Upgrade and absolute calibration of the JET scintillator-based fast-ion loss detector

The JET FILD is a scintillator-based Fast-ion Loss Detector optimized to measure fusion-born alpha-particle losses. This work covers its upgrade and absolute calibration in preparation for the following JET DT experiments. A fast scintillator material (TG-Green) has been installed in the JET FILD. A heater jacket is installed around the fiber bundle, responsible for transmitting the light from the scintillator plate, to anneal the fiber obscuring due to neutron damage. The JET FILD has been upgraded with a 1 Mpx camera and 2 MHz photomultiplier data acquisition hardware. Full-orbit simulations give an estimate of the shading effects on the scintillator plate of the first wall structures and provide a synthetic signal of the JET FILD. A detector instrument function enables absolute values of fast-ion losses using calibration factors. The calibration factors are made available in a shot-to-shot basis for the characterized species and energies and with corrections for the diagnostic conditions. The fast acquisition system sets the Nyquist frequency (1 MHz) above the typical mode frequencies (≈10² kHz), thus making it possible to identify MHD-induced fast-ion losses.

Deconstructing Sonic Hedgehog Medulloblastoma: Molecular Subtypes, Drivers, and Beyond

Medulloblastoma (MB) is a highly malignant cerebellar tumor predominantly diagnosed during childhood. Driven by pathogenic activation of sonic hedgehog (SHH) signaling, SHH subgroup MB (SHH-MB) accounts for nearly one-third of diagnoses. Extensive molecular analyses have identified biologically and clinically relevant intertumoral heterogeneity among SHH-MB tumors, prompting the recognition of novel subtypes. Beyond germline and somatic mutations promoting constitutive SHH signaling, driver alterations affect a multitude of pathways and molecular processes, including TP53 signaling, chromatin modulation, and post-transcriptional gene regulation. Here, we review recent advances in the underpinnings of SHH-MB in the context of molecular subtypes, clarify novel somatic and germline drivers, highlight cellular origins and developmental hierarchies, and describe the composition of the tumor microenvironment and its putative role in tumorigenesis.

Abstract B30: ARID1A is a haploinsufficient tumor suppressor for N-Myc transformation of neural crest cells

Large segmental chromosomal alterations are common to cancer and a feature of high-risk neuroblastoma (NBL). Though they are early or initiating events in cancer, including often being found in precancerous lesions, their contribution to tumorigenesis is poorly understood. An unproven model is that these changes promote cancer through the cumulative effect of multiple dosage-sensitive genes. Loss of heterozygosity (LOH) at 1p36 is a frequent structural rearrangement in a broad range of human cancers including NBL. Approximately 70% of MYCN amplified NBL have 1p36 LOH with both mutations independently contributing to tumor aggressiveness in NBL. Two tumor suppressor regions have been proposed to exist in 1p36, a distal and proximal region, which have MYCN-independent and dependent roles. Through CRISPR/Cas9 genome editing of primary mouse neural crest cells (NCCs), a source for NBL, we found that loss of the chromatin remodeling factor Chd5 conferred most of the tumor-suppressor effects of 1p36 LOH in in vitro cell transformation assays in cells with endogenous levels of N-Myc. In contrast, when N-Myc was overexpressed, tumor evolution of NCCs genome edited to have randomly sized 1p36 deletions showed a reduction in tumor latency that significantly correlated with deletion of Arid1a. The Arid1a deletions that were selected for ranged from small indels up to large 1p36 deletions, indicating that large deletions are tolerated to achieve loss of a single critical tumor suppressor. Further, using lentiviral Cre-induced deletion of floxed Arid1a in isolated NCCs, we found that Arid1a is a haploinsufficient tumor suppressor in MYCN-driven transformation of NCCs. As Arid1a is a subunit of the chromatin remodeling complex SWI/SNF, which is mutated in 20% of cancers, Arid1a synthetic lethal therapies are being developed for adult malignancies. We are currently verifying those proposed therapies in NBL and are using small-molecule screening of cells lines derived from Arid1a wild-type, het, or null tumors to identify additional synthetic lethalities. Our findings indicate that context, such as the status of MYCN as an oncogene, dictates which 1p36 gene is the critical tumor suppressor, establishing 1p36 LOH as multifaceted not cumulative, as was previously believed.

