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1 From the St. Eriks Eye Hospital, Stockholm, Sweden; the 2 Department of Oncology and Pathology, Karolinska Hospital, Stockholm, Sweden; the 3 Regina Elena Cancer Institute, Rome, Italy; and the 4 Department of Immunology, Roswell Park Cancer Institute, Buffalo, New York.
| Abstract |
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METHODS. In the present study HLA class I antigen, ß2-microglobulin (ß2-m), and HLA class II antigen expression was analyzed in primary uveal melanoma lesions by immunoperoxidase staining with monoclonal antibodies of 65 archival clinical samples. The results were correlated with the clinical course of the disease.
RESULTS. HLA class I antigen expression and ß2-m expression were downregulated in 40 and 35 lesions, respectively. HLA class II antigens were expressed in 30 lesions. Patients with high HLA class I, including ß2-m, and HLA class II antigen expression in their primary melanoma lesions had a significantly decreased survival (P = 0.009, P < 0.001, and P = 0.006, respectively).
CONCLUSIONS. The findings argue against a major role of cytotoxic T-lymphocyte (CTL)mediated control of tumor growth in the clinical course of uveal melanoma and are compatible with a potential role of NK-cellmediated control of hematogenic metastatic spread.
| Introduction |
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As in other types of malignant melanoma, immunologic events are believed to play an important role in the clinical course of uveal melanoma. This possibility has stimulated interest in the analysis of the expression of HLA antigens in uveal melanoma lesions, because these molecules are thought to play a major role in the interactions of melanoma cells with the hosts immune system. HLA class I antigens, which consist of a polymorphic heavy chain noncovalently associated with ß2-microglobulin (ß2-m), restrict the interaction of target cells with cytotoxic T lymphocytes (CTLs).3 HLA class II molecules, predominantly expressed on immunologically active cells, are required for antigen presentation of peptides to helper T cells.3 This process is a key event in the activation of immune responses.
Major histocompatibility complex (MHC) class I antigen downregulation is common among human tumors and is believed to be an important factor in their escape from recognition and destruction by HLA class I antigenrestricted, tumor-associated, antigen-specific CTLs.4 In contrast, MHC class I antigen loss may result in increased sensitivity of malignant cells to NK cells.5 Ma and Niederkorn6 have reported that TGF-ß can alter MHC class I antigen expression and the susceptibility of ocular melanoma cells to NK-cellmediated cytolysis. The association of HLA class I antigen downregulation in malignant lesions with poor prognosis in various types of malignancies suggests that CTLs play a major role in tumor growth control. HLA class II antigens have been found in a number of malignancies, although with variable frequency.7 The role of HLA class II antigens in the interaction of malignant cells with immune cells remains to be determined, because the evidence of the association of HLA class II antigen expression in malignant lesions with the clinical course of the disease is conflicting.8
Analysis of a limited number of frozen primary uveal melanoma lesions has shown an association between HLA class I antigen downregulation and favorable prognosis,9 and Crowder et al.10 have demonstrated that immunoreactivity to HLA class I and II was greater in epithelioid than spindle cell uveal melanoma. Because these findings are unexpected, in the present study we retrospectively determined HLA class I and HLA class II antigen expression in a large number of primary uveal melanoma lesions by immunoperoxidase staining of formalin-fixed, paraffin-embedded tissue sections with monoclonal antibodies (mAbs). Furthermore, we correlated the immunostaining results with the clinical course of the disease to assess their clinical significance.
| Materials and Methods |
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The study was reviewed and approved by the local ethics committee at the Karolinska Institute, and the committee deemed that it conformed to the generally accepted principles of ethics in research, in accordance with the Helsinki Declaration.
Monoclonal and Polyclonal Antibodies
The mAb HC-10, which recognizes a determinant expressed on
HLA-A10, -A28, -A29, -A30, -A31, -A32, and -A33 heavy chains and on
virtually all HLA-B heavy chains; the anti-ß2-m mAb L368; and the
anti-HLA class II mAb LGII-612.14 were developed and characterized as
described elsewhere.11
12
13
The hybridoma secreting the
anti-CD44 mAb IM-7 was purchased from the American Type Culture
Collection (Rockville, MD). The biotinylated anti-mouse IgG antibodies
were purchased from Vector Laboratories (Burlingame, CA).
Immunostaining Protocol
Immunostaining of tissue sections was performed using the
standard avidin-biotin complex technique. Briefly, 4-µm
formalin-fixed, paraffin-embedded tissue sections were cut from each of
the selected 70 tumor specimens. Tissue sections were then
deparaffinized and rehydrated, and endogenous peroxidase was blocked
with H2O2 for 30 minutes at
room temperature. No antigen retrieval was performed before the
antibody incubation. Tissue sections were then rinsed in Tris and
phosphate-buffered saline (Tris-PBS, pH 7.6) and incubated with
blocking serum (1% bovine serum albumin) for 20 minutes at room
temperature followed by an overnight incubation at 8°C with an excess
of anti-HLA mAb. Biotinylated anti-mouse IgG antibodies were then
added, and incubation was continued for an additional 30 minutes at
room temperature. The avidin-biotin complex (Vector Laboratories) was
then added. The peroxidase reaction was developed for 6 minutes at room
temperature using 0.6 mg/ml 3'3-diaminobenzidine tetrahydrochloride
(DAB) with 0.03% hydrogen peroxide. Counterstaining was performed with
Mayers hematoxylin. Tris-PBS was used for rinsings between the
different steps.
