Distinct CD4+ CD8+ double-positive T cells in the blood and liver of patients during chronic hepatitis B and C

CD4(+) and CD8(+) T cells, the main effectors of adaptive cellular immune responses, differentiate from immature, non-functional CD4(+)CD8(+) double-positive T (DPT) cells in the thymus. Increased proportions of circulating DPT lymphocytes have been observed during acute viral infections; in chronic viral diseases, the role and repartition of extra-thymic DPT cells remain largely uncharacterized. We performed a phenotypic analysis of DPT cells in blood and liver from patients chronically infected by hepatitis C (HCV) or B (HBV) viruses. The highest percentages of DPT cells, predominantly CD4(high)CD8(low), were observed in patients infected by HCV, while HBV-infected patients mostly displayed CD4(low)CD8(high) and CD4(high)CD8(high) DPT cells. All proportions of DPT cells were higher in liver than in blood with, for each subpopulation referred to above, a correlation between their frequencies in these two compartments. In HCV patients, intra-hepatic DPT cells displayed more heterogeneous activation, differentiation and memory phenotypes than in the blood; most of them expressed CD1a, a marker of T cell development in the thymus. Ex vivo, the inoculation of liver slices with HCV produced in cell culture was accompanied by a disappearance of CD8(high) cells, suggesting a direct effect of the virus on the phenotype of DPT cells in the liver. Our results suggest that, in half of the patients, chronic HCV infection promotes the production of DPT cells, perhaps by their re-induction in the thymus and selection in the liver.     

Differential susceptibility of peripheral blood CD5 and CD5 B cells to apoptosis in chronic hepatitis C patients

A body of evidence has suggested a close link between chronic hepatitis C virus (HCV) infection and B cell abnormalities, including mixed cryoglobulinemia, rheumatoid factor (RF) production, and lymphoproliferative disorders that may develop into non-Hodgkin’s lymphoma. Recent studies have demonstrated the expansion of CD5⁺ B cells in the peripheral blood of chronic hepatitis C patients (CHC). As CD5⁺ B cells, which are capable of producing autoantibodies and RF, are apparently crucial for the development of HCV-associated pathogenesis, the fate of both the CD5⁺ and CD5⁻ B cell subsets upon chronic HCV infection is of interest. In this study, the degree to which chronic HCV infection induces apoptosis in each B cell subset was investigated. Our results demonstrated that peripheral CD5⁻ B cells were more susceptible to apoptosis than CD5⁺ B cells in CHC. Furthermore, plasma levels of IL-4, IL-10, and IL-12 were significantly elevated in CHC, thus suggesting that these interleukins protect CD5⁺ B cells from apoptosis. The rationale for the differential susceptibility of distinct B cell subsets in CHC is also discussed with regard to extrahepatic manifestations associated with chronic HCV infection.     

Modulation of the CD8+-T-cell response by CD4+ CD25+ regulatory T cells in patients with hepatitis B virus infection

CD4+ CD25+ regulatory T cells have been shown to maintain peripheral tolerance against self and foreign antigens. In this study we analyzed the effect of circulating CD4+ CD25+ T cells on CD8+-T-cell responses of patients with chronic and resolved hepatitis B virus (HBV) infection. We demonstrated that circulating CD4+ CD25+ T cells modulate the function and expansion of HBV-specific CD8+ cells ex vivo in all patients, regardless of whether they have chronic or resolved HBV infection. The possible role of CD4+ CD25+ T cells in the pathogenesis of chronic HBV infection is not supported by these data. However, these results might have implications for optimizing future immunotherapeutic approaches to HBV treatment.     

Memory CD4 T cells that express CXCR5 provide accelerated help to B cells

CD4 T cell help for B cells is critical for effective Ab responses. Although many of the molecules involved in helper functions of naive CD4 T cells have been characterized, much less is known about the helper capabilities of memory CD4 T cells, an important consideration for the design of vaccines that aim to prime protective memory CD4 T cells. In this study, we demonstrate that memory CD4 T cells enable B cells to expand more rapidly and class switch earlier than do primary responding CD4 T cells. This accelerated response does not require large numbers of memory cells, and similar numbers of primary responding cells provide less effective help than do memory cells. However, only memory CD4 T cells that express the B cell follicle homing molecule, CXCR5, are able to accelerate the response, suggesting that the rapidity of the Ab response depends on the ability of CD4 memory T cells to migrate quickly toward B cells.     