Citation Format: Kirby Wallace, Jesus Garcia-Lopez, Joel Otero, Rachelle Olsen, Chelsea DeVaux, Ashton King, Andrew Davidoff, Kevin Freeman. ARID1A is a haploinsufficient tumor suppressor for N-Myc transformation of neural crest cells [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr B30.

Germline Elongator mutations in Sonic Hedgehog medulloblastoma

Cancer genomics has revealed many genes and core molecular processes that contribute to human malignancies, but the genetic and molecular bases of many rare cancers remains unclear. Genetic predisposition accounts for 5 to 10% of cancer diagnoses in children1,2, and genetic events that cooperate with known somatic driver events are poorly understood. Pathogenic germline variants in established cancer predisposition genes have been recently identified in 5% of patients with the malignant brain tumour medulloblastoma3. Here, by analysing all protein-coding genes, we identify and replicate rare germline loss-of-function variants across ELP1 in 14% of paediatric patients with the medulloblastoma subgroup Sonic Hedgehog (MBSHH). ELP1 was the most common medulloblastoma predisposition gene and increased the prevalence of genetic predisposition to 40% among paediatric patients with MBSHH. Parent-offspring and pedigree analyses identified two families with a history of paediatric medulloblastoma. ELP1-associated medulloblastomas were restricted to the molecular SHHα subtype4 and characterized by universal biallelic inactivation of ELP1 owing to somatic loss of chromosome arm 9q. Most ELP1-associated medulloblastomas also exhibited somatic alterations in PTCH1, which suggests that germline ELP1 loss-of-function variants predispose individuals to tumour development in combination with constitutive activation of SHH signalling. ELP1 is the largest subunit of the evolutionarily conserved Elongator complex, which catalyses translational elongation through tRNA modifications at the wobble (U34) position5,6. Tumours from patients with ELP1-associated MBSHH were characterized by a destabilized Elongator complex, loss of Elongator-dependent tRNA modifications, codon-dependent translational reprogramming, and induction of the unfolded protein response, consistent with loss of protein homeostasis due to Elongator deficiency in model systems7-9. Thus, genetic predisposition to proteome instability may be a determinant in the pathogenesis of paediatric brain cancers. These results support investigation of the role of protein homeostasis in other cancer types and potential for therapeutic interference.

Activation of Estrogen Receptor Alpha by Decitabine Inhibits Osteosarcoma Growth and Metastasis

Osteosarcoma is a malignant tumor in the bone, which originates from normal osteoblasts or osteoblast precursors. Normal osteoblasts express estrogen receptor alpha (ERα); however, osteosarcomas do not express ERα due to promoter DNA methylation. Here we show that treatment of 143B osteosarcoma cells with decitabine (DAC, 5-Aza-2'-deoxycytidine) induces expression of ERα and leads to decreased proliferation and concurrent induction of osteoblast differentiation. DAC exposure reduced protein expression of metastasis-associated markers VIMENTIN, SLUG, ZEB1, and MMP9, with a concurrent decrease in mRNA expression of known stem cell markers SOX2, OCT4, and NANOG. Treatment with 17β-estradiol (E2) synergized with DAC to reduce proliferation. Overexpression of ERα inhibited proliferation and induced osteoblast differentiation, whereas knockout of ERα by CRISPR/Cas9 prevented the effects of DAC. In an orthotopic model of osteosarcoma, DAC inhibited tumor growth and metastasis of 143B cells injected into the tibia of NOD SCID gamma mice. Furthermore, ERα overexpression reduced tumor growth and metastasis, and ERα knockout prevented the effects of DAC in vivo. Together, these experiments provide preclinical evidence that the FDA-approved DNA methylation inhibitor DAC may be repurposed to treat patients with osteosarcoma based on its efficacy to decrease proliferation, to induce osteoblast differentiation, and to reduce metastasis to visceral organs.Significance: These findings describe the effects of DNA methyltransferase inhibition on ERα and its potential role as a tumor suppressor in osteosarcoma.See related commentary by Roberts, p. 1034 See related article by El Ayachi and colleagues; Cancer Res 79(5);982-93.

