AllergoOncology - the impact of allergy in oncology: EAACI position paper.

Th2 immunity and allergic immune surveillance play critical roles in host responses to pathogens, parasites and allergens. Numerous studies have reported significant links between Th2 responses and cancer, including insights into the functions of IgE antibodies and associated effector cells in both antitumour immune surveillance and therapy. The interdisciplinary field of AllergoOncology was given Task Force status by the European Academy of Allergy and Clinical Immunology in 2014. Affiliated expert groups focus on the interface between allergic responses and cancer, applied to immune surveillance, immunomodulation and the functions of IgE-mediated immune responses against cancer, to derive novel insights into more effective treatments. Coincident with rapid expansion in clinical application of cancer immunotherapies, here we review the current state-of-the-art and future translational opportunities, as well as challenges in this relatively new field. Recent developments include improved understanding of Th2 antibodies, intratumoral innate allergy effector cells and mediators, IgE-mediated tumour antigen cross-presentation by dendritic cells, as well as immunotherapeutic strategies such as vaccines and recombinant antibodies, and finally, the management of allergy in daily clinical oncology. Shedding light on the crosstalk between allergic response and cancer is paving the way for new avenues of treatment.

In vivo evolution of HIV-1 co-receptor usage and sensitivity to chemokine-mediated suppression.

Following the identification of the C-C chemokines RANTES, MIP-1alpha and MIP-1beta as major human immunodeficiency virus (HIV)-suppressive factors produced by CD8+ T cells, several chemokine receptors were found to serve as membrane co-receptors for primate immunodeficiency lentiretroviruses. The two most widely used co-receptors thus far recognized, CCR5 and CXCR4, are expressed by both activated T lymphocytes and mononuclear phagocytes. CCR5, a specific RANTES, MIP-1alpha and MIP-1 receptor, is used preferentially by non-MT2-tropic HIV-1 and HIV-2 strains and by simian immunodeficiency virus (SIV), whereas CXCR4, a receptor for the C-X-C chemokine SDF-1, is used by MT2-tropic HIV-1 and HIV-2, but not by SIV. Other receptors with a more restricted cellular distribution, such as CCR2b, CCR3 and STRL33, can also function as co-receptors for selected viral isolates. The third variable region (V3) of the gp120 envelope glycoprotein of HIV-1 has been fingered as a critical determinant of the co-receptor choice. Here, we document a consistent pattern of evolution of viral co-receptor usage and sensitivity to chemokine-mediated suppression in a longitudinal follow-up of children with progressive HIV-1 infection. Viral isolates obtained during the asymptomatic stages generally used only CCR5 as a co-receptor and were inhibited by RANTES, MIP-1alpha and MIP-1beta, but not by SDF-1. By contrast, the majority of the isolates derived after the progression of the disease were resistant to C-C chemokines, having acquired the ability to use CXCR4 and, in some cases, CCR3, while gradually losing CCR5 usage. Surprisingly, most of these isolates were also insensitive to SDF-1, even when used in combination with RANTES. An early acquisition of CXCR4 usage predicted a poor prognosis. In children who progressed to AIDS without a shift to CXCR4 usage, all the sequential isolates were CCR5-dependent but showed a reduced sensitivity to C-C chemokines. Discrete changes in the V3 domain of gp120 were associated with the loss of sensitivity to C-C chemokines and the shift in co-receptor usage. These results suggest an adaptive evolution of HIV-1 in vivo, leading to escape from the control of the antiviral C-C chemokines.

Efficient destruction of human immunodeficiency virus in human serum by inhibiting the protective action of complement factor H and decay accelerating factor (DAF, CD55).