CXCR1+CD4+ T cells in human allergic disease

Chemokine receptors play an important role in the migration of leukocytes to sites of allergic inflammation in humans. In this study, we have identified increased expression of the chemokine receptor CXCR1 on CD4+ T lymphocytes derived from patients with atopic disease compared with normal donors. Enhanced expression of CXCR1 by atopic donors was identified on freshly isolated peripheral blood cells and on expanded cell populations derived from nasal mucosal biopsies and from the periphery. Identification of CXCR1 expression on CD4 cells in the nasal mucosa was confirmed by double immunofluorescence. In addition, expression of CXCR1 was dramatically decreased in patients undergoing successful treatment of allergic rhinitis by specific immunotherapy. CXCR1 provided a functional receptor capable of regulating T cells in the context of allergic disease, since expression of CXC chemokine ligand 8 was up-regulated at the site of allergic inflammation and freshly isolated CXCR1+CD4+ cells from atopic donors showed an enhanced functional response to this ligand. CXCR1 expression on CD4+ T cells was increased in vitro in response to the pro-Th2 cytokine IL-4. Phenotypic analysis reveals that IFN-gamma expression was lower in the CXCR1+CD4+ cells. The identification of CXCR1 as a marker of allergic rhinitis reveals a possible target for therapeutic intervention in atopic disease.     

CD4+CXCR4highCD69+ T cells accumulate in lung adenocarcinoma

The chemokine receptor CXCR4 is involved in the growth and metastasis of tumor cells. However, the expression of its ligand, the chemokine CXCL12, in tumors and its role in regulating the accumulation of immune cells within the tumors is not clear. Using ELISA and immunohistochemistry we found that CXCL12 is expressed in the majority of nonsmall cell lung cancer tissue sections obtained from stage IA to IIB nonsmall cell lung cancer patients undergoing operation. Histopathologic examination of these sections indicated that high CXCL12 expression correlated with increased tumor inflammation. In addition, disease recurrence rates in a subgroup of adenocarcinoma patients showed a tendency to correlate with high CXCL12 expression in the tumor. Isolation of adenocarcinoma-infiltrating immune cells demonstrated an increase in the percentage of CD4+CD69+CXCR4+ T cells as compared with normal lung tissue. About 30% of these cells expressed the regulatory T cell markers CD25high and FoxP3. The percentage of CD8 T cells within the tumor did not change, however; the percentage of NK and NK T cells was significantly reduced. In correlation with CXCR4 expression, CD4 T cells showed increased migration in response to CXCL12 compared with CD8 T cells and NK cells. Overall, these observations suggest that CXCL12 expression may influence tumor progression by shaping the immune cell population infiltrating lung adenocarcinoma tumors.     

Engineering HIV-resistant human CD4+ T cells with CXCR4-specific zinc-finger nucleases

HIV-1 entry requires the cell surface expression of CD4 and either the CCR5 or CXCR4 coreceptors on host cells. Individuals homozygous for the ccr5Δ32 polymorphism do not express CCR5 and are protected from infection by CCR5-tropic (R5) virus strains. As an approach to inactivating CCR5, we introduced CCR5-specific zinc-finger nucleases into human CD4+ T cells prior to adoptive transfer, but the need to protect cells from virus strains that use CXCR4 (X4) in place of or in addition to CCR5 (R5X4) remains. Here we describe engineering a pair of zinc finger nucleases that, when introduced into human T cells, efficiently disrupt cxcr4 by cleavage and error-prone non-homologous DNA end-joining. The resulting cells proliferated normally and were resistant to infection by X4-tropic HIV-1 strains. CXCR4 could also be inactivated in ccr5Δ32 CD4+ T cells, and we show that such cells were resistant to all strains of HIV-1 tested. Loss of CXCR4 also provided protection from X4 HIV-1 in a humanized mouse model, though this protection was lost over time due to the emergence of R5-tropic viral mutants. These data suggest that CXCR4-specific ZFNs may prove useful in establishing resistance to CXCR4-tropic HIV for autologous transplant in HIV-infected individuals.     

