Long-term protection against SIV-induced disease in macaques vaccinated with a live attenuated HIV-2 vaccine.

The aim of this study was to test the ability of a live attenuated human immunodeficiency virus type 2 (HIV-2) vaccine to protect cynomolgus monkeys against superinfection with a pathogenic simian immunodeficiency virus (SIVsm). This report is an update on our previously reported observation period of nine months. The new data here show that three of four monkeys vaccinated with live HIV-2 were protected against immunosuppression and SIV-induced disease during more than five years of follow-up. The quality of the immunity was permissive for infection, but monkeys that survived showed restricted viral replication in peripheral blood and lymph nodes. This study shows that it is possible to induce protection against a pathogenic heterologous primate lentivirus and to prevent disease in vaccinated monkeys even if infection is not prevented. These findings provide evidence that protection against AIDS can be achieved by immunization.

Multicenter evaluation of a new 4th generation HIV screening assay Elecsys HIV combi.

Fourth-generation screening assays which permit a simultaneous detection of human immunodeficiency virus (HIV) antigen and antibody reduce the diagnostic window on average by four days in comparison to third-generation antibody assays. Recently, the new automated Elecsys HIV combi was compared in a multicenter study to alternative fourth- and third-generation assays, p24 antigen test and HIV-1 RNA RT-PCR. A total of 104 serocon-version panels, samples of the acute phase of infection after seroconversion (n = 33), anti-HIV-1 positive specimens (n = 572) from patients in different stages of the disease, 535 subtyped samples from different geographical locations, including group M (subtypes A-J) and group O, anti-HIV-2 positive sera (n = 364), dilutions of cell culture supernatants (n = 60) infected with different HIV-1 subtypes, selected performance panels, 8406 unselected samples from blood donors originating from different blood transfusion centers, 3810 unselected sera from daily routine and from hospitalized patients, 9927 unselected samples from South Africa and 1943 potentially interfering samples were tested with the Elecsys HIV combi. Elecsys HIV combi showed a comparable sensitivity to HIV-1 Ag stand-alone assays for early detection of HIV infection in seroconversion panels. The mean time delay of Elecsys HIV combi (last negative sample + 1 day) in comparison to HIV-1 RT-PCR for 92 panels tested with both methods was 3.23 days. The diagnostic window was reduced with Elecsys HIV combi between 1.56 and 5.32 days in comparison to third-generation assays. The specificity of Elecsys HIV combi in blood donors was 99.80% after repeated testing. Our results show that a fourth-generation assay with improved specificity and sensitivity like the Elecsys HIV combi is suitable for blood donor screening due to its low number of false positives and since it detects HIV p24 antigen with a comparable sensitivity to single antigen assays.

Enzyme immunoassays for the demonstration of antibodies to HIV-2SBL-6669 and HTLV-IV (SIVmac).

Enzyme-linked immunosorbent assays (ELISA) were developed for the demonstration of antibodies to HIV-2 using disrupted virions of the SBL-6669 isolate of HIV-2 and the so-called human T-lymphotropic virus type IV (HTLV-IV), recently found to be identical with the simian immunodeficiency virus (SIVmac), as antigens. Three hundred sera from West African subjects, attending an outward clinic in Bissau for examination of suspected tuberculosis, were tested by these two assays as well as by a commercially available anti-HIV-2 ELISA (ELAVIA II). Fifty of these sera were positive in all three ELISAs as well as in Western blot tests against HTLV-IV. Thirty-eight of these positive sera were also tested by an anti-HIV-2 Western blot kit (LAV-Blot II) with positive results. The ELISAs based on SBL-6669 and HTLV-IV antigens had a specificity of 99.6% (one false positive among 250 negative sera) whereas the specificity of ELAVIA II was 94.6% using the recommended cut-off value and 98.4% using a higher cut-off value. Another 58 sera from West African patients, clinically suspected of having AIDS or HIV-related disease, were tested for HIV-2/HTLV-IV antibodies by Western blot and by ELISA against SBL-6669 and HTLV-IV antigens; all of the 30 sera which were positive by Western blot were found to be positive in both ELISAs.(ABSTRACT TRUNCATED AT 250 WORDS)

Infection of cynomolgus monkeys with HIV-2 protects against pathogenic consequences of a subsequent simian immunodeficiency virus infection.

