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Both Regulatory T Cells and Antitumor Effector T Cells Are Primed in the Same Draining Lymph Nodes during Tumor Progression¹

Toru Hiura^2,*, Hiroshi Kagamu^2,3,*, Satoru Miura^*, Akira Ishida^*, Hiroshi Tanaka^*, Junta Tanaka^*, Fumitake Gejyo^* and Hirohisa Yoshizawa

^* Graduate School of Medical and Dental Sciences, Course for Biological Functions and Medical Control, Department of Homeostatic Regulation and Development, Division of Respiratory Medicine, Niigata University, Niigata, Japan; and Bioscience Medical Center, Niigata University Medical and Dental Hospital, Niigata, Japan

	Abstract

Top Abstract Introduction Materials and Methods Results Discussion Disclosures References

 
The peripheral tolerance mechanism prevents effective antitumor immunity, even though tumor cells possess recognizable tumor-associated Ags. Recently, it has been elucidated that regulatory T cells (Treg) play a critical role in maintaining not only self-tolerance, but also tolerance of tumor cells. However, because the Treg that maintain self-tolerance arise naturally in the thymus and are thought to be anergic in peripheral, it is still unclear where and when Treg for tumor cells are generated. In this study we analyze tumor-draining lymph nodes (LNs) and demonstrate that both antitumor effector T cells and Treg capable of abrogating the antitumor reactivity of the effector T cells are primed in the same LNs during tumor progression. The regulatory activity generated in tumor-draining LNs exclusively belonged to the CD4⁺ T cell subpopulation that expresses both CD25 and a high level of CD62L. Forkhead/winged helix transcription factor gene expression was detected only in the CD62L^highCD4⁺CD25⁺ T cells. CD62L^highCD4⁺CD25⁺ Treg and CD62L^lowCD4⁺CD25⁺ T cells, which possess effector T cell functions, had comparable expression of LFA-1, VLA-4, CTLA-4, lymphocyte activation gene-3, and glucocorticoid-induced TNFR. Thus, only CD62L expression could distinguish regulatory CD4⁺CD25⁺ cells from effector CD4⁺CD25⁺ cells in draining LNs as a surface marker. The Treg generated in tumor-draining LNs possess the same functional properties as the Treg that arise naturally in the thymus but recognize tumor-associated Ag. CD62L^highCD4⁺CD25⁺ Treg contained a subpopulation that expressed CD86. Blocking experiments revealed that ligation of CTLA-4 on effector T cells by CD86 on Treg plays a pivotal role in regulating CD4⁺ effector T cells.

	Introduction

Top Abstract Introduction Materials and Methods Results Discussion Disclosures References

 
The purpose of the immune system is to discriminate and eliminate invading nonself. To do this, it possesses not only an effector system to eliminate nonself, but also a regulatory system that abrogates the attack of effector cells against self-somatic cells. Thus, the balance between immunity and tolerance determines the outcome of an immune reaction. Although tumor cells have Ags altered by mutation, a lack of danger signals and antigenic similarity to self-somatic cells, from which tumor cells are derived, engage the peripheral tolerance mechanism (1, 2). This tolerance makes it difficult to obtain effective antitumor immunity.

Recent studies revealed CD4⁺ T cells that constitutively express CD25 to play a critical role in maintaining peripheral tolerance during infection, transplantation, autoimmunity, and tumor immunity (2, 3, 4, 5, 6, 7). CD4⁺CD25⁺ regulatory T cells (Treg)⁴ that arise naturally in the thymus to maintain self-tolerance are considered anergic in peripheral (8). However, it has been demonstrated that Treg proliferate in peripheral tissues in response to antigenic stimulation and can be converted from naive CD4⁺ T cells (9, 10). Thus, it is still unclear where and when Treg are generated for tumor cells.

APCs that acquire Ags migrate into secondary lymphoid organs, where the Ag information is converted to adaptive immune responses. Although CD4⁺CD25⁺ is the best surrogate marker, it is difficult to distinguish Treg based on CD25 expression, especially in lymph nodes (LNs) where T cell priming is going on, because the expression of CD25 is also up-regulated on effector T cells upon TCR engagement before clonal expansion. This problem makes it impossible to analyze how regulatory T cells are primed in LNs. We reported that effector T cells, which are capable of mediating antitumor reactivity, are primed in LNs draining growing tumors and that these T cells exclusively belong to the CD62L^low subpopulation (11). Additional CD40 stimulation as help signals for APC resulted in increased numbers of CD62L^low T cells in draining LNs (12, 13). CD62L^high T cells have been considered naive cells that have never been encountered by cognate Ag. However, our findings suggested that CD62L^high tumor-draining LN T cells contained a regulatory subpopulation, because the elimination of CD62L^high cells promotes the generation of highly potent antitumor T cells upon stimulation with CD3 (14). Recent studies have demonstrated that CD62L^high CD4⁺CD25⁺ T cells possess superior suppressive activity (15, 16, 17, 18).

