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Biomedical subjects

F Shapiro

Publications and source records attributed to F Shapiro.

At least 37 records · Page 2Linked to original sources

Musculoskeletal trauma in children.

MR imaging has facilitated the study of pediatric injuries by demonstrating the extraosseous and cartilaginous component of these lesions. In injuries to the epiphysis and physis, osteochondral injuries and avulsion injuries, the cartilaginous component is usually the most important part of the lesion. Stress fractures and other injuries to the marrow also can be demonstrated with MR imaging. In the context of musculoskeletal injuries in children, MR imaging is most valuable in demonstrating the extent of injuries to radiographically occult areas.

Adolescent↗

High-intensity intravenous cyclophosphamide and cisplatin, interim surgical debulking, and intraperitoneal cisplatin in advanced ovarian carcinoma: a pilot trial with ten-year follow-up.

PURPOSE: This trial was undertaken to study the effect of intensified intravenous cyclophosphamide/cisplatin and interim surgical debulking, followed by intraperitoneal cisplatin on surgically defined complete remission rate and survival in advanced ovarian cancer. PATIENTS AND METHODS: Forty patients with stage IIB through IV ovarian cancer were entered and 36 were evaluable for response and survival and approximately 10 years. Following a first laparotomy for diagnosis and debulking, the patients received two cycles, spaced 28 days apart, of intravenous cisplatin 30-40 mg/m2/day with hypertonic saline for 4 to 5 days and cyclophosphamide 200 mg/m2/day for 5 days. A second laparotomy was done to further debulk remaining cancer and to place an intraperitoneal catheter. Four cycles of intraperitoneal cisplatin at 50 or 100 mg/m2 were administered 21 days apart and followed by a third laparotomy to define response and plan any further therapy. RESULTS: The surgically confirmed complete response rate was 47% and median survival is 68.3 months for this group. Ten of the 17 patients (58.8%) relapsed following complete response at a median of 19.5 months (range, 5-98). Both aggressive chemotherapy and surgery seemed to play a role in inducing this high complete response rate. Traditional prognostic factors, including stage and diameter of largest residual disease, had little apparent effect on likelihood of complete response or survival, whereas tumor grade had a more significant effect on survival. Nadir fever was experienced by 33% of patients but peripheral neuropathy was dose limiting. CONCLUSION: In the context of recent data failing to support any clinical benefit to modest increases in dose escalations of cisplatin or carboplatin, in this trial the high complete response rate suggests that the multimodality approach (i.e., interval surgical debulking and intraperitoneal cisplatin) is worthy of further study. The high relapse rate among complete responders and the unacceptable neurotoxicity also suggest that modifications could improve the results. The use of newer agents and further intensification (substituting carboplatin for cisplatin and the use of paclitaxel) with stem cell support are two examples.

Antineoplastic Combined Chemotherapy Protocols↗

Variable conformation of GAP junctions linking bone cells: a transmission electron microscopic study of linear, stacked linear, curvilinear, oval, and annular junctions.

There is a marked variability in the conformation of bone cell gap junctions in newborn murine cortical bone as defined by transmission electron microscopy (TEM). Studies were done in newborn BALB/c mouse and Sprague-Dawley rat femurs and tibias. Femoral and tibial cortices were dissected into 1 mm3 fragments and prepared in standardized fashion using modified Karnovsky fixation, 7.5% EDTA decalcification, 1% osmium tetroxide-sym collidine buffer with 1% lanthanum nitrate postfixation, Epon resin, 60 nm sections, lead citrate/uranyl acetate staining, and examination at 60 kV. Previous TEM descriptions of bone junctions have, with rare exceptions, noted only isolated linear or mildly curvilinear structures. In this study we noted gap junctional shapes on thin-section TEM preparations of osteoblasts and osteocytes to be extremely variable and complex encompassing linear, curvilinear, stacked linear, oval, and annular conformations. Multiple observations revealed linear gap junctions linking surface osteoblast cell bodies; linear, curvilinear, stacked linear, and oval junctions linking osteoblast processes in osteoid; linear and curvilinear junctions where cell processes joined with osteocyte cell bodies and each of the five conformations linking osteocyte processes within canaliculi. The annular junctions were found within osteoblast and osteocyte cytoplasm and in osteocyte cell processes within canaliculi. The annular junctions are intracellular, degenerating structures which appear as ultrastructural markers of gap junction involution. The more complex shapes reported here must be considered in (1) interpreting quantitative studies using freeze-fracture replicas, thin sections, and confocal microscopy immunolabeled junction connexin-43 components and (2) assessing gap junction biogenesis and turnover. 3-D reconstruction of bone junctions will enhance our understanding of these complex conformations.