Simian immunodeficiency virus (SIV) infection in cynomolgus macaques leads to severe immunodeficiency with a fatal outcome. In contrast, HIV-2 infects these primates without apparently causing any immunological abnormalities. In this study three cynomolgus monkeys were experimentally infected with HIV-2 strain SBL-K135 and 168 days later challenged with 10-100 animal infectious doses of the closely related SIV strain SM to study protective immunity. At the time of SIV challenge the HIV-2-infected monkeys had neutralizing antibodies against HIV-2, but virus could no longer be recovered from their peripheral blood mononuclear cells (PBMCs) and no clinical symptoms or decrease in CD4+ lymphocytes were observed. Follow-up for 9 months after challenge with SIV showed that the HIV-2-infected monkeys were protected against SIV-induced immunodeficiency (no decrease of CD4+ lymphocytes) and lymphadenopathy. However, they were not resistant to SIV infection since virus could be recovered from their PBMCs and they developed anamnestic antibody responses. Four naive control monkeys which were inoculated with the same dose of SIV became persistently infected and developed a decrease of the absolute numbers of CD4+ cells and showed a marked lymphadenopathy. Two out of four control animals died 58-265 days postinfection with an immunosuppressive disease. Immunohistochemical examination showed abundant viral antigen in lymph-node biopsies from the SIV-infected control monkeys but absence of SIV or HIV-2 antigens in the biopsies from the three HIV-2-preinfected and SIV-superinfected monkeys. The present study demonstrates possibilities for induction of immunity against immunodeficiency induced by a primate lentivirus, a concept with application also to HIV infection and AIDS in man.

Live attenuated simian immunodeficiency virus (SIV)mac in macaques can induce protection against mucosal infection with SIVsm.

OBJECTIVE: To investigate whether vaccination of macaques with attenuated simian immunodeficiency virus (SIV)macC8 could induce long-term protective immunity against rectal exposure to SIVsm and intravenous exposure to the more divergent HIV-2. DESIGN AND METHODS: Eight months after vaccination with live attenuated SIVmacC8, four cynomolgus monkeys were challenged with SIVsm intrarectally and another four vaccinated monkeys were challenged with HIV-2 intravenously. Sixteen months after SIVmacC8 vaccination, another two monkeys were challenged with SIVsm across the rectal mucosa. Two vaccinees shown to be protected against SIVsm were rechallenged 8 months after the first challenge. Ten naive animals were used as controls. Serum antigenaemia, virus isolation, antibody responses, cell-mediated immunity and CD4+ and CD8+ T-cell subpopulations were monitored. PCR-based assays were used to distinguish between virus populations. RESULTS: At the time of challenge, eight out of 10 vaccinees were PCR-positive for SIVmacC8 DNA but no virus could be isolated from peripheral blood mononuclear cells. After SIVsm challenge, three out of six vaccinees were repeatedly SIVsm PCR-negative. In one of the three infected monkeys, the challenge virus was initially suppressed but the monkey ultimately developed AIDS after increased replication of the pathogenic virus. Rechallenged monkeys remained protected. All HIV-2-challenged vaccinees became superinfected. All controls became infected with either SIVsm or HIV-2. At the time of challenge the vaccinees had neutralizing antibodies to SIVmac but no demonstrable cross-neutralizing antibodies to SIVsm or HIV-2. Titres of antigen-binding or neutralizing antibodies did not correlate with protection. Cytotoxic T-cell responses to SIV Gag/Pol and virus-specific T-cell proliferative responses were low. CONCLUSION: The live attenuated SIVmacC8 vaccine was able to induce long-term protection against heterologous intrarectal SIVsm challenge in a proportion of macaques but not against the more divergent HIV-2, which was given intravenously.