In this study we demonstrate that the expression of CD62L distinguishes regulatory CD4⁺CD25⁺ cells from effector CD4⁺CD25⁺ T cells and that both antitumor effector T cells and regulatory T cells, which are capable of abrogating the therapeutic efficacy of the antitumor effector T cells in vivo, are primed in the same tumor-draining LNs with different kinetics. CTLA-4 ligation by CD86 exclusively expressed on regulatory CD62L^highCD4⁺CD25⁺ LN T cells plays a pivotal role in regulating effector CD4⁺ T cell functions via direct T-T interaction.

	Materials and Methods

Top Abstract Introduction Materials and Methods Results Discussion Disclosures References

 
Mice

Female C57BL/6J (B6) mice were purchased from CLEA Laboratory. They were maintained in a specific pathogen-free environment and used for experiments at the age of 8–10 wk. All animal experiments were conducted with the permission of the Niigata University ethics committee for animal experiments.

Tumors

MCA 205 is a fibrosarcoma of B6 origin induced by i.m. injection of 3-methylcholanthrene (19). Single-cell suspensions were prepared from solid tumors by enzymatic digestion as described previously (20). An MCA 205 tumor cell line was established and maintained in vitro.

mAbs and flow cytometry

Hybridomas producing mAbs against murine CD4 (GK1.5, L3T4), CD8 (2.43, Lyt-2), CD3 (2C11), and murine CD62L (MEL14) were obtained from American Type Culture Collection. Anti-CD4 mAb, anti-CD8 mAb, and anti-CD62L mAb were produced as ascites fluid from sublethally irradiated (500 cGy) DBA/2 mice. PE-conjugated anti-CD80 (16-10A), anti-CD86 (GL1), anti-CD62L (MEL14), anti-CTLA-4 (UC10-4F10-11), anti-lymphocyte activation gene-3 (anti-LAG3; C9B7W), anti-CD8 (2.43), and anti-CD25 (PC61) mAbs and FITC-conjugated anti-Thy1.2 (30-H12), and anti-CD4 (GK1.5) mAbs were purchased from BD Pharmingen. PE-conjugated anti-glucocorticoid-induced TNFR (anti-GITR; 108619) mAb was purchased from R&D Systems. Analyses of cell surface phenotypes were conducted by direct immunofluorescent staining of 0.5–1 x 10⁶ cells with conjugated mAbs. In each sample, 10,000 cells were analyzed using a FACScan flow microfluorometer (BD Biosciences). PE-conjugated subclass-matched Abs used as isotype controls were also purchased from BD Pharmingen.

Fractionation of T cells

T cells in the LN cell suspension were concentrated by passing through nylon wool columns (Wako Pure Chemical Industries). To yield highly purified (>90%) cells with down-regulated CD62L expression (CD62L^low), LN T cells were further isolated by a panning technique using T-25 flasks precoated with goat anti-rat Ig Ab (Jackson ImmunoResearch Laboratories)/anti-CD62L mAb (MEL14) and sheep anti-rat-Ig Ab/anti-CD62L mAb-coated Dynabeads M-450 (Dynal Biotech). T cells with high CD62L expression (CD62L^high) were obtained as cells attached to flasks coated with goat anti-rat Ig Ab/anti-CD62L mAb. In some experiments cells were also separated into CD4⁺ and CD8⁺ cells by depletion using magnetic beads as described previously (14). For in vitro experiments, highly purified CD4⁺ cells were obtained using anti-CD4 mAb-coated Dynabeads and Detachabeads (Dynal Biotech) according to the manufacturer’s instructions. CD25⁺ cells were isolated using PE-conjugated anti-CD25 mAb and anti-PE microbeads (Miltenyi Biotec) according to the manufacturer’s directions. Cell purity was >90%.

Bone marrow-derived dendritic cells (DCs)

DCs were generated from bone marrow cells as described previously. In brief, bone marrow cells obtained from femurs and tibias of naive mice were placed in T-75 flasks for 2 h at 37°C in complete medium (CM) containing 10 ng/ml rmGM-CSF (a gift from KIRIN). Nonadherent cells were collected by aspirating the medium and were transferred into fresh flasks. On day 6, nonadherent cells were harvested by gentle pipetting. CM consists of RPMI 1640 medium supplemented with 10% heat-inactivated LPS-qualified FCS, 0.1 mM nonessential amino acids, 1 µM sodium pyruvate, 100 U/ml penicillin, 100 µg/ml streptomycin sulfate (all from Invitrogen Life Technologies), and 5 x 10^–5 M 2-ME (Sigma-Aldrich).

