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Original Article |
steinma{at}rockvax.rockefeller.edu
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Key Words: TRANCE dendritic cells T cell immunization
TRANCE, a recently described member of the TNF family 9, is a regulator of the immune system and of bone development (for a review, see reference 10). TRANCE is expressed on activated T cells 11, and a major target for TRANCE in the immune system appears to be mature DCs that express a high level of TRANCE receptor (TRANCE-R) 812. In vitro, TRANCE promotes the survival of mature DCs, most likely by upregulating the expression of Bcl-XL 8, and induces the production of proinflammatory cytokines, such as IL-1 and IL-6, and cytokines that stimulate and induce differentiation of T cells, such as IL-12 and IL-15 1113. Therefore, TRANCE is likely to act as a positive feedback regulator during productive T cell–DC interactions 10.
In this study, we have treated antigen-pulsed mature DCs with soluble TRANCE, injected the cells subcutaneously, and then evaluated their numbers and function in LNs. We have found that TRANCE treatment greatly enhances the number and persistence of antigen-presenting DCs in the draining LNs, and increases the ensuing primary and memory T cell responses. Thus, our results indicate that the longevity and abundance of antigen-pulsed DCs are critical factors in the magnitude of a T cell response to antigen in vivo, and provide a potential avenue to improve the efficacy of DC-based immunotherapy in humans.
Proliferation Assays for T Cell Priming and Cytokine Production.
Presentation of Antigens by DCs That Have Migrated to LNs.
Measurement of Delayed-Type Hypersensitivity.
Labeling and Migration of DCs.
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Introduction
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Abstract
Introduction
Materials and Methods
Results
Discussion
References
Dendritic cells (DCs) are antigen-presenting cells specialized to initiate T cell immunity, and as such can be regarded as nature's adjuvant 12. DCs have the capacity in vivo to migrate from tissues, where they encounter antigens, to the T cell areas of lymphoid tissues, where immune responses begin 2345. DCs reside in tissues as immature cells, specialized to capture and process antigens, and, after antigen capture, they mature in response to inflammatory stimuli characterized by an upregulation of MHC and T cell costimulatory molecules 2. DCs then migrate to the draining LN and stimulate antigen-specific T cells to initiate an immune response. However, several reports suggest that the life span of DCs in the LN is short. Although DCs migrate to the LNs via afferent lymphatics, they are not found in the efferent lymph 67. It is difficult to identify DCs in the LN >2 d after subcutaneous injection 45. In tissue culture, fully differentiated or mature DCs undergo rapid apoptosis, but this can be delayed substantially by treatment with several members of the TNF family, including CD40 ligand (CD40L), TNF-related activation-induced cytokine (TRANCE), and TNF 8.
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Materials and Methods
Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
Dendritic Cells.
DCs were generated from bone marrow progenitors, using GM-CSF as described 1415. On day 6 of culture, the immature DCs were pulsed for 6 h with 10 µg/ml purified protein derivative (PPD) from Mycobacterium tuberculosis (Statens Serum Institute) or OVA (Sigma Chemical Co.) in complete medium (RPMI 1640 supplemented with 5% FCS, 50 µM 2-ME, and 20 µg/ml gentamicin). The cells were then dislodged and transferred to fresh 100-mm culture dishes at 106/ml to allow DC maturation. On day 7, the mature DCs were pulsed overnight with recombinant, soluble TRANCE (1 µg/ml) 8. On day 8, the DCs were washed twice in HBSS and resuspended in HBSS for injection into the footpads of mice (5 x 105 cells per footpad).
