Possible therapeutic vaccine strategy against human immunodeficiency virus escape from reverse transcriptase inhibitors studied in HLA-A2 transgenic mice

Humanized mice for the development and testing of human vaccines

Mouse models of human disease form a link between genetics and biology. However, mice and humans differ in many aspects of immune system biology. These differences might explain, in part, why many successful preclinical immunotherapy studies in mice turn out to be unsuccessful when used in clinical trials in humans. Pioneering studies in the late 1980s demonstrated the reconstitution of human lympho-hematopoietic cells in immunodeficient mice. Since this time, immunodeficient mice are being tested as hosts for human hematopoietic organs or cells in an effort to create an in vivo model of the complete human immune system. Such Humouse models could permit us to generate and test novel human vaccines.

Viral adaptation to host immune responses occurs in chronic hepatitis B virus (HBV) infection, and adaptation is greatest in HBV e antigen-negative disease

Hepatitis B virus (HBV)-specific T-cell responses are important in the natural history of HBV infection. The number of known HBV-specific T-cell epitopes is limited, and it is not clear whether viral evolution occurs in chronic HBV infection. We aimed to identify novel HBV T-cell epitopes by examining the relationship between HBV sequence variation and the human leukocyte antigen (HLA) type in a large prospective clinic-based cohort of Asian patients with chronic HBV infection recruited in Australia and China (n = 119). High-resolution 4-digit HLA class I and II typing and full-length HBV sequencing were undertaken for treatment-naïve individuals (52% with genotype B, 48% with genotype C, 63% HBV e antigen [HBeAg] positive). Statistically significant associations between HLA types and HBV sequence variation were identified (n = 49) at 41 sites in the HBV genome. Using prediction programs, we determined scores for binding between peptides containing these polymorphisms and associated HLA types. Among the regions that could be tested, HLA binding was predicted for 14/18 (78%). We identified several HLA-associated polymorphisms involving likely known anchor residues that resulted in altered predicted binding scores. Some HLA-associated polymorphisms fell within known T-cell epitopes with matching HLA restriction. Enhanced viral adaptation (defined as the presence of the relevant HLA and the escaped amino acid) was independently associated with HBeAg-negative disease (P = 0.003). Thus, HBV appears to be under immune pressure in chronic HBV infection, particularly in HBeAg-negative disease.

Drug resistance mutations and the cellular immune response: a valuable synergy for the development of novel immune therapies

PURPOSE OF REVIEW

The escape of HIV-1 is a cardinal feature of the virus and a major hindrance to the development of effective therapeutic strategies. In highly active antiretroviral therapy-treated patients, the virus is subjected to selective pressures from cellular immune response directed against the viral proteome and antiretroviral treatment targetting a few genes of the HIV-1 genome. This review will focus on the relationship between these two pressures and its potential advantage in the development of novel immune therapies.

RECENT FINDINGS

Recent studies have investigated the conflicting selective forces between viral fitness and escape to immunological and therapeutic pressures in natural HIV infection and the SIV model. Simultaneous pressures driven by cytotoxic T lymphocytes and highly active antiretroviral therapy could potentially reduce viral fitness, leading to better control of the viral load. Two studies have described a potential therapeutic vaccine strategy against viral escape mutant epitopes from reverse transcriptase inhibitors.

SUMMARY

The emergence of multidrug-resistant viruses is associated with enhanced T-cell-mediated immune response as a possible consequence of reduced viral fitness. Amino acid substitutions generate potential cytotoxic T-lymphocyte epitopes that may elicit new reactivities against mutated viruses. Both could significantly enhance the immune response through direct and indirect mechanisms.

Peptide inhibition of HIV-1: current status and future potential

More than 2 decades of intensive research has focused on defining replication mechanisms of HIV type 1 (HIV-1), the etiologic agent of AIDS. The delineation of strategies for combating this viral infection has yielded many innovative approaches toward this end. HIV-1 is a lentivirus in the family retroviridae that is relatively small with regard to both structure and genome size, having a diploid RNA genome of approximately 9 kb, with only three major genes and several gene products resulting from alternate splicing and translational frameshifting. Most marketed drugs for treating AIDS are inhibitors of HIV-1 reverse transcriptase or protease enzymes, but new targets include the integrase enzyme, cell surface interactions that facilitate viral entry, and also virus particle maturation and assembly. The emergence of drug-resistant variants of HIV-1 has been the main impediment to successful treatment of AIDS. Thus, there is a pressing need to develop novel treatment strategies targeting multiple stages of the virus life-cycle. Research efforts aimed at developing successful means for combating HIV-1 infection have included development of peptide inhibitors of HIV-1. This article summarizes past and current endeavors in the development of peptides that inhibit replication of HIV-1 and the role of peptide inhibitors in the search for new anti-HIV drugs.

Vaccination against drug resistance in HIV infection

HIV-1 resistance to currently employed antiretroviral drugs and drug-associated adverse reactions and toxicity point to a need for additional measures to control HIV-1 replication in HIV-infected patients. The immune system of HIV-infected individuals mount an immune response against the regions harboring drug-resistance mutations, sometimes stronger than that against the parental wild-type sequences. A potent cross-reactive immune response against drug-resistant pol proteins can suppress the replication of drug-escaping HIV. This suggests the possibility for a vaccination against existing and anticipated drug-resistant HIV variants. If successful, therapeutic vaccines against drug resistance would ease the therapeutic modalities and limit the spread of drug-resistant HIV. A better understanding of the complex interactions between patterns of drug-resistance mutations, immune responses against these mutations and their antigen presentation by particular human lymphocyte antigen alleles could help to tailor these vaccines after new drugs/new mutations. In this review, we describe the developments in the field of immunization against mutations conferring drug resistance and evaluate their prospects for human vaccination.