Diagnosis of primary HIV-1 infection and duration of follow-up after HIV exposure. Karolinska Institute Primary HIV Infection Study Group.

OBJECTIVE: To determine the sensitivity of 33 currently available and seven earlier tests for the detection of HIV or HIV antibody in primary HIV-1 infection, to estimate the duration of the 'window period' and the influence of early initiated antiretroviral treatment (ART). DESIGN: A prospective cohort study of 38 patients with primary HIV-1 infection. ART was initiated at a median time of 13 (range 0-23) days after the onset of symptoms in 10 patients. MAIN OUTCOME MEASURES: The time from infection to onset of symptoms and from onset of symptoms to the appearance of HIV antibody as measured by 36 different tests, and the start and duration of viraemia, as detected by four different tests. RESULTS: The illness appeared 13-15 days after infection in 12 of 15 determinable cases, and seroconversion was detected within 1-2 weeks after the onset of illness by 27 of 30 currently available tests for HIV antibody, in contrast to the 2-7 weeks or more needed by the old tests. HIV RNA appeared during the week preceding the onset of illness and was detected in all subsequent samples, except when ART had been initiated, which also induced a delay of the antibody response. CONCLUSION: Many tests for HIV or HIV antibody can now be employed for an early confirmation of primary HIV infection (PHI). Currently available screening tests proved much more sensitive than older tests, and seroconversion was usually detected within one month after infection. Consequently, in Sweden we now recommend only 3 months of follow-up after most cases of HIV exposure.

A capture enzyme immunoassay for detection of HIV-2/SIV antigen.

An antigen capture enzyme immunoassay was developed for the demonstration of human immunodeficiency virus type 2 (HIV-2) and simian immunodeficiency virus (SIV). The assay (HIV-2 CE) has a sensitivity of approximately 250 pg/ml of HIV-2/SIV antigen. The HIV-2 CE was 4-16 times more sensitive than the Abbott HIV-1 antigen assay for detection of HIV-2/SIV antigen in cell culture supernatant. The sensitivity for detection of HIV-2/SIV antigen in serum or plasma was 98.5% in the HIV-2 CE and 95.5% in the Abbott HIV-1 antigen assay. The specificity of the HIV-2 CE was 99.2% (one false positive among 119 negative sera) whereas the Abbott assay was 100% specific. The HIV-2 CE detected antigen in supernatants from cultures of peripheral blood mononuclear cells of macaque monkeys infected with HIV-2 or SIV about 1 week before a reverse transcriptase (RT) microassay was positive and remained positive for at least 1 week after the RT assay had become negative. Three cultures from persistently infected monkeys were positive only in the HIV-2 CE, reflecting a higher sensitivity compared to the RT microassay. Thus, the HIV-2 CE was more sensitive than the Abbott HIV-1 antigen assay for detection of HIV-2/SIV antigen in culture supernatants as well as in serum/plasma. Furthermore, the HIV-2 CE showed a higher sensitivity than the RT microassay for detection of HIV-2/SIV in cell culture supernatants.

HIV-2-associated AIDS and HIV-2 seroprevalence in Bissau, Guinea-Bissau.

