[Acute exacerbation of chronic CLL with multiple pathological fractures : A rarity]. / Akute Exazerbation einer chronischen CLL mit multiplen pathologischen Frakturen : Eine Seltenheit.

Chronic lymphatic leukaemia (CLL) is one of the most common leukaemic diseases in middle Europe. Pathological fractures are rare findings in patients with CLL. The diagnosis of CLL is in most cases an incidental finding as it often stays asymptomatic for years. This article presents an interesting case of a 65-year-old male patient with known asymptomatic CLL for 5 years and fractures of the proximal femur and proximal radius after trauma. During the hospital stay the patient suffered multiple pathological fractures with histological findings of bony infiltration of the CLL and an acute phase, which was treated by combination chemotherapy.

Condensed versus standard schedule of high-dose cytarabine consolidation therapy with pegfilgrastim growth factor support in acute myeloid leukemia.

The aim of this cohort study was to compare a condensed schedule of consolidation therapy with high-dose cytarabine on days 1, 2 and 3 (HDAC-123) with the HDAC schedule given on days 1, 3 and 5 (HDAC-135) as well as to evaluate the prophylactic use of pegfilgrastim after chemotherapy in younger patients with acute myeloid leukemia in first complete remission. One hundred and seventy-six patients were treated with HDAC-135 and 392 patients with HDAC-123 with prophylactic pegfilgrastim at days 10 and 8, respectively, in the AMLSG 07-04 and the German AML Intergroup protocol. Time from start to chemotherapy until hematologic recovery with white blood cells >1.0 G/l and neutrophils >0.5 G/l was in median 4 days shorter in patients receiving HDAC-123 compared with HDAC-135 (P<0.0001, each), and further reduced by 2 days (P<0.0001) by pegfilgrastim. Rates of infections were reduced by HDAC-123 (P<0.0001) and pegfilgrastim (P=0.002). Days in hospital and platelet transfusions were significantly reduced by HDAC-123 compared with HDAC-135. Survival was neither affected by HDAC-123 versus HDAC-135 nor by pegfilgrastim. In conclusion, consolidation therapy with HDAC-123 leads to faster hematologic recovery and less infections, platelet transfusions as well as days in hospital without affecting survival.

Acute myeloid leukemia derived from lympho-myeloid clonal hematopoiesis.

We studied acute myeloid leukemia (AML) patients with lympho-myeloid clonal hematopoiesis (LM-CH), defined by the presence of DNA methyltransferase 3A (DNMT3A) mutations in both the myeloid and lymphoid T-cell compartment. Diagnostic, complete remission (CR) and relapse samples were sequenced for 34 leukemia-related genes in 171 DNMT3A mutated adult AML patients. AML with LM-CH was found in 40 patients (23%) and was associated with clonal hematopoiesis of indeterminate potential years before AML, older age, secondary AML and more frequent MDS-type co-mutations (TET2, RUNX1 and EZH2). In 82% of AML patients with LM-CH, the preleukemic clone was refractory to chemotherapy and was the founding clone for relapse. Both LM-CH and non-LM-CH MRD-positive AML patients who achieved CR had a high risk of relapse after 10 years (75% and 75%, respectively) compared with patients without clonal hematopoiesis in CR with negative MRD (27% relapse rate). Long-term survival of patients with LM-CH was only seen after allogeneic hematopoietic stem cell transplantation (HSCT). We define AML patients with LM-CH as a distinct high-risk group of AML patients that can be identified at diagnosis through mutation analysis in T cells and should be considered for HSCT.

A prospective randomised phase-II trial with gemcitabine versus gemcitabine plus sunitinib in advanced pancreatic cancer: a study of the CESAR Central European Society for Anticancer Drug Research-EWIV.

