Plerixafor and G-CSF for autologous stem cell mobilization in patients with NHL, Hodgkin's lymphoma and multiple myeloma: results from the expanded access program.

Before US regulatory approval, an expanded access program provided plerixafor to patients with non-Hodgkin's lymphoma (NHL), Hodgkin's lymphoma (HD) or multiple myeloma (MM) who had not previously failed mobilization and were otherwise candidates for auto-SCT. Patients received granulocyte-CSF (G-CSF) 10 mcg/kg daily and plerixafor 0.24 mg/kg starting on day 4 with apheresis on day 5; all repeated daily until collection was complete. Overall, 104 patients received 1 dose of plerixafor. The addition of plerixafor to G-CSF resulted in a median threefold increase in peripheral blood CD34+ cell count between days 4 and 5. Among 43 NHL patients, 74% met the target of 5 × 10(6) CD34+ cells/kg (median, 1 day apheresis, range 1-5 days); among 7 HD patients, 57% met the target of 5 × 10(6) CD34+ cells/kg (median, 2 days apheresis, range 1-3); and among 54 MM patients, 89% met the target of 6 × 10(6) CD34+ cells/kg (median, 1 day apheresis, range 1-4). Overall, 93% of patients had 2 × 10(6) CD34+ cells/kg collected within 1-3 days. Plerixafor-related toxicities were minimal. Engraftment kinetics, graft durability and transplant outcomes demonstrated no unexpected outcomes. Efficacy and safety results were similar to results in phase II and III clinical trials.

A simple qualitive procedure for the detection of chloroquine in urine for use in clinical analytical toxicology in resource poor settings.

Objective: To develop and validate a simple procedure for the qualitative determination of chloroquine in urine with potential for use in developing countries lacking sophisticated analytical equipment and expensive reagents. Design: This was a laboratory based study making use of which combines a colorimetric test, Dill-Glazko's test, and UV/Visible absorbance spectrometry to confirm the presence of chloroquine. The spectrophotometric method was cross validated with the standard Baselt's method for quantification of chloroquine in biological fluids. Setting: Pharmacology laboratory at the Department of Clinical Pharmacology, College of Health Sciences, University of Zimbabwe. Main Outcome Measures: Recovery of the methods was assessed by comparing the peak absorbances and the resolution of the peaks at 329nm and 343nm. Sensitivity and specificity was determined by analysing in a blinded manner. The limits of detection of both the Dill-Glazko's test and the confirmatory test was determined. Results: In the prevalidation procedures increasing the volume of the ethylacetate and the volume of the lower aqueous layer extracted was found to increase the recovery of the confirmatory test. There was a significant difference between both the peak absorbances and the peak resolution for the two methods (p<0.0001). The confirmatory test had a sensitivity of 90% and a specificity of 100%, whereas the Baselt's method had a sensitivity of 83.3% and a specificity of 96.7%. The limit of detection of the Dill-Glazko's test was 15mg/Land that of the confirmatory test was 5mg/L. Conclusions: The confirmatory test had better recovery and was more sensitivity compared with the Baselt's method. The limit of detection of the combination method (Dill-Glazko's plus confirmatory test) was 15mg/L. The combination test showed appreciable sensitivity to be suitable for application to clinical toxicology.

Obesity is an independent predictor of poor survival in metastatic breast cancer: retrospective analysis of a patient cohort whose treatment included high-dose chemotherapy and autologous stem cell support.

The purpose of the study was to identify predictors of long-term survival in metastatic breast cancer (MBC). A cohort of 96 patients, who received high-dose chemotherapy with autologous stem cell support (HD-ASCT) as part of their treatment, was analyzed. Percent long-term survival at 10 years was 24.5% (CI 17.2-34.9%) when metastasis was diagnosed and 14.4% (CI 8.7-23.9%) when MBC was diagnosed. Survival was impacted significantly by body mass index (BMI). Median overall survival from initial diagnosis or from time of metastasis for patients with BMIs ≤30 and >30 (obese) was 7.1 (CI 4.4-8.7) and 3.2 years (2.41-6.75), respectively, or 3.2 or 2.3 years (all P = 0.02). Also, obesity was the only independent patient-related predictor of time to metastasis and of survival. While obesity is linked with poor outcomes in earlier stages of breast cancer, this has not been previously reported for MBC.

