The development of an HIV vaccine is an important, but difficult goal, but researchers at the Massachusetts Institute of Technology (MIT) recently reported on an important advance in this area. One challenge in developing an HIV vaccine has been the difficulty in measuring how effective a vaccine is in producing an immune response. The MIT researchers have resolved that challenge by developing a high-throughput automated assay to evaluate individual T-cell response.

The researchers recently reported their research in the Journal of Clinical Investigation (1). CD8⁺ T cells are an important element of the immune response to viral infection, and an inadequate CD8⁺ T cell response is thought to be partly responsible for the infection that arises following infection with HIV (1). Scientists would like their vaccines to provoke T cells to recognize and kill HIV-infected cells, but it is not easy to monitor whether T cells are provoking an adequate or inadequate response, according to a MIT press release describing the research.

The researchers pointed to two key challenges. Although IFN-γ production is used as a measure of T cell function, the relationship between cytokine production and the ability of a cell to lyse virus-infected cells is not clear. Additionally, the ability to assess multiple CD8⁺ T cell functions with single-cell resolution using freshly isolated blood samples and recovering these cells for further functional analyses also has been a challenge (1).

To address these issues, the researchers developed a high-throughput, automated assay in 125-pl microwells to simultaneously evaluate the ability of thousands of individual CD8⁺ T cells from HIV-infected patients to mediate lysis and to produce cytokines (1). Using this approach, the researchers could detect whether the T cells killed the infected cells with probes that glow when the dying cells’ nuclei become compromised. The next step was to measure  interferon gamma production with a microengraving technique that the researchers had earlier developed. Secretions from each cell are imprinted on a glass slide, which can then be tested for the presence of specific proteins. Because each cell has its own “address” on the slide, the secretions can be traced back to individual cells, and their interferon gamma production can be correlated directly to their cell-killing ability, according to the MIT release. The same technology could potentially be adapted to measure cells’ output of any other immune system protein. In this study, the researchers found that while the percentage of T cells that secrete interferon gamma is similar to the percentage of those that kill infected cells, the populations are not identical. In future studies, the researchers hope to find markers that correlate with cell-killing ability, thereby making it easier to evaluate a potential vaccine’s effectiveness, according to the MIT release.

Although more research will be needed to develop the technology to the point where it can be used routinely in vaccine trials for large-scale studies of patient samples, it is a positive accomplishment in gaining understanding for developing an HIV vaccine.

Source

1. N. Varadarajan et al., “A High-Throughput Single-Cell Analysis of Human CD8+ T Cell Functions Reveals Discordance for Cytokine Secretion and Cytolysis,” J. Clin. Invest. online, DOI:10.1172/JCI58653, Oct. 3, 2011.