Intracellular expression of antibody fragments directed against HIV reverse transcriptase prevents HIV infection in vitro

The Role of Antibodies in the Treatment of SARS-CoV-2 Virus Infection, and Evaluating Their Contribution to Antibody-Dependent Enhancement of Infection

Antibodies play a crucial role in the immune response, in fighting off pathogens as well as helping create strong immunological memory. Antibody-dependent enhancement (ADE) occurs when non-neutralising antibodies recognise and bind to a pathogen, but are unable to prevent infection, and is widely known and is reported as occurring in infection caused by several viruses. This narrative review explores the ADE phenomenon, its occurrence in viral infections and evaluates its role in infection by SARS-CoV-2 virus, which causes coronavirus disease 2019 (COVID-19). As of yet, there is no clear evidence of ADE in SARS-CoV-2, though this area is still subject to further study.

Downregulation of α-Synuclein Protein Levels by an Intracellular Single-Chain Antibody

BACKGROUND

Accumulation of α-synuclein (αSyn) in the dopaminergic neurons is a common pathology seen in patients with Parkinson's disease (PD). Overproduction of αSyn potentiates the formation of oligomeric αSyn aggregates and enhances dopaminergic neuron degeneration. Downregulating intracellular monomeric αSyn prevents the formation of αSyn oligomers and is a potential therapeutic strategy to attenuate the progression of PD.

OBJECTIVE

The purpose of this study is to investigate the efficacy of gene delivery of αSyn-specific single-chain antibodies in vitro and in vivo.

METHODS AND RESULTS

The plasmids for αSyn and selective antibodies (NAC32, D10, and VH14) were constructed and were transfected to HEK293 and SH-SY5Y cells. Co-expression of αSyn with NAC32, but not D10 or VH14, profoundly downregulated αSyn protein, but not αSyn mRNA levels in these cells. The interaction of αSyn and NAC32 antibody was next examined in vivo. Adeno-associated virus (AAV)-αSyn combined with AAV-NAC32 or AAV-sc6H4 (a negative control virus) were stereotactically injected into the substantia nigra of adult rats. AAV-NAC32 significantly reduced AAV-encoded αSyn levels in the substantia nigra and striatum and increased tyrosine hydroxylase immunoreactivity in the striatum. Also, in the animals injected with AAV-NAC32 alone, endogenous αSyn protein levels were significantly downregulated in the substantia nigra.

CONCLUSION

Our data suggest that AAV-mediated gene transfer of NAC32 is a feasible approach for reducing the expression of target αSyn protein in brain.

Intracellular expression of an anti-idiotypic antibody single-chain variable fragment reduces porcine reproductive and respiratory syndrome virus infection in MARC-145 cells

BACKGROUND

Porcine reproductive and respiratory syndrome virus (PRRSV) is the causative agent of porcine reproductive and respiratory syndrome; it is one of the most economically important viral diseases affecting the swine industry worldwide. At present, neither live-attenuated nor inactivated PRRSV vaccines can provide sustainable disease control. Our previous studies have demonstrated that PRRSV infection can produce the auto-anti-idiotypic antibodies (aAb2s) specific to the idiotypic antibodies against PRRSV GP5, which plays an important role in the host immune responses to PRRSV infection. In the present study, a single-chain variable antibody fragment (scFv) from the monoclonal anti-idiotypic antibody specific for the idiotypic antibody against GP5 was expressed in MARC-145 cells and its effect on virus infection in vitro was evaluated.

METHODS

An scFv was constructed from the anti-idiotypic antibody (Mab2-5G2) and was named 5G2scFv. The lentiviral vector system was used as a vehicle to deliver 5G2scFv into MARC-145 cells. The effect of 5G2scFv expression in MARC-145 was analysed by determining the PRRSV N protein level and the virus titre in the supernatant. Virus attachment and the level of type I interferon (IFN) were determined to elucidate the mechanism of the scFv effect.

RESULTS

5G2scFv was delivered in MARC-145 cells using the lentiviral vector system as confirmed by the western blot and indirect immunofluorescence assays. The PRRSV challenge experiments demonstrated that expressed 5G2scFv in MARC-145 strongly reduced PRRSV infection and replication by inhibiting protein synthesis and progeny virus production. This effect was not due to the change of viability or virus binding, but increased IFN-α at messenger RNA and protein levels.

CONCLUSIONS

The expression of the anti-idiotypic antibody 5G2scFv in MARC-145 cells has the interferential effect on PRRSV infection in the cells by induction of IFN-α, which provides a novel therapeutic approach for PRRSV infection.

Functions of Antibodies

Antibodies can impact pathogens in the presence or in the absence of effector cells or effector molecules such as complement, and experiments can often sort out with precision the mechanisms by which an antibody inhibits a pathogen in vitro . In addition, in vivo models, particularly those engineered to knock in or knock out effector cells or effector molecules, are excellent tools for understanding antibody functions. However, it is highly likely that multiple antibody functions occur simultaneously or sequentially in the presence of an infecting organism in vivo . The most critical incentive for measuring antibody functions is to provide a basis for vaccine development and for the development of therapeutic antibodies. In this respect, some functions, such as virus neutralization, serve to inhibit the acquisition of a pathogen or limit its pathogenesis. However, antibodies can also enhance replication or contribute to pathogenesis. This review emphasizes those antibody functions that are potentially beneficial to the host. In addition, this review will focus on the effects of antibodies on organisms themselves, rather than on the toxins the organisms may produce.

Current progress and challenges in HIV gene therapy

HIV-1 causes AIDS, a syndrome that affects millions of people globally. Existing HAART is efficient in slowing down disease progression but cannot eradicate the virus. Furthermore the severity of the side effects and the emergence of drug-resistant mutants call for better therapy. Gene therapy serves as an attractive alternative as it reconstitutes the immune system with HIV-resistant cells and could thereby provide a potential cure. The feasibility of this approach was first demonstrated with the 'Berlin patient', who was functionally cured from HIV/AIDS with undetectable HIV-1 viral load after transplantation of bone marrow harboring a naturally occurring CCR5 mutation that blocks viral entry. Here, we give an overview of the current status of HIV gene therapy and remaining challenges and obstacles.

Baculovirus display of single chain antibody (scFv) using a novel signal peptide

Background

Cells permissive to virus can become refractory to viral replication upon intracellular expression of single chain fragment variable (scFv) antibodies directed towards viral structural or regulatory proteins, or virus-coded enzymes. For example, an intrabody derived from MH-SVM33, a monoclonal antibody against a conserved C-terminal epitope of the HIV-1 matrix protein (MAp17), was found to exert an inhibitory effect on HIV-1 replication.

