A simple method for overproduction and purification of p24 Gag protein of human immunodeficiency virus type 1

A synthetic gag p24 epitope chemically coupled to BSA through a decaalanine peptide enhances HIV type 1 serodiagnostic ability by several folds

p24 is an immunodominant gag core protein of HIV-1. The synthetic immunodominant epitope of p24 and the recombinant p24 show poor immunoreactivity and specificity, respectively. Their application is, therefore, severely limited in the serodiagnosis of HIV-1, although it is an important marker for early diagnosis. These limitations have been overcome by conjugating the synthetic p24 to BSA through a decaalanine peptide spacer. The engineered p24 shows about 5-fold more efficient immunoreactivity than the synthetic p24, and, at the same time, shows a several fold reduction in nonspecific cross-reactivity as compared to recombinant p24. Our strategy to conjugate the p24 peptide epitope to BSA worked well as a consistent and reliable immunodiagnostic marker. This strategy may also prove useful for the diagnosis of other diseases.

Earlier detection of human immunodeficiency virus type 1 p24 antigen and immunoglobulin G and M antibodies to p17 antigen in seroconversion serum panels by immune complex transfer enzyme immunoassays

For earlier diagnosis of human immunodeficiency virus type 1 (HIV-1) infection, the sensitivities of immune complex transfer enzyme immunoassays for HIV-1 p24 antigen and antibody immunoglobulin G (IgG) to HIV-1 p17 antigen were improved approximately 25- and 90-fold, respectively, over those of the previous immunoassays by performing solid-phase immunoreactions with shaking and increasing the serum sample volumes, and immune complex transfer enzyme immunoassay of antibody IgM to p17 antigen was also performed in the same way as the improved immunoassay of antibody IgG to p17 antigen. By the improved immunoassays, p24 antigen and antibody IgG to p17 antigen were detected earlier in 32 and 53%, respectively, of the HIV-1 seroconversion serum panels tested than before the improvements, and p24 antigen was detected as early as or earlier than HIV-1 RNA by reverse transcriptase-PCR (RT-PCR) in all of the panels tested. In 4 panels out of 19 tested, antibody IgG to p17 antigen or both antibodies IgG and IgM to p17 antigen were detected earlier than p24 antigen and RNA, although the antibody levels declined slightly before their steep increases usually observed after p24 antigen and RNA. Thus, the window period in diagnosis of HIV-1 infection can be shortened by detection of p24 antigen with the improved immunoassay as much as by detection of RNA with RT-PCR and, in some cases, more by detection of antibodies IgG and IgM to p17 antigen with the improved immunoassays than by detections of p24 antigen with the improved immunoassay and RNA with RT-PCR.

Gag-derived proteins of HIV-1 isolates from Indian patients: cloning, expression, and purification of p24 of B- and C-subtypes

A simple and efficient method for hyperexpression in Escherichia coli and purification of capsid protein, p24, of human immunodeficiency virus type 1 (HIV-1) of both B- and C-subtypes is described. DNA-encoding p24 of C-subtype was cloned from C-subtype gag sequence which was obtained by PCR amplification using DNA extracted from peripheral blood mononuclear lymphocytes (PBMLs) of an HIV-1-infected patient from India. DNA-encoding p24B protein was amplified directly by two-step PCR using genomic DNA obtained from PBMLs of an HIV-infected individual. A T7 promoter-based expression system was optimized for hyperexpression of p24 in the soluble form. Both p24 (B- and C-subtype) were purified to near homogeneity using conventional chromatographic techniques. Purification of p24 (C subtype) was described for the first time with yield of 53 mg from 1 liter of culture. The yield of p24 (B-subtype) was 67 mg from 1 liter of culture, which was severalfold better than reported earlier. The immunoreactivity of both types of p24 to sera from HIV-infected individuals was comparable. This report describes a simple, highly efficient, and reproducible method for obtaining large quantities of highly pure p24 of both B- and C-subtype, which can be used for structural, biochemical, and immunological characterization and, eventually, for diagnostic and prognostic applications.