HCV-specific interleukin-21+CD4+ T cells responses associated with viral control through the modulation of HCV-specific CD8+ T cells function in chronic hepatitis C patients

Interleukin-21 (IL-21)+CD4+ T cells are involved in the immune response against hepatitis B virus (HBV) by secreting IL-21. However, the role of IL-21+CD4+ T cells in the immune response against chronic hepatitis C (CHC) virus infection is poorly understood. This study aimed to investigate the role of IL-21+CD4+ T cells in CHC patients and the potential mechanisms. The study subjects included nineteen CHC patients who were grouped by viral load (low, < 10⁶ RNA copies/ml, n = 8; high, > 10⁶ RNA copies/ml, n = 11). The peripheral frequency of HCV-specific IL-21+CD4+ T cells was higher in the low viral load group and was negatively correlated with the serum HCV RNA viral load in all CHC patients. Meanwhile, IL-21+ cells accumulated in the liver in the low viral load group. In vitro, IL-21 treatment increased the expression of proliferation markers and cytolytic molecules on HCV-specific CD8+ T cells. In summary, these findings suggest that HCV-specific IL-21+CD4+ T cells might contribute to HCV control by rescuing HCV-specific CD8+ T cells in CHC patients.     

ICOS deficiency is associated with a severe reduction of CXCR5+CD4 germinal center Th cells

ICOS is expressed on activated T cells and particularly on CXCR5+ follicular Th cells in germinal centers (GC). Its deletion leads to a profound deficiency in memory B cell formation and switched Ab response in humans. Here, we show that in ICOS-deficient patients the generation of GCs is severely disturbed, and the numbers of circulating CXCR5+CD45RO+ memory CD4 T cells are significantly reduced, indicating an essential role of ICOS in the differentiation of CXCR5+CD4 T cells. The GC-specific CD57+CXCR5+ subpopulation is virtually absent. In ICOS-/- mice, the decrease of circulating CXCR5+CD4 T cells reflects the reduction of CXCR5+ follicular Th cells in lymph nodes and spleen. Therefore, in concurrence with the absence of CXCR5+ T cells in the blood of CD40L-deficient patients, these data support the hypothesis that circulating CD57+CXCR5+ T cells are GC derived and thus may serve as a surrogate marker for the presence of functional GCs in humans.     

T cells with a CD4+CD25+ regulatory phenotype suppress in vitro proliferation of virus-specific CD8+ T cells during chronic hepatitis C virus infection

Chronic hepatitis C virus (HCV) infection is associated with impaired proliferative, cytokine, and cytotoxic effector functions of HCV-specific CD8(+) T cells that probably contribute significantly to viral persistence. Here, we investigated the potential role of T cells with a CD4(+)CD25(+) regulatory phenotype in suppressing virus-specific CD8(+) T-cell proliferation during chronic HCV infection. In vitro depletion studies and coculture experiments revealed that peptide specific proliferation as well as gamma interferon production of HCV-specific CD8(+) T cells were inhibited by CD4(+)CD25(+) T cells. This inhibition was dose dependent, required direct cell-cell contact, and was independent of interleukin-10 and transforming growth factor beta. Interestingly, the T-cell-mediated suppression in chronically HCV-infected patients was not restricted to HCV-specific CD8(+) T cells but also to influenza virus-specific CD8(+) T cells. Importantly, CD4(+)CD25(+) T cells from persons recovered from HCV infection and from healthy blood donors exhibited significantly less suppressor activity. Thus, the inhibition of virus-specific CD8(+) T-cell proliferation was enhanced in chronically HCV-infected patients. This was associated with a higher frequency of circulating CD4(+)CD25(+) cells observed in this patient group. Taken together, our results suggest that chronic HCV infection leads to the expansion of CD4(+)CD25(+) T cells that are able to suppress CD8(+) T-cell responses to different viral antigens. Our results further suggest that CD4(+)CD25(+) T cells may contribute to viral persistence in chronically HCV-infected patients and may be a target for immunotherapy of chronic hepatitis C.     

Longitudinal analysis of CD8+ T cells specific for structural and nonstructural hepatitis B virus proteins in patients with chronic hepatitis B: implications for immunotherapy

