Trafficking of human immunodeficiency virus type 1-specific CD8+ T cells to gut-associated lymphoid tissue during chronic infection

Abstract

Gut-associated lymphoid tissue (GALT) is a significant but understudied lymphoid organ, harboring a majority of the body's total lymphocyte population. GALT is also an important portal of entry for human immunodeficiency virus (HIV), a major site of viral replication and CD4(+) T-cell depletion, and a frequent site of AIDS-related opportunistic infections and neoplasms. However, little is known about HIV-specific cell-mediated immune responses in GALT. Using lymphocytes isolated from rectal biopsies, we have determined the frequency and phenotype of HIV-specific CD8(+) T cells in human GALT. GALT CD8(+) T cells were predominantly CD45RO(+) and expressed CXCR4 and CCR5. In 10 clinically stable, chronically infected individuals, the frequency of HIV Gag (SL9)-specific CD8(+) T cells was increased in GALT relative to peripheral blood mononuclear cells by up to 4.6-fold, while that of cytomegalovirus (CMV)-specific CD8(+) T cells was significantly reduced (P = 0.012). Both HIV- and CMV-specific CD8(+) T cells in GALT expressed CCR5, but only HIV-specific CD8(+) T cells expressed alpha E beta 7 integrin, suggesting that mucosal priming may account for their retention in GALT. Chronically infected individuals exhibited striking depletion of GALT CD4(+) T cells expressing CXCR4, CCR5, and alpha E beta 7 integrin, but CD4(+)/CD8(+) T-cell ratios in blood and GALT were similar. The percentage of GALT CD8(+) T cells expressing alpha E beta 7 was significantly decreased in infected individuals, suggesting that HIV infection may perturb lymphocyte retention in GALT. These studies demonstrate the feasibility of using tetramers to assess HIV-specific T cells in GALT and reveal that GALT is the site of an active CD8(+) T-cell response during chronic infection.

FIG. 1.

CD4⁺/CD8⁺ T-cell ratios in blood and GALT. Values were determined by four-color flow cytometry. Results shown are for 5 healthy controls (left) and 10 HIV-positive individuals (right). Linear regression analysis was used to generate lines and curves with a 95% confidence interval.

FIG. 2.

Phenotype of GALT CD8⁺ T cells. PBMC and GALT from HIV-positive individuals and controls (not shown) were stained with monoclonal antibodies to the αβ T-cell receptor (top left), CD45RO isoform (top right), CD69 antigen (bottom left), and CD25 (bottom right). The results shown are gated on CD8⁺ T cells and are typical of those for HIV-positive patients and controls. Grey lines indicate PBMC, and black lines indicate GALT cells.

FIG. 3.

MHC class I tetramer staining of HIV- and CMV-specific CD8⁺ T cells from blood and GALT. (A) Representative results for an HIV-positive individual. Plots are gated on CD3⁺ lymphocytes. Numbers in the upper right corner of each plot represent the percentage of CD8⁺ T cells bound by HLA-A^*0201-HIV Gag SL9 (left) or CMV pp65 (right) tetramers. (B) Combined results of MHC class I tetramer staining for peripheral blood and GALT from 10 HLA-A^*0201-positive, HIV-infected individuals. Each patient is represented by a different symbol, and lines between symbols identify PBMC and GALT samples from a single individual.

FIG. 4.

Expression of β7 integrins in blood and GALT. (A) Expression of integrins α4β7 and αΕβ7 on CD4⁺ and CD8⁺ T cells from blood and GALT of HIV-negative (top) and HIV-positive (bottom) individuals. Numbers indicate the percentage of CD4⁺ or CD8⁺ lymphocytes in each quadrant. (B) Mean (bar height) and standard deviation (error bars) α4β7 and αΕβ7 levels for HIV-infected individuals and controls as stated in the text. Top, α4β7 expression. ∗, P = 0.014 for blood CD8⁺ T cells from six HIV-positive versus two HIV-negative individuals. Bottom, αΕβ7 expression. ∗ and ∗∗, P = 0.003 for GALT CD4⁺ T cells and P = 0.004 for GALT CD8⁺ T cells, respectively, from six HIV-positive versus four HIV-negative individuals.

FIG. 5.

Expression of CXCR4 and CCR5 in blood and GALT. (A) Expression of chemokine receptors CXCR4 and CCR5 on CD4⁺ and CD8⁺ T cells from blood and GALT of HIV-negative (top) and HIV-positive (bottom) individuals. Numbers indicate the percentages of CD4⁺ or CD8⁺ lymphocytes in each quadrant. (B) Mean (bar height) and standard deviation (error bars) values for HIV-infected individuals and controls as stated in the text. ∗∗, P < 0.001 for GALT CD4⁺ T cells expressing CXCR4⁺ and CCR5⁺ from seven HIV-positive versus three HIV-negative individuals.

FIG. 6.

Antigen-specific CD8⁺ T cells express lymphocyte trafficking markers. (A) Expression of CCR5 by HIV Gag (left)- and CMV (right)-specific CD8⁺ T cells in blood and GALT of patient G04. (B) Expression of αΕβ7 integrin by HIV Gag (left)- and CMV (right)-specific CD8⁺ T cells in blood and GALT of patient G25. (C) Expression of αΕβ7 integrin by CMV-specific CD8⁺ T cells in blood and GALT of patient G05.