Activation of the human complement system leads to complement deposition on human immunodeficiency virus (HIV) and HIV-infected cells without causing efficient complement-mediated lysis. Even in the presence of HIV-specific antibodies, only a few particles are destroyed, demonstrating that HIV is intrinsically resistant to human complement. Here we report that, in addition to decay accelerating factor (DAF) being partially responsible, human complement factor H (CFH), a humoral negative regulator of complement activation, is most critical for this resistance. In the presence of HIV-specific antibodies, sera devoid of CFH (total genetic deficiency or normal human serum depleted of CFH by affinity chromatography) lysed free virus and HIV-infected but not uninfected cells. In the presence of CFH, lysis of HIV was only obtained when binding of CFH to gp41 was inhibited by a monoclonal antibody against a main CFH-binding site in gp41. Since CFH is an abundant protein in serum, and high local concentration of CFH can be obtained at the surface of HIV as the result of specific interactions of CFH with the HIV envelope, it is proposed that the resistance of HIV and HIV-infected cells against complement-mediated lysis in vivo is dependent on DAF and CFH and can be overcome by suppressing this protection. Neutralization of HIV may be achieved by antibodies against DAF and, more importantly, antibodies against CFH-binding sites on HIV envelope proteins.

C-C chemokines released by lipopolysaccharide (LPS)-stimulated human macrophages suppress HIV-1 infection in both macrophages and T cells.

Human immunodeficiency virus-1 (HIV-1) expression in monocyte-derived macrophages (MDM) infected in vitro is known to be inhibited by lipopolysaccharide (LPS). However, the mechanisms are incompletely understood. We show here that HIV-1 suppression is mediated by soluble factors released by MDM stimulated with physiologically significant concentrations of LPS. LPS-conditioned supernatants from MDM inhibited HIV-1 replication in both MDM and T cells. Depletion of C-C chemokines (RANTES, MIP-1 alpha, and MIP-1 beta) neutralized the ability of LPS-conditioned supernatants to inhibit HIV-1 replication in MDM. A combination of recombinant C-C chemokines blocked HIV-1 infection as effectively as LPS. Here, we report an inhibitory effect of C-C chemokines on HIV replication in primary macrophages. Our results raise the possibility that monocytes may play a dual role in HIV infection: while representing a reservoir for the virus, they may contribute to the containment of the infection by releasing factors that suppress HIV replication not only in monocytes but also in T lymphocytes.

Antigen-driven C-C chemokine-mediated HIV-1 suppression by CD4(+) T cells from exposed uninfected individuals expressing the wild-type CCR-5 allele.

Despite repeated exposure to HIV-1, certain individuals remain persistently uninfected. Such exposed uninfected (EU) people show evidence of HIV-1-specific T cell immunity and, in rare cases, selective resistance to infection by macrophage-tropic strains of HIV-1. The latter has been associated with a 32-base pair deletion in the C-C chemokine receptor gene CCR-5, the major coreceptor of macrophage-tropic strains of HIV-1. We have undertaken an analysis of the HIV-specific T cell responses in 12 EU individuals who were either homozygous for the wild-type CCR-5 allele or heterozygous for the deletion allele (CCR-5Delta32). We have found evidence of an oligoclonal T cell response mediated by helper T cells specific for a conserved region of the HIV-1 envelope. These cells produce very high levels of C-C chemokines when stimulated by the specific antigen and suppress selectively the replication of macrophage-tropic, but not T cell-tropic, strains of HIV-1. These chemokine-producing helper cells may be part of a protective immune response that could be potentially exploited for vaccine development.

AllergoOncology: the role of IgE-mediated allergy in cancer.

Epidemiological studies have suggested inverse associations between allergic diseases and malignancies. As a proof of concept for the capability of immunoglobulin E (IgE) to destruct tumor cells, several experimental strategies have evolved to specifically target this antibody class towards relevant tumor antigens. It could be demonstrated that IgE antibodies specific to overexpressed tumor antigens have been superior to any other immunoglobulin class with respect to antibody-dependent cellular cytotoxicity (ADCC) and phagocytosis (ADCP) reactions. In an alternative approach, IgE nonspecifically attached to tumor cells proved to be a powerful adjuvant establishing tumor-specific immune memory. Active Th2 immunity could also be achieved by applying an oral immunization regimen using mimotopes, i.e. epitope mimics of tumor antigens. The induced IgE antibodies could be cross-linked by live tumor cells leading to tumoricidic mediator release. Thus, IgE antibodies may not only act in natural tumor surveillance, but could possibly also be exploited for tumor control in active and passive immunotherapy settings. Thereby, eosinophils, mast cells and macrophages can be armed with the cytophilic IgE and become potent anti-tumor effectors, able to trace viable tumor cells in the tissues. It is strongly suggested that the evolving new field AllergoOncology will give new insights into the role of IgE-mediated allergy in malignancies, possibly opening new avenues for tumor therapy.