Tumor-draining LN cells

B6 mice were inoculated s.c. with 2 x 10⁶ MCA 205 tumor cells in both flanks. Inguinal LN draining tumors were harvested. Single-cell suspensions were prepared mechanically as described previously (20).

Adoptive immunotherapy

B6 mice were injected s.c. with 1.5 x 10⁶ MCA 205 tumor cells in 100 µl of HBSS to establish s.c. tumors. Three days after inoculation, mice were sublethally irradiated (500 cGy) and then infused i.v. with T cells isolated from tumor-draining LNs. Perpendicular diameters of s.c. tumors were measured with calipers. The significance of differences in the diameters between groups was analyzed by Student t test. A value of p < 0.05 was considered significant.

Cytokine ELISA

T cells were stimulated with immobilized anti-CD3 mAb or tumor Ag-pulsed bone marrow-derived DCs in CM. Supernatants were harvested and assayed for mouse IFN- content by a quantitative sandwich enzyme immunoassay using a mouse IFN- ELISA kit (Genzyme) according to the manufacturer’s instructions.

RT-PCR

Total RNA was isolated from T cells using Isogen (Nippon Gene) and used for cDNA synthesis. The cDNAs were used as templates for PCR (94°C for 2 min, 58°C for 30 s, and 72°C for 1.5 min), and 35 cycles were performed using primers specific for forkhead/winged helix transcription factor gene (foxp3; forward, 5'-GGCCCTTCTCCAGGACAGA-3'; 5'-GCTGATCAT GGCTGGGTTGT-3'). To ensure the quality of the product, RT-PCR was also performed using primers specific for ₂-microglobulin.

Proliferation assay

T cells isolated from tumor-draining LNs were stimulated with immobilized anti-CD3 mAb for 48 h in 2 ml of CM on 24-well plates at 2 x 10⁶/ml. CD62L^low T cells were labeled with 5 µM CFSE (Molecular Probes) in HBSS at 37°C for 15 min and washed twice before CD3 stimulation. The ratio of CD62L^low T cells to CD62L^high CD4⁺CD25⁺ T cells was 2:1. After a 48-h stimulation, cells were counted and washed twice with HBSS. Then, T cells were cultured in CM supplemented with 10 U/ml human rIL-2 (gift from Shionogi) at 1 x 10⁵/ml. Three wells were analyzed for each condition.

	Results

Top Abstract Introduction Materials and Methods Results Discussion Disclosures References

 
CD62L^high T cells derived from tumor-draining LNs, but not from naive spleens, abrogated antitumor reactivity of CD62L^low LN T cells

It was believed that CD62L^high T cells are naive T cells; however, we reported that the elimination of CD62L^high T cells promotes the generation of highly potent antitumor CD4⁺ T cells upon stimulation with CD3. To determine CD62L^high LN T cells possess activity to abolish the antitumor reactivity of effector T cells primed in tumor-draining LNs, mice with established s.c. tumors were infused with 2 x 10⁶ CD62L^low LN T cells in the presence or the absence of 10 x 10⁶ CD62L^high T cells. T cells were isolated from LNs draining growing MCA 205 tumors for 12 days or from spleens of naive mice. The ratio of CD62L^low to CD62L^high T cells was approximately the same as that in LNs, because 15–25% of all T cells were CD62L^low in 12-day tumor-draining LNs. As shown in Fig. 1b, 2 x 10⁶ CD62L^low T cells alone successfully mediated the antitumor efficacy to regress s.c. tumor growth. In contrast, the s.c. tumor growth curve of the mice infused with 2 x 10⁶ CD62L^low T cells in the presence of 10 x 10⁶ CD62L^high T cells derived from tumor-draining LNs was identical with that of the no treatment group. CD62L^high T cells derived from naive splenocytes did not affect the antitumor reactivity of CD62L^low tumor-draining LN T cells. Thus, CD62L^high T cells of tumor-draining LNs contain a subpopulation that is capable of abrogating the antitumor reactivity of effector T cells primed in the same tumor-draining LNs.

