Glycoproteins and Gal-GalNAc cause Cryptosporidium to switch from an invasive sporozoite to a replicative trophozoite.

The apicomplexan parasite Cryptosporidium causes cryptosporidiosis, a diarrheal disease that can become chronic and life threatening in immunocompromised and malnourished people. There is no effective drug treatment for those most at risk of severe cryptosporidiosis. The disease pathology is due to a repeated cycle of host cell invasion and parasite replication that amplifies parasite numbers and destroys the intestinal epithelium. This study aimed to better understand the Cryptosporidium replication cycle by identifying molecules that trigger the switch from invasive sporozoite to replicative trophozoite. Our approach was to treat sporozoites of Cryptosporidium parvum and Cryptosporidium hominis, the species causing most human cryptosporidiosis, with various media under axenic conditions and examine the parasites for rounding and nuclear division as markers of trophozoite development and replication, respectively. FBS had a concentration-dependent effect on trophozoite development in both species. Trophozoite development in C. parvum, but not C. hominis, was enhanced when RPMI supplemented with 10% FBS (RPMI-FBS) was conditioned by HCT-8 cells for 3h. The effect of non-conditioned and HCT-8 conditioned RPMI-FBS on trophozoite development was abrogated by proteinase K and sodium metaperiodate pretreatment, indicating a glycoprotein trigger. Cryptosporidium parvum and C. hominis trophozoite development also was triggered by Gal-GalNAc in a concentration-dependent manner. Cryptosporidium parvum replication was greatest following treatments with Gal-GalNAc, followed by conditioned RPMI-FBS and non-conditioned RPMI-FBS (P<0.05). Cryptosporidium hominis replication was significantly less than that in C. parvum for all treatments (P<0.05), and was greatest at the highest tested concentration of Gal-GalNAc (1mM).

Immunogenicity study of Globo H analogues with modification at the reducing or nonreducing end of the tumor antigen.

Globo H-based therapeutic cancer vaccines have been tested in clinical trials for the treatment of late stage breast, ovarian, and prostate cancers. In this study, we explored Globo H analogue antigens with an attempt to enhance the antigenic properties in vaccine design. The Globo H analogues with modification at the reducing or nonreducing end were synthesized using chemoenzymatic methods, and these modified Globo H antigens were then conjugated with the carrier protein diphtheria toxoid cross-reactive material (CRM) 197 (DT), and combined with a glycolipid C34 as an adjuvant designed to induce a class switch to form the vaccine candidates. After Balb/c mice injection, the immune response was studied by a glycan array and the results showed that modification at the C-6 position of reducing end glucose of Globo H with the fluoro, azido, or phenyl group elicited IgG antibody response to specifically recognize Globo H (GH) and the GH-related epitopes, stage-specific embryonic antigen 3 (SSEA3) (also called Gb5) and stage-specific embryonic antigen 4 (SSEA4). However, only the modification of Globo H with the azido group at the C-6 position of the nonreducing end fucose could elicit a strong IgG immune response. Moreover, the antibodies induced by these vaccines were shown to recognize GH expressing tumor cells (MCF-7) and mediate the complement-dependent cell cytotoxicity against tumor cells. Our data suggest a new potential approach to cancer vaccine development.

Carbohydrate-based vaccines with a glycolipid adjuvant for breast cancer.

Globo H (GH) is a hexasaccharide specifically overexpressed on a variety of cancer cells and therefore, a good candidate for cancer vaccine development. To identify the optimal carrier and adjuvant combination, we chemically synthesized and linked GH to a carrier protein, including keyhole limpet hemocyanion, diphtheria toxoid cross-reactive material (CRM) 197 (DT), tetanus toxoid, and BSA, and combined with an adjuvant, and it was administered to mice for the study of immune response. Glycan microarray analysis of the antiserum obtained indicated that the combination of GH-DT adjuvanted with the α-galactosylceramide C34 has the highest enhancement of anti-GH IgG. Compared with the phase III clinical trial vaccine, GH-keyhole limpet hemocyanion/QS21, the GH-DT/C34 vaccine elicited more IgG antibodies, which are more selective for GH and the GH-related epitopes, stage-specific embryonic antigen 3 (SSEA3) and SSEA4, all of which were specifically overexpressed on breast cancer cells and breast cancer stem cells with SSEA4 at the highest level (>90%). We, therefore, further developed SSEA4-DT/C34 as a vaccine candidate, and after immunization, it was found that the elicited antibodies are also IgG-dominant and very specific for SSEA4.