Optimal use of G-CSF administration after hematopoietic SCT.

After hematopoietic SCT (HSCT), G-CSF is commonly used to enhance stem cell engraftment to minimize the morbidity and mortality associated with prolonged neutropenia. However, there is no consensus on the optimal use of G-CSF after high-dose chemotherapy followed by HSCT. This review was performed to evaluate the evidence regarding the use of G-CSF after autologous and allogeneic HSCT. Studies investigating the use of G-CSF in comparison to control (observation or placebo), early vs delayed initiation of G-CSF, and other approaches driven by patient-specific parameters to identify optimal use of G-CSF have been reviewed. Various outcomes such as neutrophil and platelet engraftment, post-transplant length of hospital stay, post-transplant complications such as infection and GVHD, and survival have been assessed. Finally, we provide the level of evidence for each of the outcomes analyzed while evaluating strategies for using G-CSF in patients undergoing autologous or allogeneic HSCT.

Ovarian recovery after stem cell transplantation.

Autologous or allogeneic SCT with conventional conditioning (chemotherapy with or without irradiation) has emerged as an effective and potentially curative therapy in patients with hematologic malignancies and in other selected solid tumors; however, several patients experience significant early and delayed side effects, including long-term endocrine imbalance and infertility. In spite of several reproductive recovery and pregnancy reports published in the oncology literature, review of medical literature reveals a paucity of comparable information in the SCT field. We report here four cases of ovarian recovery in patients who received hormonal replacement therapy after diagnosis of primary ovarian failure due to high-dose chemotherapy and SCT.

Cytotoxic activity of gemtuzumab ozogamicin (Mylotarg) in acute myeloid leukemia correlates with the expression of protein kinase Syk.

Acute myeloid leukemia (AML) cells express the cell surface antigen CD33 that, upon ligation with a monoclonal antibody (mAb), is a downregulator of cell growth in a Syk-dependent manner. An anti-CD33 mAb coupled to a toxin, gemtuzumab ozogamicin (GO), is used for the treatment of AML (Mylotarg). Therefore, we investigated whether the response of AML cells to GO treatment also depends on Syk expression. Forty primary AML samples (25 Syk-positive and 15 Syk-negative) were tested for their response to the anti-proliferative effects of GO and unmodified anti-CD33 mAb. A correlation between Syk expression and the response of leukemia cells to GO and anti-CD33 mAb was found. 'Blocking' of Syk by small interfering RNA resulted in unresponsiveness of AML cells to both GO and anti-CD33 mAb-mediated cytotoxicity. Syk upregulation by the de-methylating agent 5-azacytidine (5-aza) induced re-expression of Syk in some cases, resulting in enhanced GO and anti-CD33-mediated inhibition of leukemia cell growth. Thus, the cytotoxicity of both GO and anti-CD33 in primary AML samples was associated with Syk expression. 5-Aza restored Syk and increased the sensitivity of originally Syk-negative, non-responsive cells to CD33 ligation to levels of Syk-positive cells. These data have clinical significance for predicting response to GO and designing clinical trials.

CTLA-4 blockade by a human MAb enhances the capacity of AML-derived DC to induce T-cell responses against AML cells in an autologous culture system.

