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Imaging, Diagnosis, Prognosis |
Authors' Affiliations: Departments of 1 Surgery, 2 Immunohematology and Blood Transfusion, and 3 Pathology, Leiden University Medical Center, Leiden, the Netherlands
Requests for reprints: Peter J.K. Kuppen, Department of Surgery, Leiden University Medical Center, P.O. Box 9600, 2300 RC Leiden, the Netherlands. Phone: 31-526-2309; E-mail: P.J.K.Kuppen{at}lumc.nl.
| Abstract |
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Key Words: Antigen-presenting cells adenocarcinoma CD1a CD208 tumor-infiltrating leukocytes
40% of patients, which drastically deteriorates their clinical prognosis. Other established treatment modalities, as chemotherapy, have limited effects on the prognosis. Patients' clinical prognosis depends on several clinicopathologic factors, including depth of invasive growth and presence of lymph node metastasis and distant metastasis. In an article from the Colorectal Cancer Working Group of the American Joint Committee on Cancer Consensus Conference on Prognostic Factors (1), the host lymphoid response to the tumor was included among variables that have shown to be promising prognostic factors, but it still needs further evaluation and confirmation before inclusion in routine pathologic reports. To gain insight into the complex mechanisms of an antitumor immune response, several studies aimed at an accurate and qualitative classification of inflammatory infiltrates, taking into account the type of recruited immune effectors and their anatomic localization within the tumor tissue (i.e., intraepithelial, stromal, or advancing border; refs. 25). These studies showed that the presence of tumor-infiltrating T lymphocytes in direct contact with tumor cells (i.e., intraepithelial and/or advancing margin) correlates with clinical outcome. They established a firm basis for the hypothesis that tumor growth is directly influenced by the host cellular immune system. Dendritic cells are considered to be the most potent antigen-presenting cells to initiate and maintain an immune response to pathogens and are found in various types of solid tumors (6). They play a crucial role in the activation, stimulation, and recruitment of T lymphocytes. Dendritic cells are very heterogeneous with respect to their maturation, differentiation, and activation status. They express a variety of molecules, including CD1a, CD40, CD80, CD86, CD208, and HLA class II. In nonlymphoid tissues, such as the skin and mucosa, dendritic cells are immature, express S-100 and CD1a, and are able to endocytose and process antigens and apoptotic cells through a variety of receptors. After stimulation, dendritic cells mature and migrate to lymph nodes or secondary lymphoid tissue, where they present the captured antigens in a MHC-restricted way to the cellular arm of the immune system. Mature dendritic cells are characterized by their potent capacity to activate naive T lymphocytes due to the high expression of HLA class II and costimulatory molecules like CD40, CD80, and CD86.
The clinical significance of tumor-infiltrating dendritic cells has been reported in a variety of human solid tumors as shown by correlations found between the presence of tumor-infiltrating dendritic cells and clinical prognosis (610). Because of their potent capacity to augment an antitumor immune response, dendritic cells are also increasingly used in (pre)clinical immune vaccination trials.
In our previous study, we showed that the infiltration of dendritic cells in colorectal cancer is correlated with local immune interactions and patient prognosis (11). In this study, we evaluated whether there is an association between the presence and maturation status of tumor-infiltrating dendritic cells, T lymphocytes, and clinical course in 104 primary tumor samples of patients with colorectal cancer. In addition to S-100 protein and HLA class II as general dendritic cell markers, we used CD1a and CD208 as more specific functional dendritic cell markers.
| Materials and Methods |
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A negative control was included for each tumor sample by using PBS/bovine serum albumin instead of S-100 and laminin or HLA-DR-DP and laminin antibodies in the overnight incubations.
Microscopic evaluation of tumor sections. All cell counts were done using a Zeiss Axioscope (Sliedrecht, Netherlands) at a x200 magnification (x20 objective and x10 eyepiece). Cases were scored blindly with respect to patient history, presentation, and previous scoring by two independent observers. Dendritic cells were identified by their brown membranous staining pattern, ovoid nuclei, and cytoplasmic flame-like extensions. Structures that were morphologically distinctly distinguishable from dendritic cells, like myenteric plexuses, nerve sheaths, and granulocytes, were excluded. For each section, 25 areas of a representative field of tumor were assessed using an ocular grid comprising a high-power field area of 0.38 mm2. Assisted by the laminin staining (stroma, basal membrane-like structure), tumor areas were divided into three anatomic compartments (i.e., tumor epithelium, tumor stroma, and advancing tumor margin). For each case, the total number of dendritic cells per square millimeter tumor or stroma was calculated for all three compartments. A serial H&E-stained section was examined for orientation and confirmation of the histologic diagnosis.