Effect of Gb3 in lipid rafts in resistance to Shiga-like toxin of mutant Vero cells.

Shiga-like toxin 1 (Stx1), produced by enterohemorrhagic Escherichia coli, binds to its receptor, globotriaosylceramide (Gb3), on target cell membranes, as a prerequisite for inducing host cell intoxication. To examine further toxin-receptor interactions, we established an Stx1-resistant clone of Vero cells by chemical mutagenesis. The mutant cells, expressed Gb3, but did not bind Stx1. These mutant cells were larger and had more Gb3 per cell than wild-type cells. Gb3 from both wild-type and mutant Vero cells was recovered in lipid rafts, isolated from cell lysates as detergent resistant membranes (DRMs); the DRMs derived from mutant cells had a lower density of Gb3 than did those from wild-type cells. Stx1 did not bind to the DRMs of mutant cells, both by ELISA and surface plasmon resonance. However, Stx1 bound to Gb3 separated by thin-layer chromatograms from the DRMs of mutant cells. The results indicate that not only presence of Gb3 but also Gb3 density on lipid rafts were important for Stx binding.

Efficient metabolic engineering of GM3 on tumor cells by N-phenylacetyl-D-mannosamine.

Abnormal carbohydrates expressed on tumor cells, which are termed tumor-associated carbohydrate antigens (TACAs), are potential targets for the development of cancer vaccines. However, immune tolerance to TACAs has severely hindered progress in this area. To overcome this problem, we have developed a novel immunotherapeutic strategy based on synthetic cancer vaccines and metabolic engineering of TACAs on tumor cells. One critical step of this new strategy is metabolic engineering of cancer, namely, to induce expression of an artificial form of a TACA by supplying tumors with an artificial monosaccharide precursor. To identify the proper precursor for this application, N-propionyl, N-butanoyl, N-isobutanoyl, and N-phenylacetyl derivatives of d-mannosamine were synthesized, and their efficiency as biosynthetic precursors in modifying sialic acid and inducing expression of modified forms of GM3 antigen on tumor cells was investigated. For this purpose, tumor cells were incubated with different N-acyl-d-mannosamines, and modified forms of GM3 expressed on tumor cells were analyzed by flow cytometry using antigen-specific antisera. N-Phenylacetyl-d-mannosamine was efficiently incorporated in a time- and dose-dependent manner to bioengineer GM3 expression by several tumor cell lines, including K562, SKMEL-28, and B16-F0. Moreover, these tumor cell lines also exhibited ManPAc-dependent sensitivity to cytotoxicity mediated by anti-PAcGM3 immune serum and complement. These results provide an important validation for this novel therapeutic strategy. Because N-phenylacetyl GM3-protein conjugates are particularly immunogenic, the combination of an N-phenylacetyl GM3 conjugate vaccine with systemic N-phenylacetyl-d-mannosamine treatment is a promising immunotherapy for future development and application to melanoma and other GM3-bearing tumors.

Enhanced pro-inflammatory chemokine/cytokine response triggered by pathogenic Entamoeba histolytica : basis of invasive disease.