BACKGROUND: Cells from AML patients can differentiate into the phenotype of DC when cultured with GM-CSF and IL-4. Such cytokine-treated AML-derived DC (AML-DC) can stimulate autologous T cells. In this study we examined whether an anti-CTLA-4 MAb (MDX-010) could enhance the generation of autologous anti-AML T cells. METHODS: MAb MDX-010 was added to AML PBMC cultures in the presence of GM-CSF and IL-4, a previously reported AML-DC culture method of generating anti-AML T cells. T-cell activation and proliferation were examined thereafter. RESULTS: Addition of MDX-010 to GM-CSF/IL-4-conditioned AML-DC cultures induced a mean seven-fold increase in the numbers of autologous T cells compared with cultures without MDX-010 (P < 0.007). T cells stimulated by AML-DC with CTLA-4 blockade were significantly more cytotoxic towards autologous AML cells than those without MDX-010 (42 +/- 23% vs. 26 +/- 15%, E:T ratio of 20). T cells stimulated by AML-DC with CTLA-4 blockade had significantly greater proportions of T cells producing IFN-gamma in response to autologous AML cells than those cultured with AML-DC alone (10.7 +/- 4.7% vs. 4.5 +/- 2.4% for CD4+ IFN-gamma+ CD69+ and 9.8 +/- 4.1% vs. 4 +/- 2.1% for CD8+ IFN-gamma+ CD69+ with or without MDX-010; n = 7; P < 0.007, P < 0.003, respectively). DISCUSSION: CTLA-4 blockade enhances the activity and numbers of AML-reactive T cells that can be stimulated by autologous AML-DC and may enhance the efficacy of adoptive immunotherapy of AML.

High-dose CEB vs BEAM with autologous stem cell transplant in lymphoma.

Between January 1996 and July 2002, 72 patients with non-Hodgkin's lymphoma or Hodgkin's disease underwent high-dose chemotherapy with autologous stem cell transplant conditioned with either cyclophosphamide, etoposide, carmustine (CEB) or carmustine, etoposide, cytarabine, melphalan (BEAM) at a single institution. In all, 52 patients received CEB and 20 patients received the BEAM regimen. Patient characteristics that were significantly different between the two groups are tumor grade and extranodal involvement (P = 0.0196, 0.0341, respectively). Regimen-related toxicities examined yielded only diarrhea occurring at a higher rate in the BEAM group (81 vs 51%, P = 0.0026), although cases were milder (92 vs 57%). Patients treated with CEB developed mucositis at a slightly higher rate (79%) than patients treated with BEAM (75%), but this difference did not reach statistical significance. However, the mucositis that occurred within the BEAM group was predominately mild (67%) in contrast to the predominance of moderate to severe cases in the CEB group (74%). In addition, patients treated with CEB required growth factor support for a longer time than patients treated with BEAM (P = 0.0399). Response rates were high in both groups, with trends favoring the BEAM group. Overall survival was higher after treatment with BEAM than with CEB (84 vs 60%).

Improving the efficiency of PBPC collection by pre-apheresis peripheral blood and mid-apheresis product measurements of CD34 cells.

