Synthesis of purine derivatives of potential immunomodulatory activity.

Moving from the interest as immunomodulatory agent of ST789 was studied the synthesis of series of N9alkylated hypoxanthine and adenine. The synthesis and the chemical physical properties of these derivatives are here described.

Engineering viral promoters for gene transfer to human neuroblasts.

1. The strength and activity of several viral promoters in human neuroblasts were evaluated in vitro. 2. Several luciferase reporter gene constructs under the control of different viral promoters (HIV-1 LTR, HTLV-I LTR, MMTV LTR, RSV LTR, CMV, SV40), in the presence or in the absence of the viral SV40 enhancer, were transfected into two well-established human neural cell lines, including one derived from human embryonic olfactory cells (B4) and one derived from an adrenal neuroblastoma (SH-SY-5Y). The epithelial cell line HeLa was used as a control. 3. The enzymatic activity of luciferase was evaluated after normalization with an internal control. The results indicated that in the context of the reporter gene constructs, the CMV promoter alone was, overall, the most active in any tested cell line. However, addition of the SV40 enhancer to the CMV promoter abolished luciferase activity in SH-SY-5Y cells while significantly increasing luciferase expression in the CNS derived B4 fetal neuroblasts. 4. The results suggest that gene therapeutic vectors aimed to promote enzymatic activity through gene transfer into undifferentiated human neural cells are feasible. However, since differences in promoter activity in neuroectodermal-derived cells are very relevant, gene construct variants should be considered to optimize the system.

Processing of human cord blood by three different procedures for red blood cell depletion and mononuclear cell recovery.

BACKGROUND AND OBJECTIVES: Human cord blood (CB) is an important source of stem cells which may be used for hematopoietic reconstitution as an alternative to bone marrow transplantation. Banking of CB would be accomplished by removing red blood cells (RBC) and plasma from CB collections. Our aim was to compare three different procedures for CB processing. MATERIALS AND METHODS: Poligeline, hydroxyethyl starch gel (HES) and gelatin were used as separation media in processing 79 CB units for RBC depletion and mononuclear cell (MNC) recovery. RESULTS: The best MNC recoveries were obtained performing the HES- and the gelatin-based procedures (80.9 and 84.7%, respectively), but the gelatin procedure allowed us to obtain the highest RBC depletion (96.4%); CD34+ cell recovery was higher using HES or gelatin as separation media (85.6 and 85.9%, respectively). CONCLUSION: The best results, as far as RBC removal and MNC recovery are concerned, were obtained by using gelatin as RBC sedimentation medium. Gelatin is a low-cost, animal-derived reagent, which has been successfully used for CB transplantation; the procedure is simple to perform and appears to be suitable for large-scale banking in view of CB transplantation.

Retinol (vitamin A) and retinal-binding protein serum levels in children with cancer at onset.

The aim of the study was to evaluate vitamin A (Vit A) plasma levels in children with newly diagnosed neoplasia (NDN) admitted to the Department of Hematology-Oncology of G. Gaslini Institute. Vit A levels, retinol-binding protein (RBP), and nutritional status were evaluated in 54 children with NDN (22 solid tumors other than neuroblastoma, 16 neuroblastomas, 9 lymphomas, 7 acute lymphoblastic leukemia). Biochemical test results were also compared with those of 47 healthy controls (HC) comparable for sex and age. In children with NDN, mean Vit A plasma level results were 350 micrograms/L (95% CI 288-412); in HC they were 517 micrograms/L (95% CI 471-563), P < 0.001. Mean RBP value results were 3.2 mg/dL (95% CI 2.6-3.9) in NDN and 4.9 mg/dL in HC (95% CI 4.5-5.3), P < 0.001. Fifteen (28%) out of 54 children with NDN were classified as well-nourished, 27/54 (50%) were considered at risk of malnutrition, and 12 (22%) were malnourished. Children with NDN presented reduced Vit A and RBP mean values compared with those of HC. Further studies are needed to better evaluate Vit A metabolism in children with cancer at onset.

Angiogenic and angiostatic microenvironment in tumors--role of gangliosides.

