Enhanced Levels of Functional HIV-1 Co-Receptors on Human Mucosal T Cells Demonstrated Using Intestinal Biopsy Tissue Peter A

CONCISE COMMUNICATION

Enhanced levels of functional HIV-1 co-receptors on human mucosal T cells demonstrated using intestinal biopsy tissue Peter A. Anton1,2, Julie Elliott1,2, Michael A. Poles1,2, Ian M. McGowan1, Jose Matud2, Lance E. Hultin2, Kathie Grovit-Ferbas2, Charles R. Mackay3, Irvin S.Y. Chen2 and Janis V. Giorgi2

Objective: To examine compartmental differences in co-receptor expression on CD4 lymphocytes between blood and gut using endoscopic biopsies. Design: Mucosal and peripheral CD4 T cells from healthy controls were compared for co-receptor expression and vulnerability to infection by HIV-1. Methods: Expression of CCR5 and CXCR4 was quanti®ed by ¯ow cytometry on isolated mucosal CD4 lymphocytes obtained from endoscopic biopsies and blood from healthy controls. Vulnerability to in vitro infection by both R5 and X4 strains was assessed by measuring p24. Results: Biopsies yielded suf®cient lymphocytes for ¯ow cytometric characterization and infectivity studies. The percentage of mucosal CD4 T lymphocytes that expressed CCR5 and the per cell expression of CCR5 were both signi®cantly increased compared with that in peripheral blood CD4 T lymphocytes. CXCR4 was expressed on the majority of CD4 lymphocytes in both compartments. In vitro infection of mucosal mononuclear cells supported greater viral replication of both R5 and X4 strains than peripheral blood mononuclear cells. Conclusions: Enhanced expression of CXCR4 and CCR5 on CD4 lymphocytes in normal intestinal mucosa predicts increased vulnerability to infection by both R5 and X4 HIV-1. Endoscopic biopsies provide a useful mucosal tissue sampling technique to identify compartmental immunologic differences that may be exploited by HIV-1 in establishing initial mucosal infection. & 2000 Lippincott Williams & Wilkins

AIDS 2000, 14:1761±1765

Keywords: human, gastrointestinal, mucosal, HIV-1 co-receptors, CCR5, CXCR4, HIV-1 biopsy

From the 1Center for HIV and Digestive Diseases, Division of Digestive Diseases and the 2Department of Medicine and the UCLA AIDS Institute, UCLA School of Medicine, Los Angeles, California and 3LeukoSite Inc., Cambridge, Massachussetts, USA. Sponsorship: This study was supported by NIH grants AI 28697 (P.A.A., I.S.Y.C.) and AI 28697, 36704, 37613 (J.V.G.), and by the Macy's Foundation. Requests for reprints to Dr P. Anton, University of California at Los Angeles, 675 Charles E. Young Drive South, MRL 2734, Los Angeles, California 90095, USA. Date of receipt: 6 September 1999; revised: 3 March 2000; accepted: 28 April 2000.

ISSN 0269-9370 & 2000 Lippincott Williams & Wilkins 1761 1762 AIDS 2000, Vol 14 No 12