The virulence of Entamoeba histolytica is governed by adhesion/colonization in the gut which is mediated by a galactose specific lectin. Two morphologically identical but distinct species i.e. pathogenic E. histolytica and non-pathogenic E. dispar, can be differentiated by distinct epitopes in the lectin. Both species bind to colonic epithelial cells, but only E. histolytica infection induces an inflammatory response and subsequent pathogenesis. Thus, comparing the responses of the intestinal cells to pathogenic and non-pathogenic lectins is a point of interest. The pathogenic lectin causes cytolysis of epithelial and immune-competent cells. Our data (both qualitative and mRNA quantitation) indicate that the epithelial cells responded to E. histolytica lectin with an increased expression of pro-inflammatory IL-2, IL-6, IL-8, MIP-1alpha, MCP-1, RANTES, GROalpha and GMCSF as compared to E. dispar lectin. The pathogenic LCM induced a significant increase in intracellular calcium concentration, proliferative response and chemotaxis of lymphocytes from ALA patients as compared to non-pathogenic LCM. High RANTES and IL-6 were induced in patients' lymphocytes by pathogenic LCM, along with their receptors CCR5 and CD126 as compared to NP-LCM. The local release of such a complex network of cytokines/chemokines could explain the histopathology of E. histolytica infection. The comparative low levels of these chemokines/pro-inflammatory cytokines and high levels of anti-inflammatory IL-10 in response to non-pathogenic E. dispar could explain the absence of an acute inflammatory response and the disease process. The cytokines and chemokines may provide a mechanism for initiation, amplification or containment of inflammation during disease state.

Binding of galectin-1 (gal-1) on trophoblast cells and inhibition of hormone production of trophoblast tumor cells in vitro by gal-1.

Galectin-1 (gal-1), a member of the mammalian beta-galactoside-binding proteins, recognizes preferentially Galbeta1-4GlcNAc sequences of oligosaccharides associated with several cell surface glycoconjugates. As demonstrated histochemically, the lectin recognizes appropriate glycoepitopes on the syncytiotrophoblast and on chorionic carcinoma cells (BeWo). Freshly isolated trophoblast cells and trophoblast tumor cells Jeg3 did not bind gal-1. BeWo cells in contrast to Jeg3 form a syncytium in vitro and synthesize progesterone as well as hCG. BeWo cells were used as an approach to study the effects of gal-1 on hormone production. The lectin decreased cellular hCG and progesterone production as well as hCGbeta gene transcription as measured by real-time RT-PCR. Gal-1 mediated inhibition of cellular progesterone production was reduced in the presence of a Thomsen-Friedenreich (TF)-polyacrylamide conjugate. Inhibition of cellular hCG and progesterone production was also induced by anti-TF monoclonal antibodies. The results demonstrate that ligation of Galbeta1-4GlcNAc and Galbeta1-3GalNAc (TF) epitopes on BeWo cells may have regulatory effects on hCG and progesterone production.

Clinical development of the STn-KLH vaccine (Theratope).

The development of active specific immunotherapy depends on the identification of altered cancer cell-specific molecules or epitopes that are immunogenic. Many cancer-specific peptide or glycoprotein target antigens have been identified. Tumors carrying aberrant epitopes as a result of underglycosylation of mucins are associated with poor prognosis in many epithelial cancers. The aberrant mucin sialyl-Tn (STn) epitope, in addition to being a predictor of poor prognosis when expressed in tumors, is associated with increased aggressiveness and metastatic potential, making it a promising target for immunotherapy. The STn-keyhole limpet hemocyanin (KLH) vaccine (Theratope) is an investigational active specific immunotherapy consisting of a synthetic STn epitope conjugated to a high molecular weight protein carrier, KLH. The immune response generated by the STn-KLH vaccine is both humoral and cellular. More than 1000 breast cancer patients with metastatic disease are currently enrolled in a phase III clinical trial to assess the safety and efficacy of the STn-KLH vaccine. Interim analysis from a current phase III trial has confirmed the safety of the STn-KLH vaccine, and the clinical outcome awaits the final analysis expected in 2003.

Imbalanced substrate specificity of mutant beta-galactosidase in patients with Morquio B disease.