During a 6-month period in 1987, we examined patients clinically suspected of the acquired immune deficiency syndrome (AIDS) at the national hospital in Bissau, the capital of Guinea-Bissau, and found 20 cases that fulfilled the criteria for AIDS. The two most prevalent major symptoms were weight loss and diarrhea, and the most common minor symptoms generalized lymphadenopathy and generalized dermatitis. Six of 20 patients died within a couple of months. Nineteen of 20 patients were tested for human immunodeficiency virus type 1 (HIV-1) and type 2 (HIV-2) antibodies and were shown to be HIV-2 seropositive. During the same time period, a seroprevalence study of HIV-2 and HIV-1 was carried out, including 2,122 patients or healthy persons in Bissau. Antibodies to HIV-2 were demonstrated by enzyme-linked immunosorbent assay and verified by Western blot analysis in 8.6% (46/535) of prenatal women, in 7.9% (9/114) of women attending a family-planning clinic, in 4.4% (19/427) of applicants for scholarships, in 17.6% (16/91) of blood donors tested during the first 2 months and 5.3% (10/189) of blood donors tested during the following months, in 5.7% (2/35) of police officers, in 36.7% (11/30) of female prostitutes, in 15.8% (97/614) of outpatients suspected of having tuberculosis, and in 55.2% (48/87) of patients clinically suspected of AIDS or AIDS-related disease. One of 2,001 subjects tested had antibodies specific for HIV-1. Another subject had an antibody pattern compatible with both HIV-1 and HIV-2 infections.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental infection of cynomolgus monkeys (Macaca fascicularis) with HIV-2.

Ten healthy adult cynomolgus monkeys (Macaca fascicularis) were inoculated with two different isolates of human immunodeficiency virus type 2 (HIV-2), SBL-6669 and SBL-K135, to establish an animal model for HIV infection. HIV-2SBL-6669 had been propagated for a long time in continuous human cell lines whereas HIV-2SBL-K135 had been grown only in fresh human and monkey lymphocyte cultures or previously for a short time in a continuous cell line. Virus was isolated from three or four animals inoculated with HIV-2SBL-K135 but in none of six monkeys inoculated with HIV-2SBL-6669. All animals seroconverted although the antibody response was higher in SBL-K135 virus-infected monkeys. Varying degrees of lymphadenopathy were observed but there were no significant changes in the numbers of CD4+ and CD8+ T cells. The infection was transferred to two monkeys inoculated with blood from a previously SBL-K135 virus-infected monkey. Four animals inoculated with HIV-2SBL-K135, which had never been propagated in continuous human cell lines, showed strong antibody responses against both gag- and env- encoded proteins of HIV-2. None of the SBL-6669 infected monkeys showed antibodies to core proteins. HIV-2 infection of cynomolgus monkeys represents a useful experimental model for HIV vaccine trials and antiviral testing.

Long-standing protection of macaques against cell-free HIV-2 with a HIV-2 iscom vaccine.

We investigated the capacity of two immunostimulating-complex (iscom) formulations including inactivated native HIV-2 viral proteins and selected peptides to induce protective immunity against HIV-2 in a nonhuman primate. Four cynomolgus monkeys were first immunized with five i.m. injections of purified detergent-disrupted HIV-2 virions (total dose, 0.7 mg) in iscoms over a period of 16 months. At months 18 and 20, all four macaques were given booster immunizations with iscom-coupled V3-derived synthetic peptides representing a dominating neutralizing region of HIV-2 gp125. Two weeks after the final dose of vaccine, the four vaccinated animals, together with four controls, were challenged i.v. with 10 monkey infectious doses (MID50) of monkey-cell-grown homologous cell-free virus, HIV-2SBL-6669/H5. After the challenge, the four control animals became readily infected; however, three of four vaccinated animals were protected as shown by repeated negative virus isolations and negative polymerase chain reaction for viral DNA and by failure to transmit HIV-2 infection with whole blood and lymph node cells into naive cynomolgus macaques. One of three protected animals showed an anamnestic antibody response to a dominating antigenic site, indicating possible limited virus replication. The vaccine-protected monkeys were subsequently resistant to rechallenge infection at 12, 15, and 18 months after the first challenge, suggesting that a reasonable duration of protective immunity had been induced by the vaccine.

Experimental infection of cynomolgus monkeys (Macaca fascicularis) with simian immunodeficiency virus (SIVsm).

