Surgical treatment of recurring preauricular sinus: supra-auricular approach

Congenital preauricular sinus is a malformation of the preauricular soft tissues with an incidence ranging between 0.1 and 0.9% in Europe and the United States. It presents a high risk of recurrence when treated by a standard surgical technique (simple sinectomy), the incidence of which is reported to be between 19% and 40%. The supra-auricular approach, proposed by Prasad et al. in 1990, is easier to perform and presents a lower recurrence risk. Personal experience is presented in the treatment of congenital preauricular sinus with the supra-auricular approach as first choice or in the case of recurrence following previous standard surgery. This report includes a short review of the literature in order not only to focus on the supra-auricular approach and check the efficacy as far as concerns reduction of recurrence risk but also to contribute to a more widespread use of this method.

Iatrogenic benign paroxysmal positional vertigo: review and personal experience in dental and maxillo-facial surgery

The post-traumatic origin of benign paroxysmal positional vertigo remains the most likely, from a patho-physiologic point of view. Benign paroxysmal positional vertigo due to surgical "traumas" has been described in the medical literature. According to personal experience, these iatrogenic cases represent a rare possibility and may be the consequence of surgical interventions differing according to the anatomical district involved and surgical technique performed. The temporal relationship with the surgical action and clinical features may be involved in some of these cases, even if it is not possible to define any real cause-effect link. Herewith some cases of paroxysmal positional vertigo are described, strongly held to be of iatrogenic origin, focusing on dental and maxillo-facial surgery as risk factors for benign paroxysmal positional vertigo.

Paroxysmal positional vertigo: short- and long-term clinical and methodological analyses of 794 patients

Between 1995 and 2001, eight Italian clinical centres used the same diagnostic and therapeutic protocol in order to assess the clinical progress of paroxysmal positional vertigo and the benefits of an appropriate follow-up in prevention of relapse. The study population comprises 794 patients affected by paroxysmal positional vertigo. The study protocol comprised diagnostic staging including a complete otoneurological test, an anamnestic questionnaire aimed at identifying any possible risk factor, a blood test in basal conditions and monitoring of blood pressure. If necessary, more specific instrumental tests have been carried out. Appropriate rehabilitative manoeuvres were performed from 1 to 3 times within the same session. The patient was checked 3-5 days later: in the presence of a positive result, the treatment was repeated; if negative, patients were seen at clinical follow-up 7, 30, 180 and 365 days after recovery. Wherever possible, patients have been contacted 2 years after the first treatment and asked to answer a questionnaire and to attend for a clinical check-up. The incidence of paroxysmal positional vertigo appeared to be higher in females and in patients aged 50-70 years, being low in patients under 30. In 88.8% of cases posterior semicircular canals showed a significant involvement; in 6.8% of cases, only involvement of lateral semicircular canals; monolateral (2.7%) and bilateral (1.7%) multicanalar forms were rare. Paroxysmal positional vertigo forms involving posterior semicircular canals have been treated with Semont (simplified by Toupet), Epley, Parnes Price-Jones manoeuvres; those, involving lateral semicircular canals with Vannucchi-Vicini forced position and "barbecue" or Gufoni manoeuvre. Whilst all these manoeuvres were equally effective, longer recovery times have been observed in paroxysmal positional vertigo forms involving lateral semicircular canals when the Vannucchi-Vicini forced position was ineffective. Any relapses have been evaluated at least 15 days after a negative clinical pattern. Possible involvement of other semicircular canals (recurrence) some time after the first onset has been considered separately. Follow-up at 6 months showed recurrence in 12.4% of cases, while being chronic in 1.5% of cases. Only 9.3% of cases showed recurrence at 6 months, no statistically significant difference being observed between vertical (8.9%) and lateral canal (9.6%), forms. Relapses occurred in 3.1% of cases, in one third of which at least two risk factors were detected.

[Ki67 and p53 in laryngeal epithelial lesions: correlations with risk factors]

Laryngeal carcinoma-the prototype of epithelial tumors in the head and neck region-has been the greatest source of information on the biological behavior of such neoplasms. Many Authors have suggested that smoke, and to a lesser extent alcohol, play a role in the genesis of this carcinoma although the exact biological mechanism for such involvement is still not clear. The present study analyzed two important biological indicators (p53 and Ki67) in benign and malignant epithelial lesions of the larynx in an attempt to obtain information on what mechanism correlates the risk factors with the neoplasm. In a group of 172 patients, an in vivo sampling of cells was taken during microlaryngoscopy. These cells were then tested using the immunocytochemical method and the results showed that the neoplastic tissue was significantly more positive to these markers than the pre-cancerous tissues and benign lesions. Moreover, there was also an interesting correlation between the degree of positivity to p53 and exposure to smoke, and to a lesser extent to alcohol, in the oncological patients. Together with other similar results found in the literature, these results hint at a possible explanation for the carcinogenic power of smoke in the larynx and, in general, in the upper respiratory-digestive tract.

