No abstract

ABSTRACT

The Schwann cells in maturing neuroblastomas differ genetically from the neuronal cells. The normal number of chromosomes in Schwann cells and the abnormal number in neuroblastic ganglionic cells suggests that Schwann cells are a reactive population of normal cells that invade the neuroblastoma. Near-trip-loidy of neuroblastoma cells and intact chromosome 1 are presumably genetic prerequisites for spontaneous organoid maturation, because we found no diploidy or chromosome 1 depletions in the neuronal cells of spontaneously maturing neuroblastomas.

Incubation of low density lipoprotein (LDL) with endothelial cells or smooth muscle cells overnight has resulted in an oxtdative modification of LDL that results in its recognition by macrophages by way of the acetyl LDL receptor. In the present study, we examined whether macrophages themselves can oxidize and modify LDL in a manner similar to that of endothelial cells. Incubation of 125 l-labeled LDL with resident or thioglycollate-elicited macrophages for 24 hours in Ham's F-10 medium resulted in the appearance of thiobarbituric acid (TBA) reactive materials and trichloroacetic acid (TCA) soluble radioactivity in the medium. The LDL harvested from these incubations showed increased electrophoretic mobility and was degraded rapidly when added to fresh macrophages as compared to LDL previously incubated in the absence of cells. T he accumulation of lipid-laden foam cells of monocvte origin in the aortic intima is an early event in the development of atherosclerosis.1 " 3 Monocyte-macrophages take up and degrade native low density lipoprotein (LDL) by way of the classical LDL (B/E) receptor, but only at rather low rates. 4 On the other hand, chemically acetylated LDL and other chemically modified forms of LDL 5 -6 are taken up much more rapidly by a distinct, alternative receptor, designated the acetyl LDL or scavenger receptor. 7Incubation of macrophages with these chemically modified forms readily generates foam cells whereas it is difficult to generate foam cells by incubation with native LDL 4 unless very long incubation times are used.8 Incubation of native LDL overnight with cultured endothelial cells has been shown to result in a modification that converts LDL to a form recognized by the same receptor that recognizes acetyl LDL.9 " 11 This modification has been shown to depend upon the presence of trace metals in the medium, to involve extensive lipid peroxidation, and to require the ac- tion of a phospholipase A 2 . 12 ' 13 The peroxidation of LDL lipids during such incubations has been shown to account for the cytotoxicity of LDL for cultured endothelial cells. 14 All of these changes can be blocked by the addition of alpha-tocopherol, butylated hydroxytoluene (BHT), or by probucol, a drug used in the management of hyperlipoproteinemia. 15 Since macrophages generate active oxygen species, which may play a role in their ability to scavenge and kill cells, it seemed likely that they might share the ability to oxidatively modify LDL. It was recently reported 16 ' 17 that LDL is oxidized by human monocytes and neutrophils and that the electrophoretic mobility of LDL is increased after incubation with cultured porcine monocytes. We report here that mouse peritoneal macrophages, like circulating human monocytes, can cause extensive oxidation of LDL lipids. We show further that the modified LDL is specifically recognized by the acetyl LDL receptor on the same cells that oxidized the LDL and, finally, that this macrophage-modified LDL competes with endothelial cellmodified LDL for uptake and degradation.

Leukaemic stem cells in patients with CD33(+) AML express CD33. This observation is in favour of novel treatment concepts employing CD33-targeting antibodies in AML.

