SM, MAP, and MM designed the study. SM, KTR, PR, and MM analyzed the data. SM, AS, AL, and MM enrolled patients. SM, MAP, KTR, DB, PR, and MM contributed to writing the paper. MAP is the gastroenterologist who performed all the study procedures and specimen collection. SM, PJP, VM, and PL collected data or carried out experiments for the study. KTR and PR provided immunohistochemistry and quantification of T cells in the LP, in situ hybridization and identification of cells with HIV gene expression, and the photomicrographs for this manuscript.
The authors have declared that they do not have commercial or other associations that might cause a conflict of interest.
During acute and early HIV-1 infection (AEI), up to 60% of CD4+ T cells in the lamina propria of the lower gastrointestinal (GI) tract are lost as early as 2–4 wk after infection. Reconstitution in the peripheral blood during therapy with highly active antiretroviral therapy (HAART) is well established. However, the extent of immune reconstitution in the GI tract is unknown.
Fifty-four AEI patients and 18 uninfected control participants underwent colonic biopsy. Forty of the 54 AEI patients were followed after initiation of antiretroviral therapy (18 were studied longitudinally with sequential biopsies over a 3-y period after beginning HAART, and 22 were studied cross sectionally after 1–7 y of uninterrupted therapy). Lymphocyte subsets, markers of immune activation and memory in the peripheral blood and GI tract were determined by flow cytometry and immunohistochemistry. In situ hybridization was performed in order to identify persistent HIV-1 RNA expression. Of the patients studied, 70% maintained, on average, a 50%–60% depletion of lamina propria lymphocytes despite 1–7 y of HAART. Lymphocytes expressing CCR5 and both CCR5 and CXCR4 were persistently and preferentially depleted. Levels of immune activation in the memory cell population, CD45RO+ HLA-DR+, returned to levels seen in the uninfected control participants in the peripheral blood, but were elevated in the GI tract of patients with persistent CD4+ T cell depletion despite therapy. Rare HIV-1 RNA–expressing cells were detected by in situ hybridization.
Apparently suppressive treatment with HAART during acute and early infection does not lead to complete immune reconstitution in the GI mucosa in the majority of patients studied, despite immune reconstitution in the peripheral blood. Though the mechanism remains obscure, the data suggest that there is either viral or immune-mediated accelerated T cell destruction or, possibly, alterations in T cell homing to the GI tract. Although clinically silent over the short term, the long-term consequences of the persistence of this lesion may emerge as the HIV-1–infected population survives longer owing to the benefits of HAART.
Despite early initiation of anti-HIV therapy, loss of T cells in the gastrointestinal mucosa persisted for years in most members of a clinical cohort identified early after HIV-1 infection.
AIDS causes disease by inactivating the body's immune response against infection. The AIDS virus (HIV) is most active against the white blood cells called T lymphocytes, particularly the CD4 T lymphocytes, which recognize infection and activate other cells of the immune system to fight it. In what was formerly believed to be a gradual process, HIV infection is now known to deplete a subset of the body's CD4 lymphocytes, called memory cells, quite rapidly—over only a few days—within a few weeks after a person becomes infected with the AIDS virus. This was not known until recently because researchers were counting CD4 cells only in blood, while a majority of the memory lymphocytes are located in and around the digestive system. It is these intestinal memory lymphocytes that are rapidly wiped out, while those in the blood fall much more gradually, usually over several years. Few studies of mucosal lymphocytes have been done in humans because such studies require biopsies of the intestinal lining (mucosa).
Although CD4 cells in the blood can return and remain at normal levels when HIV infection is treated with antiviral drugs, it has been unclear as to whether the mucosal CD4 cells return as well. People who begin treatment as soon as possible after becoming infected with HIV might seem to have the best chance of regaining their mucosal immunity, compared to those who wait until the CD4 cells in their blood have fallen, which is a generally accepted reason to start medication for HIV. Therefore, the researchers wanted to see whether people who start treatment early after becoming infected with HIV might experience restoration of their mucosal immunity over time and, if so, what kinds of lymphocytes would return.