Draining LNs (popliteal LNs), cervical LNs, and spleen were harvested from different groups of mice (C57BL/6 or BALB/c; Taconic Farms), and single cell suspensions were prepared. Cells were restimulated in vitro with 10-fold serial dilutions of PPD (0.1–10 µg/ml) or OVA, for 3 d in triplicate in flat-bottomed 96-well plates at 3 x 105 LN cells/well in 200 µl of Click's medium (GIBCO BRL) supplemented with 0.5% normal mouse serum, L-glutamine, penicillin-streptomycin, Hepes, and 2-ME. [3H]thymidine was added for the last 8 h of culture, and thymidine incorporation was measured using standard scintillation procedures. For cytokine production, cells prepared as described above were cultured at 3 x 106/ml in complete Click's medium in the presence of 10 µg/ml of PPD or OVA for 48 h. Supernatants were then assessed for IFN-
and IL-4 by ELISA (R&D Systems).
LN DCs were purified using CD11c-MACS beads (Miltenyi Biotec) after digestion in 400 U/ml collagenase following the manufacturer's instructions. DO11-10 CD4+ T cells were purified from LNs of DO11-10 TCR transgenic mice (provided by Dr. Dennis Loh) using CD4 magnetic beads (Miltenyi Biotec). 5 x 104 DO11-10 CD4+ T cells were cultured in RPMI 1640 supplemented with 10% FCS, 2-ME, L-glutamine, penicillin-streptomycin, with various numbers of CD11c+ cells in round-bottomed 96-well plates for 4 d and pulsed with [3H]thymidine during the last 8 h of culture.
4.5 or 9 wk after priming with antigen-pulsed DCs in the left hind footpad, mice were challenged by the injection of 30 µg PPD in PBS in the right hind footpad, and PBS only in the left footpad. Footpad swelling was measured after 24 and 48 h and recorded as the difference between right and left footpad thickness.
To follow the migration of bone marrow–derived DCs in draining LNs after footpad injection, cells were labeled before injection with 5-chloromethyl-fluorescein diacetate (CMFDA) or 5-(and 6)-(((4-chloromethyl)benzoyl)amino)tetramethylrhodamine (CMTMR) according to the manufacturer's protocol (Molecular Probes). DCs were incubated for 30 min at 37°C in 10 µM CMFDA or CMTMR in serum-free RPMI, and then another 30 min at 37°C in serum-free RPMI. The DCs were washed, counted, and injected in both hind footpads (5 x 105 per footpad). For confocal microscopy, the draining popliteal LNs were harvested at various time points after injection, processed, and analyzed by confocal microscopy as described previously 5. For FACS® analysis, popliteal LNs were harvested, then digested with 400 U/ml collagenase (Sigma Chemical Co.) for 30 min at 37°C in RPMI, 1% FCS. EDTA at a final concentration of 10 mM was added during the last 5 min. Total LN cells were counted and then stained with PE-conjugated anti-CD11c mAb (PharMingen). After gating on live cells, 106 events were acquired to quantify the absolute number of migrating DCs per LN (CD11c+ and FL1high).
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Results
Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
Enhancement of Antigen-specific Primary Th Cell Responses by TRANCE-treated DCs.
To determine whether the pretreatment of antigen-pulsed mature DCs ex vivo with TNF family members such as TRANCE would enhance the adjuvant effect of DCs in vivo, we used the PPD from mycobacteria, a classical antigen for T cell–mediated immunity and an antigen known to be presented by DCs in mice 14. DCs were prepared from bone marrow progenitors stimulated with GM-CSF 1415. PPD was added for 6 h on day 6 of the cultures, when most of the DCs were in an immature state. These immature DCs display efficient endocytic activity 14 and sequester most of their antigen-presenting MHC class II products within intracellular endocytic compartments (MIICs 16), but lack strong cell surface expression of CD40, TRANCE-R, and CD86 10. After the 6-h exposure to low doses of PPD, DC maturation was induced by transfer to a new culture vessel as described 1415. We confirmed that the DCs began to express high levels of CD40, TRANCE-R, and CD86 upon maturation 10. The mature DCs were then treated with or without soluble TRANCE during the last 12 h of the culture, washed, and injected subcutaneously in the hind footpads of naive mice. Aliquots of each DC preparation were further cultured in vitro to test whether a brief exposure to TRANCE was sufficient to increase DC survival. A brief exposure of mature DCs to TRANCE was indeed sufficient to enhance DC survival in vitro (Fig. 1 A), suggesting that cellular responses induced by TRANCE responsible for antiapoptotic effects on mature DCs are initiated at an early point after TRANCE stimulation 8.