G(M1)-gangliosidosis and Morquio B disease are distinct in clinical and biochemical features, but both disorders are caused by genetic defects of the same enzyme, acid beta-galactosidase (beta-Gal). We analyzed the kinetic properties of mutant beta-Gals from patients with G(M1)-gangliosidosis and Morquio B disease to examine the clinical and biochemical differences between both disorders. Five skin fibroblast lines from patients with G(M1)-gangliosidosis (2 cases; R201C/R201C and I51T/I51T), Morquio B disease (2 cases; W273L/W273L and Y83H/R482C), and galactosialidosis (1 case; Y395C/S90L) were used as enzyme sources. Residual enzyme activity in the cells was subjected to kinetic analysis. Substrate analogs including Galbeta1-3GalNAc, as an analog for G(M1)-ganglioside, and Galbeta1-4GlcNAc, as an analog for keratan sulfate, were used to determine IC(50) and K(i) for beta-Gals with an artificial substrate (4-methylumbelliferyl beta-D-galactopyranoside). Enzymatic assay method was established to examine the hydrolytic activity with the mutant beta-Gal for the substrate analogs. The mutant beta-Gal activities were inhibited by Galbeta1-3GalNAc and Galbeta1-4GlcNAc in a concentration-dependent manner. Remarkable increase in IC(50) ratio and K(i) ratio (Galbeta1-4GlcNAc/Galbeta1-3GalNAc) was observed in Morquio B disease. Relative hydrolytic activity (Galbeta1-4GlcNAc/Galbeta1-3GalNAc) was markedly decreased in Morquio B disease as compared with other subjects; controls (means+/-SD, n=4), 1.00+/-0.02; galactosialidosis, 1.03; G(M1)-gangliosidosis, 1.15 and 1.00; and Morquio B disease, 0.27 and 0.32. The mutant beta-Gals from the patients with Morquio B disease exhibited lower affinity and lower hydrolytic activity toward Galbeta1-4GlcNAc rather than Galbeta1-3GalNAc. These findings suggest that imbalanced substrate specificity of the mutant beta-Gals induces predominant accumulation of keratan sulfate and a rationale for performing differential diagnostic analysis for both disorders.

Cancer vaccines, a critical review--Part II.

Cancer vaccines have been explored clinically against melanomas, adenocarcinomas and lymphomas. Breast cancer vaccines include Theratope, MUC1 mucin peptides and HER-2/neu peptide vaccines. Phase II trials suggest prolongation of survival of advanced breast cancer patients who generate high titers of antibody to Theratope. In contrast, melanoma ganglioside vaccines, which also elicit only antibodies, have not been effective in improving survival in controlled trials. Anti-idiotype vaccines for solid tumors, which depend upon mimicry of the tumor-associated antigens, have also had limited success. In lymphomas, where the idiotypes are the tumor-associated antigens, greater success has been achieved. A number of tumor-associated antigens have been identified in melanoma, such as the lineage related cancer-testis group (MAGE) and tyrosinase-related antigens. Non-lineage related antigens shared among a variety of very different tumors have recently been demonstrated too, which may permit immunization against more than one tumor group. Telomerase and MG50, one of several interleukin-1 receptor antagonist molecules, are both immunogenic and widespread in their representation. Carcinoembryonic antigen is the basis for vaccines against many adenocarcinomas. Both viral and non-viral vectors are being used to improve the reactivity to peptides in adenocarcinomas. Dendritic cell-carried vaccines, which package the antigens ex vivo rather than depending upon in vivo uptake, are being extensively explored in clinical models to improve the effectiveness of defined vaccines, such as peptides and RNA. 'Naked' DNA vaccines injected intramuscularly also have their advocates. Among the most recent attempts to improve the immunogenicity of vaccines is the use of antigens newly identified by genomic techniques and 'superagonist' peptide mimics, selected from combinatorial peptide libraries. These modern biochemical and molecular biological methods may greatly expand our ability to immunize against tumor antigens, which are essentially 'self' molecules. Finally, a greater understanding of ways in which tumors escape immunological detection or thwart immunological responses should lead to improved strategies against the tumor to augment the effect of vaccination.

Mechanisms of attachment and internalization of Cryptosporidium parvum to biliary and intestinal epithelial cells.