The researchers studied people who started treatment for HIV within a few weeks to months of becoming infected and who then remained on treatment. Some volunteers underwent biopsies of the intestinal mucosa before starting treatment and then at various points from 1 y until as long as 3 y after infection. Others volunteered for biopsy only one time, anywhere from less than 1 y to 7 y following treatment. The biopsy specimens were examined under the microscope and with a technique called flow cytometry using specific staining methods to assess their structure and functional characteristics. Results were compared to biopsies from a group of HIV-uninfected volunteers.
The researchers found that the percentage of CD4 lymphocytes dropped much lower in the intestinal mucosa than in blood during early infection and then, unlike in blood, remained low even after several years of treatment for HIV. In the microscope images, they found that mucosal CD4 cells were lost mostly from regions of active battle against invading germs, rather than from “training sites” for new CD4 cells. Over time, only 30% of the volunteers showed return of CD4 cells to normal levels in these active sites.
Unlike T lymphocytes in the blood, which tend to return to a resting state after HIV is treated, the T lymphocytes in the intestinal mucosa tended to persist in an activated state despite HIV treatment, even though only a tiny fraction of these cells were found to be infected with HIV. A high level of activation of mucosal lymphocytes soon after infection was found to predict poor restoration of mucosal CD4 cells over time.
These experiments confirm that studying easily obtained blood lymphocytes provides only a limited view of how HIV affects the immune system as a whole. The finding that immune cells of the intestinal mucosa remain depleted and over-activated for years despite antiretroviral treatment raises the concern that over time this will result in clinical problems. Fortunately, this does not appear to be the case in most people currently being treated for HIV, some for as long as 10 y, but the results of this study suggest that we should remain vigilant for gastrointestinal problems resulting from impaired immunity over time. The finding that mucosal lymphocytes do appear to return to normal levels in a minority of volunteers is of interest, and suggests that early interventions to reduce activation of intestinal T cells (such as antimicrobial or immunomodulatory treatment) might be worth investigating in those recently infected with HIV. Finally, these results suggest that a vaccine to prevent HIV may need to stimulate immune responses that can act very quickly following infection, before the bulk of lymphocytes capable of countering the infection are lost, perhaps irreversibly.
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Over the past 25 y, more than 25 million individuals have succumbed to the complications of HIV-1 infection [
During acute and early HIV-1 infection (AEI), there is selective depletion of CD4+ T cells in the gastrointestinal (GI) lamina propria (LP) compared with levels measured in the peripheral blood [
These findings have reignited interest in the impact of HAART on CD4+ T cell reconstitution in the GI tract compared with the peripheral blood. Guadalupe et al. have reported that of two patients treated during primary HIV-1 infection, near-complete mucosal reconstitution occurred in one patient, whereas the second patient showed incomplete restoration despite 5 y of antiretroviral therapy [
To address this issue conclusively, we undertook the present study. Our aims were: (1) to determine the effect of uninterrupted antiretroviral therapy initiated during AEI on the reconstitution of GI mucosal T-lymphocyte population; (2) to examine the phenotype of mucosal lymphocytes prior to and during long-term antiretroviral therapy; and (3) to examine clinical, immunological, and virological factors involved in the reconstitution of the GI immune system during antiretroviral therapy. We prospectively followed 18 individuals identified and treated during AEI, and performed recto-sigmoid colonic biopsies on these individuals prior to treatment and serially up to 32 mo following the initiation of treatment. In addition, we extended our cross-sectional colonic biopsy studies to include a total of 22 individuals who were also treated during acute and early infection. We therefore examined a relatively large cohort of patients, all treated during AEI, to determine whether CD4+ T cell numbers reconstitute to the same extent in the GI tract as observed in the peripheral blood. An additional 14 individuals with AEI provided biopsy specimens only prior to treatment.
Peripheral blood and recto-sigmoid colonic mucosal tissue were collected from HIV-1–infected patients and HIV-1–uninfected control participants. Informed consent was obtained from all patients and the study was approved by the Institutional Review Boards of the Rockefeller University, Bellevue Hospital Center (New York, New York, United States), and Manhattan Veteran's Administration Hospital Center (New York, New York, United States). All clinical investigation was conducted according to the principles expressed in the Helsinki Declaration.