BACKGROUND: Pancreatic ductal adenocarcinoma (PDAC) is one of the most common malignant tumours and is still associated with a poor prognosis in advanced disease. To improve the standard therapy with gemcitabine, we initiated a prospective randomised phase-II trial with gemcitabine (GEM) versus gemcitabine plus sunitinib (SUNGEM) based on data of in vitro trials and phase-I data for the combination treatment. The rational of adding sunitinib was its putative antiangiogenic mechanism of action. METHODS: A total of 106 eligible patients with locally advanced, unresectable or metastatic PDAC without previous system therapy were randomised to receive GEM at a dosage of 1.000mg/m(2) d1, 8, 15 q28 versus a combination of SUNGEM at a dosage of GEM 1.000mg/m(2) d1+8 and sunitinib 50mg p.o. d1-14, q21d. The primary end-point was progression free survival (PFS), secondary end-points were overall survival (OS), toxicity and overall response rate (ORR). RESULTS: The confirmatory analysis of PFS was based on the intend-to-treat (ITT) population (N=106). The median PFS was 13.3 weeks (95% confidence interval (95%-CI): 10.4-18.1 weeks) for GEM and 11.6 weeks for SUNGEM (95%-CI: 7.0-18.0 weeks; p=0.78 one-sided log-rank). The ORR was 6.1% (95%-CI: 0.7-20.2%) for GEM and for 7.1% (95%-CI: 0.9-23.5%) for SUNGEM (p=0.87). The median time to progression (TTP) was 14.0 weeks (95%-CI: 12.4-22.3 weeks) for GEM and 18.0 weeks (95%-CI: 11.3-19.3 weeks) for SUNGEM (p=0.60; two-sided log-rank). The median OS was 36.7 weeks (95%-CI: 20.6-49.0 weeks) for the GEM arm and 30.4 weeks (95%-CI: 18.1-37.6 weeks) for the SUNGEM (p=0.78, one-sided log-rank). In regard to toxicities, suspected SAEs were reported in 53.7% in the GEM arm and 71.2% in the SUNGEM arm. Grade 3 and 4 neutropenia was statistically significantly higher in the SUNGEM arm with 48.1% versus 27.8% in the GEM arm (p=0.045, two sided log-rank). CONCLUSIONS: The combination SUNGEM was not sufficient superior in locally advanced or metastatic PDAC compared to GEM alone in regard to efficacy but was associated with more toxicity.

Evidence for unapparent Brucella canis infections among adults with occupational exposure to dogs.

Human serological assays designed to detect brucellosis will miss infections caused by Brucella canis, and low levels of periodic bacteremia limit diagnosis by blood culture. Recent B. canis outbreaks in dogs and concomitant illnesses in caretakers suggest that unapparent human infections may be occurring. With more than a quarter of a million persons in occupations involving dogs, and nearly 80 million dog owners in the United States, this pathogen is an under-recognized human health threat. To investigate occupational exposure to B. canis, we adapted a commercial canine serological assay and present the first controlled seroepidemiological study of human B. canis infections in recent years. 306 adults with occupational exposure to dogs and 101 non-matched, non-canine-exposed subjects were enrolled. Antibodies were detected using the canine D-Tec(®) CB rapid slide agglutination test (RSAT) kit with a secondary 2-mercaptoethanol (ME)-RSAT. Results were validated on a blinded subset of sera with an additional RSAT and indirect enzyme-linked immunoassay at the National Administration of Laboratories and Health Institutes (ANLIS) in Argentina. Seroprevalence ranged from 10.8% (RSAT) to 3.6% (ME-RSAT) among canine-exposed subjects. Kennel employees were more likely to test RSAT seropositive compared with other canine exposures (OR = 2.7; 95% CI, 1.3-5.8); however, low seroprevalence limited meaningful occupational risk factor analyses. Two seropositive participants reported experiencing symptoms consistent with brucellosis and having exposure to B. canis-infected dogs; however, temporality of symptom onset with reported exposure could not be determined. D-Tec(®) CB results had substantial agreement with ANLIS assays (Cohen's kappa = 0.60-0.68). These data add to a growing body of literature suggesting that people occupationally exposed to dogs may be at risk of unapparent B. canis infection. It seems prudent to consider B. canis as an occupational public health concern and encourage the development of serological assays to detect human B. canis infections.

No serologic evidence for zoonotic canine respiratory coronavirus infections among immunocompetent adults.