Abstract B19: ARID1A is a 1p36 tumor suppressor that collaborates with N-Myc in neuroblastoma

Neuroblastoma (NB) is an embryonal cancer of the sympathetic nervous system (SNS) that causes 15% of pediatric cancer deaths. A major barrier to advancing targeted therapy in NB is identifying the unknown oncogenes and tumor suppressors that are buried within large segmental chromosomal gains and losses that characterize high-risk NB. To assist in identifying them, we have established a novel system for studying NB based on the transformation of neural crest cells (NCCs), the progenitor cells of the SNS, isolated from mouse embryonic day 9.5 trunk neural tube explants. Based on pathology and gene expression analysis, we have demonstrated that the enforced expression of N-Myc in wild-type NCCs generates phenotypically and molecularly accurate NB that most closely models MYCN-amplified NB. Using this system we next addressed a longstanding problem in the NB field. Though 70% of MYCN-amplified NBs have 1p36 deletions, representing ~28% of high-risk NBs, the 1p36 tumor suppressor that collaborates with N-Myc is unknown. Using CRISPR/Cas9 technology in primary NCCs, we screened multiple 1p36 candidate tumor suppressors in a tumorsphere-forming assay. We found tumorspheres only formed when two chromatin-remodeling factors, CHD5 and ARID1A, were both lost, though their loss was not sufficient to generate tumors in vivo. Therefore, we next tested whether deletion of Chd5 and Arid1a, Arid1a alone, or deletion of the entire syntenic 1p36 region, as validated by FISH and karyotype analysis, is selected for during N-Myc driven transformation of primary NCCs. To achieve this, we started with low-efficiency deletion of each target in three independently derived NCC lines and then allowed clonal evolution during tumorigenesis to identify the favored deletion for N-Myc overexpressing NCCs. Tumors with CRISPR/Cas9 targeted 1p36 genes formed with a reduced latency of ~50 days over control (p<0.05), indicating that there was loss of an N-Myc collaborating tumor suppressor. From whole-exome sequencing we observed clonal selection from parental lines to tumors for both indel mutations in Arid1a and for larger deletions that encompassed Arid1a and surrounding genes. Arid1a mutations went from below level of detection in the parental NCC lines to >80% of the reads in the daughter tumors. We also saw selection for indel mutations and deletions of CHD5, but not in every tumor analyzed and no selection for loss of the entire 1p36 locus in any tumor. Using ex vivo adeno-cre mediated deletion of one or both floxed Arid1a alleles in NCCs, we found that loss of one Arid1a allele significantly (p=0.02) decreased latency by ~40 days over control in collaboration with N-Myc. Loss of both alleles conferred no advantage, indicating that when combined with N-Myc, ARID1A is an obligate haplo-insufficient tumor suppressor. In sum, these tumor studies support a model in which loss of one Arid1a, but not the entire syntenic 1p36 locus, is strongly selected for during N-Myc driven NB tumorigenesis, suggesting that Arid1a is the critical 1p36 tumor suppressor. The next step in this longstanding problem is to understand why loss of ARID1A collaborates with MYCN amplification and to exploit this discovery to improve treatment for MYCN amplified/1p36 deleted NBs.

Citation Format: Jesus Garcia-Lopez, Kirby Wallace, Joel Otero, Rachelle Olsen, David Finkelstein, Jerold Rehg, Yongdong Wang, Kevin Freeman. ARID1A is a 1p36 tumor suppressor that collaborates with N-Myc in neuroblastoma [abstract]. In: Proceedings of the AACR Special Conference: Pediatric Cancer Research: From Basic Science to the Clinic; 2017 Dec 3-6; Atlanta, Georgia. Philadelphia (PA): AACR; Cancer Res 2018;78(19 Suppl):Abstract nr B19.