Five healthy cynomolgus monkeys were inoculated intravenously with simian immunodeficiency virus (SIVsm) propagated in human lymphocytes. All five animals became infected. Virus was recovered from blood mononuclear cells and viral antigen was detected in serum 12 days postinoculation (PI) in all inoculated animals. Virus was also isolated in all five animals tested 74 to 226 days PI. Antibodies to different structural proteins of SIV and HIV-2 were demonstrated by ELISA, Western blot, and radioimmunoprecipitation assay from day 31 PI concomitantly with a reduction of viral proteins in the serum. Reappearance of antigen accompanied by a fall in antibody to gag products (p26) was observed in two monkeys 69 days PI. All SIV-infected monkeys showed a pronounced decrease in CD4+ lymphocytes demonstrable already 12 days PI. They also developed persistent lymphadenopathy. Thus, infection of cynomolgus monkeys with SIVsm mimics events in human immunodeficiency virus infection in humans but the course of evolution of pathogenic events in the monkey is markedly compressed. This experimental model will be useful for evaluation of HIV vaccines and antiviral testing.

Non-specific precipitin reactions of IgG at low ionic strength.

Precipitin reactions apparently not involving specific antibodies were obtained in immunodiffusion experiments performed at low salt concentration between IgG and the muscle proteins, actin and tropomyosin. The precipitates, which dissolved at physiologic ionic strength, may result from electrostatic interaction of molecules of different net charge and different distribution and number of charged groups.

A radioimmunoassay for determination of anti-actin antibodies.

The reaction of spontaneously occurring human anti-human antibodies and experimentally produced rabbit anti-actin antibodies was investigated in a solid-phase radioimmunoassay (RIA). Three structurally different in vitro forms of actin monomeric G-actin filamentous F-actin and aggregated denatured actin were used as antigens. Human anti-actin antibodies reacted with F- and G-actin but not with aggregated actin, while rabbit anti-actin antibodies gave a strong reaction with all 3 forms of actin indicating differences in antibody specificities. The results of the anti-actin RIA were compared with those obtained by indirect immunofluorescence (IFL) on cryostat sections of rat stomach. The anti-actin RIA discriminated between patients' sera and control sera in most cases, although the indirect IFL test gave more conclusive results. The seemingly low sensitivity of the anti-actin RIA compared with that of indirect IFL test for detection of human anti-actin antibodies is probably due to favourable antigen distribution in tissue, not available in the solid phase. The anti-actin RIA was able to detect anti-actin antibodies in 8 out of 8 immunized rabbits although only two produced antibodies detectable by indirect IFL. The differences in reactivity between the two methods may depend on the presence of aggregated denatured actin in the antigen preparation used for immunization and exposure of the corresponding antigenic determinants of actin on the solid phase.

Reactivity of sera from patients with liver disease with glutaraldehyde-treated erythrocytes: role for false positive results in hemagglutination tests.

The use of glutaraldehyde as a coupling reagent in the passive hemagglutination test (HA) has gained wide application, especially for the coating of red blood cells (RBC) with glutaraldehyde-polymerized human serum albumin (pHSA), for studies of the albumin receptor on hepatitis B surface antigen (HBsAg) or for the detection of anti-albumin antibodies (AAA). Here we report a previously unrecognized reactivity with glutaraldehyde-treated RBC mainly with sera from patients with liver disease. The highest incidences of this reaction were found in patients with acute viral hepatitis A and B, namely 44 of 50 (88%) and 31 of 50 (62%) respectively. In 234 HBsAg carriers the frequency was low (3%). This reactivity was also observed in 19 of 50 sera from patients with chronic liver disease documented by biopsy, but not in sera from 68 healthy subjects. By immunofluorescence on glutaraldehyde-treated RBC it was shown that the corresponding antibodies belonged mainly to the IgM class. In all HBsAg-negative patients studied the HA titer against glutaraldehyde-treated RBC was in agreement with the titer against RBC coated with pHSA or pBSA (polymerized bovine serum albumin). Absorption with pHSA abolished the reaction with glutaraldehyde-treated RBC in 7 of 8 sera, suggesting a common reactivity between glutaraldehyde-polymerized HSA and glutaraldehyde-treated RBC. Apart from the possible clinical importance of these antibodies, their existence is a possible source of false positive results when glutaraldehyde is used as a coupling reagent for immunological assays, in particular with sera from patients with liver diseases.

