Immunotherapeutic strategies in the treatment of HIV infection and AIDS

Human retroviruses after 20 years: a perspective from the past and prospects for their future control

Among viruses the human retroviruses may be of special interest to immunologists, because they target cells of the immune system, particularly mature CD4+ T cells, impair their function and cause them to grow abnormally (human T-cell leukemia virus, HTLV) or to die (human immunodeficiency virus, HIV). Human retroviruses cause disease ranging from neurological disorders and leukemias (HTLV-1) to AIDS (acquired immunodeficiency virus) (HIV) and promote development of several types of malignancies (HIV). They share many common features, but their contrasts are greater, especially the far greater replication and variation of HIV associated with its greater genomic complexity. Both have evolved striking redundancy for mechanisms which promote their survival. Thus, HTLV has redundant mechanisms for promoting growth of provirus containing T cells needed for virus continuity, because it is chiefly through its cellular DNA provirus that HTLV replicates and not through production of virions. Conversely, HIV has redundancy in its mechanisms for promoting virion replication and escape from the host immune system. It is via these redundant mechanisms that they produce disease: leukemias from mechanisms promoting T-cell proliferation (HTLV-1) and AIDS from mechanisms promoting virus replication and T-cell death (HIV). The practical challenges for the future are clear. For HTLV-1, education and control of breastfeeding. For HIV, the formidable tasks now ahead in part demand new kinds of talent, talents that will foster greater insights into the development of therapy for the developing countries, new forms of less toxic therapies for all infected persons, a continued and expanded commitment to education, and a persistent 'never say die' commitment to the development of a truly preventive vaccine with all the scientific and nonscientific challenges that these objectives face.

Long-term immunotherapy in HIV infection, combined with short-term antiretroviral treatment

Forty asymptomatic HIV-infected individuals with CD4+ lymphocyte levels above 400 × 106/1 were immunized over 5 years with recombinant envelope glycoprotein gp160 (rgp160). After 5 years there was a trend towards more nonprogressors in the immunized group as compared to the matched controls. Since immunizations could activate HIV, the first 6 immunizations were followed by 2 weeks of zidovudine or placebo, double-blind. The viral load did not change during the first 6 months and was not different from that of the matched controls after 5 years. The best effect on CD4+ lymphocyte development was seen in individuals with a high viral load randomized to rgp160+zidovudine and in individuals with a low viral load randomized to rgp160+placebo. We conclude that rgp160 is safe and results in temporarily improved CD4+ development. Concomitant antiviral treatment might be of benefit, especially in patients with a more advanced disease and can today be given with more effective combinations.

Chimeric HIV-1 virus-like particles containing gp120 epitopes as a result of a ribosomal frameshift elicit Gag- and SU-specific murine cytotoxic T-lymphocyte activities

Insect cell expression of the HIV-1 Gag precursor protein by recombinant baculoviruses results in the assembly and budding of noninfectious virus-like particles (VLPs). The VLPs resemble immature virus in ultrastructural morphology and can be purified by conventional retroviral techniques. The virus-like appearance of the particles suggested that they could be used to package additional peptides. The retroviral frameshift mechanism was used to translate the pol gene products by expressing additional genetic information as chimeric Gag-Pol fusion proteins. Sequences encoding the carboxyl 65% of the HIV-1 surface glycoprotein (gp120, SU) were inserted into the Gag-Pol reading frame immediately downstream of the Gag stop codon. The assembly and budding of large quantities of Gag and chimeric Gag-SU VLPs were observed by standard transmission electron microscopy. The presence of gp120 epitopes in the Gag-SU VLPs was confirmed by immunoelectron microscopy and Western blot analysis using monoclonal anti-gp120 antibodies. Mice inoculated with the Gag-SU pseudovirions developed cytotoxic lymphocyte responses to both HIV-1 Gag and Env epitopes yet humoral immune responses only to Gag epitopes. The chimeric Gag-SU particles may have applications as vaccines or immunotherapeutic treatments for HIV-1 infection. In addition, the frameshift mechanism can be applied to the packaging of other viral or cellular proteins.

Role of polymorphic residues of human leucocyte antigen-DR molecules on the binding of human immunodeficiency virus peptides

A study was made of the binding properties of 96 human immunodeficiency virus peptides to human leucocyte antigen (HLA)-DR1 and HLA-DR103 molecules, which differ by three amino acids at positions 67, 70 and 71 in the beta chains. The affinity of the peptides was characterized by their inhibitory concentrations in competitive binding assays which displace half of the labelled influenza haemagglutinin peptide HA306-318 (IC50). Among the high-affinity peptides (IC50 < or = 1 microM), seven bound to DR1, three to DR103 and five equally well to both alleles (promiscuous peptides). Thirty-two other peptides showed medium or low affinity for DR molecules. The role of polymorphic residues was analysed using six mutated DR molecules, intermediates between DR1 and DR103 and differing by one or two substitutions at positions 67, 70 or 71. We reached the same conclusions when using DR1-specific or DR103-specific peptides: modification of residue 70 had no effect on peptide affinity, but single substitution at positions 67 or 71 decreased the allele specificity of the peptides while double substitution at 67 and 71 completely reversed the peptide specificity. In functional assays, DR-binding peptides are able to outcompete specific T-cell proliferation. Furthermore, modification at position 67 or 70 significantly affects the T-cell response and mutation at position 71 abolishes completely the T-cell proliferation. Thus, the polymorphic positions 67 and 71 contributed to the peptide binding with direct effects on T-cell receptor (TCR) recognition while position 70 seems to be mostly engaged in TCR interactions. Furthermore, our results suggest that polymorphic residues may select allele-specific peptides and also influence the conformation of promiscuous peptides.