High-efficiency gene transfer and pharmacologic selection of genetically engineered human keratinocytes

Low efficiencies of gene transfer to somatic cells have frustrated therapeutic gene delivery efforts in a wide array of tissues including the skin. Production of populations of keratinocytes in which all cells contain the desired therapeutic gene may be important in future genetic therapies. This may be the case in disorders such as epidermolysis bullosa and ichthyosis, where a failure to correct the vast majority of cells within tissue could perpetuate central disease features such as skin fragility and defective barrier function. We have refined retroviral gene transfer parameters to achieve significant improvements in gene delivery efficiencies to human keratinocytes compared to those previously reported. We have also generated retroviral vectors that allow rapid pharmacologic selection of human keratinocytes without interfering with the potential of these cells to regenerate epidermis in vivo--we determined that blasticidin is superior to the commonly used neomycin. The combined capabilities for efficient retroviral gene transfer and effective pharmacologic selection allow production of entirely engineered populations of human keratinocytes for use in future efforts to achieve effective cutaneous gene delivery.

[Preserving remnant liver function after major hepatic vein occlusion]

OBJECTIVE

To observe the pathological changes of the remained hepatic lobe after major hepatic vein (MHV) occlusion.

METHOD

Seventy-eight rats were randomly divided into the control group, the ligation group of segmental hepatic vein, the stricture group of left MHV, and the ligation group of left MHV. The pathology, hepatic microcirculation and hemodynamic changes of the involved hepatic lobe of MHV occlusion were dynamically determined.

RESULT

Necrosis occurred in the hepatocytes at the first postoperative day in the ligation group of MHV. Extensive collaterals between the hepatic veins and the portal veins appeared in the periphery of involved liver lobe in the stricture group of MHV. The levels of endotoxin and TXB(2)/6-Keto-PGF1alpha in the blood of portal vein obviously increased in the ligation group of MHV and also increased in the stricture group of MHV. The levels of endotoxin and TXB(2)/6-Keto-PGF1alpha in the blood of portal vein in the ligation and stricture group of MHV were apparently higher than those in the ligation group of segmental hepatic vein and in the control group.

CONCLUSION

The involved liver tissue can not tolerate complete MHV occlusion. The hepatic tissue lacking of MHV drain not only loss its function, but also cause endotoxemia and disorder of hepatic microcirculation. The involved hepatic lobe after the MHV ligation should have been resected at the same time.

[A technique of constructing human chromosomal band-specific probe pools using degenerate oligonucleotide primer]

OBJECTIVE

To establish a rapid and efficient technique of constructing human chromosomal band specific probe pools and their libraries.

METHODS

A modified method of combining chromosome microdissection with degenerate oligonucleotide primed PCR(DOP-PCR) was used. 3p23-p26, 3q21-q22 and 4p12- p16 band from human chromosomes were microdissected and amplified as probe pools. The origins of the PCR products were determined by chromosome fluorescence in situ hybridization. The PCR products and pUC19 were digested by Xho I and Sal I respectively, and linke up. The DH5alpha were transformed by the recombinated vectors as the specific band libraries. The inserts were digested by EcoR I and Hind III, then measured by electrophoretic analysis. And the copies of inserts were identified by in situ bacterial colony hybridization with genomic DNA.

RESULTS

All the three probe pools showed the special yellow-green signals in their microdissection responsible bands. The sizes of DOP-PCR products ranged from 300bp to 1800bp. 3q21-q22 probe pool generated about 1.2 x 10(4) clones. The average size of inserts was about 420bp by analysis of 30 positive clones. The rate of single-copy and low-repeated sequences was about 81%(178/220), while the rate of middle-repeated and high- repeated sequences was about 19%(42/220).

CONCLUSION

The results proved that the modified microdissection combining DOP-PCR technique provided a simple and efficient method to construct the human chromosome band-specific probe pools and might contribute to gene cloning and complete sequencing of human genome.