Zoonotic diseases continue to emerge and threaten both human and animal health. Overcrowded shelters and breeding kennels create the perfect environment for amplified infectious disease transmission among dogs and present a critical opportunity for zoonotic pathogens to emerge and infect people who work in close contact with dogs. Coronaviruses' widespread prevalence, extensive host range, various disease manifestations and increased frequency of recombination events all underline their potential for interspecies transmission (Methods Mol. Biol. 2008, 454, 43). The objectives of this study were to determine whether people with occupational contact with dogs were more likely to have antibodies against canine respiratory coronavirus (CRCoV) compared to persons with no dog exposure. A seroepidemiological cohort study was completed, for which 302 canine-exposed and 99 non-canine-exposed study subjects enrolled in the study by providing a serum sample and completing a self-administered questionnaire. A competitive enzyme-linked immunosorbent assay (ELISA) was developed to detect human antibodies against CRCoV while controlling for cross-reacting antibodies against the human coronavirus OC43. All study subjects were negative for antibodies against CRCoV by this competitive ELISA. This study supports the premise that humans are not at risk for CRCoV infections; however, infrequent cross-species transmission of CRCoV cannot be ruled out.

Prognostic implications and molecular associations of NADH dehydrogenase subunit 4 (ND4) mutations in acute myeloid leukemia.

To study the prevalence and prognostic importance of mutations in NADH dehydrogenase subunit 4 (ND4), a mitochondrial encoded transmembrane component of the electron transport chain respiratory Complex I, 452 AML patients were examined for ND4 mutations by direct sequencing. The prognostic impact of ND4 mutations was evaluated in the context of other clinical prognostic markers and genetic risk factors. In all, 29 of 452 patients (6.4%) had either somatic (n=12) or germline (n=17) ND4 mutations predicted to affect translation. Somatic mutations were more likely to be heteroplasmic (P<0.001), to occur in predicted transmembrane domains (P<0.001) and were predicted to have damaging effects upon translation (P<0.001). Patients with somatically acquired ND4 mutations had significantly longer relapse-free survival (P=0.017) and overall survival (OS) (P=0.021) than ND4(wildtype) patients. Multivariate analysis also demonstrated a tendency for increased survival in patients with somatic ND4 mutations (RFS: hazard ratio (HR) 0.25, confidence interval (CI) 0.06-1.01, P=0.052; OS: HR 0.29, CI 0.74-1.20, P=0.089). Somatic ND4(mutated) patients had a higher prevalence of concomitant DNMT3A mutations (P=0.023) and a higher percentage of the NPM1/FLT3-ITD low-risk genotype (P=0.021). Germline affected cases showed higher BAALC (P=0.036) and MLL5 (P=0.051) expression levels. Further studies are warranted to validate the favorable prognostic influence of acquired ND4 mutations in AML.

Long-term survival data from a phase 3 study of Filgrastim as an adjunct to chemotherapy in adults with de novo acute myeloid leukemia.

We previously reported the results of a double-blind, placebo-controlled study of Filgrastim in patients with de novo AML undergoing induction and consolidation chemotherapy. The study demonstrated that Filgrastim was effective and well tolerated and had no impact on complete remission or survival. We now report follow-up data on these patients, assessing long-term effects with emphasis on prognostic indicators. After a median follow-up of 7 years, 434 (83%) patients were dead, 73 (14%) were alive, and 14 (3%) were lost to follow-up. The proportions of deaths were similar in the Filgrastim (83%) and placebo (84%) groups. No differences in median time to death (1.04 years Filgrastim, 1.13 years placebo; P = 0.97) or median disease-free survival (0.86 years Filgrastim, 0.79 years placebo; P = 0.52) were evident. Proportional hazard modeling identified age, performance status, and French-American-British subtype as independent predictors for survival (P < 0.001, P = 0.005, and P = 0.036, respectively), whereas cytogenetic status was not (P = 0.118). Filgrastim had no effect on overall survival in any of these subgroup analyses as none of the treatment comparisons were statistically significant. These findings indicate that Filgrastim can be effectively used to support patients with AML undergoing induction and consolidation chemotherapy without worsening long-term disease outcome.

Individual patient data-based meta-analysis of patients aged 16 to 60 years with core binding factor acute myeloid leukemia: a survey of the German Acute Myeloid Leukemia Intergroup.