Gangliosides are important components of the cell membrane that are usually shed in the surrounding microenvironment by neoplastic cells. Gangliosides can also modulate the angiogenic response of microvessels stimulated by angiogenic factors. The experiments reported here make a contribution to the assessment of the nature of this angiogenic modulation, by demonstrating that a) GM3 gangliosides can block the proliferation of endothelium induced by neoplastic cells from human tumors of five different origins; b) this block also occurs when the endothelial cells are preincubated with GM3 and disappears when the cells are returned to a medium poor in GM3; c) in the presence of GM3 the capacity of the endothelial cells to bind to fibronectin and to collagen types I and IV was sharply reduced; d) concentrations of GM3 able to block endothelial cell growth are counteracted by addition to the medium of GT1b ganglioside. The data suggest that the prevalence of a microenvironment rich in GM3 prevents proliferation of vascular endothelium, but the appropriate presence of another ganglioside, such as GT1b, nullifies the effect. Modulation of the angiogenic response of vascular endothelium to angiogenic factors released by tumors is probably dependent on the distribution and activity of growth factor receptors on the endothelial cell surface. The nature and concentration of the gangliosides in the endothelial microenvironment have a decisive influence on this event and possibly on the progression of tumor-induced angiogenesis.

Lymphoblastoid cells transfected with c-myc: downregulation of EBV-lytic antigens and impaired response of autologous CD4+ T cells in vitro.

Normal EBV-positive lymphoblastoid B-cell lines (LCL) were transfected with vectors containing the c-myc oncogene (pHEBO-E(mu)-myc) or control vectors (pHEBO-E(mu)) and analyzed for the expression of EBV-lytic and latent antigens. While EBV-latent antigens were normal in the c-myc transfectants, there was an almost complete downregulation of EBV-lytic antigens, including BZLF1, EA(D), gp340 and VCA. These observations were consistently repeated on 6 different LCLs transfected with c-myc. Unlike control LCLs, the c-myc transfectants did not release infectious EBV. PCR analysis demonstrated that BZLF1 mRNA was virtually absent in c-myc transfectants, possibly suggesting that the deregulated c-myc imposed a block in the EBV-lytic cycle at this particular level. c-myc transfectants failed to sustain the proliferative response of autologous CD4+ T-cell clones with specificity for EBV-lytic antigens. However, they regained this capacity after incubation with ultraviolet-inactivated EBV or gp340 antigen in vitro, also indicating that their antigen-presenting capacities were not impaired. c-myc transfectants failed to elicit a secondary proliferative response by autologous CD4+ T cells purified from the peripheral blood of EBV-seropositive donors. Exposure of c-myc transfectants to UV-inactivated EBV again resulted in a proliferative CD4+ T-cell response comparable to that elicited by the control LCLs. Collectively, our data provide evidence for the remarkable ability of an oncogene to influence the life cycle of a virus and to modify the antigenicity of the infected cells.

Adhesion of human neuroblasts to HIV-1 tat.

Several neuropathologic findings in infants and children with human immunodeficiency virus type-1 (HIV-1) infection are different from those observed in adults, probably related to the fact that the retroviral infection occurs in the setting of neuro-development. This report describes the interaction and biologic activity of tat, the HIV-1 trans-activating protein on human neuroblasts. Two human neuroblastoma cell lines, LAN-5 and GI-CA-N, have been studied for their capability to adhere to tat (full recombinant protein) and to two different peptide residues of it. Both cells adhere to tat and tat46-60 basic domain, although not to tat65-80 residue, which contains the RGD (arginine-glycine-aspartic acid) motif. Adhesion to collagen I was inhibited by preincubating GI-CA-N cells with tat,46-60 although not with tat,65-80 indicating the capability of the basic residue to interfere with collagen I-induced cellular adhesion. The expression of 200-kD neurofilaments induced by collagen I was not induced by tat,46-60 indicating that neural differentiation along the same pathway is not mimicked by this peptide. Neuroblast cell proliferation was not affected by adhesion to tat46-60 nor to tat.65-80 GI-CA-N cells are not permissive to HIV-1 infection. However, proviral DNA was documented in the cell lysate for 14 consecutive in vitro passages, whereas HIV-1 transcription was never detectable. This would exclude the possibility that tat would be transduced by these cells. GI-CA-N stained negative for CD4, although positive for Gal-C, which may explain HIV-1 entry. Results show that immature human neural cells interact with tat protein and/or its basic residue in vitro. A mechanism similar to that herein described would possibly be active in vivo, which may help in clarifying the pathogenic mechanisms of neurologic dysfunction and destruction of the CNS observed in infants infected with HIV-1.

Synthetic biological response modifiers. Part II. Synthesis and immunomodulatory properties of some: N2-[omega-(pyrimidin-1-yl)carboxyalkyl]-L-arginines.