Endoscopic biopsies were obtained from macroscopically normal colonic mucosa and were processed as described previously [
Immediately after acquisition, mucosal mononuclear cells (MMCs) were enzymatically isolated from mucosal biopsies using a 30-min incubation in collagenase type II (Clostridiopeptidase A, Sigma-Aldrich, St. Louis, Missouri, United States) followed by mechanical separation through a blunt-ended 16-gauge needle. The digested cell suspension was strained through a 70-μm disposable plastic strainer. Immediately after isolation, cells were washed with PBS and resuspended in PBS containing antibodies for flow cytometry. Peripheral blood mononuclear cells (PBMCs) were prepared by centrifugation on a Ficoll-Hypaque density gradient (Mediatech). PBMCs were stained for flow cytometry immediately after isolation.
Cell surface expression of lymphocyte antigens was identified by monoclonal antibody staining of freshly isolated MMCs and PBMCs, followed by flow cytometry using a FACSCalibur (Becton-Dickinson, Palo Alto, California, United States) with analysis using CellQuest software (Becton-Dickinson). Monoclonal antibodies used in this study included: anti-human CD3-fluorescein isothiocyanate (FITC) (clone UCHT1) (Becton-Dickinson), anti-human CD3-phycoerythrin (PE) (clone SK-7) (Becton-Dickinson), anti-human CD3-peridinin chlorophyll-α protein (PerCP) (clone SK-7) (Becton-Dickinson), anti-human CD4-allophycocyanin (clone RPA T4) (PharMingen, San Diego, California, United States), anti-human CD8 PE (clone RPA T8) (PharMingen), anti-human CXCR4-PE (clone 12G5) (PharMingen), anti-human CCR5-FITC (clone 2D7/CCR5) (PharMingen), anti-human HLA-DR PerCP (clone L243, BD Biosciences Pharmingen, San Diego, California, United States), anti-human CD45RO PE (clone UCHL1, BD Biosciences Pharmingen), anti-human Ki67 FITC (clone B56, BD Biosciences Pharmingen), anti-human CCR7 PE (clone 3D12, BD Biosciences Pharmingen), anti-human CD62L allophycocyanin (clone Dreg56, BD Biosciences Pharmingen), and the appropriate isotype controls. During flow cytometry, lymphocytes, initially identified by their forward- and side-scatter characteristics, were subject to phenotypic analysis. Dead cells were excluded from analysis using 7-aminoactinomycin D [
To determine the percentages of CD4+ and CD8+ cells in the T cell population, gated lymphocytes were initially examined for the expression of CD3. The CD3+ lymphocytes were then analyzed for expression of CD4 and CD8 receptors. To evaluate the expression of chemokine co-receptors, gated lymphocytes were initially examined for the expression of CD4 receptors. The CD4+ lymphocytes were further examined for the expression of chemokine co-receptors CCR5 and CXCR4. To examine for activated memory cells, gated CD4+ and CD8+ lymphocytes were examined for the expression of CD45RO and HLA-DR. Central and effector memory cells were evaluated by the expression of CD62L and CCR7 on gated CD4+ and CD8+ lymphocytes.
All immunohistochemistry and in-situ hybridization sections were examined independently by two board-certified pathologists with significant experience in the field.
For light-microscopic evaluation, tissues were fixed in 4% neutral-buffered formalin and embedded in paraffin. Sections (of 5 μm thickness) were cut and stained with hematoxylin-and-eosin and Giemsa stains. Immunohistochemistry was also performed on paraffin-embedded sections after high-temperature antigen retrieval as described previously [
CD4+ or CD8+ cells in the LP (effector site) and the organized lymphoid tissue (OLT) (inductive site) were quantified separately. Using a 40× objective, a standard area was set (unit area), and a photomicrograph was taken with a Zeiss AxioImager M1 microscope equipped with AxioCam MRc5 digital camera (Zeiss, Jena, Germany). Fifteen nonoverlapping unit areas were selected for the LP, and between two and five unit areas were selected for the OLT, depending upon the size of the T-dependent zone. Using AxioVision (Release 4.5) software (Zeiss), positive cells showing lymphocyte morphology were counted. Because macrophages and dendritic cells also express CD4 in high intensity, manual counting was chosen instead of automatic measurement. Owing to technical reasons (high background signal, lack of adequate material, inadequate staining, etc.), data were available only on 30 out of the 40 patients.
