Influence des antigènes de groupes sanguins en transplantation

Blood group antigens seem to be implied in the mechanisms of tissue and cell rejection. All erythrocyte blood groups are not only demonstrated on red cells. Some of them can be observed on several tissues of the body, particularly antigens of ABO, Hh, Lewis and I(i) systems... These ubiquitory antigens, called "histo-antigens" are developed very early at the various embryofetal stages depending on the tissues. The ABO system plays a fundamental role in graft and transplant. If the ABO compatibility is fundamental for the prognosis of a kidney, liver and heart transplantation, it has only a minor effect on the marrow, bone or cornea transplantation. The physiopathologic mechanisms are known, for the main points, and in connection with ABH antigens presence. Recent works show that systems RH, FY and JK could play a role in the process of graft rejection.

Regulation of metastasis-suppressive gene Nm23-H1 on glycosyl-transferases involved in the synthesis of sialyl Lewis antigens

By using reverse transcriptase-polymerase chain reaction (RT-PCR), the mRNA expressions of three families of glycosyltransferases involved in the synthesis of sialyl Lewis antigens were determined in H7721 human hepatocarcinoma cell line before and after the transfection of metastasis-suppressive gene nm23-H1. These glycosyltransferases included alpha1,3fucosyltransferase (alpha1,3FucT)-III, -IV, -VI, -VII, and -IX, alpha2,3-sialyltransferase (ST3Gal)-I, -II, -III, and -IV as well as O-glycan core 2 beta1,6 N-acetylglucosaminyltransferase (C2GnT)-I and -II. In mock cells transfected with the vector, the expression-order of alpha1,3FucTs was IV>VI>III>VII>IX, that of ST3Gals was IV>I>II>III, and that of C2GnT was I>II. Nm23-H1 downregulated the mRNA expressions of all five subtypes of alpha1,3FucT and -I, -III, -IV subtypes of ST3Gal, but not ST3Gal-II and C2GnT-I, II. On the other hand, the expressions of cell surface sialyl Lewis X (SLe(x)) and alpha2,3 sialyl residues were decreased on nm23-H1 transfected cells as detected with monoclonal antibody of SLe(x) and enzyme-labeled lectins, respectively. Since SLe(x) was reported to be a metastasis-associated glycan structure, the reduced expressions of SLe(x) and some enzymes related to its synthesis may be one of the mechanisms to explain the metastasis-suppressive effect of nm23-H1.

Enhanced Efficacy of Radioimmunotherapy with 90Y-CHX-A″-DTPA-hu3S193 by Inhibition of Epidermal Growth Factor Receptor (EGFR) Signaling with EGFR Tyrosine Kinase Inhibitor AG1478

PURPOSE

Monoclonal antibodies and tyrosine kinase inhibitors specific for the epidermal growth factor receptor (EGFR) have been shown to enhance the effect of external beam radiation on EGFR-positive tumors. The effect of EGFR signaling abrogation by EGFR tyrosine kinase inhibitor on the efficacy of radioimmunotherapy has not been reported previously. This study investigated the effect of EGFR tyrosine kinase inhibition on the efficacy of radioimmunotherapy in a human cancer xenograft model.

EXPERIMENTAL DESIGN

The humanized anti-Lewis Y antibody hu3S193 and the EGFR tyrosine kinase inhibitor AG1478 were studied. BALB/c nude mice were engrafted with A431 squamous carcinoma cells. Initial biodistribution properties of the 90Y-CHX-A''-DTPA-hu3S193 were evaluated in this model. In therapy experiments, cohorts of four to five xenografted mice were treated with saline as placebo, 0.4 mg AG1478 i.p. (six doses over 2 weeks), single i.v. injections of unlabeled hu3S193, or 90Y-CHX-A''-DTPA-hu3S193 (12.5, 25, 50, or 100 microCi). The combination of 0.4 mg AG1478 i.p. and 25 microCi 90Y-CHX-A''-DTPA-hu3S193 i.v. was subsequently evaluated in the A431 model.