Effects of cannabinoids on preimplantation mouse embryo development and implantation are mediated by brain-type cannabinoid receptors

We examined the relative importance of G (Gi) protein-coupled brain-type (CB1-R) and spleen-type (CB2-R) cannabinoid receptors in preimplantation embryo development using agonists and antagonists specific to CB1-R and CB2-R. The results establish that endogenous cannabinoid ligands, anandamide and sn-2 arachidonoylglycerol, arrest embryo development in vitro, and this effect is reversed by CB1-R antagonists SR141716A or AM 251, but not by SR144528, a CB2-R antagonist. A CB2-R selective agonist AM 663 failed to affect embryo development. These results suggest that cannabinoid effects on embryo development are mediated by CB1-R. We also observed that delta9-tetrahydrocannabinol ([-]THC) infused in the presence of cytochrome P450 inhibitors interfered with blastocyst implantation. This adverse effect was reversed by coinfusion of SR141716A. The less active stereoisomer (+)THC plus the inhibitors failed to affect implantation. Analysis of tissue levels demonstrated that uterine accumulation of (-)THC occurred when it was infused in the presence of the P450 inhibitors. These results demonstrate that the uterus and perhaps the embryo have the cytochrome P450 enzymes to metabolize (-)THC and neutralize its adverse effects on implantation. Collectively, the present study demonstrates that cannabinoid effects on embryo development and implantation are mediated by embryonic and/or uterine CB1-R, but not CB2-R.

Telomeric sequences from human herpesvirus 6 do not mediate nuclear retention of episomal DNA in human cells

Telomeric repeat sequences (TRS) have been identified close to, but not at, the genome termini of several lymphotropic herpesviruses, including human herpesviruses 6 and 7 (HHV-6, HHV-7). The functional significance of these motifs remains uncertain. Since telomeric sequences can mediate stable retention of episomal DNA in yeast, we have tested whether the TRS motifs from HHV-6 might mediate a similar function in human cells. Several candidate sequences were assessed for their ability to provide nuclear retention to an autonomously replicating vector in rapidly dividing human tissue culture cells, including HHV-6 TRS DNA, as well as telomeric DNA from human cells and sequences from Epstein-Barr virus (EBV). However, only a vector carrying the EBV-derived retention mechanism showed a significant level of nuclear retention. Neither the HHV-6 TRS motifs, nor human telomeric sequences, mediated nuclear retention of episomal DNA in human cells.

Characterization of hydrogen bonding in the complex of adenosine deaminase with a transition state analogue: a Raman spectroscopic study

The Raman spectra of purine ribonucleoside as well as a stable model compound (1-methoxyl-1,6-dihydropurine ribonucleoside), free in solution and bound into its complex with adenosine deaminase (ADA), have been studied by Raman difference spectroscopy. Using purine riboside analogues labeled with 15N1 or 13C6 and the theoretical frequency normal-mode analyses of these molecules using ab initio quantum mechanic methods, we have positively identified many of the Raman bands in the enzyme-bound inhibitor. The spectrum of the enzyme-bound inhibitor is consistent with the enzyme-catalyzed hydration of the purine base to yield 1-hydroxyl-1,6-dihydropurine ribonucleoside, as suggested earlier by X-ray crystallographic studies. In addition, the Raman data and subsequent vibrational analyses show that the binding-induced Raman spectral changes of the inhibitor can be modeled by the formation of a strong hydrogen bond to its N1-H bond. This hydrogen bond, apparently between the N1-H of the inhibitor and the Odelta1 of Glu217 in ADA, causes a substantial N1-H bending frequency increase of about 50-100 cm-1 compared to its solution value, and this results in an estimated enthalpy of the hydrogen bond of 4-10 kcal/mol. The relationship of transition state stabilization in the catalytic strategy of this efficient enzyme to such a bonding pattern is discussed.

Frequency-stable and ultranarrow-linewidth semiconductor laser locked directly to an atomic-cesium transition

We describe a new method for semiconductor laser FM noise reduction. A Doppler-free Faraday resonance in Cs vapor provided optical feedback, and FM sideband saturation spectroscopy in a second Cs cell provided electronic feedback. The combined optical and electronic feedback allowed us to reduce the low-frequency FM noise power by more than 6 orders of magnitude, which resulted in a sub-100-Hz-linewidth semiconductor laser locked directly to an atomic transition frequency.

AM630 is an inverse agonist at the human cannabinoid CB1 receptor

The present investigation examines WIN 55,212-2 and AM630 at the cloned human cannabinoid CB1 receptor stably expressed in Chinese hamster ovary (CHO) cells. The effect of various concentrations of WIN 55,212-2 and AM630 on basal [35S]GTPgammaS binding to cell membranes was determined. WIN 55,212-2 (100 microM) stimulated basal [35S]GTPgammaS binding 77.9% with an EC50 value of 0.36 microM. Conversely, AM630 (100 microM) inhibited basal [35S]GTPgammaS binding by 20.9% with an EC50 value of 0.90 microM. These results show that WIN 55,212-2 is an agonist and AM630 is an inverse agonist in this system.