BACKGROUND: The adequacy of HPC collection for BMT is typically assessed by the number of CD34 cells. However, during a series of leukapheresis procedures (LP) the CD34 value on the final HPC product may not be available for testing until late evening, sometimes resulting in additional, retrospectively unnecessary, LP in order to ensure an adequate HPC collection (>5x10(6) CD34/kg). We hypothesized that an estimate of the CD34 content of HPC products prior to 16:00 h on the day of LP would permit improved HPC collection planning. We therefore assessed the effectiveness of predicting the total amount of CD34 cells that would be collected in a given LP by either (a) the concentration of CD34 cells/microL in peripheral blood prior to LP (pre-CD34) or (b) the predicted total amount of CD34 cells to be collected based on sampling the LP product at the mid-point of each LP. We also compared the number of LP per patient and total HPC collected for the study group with data from the previous calendar year. METHODS: Allogeneic and autologous BMT donors who completed a 20-L HPC collection between September 2002 and February 2003 were eligible. CD34 cells were measured on blood drawn prior to LP and from the HPC product at the mid-point (10 L) of LP. The CD34 content of the final LP was predicted by doubling the value of total CD34 cells at the mid-run (MRp-CD34). The MRp-CD34/kg and the cumulative CD34/kg collected were made available before 16:00 h and used to determine the need for additional LP. The true CD34 content of each HPC collection was also measured from the final product the next day (CD34-FP). RESULTS: A 20-L LP was completed and data were available from 31 patients and nine allogeneic donors who underwent a total of 85 LP for diagnoses, including 11 myeloma, 10 lymphoma, seven HD, three acute leukemia and five others. The mean (range) and correlation (R2) vs. the CD34-FP were, for pre-CD34, 54 CD34/microL (0.3-232), R2=0.66 (P<0.01), and for MRp-CD34, 3.2x10(6) CD34/kg (0.04-22.48), R2=0.90 (P<0.01). The mean number of CD34/kg collected per LP in the patients/donors was 3.4x10(6) CD34/kg (0.05-18.94). The median number of CD34 cells employed for transplant in the study group vs. controls (5.7 vs. 5.6x10(6)/kg) and the time to engraftment of neutrophils (12 vs. 11 days) and platelets (12 vs. 12 days) was similar to historical controls. However, the study group had a significantly lower median number of LP (three vs. two; P<0.02) to obtain the required collection of 5x10(6) CD34 cells/kg. DISCUSSION: Both the pre-CD34 and the MRp-CD34 were significantly correlated with CD34-FP. However, the CD34-FP was more reliably predicted by MRp-CD34. Early availability of mid-run CD34 values was associated with a significant reduction in the number of LP required to collect 5x10(6) CD34 cells/kg, without reduction in the number of CD34 cells for transplant or prolongation of days to neutrophil or platelet engraftment.

FLAG chemotherapy followed by allogeneic stem cell transplant using nonmyeloablative conditioning induces regression of myelofibrosis with myeloid metaplasia.

A 38-year-old woman with agnogenic myeloid metaplasia complicated by the poor prognostic factors of severe osteosclerosis, prominent hepatosplenomegaly, and profound anemia was treated with FLAG chemotherapy to decrease her organomegaly before undergoing a nonmyeloablative allogeneic stem cell transplant from a matched-sibling donor. The patient's pre- and post transplant course were complicated by an autoimmune disorder and her post transplant course was complicated by severe hepatic and gastrointestinal GVHD. A technetium-99m sulfur colloid scan 4 months post transplant and bone marrow studies 8 months post transplant demonstrated intramedullary hematopoiesis, complete resolution of marrow fibrosis, and partial resolution of osteosclerosis.

Direct effect of bispecific anti-CD33 x anti-CD64 antibody on proliferation and signaling in myeloid cells.

Bispecific anti-CD33 x anti-CD64 antibody (BsAb) directly inhibited proliferation and colony formation of human acute myeloid leukemia cell lines, without affecting the function of normal monocytes. Addition of BsAb to normal monocytes induced tyrosine phosphorylation of Cbl and Vav, association of these molecules with CD33, and downstream signaling. In leukemia cells that were insensitive to BsAb treatment, Vav and Cbl were constitutively phosphorylated and, therefore, constitutively associated with CD33. Direct growth inhibition is an additional mechanism by which BsAb may be useful in the therapy of AML.

Beneficial effect of intravenous lidocaine in cutaneous chronic graft-versus-host disease secondary to donor lymphocyte infusion.

We report two cases of refractory chronic graft-versus-host disease after donor lymphocyte infusions in which the skin lesions improved dramatically with the use of intravenous pulses of lidocaine. This form of therapy has been used successfully for the cutaneous involvement of scleroderma and may have vasodilator and anti-inflammatory effects.

Characterization of a new monoclonal antibody 6G7 that recognizes a unique antigen on myeloid and lymphoid cells.

