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1 Skin Cancer Unit, German Cancer Research Center Heidelberg and University Hospital Mannheim, Mannheim, Germany and 2 Division of Cellular Immunology, German Cancer Research Center Heidelberg, Heidelberg, Germany
Requests for reprints: Philipp Beckhove or Dirk Schadendorf, Deutsches Krebsforschungszentrum, Abteilung für zelluläre Immunologie, Im Neuenheimer Feld 280, 69120 Heidelberg, Germany. Phone: 49-6221-42-3743; Fax 49-6221-42-3702; E-mail: p.beckhove{at}dkfz.de or d.schadendorf{at}dkfz.de.
| Abstract |
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enzyme-linked immunospot, we investigated reactivity of T cells from bone marrow and peripheral blood to melanoma lysate-pulsed autologous dendritic cells in 40 melanoma patients. Melanoma-reactive T cells were present in the bone marrow of seven patients and in peripheral blood of four patients. In the bone marrow, melanoma-reactive T cells were present in 6 of 21 stage IV patients and in 1 of 10 stage III patients, whereas none were detected in stage I to II patients (0 of 9). The occurrence of tumor-reactive bone marrow T cells in melanoma patients was associated with advanced disease stage, disease duration and tumor load, and independent of treatment. These findings provide new insights into the generation of T-cell responses in melanoma patients. (Cancer Res 2006; 66(12): 5997-6001) | Introduction |
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The immunogenicity of malignant melanoma is well established, and tumor-reactive T cells were found in the peripheral blood of tumor patients (6). Clinically, overt metastasis of melanoma to the bone is an infrequent event occurring in advanced stages of the disease (7). Recent studies described melanoma micrometastasis to the bone marrow in stage III to IV patients (8, 9). Although there is some indication that detection of tyrosinase mRNA (9) or immunomagnetic detection of melanoma cells in bone marrow (10) may be associated with a worse prognosis, current data do not support the routine use of bone marrow sampling for staging or stratification purposes. Recently, melanoma-reactive CD8+ T cells have been described in the bone marrow of five tumor-free melanoma patients after experimental immunotherapy (11). Using peptide-MHC tetramers and flow cytometry, these cells were at either the same or higher frequency in the bone marrow as in peripheral blood of the same patients. These results are in line with the detection of memory T cells in early-stage breast cancer patients (5). Because bone marrow has been proposed as an alternative source for tumor-specific T cells for the use in adoptive transfer strategies (5), we investigated the occurrence of melanoma-reactive T cells in melanoma patients of different disease stages.
| Materials and Methods |
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Generation of dendritic cells and T lymphocytes. Dendritic cells were generated as described previously (5). In short, peripheral blood mononuclear cells were obtained by density gradient centrifugation and were subsequently allowed to adhere to plastic. Adherent cells were cultured in X-VIVO 20 medium (Cambrex BioScience, East Rutherford, NJ), recombinant human granulocyte macrophage colony-stimulating factor (50 ng/mL; Essex Pharma, Munich, Germany), and recombinant human interleukin (IL)-4 (1,000 IU/mL; PromoCell, Heidelberg, Germany) for the generation of dendritic cell. After 1 week of culture, dendritic cell was harvested, counted, depleted of contaminating T and B lymphocytes, and used for enzyme-linked immunospot (ELISpot) analysis. Nonadherent cells were maintained in RPMI 1640 (Invitrogen, Karlsruhe, Germany) supplemented with 8% human AB serum (Sigma, Deisenhofen, Germany), recombinant human IL-2 (100 units/mL; PromoCell), and recombinant human IL-4 (60 units/mL). After 1 week, T cells were depleted of contaminating CD15+, CD19+, and CD56+ cells and used for ELISpot analysis.
Cell lines and lysates. U-937 is a histiocytic lymphoma cell line (13) and was obtained from the American Type Culture Collection (Manassas, VA). SK-MEL-23, a kind gift of Dr. L.J. Old (Memorial Sloan-Kettering Cancer Center, New York, NY), is a highly pigmented melanoma cell line. Cells were lysed by five cycles of freezing and thawing. Dendritic cells were pulsed with lysates for 20 hours at a concentration of 200 µg/1 x 106 cells/mL.
IFN-
ELISpot. ELISpot analysis was done as described previously (5). In short, 96-well nitrocellulose filtration plates (Millipore, Schwalbach, Germany) were coated with the monoclonal antibody 1-D1K (Mabtech, Nacka Strand, Sweden). Dendritic cell pulsed with different lysates was coincubated with autologous T cells (1:5, dendritic cell to T cell ratio) for 40 hours. All samples were analyzed at least in triplicates. Plates were developed using a biotinylated secondary antibody (clone 7-B6-1, Mabtech), streptavidin-alkaline phosphatase conjugate, and the chromogenic substrate nitroblue tetrazolium/5-bromo-4-chloro-3-indolyl phosphate. Spots were automatically counted with the use of a computer-assisted video image analyzer (KS Elispot, Zeiss, Goettingen, Germany). Individuals were considered as responders if the number of spots formed in the presence of dendritic cell loaded with tumor lysate was significantly higher than in the presence of control lysate-pulsed dendritic cell.