Tumor immunoscintigraphy by means of radiolabeled monoclonal antibodies: multicenter studies of the Italian National Research Council--Special Project "Biomedical Engineering".

Four radioimmunopharmaceuticals (99mTc- and 111In-labeled anti-melanoma and 111In- and 131I-labeled anti-carcinoembryonic antigen F(ab')2 fragments derived from monoclonal antibodies 225.28S and F023C5) were developed by means of a collaborative effort coordinated by the Italian National Research Council, Special Project "Biomedical Engineering." After appropriate pilot studies, the radioimmunopharmaceuticals, prepared by Sorin Biomedica (Saluggia, Italy), were distributed to 31 Nuclear Medicine departments in Italy and in 10 other European countries within the framework of three immunoscintigraphy multicenter studies. A total of 1245 patients were studied, 898 of whom carried 1725 documented tumor lesions; 1596 of 2193 tumor lesions (468 of which were previously unknown) were imaged by immunoscintigraphy in 785 of 990 lesion-bearing patients. Among the occult lesions, 173 were imaged in 92 patients admitted to the study as lesion-free patients. The results have been analyzed in terms of the reliability, reproducibility, and diagnostic usefulness of the method and of each immunoradiopharmaceutical.

Tumor cell targeting with antibody-avidin complexes and biotinylated tumor necrosis factor alpha.

Tumor pretargeting with biotinylated antibodies and avidin, followed by a delayed delivery of radioactive-labeled biotin, is currently used for in vivo diagnosis and therapy in cancer patients. Herein, we describe the use of a three-step antibody/avidin targeting approach to increase the local concentration and the persistence of biotinylated human tumor necrosis factor alpha (bio-TNF) on a mouse tumor. Mouse RMA lymphoma cells were transfected with the Thy 1.1 allele (RMA-Thy 1.1) to generate a unique tumor-associated antigen. In vitro pretargeting of RMA-Thy 1.1 cells with the biotinylated anti-Thy 1.1 monoclonal antibody 19E12 (bio-19E12) and NeutrAvidin increased the amount of bio-TNF that bound to the cell (10-20 times in comparison with non-pretargeted cells), as well as its half-life on the surface (>30 times). Furthermore, cell pretargeting reduced by more than 2 orders of magnitude the LD50 of bio-TNF in a cytolytic assay with actinomycin D. Finally, RMA-Thy 1.1 cells, pretreated in vitro with bio-TNF according to the three-step procedure and injected into syngeneic C57/BL6 mice, were less tumorigenic than controls. These results indicate that the three-step targeting approach markedly increases the amount and the persistence of bio-TNF on the cell surface and that cell-bound bio-TNF can trigger cytolytic effects in vitro and antitumor effects in vivo. Tumor pretargeting with biotinylated antibodies and avidin could be a novel strategy for increasing the therapeutic index of TNF.

Tumor targeting with biotinylated tumor necrosis factor alpha: structure-activity relationships and mechanism of action on avidin pretargeted tumor cells.

We have recently described a new strategy for targeting biotinylated tumor necrosis factor-alpha (TNF-alpha) to tumors, based on pretargeting with biotinylated antibodies and avidin. Here, we have analyzed the structure-activity relationships of several biotin-TNF-alpha conjugates and studied the mechanism of their interaction with avidin and TNF-alpha receptors on tumor cells. The study has been carried out using an in vitro model based on human melanoma Colo 38 cells and monoclonal antibody 225, an antibody against the high molecular weight melanoma-associated antigen. Immunochemical and cytotoxicity studies showed that biotin-TNF-alpha but not TNF-alpha persists for several hours on the surface of cells pretargeted with biotin-monoclonal antibody 225 and avidin and triggers cytolytic effects. Studies on the mechanism of action showed that biotin-TNF-alpha trimers can slowly dissociate from targeted cells in a bioactive form, through trimer-monomer-trimer transitions. Structure-activity relationship studies showed that nonbiotinylated subunits must be present in the biotin-TNF-alpha trimers for efficient release of bioactive TNF-alpha. Colo 38 cells targeted with biotin-TNF-alpha were able to kill mouse L-M cells in coculture experiments, indicating that the released TNF-alpha can interact also with TNF-alpha receptors expressed by bystander cells. In conclusion, the targeting complex works as a system that slowly releases bioactive TNF-alpha in the microenvironment of the targeted cell. This opens up the possibility that cells other than those reached by the targeting antibody (e.g., endothelial cells and local cells of the immune system) can be affected in vivo.

