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Recombinant-tagged proteins have a widespread use in experimental research as well as in clinical diagnostic and therapeutic approaches. Well-stocked sets of differently tagged variants of a same protein would be of great help. However, the construction of differently tagging vectors is a demanding task since cloning procedures need several tailored DNA inserts. In this study, we describe a novel vector system that allows a cost- and time-effective production of differently tagged variants of a same protein by using the same DNA fragment and a set of vectors each carrying a different tag. The design of these expression vectors is based on an intronic region that becomes functional upon cloning the insert sequence, splicing of which attaches a certain tag to the protein termini. This strategy allows for the cloning of the fragment that codes for the protein of interest, without any further modification, into different vectors, previously built and ready-to-use, each carrying a tag that will be joined to the protein. Proof of principle for our expression system, presented here, is shown through the production of a functional anti-GD2 Fab fragment tagged with biotin or polyhistidine, or a combination of both, followed by the demonstration of the functional competencies of both the protein and the tags.

UL18 is a trans-membrane viral protein expressed on human cytomegalovirus (HCMV)-infected cells, and its surface expression determines the interaction of infected cells with lymphocytes expressing the CD85j (LIR-1/ILT2) receptor. We previously showed that the UL18-CD85j interaction elicits activation of T lymphocytes. However, in in vitro cell models UL18 displays mostly undetectable surface expression. Thus, we asked how surface expression of UL18 is regulated. Domain-swapping experiments and construction of specific mutants demonstrated that two motifs on its cytoplasmic tail, homologous to YXXPhi and KKXX consensus sequences, respectively, are responsible for impairing UL18 surface expression. However, the presence of the whole HCMV genome, granted by HCMV infection of human fibroblasts, restored surface expression of either UL18 or chimeric proteins carrying the UL18 cytoplasmic tail, starting from the third day after infection. It is of note that the two motifs responsible for cytoplasmic retention are identical in all 17 HCMV strains examined. We disclosed a control mechanism used by the HCMV to regulate the availability of UL18 on the infected-cell surface to allow interaction with its ligand on T and NK cells.

UL18 is a glycoprotein encoded by the human cytomegalovirus genome and is thought to play a pivotal role during human cytomegalovirus infection, although its exact function is still a matter of debate. UL18 shares structural similarity with MHC class I and binds the receptor CD85j on immune cells. Besides UL18, CD85j binds MHC class I molecules. The binding properties of CD85j to MHC class I molecules have been thoroughly studied. Conversely, very little information is available on the CD85j/UL18 complex, namely that UL18 binds CD85j through its alpha3 domain with an affinity that is approximately 1000-fold higher than the MHC class I affinity for CD85j. Deeper knowledge of features of the UL18/CD85j complex would help to disclose the function of UL18 when it binds to CD85j. In this study we first demonstrated that the UL18alpha3 domain is not sufficient per se for binding and that beta2-microglobulin is necessary for UL18-CD85j interaction. We then dissected structural determinants of binding UL18 to CD85j. To this end, we constructed a three-dimensional model of the complex. The model was used to design mutants in selected regions of the putative interaction interface, the effects of which were measured on binding. Six regions in both the alpha2 and alpha3 domains and specific amino acids within them were identified that are potentially involved in the UL18-CD85j interaction. The higher affinity of UL18 to CD85j, compared with MHC class I, seems to be due not to additional interaction regions but to an overall better fit of the two molecules.