Statistical analysis. Numbers of IFN-
-secreting cells in ELISpot in different experimental conditions were compared using two-sided t test. Contingency tables were analyzed using Fisher's exact test. Continuous variables from two groups were compared using Mann-Whitney test. Stage dependence of tumor-reactive bone marrow T cells was analyzed using exact Cochran-Armitage test. Differences between melanoma reactivity in bone marrow and peripheral blood were analyzed using McNemar test. A significance level of
0.05 was considered significant.
| Results and Discussion |
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after stimulation by autologous dendritic cell pulsed with lysate of the well-characterized melanoma cell line SK-MEL-23 as a source of tumor antigens compared with dendritic cell loaded with U-937 lysate as a control. One representative ELISpot result is shown in Fig. 1
. We decided to use lysate of a melanoma cell line as test antigen because autologous tumor cells were not available from most patients especially in early stages, although the use of HLA-restricted peptides from defined tumor antigens has the disadvantage of a restriction to only a few CD8 T-cell epitopes in HLA-selected patients. Our methodology with the use of lysate-pulsed dendritic cell as antigen-presenting cell may underestimate the frequency of tumor-reactive CD8+ cells because it is based on the cross-presentation pathway of antigen presentation, which is less efficient (14). Nevertheless, our method has the important advantage of additionally assaying for a CD4+ response, which is an integral component of an efficient and lasting Th1-biased cellular immune response (15).
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ELISpot assays using dendritic cells pulsed with the respective peptides from the tumor antigens gp100, Melan A, MAGE3, and/or tyrosinase that were used for vaccination. Interestingly, none of the patients showed a peptide-specific immune response (data not shown) or a response against melanoma cell lysate, suggesting that the vaccination did not induce long-term memory responses.
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pretreatment (Table 1).
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Our findings lead to a modification of the interpretation of the findings reported by Letsch et al. (11) who described melanoma-reactive CD8+ T cells in bone marrow of all five tested patients.
Four of the five patients had stage IV disease (International Union Against Cancer), and four of five of the patients had received tumor peptide vaccination before the analysis. Given the higher number of patients investigated in our study and the inclusion of patients with early-stage disease, we believe that the study of Letsch et al. (11) had a bias toward advanced disease. In agreement with our interpretation of an association of bone marrow immune responsiveness with late-stage disease, four of the seven bone marrow responders in our study had measurable tumor load at the time of the bone marrow sampling. Furthermore, variables clinically associated with stage [longer disease duration and lactate dehydrogenase (LDH) activity] were also associated with the responder status in bone marrow of patients (Table 2), although such correlation was not found for peripheral blood T cells (Table 1). Interestingly, median duration of disease, as determined by the interval between the initial diagnosis and the bone marrow sampling, was longer in stage IV patients with a tumor-reactive T-cell memory in bone marrow than in those without (median, 12 months versus 43 months). Nevertheless, we did not find a significant survival advantage in patients with positive bone marrow response as analyzed by Kaplan-Meier analysis (data not shown). This discrepancy may be related to the observation that priming in the bone marrow occurred preferentially in late phases of advancing disease.
The immunobiology of melanoma may be different from breast cancer. Although for breast cancer micrometastatic disease is a negative predictor of survival (17, 18), the situation in melanoma is being debated (9, 10).
At present, the mechanism behind the occurrence of tumor-reactive effector and memory T cells in the bone marrow is not entirely clear. Although it has been shown in the mouse that the bone marrow can be a priming site for T-cell responses (1, 2), there is also evidence that T cells primed in lymph nodes or spleen can migrate to the bone marrow (3, 19). It seems plausible that tumor-reactive T cells found in the bone marrow were primed there. This would only occur in situations in which tumor antigens reach the bone marrow environment in sufficient concentration. Although formal proof is lacking, we propose from the presently available data that this happens only in advanced stages of melanoma. In cancers, which gain access to the bone marrow early, such as breast cancer, tumor-reactive T cells may be found in bone marrow also early.
In conclusion, we found a stage dependency of the occurrence of melanoma-reactive bone marrow T cells. Only a subset of advanced stage melanoma patients showed tumor-reactive T cells in their bone marrow. The frequency of these cells in the bone marrow is comparable with the situation described for breast cancer patients (5) and was not significantly related to any therapeutic intervention or treatment outcome, contrasting earlier results (11). Although not directly addressed in our study, these cells are most likely memory T cells because we detected antigen-dependent IFN-
secretion during the 40-hour stimulation period only in the CD45RA T-cell fraction (data not shown). They may be an attractive source of effector T cells from advanced stage patients for future immunotherapies because they are less exposed to the negative effect of the tumor and its microenvironment and, if primed in the bone marrow, may preferentially recognize metastatic tumor cells.
| Acknowledgments |
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| Footnotes |
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Received 2/12/04. Revised 4/ 3/06. Accepted 5/ 4/06.
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