The synthesis and chemical and physical properties of some N2-[omega-(pyrimidin-1-yl)carboxyalkyl]-L-arginines are here described. Experiments of immunopharmacological evaluations are also described.

Cloning and sequencing of isoform-specific regions of human Ca2+-independent protein kinase C (PKC)-encoding genes.

The cloning and sequencing of the isoform-specific regions of the human Ca2+-independent protein kinase C-encoding genes is described. These clones will serve as correct size probes for screening human genomic or cDNA libraries and isolating full-length clones.

Uncoordinate induction and differential regulation of HLA class-I and class-II expression by gamma-interferon in differentiating human neuroblastoma cells.

Recombinant gamma-interferon (IFN-gamma) has recently been shown to be one of the most effective inducers of neuroblastoma (NB) cell differentiation. Since increasing evidence indicates that expression of MHC class-I and class-II antigens by tumour cells is important for immunorecognition and cell targeting, we tested whether induction of NB cell differentiation by IFN-gamma is followed by expression of HLA class-I and class-II molecules. LAN-5 human NB cell line completely lacks HLA class-I antigens. Their expression was induced in a dose-dependent manner by IFN-gamma. HLA class-II molecules are also absent on LAN-5 cells, but only DP antigens were dose-dependently induced by IFN-gamma, while DR and DQ molecules were unaffected by the treatment. To confirm and extend the immunological data to all the class-II molecules, we performed Northern blot analysis, observing that DP alpha mRNA was induced in a dose- and time-dependent manner. DO beta and DZ alpha genes were also induced peaking after 3 days of IFN-gamma treatment. DR beta and DQ beta genes, which were not induced by IFN-gamma, gave a normal pattern of enzyme restriction by Southern blot. To get an insight into the regulation of HLA class-II gene expression in the neuronal model, we measured the decline of the steady-state HLA class-II mRNA. DO beta mRNA rapidly returned to baseline level after removing IFN-gamma, while the decay rates of DP alpha and DZ alpha mRNA were very slow. This might indicate different regulation at the post-transcriptional level for DO beta mRNA with respect to DP alpha and DZ alpha mRNA. To strengthen these findings we evaluated the half-lives of the mRNA after IFN-gamma induction by means of actinomycin D treatment. HLA-DO beta mRNA had a shorter half-life, while DZ alpha and DP alpha had a longer decay rate. Finally, we report that treatment of LAN-5 cells with cycloheximide did not alter the rate of transcription of the HLA-DP alpha gene, suggesting that no protein factor(s) is/are needed to maintain DP alpha gene expression.

Modulation of alpha 1 beta 1, alpha 2 beta 1 and alpha 3 beta 1 integrin heterodimers during human neuroblastoma cell differentiation.

Two human neuroblastoma cell lines, LAN-5 and GI-CA-N, have been analyzed for their capability to adhere to different extracellular matrix (ECM) components. The GI-CA-N cells adhered to all the tested substrates: laminin (LN), type I and type IV collagen (Coll I, Coll IV), vitronectin (VN), and fibronectin (FN). Conversely LAN-5 cells weakly attached to FN and VN, whilst adhesion on LN and Coll I and IV was strong and induced a rapid elongation of cell processes. By means of RT-PCR and immunoprecipitation we showed that the integrin pattern of these two lines was different and could explain their diversity in adhesion capability. Both cell lines express a large amount of the beta 1 integrin subunit, associated with different alpha chains, probably responsible for their adhesion to some ECM proteins. After treatment of LAN-5 cells with biological differentiating agents, such as gamma-interferon, alone or in combination with tumour necrosis factor-alpha (TNF-alpha), or retinoic acid, the levels of alpha 1 beta 1, alpha 2 beta 1, and alpha 3 beta 1 integrin expression were enhanced, while the amount of alpha v remained constant. In contrast, treatment of LAN-5 cells with TNF-alpha, that did not induce any maturation, or starvation in 2% foetal calf serum, that inhibited cell proliferation without affecting neural differentiation, did not induce any change in the integrin assessment. Messenger-RNAs for the two alpha 6 isoforms, A and B, were present in both cell lines. However, in LAN-5 cells, the protein product was neither detectable nor inducible by differentiation. Our results confirm the specific modulation of the alpha 1 beta 1 integrin expression in human neuronal development, and show, for the first time, the involvement of alpha 2 beta 1 and alpha 3 beta 1 heterodimers in this maturational process.

Interferon-gamma-stimulated and GTP-binding-proteins-mediated phospholipase A2 activation in human neuroblasts.