Purpose: Detection of metastatic tumor cells in bone marrow (BM) and peripheral blood (PB) of children with neuroblastoma is crucial for prognosis and planning of therapy. Aims of this large descriptive repeated survey were to evaluate the diagnostic accuracy of different techniques in diagnostic samples obtained at several disease course time points and to correlate positive results with patient clinical features and outcome., Experimental Design: BM aspirates, trephine biopsies, PB, and peripheral blood stem cell (PBSC) samples from Italian children with neuroblastoma were analyzed by morphological and histologic techniques, as well as by immunocytochemistry (IC) for disialoganglioside GD(2) and reverse transcription-PCRs (RT-PCRs) for tyrosine hydroxylase (TH) and pgp9.5 genes. The diagnostic odd ratio (DOR) was used to measure the accuracy of the different techniques., Results: A total of 2,247 evaluations were done on 561 BM, 265 PB, and 69 PBSC samples from 247 patients. IC showed the best accuracy. Whereas TH RT-PCR accuracy was satisfactory, that of pgp9.5 was very low. Positive results obtained by IC in BM and PB samples at diagnosis from stage 1, 2, and 3 patients correlated with unfavourable outcome. No correlation was found between positive results obtained by IC or TH RT-PCR in BM, PB, and PBSC samples from stage 4 patients and their outcome., Conclusions: Because of its elevated diagnostic accuracy, IC may represent a useful adjunct to conventional morphological techniques, especially in view of its potential prognostic role in patients with localized disease. Longitudinal multicenter studies are warranted to definitely establish the clinical usefulness of TH RT-PCR.

GD2 is a disialoganglioside expressed at high density on the surface of malignant cells of neuroectodermal origin, especially in neuroblastoma (NB) and melanoma. Since its expression in normal tissues is very restricted, GD2 represents an excellent target for neuroectodermal tumor targeting. Mini-antibody technology allows the production of dimeric single-chain antibodies, also called small immunoproteins (SIPs), which are composed of a scFv fused to a dimerizing domain of immunoglobulin heavy chains. Dimerization results in an increase of the total apparent affinity and a slower clearance in vivo than scFvs. These properties make SIPs very attractive molecules for tumor targeting. We isolated the variable regions from an anti-GD2 monoclonal antibody and exploited the SIP technology to generate two novel anti-GD2 SIPs. The first anti-GD2 SIP is a fully murine molecule containing the CH3 domain of mouse IgG1, whereas the second construct is a hybrid mouse-human molecule containing the CH4 domain of human IgE. Both mini-antibodies were successfully produced and shown to retain binding specificity as well as an affinity similar to that of the original antibody.

Immune evasion mechanisms of human CMV are known; however, the immune control of infection remains poorly elucidated. We show that interaction between the viral protein UL18 on infected cells and the invariant receptor CD85j/LIR-1/ILT2 expressed on CTL is relevant for the control of infection. Resting and activated CD8(+) T cells lysed UL18 expressing cells, whereas cells infected with CMV defective for UL18 were not killed. Lysis was not dependent on CD8(+) T cell Ag specificity, MHC-unrestricted and specifically blocked by anti-CD85j and anti-UL18 mAb. Moreover, soluble recombinant UL18Fc immunoprecipitated CD85j from T cells. Activation is mediated by CD85j and its pathway is unrelated to CD3/TCR engagement. UL18 is detected in immunocompromised patients with productive infection and the mechanism used in vivo by human CMV to ensure survival of the immunocompetent host may be mediated by activation signals delivered by infected cells to T lymphocytes via UL18/CD85j interactions.

The HLA class II expression is controlled by the transcriptional activator CIITA. The transcription of CIITA is controlled by different promoters, among which promoter-IV is inducible by IFN-gamma. We analysed the regulation of HLA class II molecules by IFN-gamma in a large series of human neuroblastoma cell lines. No induction of surface or intracellular HLA class II molecules and of specific mRNA was observed, in all neuroblastomas, with the exception of a nonprototypic cell line, ACN. In a large subset of neuroblastomas IFN-gamma induced expression of CIITA mRNA, derived from promoter-IV, which was not methylated. In contrast, in another subset of neuroblastomas, CIITA was not inducible by IFN-gamma and CIITA promoter-IV was either completely or partially methylated. Interestingly, the use of DNA demethylating agents restored CIITA gene transcriptional activation by IFN-gamma, but not HLA class II expression. The defect of HLA class II was not related to alterations in RFX or NF-Y transcription factors, as suggested by EMSA or RFX gene transfection experiments. In addition, the transfection of a functional CIITA cDNA failed to induce HLA class II expression in typical neuroblastoma cells. Confocal microscopy and Western blot analysis suggested a defective nuclear translocation and/or reduced protein synthesis in CIITA-transfected NB cells. Altogether, these data point to multiple mechanisms preventing HLA class II expression in the neuroblastoma, either involving CIITA promoter-IV silencing, or acting at the CIITA post-transcriptional level.