View larger version (51K): [in this window] [in a new window]   FIGURE 1. a, CD62L and CD25 expression of CD4+ T cells in 12-day tumor-draining LNs. LN cells were stained with FITC-conjugated anti-CD4 mAb, PE-conjugated anti-CD62L mAb, and PerCP-conjugated anti-CD25 mAb. Gated CD4+ cells were analyzed with a microfluorometer. b–d, Subcutaneous tumor growth of mice infused with CD62Llow T cells in the presence or the absence of CD62Lhigh T cells. Two million MCA 205 tumor cells were injected s.c. along the midline of the abdomen to establish s.c. tumors. Three days later, mice were adoptively infused i.v. with 2 x 106 CD62Llow T cells alone or with 10 x 106 CD62Lhigh T cells after sublethal whole body irradiation (500 cGy; b). CD62Llow T cells were isolated from LNs draining growing MCA 205 s.c. tumors for 12 days. CD62Lhigh T cells were isolated from tumor-draining LNs or naive splenocytes. c and d, CD62Lhigh T cells were further fractionated according to CD4, CD8, and CD25 expression using magnetic beads. One million fractionated CD62Lhigh T cells were infused into mice bearing established 3-day s.c. tumors with 2 x 106 (c) or 4 x 106 (d) CD62Llow LN T cells. Diameters of s.c. tumors were measured twice weekly with calipers, and size was recorded as the average of two perpendicular diameters. Statistical analyses were performed with Student’s t test. *, p < 0.01 compared with the no treatment group. Each group contained five mice.

Because CD4⁺CD25⁺ is the best surrogate marker for regulatory T cells identified to date, CD4⁺CD25⁺, CD4⁺CD25^–, or CD8⁺ CD62L^high T cells isolated from tumor-draining LNs were infused with CD62L^low LN T cells into mice bearing established s.c. tumors to determine which subpopulation of CD62L^high T cells mediates regulatory functions. In Fig. 1c, the antitumor efficacy of 2 x 10⁶ CD62L^low T cells was not enough to cure the s.c. tumor, which, after starting to regress, eventually grew in the mice. Neither CD62L^highCD4⁺CD25^– nor CD62L^highCD8⁺ T cells showed any additive antitumor or regulatory activity. The s.c. tumor growth curves showed no significant differences from the curve for the mice who received CD62L^low T cells alone. In contrast, CD62L^highCD4⁺CD25⁺ T cells abolished the antitumor efficacy of effector T cells, resulting in a growth curve identical with that of the no treatment group. Thus, the CD4⁺CD25⁺ subpopulation of CD62L^high LN T cells is probably made up of Treg cells, whereas CD62L^highCD4⁺CD25^– and CD8⁺ cells are functionally irrelevant naive T cells. Moreover, Fig. 1d shows that 1 x 10⁶ CD62L^highCD4⁺CD25⁺ tumor-draining LN T cells were capable of abrogating the antitumor reactivity of 4 x 10⁶ CD62L^low LN T cells, which was sufficient to cure established 3-day s.c. tumors. In contrast, the same number of CD62L^highCD4⁺CD25⁺ T cells derived from naive spleens, which are considered resident Treg (21), did not influence the therapeutic efficacy of antitumor effector T cells in vivo.

In 12-day MCA 205 s.c. tumor-draining LNs, 20% of T cells are CD62L^low, and 5–7% are CD62L^highCD4⁺CD25⁺ (Fig. 1a). The ratio of CD62L^low to CD62L^high CD4⁺CD25⁺ T cells is 3–4:1. Thus, it seems that Treg cells sufficient to abolish the antitumor reactivity of primed effector T cells are generated in tumor-bearing hosts.

CD62L^highCD4⁺CD25⁺ inhibited IFN- production by either CD4⁺ or CD8⁺ CD62L^low T cells via direct T-T interaction

To test whether CD62L^highCD4⁺CD25⁺ T cells generated in tumor-draining LNs influence cytokine production, we measured the amount of IFN- produced by 1 x 10⁵ CD62L^low T cells in the presence or the absence of 5 x 10⁴ CD62L^highCD4⁺CD25⁺ T cells in 200 µl of CM on 96-well plates. As shown in Fig. 2a, CD62L^highCD4⁺CD25⁺ T cells in tumor-draining LNs abolished the Ag-specific production of IFN- by tumor-draining LN effector T cells stimulated with 5 x 10⁴ tumor Ag-loaded DCs. As shown in Fig. 2b, CD62L^highCD4⁺CD25⁺ T cells derived from naive splenocytes did not affect the production of IFN- stimulated by tumor-associated Ag, although they inhibited IFN- production in the presence of nonspecific stimulation with immobilized anti-CD3 mAb (data not shown).

View larger version (50K): [in this window] [in a new window]   FIGURE 2. Measurement by ELISA of IFN- secreted in the medium. CD62Llow T cells 1 x 105 were cocultured with 0.5 x 105 DCs in the presence or the absence of 0.5 x 105 CD62LhighCD4+CD25+ T cells for 72 h in 200 µl of CM in 96-well plates (a and b). Before coculture with T cells, DCs were incubated with 5000 cGy-irradiated MCA 205 or LLC tumor cells overnight. The amount of IFN- produced by 1 x 106 CD62LlowCD8+ or CD4+ T cells cultured with 0.5 x 106 CD62LhighCD4+CD25+ T cells upon CD3 stimulation is shown in c and d. CD62Llow T cells on the bottom of 24-well plates were cultured with CD62LhighCD4+CD25+ T cells either on 0.4-µm pore size Transwell inserts or on the bottom. Both the Transwell inserts and 24-well plates were coated with anti-CD3 mAb. T cells were isolated from LNs draining growing MCA 205 s.c. tumors for 12 days. Three wells were analyzed for each condition. ELISA was performed in duplicate. Statistical analyses were performed by Student’s t test. *, p < 0.01.