Interferon-gamma (IFN-gamma) is a potent growth-inhibitory cytokine also endowed with differentiating activity on neural cells. Binding of IFN-gamma to its high-affinity receptor induces a rapid and transient activation of phospholipase A2 (PLA2). The mechanism coupling the IFN-gamma receptor (IFN-gamma-R) to PLA2 activation is not clearly defined, and no information is available on this mechanism in neuroblast cells. We have tested the hypothesis that GTP-binding proteins (G-proteins) may couple the IFN-gamma-R to PLA2 in the human neuroblastoma (NB) cell line LAN-5. Incubation of NB cells with IFN-gamma resulted in a rapid increase in [3H]arachidonic acid (AA) release, and this effect was blocked by pretreatment with anti-IFN-gamma antibodies. IFN-gamma-stimulated AA release was still observed in permeabilized cells that were blocked by pretreatment with anti-IFN-gamma-R antibodies. Exposure of permeabilized LAN-5 cells to guanosine 5'-[gamma-thio]triphosphate (GTP[S]), a non-hydrolysable GTP analogue, induced a dose-dependent release of [3H]AA. A non-specific nucleotide effect was excluded, since similar stimulatory effects on AA mobilization were not observed by GTP, ATP, CTP, ADP and GDP. IFN-gamma-stimulated AA release was completely blocked by the guanine nucleotide analogue that inhibits G-protein function, guanosine 5'-[beta-thio]diphosphate (GDP[S]). A role for G-proteins in IFN-gamma-R coupling to PLA2 was further supported by the inhibition of IFN-gamma-induced [3H]AA release by treatment of permeabilized cells with pertussis toxin and with the antiserum against the common alpha-subunits of G-proteins. To determine a possible contribution to AA mobilization by the phospholipase C and diacyglycerol lipase pathway or by protein kinase C activation, the effects of neomycin, a phospholipase C inhibitor, and PMA (phorbol 12-myristate 13-acetate), a direct activator of protein kinase C, were investigated. Neither neomycin nor PMA affected either basal or IFN-gamma-stimulated AA release. Ca2+ concentration, which has been shown to regulate the activity of some PLA2s, does not appear to play an important role in the regulation of the IFN-gamma-stimulated PLA2 activity, since incubating permeabilized cells in different concentrations of Ca2+ induced AA release without affecting the IFN-gamma response. Altogether, these findings suggest the existence of IFN-gamma-R, which couples a Ca(2+)-independent PLA2 activation via pertussis-toxin-sensitive G-proteins.

Protein kinase C isoenzymes in human neuroblasts. Involvement of PKC epsilon in cell differentiation.

Although neuronal cells are a major target of phorbol ester action, the activity of the various protein kinase C (PKC) isoenzymes have not been studied in detail in human neuroblasts. Differentiation of the LAN-5 human neuroblastoma cell line by interferon-gamma (IFN-gamma) is accompanied by a twofold increase in PKC activity. Since PKC is a multigene family, we investigated which isoforms were expressed in control and differentiated cells, and which of these isoenzymes is involved in neuronal differentiation. We found that: (1) PKC activity is higher in differentiated than in undifferentiated cells; (2) RT-PCR analysis showed the expression of mRNA for PKC alpha, -gamma, -delta, -epsilon and -zeta and the absence of mRNA for beta in untreated LAN-5 cells; (3) Western blot evaluation with PKC isoform-specific antibodies showed the same pattern of PKC expression in non-differentiated cells; (4) Expression of PKC epsilon mRNA was significantly enhanced by IFN-gamma-induced differentiation, while the other isoforms were not affected; (5) Differentiation of LAN-5 cells with IFN-gamma or retinoic acid induced overexpression of the PKC epsilon protein, while inhibition of cell proliferation by fetal calf serum starvation was without effect. These findings suggest that expression of PKC epsilon isoform is tightly coupled with neuronal differentiation and may play a role in the maintenance of the differentiated state.

Interferon-gamma-induced differentiation of human neuroblastoma cells increases cellular uptake and halflife of metaiodobenzylguanidine.