RESULTS

90Y-CHX-A''-DTPA-hu3S193 retained excellent immunoreactivity after radiolabeling. The biodistribution study showed excellent uptake in tumor (90.33 +/- 38.84%ID/g) peaking at 24 to 72 hours after injection and with prolonged retention. 90Y-CHX-A''-DTPA-hu3S193 significantly inhibited A431 xenograft growth at 25, 50, and 100 microCi doses. The combination of 0.4 mg AG1478 with a single dose of 25 microCi 90Y-CHX-A''-DTPA-hu3S193 resulted in a significant enhancement of efficacy compared with either agent alone (P = 0.013).

CONCLUSIONS

The efficacy of radioimmunotherapy with 90Y-CHX-A''-DTPA-hu3S193 is significantly enhanced by EGFR tyrosine kinase inhibitor AG1478. Further investigations of dosing regimens using EGFR tyrosine kinase inhibitors and radioimmunotherapy in the treatment of EGFR expressing tumors are warranted.

Carbohydrate Mimotopes in the Rational Design of Cancer Vaccines

The task of rationally designing vaccines that can effectively impact on the survival of cancer patients remains challenging. Monoclonal antibodies and T cell receptors have proven to be viable templates for the application of pharmacophore design principles to develop antigens and immunogens as these immune system molecules recognize a variety of sequentially and structurally unrelated ligands. This structural information combined with immunological assessment has contributed to the development of strategies to elicit effective humoral and cellular responses to cancer cells. Understanding the structural requirements for antibody and T cell recognition provides a basis for identifying potentially new sets of immunogens that may have both fundamental immunological and clinical value. Here we review the structural concepts and approaches used in vaccine design applications that illustrate the value and limitations of using chemical (peptide libraries) and immunological information to define novel peptide immunogens that function as mimotopes to generate immune responses targeting tumor associated carbohydrate antigens.

DC-SIGN mediates binding of dendritic cells to authentic pseudo-LewisY glycolipids of Schistosoma mansoni cercariae, the first parasite-specific ligand of DC-SIGN

During schistosomiasis, parasite-derived glycoconjugates play a key role in manipulation of the host immune response, associated with persistence of the parasite. Among the candidate host receptors that are triggered by glycoconjugates are C-type lectins (CLRs) on dendritic cells (DCs), which in concerted action with Toll-like receptors determine the balance in DCs between induction of immunity versus tolerance. Here we report that the CLR DC-SIGN mediates adhesion of DCs to authentic glycolipids derived from Schistosoma mansoni cercariae and their excretory/secretory products. Structural characterization of the glycolipids, in combination with solid phase and cellular binding studies revealed that DC-SIGN binds to the carbohydrate moieties of both glycosphingolipid species with Galbeta1-4(Fucalpha1-3)GlcNAc (Lewis(X)) and Fucalpha1-3Galbeta1-4(Fucalpha1-3)GlcNAc (pseudo-Lewis(Y)) determinants. Importantly, these data indicate that surveying DCs in the skin may encounter schistosome-derived glycolipids immediately after infection. Recent analysis of crystals of the carbohydrate binding domain of DC-SIGN bound to Lewis(X) provided insight into the ability of DC-SIGN to bind fucosylated ligands. Using molecular modeling we showed that the observed binding of the schistosome-specific pseudo-Lewis(Y) to DC-SIGN is not directly compatible with the model described. To fit pseudo-Lewis(Y) into the model, the orientation of the side chain of Phe(313) in the secondary binding site of DC-SIGN was slightly changed, which results in a perfect stacking of Phe(313) with the hydrophobic side of the galactose-linked fucose of pseudo-Lewis(Y). We propose that pathogens such as S. mansoni may use the observed flexibility in the secondary binding site of DC-SIGN to target DCs, which may contribute to immune escape.