CD62L^highCD4⁺CD25⁺ T cells abrogated proliferation of both CD4⁺ and CD8⁺CD62L^low T cells

To elucidate whether CD62L^highCD4⁺CD25⁺ T cells generated in tumor-draining LNs inhibit cell proliferation, a T cell proliferation assay was performed as described in Materials and Methods. CFSE-labeled CD62L^low T cells stimulated with immobilized anti-CD3 mAb increased the total number of cells by 7-fold during a 3-day culture period accompanied by a reduction in the intensity of CFSE (Fig. 3, a and b). CD62L^highCD4⁺CD25^– T cells did not affect CD62L^low T cell proliferation, because the total number of cells increased and the reduction in intensity of CFSE intensity during the 3-day culture was identical with that of CD62L^low T cells alone. In contrast, CD62L^low T cells stimulated in the presence of CD62L^highCD4⁺CD25⁺ T cells did not proliferate at all. CFSE intensity did not change during the 3-day culture. Fig. 3c demonstrates the relative number of CD8⁺ or CD4⁺ cells according to phenotypic analysis. Thus, CD62L^highCD4⁺CD25⁺ T cells generated in tumor-draining LNs have the ability to abrogate the proliferation of both CD4⁺ and CD8⁺ T cells.

View larger version (20K): [in this window] [in a new window]   FIGURE 3. T cell proliferation was evaluated in the presence of 10 U/ml IL-2 after stimulation with CD3. CD62Llow T cells isolated from tumor-draining LNs were labeled with CFSE and cultured alone or with CD62LhighCD4+ LN T cells at 2 x 106/ml in 2 ml of CM on 24-well plates coated with anti-CD3 mAb for 48 h. The ratio of CD62Llow to CD62Lhigh cells was 2:1. After CD3 stimulation, T cells were harvested and counted, then recultured at 0.1 x 106/ml in 2 ml of CM supplemented with 10 U/ml IL-2 on new 24-well plates. T cells were counted and analyzed with a microfluorometer every 24 h. a, Total number of cells per well. b, Percentage of T cells that still possess high levels of CFSE labeling and represent cells without division. c, Relative number of CD8+ or CD4+ T cells. Three wells were analyzed for each condition. *, p < 0.01 compared with the no stimulation group.

To examine the properties of CD62L^lowCD4⁺CD25⁺ T cells, which comprise 20–30% of the CD62L^low T cell population in 12-day tumor-draining LNs, we tested whether CD62L^low CD4⁺CD25⁺ LN T cells affect IFN- production by CD62L^lowCD4⁺CD25^– T cells. CD62L^highCD4⁺CD25⁺ T cells completely inhibited the production of IFN- by CD62L^lowCD4⁺CD25^– T cells (Fig. 4), whereas the addition of CD62L^lowCD4⁺CD25⁺ T cells increased production. Moreover, CD62L^lowCD4⁺CD25⁺ T cells alone produced the same amount of IFN- as CD62L^lowCD4⁺CD25^– T cells. In contrast, CD62L^highCD4⁺CD25⁺ T cells produced no IFN-. Thus, it is likely that CD62L^lowCD4⁺CD25⁺ cells possess effector T cell function, but not regulatory activity.

View larger version (27K): [in this window] [in a new window]   FIGURE 4. Measurement by ELISA of IFN- secreted in the medium. CD62LlowCD4+CD25– T cells alone (1 x 105) or with 0.5 x 105 T cells fractionated according to the expression of CD62L and CD25 were stimulated with immobilized anti-CD3 mAb in 200 µl of CM on 96-well plates for 48 h. *, p < 0.01.

It has been reported that mutation of Foxp3 is responsible for immune dysregulation, polyendocrinopathy, enteropathy, and X-linked inheritance, a syndrome of systemic autoimmunity in humans (22, 23). It is now believed that Foxp3 is a master switch of regulatory functions (9, 24, 25). Thus, we tested whether fractionated T cells derived from tumor-draining LNs express mRNA for Foxp3. As depicted in Fig. 5A, only CD62L^highCD4⁺CD25⁺ T cells expressed foxp3 mRNA.