BACKGROUND & AIMS: Although infection of the intestinal and biliary tracts by Cryptosporidium parvum is a major problem in patients with the acquired immunodeficiency syndrome, the specific microbial and host molecules involved in C. parvum infection are unknown. We tested the hypothesis that lectin-carbohydrate interactions and cytoskeleton reorganization are involved in the infection of biliary and intestinal epithelia by C. parvum. METHODS: In vitro models of cryptosporidial infection using human biliary and intestinal epithelial cell lines were used to assay C. parvum attachment and invasion. RESULTS: Exposure of C. parvum sporozoites to the sugar, galactose-N-acetylgalactosamine (Gal/GalNAc), and to bovine mucin reduced C. parvum attachment to biliary and intestinal epithelia up to 70%. Preincubation of cell monolayers with either lectins specific to Gal/GalNAc, or glycosidases that specifically release Gal/GalNAc oligosaccharides from glycoproteins, decreased attachment up to 80%. Cytochalasin B and cytochalasin D, but not nocodazole, decreased invasion of cells by C. parvum up to 70% without affecting attachment. During cell invasion (but not attachment), confocal microscopy showed recruitment of actin (but not tubulin) in biliary and intestinal epithelia directly adjacent to C. parvum. CONCLUSIONS: Gal/GalNAc epitopes of glycoproteins on the epithelial apical membrane and Gal/GalNAc-specific sporozoite surface lectins are involved in the mechanism(s) of C. parvum attachment to intestinal and biliary epithelial cells, and actin remodeling in host cells is required for C. parvum invasion.

Synthesis of tumor associated sialyl-T-glycopeptides and their immunogenicity.

Sialyl-T-glycopeptides were synthesized by solid-phase techniques, using a PEGA resin as the solid support. An appropriately protected building block containing alpha-Neu5Ac-(2 --> 3)-beta-Gal-(1 --> 3)-alpha-GalN3-(1-->) attached to Fmoc-Thr/Ser-OPfp was employed in a solid phase glycopeptide assembly of a 10-mer glycopeptide, using a general Fmoc/OPfp-ester strategy. Reduction of the azido group of the GalN3 residue was effected on solid-phase, using DTT and DBU. After acidolytic cleavage from the resin, the methyl ester of the sialic acid residue and acetyl groups were removed with 30% NaOMe/MeOH in MeOH and water pH 14, at -30 degrees C for 2 h. At this low temperature, the highly basic conditions did not result in any detectable beta-elimination. However, one O-acetyl group, located at the 2-position of the Gal was resistant to hydrolysis. To remove this remaining acetyl group, reaction with hydrazine hydrate in CHCl3 and MeOH at room temperature for 2.5 h was successful. The two target sequences of sialyl-T-glycopeptides were obtained in good yield. In contrast to the the analogs carrying the T-antigen, the Sial-T-glycopeptides were nonimmunogenic, supporting the idea that the sialylation is a method of circumventing the recognition by the immune system.

Tumor-associated antigens are cytokine inducers and hyporeactivity factors to the immune system.

We investigated possible mechanisms leading to the inhibition of the immune system in people with chronic disorders. Tumor cell produce protein released into the circulation, such as tumor associated antigens, may play an important role in processes preceding paralysis of the immune system. To test this hypothesis the following tumor associated antigens were used: AFP, OFP, CA-125, CA-50 and CA-19-9. Their role was assessed by modulating cytokine production in cord blood lymphocytes and peripheral white blood cells obtained from grown population of patients treated with colostrinin, an cytokine inducer. PHA, LPS and colostrinin were used as positive control in those essays. Each antigen tested individually induced IFN, TNF alpha and IL-6 in dose dependent fashion. None of the tested cytokines were spontaneously released by the cells. Data generated from these experiments indicated that tumor associated antigens are inducing type 1 cytokines in similar fashion as LPS or colostrinin. However, lymphocytes taken from patients undergoing therapy with colostrinin revealed progressive loss capability to produce type 1 cytokines as they did in case of colostrinin. The loss of the capability to respond to antigen may represent phenomenon leading to immune tolerance.