Animals↗

Infantile phosphofructokinase deficiency with arthrogryposis: clinical benefit of a ketogenic diet.

We report a 2-year-old boy with phosphofructokinase deficiency presenting in the newborn period with congenital arthrogryposis and severe myopathy, who has had significant improvement on a ketogenic diet since its institution at 4 months of age. We provide a rationale for use of this treatment and hypothesize it may be beneficial in other patients with phosphofructokinase deficiency and progressive muscular involvement. Confirmation awaits further clinical trials in carefully selected patients.

Arthrogryposis↗

Stunting syndrome in broilers: effect of glucose or maltose supplementation on digestive organs, intestinal disaccharidases, and some blood metabolites.

The effect of supplementing a cornsoybean diet (C) with glucose (G) or maltose (M) on young broilers (from hatch to 3 wk of age) affected by stunting syndrome (SS) was studied. Stunting syndrome was induced by orally administering an inoculum prepared from the intestines of SS broiler chicks. Relative to the M diet, the G diet improved growth and feed utilization and increased feed intake in naive (NA) control chickens. The C diet was intermediate in this respect. In contrast to the NA chickens, diet did not affect growth or feed utilization in SS chicks. Changes in the relative weights of the gastrointestinal tract segments were evident by 1 wk of age and hypertrophy of these segments persevered to 3 wk of age. Stunting syndrome infection was accompanied by a significant increase in pancreatic trypsin-specific activity during Weeks 1 and 2, and in chymotrypsin activity at 1 wk. During this time, amylase-specific activity was not affected. At 3 wk of age, the specific activities of amylase, trypsin, and chymotrypsin in the pancreas were lower in the inoculated vs control birds. Whereas no significant effect of SS was observed with activities of amylase in the intestinal contents, trypsin activity was higher in SS chicks at 1 wk, and that of chymotrypsin lower during Weeks 2 and 3. Relative to NA chicks, the maltase and saccharase activities of SS chicks were much lower during Week 1, but increased later on and were similar to NA chick values at 2 and 3 wk. Whereas the level of blood plasma proteins did not vary from 1 to 3 wk in the NA chicks, it increased gradually in SS chicks to a level that significantly exceeded that in their NA counterparts. Blood plasma glucose and triglyceride levels were slightly lower in the SS chicks (NS), and the blood plasma cholesterol level was significantly reduced during Week 2. Relative to NA chicks, SS infection caused a significant increase in plasma calcium during Weeks 2 and 3, accompanied by a significant reduction in blood plasma phosphorus at 2 wk only. No difference was observed in the blood plasma level of uric acid, which peaked in both treatments during Week 2, or in D-beta-hydroxybutyric acid level, which was quite stable during the experimental period. Stunting syndrome infection was accompanied by a dramatic increase in amylase and alkaline phosphatase activities in the blood plasma, and by a slight but significant decrease in activity of lactic dehydrogenase. Stunting syndrome was concluded to be an affliction not only of digestion but also of metabolism. The main depression in growth caused by SS inoculation is probably due to metabolic alterations beyond those of digestion and absorption.

Aging↗

Phase I and pharmacologic study of paclitaxel administered weekly in patients with relapsed ovarian cancer.