Results

Two versions of MH-SVM33-derived scFv were constructed in recombinant baculoviruses (BVs) and expressed in BV-infected Sf9 cells, N-myristoylation-competent scFvG2/p17 and N-myristoylation-incompetent scFvE2/p17 protein, both carrying a C-terminal HA tag. ScFvG2/p17 expression resulted in an insoluble, membrane-associated protein, whereas scFvE2/p17 was recovered in both soluble and membrane-incorporated forms. When coexpressed with the HIV-1 Pr55Gag precursor, scFvG2/p17 and scFvE2/p17 did not show any detectable negative effect on virus-like particle (VLP) assembly and egress, and both failed to be encapsidated in VLP. However, soluble scFvE2/p17 isolated from Sf9 cell lysates was capable of binding to its specific antigen, in the form of a synthetic p17 peptide or as Gag polyprotein-embedded epitope. Significant amounts of scFvE2/p17 were released in the extracellular medium of BV-infected cells in high-molecular weight, pelletable form. This particulate form corresponded to BV particles displaying scFvE2/p17 molecules, inserted into the BV envelope via the scFv N-terminal region. The BV-displayed scFvE2/p17 molecules were found to be immunologically functional, as they reacted with the C-terminal epitope of MAp17. Fusion of the N-terminal 18 amino acid residues from the scFvE2/p17 sequence (N18E2) to another scFv recognizing CD147 (scFv-M6-1B9) conferred the property of BV-display to the resulting chimeric scFv-N18E2/M6.

Conclusion

Expression of scFvE2/p17 in insect cells using a BV vector resulted in baculoviral progeny displaying scFvE2/p17. The function required for BV envelope incorporation was carried by the N-terminal octadecapeptide of scFvE2/p17, which acted as a signal peptide for BV display. Fusion of this peptide to the N-terminus of scFv molecules of interest could be applied as a general method for BV-display of scFv in a GP64- and VSV-G-independent manner.

E. coli expression of a soluble, active single-chain antibody variable fragment containing a nuclear localization signal

Single-chain antibody variable fragment (scFv) proteins consist of an antibody heavy chain variable sequence joined via a flexible linker to a light chain variable sequence. Prior work has shown that ScFv 18-2 binds the DNA-dependent protein kinase catalytic subunit (DNA-PKcs) and sensitizes cancer cells to radiation following nuclear microinjection. A potential clinical delivery strategy is based on modification of the scFv so that it can be taken up into cells and imported to the nucleus. This will require development of an expression system for a nuclear localization signal (NLS)-tagged scFv derivative. We found, however, that addition of the highly basic NLS severely compromised expression in the host-vector system used for the parental scFv. After testing a variety of host strains, fusion partners, and NLS sequences and placements, successful expression was obtained with a construct containing a stabilizing N-terminal maltose binding protein tag and a single, optimized, C-terminal NLS moiety. Amylose affinity-purified ScFv 18-2 NLS protein was stable to storage at 4 degrees C in the presence of glycerol or trehalose, bound selectively to an epitope peptide, and was cleavable at an engineered Factor Xa protease site. Following lipid-mediated uptake into cultured cells, NLS-tagged ScFv 18-2, unlike the parental ScFv 18-2, localized predominantly in the cell nucleus.

Inhibition of Papillomavirus Protein Function in Cervical Cancer Cells by Intrabody Targeting

Papillomaviruses (HPVs) are a major cause of human disease, and are responsible for approximately half a million cases of cervical cancer each year. HPVs also cause genital warts, and are the most common sexually transmitted disease in many countries. Despite their importance, there are currently no specific antivirals that are active against HPVs. Papillomavirus protein function is mediated largely by protein-protein interactions, which are difficult to inhibit using conventional approaches. To circumvent these problems, we have prepared an scFv library, and have used this to isolate high-affinity binding molecules that may stearically hinder the association of E6 with p53 and prevent E6-mediated p53 degradation in cervical cancer cells. One of the molecules isolated from the library (GTE6-1), had an affinity for 16E6 of 60nM, and bound within the first zinc finger of the protein. GTE6-1 was able to associate with non-denatured E6 following expression in mammalian cells and could inhibit E6-mediated p53 degradation in in vitro assays. E6-mediated p53 degradation is essential for the continuous growth of cervical cancer cells caused by HPV16. To examine the potential of GTE6-1 as an inhibitor of E6 function in such cells, the molecule was expressed in scFv, diabody and triabody formats in a number of cell lines that are driven to proliferate by the HPV16 oncogenes E6 and E7, including the cervical cancer cell line SiHa. In contrast to small E6-binding peptides containing the ELLG E6-binding motif, GTE6-1 expression lead to changes in nuclear structure, the appearance of apoptosis markers, and an elevation in the levels of p53. No effects were seen with a control scFv molecule, or when GTE6-1 was expressed in cells that are driven to proliferate by simian virus 40 (SV40) T-antigen. Given the accessibility of HPV-associated lesions to topical therapy, our results suggest that large interfering molecules such as intrabodies may be useful inhibitors of viral protein-protein interactions and be particularly appropriate for the treatment of HPV-associated disease.

Human single-chain antibodies inhibit replication of human immunodeficiency virus type 1 (HIV-1)

The F240 human monoclonal antibody specifically recognizes the disulfide loop-bonded immunodominant epitope of gp41 spanning residues 592-606 and expressed broadly on HIV-1 primary isolates. Despite broad reactivity with native virions and HIV-infected cells, the antibody fails to neutralize infection. However, cytoplasmic expression of single-chain antibody (scFv) directed against gp41 of HIV-1 provides a rationale means to inhibit the maturation of envelope protein. The variable regions of the heavy chain and light chain of human monoclonal antibody were amplified by PCR and linked by a 15 amino acid (GGSGS)3 linker in an orientation of VL-linker-VH and retroviral expression vectors were constructed to simultaneously express F240 scFv and eGFP to facilitate selection of scFv-producing cells. Incorporation of a human immunoglobulin signal sequence directed secretion of the F240 scFv (s-scFv) while an otherwise identical vector lacked this sequence (scFv) resulting in intracellular expression of scFv. Transduced human CD4+ H9 T cells were challenged with HIV. While both secreted and nonsecreted F240 scFv inhibited viral production, secretory F240 scFv was more potent. Thus, this novel approach to direct expression of a nonneutralizing scFv using the Ig signal sequence suggests that targeted therapy using antibodies to conserved, highly expressed epitopes may result in a decrease in viral production due to a reduction of viral assembly and/or transport and expression.

Making cell-permeable antibodies (Transbody) through fusion of protein transduction domains (PTD) with single chain variable fragment (scFv) antibodies: potential advantages over antibodies expressed within the intracellular environment (Intrabody)

Over the past decade, there has been growing interest in the use of antibodies against intracellular targets. This is currently achieved through recombinant expression of the single chain variable fragment (scFv) antibody format within the cell, which is commonly referred to as an intrabody. This possesses a number of inherent advantages over RNA interference (iRNA). Firstly, the high specificity and affinity of intrabodies to target antigens is well-established, whereas iRNA has been frequently shown to exert multiple non-specific effects. Secondly, intrabodies being proteins possess a much longer active half-life compared to iRNA. Thirdly, when the active half-life of the intracellular target molecule is long, gene silencing through iRNA would be slow to yield any effect, whereas the effects of intrabody expression would be almost instantaneous. Lastly, it is possible to design intrabodies to block certain binding interactions of a particular target molecule, while sparing others. There is, however, various technical challenges faced with intrabody expression through the application of recombinant DNA technology. In particular, protein conformational folding and structural stability of the newly-synthesized intrabody within the cell is affected by reducing conditions of the intracellular environment. Also, there are overwhelming safety concerns surrounding the application of transfected recombinant DNA in human clinical therapy, which is required to achieve intrabody expression within the cell. Of particular concern are the various viral-based vectors that are commonly-used in genetic manipulation. A novel approach around these problems would be to look at the possibility of fusing protein transduction domains (PTD) to scFv antibodies, to create a 'cell-permeable' antibody or 'Transbody'. PTD are short peptide sequences that enable proteins to translocate across the cell membrane and be internalized within the cytosol, through atypical secretory and internalization pathways. There are a number of distinct advantages that a 'Transbody' would possess over conventional intrabodies expressed within the cell. For a start, 'correct' conformational folding and disulfide bond formation can take place prior to introduction into the target cell. More importantly, the use of cell-permeable antibodies or 'Transbodies' would avoid the overwhelming safety and ethical concerns surrounding the direct application of recombinant DNA technology in human clinical therapy, which is required for intrabody expression within the cell. 'Transbodies' introduced into the cell would possess only a limited active half-life, without resulting in any permanent genetic alteration. This would allay any safety concerns with regards to their application in human clinical therapy.

