MHC-based vaccination approaches: progress and perspectives

The major histocompatibility complex (MHC) harbours genes whose primary function in regulating immune responsiveness to infection is to present foreign antigens to cytotoxic T lymphocytes (CTLs) and T helper cells. In the case of infection by human immunodeficiency virus (HIV), defining the optimal HIV epitopes that are recognised by CTLs is important for vaccine design, and this in turn will depend on the characteristics of the predominant infecting virus. Moreover, the particular MHC human leukocyte antigens (HLAs) expressed by a geographical population is important since these are likely to determine which HIV epitopes are immunodominant in the anti-HIV immune response. Consideration of these aspects has lead to the dawn of a new era of MHC-based vaccine design, in which the CTL epitopes are selected on the basis of the frequency of restricting MHC alleles. This article reviews data on the distribution patterns of molecular subtypes of HLA class I and class II extended haplotypes, discussing distribution among Asian Indians but with reference to global distributions. These data provide a genetic basis for the possible predisposition and fast progression of HIV infections in the Indian population. Since there is selective predominance of different HLA alleles and haplotypes in different populations, a dedicated screening effort is required at the global level to develop MHC-based vaccines against infectious diseases. It is hoped that this might lead to the development of multivalent, poly-epitope, subtype-specific HIV vaccines that are specific for the target geographical location.