Identification of two molecular defects in a child with leukocyte adherence deficiency

Defective Treg generation and increased type 3 immune response in leukocyte adhesion deficiency 1

In 15 Turkish LAD-1 patients and controls, we assessed the impact of pathogenic ITGB2 mutations on Th17/Treg differentiation and functions, and innate lymphoid cell (ILC) subsets. The percentage of peripheral blood Treg cells, in vitro-generated induced Tregs differentiated from naive CD4⁺ T cells were decreased despite the elevated absolute counts of CD4⁺ cells in LAD1 patients. Serum IL-23 levels were elevated in LAD1 patients. Post-curdlan stimulation, LAD1 patient-derived PBMCs produced more IL-17A. Additionally, the percentages of CD18-deficient Th17 cells expanded from total or naïve CD4⁺ T cells were higher. The blood ILC3 subset was significantly elevated in LAD1. Finally, LAD1 PBMCs showed defects in trans-well migration and proliferation and were more resistant to apoptosis. Defects in de novo generation of Tregs from CD18-deficient naïve T cells and elevated Th17s, and ILC3s in LAD1 patients' peripheral blood suggest a type 3-skewed immunity and may contribute to LAD1-associated autoimmune symptoms.

Clinical and laboratory findings in patients with leukocyte adhesion deficiency type I: A multicenter study in Turkey

Leukocyte adhesion deficiency type I is a rare primary immunodeficiency disorder characterized by mutations in the ITGB2 gene encoding CD18. We present clinical and immunological features of 15 patients with leukocyte adhesion deficiency type 1 (LAD-1). Targeted next-generation sequencing was performed with either a primary immunodeficiency gene panel comprising 266 genes or a small LAD-panel consisting of five genes for genetic analysis. To measure the expression level of integrins on the leukocyte surface, flow cytometry analysis was performed. The median age of the patients at diagnosis was 3 (1-48) months. Eleven (73%) of the 15 patients had a LAD-1 diagnosis in their first 6 months and 14 (93%) patients had consanguineous parents. Delayed separation of the umbilical cord was present in 80% (n = 12) of the patients in our cohort, whereas omphalitis was observed in 53% (n = 8) of the patients. Leukocytosis with neutrophil predominance was observed in 73% (n = 11) patients. Nine distinct variants in the ITGB2 gene in 13 of the 15 patients with LAD-1 were characterized, two of which (c.305_306delAA and c.779_786dup) are novel homozygous mutations of ITGB2. Four unrelated patients from Syria had a novel c.305_306delAA mutation that might be a founder effect for patients of Syrian origin. Four (27%) patients underwent hematopoietic stem cell transplantation. Two patients died because of HSCT complications and the other two are alive and well. Early differential diagnosis of the patients is critical in the management of the disease and genetic evaluation provides a basis for family studies and genetic counseling.

Mass spectrometric characterization of protein structures and protein complexes in condensed and gas phase

Proteins are essential for almost all physiological processes of life. They serve a myriad of functions which are as varied as their unique amino acid sequences and their corresponding three-dimensional structures. To fulfill their tasks, most proteins depend on stable physical associations, in the form of protein complexes that evolved between themselves and other proteins. In solution (condensed phase), proteins and/or protein complexes are in constant energy exchange with the surrounding solvent. Albeit methods to describe in-solution thermodynamic properties of proteins and of protein complexes are well established and broadly applied, they do not provide a broad enough access to life-science experimentalists to study all their proteins' properties at leisure. This leaves great desire to add novel methods to the analytical biochemist's toolbox. The development of electrospray ionization created the opportunity to characterize protein higher order structures and protein complexes rather elegantly by simultaneously lessening the need of sophisticated sample preparation steps. Electrospray mass spectrometry enabled us to translate proteins and protein complexes very efficiently into the gas phase under mild conditions, retaining both, intact protein complexes, and gross protein structures upon phase transition. Moreover, in the environment of the mass spectrometer (gas phase, in vacuo), analyte molecules are free of interactions with surrounding solvent molecules and, therefore, the energy of inter- and intramolecular forces can be studied independently from interference of the solvating environment. Provided that gas phase methods can give information which is relevant for understanding in-solution processes, gas phase protein structure studies and/or investigations on the characterization of protein complexes has rapidly gained more and more attention from the bioanalytical scientific community. Recent reports have shown that electrospray mass spectrometry provides direct access to six prime protein complex properties: stabilities, compositions, binding surfaces (epitopes), disassembly processes, stoichiometries, and thermodynamic parameters.