Introduction Biopsy acquisition and isolation of mucosal mononuclear cells The majority of HIV-1 transmission occurs across MMC were isolated from four endoscopic biopsies mucosal surfaces. The mechanisms associated with from each donor and were placed into 15 ml of tissue transmission are complex, but the local mucosal im- culture medium (RPMI 1640, Irvine Scienti®c, Santa mune system is likely to play a critical role in suscept- Ana, California, USA). The biopsies were maintained ibility to, or protection from, HIV-1 infection. The at room temperature on a rotating platform until normal intestinal mucosa is characterized by mild isolation (20-60 min), then removed to a 10 3 35 mm in¯ammation maintained by constitutive expression of petri-dish containing phosphate-buffered saline (PBS) locally secreted chemokines and cytokines [1±3]. with 1 mmol/l EDTA and 50 mmol/l 2- mercap- Further, gastrointestinal lymphocytes differ functionally toethanol and teased apart using 18G needles. The and phenotypically from their peripheral blood coun- disrupted tissue was incubated at 378C for 20 min in a terparts [4±6]. Virtually all mucosal CD4 lymphocytes shaking water bath. Following centrifugation, the tissue express activation markers and are of the CD45RO samples were digested with a mixture of collagenase memory subset [4±7]. and dispase (0.1 mg/ml in RPMI; Roche Molecular Biochemicals, Indianapolis, Indiana, USA) for 1 h at The vulnerability of intestinal mucosa to HIV-1 infec- 378C. Further tissue disruption was achieved by sample tion following sexual exposure or ingestion of milk passage through syringes with a series of decreasing from HIV-1-infected mothers is well recognized, but needle gauges (18G to 21G). Debris was removed using the mechanisms remain unclear. Using surgically re- a 70-ìm cell strainer (Falcon; Becton Dickinson, sected specimens, Lapenta et al. demonstrated an in- Franklin Lakes, New Jersey, USA). Isolated cells were creased expression of CCR5 on human mucosal CD4 resuspended in RPMI containing 10% fetal calf serum. T cells compared with peripheral blood mononuclear MMC, which includes primarily epithelial cells and cells (PBMC) [8]. This increase in co-receptor expres- leukocytes, were counted visually using a hemocyt- sion might augment mucosal vulnerability to HIV-1 ometer and the proportion of mononuclear cells that infection and might represent a potential target for viral were leukocytes estimated. Approximately 20% of the blockade [9,10]. total MMC were leukocytes from a mean yield of 1.3 3 106 cells (SD 1.1; n 6) per four biopsies. These results con®rm the importance of the mucosa in Viability, determined by the exclusion of trypan blue, the pathogenesis of HIV-1 disease and the role for was . 90%. convenient and repetitive methods to sample mucosal tissue using endoscopic biopsies. In this study, isolated mucosal mononuclear cells (MMC) were obtained Flow cytometry from mucosal biopsy samples and co-receptor expres- Monoclonal antibodies included CD4-¯uorescein iso- sion on CD4 cells quanti®ed by ¯ow cytometry. The thiocyanate and CD45-peridin chlorophyl protein susceptibility of MMC and PBMC to infection by both (BDIS, Mountain View, California, USA), CD8-allo- R5 and X4 strains of HIV-1 was investigated. phycocyanin (Caltag, Burlingame, California, USA), and anti-CXCR4-R-phycoerythrin (PE; Pharmingen, San Diego, California, USA). Anti-CCR5 was pro- vided by Dr Walter Newman of Leukosite, (Cam- bridge, Massachussetts, USA) and was prepared as a 1:1 Methods conjugate with PE. Analysis was carried out on a FACSCalibur (BDIS) and Cell Quest (BDIS) software. Study subjects and endoscopy Initial gating on stained PBMC from whole blood and Intestinal tissue was collected from eight healthy HIV- the isolated MMC was performed using side scatter and negative individuals undergoing elective endoscopy for CD45 ¯uorescence followed by forward- and side- a history of blood in stool or for routine polyp screen- scatter gating. A well-de®ned and separate population ing. No subjects had diarrheal symptoms or history of of mucosal leukocytes was identi®ed as CD45bright, in¯ammatory or infectious intestinal disorders. Biopsies representing 10±50% of the initial mononuclear sample were acquired from a standardized site of 30 cm in the population. Of these, 20±40% were CD4 lymphocytes rectosigmoid colon to avoid potential regional varia- and 26±41% were CD8 T cells. tion. All samples were histopathologically normal. Phlebotomy was performed immediately preceding PBMC, isolated and directly analyzed by ¯ow cytome- endoscopy; blood was collected in ethylenediamine try, showed no discernible differences in phenotypic tetraacetic acid (EDTA)-containing tubes. Informed pro®les for all surface antigens when compared with consent was obtained from all patients and the study PBMC processed through the mucosal isolation proce- was approved by the UCLA Human Subjects Protec- dure (collagenase/dispase treatment) and then stained tion Committee. (data not shown). Biopsy-derived gut T cells vulnerable to HIV Anton et al. 1763