PURPOSE: To evaluate prognostic factors for relapse-free survival (RFS) and overall survival (OS) and to assess the impact of different postremission therapies in adult patients with core binding factor (CBF) acute myeloid leukemias (AML). PATIENTS AND METHODS: Individual patient data-based meta-analysis was performed on 392 adults (median age, 42 years; range, 16 to 60 years) with CBF AML (t(8;21), n = 191; inv(16), n = 201) treated between 1993 and 2002 in prospective German AML treatment trials. RESULTS: RFS was 60% and 58% and OS was 65% and 74% in the t(8;21) and inv(16) groups after 3 years, respectively. For postremission therapy, intention-to-treat analysis revealed no difference between intensive chemotherapy and autologous transplantation in the t(8;21) group and between chemotherapy, autologous, and allogeneic transplantation in the inv(16) group. In the t(8;21) group, significant prognostic variables for longer RFS and OS were lower WBC and higher platelet counts; loss of the Y chromosome in male patients was prognostic for shorter OS. In the inv(16) group, trisomy 22 was a significant prognostic variable for longer RFS. For patients who experienced relapse, second complete remission rate was significantly lower in patients with t(8;21), resulting in a significantly inferior survival duration after relapse compared with patients with inv(16). CONCLUSION: We provide novel prognostic factors for CBF AML and show that patients with t(8;21) who experience relapse have an inferior survival duration.

Intensive chemotherapy with idarubicin, cytarabine, etoposide, and G-CSF priming in patients with advanced myelodysplastic syndrome and high-risk acute myeloid leukemia.

In an attempt to improve the complete remission (CR) rates and to prolong the remission duration especially in elderly patients > 50 years of age, we have used a combination chemotherapy of idarubicin (10 mg/m2 IV x 3 days), cytarabine (AraC, 100 mg/m2 CIVI x 7d), and etoposide (100 mg/m2 x 5 days) in combination with granulocyte colony-stimulating factor (G-CSF) priming [5 mg/kg SQ day 1 until absolute neutrophil count (ANC) recovery] for remission induction. Responding patients received two consolidation courses of idarubicin, AraC, and etoposide, followed by a late consolidation course of intermediate-dose AraC (600 mg/m2 IV every 12 h x 5 days) and amsacrine (60 mg/m2 IV x 5 days). A total of 112 patients (57 male/55 female) with a median age of 58 years (range: 22-75) have been entered and are evaluable for response: 19 refractory anemia with excess of blast cells in transformation (RAEB-T), 84 acute myeloid leukemia (AML) evolving from myelodysplastic syndrome (MDS), and 9 secondary AML after chemotherapy/radiotherapy. The overall CR rate was 62%, partial remission (PR) rate 10%, treatment failure 16%, and early death rate 12%. The CR rate was higher in patients < or = 60 years (68 vs 55%), mainly due to a lower early death rate (5 vs 21%, p<0.001). After a median follow-up of 58 months, the median overall survival is 14.5% and median duration of relapse-free survival 8 months. After 60 months, the probability of CR patients to still be in CR and alive is 16% (20% in patients < or = 60 years and 13% in patients >60 years), while the probability of overall survival is 12% (15% in patients < or = 60 years and 9% in patients > 60 years). Compared to our previous trial (AML-MDS Study 01-92) which was done with identical chemotherapy but no G-CSF priming in 110 patients with RAEB-T, AML after MDS, or secondary AML (identical median age, age range, and distribution of subtypes), the CR rate in all patients, as well as CR rate, overall survival, and relapse-free survival in patients > 60 years have significantly been improved. Thus, intensive chemotherapy with G-CSF priming is both well tolerated and highly effective for remission induction in these high-risk patients.

Risk-adapted induction and consolidation therapy in adults with de novo AML aged

We treated 305 de novo acute myeloid leukemia (AML) patients aged

Expression of the p14ARF tumor suppressor predicts survival in acute myeloid leukemia.

Cell cycle aberrations are associated with therapy outcome in many types of cancer. We analyzed mRNA expression levels of 18 cell cycle-related genes in bone marrow samples from 78 acute myeloid leukemia (AML) patients and six controls using high-throughput quantitative RT-PCR. Samples of AML patients contained significantly increased mRNA expression levels of the mdm2 and c-myc oncogenes. Also, the average expression levels of p14ARF and p16INK4A were higher in patient samples compared to controls. Leukemic blasts and control bone marrow samples did not differ significantly in the expression levels of proliferation-associated genes such as cyclin A2 and pcna. When single genes were analyzed for prognostic significance in Kaplan-Meier and Cox regression analyses, a low p14ARF level emerged as a strong and independent predictor for poor survival (P=0.04 and 0.029). Subsequently, p14ARF mRNA levels were analyzed in a second, independent patient population (n=57). Again, low p14ARF levels were associated with a worse outcome. Finally, immunohistochemistry analysis of AML tissue arrays confirmed the widespread expression of c-myc and p14ARF in AML on the protein level. Taken together, the expression of the p53 regulators mdm2 and p14ARF are altered in AML, and low p14ARF levels indicate a poor prognosis.

