Bruce Walker seeks to determine how the immune system controls chronic viral infections and to augment antiviral immunity for therapeutic benefit.
Effects of HIV Infection on Antigen Processing
HIV infection elicits a strong and multispecific cytotoxic T lymphocyte response in infected persons, yet, despite induction of this adaptive immune response, most persons progress to develop AIDS. Because peptides must be processed prior to class I presentation, we hypothesize that immunodominance is influenced by these processes. The general MHC-I-restricted antigen-processing pathway is a multistep pathway that includes the degradation of proteins by the 26S proteasome, the trimming of peptides by cytosolic aminopeptidases and in a few documented cases the tripeptidylpeptidase, and their translocation in the endoplasmic reticulum, where aminopeptidases can shorten N-extended peptides. This project will focus on defined HIV epitopes and determine the relationship between antigen processing and immune recognition, with an emphasis on determining the role of antigen processing in shaping an immunodominant response.
Anitviral Function of HIV-Specific CD8 T Cells
HIV-specific CD8 T cells are generated early after acute HIV infection in humans, and appear coincident with the rapid decline in plasma virus levels. This suggests that these cells play an important role as an antiviral host defense. However, when the generally accepted methods of CD8 T cell quantitation are used to define the magnitude of these responses directed against HIV, there is no difference between persons who control the virus to very low levels without anti-HIV drugs and those who maintain high viral loads with rapid disease progression. These data suggest differences in the antiviral activity of these cells. We have determined the viral peptides targeted by these responses and the HLA alleles that present them to the immune system and have developed a method for precise quantitation of the relative antiviral effect of these cells in an in vitro assay. The project will define the relative antiviral efficacy of immune responses targeting different epitopes in the context of different alleles, focusing on persons at the extremes of clinical outcome—those who maintain outstanding control of viremia (to undetectable levels in plasma) and those who have high viral loads and rapid disease progression. Because the cohorts are established and the assays are functional, the project can progress rapidly over the course of the summer.
Spontaneous Control of HIV as a Guide to Immunogen Design
Approximately 1 person in 300 who become infected with HIV is able to control HIV replication without the need for medication, but the reasons for this remain unclear. We have developed new techniques that allow one to measure the actual antiviral activity mediated by HIV-specific CD4 and CD8 T cells from such persons, termed "elite controllers," and have found that many of the immune responses generated in infected persons have little or no antiviral activity—as if HIV is causing the immune system to generate strong responses that are irrelevant, as if the virus were providing a decoy to the immune system. HIV-specific CD4 T cells appear to be critical for maintenance of virus-specific CD8 T cell responses, yet are thought to be lost in HIV infection. The student will use multicolor flow cytometric techniques as well as in vitro assays that assess viral replication in the presence or absence of added immune cells, in order to determine the properties of those cells that are the most potent. To define the functional properties of these cells, we will use quantitative PCR, class I and II tetramers, multicolor flow cytometry, and gene-chip analyses to determine the effector functions in a unique cohort of persons we have assembled who are able to control HIV infection without medication, and in those who fail to achieve immune control.