PURPOSE: Paclitaxel has shown significant activity in advanced ovarian cancer. In vitro studies with paclitaxel have suggested that fractionated brief infusion schedules may be more effective than the standard 24-hour infusion. We commenced a phase I evaluation of escalating-dose paclitaxel (40, 50, 60, 80, 100 mg/m2) administered weekly as a 1-hour infusion in patients with recurrent ovarian cancer. All patients had received prior paclitaxel and cisplatin therapy. All patients received standard premedication. PATIENTS AND METHODS: Eighteen patients are assessable on this phase I study. The mean age was 54 years (range, 48 to 74). The median number of prior chemotherapy regimens was three (range, two to five). The mean paclitaxel-free interval was 10.1 months (range, 1 to 24). RESULTS: A total of 194 cycles of therapy were administered, with a mean of 10 (range, one to 12) per patient. No mucositis or grade III neuropathy was seen. Alopecia occurred in one out of 18 assessable patients. The mean neutrophil nadir was 4.0 x 10(9)/L. At the top dose level (100 mg/m2) delivered, dose-intensity was 90.75% of that planned and greater than two fold the standard dose-intensity. Partial responses were seen in four of 13 assessable patients (30%). Two patients with progression of disease on standard three-week paclitaxel schedules switched to a weekly schedule with demonstrated response. Increasing paclitaxel dose correlated with measured area under the curve (AUC) (R2 = .614). Dose-limiting toxicity was reached at 100 mg/m2 with two of three patients experiencing a treatment delay, thus defining a maximum-tolerated dose of 80 mg/m2 in this group of heavily pretreated patients on this weekly schedule. CONCLUSION: (1) Paclitaxel administered as a 1-hour infusion is well tolerated; (2) this schedule of administration does not result in cumulative myelosuppression; and (3) this schedule of administration results in dose-intensive paclitaxel delivery with a favorable toxicity profile.

Adenocarcinoma, Clear Cell↗

Normal gadolinium-enhanced MR images of the developing appendicular skeleton: Part I. Cartilaginous epiphysis and physis.

OBJECTIVE: We have used gadolinium-enhanced MR imaging to define the expected normal appearance of the developing cartilaginous epiphyses and physes in neonates, infants, and children and to define the changes with maturity in epiphyseal vascular pattern. MATERIALS AND METHODS: We analyzed gadolinium-enhanced MR images of 80 normal epiphyses in 48 neonates, infants, and children who were 1 month to 15.5 years old. We studied the differences in enhancement ratios for the epiphyses and physes and the epiphyseal vascular pattern at various development stages. We correlated the MR imaging findings with histologic and injection studies of immature epiphyses. RESULTS: Gadolinium enhancement allowed differentiation between physeal and epiphyseal cartilage and revealed epiphyseal vascular canals. Enhancement proved to be greater in the physeal than in the epiphyseal cartilage (p < .001). In the unossified epiphysis, the vascular canals were mainly parallel. After the development of the secondary ossification center, these canals came to have a radial pattern (p < .0001). Comparison with cadaveric specimens confirmed how, with age, the arrangement of these canals changed. Also, physeal enhancement decreased with physeal closure. CONCLUSION: Gadolinium-enhanced MR imaging reveals differential enhancement of the physis, epiphyseal vascular canals, and epiphyseal cartilage. The pattern of epiphyseal vessels and degree of enhancement of the physis change with maturity.

Adolescent↗

Normal gadolinium-enhanced MR images of the developing appendicular skeleton: Part 2. Epiphyseal and metaphyseal marrow.

OBJECTIVE: We have studied how gadolinium enhancement of T1-weighted MR images affects the expected normal differences in signal intensity between metaphyseal hematopoietic and epiphyseal fatty marrow. We have also analyzed how enhancement affects the expected normal changes in the MR images of the marrow due to fatty conversion. MATERIALS AND METHODS: We analyzed gadolinium-enhanced MR images of normal distal femurs in 18 immature rabbits that were 5-11 weeks old and of normal proximal femurs in 18 infants, children, and young adults who were 2 months to 21 years old. In all subjects, we studied the change with age in signal intensity and enhancement ratio of the epiphyseal and metaphyseal marrow. In the rabbits, marrow composition and transformation were histologically verified. RESULTS: On unenhanced T1-weighted MR images of the rabbits and of the infants, children, and young adults, epiphyseal signal intensity always exceeded metaphyseal signal intensity; however, the enhancement ratio was always greater in the metaphysis. The signal intensity in metaphyseal and epiphyseal marrow on unenhanced MR images increased with age. However, enhancement ratios decreased with age in both areas. In the rabbits, histologic studies showed more fatty marrow in the epiphysis than in the corresponding metaphysis and an age-related increase in marrow fat at both sites. CONCLUSION: In the marrow of the extremities, gadolinium enhancement is greater in the (hematopoietic) metaphysis than in the (fatty) epiphysis. In both areas, enhancement decreases as the marrow becomes more fatty. On T1-weighted images, administration of a gadolinium-containing contrast agent reduces the normal contrast between hematopoietic and fatty marrow and obscures the changes in marrow signal intensity due to fatty conversion.

