Phase I/II studies of the toxicity and immunogenicity of recombinant gp160 and p24 vaccines in HIV-infected individuals

Production of HIV-1 p24 protein in transgenic tobacco plants

The production of antigens for vaccines in plants has the potential as a safe and cost-effective alternative to traditional production systems. Toward the development of a plant-based expression system for the production of human immunodeficiency virus type I (HIV-1) p24 capsid protein, the p24 gene was introduced into the genome of tobacco plants using Agrobacterium tumefaciens-mediated gene transfer. Southern blot analyses confirmed the presence of the p24 coding sequence within the genome of transgenic lines. Western blot analysis of protein extracts from transgenic plants identified plant-expressed p24 protein that cross-reacted with a p24-specific monoclonal antibody, thus confirming the maintenance of antigenicity. Quantification of the p24 protein using enzyme-linked immunosorbent assay (ELISA) estimated yields of approx 3.5 mg per g of soluble leaf protein. Similar accumulation levels of p24 were also detected in T1 plants, confirming that the p24 gene is transmitted stably. Our results indicate that plant-based transgenic expression represents a viable means of producing p24 for the development of HIV vaccine and for use in HIV diagnostic procedures.

HIV vaccines for prevention of infection and disease in humans

Phase I and II studies have been carried out with several candidate HIV-1 vaccines in seronegative volunteers. Vaccines consisting of rgp 120 stimulated moderate levels of neutralizing antibodies against homologous, TCLA adapted viruses, but did not induce CD8+ CTL responses. Canarypox vectors stimulate CD8+ CTL responses, but little neutralizing activity. The latter can be increased in titer by boosting recipients of canarypox vectors with rgp120 vaccines. Large-scale placebo-controlled efficacy trials are underway with two rgp120 vaccines: AIDSVAX B/B (VaxGen, Inc.) in the United States, and AIDSVAX B/E in Thailand. The canarypox-rgp120 combined regimen has been proposed for study in an intermediate-sized, "test-of-concept" efficacy trial by the NIAID-sponsored HVTN, with an experimental design intended to provide information on the potential in vitro correlates of immunity. The results from these studies, and the methodology used in their conduct, should facilitate the refinement of conventional and novel approaches to the development of safe and effective HIV vaccines.

Safety and immunogenicity of HIV recombinant envelope vaccines in HIV-infected infants and children. National Institutes of Health-sponsored Pediatric AIDS Clinical Trials Group (ACTG-218)

Study objectives were to evaluate the safety and immunogenicity of three HIV recombinant glycoproteins in HIV-infected infants and children between 1 month and 18 years of age with asymptomatic (P-1) infection. Using Chiron rgp 120 (SF-2) 15 or 50 microg; MicroGeneSys rgp 160 (IIIB) 40 or 320 microg; Genentech rgp120 (MN) 75 or 300 microg; or adjuvant control (Alum or MF-59), children were randomized to a double-blind, placebo-controlled, dose-escalating study of vaccine administered intramuscularly at entry and 1, 2, 3, 4, and 6 months later. No adverse events were attributed to study vaccines. Between 30% and 56% of volunteers exhibited a lymphoproliferative response as defined in terms of stimulation index (SI) to vaccine antigens; 65% of vaccinees but none of placebo recipients exhibited moderate or strong responses after enzyme immunoassay to HIV specific antigens. CD4 cell counts and quantitative HIV culture did not differ significantly among vaccine and control groups, nor were differences found among groups in HIV disease progression. The rgp160 and gp120 subunit vaccines were safe and immunogenic in this population.

Immune-based therapies for treatment of HIV infection

OBJECTIVE

To review the in vitro, animal, and clinical data on immune-based therapies for treatment of HIV infection.

DATA SOURCES

An extensive MEDLINE search was performed for interleukins, interferons, immunotoxins, tumor necrosis factor (TNF)-directed agents, vaccines, and gene therapy.

STUDY SELECTION

In vitro experiments with immune-based agents in cell lines infected with HIV were included. In addition, all human studies and case reports that used these agents in patients infected with HIV were selected. Additional literature included abstracts from international meetings on HIV and AIDS.

DATA EXTRACTION

Data regarding activity, efficacy, and toxicity were extracted from in vitro and in vivo studies. When conflicting data were observed, both viewpoints were stated to give an unbiased analysis. Because HIV research involves multiple social, ethical, and scientific issues, perspectives on these problems were addressed, where appropriate.

DATA SYNTHESIS

Current antiretroviral therapy is limited to short-term responses and has minimal effect on overall survival. Because the human immune response to HIV infection is effective at keeping the virus suppressed for a number of years, a focus of HIV research has been to examine immune-based therapies for treatment of HIV infection that attempt to augment enhance, or boost the patient's immune system. Interleukins, interferons, immunotoxins, TNF-directed therapies, vaccines, and gene therapy have been studied in patients infected with HIV. Properties shared among these therapeutic modalities include adverse effect profiles, response rates dependent on baseline immunocompetence, the potential to activate viral replication, the need for supportive care, and sensitive laboratory tests required for monitoring.

CONCLUSIONS

Immune-based agents represent a new approach to the treatment of HIV infection. Whereas antiretrovirals only inhibit viral replication, these agents are designed to enhance the immune system of the patient. Future attempts to manage HIV infection may combine standard nucleoside analogs with immune-based therapies.