Selection and transplantation of autologous CD34+ B-lineage negative cells in advanced-phase multiple myeloma patients: a pilot study

The feasibility of sequential positive and negative selection of mobilized CD34+ B-lineage negative cells to achieve tumour-free autografts in multiple myeloma (MM) patients was evaluated. Peripheral blood stem cells (PBSC) of 14 patients with advanced disease were mobilized. CD34+ cells were enriched in 12 of the patients by the avidin-biotin immunoabsorption technique. Subsequently, CD10+, CD19+, CD20+ and CD56+ cells (B-lin cells) were removed by immunomagnetic depletion. Minimal residual disease (MRD) was detected by flow cytometry and PCR-based molecular analysis of the patient specific IgH complementary-determining region III (CDRIII). Positive selection of stem cells produced a median recovery of 54.7% of the initial content of CD34+ cells (median purity 71.9%). Negative depletion of B-lineage cells reduced the number of CD34+ cells to 33.3% of the baseline value (median purity 72.7%). However, long-term culture assays showed the recovery of >60% of primitive haemopoietic progenitor cells after depletion of the B-lineage-positive cells. All evaluable patients had detectable disease in PBSC collections. The first step of positive selection of CD34+ cells resulted in >2 logs of tumour cell purging. However, molecular assessment showed the persistence of the disease in 6/7 cases. Immunofluorescence analysis demonstrated 1 additional log of B-cell purging by negative depletion. More importantly, molecular evaluation of IgH CDRIII region showed the disappearance of myeloma cells in 6/7 patients. 12 patients received a median of 3.9 x 106 CD34+ B-lin- cells/kg after conditioning with high-dose melphalan and showed a rapid reconstitution of haemopoiesis. These results were similar to two similar cohorts of patients who received either unmanipulated PBSC or positively selected CD34+ cells after the same conditioning regimen. Severe extrahaematological toxicity was limited to mucositis; no late infections were observed. We concluded that autotransplantation of purified CD34+ B-lin- cells was associated with a rapid and sustained recovery of haemopoiesis and low peritransplant morbidity. Sequential positive and negative enrichment of stem cells reduced tumour cell contamination in B-cell malignancies below the lower limit of detection of molecular analysis.

Use of peripheral blood stem cells for autologous transplantation in acute myeloid leukemia patients allows faster engraftment and equivalent disease-free survival compared with bone marrow cells

We compared the feasibility and efficacy of autologous bone marrow (ABMT) and peripheral blood progenitor cell transplantation (PBSCT) performed after an identical induction/consolidation in adults with acute myeloid leukemia (AML). From January 1993 to June 1996 91 consecutive AML patients were enrolled in a program consisting of anthracycline-based induction and high-dose cytarabine consolidation (NOVIA). Until May 1994 ABMT was performed; from June 1994, if PBSC collection was adequate, PBSCT was performed. Out of 88 evaluable patients, 73 obtained a complete remission (CR) and 15 were resistant. Allogeneic bone marrow transplantation was performed in 16 patients. Forty-four (50%) were given autologous stem cell transplantation. ABMT was performed in 21 cases; twenty-nine patients were given G-CSF mobilization after NOVIA administration. An adequate number of PBSC was obtained in 23/29 (79%) cases, which were then re-infused. Median times to both neutrophil and platelet recovery from transplant were significantly shorter for the PBSC group (17 vs 36 days to 500 PMN/microl, P < 0.01; 20 vs 150 days to 20000 platelets/microl, P < 0.02; 37 vs 279 days to 50000 platelets/microl, P < 0.03), as were days of hospitalization after the reinfusion (18 vs 33, P < 0.03) and median days to transfusion independence. Toxicity was not significant in either group. After a minimum follow-up for live patients of 24 months (longer than the mean time for relapse observed for the PBSC series - 14 months) the percentage of relapses was similar: 11 of 21 (52.4%) and 12 of 23 (52.1%) in the ABMT and PBSC groups, respectively. Our results indicate that autologous PBSC transplantation, performed after an intensive chemotherapy regimen, is not inferior to ABMT in terms of disease-free survival and allows faster recovery times and reduced need for transfusion support.