Apparent activation energies of protein-protein complex dissociation in the gas-phase determined by electrospray mass spectrometry

We have developed a method to determine apparent activation energies of dissociation for ionized protein-protein complexes in the gas phase using electrospray ionization mass spectrometry following the Rice-Ramsperger-Kassel-Marcus quasi-equilibrium theory. Protein-protein complexes were formed in solution, transferred into the gas phase, and separated from excess free protein by ion mobility filtering. Afterwards, complex disassembly was initiated by collision-induced dissociation with step-wise increasing energies. Relative intensities of ion signals were used to calculate apparent activation energies of dissociation in the gas phase by applying linear free energy relations. The method was developed using streptavidin tetramers. Experimentally determined apparent gas-phase activation energies for dissociation ([Formula: see text]) of complexes consisting of Fc parts from immunoglobulins (IgG-Fc) and three closely related protein G' variants (IgG-Fc•protein G'e, IgG-Fc•protein G'f, and IgG-Fc•protein G'g) show the same order of stabilities as can be inferred from their in-solution binding constants. Differences in stabilities between the protein-protein complexes correspond to single amino acid residue exchanges in the IgG-binding regions of the protein G' variants. Graphical abstract Electrospray mass spectrometry and collision-induced dissociation delivers apparent activation energies and supramolecular bond force constants of protein-protein complexes in the gas phase.

Feline leukocyte adhesion (CD18) deficiency caused by a deletion in the integrin β2 (ITGB2) gene

BACKGROUND

Leukocyte adhesion deficiency (LAD) or CD18 deficiency is an autosomal recessive immunodeficiency which has been described in people, cattle, dogs, and knockout mice.

OBJECTIVES

The study goals were to characterize the clinicopathologic, immunologic, and molecular genetic features of feline LAD (FLAD) in a neutered male adult Domestic Longhair cat with severe leukocytosis and recurrent infections.

METHODS

Flow cytometry evaluated surface expression of CD18 on neutrophils. In vitro functional assays assessed CD18-dependent neutrophil adhesion and T-cell proliferation. Genomic DNA and cDNA were used to identify a causative mutation in the coding sequence of the integrin β₂ subunit (ITGB2) gene.

RESULTS

The affected cat developed periodontitis during the first months of life followed by recurrent infections poorly responsive to antibiotic therapy, accompanied by extreme neutrophilia. Neutrophils from the proband, compared to feline controls, did not express any CD18 on the cell surface. Adhesion of affected neutrophils was severely impaired with and without phorbol-myristate-acetate activation. The proband's T-cells proliferated weakly to 1 pg but normally to 100 pg staphylococcal enterotoxin A, suggesting a CD18-independent T-cell response at higher doses. Molecular genetic analysis of the ITGB2 gene revealed a 24 bp deletion at the exon 2 to intron 2 boundary (c.46_58 + 11del), predicting premature translational termination due to abnormal splicing of exon 1 to exon 3 or 4.

CONCLUSIONS

Feline LAD exhibits features similar to LAD in other species. However, clinical episodes in FLAD appeared milder allowing for an extended life expectancy under long-term antimicrobial therapy, possibly due to an alternative, CD18-independent T-cell proliferation pathway.

Molecular characterization of leukocyte adhesion deficiency-I in Indian patients: identification of 9 novel mutations

PURPOSE

Leukocyte adhesion deficiency type-I (LAD-I) is caused by mutations in the ITGB2 gene, encoding the β2-subunit of β2-integrin (CD18) which leads to markedly reduced expression of CD18 on leukocytes resulting into recurrent life threatening infections. Here we aim to identify the molecular defects underlying LAD-I in Indian patients and correlate with the clinical presentation.

METHODS

Blood was collected from 30 patients and their parents for absolute neutrophil count, expression of CD18 and CD11 by flow cytometry and DNA extraction. PCR and DNA sequencing of the ITGB2 gene was done for mutation characterization.

RESULTS

Phenotypically, 22 patients were LAD-I(0), 1 was LAD-I(-) and 7 were LAD-I(+) showing no expression and reduced expression of CD18 respectively. Nine novel mutations in 15 patients and 11 known mutations in 16 patients were detected. Prenatal diagnosis was performed for 5 families.

CONCLUSION

In this study 30 patients were phenotypically and genotypically evaluated for a less known disease LAD-I. Unavailability of curative options to majority of the patients and high cost of supportive care emphasize the need to increase awareness about a suspicious case so that timely management can be given to the patient and prenatal diagnosis can be offered to their families.

Characterization of single amino acid substitutions in the β2 integrin subunit of patients with leukocyte adhesion deficiency (LAD)-1

Leukocyte adhesion deficiency 1 (LAD-1) is caused by defects in the β2 integrin subunit. We studied 18 missense mutations, 14 of which fail to support the surface expression of the β2 integrins. Integrins with the β2-G150D mutation fail to bind ligands, possibly due to the failure of the α1 segment of the βI domain to assume an α-helical structure. Integrins with the β2-G716A mutation are not maintained in their resting states, and the patient has the severe phenotype of LAD-1. The β2-S453N and β2-P648L mutants support the expression of integrins and adhesion functions. They should be re-classified as polymorphic variants.