Statistical analysis. A group with high and low dendritic cell infiltration was distinguished based on the 75th percentile of the average dendritic cell infiltration scores of all patients. All statistical analyses were done using the SPSS software package (SPSS, Inc., Chicago, IL). Disease-free survival data were analyzed using Kaplan-Meier survival estimation, and the log-rank test was used for comparison of the survival curves. Multivariate analysis with Cox regression was done to assess the prognostic significance of dendritic cell infiltration in the various compartments, patient factors, and tumor features for overall and disease-free survival. Statistical analysis between groups was done using the
2 test for comparing proportions. Correlations between continuous variables were evaluated using Spearman rank correlation test. Ps < 0.05 were considered significant. Ps < 0.10 were considered near significant.
| Results |
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HLA class II on tumor epithelial cells. In 29 cases (28%), tumor epithelium stained positive for HLA class II (Fig. 1D). These tumors could not be evaluated for intraepithelial infiltrating HLA class IIpositive immune cells. HLA class II expression by the tumor cells correlated significantly with the intraepithelial infiltration of CD1a-positive dendritic cells (P = 0.03). As an internal control, no correlation was found between CD1a-positive dendritic cells and HLA class II expression in tumor stroma and advancing border. No significant relationship was found between HLA class II expression on tumor cells and other tumor-infiltrating immune cells and clinicopathologic or survival variables.
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Correlation between tumor-infiltrating dendritic cells and other tumor-infiltrating lymphocytes. Tumor-infiltrating T lymphocytes and natural killer cells are generally considered to be the effector immune cell population in an antitumor immune response. To study whether tumor-infiltrating dendritic cells affect the number and behavior of these tumor-infiltrating leukocytes in colorectal cancer, we evaluated whether dendritic cell infiltration and maturation status correlated to the number of these tumor-infiltrating leukocytes. High infiltration of CD1a dendritic cells in the tumor epithelium was significantly correlated to the intraepithelial infiltration of CD4 lymphocytes (P = 0.006) and showed a trend toward intraepithelial infiltration of CD8 lymphocytes (P = 0.08; nonsignificant; Table 4). The number of infiltrating S-100 dendritic cells in the tumor epithelium was also positively correlated to the number of intraepithelial infiltrating CD4 and CD8 lymphocytes (P = 0.02 and 0.01 respectively; data not shown) as presented in our previous study (11). All other correlations between tumor-infiltrating dendritic cells and other immune cells were not significant.
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| Discussion |
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Dendritic cells in general play a key role in the development and maintenance of an immune response. It is therefore plausible to hypothesize that tumor-infiltrating dendritic cells play an important role in a cellular antitumor immune response. They do this by infiltrating, capturing, and processing tumor antigens and subsequent presentation, activation, and recruitment of lymphocytes. Several previous studies already supported this hypothesis by showing a correlation between the quantity of tumor-infiltrating dendritic cells and clinical outcome in different tumor types. Ambe et al. used S-100 protein to detect dendritic cells in colorectal cancer and found a positive correlation between the number of infiltrating dendritic cells and a favorable clinical outcome (10). This observation, however, is in contrast to our recent findings concerning S-100-positive dendritic cells in colorectal cancer (11) but also to findings obtained by others in breast, gastric, ovarian, and tongue carcinomas (9, 1215).
CD208 is a member of the lysosome-associated membrane glycoprotein family and a highly specific marker for mature dendritic cells (16). CD1a is a nonconventional antigen-presenting molecule expressed on dendritic cell subtypes. It is often being regarded as a marker for immature dendritic cells, which is down-regulated on maturation. However, different in vitro and in vivo studies have shown that CD1a can be present on both mature and immature dendritic cells (7, 17). We used CD208 and CD1a to detect tumor-infiltrating dendritic cells. Although CD1a cannot be regarded as a specific marker for immature dendritic cells, differences with the maturation marker CD208 could be accredited to an immature dendritic cell fraction of CD1a-positive dendritic cells.
In our present study, we did find a significant correlation with clinical prognosis with the dendritic cell markers CD1a and CD208. Moreover, not only the number of infiltrating dendritic cells but also the location of infiltration was of importance. This finding supports the observations of Bell et al. in breast cancer (18) and in colorectal cancer (19). CD1a-expressing dendritic cells in the advancing border and mature (CD208-expressing) dendritic cells in the tumor epithelium both showed a correlation with an adverse outcome. The cause of this negative correlation of tumor-infiltrating dendritic cells on clinical prognosis is speculative. A hypothesis is that antigen-capturing and antigen-processing (CD1a) dendritic cells on their way to the tumor cells are hindered in their function due to inhibiting factors (cytokines, chemokines, etc.) in the tumor environment, whereas maturing dendritic cells in the tumor epithelium are hindered in their way to migrate out to secondary lymphoid tissue after antigen capture and activation possibly by similar inhibitory factors.