Magnetic resonance imaging following regional limb perfusion of gadolinium contrast medium in 26 horses

BACKGROUND

Systemic administration of gadolinium contrast medium is common in small animals to increase lesion conspicuity and determine vascularisation of lesions identified with magnetic resonance imaging (MRI); however, the large volume required for systemic administration limits its use in horses.

OBJECTIVES

The purpose of this study was to assess the feasibility of administering a low dose of contrast medium via venous regional limb perfusion.

STUDY DESIGN

Prospective clinical study.

METHODS

Distal limbs of 26 horses (one limb per horse) were imaged with MRI before and after administration of 5 mL of gadopentetate dimeglumine (Magnevist^® ) diluted with 5 mL of physiological saline via a palmar/plantar digital vein with a tourniquet in place at the level of the mid aspect of the third metacarpal/metatarsal bone. Commonly assessed structures of the equine distal limb were examined for normal and abnormal contrast enhancement.

RESULTS

Twenty-five of 26 horses had adequate contrast enhancement of their distal limb. The lack of adequate contrast enhancement in one limb was likely associated with failure of the tourniquet. No adverse reactions were identified in any horse. One hundred thirty-two lesions were detected, of which, 69 contrast enhanced. Twelve lesions were detected exclusively following contrast enhancement.

MAIN LIMITATIONS

Case numbers and lesion variability yielded insufficient data to perform statistical analyses. Histopathology was not performed on sound horses to determine if the imaged structures were normal.

CONCLUSIONS

Regional limb perfusion is a feasible method to administer gadolinium contrast material to the equine distal limb for MRI. The enhancement pattern of the equine distal limb in sound horses is described. Contrast enhanced MRI of the distal equine limb helps to further characterise lesions identified with precontrast images, including adhesions and deep digital flexor tendinopathy. Contrast enhanced MRI also aids in identification of additional lesions, such as neovascularisation.

Abstract A19: Transformation of primary neural crest cells to model pediatric cancers

Neural crest cells (NCCs) are a multipotent, highly migratory cell population specified from the neural tube during embryonic development. NCCs undergo EMT (epithelial to mesenchymal transition) then migrate throughout the body forming diverse lineages including neurons, Schwann cells, melanocytes, and osteoblasts. Precursor cells from NCC lineages are thought to be the cell of origin for several pediatric and adult cancers including neuroblastoma, peripheral primitive neuroectodermal tumors (pPNET), malignant peripheral nerve sheath tumors (MPNST), cranial-facial osteosarcoma, and melanoma.

The most common pediatric cancer in infants is neuroblastoma, which arises from the sypathoadrenal lineage of trunk NCCs. To study early events in neuroblastoma oncogenesis we established a system based on transformation of primary mouse NCCs. Trunk NCCs were isolated from day E9.5 embryos, and resulted in a population that was >95% positive for the NCC markers Sox10, p75, and Ascl1 (MASH1) by immunofluorescence. Culturing primary NCCs in neurogenic differentiation media resulted in neurons positive for Tuj1, Map2, and tyrosine hydroxylase (TH).

Since a prominent category of high-risk neuroblastoma involves amplification of MYCN, we next determined whether MYCN overexpression was sufficient to transform wild-type NCCs in our assay. NCCs were isolated from C57Black6 mice and infected with MYCN retrovirus within 48hr of isolation, and then 10,000 cells/mouse were injected subcutaneously. MYCN overexpression alone generated a single tumor in 1 out of 12 mice, and the resulting tumor expressed the neuronal markers synaptophysin and tyrosine hydroxylase (TH) by immunohistochemistry (IHC).