Hematologically important mutations: leukocyte adhesion deficiency (first update)

Leukocyte adhesion deficiency (LAD) is an immunodeficiency caused by defects in the adhesion of leukocytes (especially neutrophils) to the blood vessel wall. As a result, patients with LAD suffer from severe bacterial infections and impaired wound healing, accompanied by neutrophilia. In LAD-I, mutations are found in ITGB2, the gene that encodes the β subunit of the β(2) integrins. This syndrome is characterized directly after birth by delayed separation of the umbilical cord. In the rare LAD-II disease, the fucosylation of selectin ligands is disturbed, caused by mutations in SLC35C1, the gene that encodes a GDP-fucose transporter of the Golgi system. LAD-II patients lack the H and Lewis Le(a) and Le(b) blood group antigens. Finally, in LAD-III (also called LAD-I/variant) the conformational activation of the hematopoietically expressed β integrins is disturbed, leading to leukocyte and platelet dysfunction. This last syndrome is caused by mutations in FERMT3, encoding the kindlin-3 protein in all blood cells that is involved in the regulation of β integrin conformation.

Gene therapy of canine leukocyte adhesion deficiency using lentiviral vectors with human CD11b and CD18 promoters driving canine CD18 expression

To identify cellular promoters in a self-inactivating (SIN) lentiviral vector that might be beneficial in treating children with leukocyte adhesion deficiency type 1 (LAD-1), we tested lentiviral vectors with human CD11 and CD18 leukocyte integrin proximal promoter elements directing expression of canine CD18 in animals with canine LAD (CLAD). Lentiviral vectors with either the human CD11b (637 bp) proximal promoter or the human CD18 (1,060 bp) proximal promoter resulted in the highest percentages of CD18(+) CLAD CD34(+) cells in vitro. Subsequently, two CLAD dogs were infused with autologous CD34(+) cells transduced with the hCD11b (637 bp)-cCD18 vector, and two CLAD dogs were infused with autologous CD34(+) cells transduced with the hCD18 (1,060 bp)-cCD18 vector. Each dog received a nonmyeloablative dose of 200 cGy total body irradiation (TBI) before the infusion of transduced cells. The two CLAD dogs treated with the hCD18 (1,060 bp)-cCD18 vector, and one of the two dogs treated with the hCD11b (637 bp)-cCD18 vector, had reversal of the CLAD phenotype. These studies using endogenous leukocyte integrin proximal promoters represent an important step in the development of gene therapy for children with LAD-1.

Chemotaxis of non-compressed blood polymorphonuclear leukocytes from an adolescent with severe leukocyte adhesion deficiency

We have defined the defect in a child with severe leukocyte adhesion deficiency-1 (LAD) as resulting from a single amino acid shift in CD18 (from a C to T mutation at position 533) that prevents heterodimerization with the CD11 antigens to produce beta(2) integrins-the first reported patient homozygous for this defect. Although beset by frequent infections, the patient has survived to adolescence despite the lack of these important adhesion molecules. Consistent with his clinical course is the ability of his PMN to respond chemotactically in slide preparations, albeit with difficulty because of their poor purchase on substrate. The operant adhesins are unknown; his polymorphonuclear leukocytes (PMN) remain chemotactically responsive in the presence of antibodies to alphavbeta(3) and beta(1) integrins and to integrin-associated protein (IAP). These findings indicate that not all patients with severe LAD are candidates for early bone marrow transplantation.

Genetic analysis of patients with leukocyte adhesion deficiency: genomic sequencing reveals otherwise undetectable mutations

OBJECTIVE

The aim of this study was to analyze mutations in DNA from patients with leukocyte adhesion deficiency (LAD), an immunodeficiency caused by absence of the beta(2) subunit (CD18) of the leukocyte integrins LFA-1 (CD11a/CD18), Mac-1 (CD11b/CD18), p150,95 (CD11c/CD18), and CR4 (CD11d/CD18).

METHODS

We developed genomic DNA PCR sequencing to detect mutations not only in exons but also in introns.

RESULTS

Eight LAD patients were analyzed, of which five had homozygous mutations, i.e., a 0.8-kb deletion, a branchpoint mutation in intron 5 causing mRNA missplicing, a nonsense mutation, and two missense mutations. Four of these mutations are novel. We cotransfected the two mutant CD18 proteins with normal CD11a, b, or c in COS cells. This resulted in absence of all three beta(2) integrins on the surface of cells transfected with CD18(252Arg). However, CD18(593Cys) supported some LFA-1 and p150,95 formation in COS cells. The other three patients were compound heterozygotes in which only one allele had previously been characterized, because the other alleles were undetectable at the cDNA level. We identified the unknown mutations as a novel two-nucleotide deletion, a nonsense mutation, and a single nucleotide deletion.

CONCLUSION

Our method allows identification of mutations in CD18 from genomic DNA. This opens the possibility of early prenatal diagnosis of LAD and reliable carrier detection.

Hematologically important mutations: leukocyte adhesion deficiency

Leukocyte adhesion deficiency (LAD) is an immunodeficiency caused by defects in the adhesion of leukocytes (especially neutrophils) to the blood vessel wall. As a result, patients with LAD suffer from severe bacterial infections and impaired wound healing. In LAD-I, mutations are found in INTG2, the gene that encodes the beta subunit of the beta(2) integrins. In the rare LAD-II disease, the fucosylation of selectin ligands is disturbed, caused by mutations in the gene for a GDP-fucose transporter of the Golgi. This article summarizes all known patient mutations and polymorphisms in these genes.