Discrepancy between serological complete remission and concomitant new bone lytic lesions after infusion of escalating low doses of donor lymphocytes in multiple myeloma: a case report

A graft-versus-myeloma effect has been previously induced by infusing high numbers of donor lymphocytes after allogeneic stem cell transplantation in relapsed/refractory multiple myeloma (MM) patients. A 43-year-old patient with MM refractory to standard chemotherapy and autologous transplantation received an allogeneic HLA-matched T cell-depleted marrow transplant from his sister after conditioning with single dose total-body irradiation, melphalan and cyclophosphamide. Twenty-four months after transplant neither a significant reduction of serum M protein nor evidence of acute or chronic graft-versus-host disease (GVHD) were observed. The patient was then treated with four escalating low doses of donor lymphocyte infusions (DLI) (0.1, 1.0, 5.0 and 5.0 x 106 CD3+ T cells/kg, respectively) over a 13 month period. Following the second infusion a mild liver acute GVHD and a partial, but transient, response occurred. After the last DLI the patient achieved a complete remission and developed extensive chronic GVHD. However, concomitant with the disappearance of clonal plasma cells from the marrow and of serum M protein, two new bone lytic lesions appeared requiring treatment with radiotherapy. In conclusion, escalating low doses of DLI may be effective in MM and may prevent severe acute but not chronic GVHD. However, the efficacy of DLI in extramedullary MM lesions is still unclear.

Fludarabine-containing regimens severely impair peripheral blood stem cells mobilization and collection in acute myeloid leukaemia patients

We studied the effects of an intensified induction/consolidation treatment containing fludarabine (ICE/FLAN/FLAN) on the mobilization and collection of peripheral blood stem cells (PBSC) in 31 consecutive untreated acute myeloid leukaemia (AML) patients. The complete remission (CR) rate was comparable to classic inductions (68% after ICE; 84% after ICE-FLAN I). To mobilize PBSC, 19 patients received 10 microg/kg/d of granulocyte-colony stimulating factor (G-CSF) starting at day 13 after FLAN, 13 (69%) of whom were found to be nonmobilizers. When a second G-CSF administration was performed in 10/13 patients mobilization was either not achieved (8/10) or was considered insufficient (<1 x 106 CD34+ cells/kg) (2/10) and all 13 were subsequently submitted to bone marrow harvest. The harvest was considered adequate in 12/13 (92%) patients and autologous BMT (ABMT) has so far been performed in 10/12 cases with a mean of 8.6 x 108/kg nucleated reinfused cells. The median times to neutrophil and platelet recovery after ABMT did not significantly differ from those of two previous series of patients treated with ABMT without fludarabine-containing regimens. Adequate amounts of PBSC were obtained in 6/19 (31%) patients, who were then reinfused. Median times for platelet recovery were significantly longer than in a previous series of 26 AML cases reinfused with PBSC after treatment with the ICE-NOVIA induction/consolidation regimen (125 v 20 d to 20 x 109 plt/l, P < 0.02; 218 v 37 d to 50 x 109 plt/l, P < 0.02). In addition, times for platelet recovery after ICE/FLAN/FLAN were not significantly different from those in a previous group treated with ABMT performed after ICE/NOVIA,without fludarabine. We conclude that fludarabine-containing regimens severely impair mobilization and collection of PBSC in AML patients and seem unsuitable when PBSC autotransplantation is programmed.

Clinical relevance of acute pancreatitis in allogeneic hemopoietic stem cell (bone marrow or peripheral blood) transplants

This study investigated the clinical relevance of acute pancreatitis in allogeneic hemopoietic stem cell (bone marrow or peripheral blood) transplants (BMT). We studied 26 patients undergoing BMT. The preparative regimen was busulfan and cyclophosphamide in 17 patients and total body irradiation and cyclophosphamide in 9 patients. Graft-versus-host disease (GVHD) prophylaxis consisted of cyclosporin A and short-term methotrexate in all 26 patients. The pancreas was studied using amylase and lipase serum levels, abdominal contrast-enhanced tomography, and/or ultrasound. Clinical and laboratory signs of acute pancreatitis were found in two patients with acute hepatointestinal GVHD, and in one patient with acute hepatic GVHD and cytomegalovirus infection. This patient died of multiorgan failure, with interstitial acute pancreatitis at autopsy; the other two patients recovered with general supportive care and GVHD therapy. We suggest that in the patients with complications after BMT, particularly acute hepatic/hepatointestinal GVHD, and cytomegalovirus infection, the possibility of acute pancreatitis should be considered.