Ultrasensitive immune complex transfer enzyme immunoassay of HIV-1 p24 antigen with less serum interference using 2,4-dinitrophenyl-anti-HIV-1 p24 IgG and indirectly immobilized (anti-2,4-dinitrophenyl group) Fab

In the immune complex transfer enzyme immunoassay previously reported, the immune complex consisting of 2,4-dinitrophenyl-biotinyl-bovine serum albumin-affinity-purified rabbit anti-HIV-1 p24 Fab' conjugate, HIV-1 p24 antigen and monoclonal mouse anti-HIV-1 p24 Fab'-beta-D-galactosidase conjugate was trapped on polystyrene beads coated directly with affinity-purified (anti-2,4-dinitrophenyl group) IgG and was transferred to polystyrene beads coated with biotinyl-bovine serum albumin and streptavidin. The serum volume used was limited to 10 microL due to serious serum interference, and the detection limit of HIV-1 p24 antigen was 240 fg/mL serum. In the present study, HIV-1 p24 antigen was incubated simultaneously with 2,4-dinitrophenyl-affinity-purified rabbit anti-HIV-1 p24 IgG and monoclonal mouse anti-HIV-1 p24 Fab'-beta-D-galactosidase conjugate in the presence of excess nonspecific rabbit IgG. The immune complex of the three components formed was trapped on polystyrene beads coated successively with biotinyl-bovine serum albumin, streptavidin and biotinyl-affinity-purified (anti-2,4-dinitrophenyl group) Fab'. After washing, the immune complex was eluted from the polystyrene beads with excess epsilonN-2,4-dinitrophenyl-L-lysine and transferred to polystyrene beads coated with affinity-purified goat (antirabbit IgG) IgG. The serum volume used was increased to 90 microL with only slight serum interference, and the detection limit of HIV-1 p24 antigen was lowered 9-fold to 26 fg/mL serum.

Optimal conditions of immune complex transfer enzyme immunoassay for p24 antigen of HIV-1

In the immune complex transfer enzyme immunoassay for HIV-1 p24 antigen, different preparations of anti-p24 Fab'-beta-D-galactosidase conjugate, various periods of time for immunoreactions involved, and shaking for incubations with polystyrene beads were tested. On the basis of the results of these experiments, p24 antigen was measured as follows. The antigen was reacted simultaneously with 2,4-dinitrophenyl-biotinyl-bovine serum albumin-affinity-purified rabbit anti-p24 Fab' conjugate and highly polymerized monoclonal mouse anti-p24 Fab'-beta-D-galactosidase conjugate at 37 degrees C for 2 hr. The immune complex formed comprising the three components was trapped onto colored polystyrene beads coated with affinity-purified (anti-2,4-dinitrophenyl group) IgG for 1.5 hr and was transferred to white polystyrene beads coated with streptavidin in the presence of epsilon N-2,4-dinitrophenyl-L-lysine for 1.5 hr. The incubations with polystyrene beads were performed at room temperature with shaking. beta-D-Galactosidase activity bound to the white polystyrene beads was assayed by fluorometry at 30 degrees C for 2 hr. The detection limit of p24 antigen (0.1 amol/tube and 10 amol (0.24 pg)/ml of serum) was equal to that obtained when the formation, trapping, and transferring of the immune complex were performed for 4, 16, and 3 hr, respectively, by incubation without shaking. Namely, the period of time required for the immune complex transfer enzyme immunoassay of p24 antigen was markedly shortened (25.5-7 hr) without loss of the sensitivity. By the improved immune complex transfer enzyme immunoassay, p24 antigen was detected 12-20 days earlier than the detection of antibodies to HIV-1, i.e., seroconversion by the conventional ELISA.

Shortening of the window period in diagnosis of HIV-1 infection by simultaneous detection of p24 antigen and antibody IgG to p17 and reverse transcriptase in serum with ultrasensitive enzyme immunoassay

Following HIV infection, there is a window period of 6-8 weeks, during which HIV antibodies are not detectable and the infection cannot be diagnosed by methods for detecting HIV antibodies. However, HIV antigens are detectable in the latter part of the window period, although the level of HIV antigens declines as the level of HIV antibodies increases. We developed an ultrasensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) for the simultaneous detection of both p24 antigen of HIV-1 and antibody IgGs to p17 and reverse transcriptase of HIV-1 in a single assay tube and tested 11 HIV-1 seroconversion serum panels and serum samples randomly collected from 79 HIV-1 seropositive subjects and 100 HIV-1 seronegative subjects. The simultaneous detection was shown not only to shorten the window period significantly as compared with conventional methods for HIV-1 antibody detection but also to make possible a reliable diagnosis of HIV-1 infection from the time of seroconversion until late stages of the infection.