Alterations in NF-kappaB function in transgenic epithelial tissue demonstrate a growth inhibitory role for NF-kappaB

Stratified epithelium contains a mitotically active basal layer of cells that cease proliferating, then migrate outwards and undergo terminal differentiation. The control of this process, which is abnormal in cutaneous neoplasia and inflammation, is not well understood. In normal epidermis, NF-kappaB proteins were found to exist in the cytoplasm of basal cells and then to localize in the nuclei of suprabasal cells, suggesting a role for NF-kappaB in the switch from proliferation to growth arrest and differentiation. Functional blockade of NF-kappaB by expressing dominant-negative NF-kappaB inhibitory proteins in transgenic murine and human epidermis produced hyperplastic epithelium in vivo. Consistent with this, application of a pharmacologic inhibitor of NF-kappaB to intact skin induced epidermal hyperplasia. In contrast, overexpression of active p50 and p65 NF-kappaB subunits in transgenic epithelium produced hypoplasia and growth inhibition. These data suggest that spatially restricted NF-kappaB activation occurs in stratified epithelium and indicate that NF-kappaB activation in this tissue, in contrast to its role in other settings, is important for cellular growth inhibition.

Differences in chemokine coreceptor usage between genetic subtypes of HIV-1

HIV-1 uses chemokine coreceptors for cell entry. CXCR4 is the major coreceptor for T-cell-line-adapted isolates and CCR5 for non-T-cell-line-adapted isolates. This study investigated if coreceptor usage differs between genetic subtypes of HIV-1. Eighty-one primary isolates representing nine different genetic subtypes (A-J, except I) were tested on U87.CD4 glioma cells stably expressing chemokine receptor CCR1, CCR2b, CCR3, CCR5, or CXCR4. Coreceptor usage was compared to biological phenotype of the isolates (rapid/high, syncytium-inducing or slow/low, non-syncytium-inducing) and to clinical and immunological status of the study subjects. CXCR4 usage was perfectly correlated to the biological phenotype for all subtypes; all of 26 isolates with rapid/high phenotype and none of 55 isolates with slow/low phenotype could infect the CXCR4 expressing cell line. Importantly, the CXCR4-positive, rapid/high phenotype was underrepresented among subtype C isolates. Furthermore, dual tropism for CXCR4 and CCR5 was not found among subtype D isolates. Uni- and multivariate analyses indicated that these subtype-specific differences in coreceptor usage were not due to differences in clinical status, CD4 counts, or treatment. This study shows that CXCR4 usage determines the biological phenotype for all subtypes, but that there appear to exist subtype-dependent differences in frequency of usage of certain coreceptors. This opens up the possibility that genetic subtypes may differ in important biological properties such as virulence, tissue tropism, and transmissibility.

[Clinical significance of cytokine and eosinophil cationic protein concentrations in sputum of asthmatic patients]

OBJECTIVE

To examine whether levels of inflammatory cytokines and eosinophil cationic protein (ECP) in the sputum reflect the severity of bronchial asthma.

METHOD

We collected sputum expectorated spontaneously from 15 asthmatics with acute attacks of moderate to severe degree (MS group) and 10 subjects with acute attacks of mild asthma (M group). The interleukin (IL)-5(35 ng/L) tumor necrosis factor (TNF)-alpha(M 149 +/- 59 ng/L, MS 267 +/- 147 ng/L), soluble IL-2 receptor (sIL-2R) (M 348 +/- 107 kU/L, MS 488 +/- 127 kU/L) levels in the sputum were measured with enzyme-linked immunosorbent assay, and sputum ECP (M 127 +/- 95 micrograms/L, MS 278 +/- 150 micrograms/L) concentration were measured by Immuno-CAP System.

RESULT

Sputum IL-5, TNF-alpha, sIL-2R, ECP concentrations in moderate to severe patients were significantly higher than in mild subjects.

CONCLUSION

These findings suggest that inflammatory cytokines and mediator levels are detectable in the sputum from asthmatics and they might participate in the exacerbation of asthma.

