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The Journal of Immunology, 2003, 170: 2349-2355.
Copyright © 2003 by The American Association of Immunologists

CD7 Is a Differentiation Marker That Identifies Multiple CD8 T Cell Effector Subsets1

Einar M. Aandahl2,*, Johan K. Sandberg*, Karen P. Beckerman*, Kjetil Taskén{dagger}, Walter J. Moretto* and Douglas F. Nixon*

* Gladstone Institute of Virology and Immunology, University of California, San Francisco, CA 94141; and {dagger} Department of Medical Biochemistry, University of Oslo, Oslo, Norway


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
The adaptive immune response of human CD8 T cells to invading pathogens involves the differentiation of naive cells into memory and effector cells. However, the lineage relationship between memory and effector cells and the differentiation of CD8 T cells into distinct subsets of effector cell subpopulations are subjects of considerable debate. CD7 identifies three populations of CD8 T cells: CD7 high (CD7high), low (CD7low), and negative (CD7neg) that translate into subsets with distinct functional properties. The CD7high subset contains naive and memory cells and the CD7low and CD7neg subsets contain effector cells. The effector cells can functionally be divided into cytokine-secreting effector CD8 T cells and lytic effector CD8 T cells. These data provide a model of human CD8 T cell differentiation in which specialized distinct subpopulations can be identified by expression of CD7.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
The sequence and steps involved in the differentiation and maturation of human CD8 T cells has been an issue of intense investigation into two key issues: the lineage relationship between memory and effector cells and the heterogeneity which may exist within these populations. These issues are of great importance for our understanding of the immune system in both health and disease. Recently, two models have been proposed. The first model is based on the expression of L-selectin (CD62L)3 and CCR7, which are receptors involved in homing to lymphoid tissues (1, 2). These two receptors, along with the presence or absence of CD45RA, define two subsets of memory cells: central memory and effector memory cells (3). In addition, it has also been suggested that these markers can be used to define a subset of terminally differentiated effector cells (3). This model was further developed by Champagne et al. (4) who compared HIV- and CMV-specific CD8 T cells. These reports indicate a lineage differentiation pattern in which naive cells (CD45RA+CD62L+CCR7+) upon encounter with an Ag mature into central memory cells (CD45RA-CD62L+CCR7+), effector memory cells (CD45RA-CD62L-CCR7-), and finally terminally differentiated effector cells (CD45RA+CD62L-CCR7-). However, it has recently been questioned whether these cell surface phenotypes can readily be translated into cell populations with distinct functional properties at the Ag-specific level (5, 6, 7, 8).

The second model for human T cell differentiation is based on the down-regulation of the costimulatory molecules CD27 and CD28 which, along with CD45RA, define three subsets of human CD8 T cells: naive cells (CD45RA+CD27+CD28+), memory cells (CD45RA-CD27+CD28+), and effector cells (CD45RA+CD27-CD28-) (7, 9, 10, 11). These definitions of effector and memory subsets were also recently questioned (12). Although Appay et al. (12) challenge the current concept of human CD8 T cell differentiation patterns based on the CD27 and CD28 surface phenotype, their study was limited to chronic viral infections in which there is a persistent antigenic presence.

In this study, we analyzed how the expression pattern of the costimulatory molecule CD7 correlates with CD8 T subset cell surface markers and cellular function. CD7 is a transmembrane glycoprotein which appears early in T cell ontogeny and is expressed by most T cells in the periphery (13). A subset of CD4 T cells which do not express CD7 has previously been described (14, 15, 16, 17), but the role of CD7 in CD8 T cell differentiation and maturation is unknown. Although the ligand is yet not identified, CD7 has been recognized as a costimulatory molecule (18). CD7 activates phosphatidylinositol 3-kinase which is involved in CD7-mediated regulation of integrin adhesiveness (19, 20, 21). Furthermore, it has been reported that the {beta}-galactoside-binding lectin galectin-1 binds CD7, leading to induction of apoptosis of thymocytes and T cells, with implications for certain autoimmune diseases and T cell lymphomas (22, 23, 24, 25, 26).

By examining levels of CD7 expression on CD8 T cells, we identified three phenotypically and functionally distinct cell populations. The CD7high subset contains naive cells and memory cells, and the CD7low and CD7neg subsets contain effector cells. However, the CD7low population appears to have a rapid turnover, whereas the CD7neg population seems to be a more persistent and stable population of effector cells. Furthermore, the CD7low and CD7neg populations can each be divided into two separate populations of effector cells based on their expression of cytokines vs perforin into cytokine-secreting effector CD8 T cells (TCC) and lytic effector CD8 T cells (TCL).