Long-term survival and concomitant gene expression of ribozyme-transduced CD4+ T-lymphocytes in HIV-infected patients

BACKGROUND

An anti-HIV-1 tat ribozyme, termed Rz2, has been shown to inhibit HIV-1 infection/replication and to decrease HIV-1-induced pathogenicity in T-lymphocyte cell lines and normal peripheral blood T-lymphocytes. We report here the results of a phase I gene transfer clinical trial using Rz2.

METHODS

Apheresis was used to obtain a peripheral blood cell population from each of four HIV-negative donors. After enrichment for CD4+ T-lymphocytes, ex vivo expansion and genetic manipulation (approximately equal aliquots of the cells were transduced with the ribozyme-containing (RRz2) and the control (LNL6) retroviral vector), these cells were infused into the corresponding HIV-1-positive twin recipient. Marking was assessed over an initial 24-week period and in total over an approximate 4-year period.

RESULTS

The gene transfer procedure was shown to be safe, and technically feasible. Both RRz2- and LNL6-gene-containing peripheral blood mononuclear cells (PBMC) were detected at all time points examined to 4 years. There was concomitant gene construct expression in the absence of the need for ex vivo peripheral blood cell stimulation and there was no evidence of immune elimination of the neoR T-lymphocytes nor of silencing of the Moloney murine leukemia virus long terminal repeat.

CONCLUSIONS

The proof of principle results reported here demonstrate safety and feasibility of this type of gene transfer approach. While not specifically tested, T-lymphocytes containing an anti-HIV gene construct may impact on HIV-1 viral load and CD4+ T-lymphocyte count, potentially representing a new therapeutic modality for HIV-1 infection.

Selection of single-chain antibodies that specifically interact with vesicular stomatitis virus (VSV) nucleocapsid and inhibit viral RNA synthesis

The RNA genome of non-segmented negative-strand RNA viruses is completely covered by the nucleoprotein (N) forming a ribonucleoprotein complex, the nucleocapsid. The nucleocapsid functions as the template for viral RNA synthesis that is mediated by a viral RNA-dependent RNA polymerase. It is postulated that the selection of molecules that would specifically target the nucleocapsid and thus inhibit the viral polymerase activity could represent a common approach to block negative-strand RNA viruses. Two single-chain antibody fragments (scFv) that were selected using the phage display technology and interacted specifically with vesicular stomatitis virus (VSV) nucleocapsid were characterized. The two recombinant antibodies recognize a conformational epitope on the nucleocapsid and immunoprecipitate specifically nucleocapsids from infected cell extracts. Both antibodies have a strong inhibitory effect on VSV transcription activity in vitro. Thus, they represent starting molecules for future development of in vivo viral RNA synthesis inhibitors.

Camelized rabbit-derived VH single-domain intrabodies against Vif strongly neutralize HIV-1 infectivity

We recently developed a specific single-chain antibody from immunized rabbits to HIV-1 Vif protein that was expressed intracellularly and inhibited reverse transcription and viral replication. The Vif of HIV-1 overcomes the innate antiviral activity of a cytidine deaminase Apobec3G (CEM15) that induces G to A hypermutation in the viral genome, resulting in enhancement of viral replication infectivity. Here, we have developed a minimal scaffold VH fragment with intrabody properties derived from anti-Vif single-chain antibody that was engineered to mimic camelid antibody domains. Non-specific binding of VH by its interface for the light chain variable domain (VL) was prevented through amino acid mutations in framework 2 and 4 (Val37F, G44E, L45R, W47G and W103R). Our results demonstrate that all constructed anti-Vif VH single-domains preserve the antigen-binding activity and specificity in the absence of the parent VL domain. However, only the most highly camelized domains had high levels of intracellular expression. The expression in eukaryotic cells showed that VH single-domains could correctly fold as soluble proteins in the reducing environment. The results demonstrated an excellent correlation between improvements in protein solubility with gradually increasing camelization. Camelized single-domains efficiently bound Vif protein and neutralized its infectivity enhancing function, by reducing late reverse transcripts and proviral integration. The activity of the anti-Vif single-domains was shown to be cell-specific, with inhibitory effects only in cells non-permissive that require Vif for HIV-1 replication. Moreover, cell specificity of anti-Vif intrabodies was correlated with an increase of Apobec3G, which potentiates viral inhibition. The present study strongly suggests that camelization of rabbit VH domains is a potentially useful approach for engineering intrabodies for gene therapy.

Intracellular delivery of antibodies using TAT fusion protein A

Internalization of antibodies into mammalian cells is a useful method for analyzing and regulating cellular function. In this study, we developed a novel method for the delivery of antibodies into cells using the TAT-fused protein. This fusion protein consists of two functional domains, the protein transduction domain of HIV-1 TAT and the B domain of staphylococcal protein A (SpA), which has an ability to bind to the IgG. The TAT-SpA fusion protein was mixed with fluorescence-labeled rabbit IgG and added to cells. The internalization of antibody was analyzed using confocal microscopy and flow cytometry in living cells. As a result, fluorescence-labeled IgG with the TAT-SpA fusion protein was observed intracellularly. Flow cytometry results demonstrated time course and dose dependence relationships of antibody internalization. These results suggest that the TAT-SpA fusion protein can be a useful reagent for the delivery of antibody into cells.

Intracellular antibodies and challenges facing their use as therapeutic agents

A key feature of antibodies is their ability to bind antigens with high specificity and affinity. This has led to the concept of intracellular antibodies (intrabodies), designed to mimic antibody-antigen binding, but inside cells. Antibody fragments comprising the antigen-binding variable domains are convenient formats for intrabodies, potentially allowing for intracellular functionality. Intrabodies are promising tools, capable of interfering with a wide range of molecular targets in various intracellular compartments. However, many significant challenges remain to be overcome before intrabodies can be useful therapeutic agents. Although major progress has been made in the design and selection of intrabodies, new developments and advances are needed to allow their efficient delivery and expression for treatment of human diseases.