A single-step method for the production of sugar hydrazides: intermediates for the chemoselective preparation of glycoconjugates

The ability to selectively conjugate carbohydrate molecules to a protein is a key step in the preparation of conjugate vaccines, while facile methods for linking carbohydrates to polymers or solid surfaces to produce diagnostic probes and functional microarrays are also sought. Here, we describe a simple, single-step method of producing glycosylhydrazides from unprotected sugars, which were then linked in a controlled manner to a desired carrier, through an appropriate linker. The method was chemoselective and did not require coupling reagents, and the native pyranose form of the reducing end residue was retained. Initially, mono- and disaccharide hydrazides were produced from the corresponding reducing sugars and linked to BSA through a bifunctional linker. Final exemplification of the procedure was demonstrated by the preparation of a LewisY tetrasaccharide protein conjugate, which was recognized by a LewisY monoclonal antibody indicating the preservation of the natural conformation of the tetrasaccharide in the final construct. It is envisaged that this method will have general applicability to a variety of functionally diverse reducing sugars and provide a route to highly defined glycoconjugates, without the need for elaborate synthetic strategies.

Dendritic cells recognize tumor-specific glycosylation of carcinoembryonic antigen on colorectal cancer cells through dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin

Dendritic cells play a pivotal role in the induction of antitumor immune responses. Immature dendritic cells are located intratumorally within colorectal cancer and intimately interact with tumor cells, whereas mature dendritic cells are present peripheral to the tumor. The majority of colorectal cancers overexpress carcinoembryonic antigen (CEA), and malignant transformation changes the glycosylation of CEA on colon epithelial cells, resulting in higher levels of Lewis(x) and de novo expression of Lewis(y) on tumor-associated CEA. Dendritic cells express the C-type lectin dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN) that has high affinity for nonsialylated Lewis antigens, so we hypothesized that DC-SIGN is involved in recognition of colorectal cancer cells by dendritic cells. We show that immature dendritic cells within colorectal cancer express DC-SIGN and that immature dendritic cells but not mature dendritic cells interact with tumor cells. DC-SIGN mediates these interactions through binding of Lewis(x) and Lewis(y) carbohydrates on CEA of colorectal cancer cells. In contrast, DC-SIGN does not bind CEA expressed on normal colon epithelium that contains low levels of Lewis antigens. This indicates that dendritic cells may recognize colorectal cancer cells through binding of DC-SIGN to tumor-specific glycosylation on CEA. Similar to pathogens that target DC-SIGN to escape immunosurveillance, tumor cells may interact with DC-SIGN to suppress dendritic cell functions.

A novel Helicobacter pylori cell-surface polysaccharide

Helicobacter pylori bacteria colonize the gastric mucosa of more than half of the world's human population and its infection may instigate a wide spectrum of gastric diseases in the host. At the moment, there is no vaccine against H. pylori, a microorganism recognized as a category 1 human carcinogen, and treatment is limited to antibiotic management. Pioneering antigenic studies carried out by Penner and co-workers, which employed homologous H. pylori antisera specific for cell-surface lipopolysaccharide (LPS), revealed the presence of six distinct H. pylori serotypes (O1 to O6). Subsequent studies have shown that H. pylori serotype O1 expressed LPS with lengthy O-chain polysaccharide (PS) composed of Lewis blood-group structures ('Lewis O-chains'), serotype O3 LPS produced 'Lewis O-chains' attached to a heptoglycan domain, serotype O4 LPS possessed LPS with glucosylated 'Lewis O-chains' and serotype O6 LPS expressed the heptoglycan domain capped by a short 'Lewis O-chain'. These LPSs were terminated at the reducing-end by a core oligosaccharide and lipid A of conserved structures. With the intent of formulating a multivalent H. pylori LPS-based vaccine, we are studying the structural variability of H. pylori cell-surface glycans. Here, we describe the novel LPS structure produced by H. pylori serotype O2 that differed markedly from the typical H. pylori 'Lewis O-chain' structures, in that its main component was an elongated PS composed of alternating 2-, and 3-monosubstituted alpha-D-Glcp residues [-->2)-alpha-D-Glcp-(1-->3)-alpha-D-Glcp-(1-->]n. These findings revealed the bio-molecular basis for the observed serospecificity of H. pylori serotype O2, and that this unique bacterial PS must be included in the formulation of a multivalent LPS H. pylori vaccine.