After heat-mediated antigen retrieval by pressure cooking (3 min in 50 mM Tris and 2 mM EDTA [pH9]), the sections were incubated with anti-CD4 or CD8 antibodies overnight as described above. Immunodetection was performed either with the StreptABComplex/HRP (Code K0391, DakoCytomaton) using 3-amino-9-ethylcarbazole (Sigma-Aldrich) as the substrate or with APAAP (DakoCytomaton) and Fast Blue as chromogen. The sections were then heat-treated again for 5 min with 0.01 M buffered sodium citrate solution (pH 6.0). This was followed by an overnight incubation with MIB-1 (anti-Ki67 antibody, DakoCytomaton). For the second antibody, either the APAAP (DakoCytomaton) or the StreptABComplex/HRP (DakoCytomaton) visualization system was applied.
The in situ hybridization was performed on paraffin sections as described previously [
The autoradiographs were examined with a microscope equipped with epiluminescent illumination (Axiophot, Zeiss), a 3CD camera, and a PC-based image-analysis system (KS 4000, Kontron, Esching, Germany) as described previously [
Values are expressed as mean ± standard deviation. Statistical comparisons were made between PBMCs and MMCs from individuals using a paired
A total of 54 patients with AEI and 18 HIV-1–uninfected control participants were studied. Of the HIV-1–infected patients, biopsies were performed on 32 individuals during AEI prior to initiation of antiretroviral therapy. Of these 32 patients, 18 were followed longitudinally post–antiretroviral therapy initiation with recto-sigmoid biopsies at 1 y (
Patient Characteristics
The 18 HIV-1–uninfected control participants were recruited from a population undergoing screening colonoscopy at the time of study recruitment. This group comprised ten men and eight women. None of the HIV-1–infected patients or HIV-1–uninfected control participants were found to have macroscopic evidence of GI mucosal disease, nor were any concomitant pathological processes found on histological examination. All enrolled patients and control participants signed an informed-consent form that was approved by the institutional review boards of the Rockefeller University, Bellevue Hospital Center, and Manhattan Veteran's Administration Hospital Center.
In order to study the effect of antiretroviral therapy on the reconstitution of CD4+ T cells, we utilized flow cytometry to determine the percentage of CD4+ T cells in the GI tract and peripheral blood (
PBMCs and MMCs from 54 patients with AEI and 18 HIV-1–uninfected control participants were analyzed by flow cytometry. CD3+ gated lymphocytes were analyzed for the expression of CD4 and CD8.
(A) Representative flow plots from patient 336 are depicted. CD8+ T cells are shown on the
(B) A box plot depicting the comparison between CD4+ T cells derived from the blood and GI tract of 22 patients examined cross sectionally. The percentages of CD4+ T cells in the blood (white) and GI tract (grey) are compared between HIV-uninfected, AEI-untreated, and AEI groups treated for up to 1 y, 1–3 y, and 3–7 y, respectively. In these plots, the boxes extend from the first to the third quartiles, enclosing the middle 50% of the data. The middle line within each box indicates the median of the data, whereas the vertical line extends from the 10th to the 90th percentile. Means of the data are represented by filled-in squares.
(C) Comparisons between the blood and GI tract of 18 patients followed longitudinally after initiation of antiretroviral therapy. The percentages of CD4+ T cells in the blood (grey) and GI tract (black) at baseline (AEI-untreated) and following treatment are depicted per study patient.
(D) Cumulative data from the 18 patients followed longitudinally where the percentages of CD4+ T cells in the blood (white) and GI tract (grey) are compared after 1 y, 2 y, and 3 y of HAART.