Autologous transplantation of chemotherapy-purged PBSC collections from high-risk leukemia patients: a pilot study

We have recently demonstrated that the combination of the alkylating agent nitrogen mustard (NM) and etoposide (VP-16) is capable of eliminating, ex vivo, leukemic cells contaminating PBSC collections and this is associated with a significant recovery of primitive and committed hematopoietic progenitor cells. Based on these data a pilot study on autologous transplantation of NM/VP-16 purged PBSC for high-risk leukemic patients was recently initiated. Twelve patients (seven females and five males) with a median age of 46 years (range 18-57) have been treated. Two patients had acute myeloblastic leukemia (AML) resistant to conventional induction treatment, four patients had secondary AML in I complete remission (CR), one patient was in II CR after failing a previous autologous BM transplantation, while two additional AML individuals were in I CR achieved after three or more cycles of induction treatment. Two patients with high-risk acute lymphoblastic leukemia (ALL) in I CR and one patient with mantle cell lymphoma and leukemic dissemination were also included. Eight patients showed karyotypic abnormalities associated with a poor clinical outcome. The mobilizing regimens included cytosine arabinoside and mitoxantrone with (n = 6) or without fludarabine (n = 3) followed by subcutaneous administration of G-CSF (5 microg/kg/day until the completion of PBSC collection) and G-CSF alone (n = 3) (15 microg/kg/day). A median of two aphereses (range 1-3) allowed the collection of 7.2 x 10(8) TNC/kg (range 3.4-11.5), 5 x 10(6) CD34+ cells/kg (range 2.1-15.3) and 9.2 x 10(4) CFU-GM/kg (0.3-236). PBSC were treated with a constant dose of 20 microg of VP-16/ml and a median individual-adjusted dose (survival < or = 5% of steady-state BM CFU-GM) of NM of 0.7 microg/ml (range 0.25-1.25). Eleven patients were reinfused after busulfan (16 mg/kg) and Cy (120 mg/kg) conditioning with a median residual dose of 0.3 x 10(4) CFU-GM/kg (0-11.5). The median time to neutrophil engraftment (>0.5 x 10(9)/l) for evaluable patients was 25 days (range 12-59); the median time to platelet transfusion independence (>20 and >50 x 10(9)/l) was 40 days (18-95) and 69 days (29-235), respectively. Hospital discharge occurred at a median of 25 days (18-58) after stem cell reinfusion. Four individuals are alive in CR (n = 3) or with residual nodal disease (n = 1 lymphoma patient) with a follow-up of 32, 26, 3 and 14 months, respectively. Seven patients died due to disease progression or relapse (n = 5) or extrahematological transplant toxicity (n = 2). Our data suggest that pharmacological purging of leukapheresis collections of leukemic patients at high-risk of relapse is feasible and ex vivo treated cells reconstitute autologous hematopoiesis.

Allogeneic peripheral blood stem cell transplantation in patients with early-phase hematologic malignancy: a retrospective comparison of short-term outcome with bone marrow transplantation

BACKGROUND AND OBJECTIVE

Transplantation of mobilized allogeneic peripheral blood stem cells (PBSC) has recently been reported by several groups. However, few patients receiving an allograft in the early stage of their disease have been described so far.

DESIGN AND METHODS

Fifteen patients with early stage hematologic malignancies were transplanted with cryopreserved allogeneic PBSC from HLA-identical siblings. PBSC were collected after priming with 10 micrograms/kg/day of glycosylated granulocyte colony-stimulating factor (G-CSF, lenograstim). Outcomes were compared to a historical control group of 15 patients who received conventional bone marrow transplantation (BMT) from HLA-identical sibling donors. The two groups were matched for diagnosis, stage of disease, age, preparative regimen, graft-versus host (GVHD) prophylaxis, patients' and donors' gender and cytomegalovirus (CMV) serology. Diagnoses in both groups were: chronic myelogenous leukemia (CML) in first chronic phase (= 5), acute leukemia in first complete remission (CR) (= 5), non-Hodgkin's lymphoma in CR (= 1) and multiple myeloma (MM) with sensitive disease (= 4). All patients were given cyclosporin-A (CsA) and methotrexate (MTX) for GVHD prophylaxis. Preparative regimens varied according to diagnosis and included either busulfan/cyclophosphamide combination (BU/Cy) or total body irradiation/cyclophosphamide +/- melphalan (TBI/Cy +/- Mel).