Synthesis of Selected LeY and KH-1 Analogues: A Medicinal Chemistry Approach to Vaccine Optimization

[structure: see text] As part of our ongoing anticancer vaccine program, we recently found that antibodies generated in response to the KH-1-KLH construct recognized not only KH-1 antigen but also the Lewis Y (Le(y)) antigen as well, with antibody titer levels much higher than those observed after immunization with individual Le(y)-KLH vaccine constructs. In an attempt to explore the structure-antigenic relationship of these carbohydrate epitopes, several analogues of both KH-1 and Le(y) were synthesized. A convergent synthetic approach to the analogues was designed on the basis of well-established glycal methodology, employing a minimum number of building blocks to generate competent antigens with high stereoselectivity and reasonable yield.

Lewis epitopes on outer membrane vesicles of relevance to Helicobacter pylori pathogenesis

BACKGROUND

Helicobacter pylori extrudes protein- and lipopolysaccharide-enriched outer membrane vesicles from its cell surface which have been postulated to act to deliver virulence factors to the host. Lewis antigen expression by lipopolysaccharide of H. pylori cells has been implicated in a number of pathogenic roles. The aim of this study was to further characterize the expression of lipopolysaccharide on the surface of these outer membrane vesicles and, in particular, expression of Lewis antigens and their association with antibody production in the host.

MATERIALS AND METHODS

H. pylori strains were examined for outer membrane vesicle production using transmission electron microscopy and Lewis antigen expression probed using immunoelectron microscopy. Sera from patients were analyzed for cross-reacting anti-Lewis antibodies and, subsequently, absorbed using outer membrane vesicle preparations to remove the cross-reacting antibodies.

RESULTS

The formation of outer membrane vesicles by H. pylori was observed in both in vitro and in vivo samples. Furthermore, vesicles were produced following culture in either liquid or solid medium by all strains examined. Moreover, we observed the presence of Lewis epitopes on outer membrane vesicles using immunoelectron microscopy and immunoblotting. Circulating anti-Lewis antibodies were found in the sera of gastric cancer patients but not in the sera of H. pylori-negative control subjects. Absorption of patient sera with outer membrane vesicles decreased the levels of anti-Lewis autoantibodies.

CONCLUSIONS

Our results demonstrate the ability of H. pylori to generate outer membrane vesicles bearing serologically recognizable Lewis antigens on lipopolysaccharide molecules which may contribute to the chronic immune stimulation of the host. The ability of these vesicles to absorb anti-Lewis autoantibodies indicates that they may, in part, play a role in putative autoimmune aspects of H. pylori pathogenesis.

Clinical evaluation of BR96 sFv-PE40 immunotoxin therapy in canine models of spontaneously occurring invasive carcinoma

PURPOSE

The immunotoxin BR96 sFv-PE40 is an effective antitumor agent against human breast and lung carcinoma xenografts in rodents. This study was designed to (a) determine the frequency with which canine carcinoma cells express Lewis(y) (Le(y)) antigen, thereby identifying canine carcinoma types suitable for the clinical evaluation of BR96 sFv-PE40, and (b) determine the safety and efficacy of BR96 sFv-PE40 in a canine model of spontaneously occurring cancers for investigation of targeted therapy.

EXPERIMENTAL DESIGN

Carcinoma tissue samples were obtained from client-owned dogs presented for medical care. The tissues were assessed for Le(y) antigen expression using immunohistochemical methods. Dogs with tumors expressing Le(y) antigen were offered enrollment in a clinical trial to receive twice-weekly infusions of 4 to 12 mg/m(2) BR96 sFv-PE40. Clinical toxicity and response data were assessed at each treatment.