Next, we sought to follow patients longitudinally to assess the effect of antiretroviral therapy on the GI tract and peripheral blood in each study participant. Of the 32 patients that were examined during AEI, we followed 18 patients with serial biopsies over a span of 3 y. Since patient recruitment for repeated intestinal biopsies is challenging, enrolment in the longitudinal group was limited to five out of 18 at year 1, nine out of 18 at year 2, and four out of 18 at year 3 of antiretroviral treatment. In each individual studied, the percentage of CD4+ T cells remained significantly lower in the GI tract compared with the peripheral blood (
To corroborate flow cytometry–derived data and to assess for the absolute numbers of mucosal CD4+ T cells, immunohistochemistry was performed on paraffin-embedded biopsy sections. Since CD4+ T cell depletion occurs preferentially in the LP [
Immunohistochemical characterization of immune-inductive and effector sites in rectal biopsies. Using a PC-based image-analysis system (KS 4000, Kontron) a standard area was set by the image analyzer. For the LP, a total of between ten and 15 consecutive nonoverlapping fields were analyzed for each staining. For the OLT, between two and five representative areas were chosen.
(A) CD4+ T cells per unit area were determined in OLT (left panel) and LP (right panel). Mean CD4+ T cell numbers were compared between HIV-uninfected (white boxes), AEI (light grey boxes), and patients treated for up to 1 y (hatched boxes), 1–3 y (speckled boxes) and 3–7 y (dark grey boxes). In these plots, the boxes extend from the first to the third quartiles, enclosing the middle 50% of the data. The middle line within each box indicates the median of the data, whereas the vertical line extends from the 10th to the 90th percentile. Means of the data are represented by filled-in squares.
(B) A biopsy section (viewed at 40× magnification) from an HIV-uninfected control participant, showing CD4+ T cells (stained red) within the GI LP (panel I). In contrast, a pronounced reduction in LP CD4+ T cells is noted in a patient with AEI (patient no. 131) in panel II which does not correct despite antiretroviral therapy for 2 y in the same patient (panel III). Another representative study patient (no. 142) is presented, where LP CD4+ T cell depletion during AEI (panel IV) does not correct after antiretroviral therapy for 1 y (panel V).
In the other 21 patients, persistent depletion of CD4+ T cells was noted in the LP, with a mean CD4+ T cell count of 5.5 ± 1.1 cells (
Since a majority of the viruses during AEI are CCR5-tropic [
CD3+/CD4+ gated MMCs were analyzed for the expression of chemokine receptors CCR5, CXCR4, and CCR5/CXCR4 in HIV-uninfected (white boxes), AEI (light grey boxes), and patients treated for up to 1 y (hatched boxes), 1–3 y (speckled boxes), and 3–7 y (dark grey boxes). In these plots, the boxes extend from the first to the third quartiles, enclosing the middle 50% of the data. The middle line within each box indicates the median of the data, whereas the vertical line extends from the 10th to the 90th percentile. Means of the data are represented by filled-in squares.
Despite antiretroviral therapy, significant depletion persisted in the CD4+CCR5+ and CD4+ dual-positive MMCs, when compared with HIV-uninfected patients. Specifically, CD4+CCR5+ MMCs in patients treated for up to 1 y (48.6% ± 14.7%,
HIV-1 infection results in a significant increase in cellular activation, which has been shown to be of prognostic value in predicting the rate of CD4+ T cell decline without therapy [
It is well established that a majority of mucosal cells (>90%) have a memory (CD45RO+) phenotype [
In the HIV-uninfected control participants, CD8+CD45RO+HLA-DR+ PBMCs represented 4.8% ± 3.9% of the population and CD8+CD45RO+HLA-DR+ MMCs represented 19.8% ± 9.8% of the population. In comparison, during AEI, a significant increase in CD8+CD45RO+HLA-DR+ PBMCs (29.6% ± 19.5%,
Using four-color flow cytometry, co-expression of CD45RO and HLA-DR was examined on CD3+CD8+ (A) and CD3+CD4+ (B) gated lymphocytes in HIV-uninfected control participants, AEI, and patients treated for up to 1 y, 1–3 y, and 3–7 y. PBMCs are depicted in white and MMCs in grey boxes.