Ultrasensitive and more specific enzyme immunoassay (immune complex transfer enzyme immunoassay) for p24 antigen of HIV-1 in serum using affinity-purified rabbit anti-p24 Fab' and monoclonal mouse anti-p24 Fab'

Previously, an ultrasensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) for p24 antigen of HIV-1 was developed. The immune complex comprising 2,4-dinitrophenyl-biotinyl-bovine serum albumin-rabbit anti-p24 Fab' conjugate, p24 antigen, and rabbit anti-p24 Fab' -beta-D-galactosidase conjugate was trapped onto polystyrene beads coated with affinity-purified (anti-2,4-dinitrophenyl group) IgG, was eluted with epsilon N-2, 4-dintrophenyl-L-lysine, and was transferred to polystyrene beads coated with streptavidin. beta-D-Galactosidase activity bound to the streptavidin-coated polystyrene beads was assayed by fluorometry. This assay was highly sensitive. However, bound beta-D-galactosidase activity had to be assayed for a long time (20 h), and the nonspecific signal was observed in 5% serum samples from subjects with low risk of HIV infection. In the present study, the assay time for bound beta-D-galactosidase activity was shortened to 2.5 h by using 2,4-dinitrophenyl-biotinyl-bovine serum albumin-affinity-purified rabbit anti-p24 Fab' conjugate and affinity-purified rabbit anti-p24 Fab' -beta-D-galactosidase conjugate. Furthermore, the nonspecific signal was found to increase with increasing periods of time for storage of serum samples at -20 degrees C, and this increase was prevented without prolongation of the assay time for bound beta-D-galactosidase activity and without loss of the sensitivity by substituting monoclonal mouse anti-p24 Fab'-beta-D-galactosidase conjugate for affinity-purified rabbit anti-p24 Fab'beta-D-galactosidase conjugate.

Earlier diagnosis of HIV-1 infection by simultaneous detection of p24 antigen and antibody IgGs to p17 and reverse transcriptase in serum with enzyme immunoassay

Serum samples of four HIV-1 seroconversion serum panels were subjected in a single assay tube simultaneously to ultrasensitive enzyme immunoassays (immune complex transfer enzyme immunoassays) for p24 antigen of HIV-1 and for antibody IgGs to p17 and reverse transcriptase (RT) of HIV-1. Signals became positive 7-15 days earlier than the detection of antibodies to HIV-1 by conventional methods and remained strongly positive even after levels of p24 antigen declined. Thus the simultaneous detection of p24 antigen and antibody IgGs to p17 and RT made possible both as early a diagnosis of HIV-1 infection as the appearance of p24 antigen in the circulation, shortening "the window period," and as reliable a diagnosis of the infection as that by the detection of antibodies to HIV-1 from the time of seroconversion until late stages of the infection, since the serum level of antibody IgG to RT was high not only in asymptomatic carriers but also in patients with AIDS-related complex and AIDS.

Immune complex transfer enzyme immunoassay that is more sensitive and specific than western blotting for detection of antibody immunoglobulin G to human immunodeficiency virus type 1 in serum with recombinant pol and gag proteins as antigens

Antibody immunoglobulin G (IgG) to human immunodeficiency virus type 1 (HIV-1) in serum was detected by ultrasensitive enzyme immunoassays (immune complex transfer enzyme immunoassays) with recombinant reverse transcriptase (rRT), p17 (rp17) and p24 (rp24) of HIV-1 as antigens and beta-D-galactosidase from Escherichia coli as the label. The immune complex, comprising 2,4-dinitrophenyl-bovine serum albumin-recombinant protein conjugate, antibody IgG to HIV-1, and recombinant protein-beta-D-galactosidase conjugate, was trapped on polystyrene beads coated with affinity-purified (anti-2,4-dinitrophenyl group) IgG, eluted with epsilon N-2,4-dinitrophenyl-L-lysine, and transferred to polystyrene beads coated with affinity-purified (anti-human IgG gamma-chain) IgG. Bound beta-D-galactosidase activity was assayed by fluorometry. The assays were highly reproducible with no serious serum interference, and they were much more sensitive than Western immunoblotting for the corresponding antigens. Signals with rRT, rp17, and rp24 for asymptomatic carriers were at least 56,000-, 680-, and 22-fold higher, respectively, than those for seronegative individuals, and neither indeterminate nor false-positive results were observed, whereas some serum samples were false negative or false positive by Western blotting for p17 and/or p24 antigen. In some cases, seroconversion was detected earlier than by conventional methods. Therefore, these assays are suggested to be more useful than conventional methods not only for the confirmation of antibody IgGs to RT, p17, and p24 of HIV-1 in serum but also for the detection of seroconversion.