Structure-function of the putative I-domain within the integrin beta 2 subunit

The central region (residues 125-385) of the integrin beta(2) subunit is postulated to adopt an I-domain-like fold (the beta(2)I-domain) and to play a critical role in ligand binding and heterodimer formation. To understand structure-function relationships of this region of beta(2), a homolog-scanning mutagenesis approach, which entails substitution of nonconserved hydrophilic sequences within the beta(2)I-domain with their homologous counterparts of the beta(1)I-domain, has been deployed. This approach is based on the premise that beta(1) and beta(2) are highly homologous, yet recognize different ligands. Altogether, 16 segments were switched to cover the predicted outer surface of the beta(2)I-domain. When these mutant beta(2) subunits were transfected together with wild-type alpha(M) in human 293 cells, all 16 beta(2) mutants were expressed on the cell surface as heterodimers, suggesting that these 16 sequences within the beta(2)I-domain are not critically involved in heterodimer formation between the alpha(M) and beta(2) subunits. Using these mutant alpha(M)beta(2) receptors, we have mapped the epitopes of nine beta(2)I-domain specific mAbs, and found that they all recognized at least two noncontiguous segments within this domain. The requisite spatial proximity among these non-linear sequences to form the mAb epitopes supports a model of an I-domain-like fold for this region. In addition, none of the mutations that abolish the epitopes of the nine function-blocking mAbs, including segment Pro(192)-Glu(197), destroyed ligand binding of the alpha(M)beta(2) receptor, suggesting that these function-blocking mAbs inhibit alpha(M)beta(2) function allosterically. Given the recent reports implicating the segment equivalent to Pro(192)-Glu(197) in ligand binding by beta(3) integrins, these data suggest that ligand binding by the beta(2) integrins occurs via a different mechanism than beta(3). Finally, both the conformation of the beta(2)I-domain and C3bi binding activity of alpha(M)beta(2) were dependent on a high affinity Ca(2+) binding site (K(d) = 105 microm), which is most likely located within this region of beta(2).

Nonopsonic phagocytosis of Pseudomonas aeruginoas: insights from an infant with leukocyte adhesion deficiency

Children with leukocyte adhesion deficiency type I are at risk for overwhelming infection because their neutrophils lack surface beta 2 integrins (CD18/CD11) that normally interact with endothelial cell adhesion molecules and mediate migration to sites of bacterial invasion. In vitro studies of phagocytic cells from an infant with leukocyte adhesion deficiency type I demonstrated that complement receptor 3 (CD18/CD11b) mediates nonopsonic phagocytosis of some Pseudomonas aeruginosa strains and might play a control role in the control of Pseudomonas infections at sites where there are low levels of opsonins.

Genetic analysis of integrin function in man: LAD-1 and other syndromes

The integrins are cell membrane receptors composed of alpha and beta subunits which orchestrate adhesive events in all tissues of the body (Hynes, R.O., 1992. Integrins: versatility, modulation, and signalling in cell adhesion. Cell 69, 11-25; and Hynes, R.O., 1999. Cell adhesion: old and new questions. Trends Cell Biol. 9, M33-37). At present 18 alpha subunits and 8 beta subunits have been identified which are loosely organised into families. There are three inherited autosomal recessive diseases in man which involve germline mutations in genes coding for integrins. Leukocyte adhesion deficiency-1 (LAD-1) is the result of mutations in the beta2 subunit of the CD11/CD18 integrins, LFA-1, Mac-1, p150,95 and alphadbeta2. The bleeding disorder Glanzmann thrombasthenia is caused by mutations in either the alpha or beta subunit of the platelet integrin, alphaIIbbeta3. Thirdly, it is now recognised than one of the variants of the usually lethal skin blistering disorder, epidermolysis bullosa (JEB-PA), is caused by mutation in either the alpha or beta subunit of the epithelial hemidesmosome integrin, alpha6beta4. Many of the mutations cause defective alphabeta heterodimer formation. The majority of the beta subunit mutations are in the conserved N-terminal region known as the betaI domain. It is suggested that this region participates in alphabeta heterodimer formation.

A novel CD18 genomic deletion in a patient with severe leucocyte adhesion deficiency: a possible CD2/lymphocyte function-associated antigen-1 functional association in humans

Leucocyte adhesion deficiency (LAD) is an autosomal-recessive genetic disease that is characterized clinically by severe bacterial infections and caused by mutations in the CD18 gene that codes for the beta2 integrin subunit. A patient with a severe LAD phenotype was studied and the molecular basis of the disease was identified as a single homozygous defect in a Herpes virus saimiri (HVS)-transformed T-cell line. The defect identified involves a deletion of 171 bp in the cDNA that encodes part of the proteic extracellular domain. This genetic abnormality was further studied at the genomic DNA level and found to consist of a deletion of 169 bp (from -37 of intron 4 to +132 of exon 5), which abolishes the normal splicing and results in the total skipping of exon 5. The 171-bp shortened 'in-frame' mRNA not only resulted in the absence of CD18 expression on the cell surface but also in its absence in the cytoplasm of HVS T-cell lines. Functionally, the LAD-derived HVS T-cell lines showed a severe, selective T-cell activation impairment in the CD2 (but not in the CD3) pathway. This defect was not reversible when exogenous interleukin-2 (IL-2) was added, suggesting that there is also a functional interaction of the lymphocyte function-associated antigen-1 (LFA-1) protein in the CD2 signal transduction pathway in human T cells, as has been previously reported in mice and in the human Papillon-Lefèvre syndrome. Thus, HVS transformation is not only a suitable model for T-cell immunodeficiency studies and characterization, but is also a good system for investigating the immune system in pathological conditions. It may also be used in the future in cellular models for in vitro gene-therapy trials.