(C) Using immunohistochemistry, the percentage of GI cells expressing Ki67 was determined on CD4+ T cells (left panel) and CD8+ T cells (right panel). Levels in HIV-uninfected control participants (white boxes) were compared with AEI (light grey boxes) and patients treated for up to 1 y (hatched boxes), 1–3 y (speckled boxes), and 3–7 y (dark grey boxes).
In these plots, the boxes extend from the first to the third quartiles, enclosing the middle 50% of the data. The middle line within each box indicates the median of the data, whereas the vertical line extends from the 10th to the 90th percentile. Means of the data are represented by filled-in squares.
Similar, though less pronounced, results were noted in the activated memory CD4+ T cell subsets. CD3+CD4+ PBMCs co-expressing CD45RO/HLA-DR were 5.4% ± 5.0% of the CD4 population in the HIV-uninfected control participants. During AEI, there was a significant increase in this population (8.7% ± 6.5%,
To study a more specific marker of cellular dynamics, we examined the expression of Ki67 on GI mucosal CD4+ T cells and CD8+ T cells by immunohistochemistry (
Thus, while CD4+ and CD8+ lymphocyte activation reverses with treatment in the peripheral blood, it remains elevated in the GI tract. In addition, there is a persistent increase in proliferating CD4+ and CD8+ T cells in the GI tract during antiretroviral therapy.
Having established that depletion of CD4+ T cells (and the CD4:CD8 ratio) in the GI LP persists in the majority of individuals despite therapy, we sought to identify virological and immunological factors at baseline and posttreatment that could account for inter-individual differences. Patients whose CD4+ T cell numbers reconstituted to HIV-uninfected levels (Group A,
With the caveat that patient numbers were relatively limited, no significant differences were noted between groups A and B with respect to baseline viral load, baseline CD4+ T cell count, duration of infection prior to biopsy, timing of initiation of antiretroviral therapy, and duration of therapy (
Clinical Comparison between “Reconstitutors” and “Non-Reconstitutors”
Immunological Comparison between “Reconstitutors” and “Non-Reconstitutors”
GI biopsy sections were hybridized using a radiolabeled probe [
Using a 35S-labeled, single-stranded anti-sense RNA probe of HIV-1, in situ hybridization was performed on paraffin-embedded sections as described in
The present study established that in a majority of patients, 70% of our cohort, CD4+ T cells do not reconstitute in the LP of the GI tract despite uninterrupted, apparently suppressive, antiretroviral therapy for up to 5–7 y. Based on immunohistochemistry, we estimate that approximately 50%–60% of LP CD4+ T cells remain depleted when compared with HIV-uninfected control participants. CD4+ T cells expressing the CCR5 receptor or dually expressing the CCR5/CXCR4 receptors are the cell populations most severely affected. Accompanying this persistent lesion are increased levels of activated CD4+ and CD8+ T cells within the GI tract. In contrast to the degree of CD4+ T cell depletion, only rare HIV-1 RNA–expressing cells were detected by in-situ hybridization.
Recent studies of the role of the GI tract have demonstrated that the CD4+ T cells residing in the LP are selectively depleted early in the course of acute HIV-1 infection [
This is, to our knowledge, the largest study describing the effects of antiretroviral therapy initiated during AEI on CD4+ T cell reconstitution within the GI tract. Our patients were closely followed, demonstrated excellent adherence to medication regimen, and maintained undetectable plasma viral loads for the study duration. Despite this, a majority of our patients show significant mucosal CD4+ T cell depletion. In this regard, our results are in contrast to two prior short-term follow-up studies in HIV-1–infected humans [
It is important to recognize that although flow cytometry permits the characterization of cellular phenotype for a large number of cells, the data obtained thus are based on relative cellular percentages, such that an increase in one cell population can affect the percentage of the other. To overcome this potential confounder and to examine absolute numbers of cells, immunohistochemistry was employed. It is noteworthy that, while none of the patients examined by flow cytometry showed “normalization” of CD4+ T cell percentage in the GI tract, 30% of the studied patients did show “normalization” of absolute numbers of CD4+ T cells within the GI LP. This distinction needs to be taken into consideration so as not to over-interpret suggestions of “a universal lack of mucosal reconstitution.”