View larger version (41K): [in this window] [in a new window]   FIGURE 5. A, Foxp3 mRNA expression in isolated CD62LlowCD4+CD25+, CD62LlowCD4+CD25–, CD62LhighCD4+CD25+, or CD62LhighCD4+CD25– T cells derived from LNs draining MCA 205 s.c. tumors for 12 days. Total RNA was isolated from T cells and analyzed by RT-PCR for foxp3. 2-Microglobulin gene expression is shown to confirm that equal amounts of RNA were used in each RT-PCR. Results shown are representative of three separate experiments. B, GITR, LAG3, CTLA-4, VLA-4, and LFA-1 expression on isolated T cells derived from MCA 205 tumor-draining LNs. Immediately after fractionation, T cells were double stained with PE-labeled anti-CD25 and FITC-conjugated anti-GITR, anti-LAG3, anti-CTLA-4, anti-VLA-4, anti-LFA-1, or isotype control Ab. Either CD25+ or CD25– cells were gated for analyses. A total of 106 cells were analyzed for each sample. Each frame consists of 10,000 cells. Dotted lines indicate the isotype control.

Next, we analyzed the phenotype of fractionated T cells derived from tumor-draining LNs. Because it was demonstrated that CD4⁺CD25⁺ Treg cells express GITR, CTLA-4, and LAG3 (26, 27, 28, 29), we tested for these molecules and adhesion molecules that were important for T cell migration. Although CD62L^highCD4⁺CD25⁺ regulatory LN T cells have an up-regulated expression of GITR, CTLA-4, and LAG3, it is difficult to distinguish CD62L^highCD4⁺CD25⁺ T cells from CD62L^lowCD4⁺CD25⁺ T cells, which possess effector T cell properties, from these molecules (Fig. 5B). Furthermore, CD62L^highCD4⁺CD25⁺ Treg cells and CD62L^lowCD4⁺CD25⁺ effector T cells had a comparable up-regulated expression of VLA-4 and LFA-1. In contrast, CD62L^highCD4⁺CD25^– T cells possessed the naive cell phenotype, such as no VLA-4, GITR, or CTLA-4, and a low level of LFA-1.

Different kinetics of CD62L^highCD4⁺CD25⁺ and CD62L^lowCD4⁺ T cell priming in LNs draining growing s.c. tumors

To address the priming of CD62L^highCD4⁺CD25⁺ and CD62L^lowCD4⁺ T cells in LNs draining growing MCA 205 s.c. tumors, we examined the number and phenotype of LN cells. Kinetic analysis revealed that the proportion of both CD62L^lowCD4⁺ CD25⁺ and CD4⁺CD25^– T cells started to increase 7 days after s.c. tumor inoculation and peaked on the 11th day (Fig. 6). The percentage of CD62L^low T cells rapidly decreased, reaching the starting level by the 14th day. Although the proportion of CD62L^highCD4⁺CD25⁺ T cells started to increase 7 days after s.c. tumor inoculation, like that of CD62L^low cells, it kept increasing until the total number of LN cells started to decrease. The increase in CD62L^highCD4⁺CD25⁺ T cells was not caused by a nonspecific accumulation of CD62L^high cells, because the proportion of CD62L^highCD4⁺CD25^– naive T cells decreased in tumor-draining LNs. Hence, it is likely that CD62L^highCD4⁺CD25⁺ Treg cells underwent clonal expansion in tumor-draining LNs during tumor progression.

View larger version (25K): [in this window] [in a new window]   FIGURE 6. Kinetics of cellularity and the ratio of the indicated T cell subpopulations based on total T cells in LNs draining growing MCA 205 s.c. tumors. MCA 205 tumor cells (1.5 x 106) were inoculated s.c. into both flanks of mice. Inguinal LNs were harvested from three mice serially 0, 3, 7, 11, 15, and 20 days after s.c. injection and analyzed.

It has been reported that an inhibitory Ab against CTLA-4 could abrogate the induction of suppression by CD4⁺CD25⁺ Treg, and CTLA-4 expressed on Treg was thought to be important for this phenomenon (27). However, the mechanism by which Treg deliver a regulatory signal to effector T cells is still unclear. We examined the expression of CD80 and CD86 on fractionated tumor-draining LN T cells. Unexpectedly, only the CD62L^highCD4⁺CD25⁺ T cells had a subpopulation that expressed CD86 (Fig. 7). CD62L^lowCD4⁺ or CD62L^highCD4⁺CD25^– T cells did not express a detectable level of CD86 even after stimulation with CD3 (data not shown). Next, we tested whether CD86 on regulatory T cells participates in the suppression of T cell functions. CD62L^low T cells and CD62L^highCD4⁺CD25⁺ Treg cells were stimulated with immobilized anti-CD3 mAb in the presence or the absence of an inhibitory mAb against CD80, CD86, or CTLA-4. Anti-CTLA-4 as well as anti-CD86 inhibitory mAb prevented the suppression of CD62L^lowCD4⁺ T cells induced by CD62L^highCD4⁺CD25⁺ Treg cells, whereas anti-CD80 inhibitory mAb or isotype-matched irrelevant Abs did not have any influence (Fig. 8a). However, blockade of CTLA-4 or CD86 could not reverse the suppression of CD62L^lowCD8⁺ LN T cells (Fig. 8b).