RESULTS

Twenty-two of 61 carcinomas evaluated were positive for Le(y) expression, including mammary, prostate, lung, and rectal carcinomas, and 12 dogs were enrolled in the clinical trial. The primary side effect was transient emesis. Partial responses or disease stabilization were noted in dogs with inflammatory mammary, bronchogenic, rectal, and tonsillar carcinoma. At least nine of the dogs developed antibodies to the immunotoxin after two to five infusions.

CONCLUSIONS

Although development of anti-BR96 sFv-PE40 antibodies limited the long-term effectiveness of this immunotoxin in dogs, rapid clinical responses in several aggressive canine carcinomas suggest the immunotoxin has utility for treatment of certain naturally occurring tumors and that its clinical evaluation for treatment of similar human carcinomas is warranted.

Metastability of Helicobacter pylori bab adhesin genes and dynamics in Lewis b antigen binding

Heterogeneity among Helicobacter pylori strains in gastric epithelial adherence is postulated to contribute to pathogen fitness in the physiologically diverse human population. H. pylori adherence to ABO and Lewis b (Leb) blood group antigens in the human stomach is mediated by the blood group antigen-binding adhesin BabA. Approximately 70% of Swedish and U.S. H. pylori clinical isolates exhibit Leb binding, but here we show that the babA gene is present in each of 10 Leb-nonbinding strains. Fluorescence microscopy identified occasional bacterial cells with a Leb-binding phenotype in populations of Leb-nonbinding strains. Thus, nonbinding seemed to be a metastable phenotype. To model metastable transition into the virulence-associated Leb-binding mode, Leb-binding clones were isolated from nonadherent strains by panning with Leb-magnetic beads and characterized. Strain 17875 has two babA genes, babA1 (silent) and babA2 (expressed). We found that a babA2-cam derivative of strain 17875 regained Leb binding by recombination of the formerly silent babA1 gene into the expressed and partially homologous babB locus. The chimeric BabB/A adhesin binds Leb with an affinity similar to that of wild-type BabA adhesin, but its expression level was lower and was subject to phase variation through slipped-strand mispairing. Equivalent results were obtained with strain NCTC11638. We propose that adhesin metastability and heterogeneity contributes to bacterial fitness and results in some clones having potential for periodic activation and deactivation of virulence appropriate for intensity of the host response to infection.

Pretreatment with rituximab does not inhibit the human immune response against the immunogenic protein LMB-1

PURPOSE

Rituximab, a humanized monoclonal antibody directed to the CD20 antigen present on B lymphocytes, could potentially abrogate the humoral immune response to murine monoclonal antibodies or immunotoxins by depleting antibody-producing B cells.

EXPERIMENTAL DESIGN

A Phase II study of LMB-1, an immunotoxin targeting the Lewis Y tumor antigen, in combination with rituximab was conducted to test the hypothesis that rituximab could abolish or diminish the development of human antibodies to LMB-1. Five patients were treated in this study and received 375 mg/m(2) rituximab on days 1 and 7 followed by 45 micro g/kg/day LMB-1 on days 10, 12, and 14. The development of human antibodies against LMB-1 was detected using a serum neutralization and ELISA.

RESULTS

All five of the patients had a total suppression of circulating CD20/CD19 B-cell population before the administration of the first dose of the immunotoxin. Before rituximab treatment, the mean percentage of CD20/CD19-positive B cells in the five treated patients was 19.8% (range, 4.5-29.8%) of the total peripheral lymphocytes. After two doses of rituximab, CD20/CD19-positive B lymphocytes constituted </=0.1% of the total peripheral lymphocytes. Despite absent circulating antibody-producing B cells, before and during LMB-1 treatment, all of the patients developed neutralizing antibodies to the immunotoxin by day 21 of drug administration, which prevented retreatment.

CONCLUSIONS

Even though rituximab caused complete depletion of circulating CD20/CD19-positive B cells, it had no effect in suppressing the human antibody response to LMB-1 and may be of limited utility in suppressing human antibody responses to other immunogenic proteins.