The impact of monoclonal antibodies (mAbs) in the treatment of human tumors has greatly increased in recent years. mAb engineering has allowed reducing the immunogenicity of therapeutic antibodies as well as improving their biodistribution. Furthermore, engineered mAbs have been used to vehiculate toxins, drugs and other anti-neoplastic agents to the tumor site. In the case of neuroblastoma (NB), a pediatric malignancy originating from the neural crest, both murine and chimeric antibodies against the tumor associated antigen GD2 have been tested in clinical trials, either alone or in combination with cytokines. A novel promising approach to mAb engineering is the small immuno-protein (SIP) technique, whereby the variable regions of heavy and light chains of a mAb with a given specificity are connected to the dimerizing CH(3) domain of an immunoglobulin molecule. The current status of mAb therapy for NB is discussed together with our preliminary results on the generation of novel anti-GD2 molecules using the SIP technique.

In this study, a new syngeneic murine neuroblastoma (NB) model resembling stage 3 NB with thoracic localization has been set up by intramediastinal injection of tumor cells. Two NB cell lines, the murine Neuro2a, and the hybrid NXS2, have been injected in A/J mice. In vivo tumor growth and dissemination have been assessed by macroscopic and microscopic histological analysis performed at different times post injection. Tumor cell localization and growth patterns were compared to those obtained by i.v. and r.p. injections. The results indicated that in the thoracic model both tumor cell lines grow rapidly as huge tumor masses but do not metastatize to distant organs. This new model may be relevant for testing the efficacy of novel immunotherapeutic strategies for poor prognosis NB patients with localized disease.

Immunization of cancer patients with cytokine-engineered tumor cells is being currently tested in several trials. To test the feasibility of this approach in neuroblastoma (NB) patients we investigated the functional consequences of interleukin-2 (IL-2) gene transfer into NB cell lines. Two human NB cell lines were transfected with the plasmid expression vector RSV.5neo containing the human IL-2 cDNA, and their tumorigenicity was evaluated in a nude mice xenograft model after characterization of the growth patterns and phenotypic features in vitro. The combination of IL-2 gene transfection and the xenograft model in nude mice was chosen on the basis of the low or absent expression of HLA class I antigen in human NB tumors. Our aim was to evaluate the effectiveness of an immunization protocol that could elicit a nonspecific antitumor response. The IL-2 stable transfectants were morphologically identical to parental or vector-transfected cells but completely lost tumorigenicity and inhibited, through a bystander effect, the growth of parental cells injected simultaneously at the same site. Histologic and immunohistochemical analysis of the nodules showed extensive necrosis with severe endothelial damage. The infiltrating cells were mainly macrophages, while natural killer (NK) cells were scarce. However, depletion of NK cells by anti-CD122 monoclonal antibody indicated that the rejection process required NK cell activity. The relevance of these data for the development of therapeutic approaches using cytokine-engineered NB cell lines is discussed.

The human MAGE-1, MAGE-3 and MART-1 genes code for antigens that are specifically recognized by cytolytic T lymphocytes in a MHC-restricted manner. The MAGE-1 and MAGE-3 genes are expressed in tumors of different histotypes but not in normal adult tissues (with the exception of testis), while the MART-1 gene appears to be selectively expressed in melanoma. MAGE-1, MAGE-3 and MART-1 antigens may therefore constitute useful targets for specific anti-tumor immunization of cancer patients. Here we have investigated the expression of MAGE-1, MAGE-3 and MART-1 in 11 neuroblastoma (NB) cell lines and 73 NB tumor masses. MAGE-1 and MAGE-3 transcripts were detected simultaneously in 36% of the cell lines and in 16% of tumor samples. The MAGE-1 gene was never expressed alone except in one tumor. In contrast, MAGE-3 mRNA was found in approximately 40% of the NB tumor samples in the absence of MAGE-1 mRNA. No expression of the MART-1 gene was observed in any cell line or tumor sample. No correlation was found between MAGE gene expression and clinical stage, event-free survival and presence or absence of N-myc amplification.