VH3 gene usage in neutralizing human antibodies specific for the Entamoeba histolytica Gal/GalNAc lectin heavy subunit

A combinatorial human immunoglobulin gene library was constructed from peripheral lymphocytes of an asymptomatic Entamoeba histolytica cyst passer and screened for the production of Fab antibody to the parasite. One of the Fab clones, CP33, recognized the 260-kDa galactose- and N-acetyl-D-galactosamine (Gal/GalNAc)-specific lectin of E. histolytica. By shuffling the heavy and light chains of CP33 with the heavy and light chains of two libraries derived from the cyst passer and a liver abscess patient, 18 additional clones were obtained. Sequence analysis of the heavy-chain genes, including CP33-H, revealed that all the nearest V-segment germ lines belonged to the VH3 family (VH3-21, VH3-30, VH3-48, and VH3-53), but the levels of homology were only 85 to 95%. The closest D-segment germ line was D2-2 or D6-6, and for the J-segment the closest germ line was JH4b or JH6b. On the other hand, all the light-chain genes, including CP33-L, belonged to the V kappa 1 family, in which the closest V kappa germ line gene was 02/012 or L5, with the J kappa 1, J kappa 2, J kappa 4, or J kappa 5 segment. CP33 and three other Fabs obtained by light-chain shuffling were purified and analyzed further. All of these Fabs recognized the cysteine-rich domain of the 170-kDa heavy subunit of the Gal/GalNAc lectin. Preincubation of E. histolytica trophozoites with these Fabs significantly inhibited amebic adherence to Chinese hamster ovary cells and also inhibited erythrophagocytosis. The ability of the neutralizing antibodies to block erythrophagocytosis for the first time implicates the lectin in phagocytosis and VH3 antibodies in defense against parasitic infections. These results demonstrate the utility of a combinatorial human immunoglobulin gene library for identifying and characterizing neutralizing antibodies from humans with amebiasis.

Recombinant human antibodies against the reverse transcriptase of human immunodeficiency virus type-1

Inhibitory antibodies to the reverse transcriptase (RT) of human immunodeficiency virus type-1 (HIV-1) can be used to block the life cycle of the virus. We have isolated five different human single chain Fv (ScFv) antibodies specific for HIV-1 RT from an antibody phage display library. Three of these antibodies inhibited the RNA-dependent DNA polymerase (RDDP) activity of RT and one of the three (F-6) inhibited also its DNA-dependent DNA polymerase (DDDP) activity. Unexpectedly, F-6 binds to the carboxyl terminus of the large subunit of RT, which contains the ribonuclease H (RNase H) domain, and not the polymerase domain of the protein. Moreover, this binding did not inhibit the RNase H enzymatic activity. To further characterize F-6 antibody, two cyclic synthetic peptides based on the amino acids sequences of the CDR3 of F-6 were synthesized. Peptide F-6CDRH3, with the sequence of CDR3 of the heavy chain, inhibited the RDDP activity of RT while peptide F-6CDRL3, with the sequence of CDR3 of the light chain, had no effect on this activity of RT. These results indicate that some of the effects of F-6 are mediated by the CDR3 of the heavy chain. The antibodies identified here will be further tested as intrabodies for their capacity to protect human cells from HIV-1 infection.

Inhibition of HIV-1 replication in primary human T cells transduced with an intracellular anti-HIV-1 p17 antibody gene

BACKGROUND

Previously we reported that human CD4(+) T cell lines stably expressing anti-HIV-1 gag p17 scFv/Ckappa in the cytosol or nucleus were resistant to HIV-1 challenge. Inhibition of HIV-1 by anti-HIV-1 gag p17 scFv/Ckappa occurred at both the pre- and post-integration steps of the viral cycle. To simulate more closely the in vivo infection process, in this study we tested anti-HIV-1 activity of anti-HIV-1 gag p17 scFv/Ckappa in primary human T cells.

METHODS

Anti-HIV-1 gag p17 scFv/Ckappa gene that is targeted into cytoplasm was inserted into a MMLV vector and transfected into packaging cell line PT67. The recombinant virus was used to transduce primary human T cells and human CD4(+) T cell line Jurkat. Following transduction, transduction efficiency, transgene expression, and cell phenotypes were studied. Transduced cells were then challenged with 100 TCID(50) of HIV-1 IIIB and primary isolate 5AO12. Following challenge, HIV-1 replication was monitored by p24 production.

RESULTS

Both transduced Jurkat and primary human T cells expressed the transgene. The expression of the transgene did not alter cell growth and CD4 or CD8 expression. However, HIV-1 replication in scFv/Ckappa-transduced Jurkat cells was inhibited by nearly 90% as compared with vector controls. More importantly, HIV-1 replication in primary human T cells from multiple donors transduced with the anti-HIV-1 gag p17 scFv/Ckappa gene was inhibited by as much as 99% as compared with primary T cells transduced with the vector control. The inhibition of replication was not due to interference in viral entry or reverse transcription. The less that HIV-1 replicated in different donor cells, the higher the degree of protection.

CONCLUSIONS

The expression of the anti-HIV-1 gag p17 scFv/Ckappa gene construct in primary human T cells renders these cells resistant to HIV-1 and points to the potential clinical usefulness of this gene construct for anti-HIV-1 gene therapy.

Construction and characterization of an intracellular single-chain human antibody to hepatitis C virus non-structural 3 protein

BACKGROUND/AIMS

We developed a single-chain antibody fragment (scFv) to the non-structural 3 protein (NS3) of hepatitis C virus (HCV) and tested its ability to interfere with the HCV replication cycle in infected hepatocytes.

METHODS

The variable regions of the human monoclonal antibody CM3.B6 that recognizes a conformational epitope within the helicase domain of NS3 were introduced into adenoviral vectors for expression in mammalian hepatocytes. Expression and binding properties of the scFv were analyzed by immunological assays. Effects of intracellular expression of the scFv on HCV replication were assessed in primary hepatocytes isolated from explanted livers of patients with chronic HCV infection by reverse transcription-polymerase chain reaction.

RESULTS

Transduction of HepG2 cells by the recombinant adenoviruses resulted in stable, efficient expression of scFv in the cytoplasm that was non-toxic to the cells. The scFv specifically bound to its cognate antigen. Significantly, intracellular expression of scFv resulted in a decrease in HCV genomic RNA in HCV infected hepatocytes.

CONCLUSIONS

These results indicate that specific binding of a scFv to NS3 may inhibit one or more functions of this essential viral protein thus interfering with the HCV replication cycle.

Expression and folding of an antibody fragment selected in vivo for high expression levels in Escherichia coli cytoplasm

In this review, we summarize some of our results on folding and directed evolution of an antibody fragment in Escherichia coli cytoplasm. We will also discuss some attempts to construct other antibodies active in this cellular compartment.

Formation of disulfide bridges by a single-chain Fv antibody in the reducing ectopic environment of the plant cytosol

Disulfide bridge formation in the reducing environment of the cytosol is considered a rare event and is mostly linked to inactivation of protein activity. In this report the in vivo redox state of a single-chain Fv (scFv) antibody fragment in the plant cytosol was investigated. The scFv antibody fragment consists of the variable light and heavy chain domains from a mouse IgG antibody, which are connected by a flexible linker peptide. In each domain one disulfide bridge is present. The functionality of antibodies, which are normally secreted via the oxidizing environment of the endoplasmic reticulum, depends on the formation of intramolecular disulfide bridges. We demonstrate that a scFv can form intramolecular disulfide bridges and is functionally expressed in the cytosol of stably transformed plants. In addition, the formation of intermolecular disulfide bridges through a cysteine present in the linker peptide was observed. In contrast, transient expression in tobacco protoplasts resulted in a cytosolic scFv lacking disulfide bridges, which had a substantially reduced affinity for the antigen. This indicates that functionality rather than stability is determined by the presence of disulfide bridges in the in planta-expressed scFv antibody. The controversial observation of disulfide bond formation in the cytosol is discussed.