To determine whether loss of p53 could increase the transformation efficiency, NCCs from p53-compromised mice were infected with MYCN. These tumors had increased penetrance with 19 out of 19 mice developing tumors whether cells were injected into nude mice or into syngeneic C57Black6 mice with an intact immune system. Based on pathological analysis, these tumors were classified as primitive neuroectodermal tumors with divergent differentiation. Tumor regions which were diffusely positive for neuronal markers appeared neuroblastoma-like or PNET-like. Osteosarcoma was also a prominent feature in tumors with loss of p53. We also observed an additional tumor type which was negative by IHC for neuronal, Schwannian, and melanoma markers, and is not yet fully characterized. In general, mice with the fastest onset of tumor growth displayed micrometastases to the lung and liver, while mice with slower tumor growth had macrometastases to these organs. Injection of cell lines derived from the primary tumors also lead to aggressive metastasis to the lung and liver. Although metastasis from subcutaneous tumors is generally rare, it was a recurrent feature in our model which recapitulates the highly metastatic nature of human cancers derived from NCCs like neuroblastoma and melanoma.

Lastly, we determined whether NCCs were sensitive to the BET bromodomain inhibitor JQ1. JQ1 treatment significantly inhibited growth of both primary NCCs and cell lines derived from NCC tumors, while having minimal effect on NIH-3T3 fibroblasts. Furthermore, our results imply that JQ1 sensitivity in these cells is independent of MYCN expression levels.

Using primary mouse NCCs, we found that MYCN overexpression is capable of initiating cell transformation and formed a single tumor with characteristics of neuroblastoma. Additional loss of p53 resulted in a more diverse panel of tumor types, which emphasizes the ability of NCCs to contribute to multiple lineages. Our results suggest that studies utilizing primary NCCs may be beneficial to identify initiating oncogenic events in neuroblastoma and perhaps other pediatric cancers.

Citation Format: Rachelle R. Olsen, Joel H. Otero, Jesus Garcia-Lopez, Kirby A. Wallace, Zhirong Yin, Kevin W. Freeman. Transformation of primary neural crest cells to model pediatric cancers. [abstract]. In: Proceedings of the AACR Special Conference: Developmental Biology and Cancer; Nov 30-Dec 3, 2015; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(4_Suppl):Abstract nr A19.

Abstract 3955: A primary cell-based assay to identify initiating oncogenic events in neuroblastoma

The pediatric cancer neuroblastoma (NBL) forms from immature cells of the sympathetic nervous system (SNS). A prominent category of high-risk NBL is MYCN amplification with loss of heterozygosity (LOH) at 1p36. This LOH includes the chromatin remodeling factor, CHD5, a proposed tumor suppressor of NBL and can include ARID1A, a component of the SWI/SNF chromatin remodeling complex.

To identify genetic changes that cooperate with MYCN amplification in initiating NBL we developed an assay based on oncogenic transformation of neural crest cells (NCCs), the progenitors of the SNS. Isolation of NCCs from E9.5 mouse embryos resulted in a population that was ∼90% positive for the NCC markers p75, Sox10, and Ascl1, suggesting a highly enriched population.

Next, we tested the ability of N-Myc infected NCCs to form tumors in vivo. In pilot experiments using NCCs with compromised p53, we obtained subcutaneous tumors following injection of NCCs in nude mice. Resulting tumors were diffusely positive for neuronal markers such as synaptophysin, MAP2, and Tyrosine hydroxylase (TH). Tumors also contained focal areas of divergent differentiation characteristic of melanoma, Schwannoma, and osteosarcoma, all cancers that can arise from NCC lineages. To our knowledge, this is the first report of cancer from transformed primary neural crest cells.

To more closely model NBL genetics, we replaced loss of p53 with shRNA to knockdown CHD5 and ARID1A prior to N-Myc infection. Injection of the resulting NCCs also resulted in tumor formation in nude mice. Tumors were uniformly positive for neuronal markers including TH and Ascl1, as well as Phox2B, a marker of undifferentiated NBL, and with no evidence of other cancers. Future studies in understanding the interactions of N-Myc overexpression with loss of these chromatin remodeling factors should further increase our understanding of NBL development.