RESULTS

The patients in the PBSC group showed a more rapid hematopoietic reconstitution with a significant difference in the median times to 1 x 10(9) neutrophils/L (19 days vs. 26 days; p = 0.03) and to platelet transfusion independence (18 days versus 22 days; p = 0.02). This finding was associated with a significantly shorter hospitalization (28 days versus 33 days after transplantation; p = 0.01). In the PBSC series, grade II-IV acute GVHD occurred in 3 patients (20%) and grade III-IV in 1 patient (7%). In the BMT control group, grade II-IV aGVHD was reported in 2 cases (13%; p = NS) and 1 case had grade III-IV GVHD. Chronic GVHD developed in 7 patients (47%) (limited = 6; extensive = 1) undergoing PBSC transplantation and 5 patients (33%) (limited = 4; extensive = 1) in the BMT series (p = NS). No difference was found in the incidence of grade II-IV (according to the World Health Organization) mucositis, whereas PBSC recipients did have a significantly lower incidence of additional severe (grade III-IV) organ toxicity. After a median follow-up of 300 days (range 180-630), all PBSC patients are still alive with a median Karnofsky score of 100% (range 80%-100%). Thirteen patients are in CR and 2 myeloma patient are in good partial remission (PR). Also, in the BMT group the peritransplant mortality was absent; two MM patients died due to progressive disease at day +796 and +1,023, respectively; one leukemic patient died of chronic GVHD 407 days after transplantation and one additional leukemic individual relapsed 1,140 days after BMT.

INTERPRETATION AND CONCLUSIONS

This retrospective comparison suggests that allogeneic PBSC transplantation performed in the early stage of the disease is safe and may be associated with a more rapid hematopoietic reconstitution than BMT, as well as lower transplant-related toxicity and earlier hospital discharge with apparently no increased risk of acute and chronic GVHD.

Selection and transplantation of autologous hematopoietic CD34+ cells for patients with multiple myeloma

Here we review our recent experience addressing the issue of positive selection and transplantation of hematopoietic CD34+ cells to reduce neoplastic contamination in peripheral blood (PB) autografts from patients with multiple myeloma (MM). We evaluated PB samples from 30 pretreated MM patients following the administration of high dose cyclophosphamide (Cy; 7g/m2 or 4g/m2) and granulocyte-colony stimulating factor (G-CSF), for collection of circulating stem cells (PBSC) to support hematopoietic reconstitution following myeloablative radio-chemotherapy. Twenty six patients showed adequate mobilization of CD34+ progenitor cells and were submitted to PBSC collection. Circulating hematopoietic CD34+ cells were highly enriched by avidin-biotin immunoabsorption, cryopreserved, and used to reconstitute BM function after myeloablative therapy in 13 patients. The median purity of the enriched CD34+ cell population was 89.5% (range 51-94%) with a 75-fold increase compared to the pretreatment samples. The median overall recovery of CD34+ cells and CFU-GM was 58% (range 33-95%) and 45% (range 7-100%), respectively. Positive selection of CD34+ cells resulted in 2.5-3 log of plasma cells and CD19+ B-lineage cells depletion as determined by immunofluorescence studies, although DNA analysis of CDR III region of IgH gene demonstrated the persistence of minimal residual disease (MRD) in 5 out of 6 patient samples studied. Myeloma patients were reinfused with enriched CD34+ cells after myeloablative therapy consisting of total body irradiation (TBI, 1000 cGy) and high dose Melphalan (140 mg/m2) or Melphalan (200 mg/m2) alone. They received a median of 5 x 10(6) CD34+ cells/kg and showed a rapid reconstitution of hematopoiesis: the median time to 0.5 x 10(9) neutrophils, 20 and 50 x 10(9) platelets/L of PB was 10, 11 and 12 days, respectively. When we analyzed the immunological reconstitution of this group of patients, we observed a rapid and full recovery of total lymphocyte and NK cell count, although the absolute CD4+ cell count was lower than pretreatment level. These results, as well as other clinically significant parameters, did not significantly differ from those of patients (=13) receiving unmanipulated PBSC following the same pretransplant conditioning regimen. The results of this trial demonstrate that positive selection of CD34+ cells reduces the contamination of myeloma cells from the apheresis products up to 3 log and provides a cell suspension capable of restoring a normal hematopoiesis after a TBI-containing conditioning regimen. Based on this pilot trial, we have recently started a clinical study involving a double autotransplant, conditioned with melphalan (200 mg/m2) followed by melphalan (140 mg/m2) and busulphan (14 mg/kg), supported by the reinfusion of highly purified CD34+ cells.