Characterization of anti-cyclin E single-chain Fv antibodies and intrabodies in breast cancer cells: enhanced intracellular stability of novel sFv-F(c) intrabodies

Cyclin E is a critical cell cycle protein in the regulated progression of normal cells to replicate their DNA. Ectopic overexpression of cyclin E results in accelerated G(1) progression, chromosome instability, and a reduced requirement for growth factors. Dysregulated cyclin E expression is found in nearly all breast cancers examined. Toward the goal of developing a system to block cyclin E function in normal and breast cancer cells, we have developed anti-cyclin E single-chain antibodies (sFvs) for use as intrabodies. We have cloned the variable region genes from two hybridoma cell lines that produce anti-human cyclin E antibodies, linked them into sFvs, and showed their ability to bind cyclin E when expressed as sFv-F(c) fusion proteins. Engineering of the sFvs as sFv-F(c) intrabodies resulted in a dramatic increase in the sFv half-life as analyzed by pulse-chase and immunofluorescence, and these fusion intrabodies can be expressed in the cytosol or retargeted to the nucleus of breast cancer cell lines. Stable expression of a nuclear-targeted anti-cyclin E intrabody appears to inhibit the growth of the breast cancer cell line SKBR3. This work sets the stage for the development of intrabody-based inducible or tissue-specific cyclin E knockouts and for identifying cyclin E and its vital cell cycle functions as a potential gene therapy target in breast and other cancers.

Ras and p53 intracellular targeting with recombinant single-chain Fv (scFv) fragments: a novel approach for cancer therapy?

Intracellular expression of recombinant antibodies allows one to interfere with the functions of oncogenic molecules expressed in various cell compartments and has therefore a vast clinical potential in cancer therapy. We inhibited the functions of oncogenic Ras mutant forms by intracellular expression of a neutralizing single-chain antibody (scFv). In vitro studies indicated that the scFv is expressed in the cytosol of Xenopus laevis oocytes and of tumor cells, blocks ras-mediated activation processes, and induces tumor cell death. In vivo studies performed using scFv cDNA inserted into an adenoviral vector showed that the scFv dramatically affects tumor growth. Second, intracellular expression of scFvs directed against p53 indicated that these antibody fragments can be successfully targeted to cell nucleus, bind p53, and partially restore the transcriptional activity of p53 mutants in human tumor cells. Thus, intracellular scFvs directed against oncogenic molecules may represent a new class of antitumor agents.

Intrabody construction and expression III: engineering hyperstable V(H) domains

The folding of immunoglobulin domains requires the formation of a conserved structural disulfide. Therefore, as a general rule, they cannot be functionally expressed in the reducing environment of the cellular cytoplasm. We have previously reported that stability engineering can lead to the cytoplasmic expression of functional immunoglobulin V(L) domains. Here we apply rational stability engineering by consensus sequence analysis to V(H) domains. Isolated V(H) domains tend to aggregate more easily than V(L) domains; they do not refold quantitatively and are generally more difficult to handle in vitro. To overcome these problems, we successfully predicted and experimentally verified several stabilizing point mutations in the V(H) domain of a designed, catalytic Fv fragment. The effect of single mutations was additive, and they could be combined in a prototype domain with significantly improved stability against chemical denaturation and a 20-fold increased half time of irreversible thermal denaturation, at physiological temperature. This stabilized, isolated V(H) domain could be expressed solubly in the reducing cellular cytoplasm of Escherichia coli, at a yield of approximately 1.2 mg/L of shake flask culture. It remains fully functional, as evidenced by the successful reconstitution of an esterolytic Fv fragment with the V(L) domain. This success provides further evidence that consensus sequence engineering is a rational, plannable route to the construction of intrabodies.

Intrabody construction and expression. II. A synthetic catalytic Fv fragment

In general, proteins with structural disulfides cannot be expressed in the reducing environment of the cellular cytoplasm. To overcome this folding problem, we have previously engineered stabilizing mutations, predicted from a consensus sequence analysis, into isolated immunoglobulin VL domains. Here we show that such domains can be used as a framework in the construction of a functional heterodimeric Fv fragment, which was expressed solubly, with high yield in the cytoplasm of Escherichia coli. This designed catalytic intrabody, obtained from grafting the combining site of the esterolytic antibody 17E8, is active in the oxidized and the reduced state. Its construction required no special features on the part of the immunoglobulin, no single-chain linker and introduced no non-natural sequence motifs. The potential to design intrabodies with the recognition sequences of arbitrary immunoglobulins opens novel opportunities for gene therapy, cell biology, metabolic engineering and antibody biotechnology.

A novel anti-herpes simplex virus type 1-specific herpes simplex virus type 1 recombinant

A recombinant herpes simplex virus (HSV) capable of inhibiting its own replication as well as the replication of wild-type virus would have greatly increased safety as a general purpose vector for in vivo gene transfer, antitumor therapy, and viral vaccine against HSV infection. By using a tetracycline repressor (tetR)-mediated HSV-1 viral replication switch [Yao and Eriksson (1999). Hum. Gene Ther. 10, 419-427], we have generated a novel anti-HSV-1-specific HSV-1 recombinant (CJ83193) that expresses a trans-dominant negative HSV-1 UL9 origin-binding protein, UL9-C535C. The de novo synthesis of CJ83193 can be suppressed by UL9-C535C by at least 1 x 10(6)-fold in non-tetR-expressing cells, and is subject to tetracycline regulation over a range of four to five orders of magnitude in a tetR-expressing osteosarcoma line. In particular, the UL9-C535C peptides expressed from the CJ83193 genome can inhibit the replication of wild-type HSV-1 by 100- to 200-fold in single-step growth assays. The construction of CJ83193 creates a new general strategy for developing recombinant viral vectors able to function as an intracellular therapy against wild-type viral infections.

Depletion of alphaV integrins from osteosarcoma cells by intracellular antibody expression induces bone differentiation marker genes and suppresses gelatinase (MMP-2) synthesis

Integrin heterodimers sharing the common alphaV subunit are receptors for adhesion glycoproteins such as vitronectin and fibronectin. They are suggested to play an essential role in cell anchoring, differentiation, and survival. Here, we describe the construction of an expression plasmid coding for an intracellular single-chain antibody against alphaV integrin subunit. Saos-2 osteosarcoma cells transfected with this DNA construct showed an approximately 70-100% decrease in the cell surface expression of alphaVbeta3 and alphaVbeta5 integrins as shown by flow cytometry. Intracellular antibody expression had no effect on the mRNA levels of alphaV integrin. Pulse chase experiments of metabolically labeled integrins showed that the translation of precursor alphaV integrin subunit was not affected. However, the maturation of alphaV integrins as glycoproteins was slow suggesting that the transport from endoplasmic reticulum to Golgi complex was partially prevented. Depletion of alphaV integrins from Saos-2 cells led to a decreased ability to spread on fibronectin and vitronectin. Furthermore, the expression of osteoblast differentiation marker genes, alkaline phosphatase and osteopontin, was induced and concomitantly the expression of matrix metalloproteinase-2 decreased. Thus, alphaV integrins seem to be important regulators of osteosarcoma cell phenotypes. Our data also indicate that the expression of intracellular antibodies is an effective strategy to study the significance of specific integrins for cell phenotype and differentiation.