It is still unclear how tumor-infiltrating dendritic cells interact with tumor cells and other immune cells in the local tumor area. In our study, we found a distinct infiltration pattern according to the maturation and activation status of the dendritic cells. CD1a-positive dendritic cells, of which presumably a large fraction of immature dendritic cells, tended to be scattered trough the whole tumor area and were vigorously infiltrating the tumor epithelium, whereas mature (CD208) dendritic cells clustered in the peritumoral areas and could hardly be found in the tumor epithelium. It is generally presumed that immature dendritic cells are primarily equipped for a role as antigen-processing cells. Therefore, their presence in the close vicinity of tumor epithelium could be a reflection of their active amass of (tumor) antigens. It is tempting to suggest that the peritumoral clustering of mature dendritic cells reflects a state in which these dendritic cells interact directly with clusters of tumor-infiltrating lymphocytes to generate an antitumor immune response as suggested in the studies of Bell et al. (18) and Suzuki et al. (19).
A relationship between the amount of tumor-infiltrating CD1a-positive dendritic cells and expression of HLA class II on tumor cells has been observed in breast cancer (17). In the present study, we show the same correlation in colorectal cancer. Moreover, our study points out that the intraepithelial dendritic cells fraction is of importance and not the stromal or advancing border dendritic cell fraction. It is still obscure what cellular interactions lead to the found correlation. Further studies are necessary to illuminate these interactions.
In our study cohort, certain tumors contained large amounts of tumor-infiltrating dendritic cells, whereas others contained only small amounts. We could not detect any histopathologic differences between these tumors. A possible explanation could be the immunogenicity of these tumors; for example, microsatellite-instable colorectal tumors are characterized by a more vigorous infiltration of immune cells compared with microsatellite-stable colorectal tumors (20). It is hypothesized that these microsatellite-instable tumors are more immunogenic (i.e., more readily recognizable by the immune system). The differences in quantity and type of tumor-infiltrating dendritic cells are a possible reflection of this phenomenon. This hypothesis needs to be further investigated.
Antigen-pulsed and activated tumor-infiltrating dendritic cells are presumed to interact directly and indirectly with lymphocytes, like CD8- and CD4-positive T lymphocytes (CTL and T-helper cells, respectively), through membrane ligands and by secreting various cytokines, resulting in the activation and recruitment of these lymphocytes. Tumor-infiltrating CTLs are generally present in colorectal tumors and are able to spontaneously lyse colon carcinoma cell lines (21). Different studies have shown that high intraepithelial infiltration of CTL shows a beneficial effect on patient survival. In the present study, we showed that a high intraepithelial infiltration of CD1a-positive dendritic cells is correlated to a high intraepithelial infiltration of CTL and/or T-helper cells. In our previous study, we also found a correlation between tumor-infiltrating S-100-positive dendritic cells and other tumor-infiltrating leukocytes (11). It is presumable that the concerning intraepithelial dendritic cells fraction is S-100 and CD1a positive. The correlation with tumor-infiltrating leukocytes could be an independent phenomenon, reflecting the immunogenicity of the tumor, as mentioned above, but it could also suggest that the lymphocytes are actively recruited and/or activated by these dendritic cells. Bell et al. showed that T-helper cells colocalize with dendritic cells in some breast carcinoma tumors, supporting the hypothesis that tumor-infiltrating dendritic cells interact on a local level with lymphocytes to maintain an immune response. Unfortunately, we did not find supporting evidence for this hypothesis in the form of a correlation between the amount of stromal or advancing border mature dendritic cells and other immune cells in the same tumor compartments.
In summary, tumor-infiltrating dendritic cells in colorectal tumors showed a distinct infiltration pattern based on their maturation status. The presence of immature tumor-infiltrating dendritic cells in the tumor epithelium correlated to a higher infiltration of other immune cells. Furthermore, infiltration of CD208-positive (mature) dendritic cells in the tumor epithelium and CD1a-positive dendritic cells in the advancing borders was correlated to an adverse outcome. Our study showed that functional subsets of tumor-infiltrating dendritic cells affected local tumor cell-immune cell interactions and correlated to the clinical prognosis of colorectal cancer patients.
| Footnotes |
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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.
Received 7/22/04; revised 11/22/04; accepted 1/13/05.
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