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and IL-4) upon rechallenge with PPD (Fig. 1 C). Immunization with TRANCE-treated, PPD-pulsed DCs also increased the production of IFN-
by severalfold, but the production of IL-4 was not affected (Fig. 1 C). No priming was found in LNs that were distal to the site of DC injection, namely mesenteric and axillary LNs, whether DCs were treated with TRANCE or not (data not shown). However, when spleen cells were examined at a later time point (day 10), a small but significant response to PPD was noted (data not shown), suggesting a migration of primed T cells from the popliteal LNs to the spleen. Furthermore, this response was significantly higher in spleen cells from mice injected with TRANCE-treated, PPD-pulsed DCs compared with that from mice immunized with DCs that were PPD-pulsed without TRANCE treatment (data not shown). Similar results were also obtained when OVA was used as antigen (data not shown). Therefore, these results indicate that TRANCE-treated, antigen-pulsed DCs have an increased capacity to induce CD4+ T cell priming in vivo.
Enhancement of Antigen-specific Memory Responses by TRANCE-treated DCs.
The effects of DCs on the establishment of memory was then tested using the induction of delayed-type hypersensitivity (DTH) as a criterion. When mice were immunized with PPD-pulsed DCs, no significant DTH was observed 4.5 wk later (Fig. 2). However, when mice were immunized with DCs that had been pulsed with PPD and exposed to TRANCE, DTH responses were evident 4.5 and 9 wk later (Fig. 2). Taken together, these results indicate that TRANCE treatment enhances the capacity of antigen-pulsed DCs to induce both primary and secondary immune responses in vivo.
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We then determined whether DCs found in draining LNs 3 d after subcutaneous injection retained their capacity to present antigen and stimulate T cells. Immature bone marrow–derived DCs were pulsed with OVA, and then treated with TRANCE as described above. 5 x 105 cells were then injected in each footpad of BALB/c mice, and draining LNs were harvested 3 d later and digested with collagenase. CD11c+ cells were then purified and used to stimulate resting CD4+ T cells from DO11-10 TCR transgenic mice 20. As shown in Fig. 4, CD11c+ cells from mice injected with TRANCE-treated, OVA-pulsed DCs induced significantly higher proliferative responses for DO11-10 CD4+ T cells than those from mice immunized with DCs pulsed with OVA only (Fig. 4): approximately three- to fivefold more CD11c+ cells from mice immunized with OVA-pulsed DCs were required to obtain a similar T cell proliferative response than from mice immunized with TRANCE-treated, OVA-pulsed DCs. Since we consistently observed a three- to fivefold difference in the number of injected DCs in the draining LNs 3 d after immunization (Fig. 3), the results suggest that the difference in the number of antigen-pulsed DCs found in the LN is responsible for differential T cell proliferation.
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| Discussion |
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In this study, we have shown that treatment of DCs with TRANCE before immunization enhances their adjuvant capacity, which results in better T cell priming in vivo. Although DCs without prior TRANCE treatment were able to prime Th cells in the draining LNs, as assessed by antigen-specific proliferation assay and cytokine production, this primary response was strongly enhanced when DCs were pretreated with TRANCE before subcutaneous injection. Moreover, a significant memory response was observed only in mice injected with TRANCE-treated DCs. How does TRANCE produce these consequences? One possibility would be that TRANCE enhances the adjuvant property of DCs via cytokine induction. We have recently shown that TRANCE induced multiple cytokines in DCs, including IL-1, IL-6, IL-12, and IL-15 1113. Since IL-12 and IL-15 are important cytokines involved in the activation and differentiation of T cells 2122, this effect may contribute to the increased T cell responses we observed with TRANCE-pulsed DCs. IL-12 production might also explain the substantial increase in IFN-
priming and Th1 response 22 found in draining LNs of mice injected with TRANCE-pulsed DCs.