Adolescent↗

Regulation of hematopoiesis by microvascular endothelium.

The bone marrow microenvironment is a complex three dimensional structure where hematopoietic stem cells proliferate, mature, migrate into the sinusoidal space, and enter the circulation in an exquisitely regulated fashion. Stromal cells within the BM microenvironment provide a suitable environment for self-renewal, proliferation and differentiation of hematopoietic stem cells. Within the hematopoietic microenvironment, whether it is embryonic yolk sac, fetal liver, or adult bone marrow, microvascular endothelium not only acts as a gatekeeper controlling the trafficking and homing of hematopoietic progenitors, but also provides cellular contact and secretes cytokines that allows for the preservation of the steady state hematopoiesis. Recently, homogenous monolayers of bone marrow endothelial cells (BMEC) have been isolated and cultivated in tissue culture. Long-term coculture studies have shown that BMEC monolayers are unique type of endothelium and can support long-term proliferation of hematopoietic progenitor cells particularly megakaryocytic and myeloid progenitor cells by constitutive elaboration of lineage-specific cytokines such as G-CSF, GM-CSF, M-CSF, Kit-ligand, IL6, FLK-2 ligand, and leukemia inhibitory factor. Direct cellular contact between hematopoietic progenitor cells and BMEC monolayers through specific adhesion molecules including beta1, beta2 integrins and selectins play a critical role in trafficking and possibly proliferation of hematopoietic stem cells. Dysfunction of microvascular endothelial cells within the hematopoietic microenvironment may result in stem cell disorders and progression to aplastic anemias, and contribute to graft failure during bone marrow transplantation. Further studies on the role of microvascular endothelium in the regulation of hematopoietic stem cell homing and proliferation may enhance our understanding of the pathophysiology of stem cell and leukemic disorders.

Antigens, CD34↗

Dose escalation of paclitaxel with high-dose carboplatin using peripheral blood progenitor cell support in patients with advanced ovarian cancer.

A phase I study of escalating doses of paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) given in combination with high-dose carboplatin was conducted to identify the antitumor efficacy and maximum tolerated dose of paclitaxel in patients who had received sequential cycles of paclitaxel/cyclophosphamide as prior treatment for ovarian carcinoma. Eighteen patients with advanced ovarian cancer were treated in this study. Induction therapy consisted of two cycles of cyclophosphamide 3.0 g/m2 plus high-dose paclitaxel 300 mg/m2 plus filgrastim and leukapheresis to harvest peripheral blood progenitor cells, followed by four courses of rapidly cycled high-dose carboplatin with planned dose escalation of paclitaxel (150, 200, 250, and 300 mg/m2) rescued with peripheral blood progenitor cells. The study was amended after accrual of 11 patients, and the remaining seven patients received a single cycle of induction therapy with paclitaxel/cyclophosphamide, followed by four courses of rapidly cycled high-dose carboplatin with planned dose escalation of paclitaxel through levels 200 and 250 mg/m2. All 18 patients have completed therapy. Of the 15 who are evaluable for response, the pathologic complete response was 33% (five of 15 patients). The administration of escalating doses of paclitaxel in combination with high-dose carboplatin following sequential cycles of paclitaxel/cyclophosphamide induction resulted in significant nonhematopoietic toxicity. Induction with a single cycle of paclitaxel/cyclophosphamide resulted in excellent progenitor cell mobilization, and significantly ameliorated the toxicity of this approach. The response rates thus far obtained are promising and warrant further evaluation.

Adult↗

Adjuvant therapy in gynecologic malignancies. Ovarian, cervical, and endometrial cancer.

While surgery is the primary treatment for the management of gynecologic malignancies, adjuvant chemotherapy and radiation therapy play a critical role in survival for many patients. In this article, we discuss the feasibility and effectiveness of adjuvant therapy for ovarian, cervical, and endometrial cancers, and discuss current recommendations.

Antineoplastic Combined Chemotherapy Protocols↗

Salvage weekly paclitaxel in recurrent ovarian cancer.