Multicenter study of immunoscintigraphy with radiolabeled monoclonal antibodies in patients with melanoma.

A multicenter study was performed to analyze the efficacy of 99mTc- and 111In-labeled F(ab')2 fragments of monoclonal antibody (MoAb) 225.28S (reactive with a high molecular weight melanoma associated antigen) to radioimage malignant lesions in patients with melanoma. A total of 254 melanoma patients, carrying 412 documented melanoma lesions, were studied in 10 nuclear medicine departments. A total of 377 lesions were visualized in 206 patients; in particular (a) 250 of 412 known lesions were visualized in 159 of 191 patients known to carry melanoma lesions; (b) 95 occult lesions were visualized in 61 patients of the same group; and (c) 32 lesions were visualized in 15 of 63 patients without diagnosed lesions. The melanomic nature of 101 of 127 radioimaged occult lesions was confirmed by clinical criteria and/or by additional laboratory investigations. These results indicate that immunoscintigraphy with radiolabeled F(ab')2 fragments of MoAb 225.28S can provide clinically useful information. Analysis of the variables influencing the outcome of immunoscintigraphy with 99mTc- and 111In-labeled F(ab')2 fragments of MoAb 225.28S confirmed the role of size, anatomic site, and level of high molecular weight melanoma associated antigen in melanoma lesions. Such analysis also showed, for the first time, the influence (a) of the isotope used to radiolabel the antibody fragments and (b) of the clinical stage of the patients. The present study has shown good agreement in the results obtained by the 10 nuclear medicine departments, suggesting that immunoscintigraphy with radiolabeled F(ab')2 fragments of MoAb 225.28S is a reliable procedure.

IgEs targeted on tumor cells: therapeutic activity and potential in the design of tumor vaccines.

Surface-bound IgE play a central role in antiparasite immunity; to exploit IgE-driven immune mechanisms in tumor prevention and control, monoclonal IgEs of irrelevant specificity were loaded through biotin-avidin bridging onto tumor cells, either by systemic administration to tumor-bearing mice or pre-loading of tumor cells before inoculation. Here we show that systemic administration of biotinylated IgEs to mice bearing tumors pre-targeted with biotinylated antibodies and avidin significantly decreased tumor growth rate. In addition, as compared with IgG-loaded control cells, inoculation of suboptimal doses of IgE-loaded tumor cells suppressed tumor formation in a fraction of animals and induced protective host immunity by eliciting tumor-specific T-cell responses. Similarly, tumor vaccination experiments showed that irradiated tumor cells (IgE loaded by biotin-avidin bridging) conferred protective immunity at doses 100-fold lower than the corresponding control cells without IgE. Finally, in vivo depletion of eosinophils or T cells abrogated IgE-driven tumor growth inhibition. These results demonstrate that IgEs targeted on tumor cells not only possess a curative potential but also confer long-term antitumor immunity and that IgE-driven antitumor activity is not restricted to the activation of innate immunity effector mechanisms but also results from eosinophil-dependent priming of a T-cell-mediated adaptive immune response. This suggests a potential role for IgEs in the design of new cell-based tumor vaccines.

Tumor pretargeting with avidin improves the therapeutic index of biotinylated tumor necrosis factor alpha in mouse models.