Critical flanking sequences of PU.1 binding sites in myeloid-specific promoters

The myeloid-specific transcription factor PU.1 is essential for expression of p47(phox), a component of the superoxide-forming phagocyte NADPH oxidase. The consensus PU.1 binding sequence (GAGGAA) is located on the non-coding strand from position -40 to -45 relative to the transcriptional start site of the p47phox promoter. A promoter construct extending to -46 was sufficient to drive tissue-specific expression of the luciferase reporter gene, but extension of the promoter from -46 to -48 resulted in a significant increase in reporter expression. Mutations of the nucleotides G at -46 and/or T at -47 reduced both reporter expression and PU.1 binding, whereas mutations at -48 had no effect. The PU.1 binding avidity of these sequences correlated closely with their capacity to dictate reporter gene transcription. In parallel studies on the functional PU.1 site in the promoter of CD18, mutations of nucleotides G and T at positions -76 and -77 (corresponding to -46 and -47, respectively, of the p47phox promoter) reduced PU.1 binding and nearly abolished the contribution of this element to promoter activity. We conclude that the immediate flanking nucleotides of the PU.1 consensus motif have significant effects on PU.1 binding avidity and activity and that this region is the dominant cis element regulating p47phox expression.

A missense mutation in the beta-2 integrin gene (ITGB2) causes canine leukocyte adhesion deficiency

Canine leukocyte adhesion deficiency (CLAD) is a fatal immunodeficiency disease found in Irish setters. The clinical manifestations of CLAD are very similar to LAD in humans and BLAD in cattle, which are both caused by mutations in ITGB2 encoding the leukocyte integrin beta-2 subunit (CD18). Sequence analysis of the ITGB2 coding sequence from a CLAD dog and a healthy control revealed a single missense mutation, Cys36Ser. This cysteine residue is conserved among all beta integrins, and the mutation most likely disrupts a disulfide bond. The mutation showed a complete association with CLAD in Irish setters and was not found in a sample of dogs from other breeds. The causative nature of this mutation was confirmed by transduction experiments using retroviral vectors and human LAD EBV B-cells. The normal canine CD18 formed heterodimers with the human CD11 subunit, whereas gene transfer of the mutant CD18 resulted in very low levels of CD11/CD18 expression. The identification of the causative mutation for CLAD now makes it possible to identify carrier animals with a simple diagnostic DNA test, and it forms the basis for using CLAD as a large animal model for the development and evaluation of clinical treatments for human LAD.

Cytokine regulation of cellular adhesion molecule expression in inflammation

Cellular adhesion molecules (CAMs) play an essential role in tethering circulating leukocytes to the vascular endothelium at sites of inflammation. They are also instrumental in enabling leukocytes to transmigrate from blood vessels into adjacent inflamed tissues. In the absence of signals to stimulate expression of CAMs, the adhesive forces between leukocytes and the vascular endothelium are below the threshold level required to tether leukocytes. Research in the last decade has shown that several cytokines, including tumour necrosis factor alpha (TNF alpha) and interleukin-1 beta (IL-1beta), potently increase the expression of many CAMs and thus increase the adhesiveness between leukocytes and the endothelium. The CAM-inducing activity of these cytokines is therefore crucial to the regulation of inflammatory processes. Overactivation of CAM expression is linked to a number of acute and chronic inflammatory conditions, and has led to the rationale of antagonising cytokine activity and or CAM expression in order to treat these conditions. The potential application of 'adhesion' antagonists for the therapy of acute chronic inflammatory conditions is briefly discussed.

Retroviral-Mediated Gene Transfer of the Leukocyte Integrin CD18 Into Peripheral Blood CD34+ Cells Derived From a Patient With Leukocyte Adhesion Deficiency Type 1