The objectives of this study were to determine the toxicity and phase II dose of weekly paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) administration and to describe our initial experience with salvage weekly intravenous paclitaxel in women with advanced recurrent ovarian carcinoma. We conducted a phase I trial of paclitaxel administered as a 1-hour infusion in advanced ovarian cancer patients, using doses of 40 to 100 mg/m2/wk. As a follow-up study, we retrospectively reviewed the medical records of 45 patients with advanced, recurrent epithelial ovarian cancer treated between January 1, 1996, and October 30, 1996, with single-agent weekly intravenous paclitaxel (60 to 100 mg/m2, 1-hour infusions). Response for patients with measurable disease was based on improvements in physical examination or a greater than 50% reduction in the perpendicular diameters of all lesions in serial computed tomography. Since many of the patients did not have measurable disease, some evaluations of response to therapy were based on decline in serum carbohydrate antigen-125 according to published criteria. In our phase I study, 18 patients received 194 weekly courses of therapy at doses of 40, 50, 60, 80, and 100 mg/m2. The dose-limiting toxicity was defined as two or more patients with treatment delay or grade 3 toxicity (National Cancer Institute common toxicity criteria) at the same dose level. Treatment was delayed in two of three patients (for neutrophil counts < 1,500/microL at the 100 mg/m2 dose level); therefore, a phase II dose of 80 mg/m2/wk is recommended. No patient required hospitalization for neutropenia/fever. In the retrospective cohort review, the median patient age was 55 years (range, 32 to 79 years). All patients were heavily pretreated with multiple systemic chemotherapy regimens, including paclitaxel, with a median of four regimens (range, one to eight) before receiving weekly paclitaxel. Patients received a median of nine cycles of weekly paclitaxel (range, three to 37), with a median interval of 8 months (range, 1 to 32 months) between the last paclitaxel treatment and the institution of weekly therapy. Response was noted in 13 of 45 (28.9%) patients, with a median of seven treatments to achieve response. Chemotherapy was generally well tolerated, with treatments completed on a weekly schedule and only one hospitalization for nadir fever. We conclude that weekly intravenous paclitaxel is an active and well-tolerated regimen in heavily pretreated women with recurrent ovarian carcinoma. Prior therapy with paclitaxel does not preclude response to this regimen. A phase II trial of weekly paclitaxel in paclitaxel-refractory patients is under way.

Adult↗

Effects of prior therapy on the in vitro proliferative potential of stem cell factor plus filgrastim-mobilized CD34-positive progenitor cells.

The quantity of hematopoietic progenitors in an apheresis collection is defined by the number of CD34(+) cells or granulocyte macrophage colony-forming units present. These parameters are believed to give roughly equivalent information on graft quality. We here report that the in vitro proliferative potential of r-metHuSCF (stem cell factor) plus filgrastim (granulocyte colony-stimulating factor; r-metHuG-CSF) mobilized peripheral blood (PB) CD34(+) cells obtained from previously heavily treated non-Hodgkin's lymphoma patients inversely correlates with extent of prior therapy. CD34(+) cells were enriched using the CellPro Ceprate system and placed in liquid culture for 4 weeks in the presence of either r-metHuSCF, IL-3, IL-6, filgrastim (S36G), or S36G plus erythropoietin (S36GE) with a weekly exchange of media and cytokines with reestablishment of culture at the starting cell concentration (Delta assay) and enumeration of progenitors. Starting with 4 x 10(4) CD34(+) cells from apheresis samples from patients who had received <10 cycles of prior chemotherapy, progenitors were detectable in culture at 4 weeks 81% of the time as compared to 14% with CD34(+) cells from patients who had received >10 cycles and 5% for >10 cycles plus radiotherapy. The total number of progenitors generated over the duration of culture (area under the curve) was calculated using the trapezoidal rule as a novel measure of the proliferative potential of the enriched PB CD34(+) cell population. The median area under the curve of CD34(+) cells from patients receiving <10 cycles of prior chemotherapy was 7.4 and 5.7 (x10(5)) using S36G or S36GE, respectively, 1.8 and 1.9 if the patients received >10 cycles of prior chemotherapy, and 1.4 and 1.2 if the patients received >10 cycles of prior chemotherapy plus radiotherapy (P < 0.001). These data show that prior therapy impacts on the quality of PB CD34(+) cells as measured by their ability to generate committed progenitors over a number of weeks in liquid culture.