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Study subjects and samples

Blood samples were obtained from healthy blood donors under approved University of California, San Francisco Committee on Human Research Institutional Review Board protocols (n = 23). PBMC were isolated from heparinized whole blood by Ficoll-Paque PLUS density gradient centrifugation (Amersham Pharmacia Biotech, Uppsala, Sweden) and washed twice in RPMI 1640 (Life Technologies, Grand Island, NY) with 15% FCS. When used, cryopreserved samples were washed and cultured overnight before use in functional assay or analysis by flow cytometry.

Reagents

Staphylococcal enterotoxin B (SEB) and brefeldin A were purchased from Sigma-Aldrich (St. Louis, MO). The anti-CD3 Ab used in functional assays was clone 12F6 (provided by Dr. J. Wong, Massachusetts General Hospital, Boston, MA). A control peptide pool containing 23 CMV, EBV, and influenza viral peptides (catalogue no. 6747) was obtained through the National Institutes of Health AIDS Research and Reference Reagent Program (Rockville, MD). Anti-CD3 (FITC) and PerCP, anti-CD8 (FITC and allophycocyanin), anti-CD7 (FITC and PE), anti-CD27 (FITC and PE), anti-CD28 (FITC and PE), anti-IFN-{gamma} (PE), anti-TNF-{alpha} (PE), anti-IL-2 (PE), anti-perforin (FITC), anti-granzyme (FITC), anti-CD45RO (FITC and APC), and anti-CD62L (FITC) Abs were purchased from BD PharMingen (San Diego, CA). CFSE was purchased from Molecular Probes (Eugene, OR). The influenza M1 HLA-A*0201 tetramer (allophycocyanin) and the CMV PP65 HLA-A*0201 tetramer (allophycocyanin) were both purchased from Immunomics (San Diego, CA). Annexin V (BD PharMingen) staining and TUNEL (Roche Diagnostics, Indianapolis, IN) staining was performed according to the instructions from the manufacturer.

Flow cytometry

Purified PBMC were fixed in paraformaldehyde and washed in PBS with 1% BSA before incubation with a panel of fluorochrome-conjugated Abs. Intracellular staining was performed by permeabilization of cells in FACS permeabilization buffer (BD PharMingen) for 10 min before staining with Abs. The samples were analyzed using a FACSCalibur Instrument (BD PharMingen).

Cytokine flow cytometry

Freshly isolated PBMC were stimulated with Ag as noted. The cells were then incubated for 1 h before addition of brefeldin A at a final concentration of 10 µg/ml and incubated for another 5 h. The cells were then washed, fixed, permeabilized, and stained for cell surface markers and intracellular cytokines and analyzed by flow cytometry.

CFSE proliferation assay

Fresh PBMC were resuspended at a concentration of 107 cells/ml in RPMI 1640 and labeled with CFSE by incubation for 10 min in 37°C in 5% CO2 at a final concentration of 2 µM. Labeling was quenched with RPMI 1640 supplemented with 15% FCS, and the cells were washed twice before culturing in flat-bottom 96-well plates. The cells were then stimulated with SEB (100 ng/ml) or immobilized anti-CD3 (clone 12F6) combined with pure anti-CD28 (1/200 dilution; BD PharMingen). FACS analysis was performed after 96 h of incubation.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Phenotypically distinct CD8 T cell subsets defined by the level of CD7 expression

In the first sets of experiments, we identified three subsets of CD8 T cells based on levels of CD7 expression, termed CD7 high (CD7high), CD7 low (CD7low), and CD7 negative (CD7neg) (Fig. 1a). The CD7low subset was not present in the CD4 T cell population. The mean distribution of CD8 T cells in a population of healthy adult donors (n = 23) was 69.6% ± 3.0 CD7high cells, 27.5% ± 2.7 CD7low cells, and 1.9% ± 0.3 CD7neg cells. To examine the expression pattern of CD7 on CD8 T cells, we studied CD7 expression in relation to previously described subsets of T cells. CD27 and CD28 are costimulatory molecules that, along with CD45RA, have been used as cell surface markers to identify naive, memory, and effector cells (9, 10, 11, 27). The CD7high subset consists of cells which are CD27+CD28+ (Fig. 1b). CD7low and CD7neg subsets, however, are more heterogeneous with respect to CD27 and CD28 expression.