Structural convergence of antibody binding of carbohydrate determinants in Lewis Y tumor antigens

Antibodies targeting human epithelial carcinomas bearing Lewis Y (Le(y)) carbohydrate antigens provide a striking illustration of convergent immune recognition. We report a 1.9A resolution crystal structure of the Fab of a humanized antibody (hu3S193) in complex with the Le(y) tetrasaccharide, Fuc(alpha 1-->2)Gal(beta 1-->4)[Fuc(alpha 1-->3)]GlcNAc. Comparisons of the hu3S193 and BR96 antibodies bound to Le(y) tumor antigens revealed extremely similar mechanisms for recognition of the carbohydrate epitopes. Solvent plays a critical role in hu3S193 antibody binding to the Le(y) carbohydrate epitope. Specificity for Le(y) is maintained because a conserved pocket accepts an N-acetyl group of the core Gal(beta 1-->4)GlcNAc disaccharide. Closely related blood-group determinants (Le(a) and Le(b)) cannot enter the specificity pocket, making the Le(y) antibodies promising candidates for immunotherapy of epithelial cancer.

Effects of fucosylated milk of goat and mouse on Helicobacter pylori binding to Lewis b antigen

AIM: To evaluate the effects of animal milk containing fucosylated antigens on Helicobacter pylori (H pylori) binding to Lewis b antigen.

METHODS: A mammary gland expression vector containing human α1-3/4-fucosyltransferase cDNA sequences was constructed. Transient expression of human α1-3/4-fucosyltransferase cDNA in goat mammary cell and establishment of transgenic mice were performed. The adhesion inhibitory properties of milk samples were analyzed by using H pylori.

RESULTS: Goat milk samples were found to inhibit bacterial binding to Lewis b antigen. The highest inhibition was observed 42 h after injection of the plasmid. The binding activity of H pylori to Lewis b antigen reduced mostly, by 83%, however milk samples from transgenic mice did not inhibit H pylori binding to Lewis b antigen.

CONCLUSION: The use of “humanized” animal milk produced by the transgenic introduction of fucosylated antigen can perhaps provide an alternative therapy and preventive measure for H pylori infection.

Generation of anti-idiotype antibodies for application in clinical immunotherapy laboratory analyses

The chimeric monoclonal antibody ch806 specifically targets the tumor-associated mutant epidermal growth factor receptor (de 2-7EGFR or EGFRVIII) and is currently under investigation for its potential use in cancer therapy. The humanised monoclonal antibody hu3S193 specifically targets the Lewis Y epithelial antigen and is currently in Phase I clinical trials in patients with advanced breast, colon, and ovarian carcinomas. To assist the clinical evaluation of ch806 and hu3S193, laboratory assays are required to monitor their serum pharmacokinetics and quantitate any immune responses to the antibodies. Mice immunized with ch806 or hu3S193 were used to generate hybridomas producing antibodies with specific binding to ch806 or hu3S193 and competitive for antigen binding. These anti-idiotype antibodies (designated Ludwig Melbourne Hybridomas, LMH) were investigated as reagents suitable for use as positive controls for HAHA or HACA analyses and for measuring hu3S193 or ch806 in human serum. Anti-idiotypes with the ability to concurrently bind two target antibody molecules were identified, which enabled the development of highly reproducible, sensitive, specific ELISA assays for determining serum concentrations of hu3S193 and ch806 with a 3 ng/mL limit of quantitation using LMH-3 and LMH-12, respectively. BIAcore analyses determined high apparent binding affinity for both idiotypes: LMH-3 binding immobilized hu3S193, Ka = 4.76 x 10(8) M(-1); LMH-12 binding immobilised ch806, Ka = 1.74 x 10(9) M(-1). Establishment of HAHA or HACA analysis of sera samples using BIAcore was possible using LMH-3 and LMH-12 as positive controls for quantitation of immune responses to hu3S193 or ch806 in patient sera. These anti-idiotypes could also be used to study the penetrance and binding of ch806 or hu3S193 to tumor cells through immunohistochemical analysis of tumor biopsies. The generation of anti-idiotype antibodies capable of concurrently binding a target antibody on each variable domain provides reagents with high sensitivity for the assessment of safety and pharmacokinetic profiles of target antibodies administered clinically.