Citation Format: Rachelle Olsen, Joel Otero, Zhirong Yin, Jesus Garcia-Lopez, Kevin Freeman. A primary cell-based assay to identify initiating oncogenic events in neuroblastoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3955. doi:10.1158/1538-7445.AM2015-3955

Phase II study of extended schedule temozolomide in refractory gliomas

1516

Background: Temozolomide resistance is mainly mediated by the enzyme AGT that repair DNA damage in a suicide way. Inhibition of this enzyme is greater when temozolomide is administered in a extended schedule that also obtains higher exposure to the drug. Methods: Primary objective is to assess is extended schedule temozolomide can revert resistance. Patients with bidimensionally measurable high grade glioma refractory to temozolomide defined as either progression during treatment or in the following tree months of drug withdrawal were included. Temozolomide was administered at a dose of 85 mg/m2 daily for 21 consecutive days every 28 days until unacceptable toxicity or progression. Results: Up to now we have included 41 patients, 29 of them available for the first analysis. Mean age is 51.3 (23–77), male 22 (76%), ECOG 0/1/2 7 (24%)/13 (45%)/9 (31%), histology is glioblastoma 18 (61%), anaplastic astrocytoma 9 (31%), anaplastic oligodendroglioma 1 (3.4%) other high grade glioma 1. Fourteen patients received more than one line of chemotherapy before study entrance. 65% were on anticonvulsant therapy mainly with phenytoin 56% or valproic acid 42%. Response to treatment was partial in 2 (6.7%), stable in 9 (31%) progression in 13% (45%) and not assessed in 5. Response only in assessable patients was PR/SD/P 2 (8.3%)/9 (37.5%)/13 (54%). Responses were seen in oligodendroglioma and anaplastic astrocytoma. Median survival has been 5.9 months and time to progression 2 months. 80 courses have been administered with a mean per patient of 2 (1–7). Toxicity has been very mild mainly haematological and grade I and II. 7% of the patients experienced platelet toxicity grade III and 3.5% neutropenia grade III. Non haematological toxicity was mainly transaminase elevation grade I to II in 24% of patients and nausea and vomiting grade I to II in 31%. Conclusions: Extended schedule temozolomide is an active regimen in resistant patients with moderate toxicity. Resistance to temozolomide may be reverted by extended schedule of administration

[Table: see text]

Identification and characterization of SKAT-2, a novel Th2-specific zinc finger gene

We have identified a novel Kruppel-type zinc finger (ZF) gene, SKAT-2, which is selectively expressed by murine Th2 cells. The protein encoded by this gene has 14 C2H2-type ZF tandemly arrayed at its C terminus and N-terminal SCAN box and KRAB domains. SKAT-2 is tissue restricted in expression at the RNA level, detectable only in brain and at low levels in kidney and spleen and few hematopoietic cell lines. By in situ hybridization, SKAT-2 expression was found to peak in antigen-stimulated CD4(+) T cells after 2-3 days of culture under Th2 but not Th1 biasing conditions. This pattern of expression closely mirrored that of GATA-3 in the same cells. In transient transfection experiments in phorbol 12-myristate 13-acetate/ionomycin-stimulated EL4 cells, SKAT-2 was found to up-regulate the activity of the IL-4 but not the IL-5 promoter, contrasting with the ability of GATA-3 to activate both promoters. This result was confirmed using clones of EL4 cells stably expressing an inducible form of SKAT-2, thus SKAT-2 is a novel Th2-specific gene that may play a role in selective regulation of cytokine genes in T cells.