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  		FIGURE 1. Phenotypic characterization of CD8 T cells. The level of CD7 expression identifies three subsets of CD8 T cells: CD7high, CD7low, and CD7neg (a). The CD7low subset is not present in CD4 T cells. b–d, CD8 T cells were stained with different mAbs in addition to CD7. The numbered curves in the histogram in d represent CCR7 expression and refer to the numbers of the gates in the CD7/CD62L plot.

 
Although homogenous with respect to CD27 and CD28 expression, the CD7high subset is split into two populations when staining for CD45RO (Fig. 1c). This is consistent with previous reports that the CD27+CD28+ population contains both naive cells (CD45RA+) and memory cells (CD45RA-) (11). Although we have used CD45RO in this study instead of CD45RA, the CD45RO expression clearly suggests that the CD7high cells consist of two distinct populations.

Staining for CD62L provides further support for two phenotypically distinct CD7high populations. Although the CD7low and CD7neg subsets are both CD62L-, the CD7high subset is split into CD62L+ and CD62L- populations (Fig. 1d). This defines four subsets of CD8 T cells: CD7highCD62L+, CD7highCD62L-, CD7lowCD62L-, and CD7negCD62L-.

CD62L and CCR7, surface molecules essential for lymphocyte migration to lymph nodes (1, 2), have been used to discriminate between subsets of memory T cells (3). When analyzing the levels of CCR7 expression in the four subsets identified by CD7 and CD62L, we observed that the CD7highCD62L+ subset is clearly positive for CCR7. The CD7highCD62L- subset, however, is heterogeneous for CCR7, whereas the CD7lowCD62L- and CD7negCD62L- subsets are both CCR7 negative (Fig. 1d).

To investigate whether the CD7low and CD7neg subsets represent stable differentiation stages rather than transient and reversible down-regulation of CD7 cell surface expression, we sorted the CD7high, CD7low, and CD7neg CD8 T cell subsets and stimulated the cells in culture with anti-CD3/anti-CD28 and IL-2 for up to 4 days. Although the CD7high subset transiently up-regulated CD7 expression during in vitro stimulation, the CD7low and CD7neg subsets did not appear to re-express CD7 in vitro (data not shown). This is consistent with previous observations of the CD7neg subset of CD4 T cells which were reported to represent a stable differentiation state occurring late in the immune response (15).

The CD7high subset contains both naive cells and memory cells

To further investigate the two CD7high populations, we first compared the phenotype of CD8 T cells from cord blood and maternal blood (Fig. 2). Because the fetus is normally not exposed to any pathogens intrauterine, T cells in cord blood are naive cells. The majority of the CD8 T cells in the cord blood were CD7high and CD28+ (Fig. 2). This strongly suggests that the CD7high population contains naive cells.



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  		FIGURE 2. The CD7low and CD7neg subsets of CD8 T cells are not present in cord blood. PBMC isolated from cord blood and maternal blood were fixed and stained for cell surface markers. The plots are gated on the CD8 T cells.

 
In addition to naive cells, the presence of both CD45RO+ and CD62L- (Fig. 1, c and d) subpopulations suggests that the CD7high subset also contains Ag-experienced cells. The majority of the cells in the CD7high subset are CD27+CD28+ (Fig. 1b), indicating that Ag-experienced cells within the CD7high subset most likely are memory cells (11). This is further supported by the observation that the majority of the influenza-specific cells identified by using HLA-A2 tetramers refolded with an immunodominant epitope in the matrix protein are CD7high (see Fig. 6b). The influenza virus does not establish a chronic infection, and no viral sanctuaries are known. Thus, influenza-specific cells present several years after the acute infection is cleared are by definition memory cells. These observations strongly suggest that the CD7high population contains both naive and memory cells.



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  		FIGURE 6. Presence of Ag-specific cells in the CD8 T cell subsets. a, Ag-specific cells were identified by intracellular flow cytometry after stimulation with a pool of 23 peptides containing immunodominant epitopes from CMV, EBV, and influenza virus. b, Ag-specific CD8 T cells from a previously influenza-infected donor (clinical disease 4 years before the study) were identified with an influenza M1 HLA-A*0201 tetramer and cell surface markers and compared with CMV-specific cells identified by a PP65 HLA-A*0201 tetramer.