The cytotoxic T-cell response in chronic hepatitis B virus (HBV) infection has been described as weak and mono- or oligospecific in comparison to the more robust virus-specific T-cell response present in resolved infection. However, chronic hepatitis B is a heterogeneous disease with markedly variable levels of virus replication and liver disease activity. Here we analyzed (both directly ex vivo and after in vitro stimulation) the HBV-specific CD8 T-cell responses against structural and nonstructural HBV proteins longitudinally in patients with different patterns of chronic infections. We found that the profiles of virus-specific CD8(+)-T-cell responses during chronic infections are highly heterogeneous and influenced more by the level of HBV replication than by the activity of liver disease. An HBV DNA load of <10(7) copies/ml appears to be the threshold below which circulating multispecific HBV-specific CD8(+) T cells are consistently detected. Furthermore, CD8(+) T cells with different specificities are differentially regulated during chronic infections. HBV core-specific CD8(+) T cells are associated with viral control, while CD8(+) T cells specific for envelope and polymerase epitopes can occasionally be found in the setting of high levels (>10(7) copies) of HBV replication. These findings have implications for the design of immunotherapy for chronic HBV infections.     

Increased CD4+/CD8+ double-positive T cells in chronic Chagasic patients

Background

CD4+/CD8+ double positive (DP) T cells have been described in healthy individuals as well as in patients with autoimmune and chronic infectious diseases. In chronic viral infections, this cell subset has effector memory phenotype and displays antigen specificity. No previous studies of double positive T cells in parasite infections have been carried out.

Methodology/Principal Findings

Seventeen chronic chagasic patients (7 asymptomatic and 10 symptomatic) and 24 non-infected donors, including 12 healthy and 12 with non-chagasic cardiomyopathy donors were analyzed. Peripheral blood was stained for CD3, CD4, CD8, HLA-DR and CD38, and lymphocytes for intracellular perforin. Antigen specificity was assessed using HLA*A2 tetramers loaded with T. cruzi K1 or influenza virus epitopes. Surface expression of CD107 and intracellular IFN-γ production were determined in K1-specific DP T cells from 11 chagasic donors. Heart tissue from a chronic chagasic patient was stained for both CD8 and CD4 by immunochemistry. Chagasic patients showed higher frequencies of DP T cells (2.1%±0.9) compared with healthy (1.1%±0.5) and non-chagasic cardiomyopathy (1.2%±0.4) donors. DP T cells from Chagasic patients also expressed more HLA-DR, CD38 and perforin and had higher frequencies of T. cruzi K1-specific cells. IFN-γ production in K1-specific cells was higher in asymptomatic patients after polyclonal stimulation, while these cells tended to degranulate more in symptomatic donors. Immunochemistry revealed that double positive T cells infiltrate the cardiac tissue of a chagasic donor.

Conclusions

Chagasic patients have higher percentages of circulating double positive T cells expressing activation markers, potential effector molecules and greater class I antigenic specificity against T. cruzi. Although K1 tetramer positive DP T cell produced little IFN-γ, they displayed degranulation activity that was increased in symptomatic patients. Moreover, K1-specific DP T cells can migrate to the heart tissue.     

Circulating CXCR5+CD4+ T cells assist in the survival and growth of primary diffuse large B cell lymphoma cells through interleukin 10 pathway

Diffuse large B cell lymphoma (DLBCL) is a common and aggressive cancer caused by the malignant transformation of B cells. Although it has been established that the follicular helper T (Tfh) cells play a central role in B cell development, little information is available on their involvement in DLBCL pathogenesis. We studied the role of the peripheral Tfh equivalent, the CXCR5⁺ CD4⁺ T cells, in DLBCL. Data showed that compared to CXCR5^- CD4⁺ T cells, CXCR5⁺ CD4⁺ T cells were significantly more effective at promoting the proliferation as well as inhibiting the apoptosis of primary autologous DLBCL tumor cells. Surprisingly, we found that at equal cell numbers, CXCR5⁺ CD4⁺ T cells in DLBCL patients secreted significantly less interleukin (IL)-21 than CXCR5^- CD4⁺ T cells, while the level of IL-10 secretion was significant elevated in the CXCR5⁺ compartment compared to the CXCR5^- compartment. Neutralization of IL-10 in the primary DLBCL-CXCR5⁺ CD4⁺ T cell coculture compromised the CXCR5⁺ CD4⁺ T cell-mediated pro-tumor effects, in a manner that was dependent on the concentration of anti-IL-10 antibodies. The CXCR5⁺ compartment also contained significantly lower frequencies of cytotoxic CD4⁺ T cells than the CXCR5^- compartment. In conclusion, our investigations discovered a previously unknown pro-tumor role of CXCR5-expressing circulating CD4⁺ T cells, which assisted the survival and proliferation of primary DLBCL cells through IL-10.     

