia / 대한혈액학회지

Hairy cell leukemia (HCL) is a chronic B- cell disorder characterized by the presence of typical hairy cells in the peripheral blood and marrow, pancytopenia, and a variable degree of splenomegaly. Identification of typical hairy cells in the peripheral blood and demonstration of tartrate-resistant acid phosphatase (TRAP) are critical findings in HCL. Hepatic involvement of HCL is a common feature and liver biopsy show diffuse mono-nuclear cell infiltration throughout the hepatic sinusoids and in the portal areas. We report a case of hairy cell leukemia in a 52-year-old man who presented with pneumonia and hepatic infiltration with review of the literatures.

Hairy Cell Leukemia: A case report

Hairy cell leukemia is an uncommon lymphoreticular disorder which primarily involves bone marrow, spleen, and peripheral blood. Patients, mostly men, present with splenomegaly and pancytopenia usually. A 62-year-old man was admitted with an abdominnal mass which had grown slowly for 20 years. On physical examination, an enlarged spleen was palpated without tenderness. An abdominal CT scan showed a diffusely enlarged spleen, which measured 20 cm in greatest dimension. In the peripheral blood, many atypical lymphocytes with abundant, delicate, surface projections were noted. They had tartrate-resistant acid phosphatase(TRAP) activity. Thrombocytopenia (60,000/mm3) was observed in the complete blood counts, Other laboratory data were within normal limits. He underwent splenectomy. The submitted spleen measured 26x15x5 cm and weighed 2150 gm. It was well encapsulated and the outer surface was smooth. Cut surfaces were diffusely dark-red. White and red pulps were indistinct. There was no mass-like lesion. Microscopically, the spleen consisted of monotonous mononulcear cells which involved red pulp. The white pulp was diminished, and could be barely recognized. Cells had small round nuclei and abundant cytoplasm. Ultrastructurally, cells with numerous slender surface projections were noted. In Korea, hairy cell leukemia is exceedingly rare. We report a case of hairy cell leukemia with characteristic pathologic features of spleen as well as those of peripheral blood.

Hairy cell transformation of human peripheral blood lymphocytes by Coxiella burnetii

Hairy cell (HC) transformation of human peripheral blood lymphocytes (PBL) by Coxiella burnetii was studied to clarify the significance of persistency of C. burnetii in a hairy cell line (designated "TOL"). TOL cells which exhibited HC characteristics in hairy cell leukemia (HCL) were persistently infected with C. burnetii. Two strains of C. burnetii, our isolate from TOL cells and the original isolate in 1935, the Nine Mile strain from American Type Culture Collection (ATCC, U.S.A), were inoculated to PBL cultures. HC transformation not only by our isolates (87%) but also by Nine Mile strain (100%) was demonstrated in an average of 20 days. The original observation that Coxiella induced HC transformation in vitro was also confirmed in experiments with PBL exposed to C. burnetii in vivo. Spontaneous development of HC were observed in cultures of PBL only from coxiellemic cases (12/24) but not from C. burnetii negative cases (0/57). All HC cell lines (34) as determined by their morphology and cytochemical markers of HC in HCL remained infected with C. burnetii invariably.