Distribution and compartmentalization of human circulating and tissue-resident memory T cell subsets

Abstract

Knowledge of human T cells derives chiefly from studies of peripheral blood, whereas their distribution and function in tissues remains largely unknown. Here, we present a unique analysis of human T cells in lymphoid and mucosal tissues obtained from individual organ donors, revealing tissue-intrinsic compartmentalization of naive, effector, and memory subsets conserved between diverse individuals. Effector memory CD4(+) T cells producing IL-2 predominated in mucosal tissues and accumulated as central memory subsets in lymphoid tissue, whereas CD8(+) T cells were maintained as naive subsets in lymphoid tissues and IFN-γ-producing effector memory CD8(+) T cells in mucosal sites. The T cell activation marker CD69 was constitutively expressed by memory T cells in all tissues, distinguishing them from circulating subsets, with mucosal memory T cells exhibiting additional distinct phenotypic and functional properties. Our results provide an assessment of human T cell compartmentalization as a new baseline for understanding human adaptive immunity.

Figure 1. Lymphocyte subset frequency is intrinsic to the tissue site within and between individuals

Lymphocytes were isolated from the tissues indicated in Table 1 and analyzed by flow cytometry. (A) Representative flow cytometry plots showing CD3 and CD20 expression, indicating T and B cell subsets, respectively, gated on forward and side scatter lymphocyte populations. Tissue designations from left to right: BLD, blood; LLN, lung lymph node; JEJ, jejunum; SPL, spleen; LUN, lung; ILE, ileum; ILN, inguinal lymph node; MLN, mesenteric lymph node; COL, colon. Data derive from Donor 3. (B) Upper: Graph shows relative T and B cell frequency in the nine tissue sites compiled from 14 donors (donor #’s 1–4, 7–10, 12, 13, 20, 27, 33, 40), plotted as the ratio of T:B cell frequency in each tissue site ±SEM. Lower: CD4⁺ and CD8⁺ T cell subset composition in different human tissue sites calculated as the mean ratio CD4⁺:CD8⁺ T cell frequency ±SEM within CD3⁺ cells from 17 individual donors (donor #’s 1–4, 7–10, 12, 13, 16, 18, 26, 27, 33, 39, 40). Individualized datasets for each donor are shown in Table S1.

Figure 2. Memory T cells predominate throughout the body and vary with age in lymphoid compartments

Lymphocytes isolated from indicated donor tissues were analyzed for CD45RO expression to delineate memory cells from CD45RA-expressing subsets representing either naïve or terminal effector cells. (A) Representative flow cytometry analysis of CD45RA and CD45RO expression from CD4⁺ T cells (left) and CD8⁺ T cells (right) from Donor 39, aged 32. Tissue designations from left to right: BLD, blood; LLN, lung lymph node; JEJ, jejunum; SPL, spleen; LUN, lung; ILE, ileum; ILN, inguinal lymph node; MLN, mesenteric lymph node; COL, colon. (B) Change in memory T cell frequency and distribution in different age groups. Plots show the mean frequency (±SEM) of memory (CD45RO⁺) CD4⁺ (left) and CD8⁺ (right) T cells in different tissues compiled from individuals of 3 age groupings: young (<20yrs; n=5), middle (30–50yrs, n=7) and older (50–60yrs, n=5). Differences in the overall proportion of memory CD4 T cells is highly significant (***) comparing the <20 to the 30–50yr (p=3×10⁻⁷) or comparing the <20 to the 51–60yr group (p=0.0005), but not significant comparing the 30–50yr to the 51–60yr groups (p=0.57). For CD8⁺ T cells, differences in the proportion of memory T cells was significant (**) comparing the <20yr to the 30–50yr (p=0.003), or to the 51–60yr group (p=0.04), but not significant between the 30–50yr and 51–60yr groups (p=0.33). CD45RO frequency for each of the 17 donors analyzed (donor #’s 1, 2, 3, 7, 8, 9, 10, 12, 13, 16, 18, 20, 27, 29, 33, 39, 40) is shown in Table S1.