We generated a monoclonal antibody (mAb) 6G7, which recognizes a 220-kD antigen on selected subpopulations of normal myeloid and lymphoid cells and their malignant counterparts. 6G7 reacts with 90-95% of peripheral blood B cells, 70-80% of CD8(+) cells, 30-35% of CD4(+) cells, 20-40% of monocytes, and 20-40% of CD34(+) cells from bone marrow. 6G7 reacts with leukemic blasts in acute myeloid leukemia (14/16), adult acute lymphoblastic leukemia (ALL) (5/5), pediatric ALL (5/9), chronic lymphocytic leukemia (8/8), follicular lymphoma (7/7), and Burkitt's lymphoma (1/1). Long-term bone marrow culture of 6G7(+/-) cells showed the majority of clonogenic hematopoietic cells were in mAb 6G7 subpopulation. An immunotoxin of 6G7 and ricin A chain was cytotoxic to 6G7(+) leukemia cell lines. mAb 6G7 has potential clinical applications for targeted immunotherapy of both leukemia and lymphoma.

Caution in the use of 2-iminothiolane (Traut's reagent) as a cross-linking agent for peptides. The formation of N-peptidyl-2-iminothiolanes with bombesin (BN) antagonist (D-Trp(6),Leu(13)-psi[CH(2)NH]-Phe(14))BN(6-14) and D-Trp-Gln-Trp-NH(2).

During a study aimed at generating a bispecific molecule between BN antagonist (D-Trp(6),Leu(13)-psi[CH(2)NH]-Phe(14))BN(6-14) (Antag1) and mAb22 (anti-FcgammaRI), we attempted to cross-link the two molecules by introducing a thiol group into Antag1 via 2-iminothiolane (2-IT, Traut's reagent). We found that reaction of Antag1 with 2-IT, when observed using HPLC, affords two products, but that the later eluting peptide is rapidly transformed into the earlier eluting peptide. To understand what was occurring we synthesized a model peptide, D-Trp-Gln-Trp-NH(2) (TP1), the N-terminal tripeptide of Antag1. Reaction of TP1 with 2-IT for 5 min gave products 1a and 3a; the concentration of 1a decreased with reaction time, whereas that of 3a increased. Thiol 1a, the expected Traut product, was identified by collecting it in a vial containing N-methylmaleimide and then isolating the resultant Michael addition product 2a, which was confirmed by mass spectrometry. Thiol 1a is stable at acidic pH, but is unstable at pH 7.8, cyclizes and loses NH3 to give N-TP1-2-iminothiolane (3a), ES-MS (m/z) [602.1 (M+H)(+)], as well as regenerating TP1. Repeat reaction with Antag1 and 2-IT allowed us to isolate N-Antag1-2-iminothiolane (3b), FAB-MS (m/z) [1212.8 (M+H)(+)] and trap the normal Traut product 1b as its N-methylmaleimide Michael addition product 2b, ES-MS (m/z) [1340.8 (M+H)(+)]. Thiol 1b is also stable at acidic pH, but when neutralized is unstable and cyclizes, forming 3b and Antag1.

Cytotoxicity of anti-CD64-ricin a chain immunotoxin against human acute myeloid leukemia cells in vitro and in SCID mice.

Blast cells from patients with acute myeloid leukemia (AML) commonly express CD64, the high-affinity receptor for immunoglobulin G (FcgammaRI). An immunotoxin (MDX-44) was constructed by coupling humanized anti-CD64 monoclonal antibody (mAb) H22 via a bivalent linker to deglycosylated ricin A-chain (RA). Human leukemia cell lines were incubated with MDX-44 or H22/free RA. The effect of MDX-44 on the proliferation of leukemia cells was assessed by [(3)H]thymidine incorporation. In the presence of interferon-gamma (IFN-gamma), MDX-44 significantly inhibited the proliferation of CD64(+) HL-60, NB4, and U937 cells in 72-h cultures in a dose-dependent manner. The mechanism of action appeared to be the induction of apoptosis, as measured by propidium iodide staining and flow cytometry analysis. However, CD64(-) KG-1a and Daudi cells were not affected by MDX-44/IFN-gamma. Incubating HL-60 cells with MDX-44/IFN-gamma resulted in a 99% decrease in colony-forming units, whereas colony-forming cells in normal bone marrow were not significantly suppressed by such treatment. Cells from 60% of AML patients (6/10) were inhibited by MDX-44/IFN-gamma, and the inhibition was correlated with CD64 expression on these cells (r = 0.65). In a human AML model in NOD/SCID mice, MDX-44/IFN-gamma inhibited 95-98% of peritoneal exudate AML cell proliferation and 85-90% of solid leukemia masses. The effect of MDX-44 on AML cells was dependent on activation of cells by IFN-gamma. MDX-44/IFN-gamma may have value in the therapy of AML cells expressing cell-surface CD64.

