Optimization of methods to assess human mucosal T-cell responses to HIV infection

The majority of HIV-1 infections occur via sexual transmission at mucosal epithelia lining the vagina, cervix or rectum. Mucosal tissues also serve as viral reservoirs. However, our knowledge of human mucosal T-cell responses is limited. There is a need for reliable, sensitive, and reproducible methods for assessing mucosal immunity. Here we report on the collaborative efforts of two laboratories to optimize methods for processing, culturing, and analyzing mucosal lymphocytes. Rectal biopsy tissue was obtained by flexible sigmoidoscopy, which is rapid, minimally invasive, and well tolerated. Of the four methods compared for isolating mucosal mononuclear cells (MMC), collagenase digestion reproducibly yielded the most lymphocytes (4-7 × 10⁶). Furthermore, 0.5-1 × 10⁶ MMC could be polyclonally expanded to yield 17 × 10⁶ CD8+ T cells allowing mapping of responses to overlapping peptides spanning the HIV-1 genome using IFN-γ enzyme-linked immunospot (ELISpot). Expansion also reduced the spontaneous IFN-γ production normally detected in fresh MMC. Piperacillin-tazobactam and amphotericin B reduced contamination of MMC cultures to 4%. Taken together, these methods will be useful for studies of mucosal immunity to HIV-1 and other pathogens during natural infection and following vaccination.