To estimate the number of CCR5 molecules per CD4 1NL4-3 at an multiplicity of infection of 0.01. Prior to lymphocyte, the observed CCR5 relative ¯uorescence plating, the cells were washed twice to remove free intensity (RFI) was multiplied by a calibration factor, virus and adherent p24. Following plating, 30 ìl super- speci®cally 44, determined for our FACSCalibur. This natant was sampled at 18, 72 and 130 h for estimation calibration factor is the number of molecules of PE of p24 production (per 104 CD4 lymphocytes) using detected per RFI channel number. For monoclonal enzyme-linked immunosorbent assay (ELISA; Coulter antibody prepared as 1:1 conjugates with PE, such as Corp., Miami, Florida, USA). CD4 percentages were our anti-CCR5, the RFI channel number can be determined by ¯ow cytometry and were used to multiplied by the calibration factor to estimate the determine the number of CD4 lymphocytes in the number of antibody molecules bound per cell [11]. cultures. This calculation was not performed for CXCR4 as it was not available as a 1:1 conjugate. IL-2 was required to maintain viability of mucosal cell populations. As IL-2 is known to upregulate CCR5 In vitro infection studies and could enhance viral replication [12,13], PBMC MMC and PBMC were assessed for in vitro HIV-1 from the same patient were exposed to infectious virus infection. Isolated MMC were cultured for 3 days in both with and without IL-2 present in the culture Iscove's DMEM medium (Gibco BRL, Rockville, media to control for the IL-2 effect. Maryland, USA) supplemented with 10% human serum, containing 10 ìg/ml gentamycin, penicillin, strep- tomycin (Gibco) and glutamine. Interleukin 2 (IL-2; Statistical methodology Amgen, Thousand Oaks, California, USA) was added Two-sided Wilcoxon signed rank tests were used to at 20 IU/ml. A total of 1 3 105 MMC and 1 3 105 examine difference in phenotypic marker values be- PBMC were plated in a 96-well plate in 100 ìl tween blood and gut samples; P values < 0.05 were medium after a 3-h infection with HIV-1SX or HIV- considered statistically signi®cant.

(a) (b)

104 100 30 18000 BLOOD BLOOD 3 10 16000 17% 20 3 225 80 102 Lymphocyte ϩ 14000 10 1 10 CD4 12000 60 ϩ 10000 104 30 GUT GUT 3 40 11 416 8000 CD4-FITC 10 90% 20 6000

2 Frequency of events 10 Lymphocytes Expressing CCR5 ϩ 20 10 4000 101 2000 0 1 2 3 4

1 2 3 4 % of CD4 10 10 10 10 BLOOD GUT

10 10 10 10 BLOOD GUT CCR5 Molecules per CCR5 Fluorescence CCR5-PE

Fig. 1. CCR5 receptor expression on CD4 lymphocytes from blood and from gut mucosa. (a) The percentage of CCR5-expression of CD4 lymphocytes from blood and gut of six subjects are shown accompanied by the inset ¯ow cytometry scatter plots (CCR5 and CD4 staining) for blood and gut of a representative subject. The number on the upper right quadrant of each inset plot indicates the percentage of CD4 lymphocytes in that subject's compartments (blood or gut) that expressed CCR5. The gut samples of all six subjects had a greater percentage of CCR5CD4 cells compared with blood (P 0.03); differences ranged from 2.0-fold to 5.4-fold. (b) The number of CCR5 receptors per cell on blood and gut CD4 lymphocytes of the same six subjects are shown accompanied by ¯ow cytometry histograms of a representative subject. The rightward shift of mean ¯uorescence index in the CCR5CD4 mucosal cells in the inset histogram illustrates the increased numbers of CCR5 receptors per CD4 lymphocyte, while the numbers above the bars indicates the number of molecules of CCR5 expressed per CCR5CD4 lymphocyte in the blood and gut of that individual. The gut samples of all six subjects had higher expression of CCR5 molecules per cell compared with the blood (P 0.03); differences ranged from 1.4-fold to 3.5-fold. Symbols for each person are the same as those used in (a). 1764 AIDS 2000, Vol 14 No 12