Use of capecitabine as first-line therapy in patients with metastatic breast cancer relapsing after high-dose chemotherapy and autologous stem cell support.

High-dose chemotherapy with autologous stem cell support (HDC-ASCS) can produce high complete remission rates in patients with metastatic breast cancer (MBC). However, the majority of those so treated will relapse within 3 years. The ability of such patients to tolerate further myelosuppressive chemotherapy may be limited and the best therapy is undefined. In this retrospective study we assessed the role of capecitabine as initial therapy after relapse. Ten patients (median age = 47 years; oestrogen receptor-positive, n = 4; visceral disease, n = 6; prior anthracycline, n = 8, prior taxanes, n = 10), whose disease progressed at a median of 246 days (range 69-480) after HDC-ASCS and who were treated with capecitabine (2500 mg/m2 per day for 2 weeks of a 3-week cycle) as initial therapy for relapse, were assessed retrospectively for response and toxicity. They received a median of eight cycles (range 4-24) of capecitabine. The toxicities encountered while receiving capecitabine were: hand-foot syndrome (grade 1, n = 3; grade 2, n = 4; grade 3, n = 1); diarrhoea (grade 1, n = 1; grade 2, n = 3); nausea (n = 2) and fatigue (n = 5). Haematological toxicity was seen in only one patient. No patient required hospitalization for toxicity. Three achieved a complete remission, four a partial remission and three disease stabilization. After a median follow-up of 183 days from commencing capecitabine (range 97-540), all patients were alive and five were in remission. Five progressed after remissions that lasted between 63 and 252 days. Oral capecitabine is an active and well-tolerated agent when used alone as first-line therapy in patients who have relapsed after HDC-ASCS for MBC.

Autologous bone marrow transplantation for acute myeloid leukemia in remission or first relapse using monoclonal antibody-purged marrow: results of phase II studies with long-term follow-up.

One hundred and thirty-eight patients with AML underwent ABMT with monoclonal antibody plus complement-purged marrow between August 1984 and March 1997. One hundred and ten patients were in CR (CR1: 23; CR2/3: 87) and 28 were in first relapse (R1) at ABMT. Preparative regimens included busulfan (16 mg/kg) and CY (120 mg/kg) (n = 93), CY (120 mg/kg over 2 days) with TBI (1200 cGy) (n = 35), and busulfan (16 mg/kg) plus etoposide (60 mg/kg) (n = 10). CR1 patients treated with CY/TBI (n = 7) had 3- and 5-year disease-free survival (DFS) rates of 71% and 57%. CR1 patients treated with BU/CY (n = 12), had 3- and 5-year DFS rates of 45%. Three and 5-year DFS for CR2/3 patients treated with CY/TBI (n = 26) was 23%. Three- and 5-year DFS for patients in CR2/3 treated with BU/CY (n = 55) was 31 and 28%. Three- and 5-year DFS for patients in R1 treated with BU/CY (n = 26) was 37%. In multivariate analysis, increased age was associated with greater risk of death and relapse. For CR2/3 patients, the length of CR1 was a significant predictor of DFS. ABMT performed in CR or R1 results in excellent 5-year DFS and OS. The contribution of purging may require a randomized trial comparing purged vs unpurged stem cell infusions.