Inhibition of cytoplasmic antigen, glucose- 6-phosphate dehydrogenase, by VH-CH1, an intracellular Fd fragment antibody derived from a semisynthetic Fd fragment phage display library

A library of Fd fragment antibody binding proteins was created by random mutation of 15 nucleotides within the CDRIII region of the immunoglobulin heavy chain gene and displayed as Fd coat protein fusion constructs of M13 phage. The library was screened for those VHbinding sites that bound glucose-6-phosphate dehydrogenase (G6PD). One isolate (DH27bp) inhibited G6PD activity by 85 %. The DH27bpgene was re-engineered, placed in a eukaryotic expression vector having an isopropyl-beta-delta-thiogalactopyranoside (IPTG) inducible promoter, and transfected and then expressed in Chinese hamster V79 cells. G6PD activity was completely inhibited. Removal of IPTG reverted the cell to full G6PD activity. The intracellular dynamics of the G6PD/DH27bpcomplex showed that when the proteasomes of cells expressing DH27bpwere inhibited (N -acetyl-Leu-Leu-norleucinal or lactacystin) G6PD activity increased. Metabolic labelling of newly synthesized IPTG-induced proteins during/absence of proteasomal inhibitors showed that both G6PD and DH27bpare signaled for degradation when the intracellular complex is formed. Furthermore, semi-quantitative RT/PCR demonstrated that G6PD mRNA is upregulated over the time course of G6PD inactivation by DH27bpFd binding protein. These effects were not observed in those cells expressing a non-mutated Fd (UMHC) or in IPTG-treated non-transduced V79 cells. Our results demonstrate that an Fd-based intracellular binding protein can find and disable the function of a specific intracellular target and once the Fd expression is repressed the activity of intracellular targeted protein can revert to normal.

Properties of monoclonal antibodies directed against hepatitis B virus polymerase protein

Hepadnavirus polymerases are multifunctional enzymes that play critical roles during the viral life cycle but have been difficult to study due to a lack of a well-defined panel of monoclonal antibodies (MAbs). We have used recombinant human hepatitis B virus (HBV) polymerase (Pol) expressed in and purified from baculovirus-infected insect cells to generate a panel of six MAbs directed against HBV Pol protein. Such MAbs were subsequently characterized with respect to their isotypes and functions in analytical and preparative assays. Using these MAbs as probes together with various deletion mutants of Pol expressed in insect cells, we mapped the B-cell epitopes of Pol recognized by these MAbs to amino acids (aa) 8 to 20 and 20 to 30 in the terminal protein (TP) region of Pol, to aa 225 to 250 in the spacer region, and to aa 800 to 832 in the RNase H domain. Confocal microscopy and immunocytochemical studies using various Pol-specific MAbs revealed that the protein itself appears to be exclusively localized to the cytoplasm. Finally, MAbs specific for the TP domain, but not MAbs specific for the spacer or RNase H regions of Pol, appeared to inhibit Pol function in the in vitro priming assay, suggesting that antibody-mediated interference with TP may now be assessed in the context of HBV replication.

Protection of retrovirus-induced disease by transplantation of bone marrow cells transduced with MuLV env gene via retrovirus vector

Fv-4 is a mouse gene that dominantly confers resistance to infection by ecotropic murine leukemia virus (MuLV). We have demonstrated previously that bone marrow chimeras in which hematopoietic cells were replaced with cells expressing Fv-4 resistant (Fv-4r) gene product became refractory to Friend leukemia virus (FLV)-induced leukemogenesis. To induce in vivo resistance against retrovirus-induced diseases by retroviral vector-mediated gene transduction, we introduced Fv-4 env gene into bone marrow cells of FLV-susceptible C3H/He (C3H) mice with retroviral vector (pLSF) derived from murine Friend spleen focus forming virus (SFFV) and the cells were transplanted into lethally irradiated C3H mice. After the bone marrow transplantation, Fv-4r gene product was successfully expressed on erythroid and myeloid cells, while lymphoid cells were only weakly expressing Fv-4r gene product. The C3H mice expressing relatively higher amounts of Fv-4r gene product were rendered resistant to FLV-induced erythroleukemia, while mice expressing lower amounts of the Fv-4r gene product were still susceptible. Effective protection of FLV-induced leukemia in these mice suggested that the Fv-4r gene expression by erythroid cells that were the major target of FLV infection might be critical for resisting FLV-induced leukemia. Thus, gene therapy model by transducing Fv-4r env gene using bone marrow transplantation would provide a useful protection model system of retrovirus-induced diseases.

Inhibition of replication of HIV-1 at both early and late stages of the viral life cycle by single-chain antibody against viral integrase

Retroviruses including HIV-1 integrates a DNA copy of their RNA genome into cellular DNA of the infected cell. This reaction, essential and unique to replication of retroviruses, is mediated by the viral enzyme, integrase (IN). We constructed a recombinant gene encoding a single-chain, antigen-binding peptide (scAb2-19), which interacted with a carboxyl terminal part of HIV-1 IN. HeLa CD4 cells expressing scAb2-19 localized in either cytoplasmic or nuclear compartment were resistant to HIV-1 infection at an multiplicity of infection (MOI) of 0.25 or 0.063, but the resistance was overcome when MOI was increased to 1. To determine whether this resistance was due to inhibition of the early events, transduction experiments were performed with a replication-incompetent HIV-1 vector carrying bacterial lacZ driven by an internal Tat-independent cytomegalovirus immediate early promoter. Both cytoplasmic and nuclear expressions of scAb2-19 resulted in decrease in the transduction efficiency on HeLa CD4 cells. This implies that an early step of replication--before or during integration--was affected by the scAb2-19. Furthermore, cytoplasmic expression of scAb2-19 did not affect the viral amount released from the cells transfected with HIV-1 infectious clone DNA (pLAI). However, infectivity relative to reverse transcriptase activity was lower for virions released from the 293T cells cotransfected with pLAI and the cytoplasmic scAb2-19 expression plasmid than for those released from the 293T cells transfected with pLAI alone. This implies that scAb2-19 reduced infectivity of released virions by interfering a late step of the viral replication. The single-chain, antigen-binding peptide molecule may prove useful not only for studies of the functions of IN and its role in the viral life cycle but also for developing a gene therapy strategy against AIDS.

High level accumulation of single-chain variable fragments in the cytosol of transgenic Petunia hybrida

The accumulation of five murine single-chain variable fragments, binding to dihydroflavonol 4-reductase, was analyzed in transgenic Petunia hybrida plants. The five scFv-encoding sequences were cloned in an optimized plant transformation vector for expression in the cytosol under control of the 35S promoter. In a transient expression assay we found that the scFv expression levels were reproducible and correlated with those in stably transformed petunia. Our results show that accumulation in the cytosol strongly depends on the intrinsic properties of the scFv fragment. Three of the five scFv fragments accumulated to unexpectedly high levels in the cytosol of the primary transformants, but no phenotypic effect could be detected. Experimental results indicate that one of the scFv fragments accumulated in the cytosol to 1% of the total soluble protein as a functional antigen-binding protein in the absence of disulphide bonds. This observation supports the idea that certain antibody fragments do not need disulphide bonds to be stable and functional. Such scFv scaffolds provide new opportunities to design scFv fragments for immunomodulation in the cytosol.