Development and evaluation of a flow-cytometric assay of specific cell-mediated immune response in activated whole blood for the detection of cell-mediated immunity against varicella-zoster virus.

A new assay for the detection of specific cell-mediated immune (CMI) responses is described. Whole blood, diluted 1/10 in medium, was cultured in the presence or the absence of specific antigens. Results were assessed by flow cytometric analysis with or without immunophenotyping to detect proliferating lymphoblasts among cultured cells. Interferon-gamma, IL-10, and IL-5 in culture supernatants are measured by ELISAs. The assay was evaluated using samples from 37 VZV-antibody-positive children with a history of chickenpox and samples from 15 seronegative children without a history of chickenpox; it displayed a sensitivity of 95% and a specificity of 100% for the detection of varicella-zoster virus (VZV)-specific CMI. The intraassay and interassay variations of the new test were lower than with the conventional assay for CMI, detecting thymidine incorporation in peripheral blood mononuclear cells (PBMCs). Cytokines were detected in only 70% of cultures from VZV-antibody-positive subjects. The cytokine response was restricted to IFN-gamma in most cases. The Flow-cytometric Assay of Specific Cell-mediated Immune response in Activated whole blood (FASCIA) is a precise and accurate yet simple and convenient test that can be readily employed for the examination of single samples as well as for large-scale studies.

Fine characterization of a V3-region neutralizing epitope in human immunodeficiency virus type 2.

We have previously identified two distinct antigenic sites in the third variable region (V3) of human immunodeficiency virus type 2 (HIV-2) corresponding to the principal neutralizing determinant (PND) of HIV-1, the conserved Phe-His-Ser-Gln and Trp-Cys-Arg motifs (positions 315-318 and 329-331), which possibly interact to form a discontinuous antigenic site. The aim of this study was to further identify and characterize the immunogenic sites in the V3-loop of HIV-2 that are important in the binding of neutralizing antibodies and to study in detail the importance of different configurations of peptides corresponding to this region. Peptides representing modifications of the V3-region of HIV-2(SBL6669-ISY) were used for immunization of guinea pigs. With one exception, both the Phe-His-Ser-Gln and the Trp-Cys-Arg motifs were required in the peptide sequences to obtain neutralizing hyperimmune guinea pig sera, and the highest titers were obtained after immunization with 20-27 amino acids (aa) long peptides. Neither substitutions nor deletions of residues between the two motifs, nor the addition of peptide sequences representing a T-helper epitope improved the induction of neutralizing antibodies. Computer simulation modeling revealed that the Phe-315, His-316, Trp-329 and Cys-330 are likely to participate in the formation of a discontinuous epitope. Taken together, these data support the hypothesis that the well conserved motifs FHSQ (positions 315-318) and WCR (positions 329-331) of the HIV-2(SBL6669) V3 region are important targets for neutralizing antibodies, and this may have implications for the design of a future HIV-2 vaccine.

Visceral leishmaniasis in Somalia. Significance of IgG subclasses and of IgE response.

We have determined the levels of IgG subclasses and IgE as well as specific antibodies of these isotypes in sera from 22 patients with clinical visceral leishmaniasis (VL) from Somalia. The results are compared with those obtained from 30 Somali and 23 Swedish controls. We found markedly increased concentrations of IgG1 in the VL sera, indicating that the pronounced increase in IgG in VL which is generally considered to be due to polyclonal B-cell activation is mainly restricted to this subclass. The IgG2 concentrations were significantly decreased. The IgG3 and IgG4 concentrations, on the other hand, did not differ between the two groups of Somali sera. The Somali control sera contained higher concentrations of IgG1 and IgG3, but significantly lower concentrations of IgG2 as compared to Swedish controls. The IgG4 values, on the other hand, were not different between the two groups of control sera. Anti-leishmania antibodies belonging to all IgG subclasses, were found in the patients' sera. There was no significant difference in total IgE between sera from VL patients and controls and specific IgE antibodies were only detected in a few patients. The Western blot assay (WB), revealed the presence of two bands corresponding to 74 kDa and 88 kDa in all patients' sera, indicating a possible diagnostic role for WB in this particular population.