Biochemical characterization of the Cys138Arg substitution associated with the AB variant form of GM2 gangliosidosis: evidence that Cys138 is required for the recognition of the GM2 activator/GM2 ganglioside complex by beta-hexosaminidase A

The function of the GM2 activator protein is to act as a substrate-specific cofactor in the hydrolysis of GM2 ganglioside by beta-hexosaminidase A. Mutations in the gene encoding it result in the AB variant form of GM2 gangliosidosis. One such mutation, Cys138 Arg, results in the mutant protein being retained and degraded in the endoplasmic reticulum of mammalian cells. In order to characterize the biochemical effects of this substitution, we expressed the mutant protein in transformed bacteria. We first compared the wild-type protein produced by two bacterial expression methods, one requiring protein refolding, with activator purified from the medium of transfected CHO cells. The "activity" and circular dichroism spectrum (alpha-helical content) of all three proteins were similar, justifying the use of refolded activator from transformed bacteria in structure/function studies. Second, the mutant protein was expressed in both bacterial systems and in each retained approximately 2% of the wild type's specific activity. The presence of even this small amount of activity in the mutant protein coupled with a calculated alpha-helical content nearly identical to the wild type, strongly suggest that no major tertiary or secondary structural changes, respectively, had occurred due to the mutation. However, we demonstrate that its heat stability at 60 degrees C is reduced 14-fold, suggesting some localized change in tertiary structure. The loss of a disulfide loop was confirmed by reacting the mutant protein with Ellman's reagent. A kinetic analysis detected a large increase in the apparent K(m) of beta-hexosaminidase A for the mutant; however, there was no apparent change in Vmax. A fluorescence dequenching assay was used to evaluate the ability of the mutant protein to transport lipids and bind GM2 ganglioside. These assays detected no difference between the wild-type and mutant proteins, indicating that the Cys138 Arg substitution has no effect on these functions. We conclude that the mutation specifically affects a domain in the activator protein that is responsible for the recognition of the activator-GM2 ganglioside complex by beta-hexosaminidase A.

[Methodology for designing pathological models of acute renal failure]

This paper reports the methodological study on the following five pathological models of acute renal failure (ARF): 1. glycerine-induced ARF in rats; 2. noradrenaline-induced ARF in dogs; 3. ARF model caused by shutting left renal artery in dogs; 4. hydrargyrism-induced ARF in rabbits; and 5. gentamycin-induced ARF in rats.

Functional identification and analysis of cis-acting sequences which mediate genome cleavage and packaging in human herpesvirus 6

Sequences present at the genomic termini of herpesviruses become linked during lytic-phase replication and provide the substrate for cleavage and packaging of unit length viral genomes. We have previously shown that homologs of the consensus herpesvirus cleavage-packaging signals, pac1 and pac2, are located at the left and right genomic termini of human herpesvirus 6 (HHV-6), respectively. Immediately adjacent to these elements are two distinct arrays of human telomeric repeat sequences (TRS). We now show that the unique sequence element formed at the junction of HHV-6B genome concatemers (pac2-pac1) is necessary and sufficient for virally mediated cleavage of plasmid DNAs containing the HHV-6B lytic-phase origin of DNA replication (oriLyt). The concatemeric junction sequence also allowed for the packaging of these plasmid molecules into intracellular nucleocapsids as well as mature, infectious viral particles. In addition, this element significantly enhanced the replication efficiency of oriLyt-containing plasmids in virally infected cells. Experiments revealed that the concatemeric junction sequence possesses an unusual, S1 nuclease-sensitive conformation (anisomorphic DNA), which might play a role in this apparent enhancement of DNA replication--although additional studies will be required to test this hypothesis. Finally, we also analyzed whether the presence of flanking viral TRS had any effect on the functional activity of the minimal concatemeric junction (pac2-pac1). These experiments revealed that the TRS motifs, either alone or in combination, had no effect on the efficiency of virally mediated DNA replication or DNA cleavage. Taken together, these data show that the cleavage and packaging of HHV-6 DNA are mediated by cis-acting consensus sequences similar to those found in other herpesviruses, and that these sequences also influence the efficiency of HHV-6 DNA replication. Since the adjacent TRS do not influence either viral cleavage and packaging or viral DNA replication, their function remains uncertain.