Figure 3. Distinct tissue distribution and subset composition of naïve, memory and terminal effector CD4⁺ and CD8⁺ T cell subsets

(A) Coordinate expression of CD45RA and CCR7 by CD4⁺ (left) and CD8⁺ (Right) T cells in blood and 8 tissue sites delineates four subsets corresponding to naïve (CD45RA⁺CCR7⁺, upper right quadrant), terminal effector (Temra, CD45RA⁺CCR7⁻, upper left quadrant), central memory (Tcm, CD45RA⁻CCR7⁺, lower right quadrant), effector-memory (Tem, CD45RA⁻CCR7⁻, lower left quadrant). Results shown are from Donor 41, representative of nine donors. (B) Frequency of naïve (red), Temra (black), Tcm (yellow) and Tem (grey) CD4⁺ (left) and CD8⁺ (right) T cell subsets in each tissue site, compiled from nine donors (donor #’s 3, 15, 39, 40, 41, 42, 43, 44, 45; individualized datasets for each donor shown in Table S2). Small individual graphs show frequency of each subset in each site expressed as mean±SEM, calculated from dot plots as in (A). Lower: Large composite graphs show average frequency of each subset (naïve, Temra, Tcm, Tem) within CD4⁺ (left) or CD8⁺ (right) T cells in each tissue site.

Figure 4. CD69 expression distinguishes tissue-resident from circulating memory T cell subsets

(A) Mean frequency (±SEM) of CD69⁺ T cells gated on CD45RA⁺ (red bars) and CD45RO⁺ (blue bars) CD4⁺ (left) and CD8⁺ (right) T cells in blood and tissues compiled from 19 donors (donor #’s 1, 7, 8, 9, 10, 12, 13,14,15, 27, 29, 33, 39, 40, 41, 42, 43, 44, 45; individual frequencies from each tissue of each donor are shown in Table S3, top portion). (B) IL-7 receptor (CD127) is expressed by the majority of CD69⁺ tissue-resident memory T cells in lymphoid and mucosal sites. Flow cytometry plots show CD127 expression as a function of CD69 expression gated on CD45RO⁺ CD4⁺ (upper) or CD8⁺ (lower) T cells in blood and indicated tissue sites. Results are from Donor 41 and representative of five donors. (C) CCR7 and CD69 expression by CD45RO⁺ CD4⁺ (upper row) and CD8⁺ (lower row) T cells delineates four subsets: circulating central memory (Tcm:CCR7⁺CD69⁻), circulating effector-memory (Tem:CCR7⁻CD69⁻) cells, resident Tcm (rTcm:CCR7⁺CD69⁺) and resident Tem (rTem:CCR7⁻CD69⁺) subsets (see leftmost quadrant diagram). Results are from Donor 39 and representative of seven donors.

Figure 5. The integrin CD103 (αEβ7) specifically marks mucosal CD8 T cells

(A) Expression of CD103 by CD45RO⁺ (blue histogram) and CD45RA⁺(red-filled histogram) CD4⁺ (left) and CD8⁺ (right) T cells from blood and 8 tissue sites. Results are shown from Donor 40 and are representative of 11 donors. (B) CD103 expression on CD45RO⁺ and CD45RA⁺ CD4⁺ (left) and CD8⁺ (right) T cells shown as percent CD103⁺ for each subset from each tissue site compiled from 11 donors (donor #’s 1, 7, 8, 9, 10, 12, 13, 14, 15, 27, 29, 33; individual frequencies for each donor in each site are presented in Table S3, lower part).

Figure 6. Functional profile of T cells in lymphoid and mucosal tissues

T cells purified from indicated tissue sites were stimulated for 4hrs with PMA/ionomycin and cytokine production was assessed by intracellular cytokine staining (ICS). (A) IFN-γ and IL-2 production by CD4⁺ and CD8⁺ T cells in different tissue sites, with gates drawn based on unstimulated controls. Numbers in quadrants indicates percent of CD4⁺ T cells (left) or CD8⁺ T cells (right) producing IFN-γ, IL-2 or both cytokines. Results are from Donor 29, representative of four donors (#18, 26, 27, and 29) from which coordinate analysis of IFN-γ and IL-2 production was accomplished. (B) Individual pie chart diagrams showing the frequency of CD4⁺ and CD8⁺ T cells with rapid cytokine producing capacity in each tissue site from one donor, representative of four donors, showing a high proportion of quiescent CD4⁺ T cells in each site and a minority population of effector-memory CD4⁺ or CD8⁺ T cells. (C) IL-17 production is confined to memory CD4⁺ T cells in mucosal sites. Upper: Representative ICS analysis of IL-17 production from spleen, mucosal draining LN, lung and intestinal sites from Donor 9. Lower: Mean IL-17 production (±SEM) from blood and tissue of five donors where we analyzed IL-17 expression (Donor #’s 9, 10, 18, 26, 27).