Antigens, CD34↗

The impact of diabetes mellitus on the toxicity of therapy for advanced ovarian cancer.

A retrospective review was undertaken to obtain more precise information about neurotoxicity, nephrotoxicity, and the effects of dexamethasone on the frequency and severity of hyperglycemia in diabetic patients with epithelial ovarian cancer treated with paclitaxel and/or cisplatin. Thirty-three patients were identified from 1254 patients over a 10-year period. In the cisplatin-treated patients, 21 of 24 (67%) had progression of neurological symptoms, three experienced grade 3 sensory neuropathy, and two had ototoxicity. Four patients had evidence of mild nephrotoxicity and two required a 50% dose reduction. In the group of patients treated with paclitaxel, 9 of the 18 (50%) had progression of symptoms, 2 to grade 3, and 2 had ototoxicity. No discontinuation of therapy due to neuropathy was required and no patient had evidence of drug-induced autonomic nervous system dysfunction. Hyperglycemia was frequently exacerbated, and 5 patients required treatment change, but no patient was hospitalized in relation to this. Our results indicate that the paclitaxel/cisplatin combination regimen or paclitaxel alone could be safely administered in diabetic patients at standard doses, with concurrent glucose and creatinine monitoring, as well as history of neurological symptoms and physical examination.

Adult↗

Treatment of resistant gestational choriocarcinoma with taxol: a report of two cases.

Two patients with resistant gestational choriocarcinoma were treated w with Taxol after extensive prior chemotherapy including EMACO and platinum-based salvage chemotherapy. Both patients showed significant responses to Taxol. One patient relapsed in the brain and liver after treatment and died. Taxol was combined with carboplatin in the other patient who achieved sustained clinical and hormonal remission after craniotomy and excision of resistant disease in the brain.

Adult↗

Eye movement desensitization and reprocessing (EMDR): evaluation of controlled PTSD research.

The completed controlled PTSD research on eye movement desensitization and reprocessing (EMDR) is placed within the context of other methods used in the treatment of post-traumatic stress disorder. A number of studies are presented that support EMDR as an empirically validated method. However, in several studies, clinical standards have not always been integrated with rigorous scientific methodology. The suggested standards include fidelity checks for the method being tested, the use of appropriate psychometrics, and assessment of co-morbidity factors. At the same time, because of common misconceptions about the method, a variety of problematic issues are discussed.

Clinical Trials as Topic↗

Errors of context and review of eye movement desensitization and reprocessing research.

The development of eye movement desensitization and reprocessing (EMDR) has been marked by an emphasis on research, beginning with its introduction by a controlled study in 1989. However, misconceptions regarding the method abound. A recent inaccurate literature review demonstrates the need for more careful scrutiny. To date, 12 controlled studies have been completed in the area of PTSD, most of which support EMDR's efficacy. Nevertheless, a careful examination of a number of studies and of a recent literature review reveal the need for greater methodological rigor and higher clinical standards in both the research and research evaluation process.

Clinical Trials as Topic↗

The effects of Flk-2/flt3 ligand as compared with c-kit ligand on short-term and long-term proliferation of CD34+ hematopoietic progenitors elicited from human fetal liver, umbilical cord blood, bone marrow, and mobilized peripheral blood.

The Flk-2/flt3 ligand (FL) was evaluated and compared with c-kit ligand (KL) for its in vitro proliferative effects on CD34+ cells from human fetal liver, umbilical cord blood, bone marrow, and mobilized peripheral blood. Using a 7-day liquid culture system, FL in combination with interleukin-3 (IL-3), interleukin-6 (IL-6), and granulocyte colony-stimulating factor (G-CSF) was comparable with KL in combination with IL-3, IL-6, and G-CSF for the expansion of hematopoietic progenitors. When FL-containing cultures were assayed after 21 or 28 days, a greater number of progenitors were generated as compared with KL-containing cultures. Using bone marrow microvascular endothelial cells as support stroma, cultures supplemented with FL generated a greater number of progenitors in both the nonadherent and adherent layers at day 35. These data suggest that FL ligand, in combination with other cytokines, can be used for short-term ex vivo expansion of hematopoietic progenitors and facilitates the preservation and possible expansion of primitive cells capable of long-term generation of progenitors.

Antigens, CD34↗