Staining Assessment
Tissue sections were read independently by two investigators
(SS, CE) without knowledge of the results obtained by the other
investigator or of the survival data. Furthermore, each investigator
read all the slides twice without knowledge of the results obtained in
the previous reading. All stained cells were considered positive,
irrespective of staining intensity. The immunoreactivity was
differentiated from melanin pigment, as reported
previously.14
Specifically, the dark brown, finely
granular appearance of the immune-reaction product could be separated
from the coarse granular appearance of the melanin pigment. Results
were scored as low when less than 30% of melanoma cells were stained
and high when more than 30% of melanoma cells were stained.
Concordance between observers was 93% for HLA class 1 antigens, 87%
for ß2-m, and 93% for HLA class II antigens. The interobserver
reproducibility using the
test was 0.90 for HLA class I antigens,
0.78 for ß2-m, and 0.88 for HLA class II antigens. When the results
obtained by the investigators were not concordant, those obtained by
the first investigator (SS, who is a senior pathologist) were used for
the analysis.
Statistical Analysis
Survival data without loss to follow-up were obtained, according
to the tenets of the Declaration of Helsinki, for all patients with
uveal melanoma from the Swedish National Causes of Death Registry. Time
from the date of surgery to death or the end of 1996 was considered
censored if the patient was alive at the end of 1996 or had died of any
other than a melanoma-related cause. The log-rank test was used to
assess survival differences. The
2 test was
used to measure association of HLA antigen expression with metastasis
development and cell type. The
test was used for assessing
interobserver reproducibility. The significance level was set at 0.05.
Calculations were performed by computer (Statistica, ver. 5.5;
StatSoft, Tulsa, OK; and MedCalc; MedCalc Software, Mariakerke,
Belgium).
| Results |
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HLA class I antigen, ß2-m, and HLA class II antigen expression in the 65 primary uveal melanoma lesions was associated with poor clinical outcome (Figs. 1A 1B 1C) . Thus, high expression of these markers in the lesions correlated significantly with development of metastases (P = 0.013, P < 0.001, and P = 0.021, respectively). These associations appear to be specific, because expression in primary uveal melanoma lesions of CD44, which is also a cell surface protein, was not correlated with clinical outcome (P = 0.334; data not shown). None of the patients (n = 14) who were negative for HLA class II died of uveal melanoma (data not shown).
| Discussion |
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Similar to our findings, experimental melanoma cells that express high MHC class I antigen levels are more resistant to intravenous lysis by NK cells than those with low MHC class I antigen levels.19 Also, intravenous injection of MHC class Ipositive clones from a murine fibrosarcoma was reported to be oncogenic, whereas subcutaneous injection of MHC class Inegative clones from the same tumor was more oncogenic than that of their MHC class Ipositive counterparts.20 The critical role of NK-cellmediated cytotoxicity in uveal melanoma is also supported experimentally by the observation that NK-cell depletion results in increased number and growth of hepatic micrometastases.21 Furthermore, Ma et al.,22 using a nude mice model, showed that disruption of NK-cell activity increased the metastatic spread of uveal melanoma cells. Uveal melanoma cells appear, however, to have evolved other means to escape NK-mediated surveillance, including production of a macrophage-inhibitory factor that prevents lysis by NK cells.23
In the present study, HLA class II antigens were detected in a significantly higher percentage of primary uveal melanoma lesions than that reported by Jager et al.24 Although it cannot be excluded that this reflects differences in the sensitivity of the immunohistochemical assays used in the two studies, we favor the possibility that the low HLA class II antigen expression described by Jager et al.24 is caused by the exposure to x-ray irradiation before enucleation of the uveal melanoma analyzed in the study. Our interpretation is supported by the correlation found in another study between HLA-DQ expression in a uveal melanoma and a ciliary body localization of the tumor and between a low HLA-DQ and -DP expression and an intact Bruchs membrane.9
HLA class II antigen expression in primary uveal melanoma lesions has clinical significance, because none of the patients who did not express HLA class II antigens in their primary lesions (14 cases) died of uveal melanoma. In contrast, 18 of the 30 patients with high HLA class II antigens died of uveal melanoma. To the best of our knowledge, this is a novel finding. Its mechanism is not readily apparent. Conflicting information is available about the clinical significance of HLA class II antigen expression in cutaneous melanoma.25
It has been demonstrated that HLA class II antigenbearing melanoma cells induce the secretion of immunosuppressive cytokine IL-10 by T cells, resulting in T-cell anergy.26 This may explain the association between high HLA class II antigen expression in primary uveal melanoma lesions and poor prognosis. Alternatively, the observed correlation may reflect the resistance of hematogenously spreading melanoma cells with high HLA class I as well as HLA class II antigen expression to NK-cell lysis, because HLA class I and class II antigens may share a common regulatory pathway.15 Regardless of the underlying mechanisms, assessment of HLA antigen expression in uveal melanoma lesions may be of value for determining whether immunotherapeutic strategies in individual patients should be directed toward T cells or NK cells.
| Acknowledgements |
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| Footnotes |
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Submitted for publication March 19, 2001; revised April 23, 2001; accepted May 15, 2001.
Commercial relationships policy: N.
The publication costs of this article were defrayed in part by page
charge payment. This article must therefore be marked
"advertisement" in accordance with 18 U.S.C.
1734
solely to indicate this fact.
Corresponding author: Olle Larsson, CCK R8: 04, Department of Oncology and Pathology, Karolinska Hospital, S-171 76 Stockholm, Sweden. olle.larsson{at}onkpat.ki.se
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