Antibodies directed against Lewis-Y antigen inhibit signaling of Lewis-Y modified ErbB receptors

The majority of cancer cells derived from epithelial tissue express Lewis-Y (LeY) type difucosylated oligosaccharides on their plasma membrane. This results in the modification of cell surface receptors by the LeY antigen. We used the epidermal growth factor (EGF) receptor family members ErbB1 and ErbB2 as model systems to investigate whether the sugar moiety can be exploited to block signaling by growth factor receptors in human tumor cells (i.e., SKBR-3 and A431, derived from a breast cancer and a vulval carcinoma, respectively). The monoclonal anti-LeY antibody ABL364 and its humanized version IGN311 immunoprecipitated ErbB1 and ErbB2 from detergent lysates of A431 and SKBR-3, respectively. ABL364 and IGN311 blocked EGF- and heregulin-stimulated phosphorylation of mitogen-activated protein kinase [MAPK = extracellular signal-regulated kinase 1/2] in SKBR-3 and A431 cells. The effect was comparable in magnitude with that of trastuzumab (Herceptin) and apparently noncompetitive with respect to EGF. Stimulation of MAPK by ErbB was dynamin dependent and contingent on receptor internalization. ABL364 and IGN311 changed the intracellular localization of fluorescent EGF-containing endosomes and accelerated recycling of intracellular [(125)I]EGF to the plasma membrane. Taken together, these observations show that antibodies directed against carbohydrate side chains of ErbB receptors are capable of inhibiting ErbB-mediated signaling. The ability of these antibodies to reroute receptor trafficking provides a mechanistic explanation for their inhibitory action.

Killing of target cells by redirected granzyme B in the absence of perforin

Granzyme B (GzmB) is a potent apoptosis-inducing serine protease of cytotoxic lymphocytes. Following receptor-mediated endocytosis, GzmB is supposed to enter the cytosol through perforin-mediated membrane disruption. We investigated whether retargeting of GzmB to Lewis Y positive surface receptors could lead to perforin-independent target cell death. We coupled recombinant GzmB to the Lewis Y-binding antibody dsFv-B3. Targeting of GzmB to Lewis Y positive cells triggered cell death with similar efficacy as dsFv-B3 targeted Pseudomonas exotoxin fragment 38 (PE38). Since GzmB was only weakly inhibited by plasma proteins, GzmB-based immunoconjugates should be useful as a new class of immunotoxins with low immunogenicity utilizing programmed cell death for therapeutic purposes.

Is antenatal antibody screening worthwhile in the Zimbabwean population?

OBJECTIVES

To determine the incidence of clinically significant allo-antibodies in antenatal care (ANC) patients, and make recommendations on laboratory management of such cases in similar settings in Zimbabwe.

DESIGN

A retrospective study.

SETTING

Harare Central Hospital, a tertiary medical centre in Harare.

SUBJECTS

Patients attending the ANC clinic at Harare Central Hospital.

MAIN OUTCOME MEASURES

Blood group tests, allo-antibody screen, development of haemolytic disease of the newborn.