Leukocyte adhesion deficiency or LAD is a congenital immunodeficiency disease characterized by recurrent bacterial infections in which the leukocytes from affected children fail to adhere to endothelial cells and migrate to the site of infection due to heterogeneous defects in the leukocyte integrin CD18 subunit. To assess the feasibility of human gene therapy of LAD, we transduced granulocyte colony-stimulating factor (G-CSF)-mobilized, CD34+peripheral blood stem cells derived from a patient with the severe form of LAD using supernatant from the retroviral vector PG13/LgCD18. The highest transduction frequencies (31%) were found after exposure of the cells to retroviral vector on a substrate of recombinant fibronectin fragment CH-296 in the presence of growth factors interleukin-3 (IL-3), IL-6, and stem cell factor. When the phenotype of the transduced cells was monitored by fluorescence-activated cell sorting following in vitro differentiation with growth factors G-CSF and granulocyte-macrophage CSF (GM-CSF), CD11a surface expression was detected immediately after transduction. CD11b and CD11c were expressed at low levels immediately following transduction, but increased over 3 weeks in culture. Adhesion of the transduced cells was nearly double that of nontransduced cells in a cell adhesion assay using human umbilical vein endothelial cells. Transduced cells also demonstrated the ability to undergo a respiratory burst in response to opsonized zymosan, a CD11/CD18-dependent ligand. These experiments show that retrovirus-mediated gene transfer of the CD18 subunit complements the defect in LAD CD34+ cells resulting in CD11/CD18 surface expression, and that the differentiated myelomonocytic cells derived from the transduced LAD CD34+ cells display CD11/CD18-mediated adhesion function. These results indicate that ex vivo gene transfer of CD18 into LAD CD34+ cells, followed by re-infusion of the transduced cells, may represent a therapeutic approach to LAD.

Retroviral-Mediated Gene Transfer of the Leukocyte Integrin CD18 Into Peripheral Blood CD34+ Cells Derived From a Patient With Leukocyte Adhesion Deficiency Type 1

Leukocyte adhesion deficiency or LAD is a congenital immunodeficiency disease characterized by recurrent bacterial infections in which the leukocytes from affected children fail to adhere to endothelial cells and migrate to the site of infection due to heterogeneous defects in the leukocyte integrin CD18 subunit. To assess the feasibility of human gene therapy of LAD, we transduced granulocyte colony-stimulating factor (G-CSF)-mobilized, CD34+peripheral blood stem cells derived from a patient with the severe form of LAD using supernatant from the retroviral vector PG13/LgCD18. The highest transduction frequencies (31%) were found after exposure of the cells to retroviral vector on a substrate of recombinant fibronectin fragment CH-296 in the presence of growth factors interleukin-3 (IL-3), IL-6, and stem cell factor. When the phenotype of the transduced cells was monitored by fluorescence-activated cell sorting following in vitro differentiation with growth factors G-CSF and granulocyte-macrophage CSF (GM-CSF), CD11a surface expression was detected immediately after transduction. CD11b and CD11c were expressed at low levels immediately following transduction, but increased over 3 weeks in culture. Adhesion of the transduced cells was nearly double that of nontransduced cells in a cell adhesion assay using human umbilical vein endothelial cells. Transduced cells also demonstrated the ability to undergo a respiratory burst in response to opsonized zymosan, a CD11/CD18-dependent ligand. These experiments show that retrovirus-mediated gene transfer of the CD18 subunit complements the defect in LAD CD34+ cells resulting in CD11/CD18 surface expression, and that the differentiated myelomonocytic cells derived from the transduced LAD CD34+ cells display CD11/CD18-mediated adhesion function. These results indicate that ex vivo gene transfer of CD18 into LAD CD34+ cells, followed by re-infusion of the transduced cells, may represent a therapeutic approach to LAD.

Identification of functional domains on gC1Q-R, a cell surface protein that binds to the globular "heads" of C1Q, using monoclonal antibodies and synthetic peptides

A membrane protein (33 kDa) that binds to the globular "heads" of C1q (gC1q-R) has been recently described. The full length cDNA encoding gC1q-R has been cloned, expressed in E. coli and using the purified recombinant protein (rgC1q-R) as an immunogen, a panel of IgG monoclonal antibodies (MAb) has been produced by fusion of spleen cells from hyperimmunized BALB/c mice with NSO mouse myeloma partners. From this fusion, 60 anti-gC1q-R hybridomas were selected and evaluated for their ability to (1) discriminate between the mature form (MF) of gC1q-R (residues 74-282) and a truncated form (TF) lacking residues 74-95, which contains a major C1q binding site, (2) recognize two functionally defined synthetic peptides derived from the NH2-(XN18) and COOH-(XC15) terminus of gC1q-R, and (3) bind to microtiter well fixed intact Raji cells. Several clones were identified: MAbs 46.23 and 60.11 (IgG1 kappa), reacted strongly with ELISA plate-fixed intact Raji and K562 cells, MF, and the XN18 peptide, but had poor or no reactivity with TF; MAbs 74.5.2 > 25.15 (IgG1 kappa) recognized both MF and TF and are directed against epitopes in the XC15 peptide that contains a binding site for high-molecular-weight kininogen and Factor XII.

