[465] Tyrosinase-Related Protein2 (trp2) Is a Melanocyte Differentiation Antigen (MDA) Useful for Surgical Pathology.

Francesca Avogadri, Jodie Tassello, Denise Frosina, Nicole Hanson, Megan Holz, Erika Ritter, Taha Mehgroub, Klaus J Busam, Achim A Jungbluth. Memorial Sloan-Kettering Cancer Center, New York, NY

Background: MDAs are expressed in cells and tumors of melanocytic lineage. MDAs such as gp100, Melan-A/MART1, and tyrosinase and their corresponding antibodies HMB45, A103, and T311 serve as important diagnostic tools in surgical pathology and are also employed as vaccine targets for the immunotherapy o malignant Melanoma (mM). However, little is known about trp2, another MDA, functionally a Dopachrome Tautomerase (DCT). In the present study, we determined the specificity of a novel anti-trp2 mAb clone C9 and analyzed the expression of trp2 in panels of normal and tumor tissue.
Design: MAb C9 to trp2 was obtained commercially. C9 was tested for specificity by Western Botting (WB) and ELSIA with rt-PCR tested cell lines and mM specimens. Its suitability for IHC was tested in in cell line pellets as well as in panels of normal and tumor tissues pre-typed by rt-PCR.
Results: In WB and ELISA, mAb C9 was reactive solely with trp2 mRNA-positive cell lines and tissues as well as the trp2 protein respectively but not with trp2-negative cell lines and not with unrelated proteins. In IHC, mAb C9 worked well in frozen and FFPE tissue employing antigen retrieval. In skin, typical staining of the melanocytes was present. Immunostaining of mAb C9 was completely inhibted by blocking with trp2 protein and not with other proteins. IHC of mM cell lines corresponded to the trp2 mRNA expression. 16/19 (84%) primary mMs and 19/33 (64%) metastatic mMs were C9 positive, both showing a mostly homogenous staining pattern. Several HMB45-negative cases, were trp2-positive. 10/10 mucosal mM were also trp2 positive. 6/6 desmoplastic mMs were negative. C9 reactivity was only focally present in only 2/9 angiomyolipomas. Besides melanocytes, no C9 reactivity was seen in normal tissues. Panels of non-melanocyic tumors such as carcinomas of colon, breast, lung, ovary, kidney and several sarcoma types were all C9-negative.
Conclusions: MDAs are important diagnostic tools as well as potential vaccine targets for the immunotherapy of mM. Here we show that mAb C9 is a novel specific marker for the detection of trp2. Expression of trp2 in mM parallels other MDAs such as Melan-A and tyrosinase being present in a high percentage of primary and metastatic mMs. Trp2 is a useful diagnostic marker and a potential vaccine target for melanoma.
Category: Dermatopathology

Tuesday, March 1, 2011 9:30 AM

Poster Session III # 116, Tuesday Morning


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