Genetic engineering in the pig. Gene knockout and alternative techniques

Since endothelial cells (EC) are the major target cells during hyperacute rejection and are likely in delayed graft rejection, most of the genetic engineering of the xenotransplant donor is aimed at modifying their properties. Among the various strategies that are reviewed are the genotypic or phenotypic knockout of the alpha 1,3Gal antigen, which is a major target of xenoantibodies and is also probably involved in innate cellular response. In addition, the success of the transgeny of complement regulatory proteins is well established. In vitro data from analyses of the mechanisms of endothelial cell activation also suggest that other molecules could be used to regulate apoptosis or thrombotic microenvironment or to minimize recipient T-cell activation by inhibiting costimulatory proteins such as CD40 or B7. Alternative to usual knockout techniques (thus far not available in pigs, where no ES cells have been derived) will be presented.

Intracellular expression in pig cells of anti-alpha1,3galactosyltransferase single-chain FV antibodies reduces Gal alpha1,3Gal expression and inhibits cytotoxicity mediated by anti-Gal xenoantibodies

BACKGROUND

The carbohydrate structure Gal alpha1,3Gal expressed on pig cells is the major antigen recognized by xenoreactive natural antibodies in the higher primates. In xenotransplantation, natural antibodies binding to that structure initiate hyperacute rejection, and the anti-Gal alpha1,3Gal antibodies that are elicited probably take part in later phases of vascularized graft rejection. This epitope also appears to be involved in innate cellular responses. Inactivation of alpha1,3 galactosyltransferase in transgenic pigs would certainly lead to the success of xenotransplantation, but gene knockout in pigs is not feasible yet.

METHODS

As a novel strategy to inhibit alpha1,3 galactosylation, we generated recombinant single-chain Fv (ScFv) antibodies directed against pig alpha1,3-galactosyltransferase and evaluated the effect of their intracellular expression on enzyme activity and Gal alpha1,3Gal expression.

RESULTS

After in vitro transfection in pig cells, the scFv antibody anti-pig alpha1,3-galactosyltransferase reduced the amount or function of enzyme by up to 70% as evidenced by immunofluorescence and measurement of cell-associated activity. Consequently, Gal alpha1,3Gal on cell membranes was reduced to the same extent. This led to a profound (more than 90%) reduction in the cytotoxicity involving anti-Gal antibodies and complement.

CONCLUSION

Although not sufficient to knock out the overall human anti-pig natural xenoreactivity, intracellular expression of the scFv antibody anti-alpha1,3-galactosyltransferase in pig cells significantly decreases the amount of Gal alpha1,3Gal and could be important to protect cells from elicited antibodies as well as from innate effectors.

Intracellular expression and functional properties of an anti-p21Ras scFv derived from a rat hybridoma containing specific lambda and irrelevant kappa light chains

A rat single-chain Fv (Y238 scFv) was derived from the Y13-238 monoclonal antibody, a non-neutralizing anti-Ras antibody. The Y13-238 hybridoma expresses two functional light chains. N-terminus microsequencing of these chains showed the presence of the Y3 Ag1.2.3 Vkappa chain derived from the rat fusion partner and of a rat Vlambda chain. Primers designed for rat Vlambda amplification allowed the cloning of a functional scFv that could bind p21Ras. The kinetics of interaction of purified Y238 scFv with the p21Ras protein was evaluated by BIAcore with a NTA sensor chip and gave an apparent affinity constant in the nanomolar range (K(D)=4.58+/-0.63 nM). Immunoprecipitation experiments of Y238 scFv expressed in Xenopus laevis oocytes confirmed the specificity of the scFv for the Ras protein. Y238 scFv could be intracellularly expressed in oocytes and in mammaliam cells without adverse effect on the Ras signalling cascade. This scFv was therefore used as control in experiments where another anti-Ras scFv (Y259 scFv, derived from the neutralizing anti-Ras mAb Y13-259) blocked the Ras pathway in vitro and led to tumor regression in a nude mouse model [Cochet, O., Kenigsberg, M., Delumeau, I., Virone-Oddos, A., Multon, M.C., Fridman, W.H., Schweighoffer, F., Teillaud, J.L., Tocqué, B., 1998. Intracellular expression of an antibody fragment-neutralizing p21 ras promotes tumor regression. Cancer Res. 58, 1170-1176.]. Finally, BIAcore analyses indicated that the epitopes recognized by Y238 and Y259 scFvs are not overlapping and allowed a more precise definition of the Y13-238 epitope.

Genetically engineered antibodies in gene transfer and gene therapy

Our ability to produce and engineer human monoclonal antibodies provides a basis for the development of novel therapeutical strategies against a variety of diseases. These strategies not only include improved passive immunotherapy but also more sophisticated antibody-based gene therapies involving gene transfer approaches. Four of the major applications of antibody gene engineering in the field of gene therapy are reviewed here. These are (1) the redefinition of viral vector tropism of infection for better transduction of cells of therapeutical interest, (2) the grafting of new cell recognition activities to effector cells of the immune system to kill cancer and pathogen-infected cells, (3) the inhibition of cellular and viral functions through intracellular expression of antibody-derived molecules, and (4) the systemic delivery of therapeutic monoclonal antibodies by non-B cells in living organisms.

Production of uninfectious human immunodeficiency virus type 1 containing viral protein R fused to a single-chain antibody against viral integrase

A single-chain antibody (scAb) against human immunodeficiency virus type 1 (HIV-1) integrase was expressed as a fusion protein of scAb and HIV-1 viral protein R (Vpr), together with the HIV-1 genome, in human 293T cells. The expression did not affect virion production much but markedly reduced the infectivity of progeny virions. The fusion protein was found to be incorporated into the virions. The incorporation appears to account for the reduced infectivity.

Inhibition of activating transcription factor 1- and cAMP-responsive element-binding protein-activated transcription by an intracellular single chain Fv fragment

Activating transcription factor 1 (ATF1) and cAMP-responsive element (CRE)-binding protein (CREB) activate transcription through CREs located in the promoters of cellular and viral genes. We previously described a monoclonal antibody (mAb41.4) that prevents ATF1 binding to DNA and reduces CRE-driven promoter activity in vitro (Orten, D. J., Strawhecker, J. M., Sanderson, S. D., Huang, D., Prytowsky, M. B. , and Hinrichs, S. H. (1994) J. Biol. Chem. 269, 32254-32263). A single chain Fv (scFv) fragment from the mAb41.4-expressing hybridoma was generated to provide a means to investigate transcription factor function via intracellular expression of the scFv fragment. The affinity of scFv4 (subgroup: VL kappa-III, VH miscellaneous) for ATF1 was similar to that of the parental mAb and the Fab fragment, but it demonstrated greater inhibitory activity and reacted with CREB. scFv4 disrupted the binding of both ATF1 and CREB in electrophoretic mobility shift assays and reduced expression of CRE-driven expression in vitro. Transient expression of scFv had no effect on the non-CRE-containing adenovirus major late promoter. The proliferating cell nuclear antigen promoter, containing two CREs, was significantly more sensitive to inhibition by scFv than the cytomegalovirus immediate-early promoter, containing five CREs. Cotransfection of either ATF1 or CREB in the presence of scFv restored basal levels of expression. The intracellular expression of scFv provides a unique means to investigate the roles of the transcription factors ATF1 and CREB.