Overproduction, purification, and diagnostic use of the recombinant HIV-1 Gag proteins, the precursor protein p55 and the processed products p17, p24, and p15

HIV-1 Gag protein precursor p55, and its processed products, p17, p24, and p15 were overproduced in Escherichia coli and purified to near homogeneity. To study the antigenic properties and the potentiality as the diagnostic and prognostic reagents, varying amounts of the purified Gag proteins were dotted onto the polyvinylidene difluoride membrane and reacted with 40 sera of HIV-1-infected individuals (35 AC, 1 ARC, and 4 AIDS patients) and 10 sera of normal healthy donors. p55 reacted with 40 (100%) sera of HIV-1 carriers, while p17, p24, and p15 reacted with 37 (92.5%), 35 (87.5%) and 34 (85%) of the 40 sera of HIV-1 carriers, respectively. On the whole, the reaction of p55 was especially strong and that of p15 was the weakest. p55 showed the strongest reaction among the four Gag proteins with all specimens, and it showed a positive reaction with a carrier serum with which none of the processed Gag proteins showed a positive reaction. Therefore, p55 is the most useful antigen among the four Gag proteins for detection of the Gag antibodies and may even be one of the most useful antigens for the diagnosis of HIV-1 infection.

Measurement of human immunodeficiency virus type 1 p24 in serum by an ultrasensitive enzyme immunoassay, the two-site immune complex transfer enzyme immunoassay

Human immunodeficiency virus type 1 (HIV-1) p24 antigen was measured by an ultrasensitive enzyme immunoassay (two-site immune complex transfer enzyme immunoassay). The antigen was reacted simultaneously with 2,4-dinitrophenyl-biotinyl-bovine serum albumin-anti-recombinant p24 (rp24) Fab' conjugate and anti-rp24 Fab'-beta-D-galactosidase conjugate. The complex that was formed, comprising the three components, was transferred from polystyrene beads coated with affinity-purified (anti-2,4-dinitrophenyl group) immunoglobulin G (IgG) to polystyrene beads coated with streptavidin. The detection limit of rp24 was 2.4 fg (0.1 amol) per assay or 0.24 pg/ml with as little as 10 microliters of serum. When sera were treated at low pH, p24 was detected in 34 (68%) of 50 serum samples from asymptomatic carriers, in 25 (86%) of 29 serum samples from patients with advanced HIV-1 infection, and in none of 117 serum samples from HIV-1-seronegative individuals. Levels of p24 in serum were inversely correlated to those of anti-HIV-1 p24 IgG, and the recovery of rp24 added to serum decreased to zero with increasing levels of anti-HIV-1 p24 IgG in serum. This sensitive method may be used as a powerful tool for investigating the disease.

Production and simple purification of a protein encoded by part of the gag gene of HIV-1 in the Escherichia coli HB101F+ expression system inducible by lactose and isopropyl-beta-D-thiogalactopyranoside

The development of the Escherichia coli expression system, which was prepared by transferring the F' episome from strain 71/18 to a highly to a transformable F- strain HB101, is described. These new HB101 (F+) cells, which produced high levels of lac repressor, were capable of taking up lactose and grew under strict selection conditions. A relatively simple two-step purification of part of a protein (M(r) 27,000) encoded by the gag gene of HIV-1 in this expression system is described. The supernatant prepared by removal of cell debris was precipitated by 30% saturation of ammonium sulphate. The protein spectrum was characterized by gel electrophoresis, immunoblotting and ion-exchange titration curves. Optimum separation was achieved using a strong anion exchanger (Mono Q) at pH 8.0. The purified protein did not cross-react with antibodies to E. coli.

Overexpression and simple purification of human immunodeficiency virus-1 gag epitope derived from a recombinant antigen in E. coli and its use in ELISA

To develop a test for diagnosis of human immunodeficiency virus-1 (HIV-1) exposure sensitivity, a part of the gag gene was cloned and expressed in Escherichia coli, using expression vectors containing a trp promoter. The immunoreactivity of recombinant protein was determined using HIV-1 specific antibodies in a Western blot analysis. The recombinant plasmid, pYHCgag3, gag gene was fused to the trpE' gene linked to the hydroxylamine (HA) cleavage recognition sequence which was induced to overexpress a core antigen (gag a.a. 121-398 from plasmid BH10) as fusion protein in the form of insoluble inclusion body. Recombinant gag was purified by a simple single step purification procedure. After partial purification of inclusion bodies and subject to the HA-cleavage treatment, gag protein was further purified to homogeneity using DEAE-Sepharose chromatography. The purified core antigen offered reliable results with high sensitivity and specificity for identification of HIV-1 antibodies when tested in the enzyme-linked immunosorbent assay (ELISA). These results suggest that mass production of recombinant core antigen will provide a valuable resource to HIV-1 serodiagnostics for the screening of large groups of blood donors to prevent HIV-1 infection.