Cycling status of CD34+ cells mobilized into peripheral blood of healthy donors by recombinant human granulocyte colony-stimulating factor

In this study, we assessed the functional and kinetic characteristics of highly purified hematopoietic CD34+ cells from the apheresis products of 16 normal donors undergoing glycosylated granulocyte colony-stimulating factor (G-CSF) treatment for peripheral blood stem cells (PBSC) mobilization and transplantation in allogeneic recipients. Mobilized CD34+ cells were evaluated for their colony-forming capacity and trilineage proliferative response to selected recombinant human (rh) CSF in vitro and the content of very primitive long-term culture initiating cells (LTC-IC). In addition, the cycling status of circulating CD34+ cells, including committed clonogenic progenitor cells and the more immature LTC-IC, was determined by the cytosine arabinoside (Ara-C) suicide test and the acridine orange flow cytometric technique. By comparison, bone marrow (BM) CD34+ cells from the same individuals were studied under steady-state conditions and during G-CSF administration. Clonogenic assays in methylcellulose showed the same frequency of colony-forming unit cells (CFU-C) when PB-primed CD34+ cells and BM cells were stimulated with phytohemagglutinin-lymphocyte-conditioned medium (PHA-LCM). However, mobilized CD34+ cells were significantly more responsive than their steady-state BM counterparts to interleukin-3 (IL-3) and stem cell factor (SCF) combined with G-CSF or IL-3 in presence of erythropoietin (Epo). In cultures added with SCF, IL-3, and Epo, we found a mean increase of 1.5- +/- 1-fold (standard error of the mean [SEM]) of PB CFU-granulocyte-macrophage and erythroid progenitors (burst-forming units-erythroid) as compared with BM CD34+ cells (P < .05). Conversely, circulating and BM megakaryocyte precursors (CFU-megakaryocyte) showed the same clonogenic efficiency in response to IL-3, granulocyte-macrophage-CSF and IL-3, IL-6, and Epo. After 5 weeks of liquid culture supported by the engineered murine stromal cell line M2-10B4 to produce G-CSF and IL-3, we reported 48.2 +/- 35 (SEM) and 62.5 +/- 54 (SEM) LTC-IC per 10(4) CD34+ cells in PB and steady-state BM, respectively (P = not significant). The Ara-C suicide assay showed that 4% +/- 5% (standard deviation [SD]) of committed precursors and 1% +/- 3% (SEM) of LTC-IC in PB are in S-phase as compared with 25.5% +/- 12% (SD) and 21% +/- 8% (SEM) of baseline BM, respectively (P < .001). However, longer incubation with Ara-C (16 to 18 hours), in the presence of SCF, IL-3 and G-CSF, or IL-6, showed that more than 60% of LTC-IC are actually cycling, with no difference being found with BM cells. Furthermore, studies of cell-cycle distribution on PB and BM CD34+ cells confirmed the low number of circulating progenitor cells in S- and G2M-phase, whereas simultaneous DNA/RNA analysis showed that the majority of PB CD34+ cells are not quiescent (ie, in G0-phase), being in G1-phase with a significant difference with baseline and G-CSF-treated BM (80% +/- 5% [SEM] v 61.9% +/- 6% [SEM] and 48% +/- 4% [SEM], respectively; P < .05). Moreover, G-CSF administration prevented apoptosis in a small but significant proportion of mobilized CD34+ cells. Thus, our results indicate that mobilized and BM CD34+ cells can be considered equivalent for the frequency of both committed and more immature hematopoietic progenitor cells, although they show different kinetic and functional profiles. In contrast with previous reports, we found that PB CD34+ cells, including very primitive LTC-IC, are cycling and ready to progress into S-phase under CSF stimulation. This finding should be taken into account for a better understanding of PBSC transplantation.