Molecular characterization of leukocyte adhesion deficiency in six patients

Leukocyte adhesion deficiency (LAD) is caused by defects in the CD18 gene, which codes for the common beta 2 subunit of the leukocyte integrins LFA-1, Mac-1 and p150,95. Failure to produce a functional beta 2 subunit results in the defective expression of all three leukocyte integrins, and the leukocytes of LAD patients have subnormal adhesion properties. Six patients with LAD were studied. Patient B was homozygous and carried a G284S mutation. A two-bp (GA) deletion at position 1256 (1256 delta GA) was found in the cDNA of patient C, who also had an abnormally large mRNA of 4.3 kb. Patients E and K were siblings and were heterozygous at the genomic level. One defective allele contained a mutation in intron 6/7 which created a preemptive 3' splice site. The resulting mRNA has 12 extra bases at the junction of exons 6 and 7, coding for four extra residues PSSQ in the protein. The same allele also carried a R586W mutation. The other allele was transcribed at a low level and was not characterized. Patient G carried a L149P mutation in one allele; again, the other allele was not characterized due to low transcription levels. Patient R carried two mutant alleles with G284S and R593C mutations respectively. The G284S mutation and the 1256 delta GA deletion have not been reported previously. CD18 cDNA carrying the abnormalities were cotransfected with normal CD11a or CD11b cDNA into COS cells. Expression of the LFA-1 (CD11a/CD18) and Mac-1 (CD11b/CD18) antigens on COS cells was not detected, suggesting that these two mutations are sufficient to account for LAD.

Breakthroughs in the understanding and therapy of primary immunodeficiency

In the 40 years since Ogden Bruton discovered agammaglobulinemia, more than 50 additional immunodeficiency syndromes have been described. Until recently, there was little insight into the fundamental problems underlying a majority of these conditions. Recently, however, the molecular bases of three X-linked immunodeficiency disorders have been reported. These include X-linked immunodeficiency with hyper IgM, X-linked agammaglobulinemia, and X-linked severe combined immunodeficiency. These remarkable accomplishments have been made possible through a combination of new knowledge of molecular signaling mechanisms between and within cells of the immune system and greatly improved approaches to disease loci mapping within the human genome. Improvements in the therapy of immunodeficiency diseases have been impressive, and the development of generally safe and effective intravenous immunoglobulin preparations and T cell depletion techniques that permit the use of non-HLA-identical bone marrow donors have been the most important advances over the past 14 years. The identification and cloning of the genes for several of the primary immunodeficiency diseases have obvious implications for potential future somatic cell gene therapy for these patients. The rapidity of these advances suggests that soon there will be many more to come.

Expression from leukocyte integrin promoters in retroviral vectors

Human gene therapy for diseases involving leukocytes would be facilitated by the identification of specific promoter/enhancer sequences capable of directing high levels of tissue and stage-specific expression of the requisite cDNA when used in a retroviral vector. We tested the promoter sequences from the leukocyte integrin CD11a (LFA-1), CD11b (Mac-1), and CD18 subunits in retroviral vectors to express a reporter gene, adenosine deaminase, in the human leukocyte cell lines K562 and HL-60. The leukocyte integrins are expressed in leukocytes, and they are inducible in HL-60 cells, a model system for myeloid differentiation. Although the leukocyte integrin promoter/enhancer sequences direct the expression of reporter genes in myeloid lineage cell lines in transient transfection assays, in these studies, the leukocyte integrin promoters direct low levels of reporter gene expression following retroviral-mediated transduction in K562 and HL-60 cells and selection of stable integrants. Treatment of HL-60 cells transduced with retroviral vectors containing the leukocyte integrin promoters with retinoic acid or phorbol myristate acetate results in less than a two-fold increase in reporter gene expression. These studies indicate that: (i) expression from the leukocyte integrin promoters from stable integrants in retroviral vectors does not parallel the results observed in transient transfection assays, and (ii) additional promoter/enhancer sequences will likely be required for these promoters to direct high levels of tissue and stage-specific expression in retroviral vectors.

Characterization of two new CD18 alleles causing severe leukocyte adhesion deficiency

Leukocyte adhesion deficiency (LAD) is an autosomal recessive disease caused by heterogeneous mutations within the gene encoding the common beta subunit (CD18) of the three leukocyte integrins LFA-1 (CD11a/CD18), Mac-1 (CD11b/CD18), and p150,95 (CD11c/CD18). Based on the level of expression of CD18 on patient leukocytes, two phenotypes of LAD have been defined (severe and moderate) which correlate with the severity of the disease. We have investigated the molecular basis of the disease in two unrelated severe patients (HS and ZJO). Both patients share a complete absence of CD18 protein precursor and cell surface expression, but they differ in the level of CD18 mRNA, which is normal in HS and undetectable by Northern blot in ZJO. Determination of the primary structure of the patient HS CD18 mRNA revealed a 10-base pair deletion between nucleotides 190-200 (CD18 exon 3), which eliminates residues 41-43 and causes a frameshift into a premature termination codon 17 base pairs downstream from the deleted region. The 10-base pair frameshift deletion maps to a region of the CD18 gene where aberrant mRNA processing has been detected in HS and two other unrelated LAD patients. In the ZJO patient, amplification of lymphoblast CD18 mRNA demonstrated the presence of a non-sense mutation in the third nucleotide of the triplet encoding Cys534 (TGC-->TGA), within exon 12. Both genetic abnormalities were also detected at the genomic level, and affect the restriction pattern of their corresponding genes, thus enabling the detection of the mutant alleles among healthy heterozygous alleles in family studies. The identification of two new LAD CD18 alleles, either carrying a non-sense mutation (ZJO) or a partial gene deletion (HS), further illustrates the heterogeneity of the genetic alterations in LAD.