 
Two effector cell populations are identified by down-regulation and loss of CD7 expression

To explore the functional significance of the three CD8 T cell subsets identified by CD7 expression, we measured the frequency of cells expressing lytic molecules and cytokines within each subpopulation. Although 22.6 ± 2.0% of the cells in the CD7high subset were granzyme A+, the frequency was significantly higher in the CD7low and CD7neg subsets (76.2 ± 2.7% and 81.6 ± 2.0%, respectively). Similarly, only 2.1 ± 0.7% of the cells in the CD7high subset were perforin+, while 26.9 ± 6.4% of the CD7low and 29.5 ± 5.6% of the CD7neg subsets contained perforin (Fig. 3).



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  		FIGURE 3. High expression of lytic molecules in the CD7low and CD7neg subsets of CD8 T cells. PBMC were fixed, permeabilized, and stained for intracellular granzyme A and perforin in addition to cell surface markers. Accumulative data are shown in the graph (n = 13 for granzyme A; n = 6 for perforin; *, p < 0.05; **, p < 0.005, respectively, compared with the frequency of positive cells in the CD7high population. Statistical analysis: Wilcoxon-matched pairs test).

 
Differential expression of cytokines and cytolytic molecules in the CD7low and CD7neg subsets

To further characterize the functional potential of these three subsets, the frequency of cytokine-expressing cells was measured by intracellular cytokine flow cytometry after 6 h of stimulation with SEB. The fraction of cells expressing IFN-{gamma}, TNF-{alpha}, and IL-2 was significantly higher in the CD7low and CD7neg subsets as compared with the CD7high subset (Fig. 4a). Similar results were obtained with anti-CD3/anti-CD28 stimulation (data not shown). Thus, down-regulation and loss of CD7 expression identify two populations of CD8 T cells with a high content of cytolytic effector molecules and high level of cytokine production.



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  		FIGURE 4. Segregated expression of cytokines and perforin in the CD7low and CD7neg subsets of CD8 T cells. The graph (a) represents the expression of intracellular cytokines after 6 h of in vitro stimulation with SEB (n = 5; *, p < 0.05). b, PBMC were stimulated with SEB in vitro for 6 h, fixed, permeabilized, and costained for IL-2 and perforin or TNF-{alpha} and perforin in addition to cell surface markers. Representative data are shown. Statistical analysis: Wilcoxon-matched pairs test.

 
Although the CD7low and CD7neg subsets contain a large fraction of cells expressing both lytic molecules and cytokines, there was a marked segregation between cells expressing perforin and cytokines (Fig. 4b). Thus, cells which express perforin tend not to secrete cytokines and vice versa. This functional pattern was most clear in the case of IL-2 where perforin expression and IL-2 expression were mutually exclusive. However, a small number of TNF-{alpha}-expressing cells were positive for perforin. IFN-{gamma} expression was predominantly found in perforin-negative cells, although the segregation was less clear than that observed between IL-2 and perforin (data not shown). These data indicate that both the CD7low and the CD7neg subsets of CD8 T cells can be subdivided into cytokine-producing effector T cells (TCC) and cytolytic effector T cells (TCL).

The CD7low and CD7neg CD8 T cells subsets do not proliferate

To further examine the functional properties of the three CD8 T cell subsets, we assessed proliferative capacity with CFSE. Although the CD7high population readily proliferated in response to polyclonal stimuli (SEB or anti-CD3/anti-CD28, only SEB stimulation is shown, Fig. 5), the CD7low and CD7neg subsets were not proliferating. This is consistent with previous studies showing that effector cells have reduced proliferative capacity (3, 11)



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  		FIGURE 5. Low proliferative capacity in the CD7low and CD7neg subsets of CD8 T cells. PBMC were labeled with CFSE and stimulated with SEB for 96 h. The plots are gated on the CD7high, CD7 low, and CD7neg subsets of the CD8 T cells.

 
Ag-specific cells are present in all three CD8 T cell subsets

To explore the functional significance of the three populations based on CD7 expression, the presence of Ag-specific cells was assessed by using a pool of 23 peptides spanning immunodominant epitopes from viruses present in the population (CMV, EBV, and influenza virus). Ag-specific cells are present in all three CD8 T cell subsets (Fig. 6a). However, when specifically studying the phenotype of influenza-specific cells by tetramer staining, these cells were mainly CD7highCD28+ (Fig. 6b). In contrast to influenza, CMV establishes a chronic infection. CMV-specific cells therefore most likely constitute a heterogeneous pool of memory and effector cells. The majority of the CMV tetramer+ cells are CD7lowCD28- while a smaller fraction are CD7highCD28+. These represent effector and memory cells, respectively (Fig. 6b). The distribution of CMV-specific cells between these two subsets may be dynamic so that a larger fraction of cells is recruited from the CD7high memory subset to the CD7low effector subset in phases of active, ongoing viral replication.