RESULTS

3,000 patients were grouped and screened and 96.7% were found to be Rhesus positive, 0.5% were Rhesus Du positive and 2.8% were Rhesus negative. An overall antibody incidence of 1.7% (n = 50) was obtained, 1.0% (n = 30) of which were strongly positive and 0.7% (n = 20) were so weakly positive so that no antibodies could be identified. Antibodies identified from those patients with strongly positive antibody screen were anti-D 13.3% (n = 4), anti-E 6.7% (n = 2), anti-Jsb 3.2% (n = 1), anti-Lea 23.3% (n = 7) and anti-Leb 20% (n = 6). Antibodies of unknown specificity were detected from 20% (n = 6) of the patients. Four (13.3%) of the specimens were insufficient for antibody identification. Clinical records of those patients with a strongly positive antibody screen were examined and anti-D and anti-Jsb were observed to have caused severe to fatal Haemolytic Disease of the Newborn (HDN). The four anti-D positive cases resulted in two still births and two jaundiced babies. The single anti-Jsb positive antibody case resulted in an intra-uterine death. Antibodies that are generally considered of no clinical significance did not cause HDN in this study.

CONCLUSION

Anti-D remains the most important allo-antibody causing HDN, regardless of the availability of anti-D immunoglobulin for prophylaxis. Only Rhesus D negative women and those who have clinically significant antibodies need have repeat antibody screens during the rest of the pregnancy. In line with the current policy of screening all patients at booking, the policy on repeats is not clear and was not evident in this study.

Effect of antigenic heterogeneity on the efficacy of enhanced delivery of antibody-targeted chemotherapy in a human lung cancer intracerebral xenograft model in rats

OBJECTIVE

The SGN-15 monoclonal antibody-doxorubicin immunoconjugate is toxic to Lewis(Y) antigen-expressing cells and is effective against intracerebral tumors in nude rats when delivery is enhanced with osmotic disruption of the blood-brain barrier (BBB). We tested whether doxorubicin released locally in antigen-expressing cells would affect adjacent non-antigen-expressing cells in heterogeneously expressing intracerebral tumors.

METHODS

Nude rats with intracerebral xenografts of human small cell lung carcinoma cells with high (n = 10) or low (n = 23) Lewis(Y) antigen expression were treated with SGN-15 at a low (10 mg/kg) or high (140 mg/kg) antibody dose, administered intra-arterially with BBB disruption, and tumor volumes and antigen expression were evaluated after 6 days.

RESULTS

BBB disruption-enhanced delivery of SGN-15 (10 mg/kg) reduced the high-expressor tumor volume from 26.1 +/- 3.7 mm(3) (n = 7) in untreated control animals to 6.7 +/- 4.6 mm(3) (n = 3, P < 0.05). Untreated high-expressor tumors exhibited uniform prominent Lewis(Y) antigen staining (97.6 +/- 0.9% positive, n = 4), whereas treated tumors demonstrated areas of nil, moderate, and prominent staining (71.0 +/- 8.5% positive, n = 3, P < 0.05). In intracerebral tumors with low initial antigen expression, BBB disruption-enhanced delivery of a low dose of immunoconjugate was significantly effective, but treated tumors demonstrated low levels of antigen expression. An increase in the immunoconjugate dose did not significantly alter either efficacy or antigen expression.

CONCLUSION

Immunoconjugate delivered across the BBB was effective against antigen-positive tumor cells, but there was not an effective chemical bystander effect against antigen-negative tumor cells.

Helicobacter pylori and gastric diseases

Helicobacter pylori (H. pylori) infection is a pathogenic agent of gastric diseases, but their mechanisms are unclear. Effects of ammonia, tumor necrosis factor (TNF), and anti-Lewis autoantibodies induced after H. pylori infection on the development of gastric diseases were investigated. Ammonia disturbed the collagen metabolism in the ulcer base. Soluble TNF receptors regulate the action of TNF. The involvement of anti-Lewis autoantibodies in the development of peptic ulcer might be unlikely. Moreover, H. pylori-specific IgA in gastric juice and TNFalpha gene polymorphism in persons infected with H. pylori were studied. According to H. pylori-specific IgA titer in gastric juice, persons were divided into two histologically and endoscopically different states of disease. TNFA -857 single nucleotide polymorphism (SNP) may be associated with rugal hyperplastic gastritis and gastric carcinomas without severe atrophy. However, complete elucidation of pathogenic mechanisms of H. pylori-induced gastric diseases requires further research.