Intercellular adhesion molecule-1 concentration in sera of patients with acute and chronic liver disease: relationship to disease activity and cirrhosis

To study the influence of chronic hepatitis on intercellular adhesion molecule-1 serum concentration, we measured intercellular adhesion molecule-1 in the serum of 84 patients with chronic liver disease (17 chronic persistent hepatitis, 42 chronic active hepatitis and 25 active cirrhosis) caused by hepatitis B virus (n = 46), hepatitis C virus (n = 10) and autoimmunity (n = 28). Furthermore, 20 patients with acute viral hepatitis (16 hepatitis B virus and 4 hepatitis A virus) and 6 patients with acute drug-induced hepatitis were included. Sera from 20 healthy persons were used as control. Follow-up examinations were performed during immunosuppressive therapy in 20 patients with autoimmune chronic liver disease (13 chronic active hepatitis and 7 active cirrhosis). Intercellular adhesion molecule-1 serum concentration was significantly increased in patients with acute viral hepatitis, drug-induced hepatitis, chronic active hepatitis and active cirrhosis compared with healthy controls and with patients with chronic persistent hepatitis. Intercellular adhesion molecule-1 was also significantly increased in severe chronic active hepatitis and active cirrhosis compared with moderate chronic active hepatitis and moderate active cirrhosis. Serum concentration of intercellular adhesion molecule-1 decreased significantly in patients with autoimmune chronic liver disease after 2 mo of immunosuppression when remission was present. A close correlation between aspartate aminotransferase and intercellular adhesion molecule-1 serum levels was found. We conclude the following: (a) in chronic liver disease intercellular adhesion molecule-1 serum concentration may represent, at least in part, hepatocellular damage; and (b) intercellular adhesion molecule-1 serum level does not differentiate between chronic autoimmune and chronic viral hepatitis.

Expression of human CD18 in murine granulocytes and improved efficiency for infection of deficient human lymphoblasts

The CD18 gene encodes the beta 2-subunit of leukocyte integrins, and mutations in this gene cause extreme host susceptibility to bacterial and fungal infection. Because expression of CD18 is restricted to bone marrow-derived cells, this disorder is considered an excellent candidate for somatic gene therapy utilizing ex vivo infection of bone marrow stem cells. We have constructed a retroviral vector expressing CD18 with the Moloney murine leukemia virus (Mo-MLV) long terminal repeat (LTR) as the promoter, and high-titer ecotropic and amphotropic producer cell lines were isolated using the GP+E-86 and GP+envAM12 safe packaging cell lines. Infection of CD18-deficient lymphoblasts resulted both in expression of immunodetectable CD18 at 35-40% of normal levels on 55-60% of cells and in functional restoration of CD18-dependent aggregation. All of 16 mice transplanted with syngeneic bone marrow infected with the CD18 retrovirus expressed human CD18 on 17-36% of granulocytes at 2 weeks after transplantation, and expression was appropriately up-regulated in response to stimulation with zymosan-activated serum. This recombinant retrovirus should prove useful for further studies of somatic gene therapy for CD18 deficiency.

Familial genetic defect in a case of leukocyte adhesion deficiency

Leukocyte adhesion deficiency (LAD) is an inherited immunodeficiency disorder caused by CD18 subunit abnormality dependent defective expression of beta 2 integrins on the surface of leukocytes. On analysis of the CD18 molecular defect in a female Japanese patient with a severe deficiency LAD phenotype, neither CD11a nor CD18 molecules could be detected on the patient's EBV-transformed B lymphoblastoid cell line. The mRNA of the patient's B cells was normal in size, but was diminished in quantity, to approximately half normal levels. Sequencing of the CD18 cDNA of the patient revealed a C605 to T transition, resulting in a Pro178-->Leu substitution. This was heterozygous in the genomic DNA, and shown to be of maternal origin by family study. Only a few transcripts from the other allele without the Pro178-->Leu mutation were detectable. Northern blot analysis revealed reduced CD18 mRNA levels, not only in the patient, but also in the father and brother. These results indicate that our case is a compound heterozygote with two different mutant alleles: one causing a single amino acid substitution and the other causing defective expression of mRNA.

Independent mutations of the human CD3-epsilon gene resulting in a T cell receptor/CD3 complex immunodeficiency

The T-cell receptor (TCR) is composed of two glycoproteins (alpha and beta or gamma and delta) associated with four invariant polypeptides (CD3-gamma, delta, epsilon and zeta). The majority of TCR/CD3 complexes contain six polypeptide chains, and although there is some flexibility in the complex subunit stoichiometry the CD3-epsilon chain is central to CD3 core assembly and full complex formation. We have described previously defective expression of the TCR/CD3 complex in an immunodeficient child. We now report that two independent CD3-epsilon gene mutations present in the parents have segregated in the patient, leading to defective CD3-epsilon chain synthesis and preventing normal association and membrane expression of the TCR/CD3 complex.