A resonance Raman study of the C=C stretch modes in bovine and octopus visual pigments with isotopically labeled retinal chromophores

Previous resonance Raman spectroscopic studies of bovine and octopus rhodopsin and bathorhodopsin in the C-C stretch fingerprint region have shown drastically different spectral patterns, which suggest different chromophore-protein interactions. We have extended our resonance Raman studies of bovine and octopus pigments to the C=C stretch region in order to reveal a more detailed picture about the difference in retinal-protein interactions between these two pigments. The C=C stretch motions of the protonated retinal Schiff base are strongly coupled to form highly delocalized ethylenic modes located in the 1500 to 1650 cm-1 spectral region. In order to decouple these vibrations, a series of 11,12-D2-labeled retinals, with additional 13C labeling at C8, C10, C11 and C14, respectively, are used to determine the difference of specific C=C stretch modes between bovine and octopus pigments. Our results show that the C9=C10 and C13=C14 stretch mode are about 20 cm-1 lower in the Raman spectrum of octopus bathorhodopsin than in bovine bathorhodopsin, while the other C=C stretch modes in these two bathorhodopsins are similar. In contrast, only the C9=C10 stretch mode in octopus rhodopsin is about 10 cm-1 lower than in bovine rhodopsin, while other C=C stretches are similar.

Sustainable cutaneous gene delivery

Durable gene delivery to human skin is necessary for lasting correction of human genetic skin disease. Current cutaneous gene-delivery strategies, however, have achieved only transient gene expression, often only within a small percentage of tissue cells. The recent inability to sustain phenotypic correction of human genetic skin disease due to loss of therapeutic gene expression in regenerated epidermal tissue has highlighted this current limitation. In an effort to surmount this problem, we have generated gene delivery vectors that produce more durable gene delivery in human skin tissue in vivo.

[The study on chemical composition and crystalline structure of hypoplastic primary dental enamel]

The present study, firstly, analyzed chemical composition of hypoplastic primary teeth by electron probe analyzer and compared the hypoplastic part with the normal part in the same tooth; secondly, by X-ray diffraction analyzer, studied the hypoplastic dental enamel and the normal dental enamel, and compared the crystalline structure between different dental enamel and with that of the hydroxyapatite. The aim was to find out any change of crystalline structure. Two exfoliated hypoplastic deciduous anterior teeth were used for the electron probe study. The normal part of each tooth served as control. Determinations of weight percentage (wt%) were made for P, Al, Mg, Ca, Mn, Fe, Zn, Sr, Na, K and F. Four exfoliated hypoplastic deciduous anterior teeth and eight exfoliated normal deciduous anterior teeth were used for the X-ray diffraction study. We found by X-ray diffraction that the length of the alpha-axis of enamel crystallite and the distance of lattice plane (corresponding 300) were increased in defective enamel and could be associated with the increased content of magnesium detected by electron probe. Thus, the present study demonstrated that there were both quantity and quality changes in the enamel hypoplasia lesion, which may increase the susceptibility of the defective teeth to caries.

Catechol-O-methyltransferase Val158Met polymorphism: frequency analysis in Han Chinese subjects and allelic association of the low activity allele with bipolar affective disorder

Catechol-O-methyltransferase catalyses the O-methylation of biologically active or toxic catechols and is a major component of the metabolism of drugs and neurotransmitters such as L-dopa, noradrenaline, adrenaline, and dopamine. Human catechol-O-methyltransferase activity is an autosomal partially dominant trait and is strongly associated with a valine to methionine substitution at codon 158 of the protein. About 25% of Caucasians have low activity, 50% intermediate activity and 25% high activity as determined by either phenotypic or genotypic measurement. In black populations, the low activity allele (Met158; COMTL) is less frequent with about 7% being homozygous. Using a PCR based genotyping assay, we report that the Met158 allele is also less frequent in normal Han Chinese subjects with about 3% of the population being homozygous. Because of its role in catecholamine metabolism and several lines of evidence pointing to a locus for psychosis near the COMT gene on chromosome 22q11, we have analysed the COMT Val158Met polymorphism as a candidate susceptibility factor for bipolar affective disorder. We report an association between bipolar affective disorder and the Met158 allele (p = 0.004) and genotype (p = 0.01) in 93 affected Chinese subjects and 98 controls. We hypothesize that either the low activity allele of catechol-O-methyltransferase is a risk factor for bipolar affective disorder in Chinese populations or is in linkage disequilibrium with a nearby susceptibility gene or polymorphism.