View larger version (28K): [in this window] [in a new window]   FIGURE 7. T cells isolated from 12-day tumor-draining LNs were analyzed for the expression of CD80 or CD86. CD4+ T cells positively selected with magnetic beads were three-color-stained with FITC-labeled anti-CD80 mAb or FITC-labeled anti-CD86 mAb in the presence of PE-labeled anti-CD62L mAb and PerCP-labeled anti-CD25 mAb. Gated CD62LhighCD4+CD25+, CD62LhighCD4+CD25–,CD62LlowCD4+CD25+, or CD62LlowCD4+CD25– T cells were analyzed for CD80 or CD86 expression. A total of 107 cells were analyzed for each sample.

View larger version (16K): [in this window] [in a new window]   FIGURE 8. Proliferation assay of T cells in the presence or the absence of a blockade between CD86 and CTLA-4. CD62LlowCD4+ or CD8+ T cells (1 x 105) were cocultured with 5 x 104 CD62LhighCD4+CD25+ T cells in 200 µl of CM on 96-well plates with immobilized anti-CD3 mAb for 48 h. T cells were isolated from LNs draining MCA 205 s.c. tumors for 12 days. To inhibit the interaction between CD86 and CTLA-4, anti-CD86 mAb or anti-CTLA-4 mAb was added to the medium at 10 µg/ml during the 48 h of stimulation. T cells were recultured in 1 ml of CM supplemented with 10 U/ml IL-2 on 24-well plates at 1 x 105/ml. As a control, anti-CD80 mAb, rat IgG, or hamster IgG was added at the same concentration. Three wells were examined for each condition, and cells were enumerated every 24 h. The y-axis indicates the fold increase in number on day 2. *, p < 0.01.

	Discussion

Top Abstract Introduction Materials and Methods Results Discussion Disclosures References

CD62L^highCD4⁺CD25⁺ T cells derived from spleens of naive mice could not abrogate antitumor reactivity in vivo (Fig. 1). Moreover, Treg cells from naive mice did not inhibit the production of IFN- by antitumor effector T cells upon Ag stimulation by DCs acquired from apoptotic tumor cells (Fig. 2b), even though they had comparable suppressive activity as the Treg cells generated in tumor-draining LNs upon nonspecific CD3 stimulation. Hence, it is likely that Treg are required to receive TCR/CD3 signaling to interfere with the function of effector T cells and that the Treg generated in tumor-draining LNs recognize tumor-associated Ag.

Although it has been demonstrated that CD62L^highCD4⁺CD25⁺ T cells possess superior regulatory activity in several systems, CD62L^lowCD4⁺CD25⁺ T cells were still considered Treg cells (15, 16, 18). However, the differences in foxp3 expression and priming kinetics suggest that the CD62L^lowCD4⁺CD25⁺ T cell subpopulation in tumor-draining LNs is distinct from CD62L^highCD4⁺CD25⁺ T cells (Figs. 5A and 6). CD62L^lowCD4⁺ CD25⁺ T cells produced even more IFN- than CD62L^low CD4⁺CD25^– T cells upon CD3 stimulation (Fig. 4). Furthermore, CD62L^lowCD4⁺CD25⁺ LN T cells mediated antitumor efficacy in vivo (Fig. 1). These results indicated that CD62L^lowCD4⁺CD25⁺ T cells are effector T cells that express CD25 because of recent TCR stimulation before clonal expansion in LNs.

Little is known about the trafficking of Treg cells; however, our study shows that Treg cells generated in tumor-draining LNs have an up-regulated expression of CD62L, VLA-4, and LFA-1 (Figs. 1 and 5B). CD62L recognizes specific ligands on high endothelial venules and is considered the homing receptor for secondary lymphoid tissues (30). In contrast, VLA-4 and LFA-1 are thought to play a central role in T cell trafficking to inflammatory sites by recognizing VCAM-1 and ICAM-1 on endothelial cells. Thus, it is likely that CD62L^highCD4⁺CD25⁺ Treg cells can follow either CD62L^high naive T cells to suppress priming in secondary lymphoid organs or activated CD62L^low effector T cells that express VLA-4 and LFA-1 to suppress immune reactions in the effector phase.