The clinical use of tumor necrosis factor alpha (TNF) as an anticancer drug is limited to local or locoregional administration because of dose-limiting systemic toxicity. We investigated in animal models whether the therapeutic index of systemically administered human or murine TNF can be increased by tumor pretargeting strategies based on the biotin-avidin system. Pretargeting of s.c. mouse WEHI-164 fibrosarcoma and RMA lymphoma genetically engineered to express the Thy 1.1 antigen on the cell membrane was achieved by i.p. injection of a biotinylated anti-Thy 1.1 antibody and avidin. This pretreatment increased the antitumor activity of systemically administered biotin-TNF conjugates by at least 5-fold. In contrast, pretargeting did not increase the toxicity of biotin-TNF, as judged by animal survival and weight loss after treatment. Ex vivo analysis of tumor cells 24 h after treatment showed that biotin-TNF persisted for several hours on the surface of pretargeted tumors, but not when avidin was omitted. The potentiation of the antitumor effects was related primarily to indirect mechanisms, involving a host-mediated response. The results indicate that tumor pretargeting improves the antitumor activity of TNF. Tumor pretargeting with avidin, which is currently used to increase the uptake of radioactive-labeled biotin in patients, could represent a new strategy for improving the therapeutic index of TNF.

Immunoscintigraphy of adenocarcinomas by means of radiolabeled F(ab')2 fragments of an anti-carcinoembryonic antigen monoclonal antibody: a multicenter study.

F(ab')2 fragments of anti-carcinoembryonic antigen (CEA) monoclonal antibody F023C5, determined to be more suitable than intact IgG and Fab fragments for immunoscintigraphy, were labeled with 131I or conjugated to DTPA for instant 111In-labeling, and administered i.v. (2-3 mCi/0.5 mg) to 509 patients in 11 nuclear medicine departments: 284 patients had gastrointestinal adenocarcinomas, 204 had nongastrointestinal adenocarcinomas and 21 were control; serum CEA was elevated in 169 patients, normal in 115, and not determined in 225. The following results were obtained: (a) no adverse reactions; (b) tumor imaging in 324 patients (in particular, in 81.5% CEA-seropositive and in 69.0% CEA-seronegative patients); (c) no significant difference in sensitivity among the results of the 11 departments; (d) no significant difference in overall sensitivity between 131I-and 111In-labeled immunoradiopharmaceuticals; (e) the fraction of documented lesions imaged was 73.3% in CEA-seropositive and 53.7% in CEA-seronegative patients; (f) the detection of liver metastases was hampered, particularly when using the 111In-labeled reagent, by nonspecific radioactivity uptake; (g) the major cause of negative immunoscintigraphy results was a lack of CEA in tumor lesions, as documented by immunohistochemistry; (h) lesion size is also important since the sensitivity was 64% for lesions up to 2 cm in diameter and 84% for larger lesions; (i) many "unexpected" radiolocalizations were recorded. Most were identified as occult tumor lesions. In 35 patients, this finding contributed to the early detection of tumor recurrences.

Adoptive immunotherapy by avidin-driven cytotoxic T lymphocyte-tumor bridging.

We have shown previously that T cells, tagged with biotinylated anti-CD3 antibody fragments, can exert avidin-dependent cytolytic activity on suitably biotinylated tumor cells in vitro. In this study, we demonstrate that avidin-driven CTL-tumor bridging in vivo leads to growth inhibition of murine tumors WEHI-164 fibrosarcoma and RMA lymphoma. The biodistribution of biotin-tagged 111In-labeled T cells demonstrated a selective avidin-dependent and time-dependent accumulation of radioactivity at tumor sites. The specificity of lymphocyte tumor localization was demonstrated by the concurrent time-dependent decrease of radioactivity in the blood and in all other organs. Furthermore, we documented a therapeutic effect of the adoptively transferred T cells, i.e., a significant delay of tumor growth at early stages. All of the experiments included a control group of mice, which received all of the reagents, except avidin. These avidin-minus mice showed no specific localization and no delay in tumor growth, indicating that avidin bridging was essential for T-cell activity at tumor sites.

Identification of a human clustered G + C-rich DNA family of repeats (Sau3A family).