However, it is also possible that one of the underlying mechanisms for the enhanced T cell immune responses by TRANCE is an increase in the number of antigen-pulsed DCs that are found in the draining LNs. Similar to its effect on DC survival in vitro, TRANCE may have increased the survival of DCs at the site of injection, which would possibly increase the number of DCs migrating out of this site and into the draining LN. TRANCE may also enhance the survival of DCs that have migrated to the T cell area. Ingulli et al. 5 have shown that 24 h after subcutaneous injection, peptide-pulsed mature DCs are found in the draining LN and they interact with antigen-specific T cells. Since activated T cells express CD40L and TRANCE, which can increase the survival of DCs in situ, it is possible that the antiapoptotic molecules induced by TRANCE 8 before the subcutaneous injection may have protected antigen-presenting mature DCs against spontaneous apoptosis until they are able to fully communicate with antigen-specific T cells. In addition, TRANCE might modify the expression of those chemokine receptors, such as CCR7 2324, that favor the entry of DCs into afferent lymphatics and homing to the T cell areas. Although several of these mechanisms may operate together, we favor the theory that the effect of TRANCE is on DC numbers as opposed to "function per cell," because the efficacy of T cell stimulation by DCs isolated from the draining LNs is proportional to the number of surviving migrated DCs (Fig. 4).
Our results now suggest that the strength of DC–T cell interaction required for successful activation of antigen-specific T cells 25 can be influenced not only by the cytokine secretion profile of DCs, but also by their longevity and/or abundance at the site of T cell priming. Therefore, future experiments should determine whether the longevity and/or abundance of antigen-presenting DCs at the site of T cell priming are critical factors for the induction of T cell responses to antigens delivered by natural routes, e.g., viral infection or tumors.
Although this report focuses on the effects of TRANCE on DCs, CD40L can also enhance the survival and adjuvanticity of DCs (our unpublished data). This observation may explain previous reports that CD40L enhances DC function in vivo, allowing them to stimulate CD8+ T cells and induce CTL differentiation 26272829. However, while the expression of CD40L is restricted to CD4+ T cells, TRANCE is also expressed on activated CD8+ T cells, and may therefore confer the ability to enhance DC survival and function on CD8+ T cells as well 11. Since TNF family members are rapidly upregulated on T cells by TCR stimulation 11, our results suggest that activated T cells provide a powerful positive reinforcement to antigen-presenting DCs by enhancing their survival and cytokine production.
DC-mediated immunotherapy (i.e., the active immunization of humans with autologous DCs that have been pulsed with clinically significant antigens, including tumor, viral, and bacterial antigens [ 30, 31]) may be improved by the application of our findings. Initial studies in humans have shown that the subcutaneous injection of DCs pulsed ex vivo with protein antigen or peptide is an efficient way to prime and boost CD4+ and CD8+ T cells 32. However, recent reports suggest that current protocols result in very low rates of survival and/or migration of DCs in the draining LNs 33, indicating that the methodology is operating far below the adjuvant potential of DCs. We have also found that, despite a significant adjuvant effect, mature bone marrow–derived DCs migrated poorly to draining LN after subcutaneous injection. Exposure of DCs to TNF family members such as TRANCE or CD40L before injection is likely to improve the efficacy of DC-based immunotherapy by enhancing the in vivo survival and the number of antigen-presenting cells in draining LNs. This hypothesis is currently under investigation.
| Acknowledgments |
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Submitted: 3 November 1999
Revised: 22 November 1999
Accepted: 23 November 1999
Y. Choi, Laboratory of Immunology, Howard Hughes Medical Institute, The Rockefeller University, 1230 York Ave., New York, NY 10021. Phone: 212-327-7441; Fax: 212-327-7319; E-mail: choi@rockvax.rockefeller.edu
Abbreviations used in this paper: DC, dendritic cell; DTH, delayed-type hypersensitivity; PPD, purified protein derivative; TRANCE, TNF-related activation-induced cytokine.
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