PRAME as a Potential Target for Immunotherapy in Metastatic Uveal Melanoma

Abstract

IMPORTANCE Uveal melanoma (UM) is an intraocular primary malignant neoplasm that often gives rise to metastatic disease for which there are no effective therapies. A substantial proportion of UMs express the cancer-testis antigen PRAME (preferentially expressed antigen in melanoma), which can potentially be targeted by adoptive T-cell therapy.OBJECTIVE To determine whether there may be a rationale for PRAME-directed T-cell therapy for metastatic UM.DESIGN, SETTING, AND PARTICIPANTS An experimental study using a retrospective cohort of 64 patients with UM (median follow-up, 62 months) was conducted from January 8, 2015, to November 20, 2016, at the Leiden University Medical Center. Clinical, histopathologic, and genetic parameters were compared between 64 PRAME-positive and PRAME-negative UMs. HLA class I restricted, PRAME-specific T cells were stimulated with UM cell lines to measure their antigen-specific reactivity against these cell lines, which were analyzed for PRAME expression by real-time quantitative polymerase chain reaction. Uveal melanoma metastases from 16 unrelated patients were assessed for PRAME expression by messenger RNA fluorescence in situ hybridization and for HLA class I expression by immunofluorescence staining.MAIN OUTCOMES AND MEASURES Interferon γ production for antigen-specific reactivity and detection of PRAME and HLA class I expression in primary and metastatic UM. RESULTSOf the 64 patients in the study (31 women and 33 men; mean [SD] age at the time of enucleation, 60.6 [15.6] years), PRAME expression was negative in 35 primary UMs and positive in 29 primary UMs. Positive PRAME expression was associated with a high largest basal diameter (15.0 vs 12.0 mm; P = .005), ciliary body involvement (59% vs 26%; P = .008), and amplification of chromosome 8q (66% vs 23%; P = .002). PRAME-specific T cells reacted against 4 of 7 UM cell lines, demonstrating that T-cell reactivity correlated with PRAME expression. Metastatic UM samples were positive for PRAME messenger RNA in 11 of 16 patients and for HLA class I in 10 of 16 patients, with 8 of 16 patients demonstrating coexpression of both PRAME and HLA class I.CONCLUSIONS AND RELEVANCE PRAME is expressed in many primary and metastatic UMs, and about half of the metastatic UMs coexpress PRAME and HLA class I. The finding that PRAME-specific T cells in this study reacted against PRAME-positive UM cell lines suggests a potential role for PRAME-directed immunotherapy for selected patients with metastatic UM.

Adoptive Immunotherapy Using PRAME-Specific T Cells in Medulloblastoma

“…(29) Several authors reported PRAME expression in many cancers, but presently the biological and clinical meaning of this finding is not yet completely elucidated and, in some cases, the association between PRAME expression and disease prognosis is controversial. (30)(31)(32) In particular, in solid malignancies, including head and neck cancer, (33,34) liposarcoma,(35) uveal melanoma, (12,36) osteosarcoma, (37,38) breast cancer (39) and neuroblastoma (40) high PRAME expression correlates with advanced stage disease and poor clinical outcome, whereas in pediatric acute leukemia PRAME overexpression was found to predict good outcome. (41,42) Research.…”

HLA Class I Antigen Expression in Conjunctival Melanoma Is Not Associated With PD-L1/PD-1 Status

“…Immunofluorescence (IF) staining of HLA-A, HLA-B/C, and B2M on human paraffin-embedded CM sections was performed as previously described. 19,23 For immunohistochemistry (IHC) on mouse xenografts, the procedures were performed as described. 24 In short, primary antibodies HCA2 (mouse, anti-HLA-A, IgG1, MUB2036P, 1:50; Nordic Mubio, Uden, The Netherlands), HC10 (mouse, anti-HLA-B/C, IgG2a, MUB2037P, 1:100; Nordic Mubio), and B2M (rabbit, Z0311, 1:2000 [IHC], 1:1000 [IF]; DAKO, Glostrup, Denmark) were used for both IF and IHC staining.…”

“…In case of discrepancies, a consensus was reached by simultaneous analysis. The semiquantitative scoring system was obtained from prior studies 23,[25][26][27] : intensity was scored as 0 (absent), 1 (weak), 2 (moderate), and 3 (strong), and the percentage of positive cells as 0 (0%), 1 (1% to 5%), 2 (6% to 25%), 3 (26% to 50%), 4 (51% to 75%), and 5 (76% to 100%). A single value was reached by adding intensity and percentage and was used to create three categories: negative (0 to 2), weak (3 to 6), and positive expression (7 to 8).…”

PRAME and HLA Class I expression patterns make synovial sarcoma a suitable target for PRAME specific T-cell receptor gene therapy

“…In the past, this relation was demonstrated in more than 50 other cancer cell lines as well. 9,16 We hereby proofed that mRNA expression leads to the expression of the relevant PRAME peptide because PRAME-T-cells could only have recognized the sarcoma cells if the PRAME peptide was processed by the proteasome and presented in the context of HLA-I. Whether a full length and functional protein is transcribed as well is not certain, but not relevant either, because expression and processing of the 9-amino acid long peptide is enough for T-cell recognition.…”