Diagnosis of HIV-1 infection by detection of antibody IgG to HIV-1 in urine with ultrasensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) using recombinant proteins as antigens

Anti-HIV-1 IgG in urine was detected by an ultrasensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) using recombinant reverse transcriptase (RT), p17 and p24 as antigens, and beta-D-galactosidase from Escherichia coli as label. Anti-HIV-1 IgG in urine was reacted simultaneously with 2,4-dinitrophenyl-bovine serum albumin-recombinant protein conjugate and recombinant protein-beta-D-galactosidase conjugate. The immune complex formed, consisting of the three components, was trapped onto polystyrene balls coated with affinity-purified (anti-2,4-dinitrophenyl group) IgG. After washing, the immune complex was eluted from the polystyrene balls with excess of epsilon N-2,4-dinitrophenyl-L-lysine and transferred to clean polystyrene balls coated with affinity-purified (anti-human IgG gamma-chain) IgG. Finally, the enzyme activity bound to the last solid phase was assayed by fluorometry. Using recombinant RT as antigen, the sensitivity and specificity for 83 seropositives and 100 seronegatives were both 100%, and the lowest signal for 60 asymptomatic carriers was 8.2-fold higher than the highest signal for the seronegatives. The positivity with recombinant RT as antigen could be confirmed by using recombinant p17 and p24 as antigens. The sensitivity could be improved by a longer assay of bound beta-D-galactosidase activity by using concentrated urine samples and by the combined use of recombinant RT, p17, and p24. Thus, reliable diagnosis of HIV-1 infection was possible for asymptomatic carriers.

Detection of antibody IgG to HIV-1 in urine by ultrasensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) using recombinant p24 as antigen for diagnosis of HIV-1 infection

Anti-HIV-1 IgG in urine was detected by an ultrasensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) using recombinant p24 gag protein (p24) of HIV-1 as antigen and beta-D-galactosidase from Escherichia coli as label. Anti-HIV-1 IgG in urine was reacted simultaneously with 2,4-dinitrophenyl-bovine serum albumin-recombinant p24 conjugate and recombinant p24-beta-D-galactosidase conjugate. The complex formed, consisting of the three components, was trapped onto polystyrene balls coated with affinity-purified (anti-2,4-dinitrophenyl group) IgG, eluted with epsilon N-2,4-dinitrophenyl-L-lysine, and transferred to polystyrene balls coated with affinity-purified (anti-human IgG gamma-chain) IgG. Bound beta-D-galactosidase activity was assayed by fluorometry. This assay was at least 3,000-fold more sensitive than conventional methods. The lowest signal among 49 asymptomatic carriers was 3.1-fold higher than the highest nonspecific signal among 100 seronegative subjects. The sensitivity and specificity were both 100%. The positivity could be confirmed by preincubation of urine samples with excess of the antigen. Thus, this assay would be a powerful tool for detecting IgG antibody to HIV-1 in urine.

Use of the recombinant chimera proteins, LacZ-Env and Gag-Env, for immunological studies on HIV-1 infection

To use Env proteins as antigens for detection of the human immunodeficiency virus type-1 (HIV-1) antibodies, we attempted to overexpress the Env proteins in Escherichia coli. To study the epitopes in the Env proteins recognized by the sera of HIV carriers, various regions of the proviral DNA encoding the Env region were fused to the 3' end of the lacZ gene. The immunoblotting analysis of the LacZ-Env(512-611) and LacZ-Env(721-826) proteins with the 41 positive sera revealed that the former and the latter immunologically reacted with 100 and 78% of the sera, respectively. To avoid rare false-positive reactions due to the LacZ moiety of the fusion protein, we attempted to express the Env(512-611) alone or Gag-Env(512-611) under the control of bacteriophage T7 promoter. Although we could express only a low level of the Env(512-611) peptide in E. coli, we succeeded in producing large amounts of the Gag(121-406)-Env(512-611) and Gag(308-406)-Env(512-611) proteins as chimeric proteins. Both of these chimera proteins strongly reacted with the 41 positive sera. We purified these proteins and analyzed the immunological reactivity by dot blot with the 60 positive sera and the 84 normal sera. As little as 20 ng of the dotted proteins was enough for the reaction with the positive sera, whereas as much as 320 ng of them did not show false-positive reactions with the normal sera. We obtained highly purified Gag-Env proteins with highly specific seroreactivity, which should be useful for diagnosis and prognosis.