Osteolytic lesions of the tuber calcanei in two horses

Two adult horses were evaluated for chronic hind limb lameness. Nonseptic calcanean bursitis with associated focal osteolytic lesions at the point of insertion of the gastrocnemius tendon was diagnosed in each horse by physical and lameness examinations, radiography, ultrasonography, and synovial fluid analysis. Both horses underwent arthroscopic exploration and lavage of the affected bursa, and one horse also underwent surgical debridement of the osseous lesion. Both horses remained lame for 13 months after the surgical procedures. To our knowledge, osseous lesions of the calcaneus in horses with nonseptic calcanean bursitis have not been reported. The flexed proximoplantar-to-distoplantar tangential radiographic view of the calcaneus was essential in localizing the lesions, as was the sonogram in one horse. Arthroscopy provided a thorough evaluation of the bursa and associated tendons. On the basis of the outcome of these 2 horses, the prognosis for complete recovery for horses with this condition appears to be unfavorable. Surgical debridement of the osseous lesion was of no benefit and may have been detrimental.

CD34+ cell positive selection from mobilized peripheral blood by an indirect immunomagnetic method: effect of the type of mobilization and assessment of tumor depletion ability

Mobilized peripheral blood has been shown to be a suitable source of hematopoietic progenitor cells for autologous transplantation in oncologic patients. However, tumor cell contamination can potentially occur, although to a lesser extent than in the bone marrow. CD34+ cell positive selection has been developed as a system for the ex vivo purging of remaining tumor cells when used in mobilized peripheral blood. This method has shown a lower purification potential than that obtained with bone marrow or cord blood. The reason for this is not clear, but different groups have tried to improve the purity and yield of the positive selection on mobilized peripheral blood by predepletion of nonlymphoid cell populations, since they can induce nonspecific binding. The present study was designed to test an indirect immunomagnetic CD34+ cell selection method to make it reproducible, feasible, and effective for purging mobilized peripheral blood. Twenty-nine samples from mobilized peripheral blood were tested. The median starting CD34+ percentage was 0.8 (0.3%-4.2%), and the median final purity was 87% (32.7%-99.7%), with a median yield of 44.8% (15%-83.5%). The highest purity was reproducibly achieved when the starting percentage of CD34+ cells was higher than 0.65% (median purity 93.7, range 81%-99.7%, CV 6%) on samples obtained from patients primed with chemotherapy alone or chemotherapy plus recombinant human granulocyte-colony stimulating factor. No relation was found between the content of contaminating nucleated cells and the final CD34+ cell purity. This method showed a depletion capacity, assessed by PCR on samples contaminated with K562 leukemic cells, of about 3 logs. These results indicate that this indirect immunomagnetic method can produce high purity CD34+ cell fractions from mobilized peripheral blood with a high efficiency of tumor depletion.

Engraftment after infusion of CD34+ marrow cells in patients with breast cancer or neuroblastoma

The CD34 antigen is expressed by 1% to 4% of human and baboon marrow cells, including virtually all hematopoietic progenitors detectable by in vitro assays. Previous work from our laboratory has shown that CD34+ marrow cells can engraft lethally irradiated baboons. Because the CD34 antigen has not been detected on most solid tumors, positive selection of CD34+ cells may be used to provide marrow cells capable of engraftment, but depleted of tumor cells. In seven patients with stage IV breast cancer and two patients with stage IV neuroblastoma, 2.5 to 17.5 x 10(9) marrow cells were separated by immunoadsorption with the anti-CD34 antibody 12-8 and 50 to 260 x 10(6) positively selected cells were recovered that were 64 +/- 16% (range 35% to 92%) CD34+. The patients received 1.0 to 5.2 x 10(6) CD34-enriched cells/kg after marrow ablative therapy. Six patients engrafted, achieving granulocyte counts of greater than 500/mm3 at 34 +/- 10 (range 21 to 47) days and platelets counts of greater than 20,000/mm3 at 46 +/- 14 (range 28 to 66) days posttransplant. Five of these patients showed durable engraftment until the time of death 82 to 386 days posttransplant. One patient failed to sustain engraftment associated with metastatic marrow disease. Three patients died at days 14, 14, and 17 posttransplant, two of whom had evidence of early engraftment. These studies suggest that CD34+ marrow cells are capable of reconstituting hematopoiesis in humans.