Coreceptor usage of primary human immunodeficiency virus type 1 isolates varies according to biological phenotype

The biological phenotype of primary human immunodeficiency virus type 1 (HIV-1) isolates varies according to the severity of the HIV infection. Here we show that the two previously described groups of rapid/high, syncytium-inducing (SI) and slow/low, non-syncytium-inducing (NSI) isolates are distinguished by their ability to utilize different chemokine receptors for entry into target cells. Recent studies have identified the C-X-C chemokine receptor CXCR4 (also named fusin or Lestr) and the C-C chemokine receptor CCR5 as the principal entry cofactors for T-cell-line-tropic and non-T-cell-line-tropic HIV-1, respectively. Using U87.CD4 glioma cell lines, stably expressing the chemokine receptor CCR1, CCR2b, CCR3, CCR5, or CXCR4, we have tested chemokine receptor specificity for a panel of genetically diverse envelope glycoprotein genes cloned from primary HIV-1 isolates and have found that receptor usage was closely associated with the biological phenotype of the virus isolate but not the genetic subtype. We have also analyzed a panel of 36 well-characterized primary HIV-1 isolates for syncytium induction and replication in the same series of cell lines. Infection by slow/low viruses was restricted to cells expressing CCR5, whereas rapid/high viruses could use a variety of chemokine receptors. In addition to the regular use of CXCR4, many rapid/high viruses used CCR5 and some also used CCR3 and CCR2b. Progressive HIV-1 infection is characterized by the emergence of viruses resistant to inhibition by beta-chemokines, which corresponded to changes in coreceptor usage. The broadening of the host range may even enable the use of uncharacterized coreceptors, in that two isolates from immunodeficient patients infected the parental U87.CD4 cell line lacking any engineered coreceptor. Two primary isolates with multiple coreceptor usage were shown to consist of mixed populations, one with a narrow host range using CCR5 only and the other with a broad host range using CCR3, CCR5, or CXCR4, similar to the original population. The results show that all 36 primary HIV-1 isolates induce syncytia, provided that target cells carry the particular coreceptor required by the virus.

Association analysis of the dopamine D4 gene exon III VNTR and heroin abuse in Chinese subjects

Although social and cultural influences are clearly important, family, twin and adoption studies indicate that genes contribute significantly to substance abuse. Substance abuse is associated with novelty seeking, a heritable human personality trait which may be influenced by alleles of the dopamine D4 (DRD4) gene exon III VNTR. Consequently Kotler et al analysed the DRD4 VNTR in opiate-dependent subjects from Israel, and found a significant excess of the 7-repeat allele. We have attempted to replicate this finding using a Han Chinese case-control sample of 121 heroin-dependent subjects and 154 normal controls. We found two 7-repeat alleles which occurred exclusively in the patient group, and overall there was an excess of longer alleles, which did not reach significance (chi 2 = 7.04; P = 0.07). When the D4 VNTR was divided into 'long' (5-7 repeats) and 'short' (2-4 repeats), a significant excess of long alleles was observed in the patient group (P = 0.023, one-tailed), with an odds ratio of 2.30 (95% CI 1.07-4.93). We conclude that our findings support the hypothesis that alleles of the DRD4 exon III VNTR are susceptibility factors for heroin abuse.

Envelope glycoproteins from human immunodeficiency virus types 1 and 2 and simian immunodeficiency virus can use human CCR5 as a coreceptor for viral entry and make direct CD4-dependent interactions with this chemokine receptor

Several members of the chemokine receptor family have recently been identified as coreceptors, with CD4, for entry of human immunodeficiency virus type 1 (HIV-1) into target cells. In this report, we show that the envelope glycoproteins of several strains of HIV-2 and simian immunodeficiency virus (SIV) employ the same chemokine receptors for infection. Envelope glycoproteins from HIV-2 use CCR5 or CXCR4, while those from several strains of SIV use CCR5. Our data indicate also that some viral envelopes can use more than one coreceptor for entry and suggest that some of these coreceptors remain to be identified. To further understand how different envelope molecules use CCR5 as an entry cofactor, we show that soluble purified envelope glycoproteins (SU component) from CCR5-tropic HIV-1, HIV-2, and SIV can compete for binding of iodinated chemokine to CCR5. The competition is dependent on binding of the SU glycoprotein to cell surface CD4 and implies a direct interaction between envelope glycoproteins and CCR5. This interaction is specific since it is not observed with SU glycoprotein from a CXCR4-tropic virus or with a chemokine receptor that is not competent for viral entry (CCR1). For HIV-1, the interaction can be inhibited by antibodies specific for the V3 loop of SU. Soluble CD4 was found to potentiate binding of the HIV-2 ST and SIVmac239 envelope glycoproteins to CCR5, suggesting that a CD4-induced conformational change in SU is required for subsequent binding to CCR5. These data suggest a common fundamental mechanism by which structurally diverse HIV-1, HIV-2, and SIV envelope glycoproteins interact with CD4 and CCR5 to mediate viral entry.