Central venous catheter infections in patients with acute leukemia.

BACKGROUND: Central venous catheters (CVCs) have become an essential tool for an appropriate management of patients with acute leukemia. Infectious complications are a major concern in patients treated for acute leukemia. Although CVC-related infections are considered to be a major source of infections during neutropenia (<500/microl), data regarding the incidence of CVC-related infections are rare in acute leukemia. PATIENTS AND METHODS: We analyzed nontunneled CVCs in 58 patients with acute leukemia (22 men/36 women) in 119 chemotherapy cycles from April 1996 to January 1998 in a prospective trial. Proven CVC-related infection was defined as the isolation of the same organism from peripheral blood and CVC tip. CVC infection was suspected or possible when exit site inflammation and positive blood culture or organisms typical for CVC infection were observed. RESULTS: Mean neutropenia/cycle was 16.3 days (SD 8.0). 178 CVCs with 2,576 CVC days (mean 14.5 days, SD 7.2 days) were used in 119 cycles. Fever occurred in 87 cycles (73%). Blood stream infection was proven in 31 out of 87 febrile episodes (26.1%) with 40 isolates (8 gram-negative, 31 gram-positive, 1 Candida spp.). Colonization of the CVC tip was observed in 24 CVC lines with 28 isolates (27 gram-positive, 1 gram-negative); however, proven CVC-related infections were observed in 5 episodes only, all with coagulase-negative staphylococci. In another 6 episodes, CVC-related infection was assumed (local inflammation and gram-positive blood culture). Six further episodes had typical blood isolates (4 coagulase-negative staphylococci, 1 Candida spp.) and were considered possible CVC-related infections. In none of the remaining afebrile 32 cycles was a CVC infection observed or suspected. CONCLUSION: Gram-positive organisms contributed to the majority of CVC-related infections (16 out 17 CVC infections); however, the overall incidence of CVC infections in acute leukemia patients was 6.5/1,000 CVC days only (1.9 proven/2.3 suspected/2.3 possible/1,000 CVC days).

Donor cell-derived acute myeloid leukemia developing 14 months after matched unrelated bone marrow transplantation for chronic myeloid leukemia.

We report a patient with Ph-positive CML who developed a Ph-negative AML in donor cells 14 months after BMT from an HLA-identical male unrelated donor. The Ph translocation could not be detected by either conventional cytogenetics, FISH or RT-PCR analysis excluding relapse of CML in myeloid blast crisis. Chimerism studies were performed by variable number of tandem repeats (VNTR) analysis. These revealed donor-type hematopoiesis in both unseparated mononuclear cells and CD34+ selected blasts proving the leukemia to be of donor origin. The patient received three cycles of polychemotherapy with mitoxantrone, topotecan and ara-c resulting in CR after the first treatment cycle and reconstitution with donor hematopoiesis. A second transplant from a female alternative matched unrelated donor was performed after conditioning with fludarabine and 200 cGy TBI and was well tolerated. Nine months after the second transplant the patient is at home and in CR. T cell chimerism was studied by sex chromosome analysis and revealed complete female donor chimerism.

Inhibition of granulocyte-macrophage colony-stimulating factor receptor function by a splice variant of the common beta-receptor subunit.

The receptors for human granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), and IL-5 are composed of a ligand-specific alpha-chain (eg, alpha-GM-CSF receptor [alpha-GMR]) and a common beta-subunit (beta-GMR). Ligand binding is believed to induce assembly or conformational changes in preformed complexes containing more than one alpha- and beta-subunit in the activated receptor complex. To analyze the function of a splice variant of beta-GMR with a truncation in the intracellular domain (beta-GMR(IT)), BaF-3 cells expressing human alpha-GMR plus beta-GMR were transfected with beta-GMR(IT). In these cells, coexpression of beta-GMR(IT) inhibits GM-CSF-mediated survival and proliferation in a GM-CSF concentration-dependent manner. To analyze the effect of cytoplasmic assembly of truncated and full-length intracellular beta-GMR sequences, beta-GMR and beta-GMR(IT) were coexpressed with different chimeric alpha/beta-GMR constructs. Whereas both beta-GMR and beta-GMR(IT) generate high-affinity GMR complexes in the presence of alpha/beta-GMR, beta-GMR(IT) inhibits while beta-GMR supports proliferation and cell survival mediated by alpha/beta-GMR. Correspondingly, beta-GMR, but not beta-GMR(IT), generates functional GMR complexes when coexpressed with a defective alpha/beta-GMR construct. These data indicate that beta-GMR(IT) can inhibit survival and mitogenic signaling of the wild-type GMR and demonstrate that recruitment of alternatively spliced receptor subunits may regulate the function of heteromeric cytokine receptors.