Sau3A digestion of human G + C-rich DNA molecules yields discrete bands of approximately 70 and 140 base-pairs, under-represented in A + T-rich DNA molecules and in total DNA. We have cloned the 70 base-pair band in a plasmid vector and isolated a representative recombinant clone that identifies a new human family of repeats, the Sau3A family. The new family has been characterized for a number of parameters: genomic organization; reiteration frequency; sequence analysis; and distribution in a human genomic library. The Sau3A sequence (68 base-pairs in length, 53% G + C) is present in approximately 4 X 10(4) copies/haploid genome; the family is characterized by a cluster organization and is confined to a limited fraction (0.5%) of phages of a human genomic library. Southern blot hybridizations of the cloned sequence to restriction digests of total human DNA and of isolated genomic clones does not show the involvement of Sau3A blocks in long-range periodicities for any of the enzymes tested. The data suggest either a high sequence variability in the family or a complex organization of Sau3A sequence domains.

Linkage in human heterochromatin between highly divergent Sau3A repeats and a new family of repeated DNA sequences (HaeIII family).

The hybridization of human DNA with three non-cross-hybridizing monomers (68 bp in length) of the heterochromatic Sau3A family of DNA repeats, indicates the coexistence within a Sau3A-positive genomic block of divergent Sau3A units as well as of unrelated sequences. To gain some insight into the structure of these human heterochromatic DNA regions, three previously cloned Sau3A-positive genomic fragments (with a total length of approximately 1900 base-pairs (bp] were sequenced. The analysis of the sequences showed the presence of clustered Sau3A units with different degrees of divergence and of two DNA regions of approximately 100 bp and 291 bp in length, unrelated to the family of repeats. A consensus sequence derived from the 24 identified Sau3A monomers presents, among highly variable regions, two less variant regions of 8 bp and 10 bp in length, respectively. The Sau3A-unrelated DNA fragment 291 bp in length, used as a probe on genomic DNA digested with a series of restriction enzymes, defines a "new" family of DNA repeats possessing periodicities for HaeIII (HaeIII family). Sau3A and HaeIII repeats display a high degree of linkage in a collection of Sau3A-positive genomic recombinant phages.

Recombinant allergen Lol p II: expression, purification and characterization.

Pollen from perennial rye grass (Lolium perenne) is a major cause of type I allergies worldwide. It contains complex mixtures of proteins, among which Lol p II is a major allergen. Previously, we have reported the cloning and sequencing of Lol p II and its expression in fusion with the heavy chain of human ferritin as carrier polypeptide (Sidoli et al., 1993, J. biol. Chem. 268, 21819-21825). Here, we describe the expression, purification and characterization of a recombinant Lol p II overproduced as a non-fusion protein in the periplasm of E. coli. The recombinant allergen was expressed in high yields and was easily purified in milligram amounts. It competed with the natural Lol p II for binding to specific IgE, and it induced allergic responses in skin prick tests, indicating to be immunologically analogous to the natural protein. Biochemical analyses indicate that recombinant Lol p II is a highly stable and soluble monomeric molecule which behaves like a small globular protein.

Human recombinant antibody fragments specific for a rye-grass pollen allergen: characterization and potential applications.

One of the major allergens from the pollen of perennial rye grass (Lolium perenne), Lol pII, was used to isolate specific antibody fragments from a random combinatorial library displaying a large repertoire of human Fab on filamentous phages. After five panning cycles on recombinant Lol pII immunotubes, phage binders were isolated and the antibody fragments expressed as soluble Fab molecules in the Escherichia coli periplasm. The DNA sequencing of the clones producing antibodies with the highest binding activity showed three of them to be identical, while one differed by two amino acid substitutions in the heavy chain. The antibody fragments were produced in milligram amounts, affinity-purified and further characterized. They bound the natural allergen as well as the recombinant one, with no cross-reactivity with other allergens contained in the pollen extract of L. perenne. One antibody bound the allergen with Kd = 2.63 x 10(-9) M, as demonstrated by the surface plasmon resonance technique, and was able to compete with a fraction of serum IgE. Epitope mapping using synthetic peptides revealed that antigenic domains, located between amino acids 39 and 51 of Lol pII, are recognized by Fab and polyclonal IgE from sera of allergic donors. The Fab fragments inhibited the binding of serum IgE to the allergen. In vitro experiments on whole blood from allergic subjects showed that recombinant Fab fragments had a blocking activity on histamine release from cells challenged with recombinant Lol pII allergen. Thus, serum IgE and recombinant Fab fragments recognize common epitopes, although they represent the outcome of different maturation and/or selection processes. Our molecular and functional findings altogether indicate that allergen-specific human antibodies may be useful for the characterization of the antigenic structure of allergens. We conclude that a phage library is a powerful source of anti-allergen human antibodies with high affinity and high specificity. Moreover, these molecules may be potentially innovative reagents for the treatment of atopic allergy.