Based on the variation in CD4+ T cell reconstitution, we sought to understand clinical, immunological, and virological differences between patients. While we did not observe significant clinical differences between the “reconstitutors” and “non-reconstitutors” in terms of baseline plasma viral loads, peripheral blood CD4+ T cell count, CD4:CD8 ratio, duration of antiretroviral therapy, or the timing of onset of antiretroviral therapy, we did observe immunological differences within the GI tract: the level of activated memory CD8+ T cells at baseline and posttreatment inversely correlated with CD4+ T cell reconstitution. In other words, the higher the level of CD8+ T cell activation, the less likely that reconstitution would be observed in the GI tract. These data echo the previously observed inverse correlation between levels of activated CD8+ T cells, as measured by CD38 expression, and total CD4+ T cell counts in the peripheral blood [
Within the GI tract, there appears to be sub-compartmental variation: immune-inductive sites reconstitute better than immune-effector sites and instead resemble peripheral blood lymphocyte subsets in their reconstitution. It is currently believed that naïve lymphocytes enter inductive sites through high endothelial venules expressing mucosal addressin cell adhesion molecule-1 (MAdCAM-1) interacting with cell surface receptors, particularly α4β7 integrin [
Memory cells can be classified on the basis of
It has been suggested that there may be ongoing viral replication during antiretroviral therapy [
The consequences of persistent CD4+ T cell depletion in the GI tract are unknown at this point. It is clear that the largest reservoir of immune cells [
While previous studies have focused on the role of the GI tract during AEI, the present study establishes that there is a delay in the majority of patients in mucosal immune reconstitution despite years of apparently successful antiretroviral therapy. Taken together, these data highlight the susceptibility of mucosal sites to HIV-1 and underscore the critical need to develop better mucosal-protection strategies. Recent work in the SIV-macaque model has demonstrated that mucosal delivery of a vaccine may confer better protection against SIV challenge when compared with subcutaneous administration of the same vaccine [
Even though we believe this to be the largest study to date assessing the effect of antiretroviral therapy on the reconstitution of CD4+ T cell depletion in the GI tract, there were inherent limitations in a study of this nature. The patient population was selected and not random—particularly those who are willing to undergo repeated biopsy. Furthermore, the group of control participants was limited in size and was not matched to the HIV-1–infected study patients. Our study did not conclusively establish mechanisms of persistent CD4+ T cell depletion in the GI tract, and we were therefore unable to definitively identify factors associated with reconstitution—an issue that we believe to be important. It is likely that a larger sample size is needed to address this issue. Finally, the consequences of the persistence of the identified lesion remain obscure. Ongoing research to better understand both the mechanisms of persistent depletion and its implications is in progress.
In summary, we have shown that despite the early initiation of HAART, the marked depletion suffered by the GI mucosal immune system during acute infection does not completely reconstitute in the majority of patients. Though not clinically apparent in the short term, careful observation is warranted as the long-term consequences of this lesion may become evident as the HIV-1–infected population ages.
We thank the patients for their participation. We acknowledge the nursing staff at Rockefeller University and Bellevue Hospital Center for their clinical assistance. We would like to thank Petra Meyer, Birgit Raschdorff, and Gudrun Großschupff for their technical assistance with immunohistochemistry and in-situ hybridization, Professors David Ho, Cecilia Cheng-Mayer, and Lloyd Mayer for helpful discussion, and Wendy Chen for help with figures and tables.
acute and early HIV-1 infection
enzyme immunoassay
fluorescein isothiocyanate
gastrointestinal
highly active antiretroviral therapy
lamina propria
mucosal addressin cell adhesion molecule-1
mucosal mononuclear cell
National Institutes of Health
optical density
organized lymphoid tissue
peripheral blood mononuclear cell
phosphate-buffered saline
phycoerythrin
peridinin chlorophyll-α protein
simian immunodeficiency virus