Low frequency of apoptotic cells in the CD7neg subset

CD7 seems to be involved in the induction of apoptosis (22). Thus, the turnover might be different for the CD7high, CD7low, and CD7neg subsets. Annexin V binds to phosphatidylserine exposed in the outer layer of the cell membrane associated with early apoptotic events and the TUNEL assay identifies late apoptotic cells after DNA fragmentation has been initiated. We consistently observed a higher proportion of annexin V-positive cells in the CD7low subset than in the CD7high subset (Fig. 7), indicating a higher elimination rate in the CD7low population. In contrast, the frequency of annexin V-positive cells in the CD7neg population was nearly absent. Similar findings were observed using the TUNEL assay.



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  		FIGURE 7. The CD7neg subset does not contain apoptotic cells. Cells undergoing apoptosis were identified by staining with annexin V and the TUNEL assay in conjunction with cell surface markers.

 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
Human CD8 T cell differentiation and the precise identification of functionally relevant populations of CD8 T cells have been an area of intense investigation with significant progress over the last several years. Our study shows that CD7 can be used as a marker of CD8 T cell differentiation and to define distinct subsets of human CD8 T cells. Furthermore, CD7 distinguishes subsets of effector cells with distinct functional properties which lead to a modified definition of CD8 T cell effector cells.

The differentiation sequence of T cells in mice occurs in a linear manner with rapid proliferation and acquisition of effector functions after Ag stimulation, followed by a contraction phase, and finally a stabilization of the number of surviving virus-specific cells in the memory phase (28, 29, 30, 31). However, a parallel differentiation model has also been suggested in which memory cells develop without passing through an effector cell stage (32, 33, 34), reviewed by Kaech et al. (35). In humans, it is believed that naive T cells differentiate into memory cells directly and that the memory cells seed the effector cell population (3, 4, 11). Our findings support the latter model because both the naive cells and the memory cells are CD7high, whereas the effector cell populations have down-regulated CD7 expression. A linear model would only be possible if the down-regulation of CD7 was reversible. This appears not to be the case, at least as observed in cultures of sorted cells (data not shown).

However, the definition of effector cells on the basis of down-regulation of CD7 expression is not fully compatible with previously described models for human CD8 T cell differentiation and maturation. The CD7high population contains both naive and memory cells that are CD27+CD28+, in agreement with earlier reports (11). However, the CD7low and CD7neg cells, which both represent effector cell subsets, each contain CD27+CD28+ and CD27-CD28- subpopulations. This is not consistent with the model of Hamann et al (11) in which effector cells were defined as CD27-CD28- CD8 T cells that had re-expressed CD45RA. On the other hand, the CD7low and CD7neg subsets are CD62L- and CCR7- in line with the definition of effector memory and terminally differentiated effector cells initially introduced by Sallusto et al. (3) and others (4). Effector memory cells and terminally differentiated effector cells in this model were attributed to the re-expression of CD45RA in the terminally differentiated subset (3, 4). Recently, it was suggested that the re-expression of CD45RA does not correlate with the acquisition of effector cell properties in the final differentiation stage because cells expressing CD45RA appear earlier in the differentiation process as well and a significant proportion of CD45RA- cells contain perforin (12). This is further supported by our data showing that the CD7low and CD7neg subsets were mixed with regard to CD45 isoform expression and that the frequency of CD45RO+ cells vs CD45RO- cells within these subsets varied between individuals and did not appear to have any functional consequences.