CD62L^highCD4⁺CD25⁺ Treg cells suppressed either CD4⁺ or CD8⁺ effector T cell functions, including cytokine production and cell proliferation, in the absence of APC upon stimulation with CD3 in a cell-cell contact-dependent manner (Fig. 2. c and d, and Fig. 3). Hence, the regulatory signals sent to either CD4⁺ or CD8⁺ effector T cells were received directly from CD62L^highCD4⁺ CD25⁺ Treg cells and were not mediated by APC. It is postulated that ligation of CD80 and/or CD86 expressed on effector T cells by CTLA-4 on Treg cells causes outside-in signaling and results in suppression (31), although it is well documented that p56^lck-induced tyrosine phosphorylation, which is the major signal pathway of the TCR/CD3 complex, can be reversed by CTLA-4 ligation (32). We found that the CD62L^highCD4⁺CD25⁺ Treg cells contained a subpopulation that expressed CD86 in tumor-draining LNs (Fig. 7). Effector CD62L^lowCD4⁺ or naive CD62L^highCD4⁺ CD25^– T cells derived from tumor-draining LNs did not express CD86 or CD80 even after 48-h stimulation with immobilized anti-CD3 mAb (data not shown). The inhibitory mAb against CTLA-4 or CD86, but not CD80, completely reversed the inhibitory effect on the proliferation of CD4⁺ effector LN T cells by CD62L^highCD4⁺CD25⁺ T cells (Fig. 8). In contrast, the same treatment could not reverse the suppression of CD8⁺ effector LN T cells. CD62L^lowCD4⁺ T cells, but not CD8⁺ T cells, isolated from tumor-draining LNs expressed CTLA-4 (Fig. 5B). Our data suggested that CD86 exclusively expressed on Treg cells plays a pivotal role in regulating CD4⁺ effector T cells by interacting with CTLA-4 on effector T cells. This is a novel mechanism by which Treg cells suppress effector T cell function. This finding is compatible with recent reports demonstrating that CD4⁺CD25⁺ T cells derived from CTLA-4-deficient mice mediated suppression (33) and that T cells transfected with cDNA encoding CD86 suppressed graft-vs-host disease (34). The reason why the bioactivity of CD86 on T cells is different from that on APC is unclear; however, DCs are capable of selecting the receptor of B7 by recruiting either CD28 or CTLA-4 into immunological synapses (35). In contrast, it is unlikely that Treg cells have the ability to develop immunological synapse with effector T cells to select receptors. Moreover, it was demonstrated that CD86 expressed on T cells had a hypoglycosylated form and showed no detectable binding activity to CD28 with preserved binding to CTLA-4 (36). Thus, it is possible that CD86 on T cells preferentially give negative signaling through CTLA-4 (37).

CD62L^highCD4⁺CD25⁺ T cells regulated CD8⁺ T cell functions via mechanisms other than the CD86-CTLA-4 interaction, because the inhibitory mAb against CD86 or CTLA-4 did not abolish the suppression. Because neutralizing Ab against TGF- partially inhibited the induction of suppression, it is likely that membrane-bound TGF- participated in CD8⁺ T cell suppression (data not shown).

These results indicate that Treg cells for tumor Ags are primed in draining LNs during tumor progression and that the balance between CD62L^low effector T cell priming and CD62L^highCD4⁺ CD25⁺ Treg cell priming in secondary lymphoid organs determines the outcome of antitumor immune reactions. Our data also indicate that promoting antitumor effector CD62L^low T cell priming while eliminating CD62L^highCD4⁺CD25⁺ Treg cells or inhibiting regulatory mechanisms such as CD86-CTLA-4 interaction is critical to establishing effective antitumor immunotherapy. Furthermore, it might be possible to orchestrate adaptive immune reactions by manipulating the balance of effector and regulatory T cell priming against acquired Ags, such as infectious pathogens, alloantigens, and allergens.

	Disclosures

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The authors have no financial conflict of interest.

	Footnotes

 
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work was supported in part by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, and Culture of Japan; a Niigata University Grant for Promotion of Project; and a Niigata University Grant for Scientific Research.

² T.H. and H.K. equally contributed to this work.

³ Address correspondence and reprint requests to Dr. Hiroshi Kagamu, Division of Respiratory Medicine, Department of Homeostatic Regulation and Development, Course for Biological Functions and Medical Control, Graduate School of Medical and Dental Sciences, Niigata University, Niigata 951-8510, Japan. E-mail address: hkagamu{at}med.niigata-u.ac.jp

⁴ Abbreviations used in this paper: Treg, regulatory T cell; CM, complete medium; DC, dendritic cell; Foxp3, forkhead/winged helix transcription factor gene; GITR, glucocorticoid-induced TNFR; LAG3, lymphocyte activation gene-3; LN, lymph node; m, murine.

Received for publication April 7, 2005. Accepted for publication August 3, 2005.

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