Monoclonal Antibody HMB-45 Research Articles

False-Positive Immunostaining of Normal Epithelia and Carcinomas with Ascites Fluid Preparations of Antimelanoma Monoclonal Antibody HMB45

HMB45 is a melanoma-specific monoclonal antibody that has found widespread use in diagnostic pathology. Recent reports, however, have suggested that this antibody may cross-react with a small number of carcinomas and other epithelial cells. The authors tested the hypothesis that these latter reports represent examples of false-positive immunostaining by comparing the immunostaining on breast, salivary gland, and lung tumors with the following: (1) a commercial ascites preparation of this monoclonal antibody; (2) a protein A-purified antibody preparation derived from ascites fluid; and (3) supernatant fluid obtained from the hybridoma cell line. The authors found that all examples of nonmelanoma immunostaining in the carcinomas tested were eliminated with the nonascites fluid preparations, whereas strong immunostaining of melanomas was retained. The authors conclude that contaminated commercial ascites fluid preparations of HMB45 may account for most, if not all, of the reports of nonmelanoma immunostaining with HMB45.

Physiologic Distribution and Differentiation of Melanocytes in Human Fetal and Neonatal Skin Equivalents

There is evidence that epidermal keratinocytes play a critical role in melanocyte position and differentiation in the epidermis, although little is known about the molecular mechanisms involved. We have used an in vitro skin equivalent as a model system in which to study keratinocyte/melanocyte interactions in both fetal and neonatal skin. Because the skin equivalent model has been shown to closely simulate the morphologic and biochemical features of differentiated epidermis we hypothesized that the factors that influence melanocyte position and differnetiation would also function in this system. Localization of melanocytes in skin equivalents, using the monoclonal antibody HMB-45, established that melanocytes in fetal skin equivalents are grouped and distributed both basally and suprabasally, whereas melanocytes in neonatal skin equivalents are singly distributed among basal epidermal keratinocytes, similar to the distributions of fetal and neonatal melanocytes, respectively, in vivo. Similarly, in fetal and neonatal skin equivalents the patterns of expression of a number of melanoma/melanocyte-associated antigens closely parallels that seen in vivo. These results suggest that the skin equivalent model is an excellent system in which to study the dynamic factors that regulate melanocyte migration, proliferation, and differentiation during ontogeny and post-natal differentiation of the skin.

Reactivity of HMB-45 monoclonal antibody with sweat-gland tumours of the skin.

HMB-45, a monoclonal antibody claimed to be specific for malignant melanoma, has been observed to react with normal eccrine sweat glands and occasionally with normal mammary and bronchial epithelium. In this study we show that HMB-45 also decorates cells in approximately 15% of various sweatgland tumours of the skin. This finding, along with the reported reactivity on mammary carcinomas further outlines the lack of absolute specificity of HMB-45 for cells of the melanocytic lineage.

Metastatic Seminoma in a Patient with HIV Infection: Technical Pitfalls in a Difficult Case

A 36 year old homosexual, HIV positive, white male was evaluated for diffuse abdominal cramps. His work-up included a CT scan of the abdomen that revealed diffuse retroperitoneal adenopathy. A cervical lymph node biopsy showed follicular hyperplasia as has been described in HIV infection. An axillary lymph node biopsy disclosed tumor of uncertain origin by light microscopy. The differential diagnosis included large cell lymphoma, metastatic melanoma and metastatic germ cell tumor.Immunohistochemistry was initially misleading because of the false positive reactivity of HMB45 monoclonal antibody with tissue sections that had been fixed in B5 solution. Electron microscopic studies showed characteristic ultrastructural features of seminoma. Repeat immunohistochemistry with tissue fixed in formalin showed no reactivity with HMB-45 or S-100 and strong reactivity with placental alkaline phosphatase.Germ cell tumors are appearing in the literature as a “new set” of neoplasms which may have an increased incidence in males with HIV infection. This is the first case of seminoma in an HIV positive patient who presented with metastatic disease. (The J Histotechnol 13:299, 1990)

The appearance, density and distribution of melanocytes in human embryonic and fetal skin revealed by the anti-melanoma monoclonal antibody, HMB-45.

The presence, densities, and patterns of distribution of melanocytes in the epidermis of human embryos and fetuses, ranging in age from 40 d to 140 d estimated gestational age (EGA), were studied using the HMB-45 monoclonal antibody that recognizes an antigen in melanoma cells and fetal melanocytes. Immunostained sections of skin and epidermal sheets revealed dendritic melanocytes within the basal or intermediate layers of 50 d EGA and older skin. Melanocytes could not be identified by immunostaining or electron microscopy in younger (40-50 d EGA) epidermis or in cultured epidermal cells from these specimens. However, skin from a 45 d EGA embryo grown in organ culture for 11 d stained positively with HMB-45, suggesting that melanocytes are present at the age either in the epidermis or dermis of the explant. Double-labeling experiments using ATPase and HMB-45 confirmed the specificity of HMB-45 for melanocytes and demonstrated that melanocytes and Langerhans cells are nonoverlapping populations. Melanocytes were present in the embryonic epidermis in relatively high numbers (mean value of approximately 1050 cells/mm2); they increased in density to approximately 2300 cells/mm2 during the late first trimester and early second trimester, then declined during later stages of development to a density of approximately 800 cells/mm2, within the range of values for the newborn child and young adult. Equivalent numbers of melanocytes were recognized by silver staining and with the HMB-45 antibody in an 87 d EGA test sample, indicating that HMB-45 reacted with the total melanocytic population. Melanocytes appeared to be distributed in epidermal sheets in a regular pattern. Statistical tests used to evaluate the randomness of a population revealed a tendency toward a non-random distribution in specimens younger than 80 d EGA, just prior to appendage formation and epidermal stratification into multiple layers, however there was variability in the degree of randomness for any given age. The results of this study have closed the gap in timing between the conclusion of neural crest formation and migration (around 6 weeks) and the appearance of melanocytes in the skin between 40-50 d EGA.

Comparison of HMB-45 Monoclonal Antibody and S-100 Protein in the Immunohistochemical Diagnosis of Melanoma

The value of HMB-45 mouse monoclonal antibody in the immunohistochemical diagnosis of melanoma was compared with that of two antibodies to S-100 protein. Tissue from 32 (91.4%) of the 35 melanomas studied reacted with HMB-45, however, none of the 98 nonmelanoma tumors stained with this antibody. In contrast, 31 (88.5%) melanomas and 24 (24.4%) of the nonmelanoma neoplasms expressed S-100 protein. These results indicated that HMB-45 monoclonal antibody has a higher specificity for melanoma cells than did S-100 protein and that, because of its reactivity in routinely processed tissues, it may be helpful in surgical pathology.