Iodine labeled metaiodobenzylguanidine (MIBG) is a radiopharmaceutical employed for both diagnosis and metabolic radiotherapy of neuroblastoma (NB). Resistance to the radiotherapeutic effects of MIBG is common, due to lack of MIBG accumulation by NB cells. MIBG enters competent cells via the noradrenaline transporter; this function requires a relative cellular maturation and is missing in most NB cell lines. In vitro differentiation of NB cells can be achieved with gamma-interferon (gamma-IFN) and other agents. We have verified that gamma-IFN-induced differentiation of NB cells is specifically associated with an increase in their ability to incorporate MIBG. This phenomenon is due to enhancement of MIBG transporter activity, according to pharmacological sensitivity and semiquantitative PCR-based analysis of specific MIBG transporter mRNA. New therapeutic strategies based on both differentiation therapy and targeted radiotherapy of NB can so be devised.

Interferon-γ-induced differentiation of human neuroblastoma cells increases cellular uptake and halflife of metaiodobenzylguanidine.

Iodine labeled metaiodobenzylguanidine (MIBG) is a radiopharmaceutical employed for both diagnosis and metabolic radiotherapy of neuroblastoma (NB). Resistance to the radiotherapeutic effects of MIBG is common, due to lack of MIBG accumulation by NB cells. MIBG enters competent cells via the noradrenaline transporter; this function requires a relative cellular maturation and is missing in most NB cell lines. In vitro differentiation of NB cells can be achieved with γ-interferon (γ-IFN) and other agents. We have verified that γ-IFN-induced differentiation of NB cells is specifically associated with an increase in their ability to incorporate MIBG. This phenomenon is due to enhancement of MIBG transporter activity, according to pharmacological sensitivity and semiquantitative PCR-based analysis of specific MIBG transporter mRNA. New therapeutic strategies, based on both differentiation therapy and targeted radiotherapy of NB can so be devised.

Stimulation of receptor-coupled phospholipase A2 by interferon-gamma.

The biomolecular mechanisms that mediate signal transduction by type II (gamma) interferon (IFN) are poorly understood. IFN-gamma is a potent growth inhibitory cytokine also endowed with antiviral, immunomodulatory, and differentiating activities on various cell targets, including neural cells. IFN-gamma induced a rapid and transient activation of phospholipase A2 in LAN-5, a human neuroblastoma cell line. A consequence of phospholipase A2 activation was the release of arachidonic acid and the generation of lysophospholipids from membrane phospholipids. Treatment of pre-labeled LAN-5 cells with a receptor-saturating concentration of IFN-gamma led to a time-dependent release of [3H]arachidonic acid into the culture media and generation of [32P]lysophosphatidylcholine. Pretreatment of cultures with the phospholipase A2 inhibitor, bromophenacyl bromide, markedly inhibited both [3H]arachidonic acid release and lysophosphatidylcholine production induced by IFN-gamma treatment. Pretreatment of LAN-5 cells with nordihydroguaiaretic acid, a lipoxygenase inhibitor, or with indomethacin, a cyclooxygenase inhibitor, amplified the release of [3H]arachidonic acid and production of lysophosphatidylcholine induced by non-saturating concentrations of IFN-gamma. In parallel, and with the same time-dependent effect, a significant decrease in phosphatidylcholine labeling was observed in IFN-gamma-treated cells, further indicating that a potential signal transduction mechanism of IFN-gamma is the hydrolysis of membrane phosphatidylcholine by phospholipase A2.

gamma-Interferon increases metaiodobenzylguanidine incorporation and retention in human neuroblastoma cells.

Iodine-labeled m-iodobenzylguanidine (MIBG) is a widely used radiopharmaceutical for both diagnosis and biologically targeted radiotherapy of neuroblastoma. However, resistance to the radiotherapeutic effects of MIBG is often encountered, mainly due to lack of MIBG accumulation by neoplastic cells. We have investigated whether the induction of neuroblastoma cell differentiation modifies MIBG incorporation and retention. LAN-5 cells were selected, due to their moderate ability to take up MIBG. Treatment of these cells with gamma-interferon (IFN-gamma) resulted in morphological changes accompanied by a significant increase in overall cell-associated MIBG. Desimipramine, but not reserpine, easily depleted IFN-gamma-treated LAN-5 cells of their MIBG content. This suggests that the mechanism involved is an uptake enhancement rather than an improved storage ability. Indeed, IFN-gamma induces de nov synthesis of MIBG receptor-transporters, as demonstrated by polymerase chain reaction amplification and semiquantitative analysis. Our results suggest that pretreating neuroblastoma patients with IFN-gamma before MIBG administration may enhance the efficacy of both biologically targeted radioimaging and therapy of this tumor.

A combined evaluation of biochemical and morphological changes during human neuroblastoma cell differentiation.