We have recently shown that resting human mast cells (MCs) produce tissuetype plasminogen activator (t-PA) without simultaneously expressing plasminogen activator inhibitor 1 (PAI-1). In the present study we have identified the anaphylatoxin rhC5a as a potent inducer of PAI-1 expression in human MCs and basophils. In primary human skin MCs and primary blood basophils, exposure to rhC5a was followed by an increase from undetectable to significant levels of PAI-

CD20 is expressed in approximately onehalf of pediatric acute lymphoblastic leukemia (ALL) cases with B-cell precursor (BCP) origin. We observed that it is occasionally up-regulated during treatment. To understand the impact of this on the potential effectiveness of anti-CD20 immunotherapy, we studied 237 CD10 ؉ pediatric BCP-ALL patients with BerlinFrankfurt-Munster (BFM)-type therapy. We analyzed CD20 expression changes from diagnosis to end-induction, focusing on sample pairs with more than or equal to 0.1% residual leukemic blasts, and assessed complement-induced cytotoxicity by CD20-targeting with rituximab in vitro. CD20-positivity significantly increased from 45% in initial samples to 81% at end-induction (day 15, 71%). The levels of expression also increased; 52% of cases at end-induction had at least 90% CD20 pos leukemic cells, as opposed to 5% at diagnosis (day 15, 20%). CD20 up-regulation was frequent in highrisk patients, patients with high minimal residual disease at end-induction, and patients who suffered later from relapse, but not in TEL/AML1 cases. Notably, up-regulation occurred in viable cells sustaining chemotherapy. In vitro, CD20 up-regulation significantly enhanced rituximab cytotoxicity and could be elicited on prednisolone incubation. In conclusion, CD20 up-regulation is frequently induced in BCP-ALL during induction, and this translates into an acquired state of higher sensitivity to rituximab. IntroductionCD20 is a signature B-cell differentiation antigen strongly expressed on the surface of mature normal as well as malignant B cells. It is also expressed, but at lower levels and with larger variance, on more immature B cells and their malignant counterparts found in B-cell precursor (BCP) acute lymphoblastic leukemia (ALL). 1,2 In line with the expression patterns, anti-CD20 directed immunotherapy has been shown to elicit potent antitumor effects specifically in mature B-cell lymphoma and leukemia, where it has been incorporated into standard treatment as a valuable therapy advance. 3 To date, the most broadly evaluated compound for CD20 targeting is rituximab, a chimeric antibody that was licensed by the Food and Drug Administration in 1997 as the first anticancer monoclonal antibody. It acts by complementdependent and antibody-dependent cell-mediated cytotoxicity as well as by inducing apoptosis directly. 4 Recently, targeted therapy with rituximab has been implicated also in BCP-ALL for combination with conventional chemotherapy, 5 with at least 6 active trials listed at http://www.clinicaltrials.gov (accessed May 2008). In children with BCP-ALL, published usage has been confined mostly to anecdotal reports on relapsed or refractory disease. 6-9 Importantly, activity can be anticipated primarily in CD20 ϩ cases, which relevantly limits its applicability in pediatric BCP-ALL supposedly to less than one half of patients as determined at diagnosis. 2 During the course of an internationally collaborative study on flow cytometric minimal residual disease (MRD) assessment in childhood...

Expression of CD99 is higher on immature than on mature T cells. We postulated that this marker could be used to assess minimal residual disease (MRD) in T-lineage acute lymphoblastic leukemia (T-ALL). In diagnostic bone marrow (BM) samples from 27 children with T-ALL, expression of CD99 on leukemic lymphoblasts by flow cytometry was in median 7.7 times higher than on normal T lymphocytes from within the same sample. In 85% of cases, leukemic MFI values were higher than the mean MFI þ 2 s.d. of normal populations. We applied CD99 to study MRD in 39 follow-up samples from 15 consecutive T-ALL patients, and compared the results with those obtained with the well-established MRD-marker terminal deoxynucleotidyl transferase (TdT). Either antibody was combined in four-color flow cytometry with CD7, surfaceCD3, and cytoplasmicCD3. We found that CD99 was a valid complement to TdT in quantifying T-ALL MRD. Given a considerable interpatient variability, CD99 could be favorably used in nine patients, and TdT in other five patients. Both approaches showed a similar very low nonspecific background throughout 12 weeks from diagnosis (in median 0.002% of nucleated BM cells in patients with non-T ALL). We conclude that CD99 is a highly informative tool for MRD detection in T-ALL, bearing the advantage of surface expression in contrast to TdT.