The level of CD7 expression defines three populations of CD8 T cells. Each of these populations contains two subsets of phenotypically and functionally distinct cells. A putative model of human CD8 T cell segregation based upon the level of CD7 expression is shown in Fig. 8. As defined by the phenotype of CD8 T cells in cord blood, the CD7high population contains naive cells. In addition, the CD7high population contains long-lived influenza-specific memory cells identified by tetramer staining. However, the phenotypic and functional heterogeneity within the CD7low and CD7neg populations is intriguing as it indicates the presence of functionally distinct effector cell populations. Functional segregation of cytokines and cytolytic effector molecules has previously been reported when analyzing the whole CD8 T cell population (36), but this study provides data supporting a functional segregation of the effector cell populations into cytokine-secreting effector cells (TCC) and lytic effector cells (TCL). Thus, the immune system may operate at a highly refined level during the active immune response where TCC primarily secrete inflammatory and antiviral cytokines and contribute to the local immune response through autocrine and paracrine signaling, while TCL lyse and induce apoptosis in infected cells by secretion of perforin and granzymes. It is not clear whether these two subsets of CD7low and CD7neg cells develop independently or whether there is a sequential differentiation from TCC to TCL. Such a differentiation step could be supported by our observations that most of the TCC are CD27+CD28+ and most of the TCL are CD27-CD28- (data not shown) and that CD27 cannot be re-expressed once down-regulated (37). CD28, on the other hand, may be re-expressed to a limited extent (10).



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  		FIGURE 8. A putative model for CD8 T cell differentiation. The CD7high subset contains naive cells and memory cells. Both the naive cells and memory cells are CD27+ and CD28+ but differ in expression of CD45RO. In addition, all naive cells are CD62L+ and CCR7+, but memory cells have a variable expression of these two cell surface markers. The CD7low subset represents a population of effector cells with rapid cell turnover as shown by a high frequency of annexin V-positive cells and the CD7neg subset contains a stable population of effector cells. Each of these two subsets can be divided into lytic effector cells (TCL) and cytokine-producing effector cells (TCC). The TCL are mainly CD27-CD28- and the TCC are CD27+CD28+.

 
The functional difference between the CD7low and CD7neg subsets may be related to a different life span and turnover. A significant fraction of the CD7low subset stained positive with annexin V, which binds to phosphatidylserine exposed in the outer layer of the cell membrane early in the apoptotic process (38). This indicates that the CD7low subset represents a population of cells which either is in the contraction phase of an immune response or is a population with a stable cell count and a rapid turnover. Most likely, these cells represent an unstable population of effector cells which rapidly expands in a burst-like manner and then contracts with resolution of the immune response. Interestingly, the CD7neg population was mainly annexin V negative. This was also observed in the CD7neg subset of the CD4 T cell population (data not shown) and is consistent with earlier studies reporting that CD7neg CD4 T cells represent a stable population of cells which increases during aging, indicating a slow turnover and accumulation over time (15, 39, 40). A possible explanation for this phenomenon is that CD7neg cells may avoid galectin-1-induced apoptosis (22, 23, 26). Galectin-1 preferentially binds CD7, CD45, and CD43, which leads to clustering of these receptors into unique domains on the cell surface and induction of apoptosis (41). CD7 is essential for this process (22). Thus, galectin-1 secretion induced during immune activation (42, 43, 44) may be an important mechanism to induce apoptosis and initiate the contraction phase of the effector cell population. The CD7neg subset may, therefore, represent a small number of persistent effector cells that remain in circulation for extended periods of time.

In conclusion, our data show that CD7 expression identifies three subsets of CD8 T cells. Each of these three subpopulations contain two functionally distinct subsets. The CD7high subset contains naive and memory cells. The CD7low and CD7neg subsets are both effector cell populations, but each contains a population of cytokine-secreting effector cells (TCC) and a population of lytic effector cells (TCL). These findings both support and challenge several of the current concepts of human CD8 T cell differentiation and maturation.


   Acknowledgments
 
We acknowledge Tadesse Eshetu for excellent technical assistance. The following reagent was obtained through the National Institutes of Health AIDS Research Reagent Program, Division of AIDS, National Institute of Allergy and Infectious Diseases, National Institutes of Health: CEF Control Peptide Pool (catalog no. 6747) from Drs. Cox and Currier.


   Footnotes
 
1 This work was funded by National Institutes of Health Grant AI44595 (to D.F.N.). D.F.N. is an Elizabeth Glaser Scientist of the Elizabeth Glaser Pediatric AIDS Foundation. Back

2 Address correspondence and reprint requests to Dr. Einar Martin Aandahl, Gladstone Institute of Virology and Immunology, P.O. Box 419100, San Francisco, CA 94141-9100. E-mail address: maandahl{at}gladstone.ucsf.edu Back

3 Abbreviations used in this paper: CD62L, L-selectin; SEB, staphylococcal enterotoxin B; TCC, cytokine-secreting effector CD8 T cell; TCL, lytic effector CD8 T cell. Back

Received for publication October 17, 2002. Accepted for publication December 11, 2002.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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