Interferon-γ Increases Expression of Chemokine Receptors CCR1, CCR3, and CCR5, But Not CXCR4 in Monocytoid U937 Cells

Chemokine receptors (CR), which can mediate migration of immune cells to the site of inflammation, also function as coreceptors for human immunodeficiency virus (HIV) entry into CD4+ T lymphocytes and antigen-presenting cells. We demonstrate here that interferon-γ (IFN-γ) increases the expression of chemokine receptors CCR1, CCR3, and CCR5 in monocytoid U937 cells as detected by cell surface molecule labeling and mRNA expression, as well as by intracellular calcium mobilization and cell migration in response to specific ligands. The increased expression of these chemokine receptors also results in an enhanced HIV-1 entry into cells. Our data provide evidence for a relationship of cellular pathways that are induced by IFN-γ with those that regulate chemokine receptor expression.

Interferon-γ Increases Expression of Chemokine Receptors CCR1, CCR3, and CCR5, But Not CXCR4 in Monocytoid U937 Cells

Chemokine receptors (CR), which can mediate migration of immune cells to the site of inflammation, also function as coreceptors for human immunodeficiency virus (HIV) entry into CD4+ T lymphocytes and antigen-presenting cells. We demonstrate here that interferon-γ (IFN-γ) increases the expression of chemokine receptors CCR1, CCR3, and CCR5 in monocytoid U937 cells as detected by cell surface molecule labeling and mRNA expression, as well as by intracellular calcium mobilization and cell migration in response to specific ligands. The increased expression of these chemokine receptors also results in an enhanced HIV-1 entry into cells. Our data provide evidence for a relationship of cellular pathways that are induced by IFN-γ with those that regulate chemokine receptor expression.

The biochemistry of gene therapy for AIDS

Gene therapy has enormous potential and could in the near future involve the clinical biochemist in monitoring its efficacy. The involvement of clinical biochemists in this field could be not only in evaluating the impact of a gene-based strategy on disease progression, but also in measuring the expression of the products of therapeutic genes in treated individuals. Indeed, gene therapy presents new possibilities for the treatment of many diseases and, in particular, merits consideration in the treatment of a fatal disease like AIDS. The aim of this paper is to review the biochemical basis and clinical relevance of the gene therapy approaches directed towards the inhibition of human immunodeficiency virus type-1. We discuss the goals which have been achieved, the problems which have occurred and the efforts that are being made to solve them. In this regard, particular attention is paid to new strategies targeting 'therapeutic' enzymes to human immunodeficiency virus type-1 nucleic acids.

Neither Human Immunodeficiency Virus-1 (HIV-1) nor HIV-2 Infects Most-Primitive Human Hematopoietic Stem Cells as Assessed in Long-Term Bone Marrow Cultures

Attempts to clarify the pathophysiology of human immunodeficiency virus (HIV)-mediated bone marrow (BM) dysfunction have yielded inconsistent results regarding the susceptibility of BM progenitors to the viral infection. To specifically address this question, we exposed highly purified subpopulations of human BM progenitor cells to various HIV-1 and HIV-2 strains and assessed (pro)viral gene presence and expression in more-committed (CD34+CD38+) as well as most-primitive (CD34+CD38−) cells in long-term BM cultures. Quantitative analysis of long-term culture-initiating cells (LTCIC) failed to demonstrate adverse effects of exposing hematopoietic stem cells to HIV. Our results show that HIV-2, similar to HIV-1, does not infect hematopoietic stem cells in vitro with any significant frequency and infected cells are not present within LTCICs. Cytofluorometric analysis of CD34+ cells for surface molecules that facilitate HIV entry was consistent with the functional assay in that expression of virus receptors was predominantly on the more-committed subsets of BM progenitors. The failure to detect productive or latent HIV in the most-primitive human BM progenitor and stem cells has important implications for future therapeutic strategies, including those dealing with transduction of these cells with protective genes as a treatment modality for AIDS.

Neither Human Immunodeficiency Virus-1 (HIV-1) nor HIV-2 Infects Most-Primitive Human Hematopoietic Stem Cells as Assessed in Long-Term Bone Marrow Cultures

Attempts to clarify the pathophysiology of human immunodeficiency virus (HIV)-mediated bone marrow (BM) dysfunction have yielded inconsistent results regarding the susceptibility of BM progenitors to the viral infection. To specifically address this question, we exposed highly purified subpopulations of human BM progenitor cells to various HIV-1 and HIV-2 strains and assessed (pro)viral gene presence and expression in more-committed (CD34+CD38+) as well as most-primitive (CD34+CD38−) cells in long-term BM cultures. Quantitative analysis of long-term culture-initiating cells (LTCIC) failed to demonstrate adverse effects of exposing hematopoietic stem cells to HIV. Our results show that HIV-2, similar to HIV-1, does not infect hematopoietic stem cells in vitro with any significant frequency and infected cells are not present within LTCICs. Cytofluorometric analysis of CD34+ cells for surface molecules that facilitate HIV entry was consistent with the functional assay in that expression of virus receptors was predominantly on the more-committed subsets of BM progenitors. The failure to detect productive or latent HIV in the most-primitive human BM progenitor and stem cells has important implications for future therapeutic strategies, including those dealing with transduction of these cells with protective genes as a treatment modality for AIDS.

Cells Transfected with a Non-Neutralizing Antibody Gene Are Resistant to HIV Infection: Targeting the Endoplasmic Reticulum and Trans-Golgi Network

Plasmids containing single chain Fv (scFv) non-neutralizing human anti-HIV-1 gp41 Ab cDNA, with or without endoplasmic reticulum (ER) or trans-Golgi network (TGN) retention signals, were constructed. Stable transfectants expressing these scFvs then were generated from COS-7 cells and HIV-1-susceptible CD4+ human T cells (Jurkat). scFv without a retention signal was secreted from cells, whereas scFv with an ER or TGN retention signal remained primarily within targeted intracellular compartments. The expression of scFv, scFv-ER, and scFv-TGN did not adversely affect the appearance of uninfected cells, as measured by growth rate or CD4 expression. Pulse-chase experiments revealed that the t1/2 of scFv-ER and scFv-TGN within cells was greater than 24 h and less than 9 h, respectively. The scFv-ER and scFv-TGN bound HIV gp160, and the scFv-ER-gp160 and the scFv-TGN-gp160 complexes were stable within HIV-infected transfectants. Further studies revealed that the maturation processing of gp160 into gp120 and gp41 was blocked in the scFv-ER transfectants, but not in the scFv-TGN transfectants. Moreover, HIV replication, as measured by p24, was inhibited by up to 99% in cells transfected with scFv-ER or scFv-TGN, but was not inhibited in cells transfected with the secretory form of scFv. It is concluded that the targeting of non-neutralizing anti-HIV-1 Abs to specific intracellular compartments blocks HIV replication and represents a potential therapeutic strategy for protecting uninfected lymphopoietic stem cells from HIV-1-infected patients.

Gene therapy for infectious diseases

Gene therapy is being investigated as an alternative treatment for a wide range of infectious diseases that are not amenable to standard clinical management. Approaches to gene therapy for infectious diseases can be divided into three broad categories: (i) gene therapies based on nucleic acid moieties, including antisense DNA or RNA, RNA decoys, and catalytic RNA moieties (ribozymes); (ii) protein approaches such as transdominant negative proteins and single-chain antibodies; and (iii) immunotherapeutic approaches involving genetic vaccines or pathogen-specific lymphocytes. It is further possible that combinations of the aforementioned approaches will be used simultaneously to inhibit multiple stages of the life cycle of the infectious agent.