Cleavage of AML1/MTG8 by asymmetric hammerhead ribozymes.

The chromosomal translocation t(8;21) is one of the most frequent aberrations associated with acute myeloid leukaemia. It joins the 5' section of the AML1 gene with the almost complete open reading frame of MTG8 (ETO). The resulting fusion RNA represents a leukaemia-specific target for antisense/ribozyme inhibition. We tested several asymmetric hammerhead ribozymes targeted against the fusion site for their ability to cleave the AML1/MTG8 RNA at low magnesium concentrations. One ribozyme cleaves AML1/MTG8 RNA with high catalytic efficiency without binding or cleaving the wild-type AML1 transcript. The presence of cellular RNA does not affect the cleavage. Injection of AML1/MTG8 RNA and ribozyme RNA into Xenopus eggs or oocytes causes a specific reduction of AML1/MTG8 protein expression. Asymmetric anti-AML1/MTG8 ribozymes may be valuable modulators of AML1/MTG8 expression in leukaemic cells.

Detection and quantification of CBFB/MYH11 fusion transcripts in patients with inv(16)-positive acute myeloblastic leukemia by real-time RT-PCR.

We used a newly established real-time RT-PCR assay for the quantification of the leukemia-specific CBFB/MYH11 transcripts in inv(16)-positive acute myeloblastic leukemia. CBFB/MYH11 could be quantified over a five log range, with a detection limit of 10 molecules of a CBFB/MYH11 plasmid and a 1:10(5) dilution of RNA of the inv(16)-positive ME-1 cell line, respectively. The fusion transcripts were also quantified in 19 patients with acute myeloblastic leukemia and an inv(16) at initial diagnosis. The expression of CBFB/MYH11 varied over a two log range without correlation to clinical response or relapse rate. In nine patients, CBFB/MYH11 was also quantified during/after chemotherapy and autologous or allogeneic stem cell transplantation. All of these patients showed a similar decline of CBFB/MYH11 after intensive therapy. Six of these patients are in complete remission with a stable low-level or absent CBFB/MYH11 expression. Three patients relapsed, and their CBFB/MYH11 transcripts rose again to pretreatment levels. In two patients, this increase in CBFB/MYH11 could be detected by real-time PCR before hematological relapse. These data indicate that real-time RT-PCR can be used for the sensitive detection and quantification of CBFB/MYH11 transcripts in the follow-up of patients with inv(16)-positive AML.

Receptor-mediated endocytosis of CD34 on hematopoietic cells after stimulation with the monoclonal antibody anti-HPCA-1.

CD34 most probably acts as a receptor molecule on hematopoietic progenitor cells; however, its precise function remains to be elucidated. To track the intracellular pathway of CD34 after binding of a stimulatory antibody (anti-HPCA-1), immuno-electron microscopical analysis was performed on cells of normal bone marrow (NBMPC), acute leukemias, and the KG1a cell line. Before stimulation, CD34 was evenly distributed over the cell surface. After binding of the anti-HPCA-1, but not the anti-HPCA-2 antibody to CD34 and labeling with 30-nm immunogold, a rapid capping of CD34 and a subsequent internalization from the cell surface via clathrin-coated pits and coated vesicles was observed. The percentage of internalized CD34/immunogold complexes ranged from 8 to 80% in the NBMPC and the leukemic blasts, whereas KG1a cells showed an internalization rate of only 0.42%. Moreover, in the KG1a cells, the CD34/immunogold complexes were not associated with the coated pits. These differences in CD34 internalization did not correlate to the mRNA expression for the full-length or truncated CD34 assessed by isotype-specific real-time PCR. Taken together, evidence was found that CD34 is a surface receptor molecule that is modulated by receptor-mediated endocytosis. CD34 on KG1a cells appears to have a functional and/or structural defect, preventing modulation of this epitope.