Circulating and liver resident CD4+CD25+ regulatory T cells actively influence the antiviral immune response and disease progression in patients with hepatitis B

CD4+CD25+ regulatory T cells (Treg) have been shown to maintain immune tolerance against self and foreign Ags, but their role in persistent viral infection has not been well-defined. In this study, we investigated whether and where CD4+CD25+ Treg contribute to the development of chronic hepatitis B (CHB). One hundred twenty-one patients were enrolled, including 16 patients with acute hepatitis B, 76 with CHB, and 29 with chronic severe hepatitis B. We demonstrated that in chronic severe hepatitis B patients, the frequencies of CD4+CD25+ Treg in both PBMC and liver-infiltrating lymphocytes were significantly increased and there was a dramatic increase of FoxP3(+)-cell and inflammatory cell infiltration in the liver compared with healthy controls. In CHB patients, circulating CD4+CD25+ Treg frequency significantly correlates with serum viral load. In acute hepatitis B patients, circulating CD4+CD25+ Treg frequency was initially low and with time, the profile reversed to exhibit an increased number of circulating Treg in the convalescent phase and restored to normal levels upon resolution. In PBMC taken from infected patients, depletion of CD4+CD25+ Treg led to an increase of IFN-gamma production by HBV-Ag-stimulated PBMC. In addition, CD4+CD25+ Treg were capable of suppressing proliferation of autologous PBMC mediated by HBV Ags, which probably reflects the generation of HBV-Ag-specific Treg in circulation and in the liver of HBV-infected patients. Together, our findings suggest that CD4+CD25+ Treg play an active role not only in modulating effectors of immune response to HBV infection, but also in influencing the disease prognosis in patients with hepatitis B.     

Circulating CXCR5+CD4+ T Follicular-Like Helper Cell and Memory B Cell Responses to Human Papillomavirus Vaccines

Through the interaction of T follicular helper (Tfh) cells and B cells, efficacious vaccines can generate high-affinity, pathogen-neutralizing antibodies, and memory B cells. Using CXCR5, CXCR3, CCR6, CCR7, PD1, and ICOS as markers, Tfh-like cells can be identified in the circulation and be classified into three functionally distinct subsets that are PD1⁺ICOS⁺, PD1⁺ ICOS^-, or PD1^-ICOS^-. We used these markers to identify different subsets of CXCR5⁺CD4⁺ Tfh-like cells in response to highly immunogenic and efficacious vaccines for human papillomaviruses (HPV): Cervarix and Gardasil. In this small study, we used PBMC samples from 11 Gardasil recipients, and 8 Cervarix recipients from the Vaccine Research Center 902 Study to examine the induction of circulating Tfh-like cells and IgD^-CD38^HiCD27⁺ memory B cells by flow cytometry. PD1⁺ICOS⁺ CXCR3⁺CCR6^-CXCR5⁺CD4⁺ (Tfh1-like) cells were induced and peaked on Day (D) 7 post-first vaccination, but not as much on D7 post-third vaccination. We also observed a trend toward increase in PD1⁺ICOS⁺ CXCR3^-CCR6^-CXCR5⁺CD4⁺ (Tfh2-like) cells for both vaccines, and PD1⁺ICOS⁺ CXCR3^-CCR6⁺CXCR5⁺CD4⁺ (Tfh17-like) subset was induced by Cervarix post-first vaccination. There were also minimal changes in the other cellular subsets. In addition, Cervarix recipients had more memory B cells post-first vaccination than did Gardasil recipients at D14 and D30. We found frequencies of memory B cells at D30 correlated with anti-HPV16 and 18 antibody titers from D30, and the induction levels of memory B cells at D30 and PD1⁺ICOS⁺Tfh1-like cells at D7 post-first vaccination correlated for Cervarix. Our study showed that induction of circulating CXCR5⁺CD4⁺ Tfh-like subsets can be detected following immunization with HPV vaccines, and potentially be useful as a marker of immunogenicity of vaccines. However, further investigations should be extended to different cohorts with larger sample size to better understand the functions of these T cells, as well as their relationship with B cells and antibodies.     