Discrete regions of HIV-1 gp41 defined by syncytia-inhibiting affinity-purified human antibodies.

OBJECTIVE: Fine mapping of HIV-1 gp41 fusion-critical sites. DESIGN AND METHODS: Antibodies from human HIV-1-positive sera were affinity-purified on a panel of synthetic overlapping peptides spanning residues 526-682 of the extracellular portion of HIV-1 gp41. The syncytium-inhibiting capacity of the immunopurified antibodies and their differential reactivity on the synthetic peptides were tested. RESULTS: This approach enabled the identification of residues 583-591 (ARILAVERY), 595-599 (QQLLG), 603-609 (CSGKLIC) and 664-673 (ELLELDKWAS) as possibly involved in the fusion process. Reduction in the anti-ARILAVERY, anti-CSGKLIC and anti-ELLELDKWAS antibody titres and frequencies correlates with disease progression. Syncytia-inhibition capacity of sera did not correlate with the presence of high-titre antibodies reacting with any of the peptides tested, suggesting that most fusion-affecting antibodies are not directed towards gp41. CONCLUSIONS: This strategy may be relevant for understanding the contribution of anti-gp41 antibodies in protecting against the pathogenic effects of the virus and in the design of an effective env vaccine.

Enhanced HIV infectivity and changes in GP120 conformation associated with viral incorporation of human leucocyte antigen class I molecules.

BACKGROUND: Assembly of human immunodeficiency virus type 1 (HIV-1) occurs at the level of the plasma membrane of the host cell. During this process HIV incorporates significant quantities of cell surface-derived molecules into its lipid bilayer including human leucocyte antigen (HLA) class I and II, intercellular adhesion molecule-1 and lymphocyte function antigen-1. Several studies indicate that virion-bound host-cell-derived molecules are functional and affect the biological properties of HIV-1. Virion-associated HLA class II and intercellular adhesion molecule-1 enhance the infectivity of T-cell line-adapted (TCLA) viruses. No role for virion-associated HLA class I molecules has yet been identified. OBJECTIVE: To investigate the role of HLA class I molecules in HIV replication and infectivity. METHODS: HLA class I negative human cells lines transfected with the HLA Cw4 gene were infected with different TCLA viruses as well as primary X4 isolates. The infectivity of HLA Cw4 positive and negative viruses was determined on indicator cell lines and on phytohaemagglutinin-activated peripheral blood mononuclear cells. An entry polymerase chain reaction assay was used to determine differences in entry-competence of Cw4 positive and negative viruses. The expression of selected gp120 epitopes on native Env molecules derived from Cw4 positive and negative viruses was determined by a monoclonal antibody-based enzyme-linked immunosorbent assay. Immunoprecipitation experiments were performed to investigate the presence of gp120/HLA Cw4 complexes. Neutralization assays determined the differences in susceptibility to neutralization between HLA Cw4 negative and positive viruses. RESULTS AND CONCLUSIONS: The infectivity of primary HIV-1 X4 isolates and of TCLA viruses is increased upon viral incorporation of HLA Cw4 molecules. This effect is associated with changes in viral envelope proteins conformation including an enhanced expression of the V3 loop of gp120, and of epitopes that are exposed upon CD4 binding. The gp120 conformational changes are consistent with the formation of a multimolecular complex between HLA class I and gp120/160. HLA Cw4 incorporation is also associated to a lower susceptibility to antibody neutralization. These findings have important implications for understanding the immune response to cryptic and conformational epitopes of the viral envelope.