1. The effects of retinoic acid, gamma-interferon, cytosine arabinoside, nerve growth factor, tumor necrosis factor, and 12-O-tetradecanoylphorbol 13-acetate on the human neuroblastoma cell line, LAN-5, were studied. Intracellular levels of acetylcholinesterase, neuron-specific enolase, catecholamines and related neurotransmitters, vasointestinal peptide, and substance P were evaluated after induction. 2. Cell morphology was strongly affected by retinoic acid, gamma-interferon, cytosine arabinoside, and 12-O-tetradecanoylphorbol 13-acetate. The main effects of retinoic acid and gamma-interferon were the loosening of cell clusters and the extension of long neurites; cytosine arabinoside induced cell body swelling and marked neuritogenesis. Following 12-O-tetradecanoylphorbol 13-acetate treatment, the cells became small, round, and neuritic. Conversely, modifications induced by nerve growth factor and tumor necrosis factor were mild. Cell proliferation rate was reduced by retinoic acid, gamma-interferon, cytosine arabinoside, and 12-O-tetradecanoylphorbol 13-acetate, while nerve growth factor and tumor necrosis factor were devoid of effects. 3. Acetylcholinesterase activity was significantly stimulated by retinoic acid and by gamma-interferon. Neuron-specific enolase activity was unaffected by all treatments except 12-O-tetradecanoylphorbol 13-acetate, which enhanced it by 1.6-fold. 4. The cellular catecholamine and related metabolite content was lowered by retinoic acid and gamma-interferon, while cytosine arabinoside and, even more, 12-O-tetradecanoylphorbol 13-acetate showed a stimulatory activity on their intracellular accumulation. 5. Finally, the cell-associated vasointestinal peptide level was strikingly increased by gamma-interferon and, to a lesser extent, by retinoic acid, cytosine arabinoside, and 12-O-tetradecanoylphorbol 13-acetate. 6. It is concluded that the most relevant biochemical changes associated with LAN-5 cells differentiation involve the repertoire of neurotransmitters and neuropeptides. These events vary in quality and in quantity, likely due to the pattern complexity of gene expression triggered by each inducer in determining the diversity of neuronal phenotypes.

Wilms' tumor after treatment.

Sixty-one Wilms' tumors (WTs) from 59 patients who received preoperative therapy were studied. Twenty-seven WTs from 26 patients who did not receive preoperative treatment were also reviewed as controls. Marked and diffuse morphological changes occurred in treated cases. Necrosis affected mostly undifferentiated and replicating elements and was extensive, up to 90% of tumor mass. Minimal residual tumor, permitting recognition as Wilms', was always spared. Epithelial and rhabdomyoblastic components were more resistant to treatment; moreover, they appeared to be susceptible to differentiation and maturation. Necrosis and muscle cell differentiation seemed to have prognostic implications. Cases with extensive necrosis (greater than 90%) had a better outcome, although the difference was not statistically significant. The rhabdomyoblast/tumor mass ratio, after treatment, appears to carry prognostic meaning. Chemotherapy had no apparent effect on anaplasia.

Analysis of CD4 gene expression in human fetal brain and neuroblasts.

1. The expression of the gene codifying for CD4, the most important human immunodeficiency virus type 1 (HIV-1) receptor molecule, was analyzed in 11 fetal brains at various gestational ages and in 9 human neuroblastoma (NB) cell lines. CD4 gene expression in fetal and malignant neural cells was then compared with that observed in a hematopoietic cell line and adult hippocampus. 2. In addition, CD4 mRNA was evaluated in two NB cell lines induced to differentiate in vitro with retinoic acid (RA) or 1-(5-isoquinolinyl-sulfonyl)-2-methyl piperazine (H7), a protein kinase C inhibitor. 3. All fetal brains and NB cell lines express a 1.8-kb signal when hybridized with pT4BcDNA probe, while a 3.0-kb signal such as observed in hematopoietic human cells was found in 1 of 11 fetal brains and in 0 of 9 NB cell lines. The 1.8-kb signal was lost in all analyzed poly(A)+ mRNA samples. 4. Moreover, CD4 gene expression was not induced in either RA- or H7-treated NB cells at any tested time and dose. The analysis of NB cells by polymerase chain reaction failed to demonstrate CD4 expression in either poly(A)+ or poly(A)- RNA. 5. In conclusion, the results show that the 1.8-kb signal observed in RNA extracted from fetal or transformed human neural cells is probably due to an aspecific hybridization. However, the gene codifying for CD4 can rarely be expressed by fetal brain cells early during gestation, in still unclear circumstances.