HBcAg-specific CD4+CD25+regulatory T cells modulate immune tolerance and acute exacerbation on the natural history of chronic hepatitis B virus infection

Acute exacerbations (AEs) of chronic hepatitis B (CH-B) are accompanied by increased T cell responses to hepatitis B core and e antigens (HBcAg/HBeAg). Why patients are immunotolerant (IT) to the virus and why AEs occur spontaneously on the immunoactive phase remain unclear. The role of HBcAg-specific CD4(+)CD25(+) regulatory T (T(reg)) cells in AE and IT phases was investigated in this study. The SYFPEITHI scoring system was employed to predict MHC class II-restricted epitope peptides on HBcAg overlapping with HBeAg that were used for T(reg)-cell cloning and for the construction of MHC class II tetramers to measure T(reg) cell frequencies (T(reg) f). The results showed that HBcAg-specific T(reg) f declined during AE accompanied by increased HBcAg peptide-specific cytotoxic T lymphocyte frequencies. Predominant Foxp3-expressing T(reg) cell clones were generated from patients on the immune tolerance phase, while the majority of Th1 clones were obtained from patients on the immunoactive phase. T(reg) cells from liver and peripheral blood of CH-B patients express CD152 and PD1 antigens that exhibit suppression on PBMCs proliferation to HBcAg. These data suggest that HBcAg peptide-specific T(reg) cells modulate the IT phase, and that their decline may account for the spontaneous AEs on the natural history of chronic hepatitis B virus infection.     

CXCR6+CD4+ T cells promote mortality during Trypanosoma brucei infection

Liver macrophages internalize circulating bloodborne parasites. It remains poorly understood how this process affects the fate of the macrophages and T cell responses in the liver. Here, we report that infection by Trypanosoma brucei induced depletion of macrophages in the liver, leading to the repopulation of CXCL16-secreting intrahepatic macrophages, associated with substantial accumulation of CXCR6⁺CD4⁺ T cells in the liver. Interestingly, disruption of CXCR6 signaling did not affect control of the parasitemia, but significantly enhanced the survival of infected mice, associated with reduced inflammation and liver injury. Infected CXCR6 deficient mice displayed a reduced accumulation of CD4⁺ T cells in the liver; adoptive transfer experiments suggested that the reduction of CD4⁺ T cells in the liver was attributed to a cell intrinsic property of CXCR6 deficient CD4⁺ T cells. Importantly, infected CXCR6 deficient mice receiving wild-type CD4⁺ T cells survived significantly shorter than those receiving CXCR6 deficient CD4⁺ T cells, demonstrating that CXCR6⁺CD4⁺ T cells promote the mortality. We conclude that infection of T. brucei leads to depletion and repopulation of liver macrophages, associated with a substantial influx of CXCR6⁺CD4⁺ T cells that mediates mortality.     

Soluble CD40 ligand-activated B cells from patients with chronic hepatitis B virus infection as antigen presenting cells to induce hepatitis B virus specific cytotoxic T lymphocytes

Chronic hepatitis B virus (HBV) infection is the result of an inadequate antiviral immune response to the virus. In this study, we aimed to investigate whether the soluble CD40 ligand-activated B (CD40-B) cells could present antigen and induce specific cytotoxic T lymphocytes (CTLs) in patients with chronic HBV infection. We observed that after activated by sCD40L, the expression of CD80, CD86, major histocompatibility complex (MHC) I and II molecules on the CD40-B cells was significantly increased. Cytometry and fluorescence microscopy showed that more than 41.34% CD40-B cells were loaded by the HBcAg peptide. Furthermore, after been activated and HBcAg18–27 antigen peptide pulsed, B cells obtained from patients with chronic HBV infection could induce HBcAg18–27 specific CTLs in vitro. Taken together, our results show that B cells from patients with chronic HBV infection can be activated by sCD40L and may function as antigen presenting cells and induce HBV-specific CTLs.     

Increased frequency of circulating CCR5+ CD4+ T cells in human immunodeficiency virus type 2 infection

CCR5 expression determines susceptibility to infection, cell tropism, and the rate of human immunodeficiency virus type 1 (HIV-1) disease progression. CCR5 is also considered the major HIV-2 coreceptor in vivo, in spite of broad coreceptor use in vitro. Here we report a significantly increased proportion of memory-effector CD4 T cells expressing CCR5 in HIV-2-infected patients correlating with CD4 depletion. Moreover, HIV-2 proviral DNA was essentially restricted to memory-effector CD4, suggesting that this is the main target for HIV-2. Similar levels of proviral DNA were found in the two infection categories. Thus, the reduced viremia and slow rate of CD4 decline that characterize HIV-2 infection seem to be unrelated to coreceptor availability.