Results the PBMC cultured with IL-2. For X4 HIV-1NL4-3, viral growth accelerated over time and supernatant Co-receptor expression on mucosal and blood p24 levels in the MMC cultures at 130 h was CD4 T cells 1194 pg/ml per 104 CD4 lymphocytes compared A median of 23% [interquartile range (IQR) 18±30] of with undetectable levels in cultures of PBMC. all blood CD4 lymphocytes expressed CCR5. A median of 71% (IQR 50±87) of the mucosal CD4 lymphocytes expressed CCR5, a 2.8-fold increase over those in blood (P 0.03) (Fig. 1a). Mucosal CD4 Discussion lymphocytes also expressed signi®cantly more (2.2-fold increase) CCR5 receptors per cell (6946 molecules; Endoscopically acquired intestinal mucosal biopsies can IQR 6306±10 416) than did their CCR5-expressing be used to isolate of MMC in suf®cient quantities to CD4 lymphocyte blood counterparts (3841 molecules perform ¯ow cytometric characterization of this com- IQR 3259±4441) (P 0.03) (Fig. 1b). Taken to- partment and to undertake in vitro infection studies. gether, this is a 6.2-fold increase in total mucosal expression of CCR5 receptors on CD4 lymphocytes Our results show that there is enhanced expression of potentially available for viral infection compared with the chemokine receptor CCR5 on MMC compared that in the blood. with that on PBMC. Moreover, both the proportions of mucosal CD4 cells expressing CCR5 and the Nearly all (97%) of the detected CCR5 expression on amount of CCR5 expressed per cell were increased. In CD4 lymphocytes in both the blood and gut was on memory (CD45RO) cells. There was an increased (a) proportion of CD45RO memory cells among gut CD4 160 lymphocytes (median 95%; IQR 90±97) compared with blood (median 46%; IQR 38±53). While not all 120 memory cells expressed detectable levels of CCR5, nearly all CCR5 was on the preferentially infectable 80 memory T cells, in both compartments. 40 In contrast to the ®ndings with CCR5, high levels of

CXCR4-expressing cells were observed in both blood CD4 cells

4 0 (median 83%; IQR 75±87) and gut (median 64%; IQR 59±79) without signi®cant difference between (b) 1200 the two compartments either in percentage or in relative ¯uorescence intensity of staining with anti-

CXCR4 antibody (data not shown). Based on co- p24 (pg) per 10 800 receptor expression, mucosal lymphocytes would likely be infectable by HIV-1 strains with tropism for either co-receptor [14]. 400

In vitro infection studies of MMC compared with 0 PBMC To contrast the susceptibility to HIV-1 infection of 18 72 130 MMC with enhanced co-receptor expression with that of PBMC and to demonstrate the functional Time (h) relevance, both cellular populations were subjected to in vitro HIV-1 infection. As shown in Fig. 2, MMC Fig. 2. p24 produced by mucosal mononuclear cells (MMC) and pripheral blood mononuclear cells (PBMC) after infec- were able to support vigorous viral replication in tion with HIVSX or HIVNL4-3. Line graphs indicate the p24 culture compared with that achieved with PBMC, production at 18, 72 and 130 h after a 3-h infection with with or without IL-2. PBMC infected in the absence either R5 HIVSX (a) or X4 HIVNL4-3(b). After 72 and 130 h, the of IL-2 could not support HIV-1 replication by supernatants from the MMC cultured in the presence of either HIV-1SX or HIV-1NL4-3. When compared with 20 IU/mL interleukin 2 (IL-2) contained greater concentra- similarly cultured PBMC in the presence of IL-2, tions of p24 than the supernatants from either PBMC grown MMC produced markedly more p24 following infec- with (s) or without (.) 20 IU/mL of IL-2. The greater p24 tion with R5 and X4 isolates of HIV-1. At 72 h, production from the cultured mucosal cells suggests that they supernatant p24 levels of the R5 HIV-1SX in the are more susceptible than PBMC to replication of R5 or X4 MMC culture was 164 pg/ml per 104 CD4 lympho- HIV-1. The data are from one of two experiments that cytes compared with 51 pg/ml per 104 CD4 cells in showed similar ®ndings. Biopsy-derived gut T cells vulnerable to HIV Anton et al. 1765 contrast to previous reports, we found signi®cant normal and in¯amed mucosa. Comparison of follicular and lamina propria lymphocytes. 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