Simultaneous administration of G-CSF and GM-CSF for re-mobilization in patients with inadequate initial progenitor cell collections for autologous transplantation.

BACKGROUND: A proportion of candidates for high-dose chemotherapy with autologous PBPC support (HDC-PBPCS) will not provide an adequate PBPC yield from their first mobilization. The value of re-mobilization and the best regimen for re-mobilization in these patients is unclear. METHODS: In 23 patients who failed to provide > or = 3 x 10(6) CD34+ cells/kg after their first mobilization, PBPC were re-mobilized using a regimen of simultaneous administration of G-CSF and GM-CSF (10 microg/kg/day each) with leukaphereses (LP) starting Day 4 or 5 of CSF administration. Yields of WBC/kg, MNC/kg and CD34+ cells/kg/L of processed blood were compared between the first and second mobilization in each patient. The ability of the combined yield from the two mobilizations to achieve the desired threshold PBPC yield and the tolerability of the re-mobilization were determined. RESULTS: The re-mobilization regimen was well-tolerated and no patient discontinued the regimen because of toxicity. Median collected WBC/kg/L (1.37 x 10(7) versus 2.62 x 10(7), p = 0.0065), MNC/kg/L (0.77 x 10(7) versus 1.97 x 10(7), p = 0.0003), CD34+ cells/kg/L (1.64 x 10(7) versus 4.18 x 10(7), p = 0.001) were significantly higher after the second mobilization (G-CSF/GM-CSF combination). Percentage of CD34+ cells in the leukapheresis was also significantly higher after the second mobilization (median 0.104% versus 0.195%, p = 0.036). Twelve of 22 patients achieved the target PBPC dose (> 3 x 10(6)/CD34+ cells/kg) after two mobilizations (six patients achieved the target from the second mobilization alone). A further eight underwent HDC-PBPCS without achieving the target PBPC dose. These patients experienced a significant delay in neutrophil and platelet engraftment when compared with those patients achieving the target dose. DISCUSSION: This study demonstrates that the combination of G-CSF and GM-CSF is an effective and tolerable method for re-mobilization of PBPC in patients who fail to provide an adequate yield from their first mobilization.

Human blood dendritic cell-like B cells isolated by the 5G9 monoclonal antibody reactive with a novel 220-kDa antigen.

We developed a murine IgG1 mAb, 5G9, following immunization of a BALB/c mouse with Daudi cells. By immunoprecipitation, 5G9 reacted with a 220-kDa Ag on Daudi cells, which reduced to four subunits (55, 65, 80, and 85 kDa). mAb 5G9 bound to 40-60% of peripheral blood B cells, weakly reacted with monocytes and granulocytes, and did not bind to erythrocytes, platelets, T cells, or NK cells. mAb 5G9 brightly stained scattered cells in human tonsil sections, which appeared to be dendritic cells (DC) by morphology. mAb 5G9 also stained scattered cells in cytospin slides of monocyte-derived DC with long, thin, beaded membrane processes, morphologically distinct from other monocyte-derived DC. Positive selection of blood mononuclear cells with mAb 5G9 and sheep anti-mouse IgG Dynabeads demonstrated an enriched population of DC. By flow cytometry analysis, these cells were CD19, CD20, CD22, CD40, CD44, CD83, CD86, IgD, and HLA-Dr positive and either kappa- or lambda-L chain positive. They did not express CD3, CD4, CD5, CD10, CD11b, CD13, CD25, CD56, CD14, CD33, or CD64. Isolated 5G9+ cells were potent APCs in allogeneic MLR, compared with 5G9- PBMC, 5G9- B cells, monocytes, and monocytes cultured in IL-4 and GM-CSF for 24 h. mAb 5G9 defines a novel peripheral blood cell with B cell phenotype and DC morphology and function: DC-like B cells. The significance of this cell in immune responses requires further study.