Characterization of neutralizing sites in the second variable and fourth variable region in gp125 and a conserved region in gp36 of human immunodeficiency virus type 2.

Several determinants of human immunodeficiency virus (HIV) have been suggested to harbor sites important for neutralization. The third variable region (V3) of the envelope glycoprotein (gp) is an important neutralizing determinant for both serotypes of HIV. The localization of additional neutralizing regions is an urgent task because the virus appears to mutate to phenotypes that escape neutralizing antibodies. Therefore, we have focused on the possibility of finding other immunodominant regions in the envelope glycoproteins of human immunodeficiency virus type 2 (HIV-2). By immunization of guinea pigs with peptides corresponding to different selected regions of gp125 and gp36, we have found three antigenic determinants located in the V2 and V4 regions of the envelope protein gp125, and one region in the glycoprotein gp36, which are important for human antibody binding and also as targets for neutralization. The peptide representing the V2 region had the most pronounced capacity to induce neutralizing anti-HIV-2 antibodies in guinea pigs. Neutralizing activity was also detected in an antipeptide guinea pig sera representing a linear site in gp36, amino acids 644-658. A substitution set of peptides representing the conserved antigenic site in the central part of gp36 was used to identify the role of individual amino acids important for human antibody binding.

Prevention of HIV-2 and SIVSM infection in cynomolgus monkeys by active or passive immunization.

We have established experimental infection with HIV-2 and SIVsm in cynomolgus monkeys and successfully used these models for vaccine experiments. Protection against homologous HIV-2 infection was demonstrated in two of two monkeys immunized with a Triton-X100-treated whole HIV-2SBL-6669 vaccine in incomplete Freund's adjuvant and in 2 of 4 monkeys immunized with a formalin-inactivated whole HIV-2 vaccine in RIBI adjuvant. Monkeys preinfected with a live poorly replicating HIV-2 strain were shown to develop cross-protection against SIV-induced disease. We have shown also that HIV-2 and SIVsm infection in cynomolgus monkeys can be prevented by passive immunization. These results raise hope for effective immunization against HIV infections in humans.

Outcome of immunization of cynomolgus monkeys with recombinant Semliki Forest virus encoding human immunodeficiency virus type 1 envelope protein and challenge with a high dose of SHIV-4 virus.

Infection of macaques with chimeric simian-human immunodeficiency viruses (SHIVs) allows evaluation of HIV-1 envelope vaccines. SHIV-4 is based on SIVmac239 but carries the env, tat, and rev genes of HIV-1IIIB. In this study we used Semliki Forest virus (SFV) RNA vectors to express the envelope protein gp160 of HIV-1IIIB in cynomolgus macaques. Monkeys were immunized four times with recombinant suicide SFV. Whereas two of four monkeys showed T cell-proliferative responses, only one monkey had demonstrable levels of antibodies to HIV-1 gp41 and gp120 as shown by enzyme-linked immunosorbent assay (ELISA) and Western blot. The vaccinated monkeys and four control animals were challenged with 10,000 MID100 (100% minimum infectious doses) of cell-free monkey cell-grown SHIV-4 virus. As demonstrated by virus isolation, all macaques became infected after challenge. All vaccinated monkeys showed an HIV-1-specific anamnestic T cell-proliferative response. Three of four vaccines had developed HIV-1-Env-specific antibodies 2 weeks after challenge whereas none of the four controls showed any detectable immune response at this time point. Furthermore, three of four vaccinated monkeys had no demonstrable viral antigenemia and low viral load as opposed to one of the four naive control animals.