Examining stem cell characteristics in melanoma

Though in its fledgling stages, this is precisely what researchers from the Wistar Institute in Philadelphia, Pa., are attempting to accomplish, focussing on the antecedent cell lines of malignant melanoma. By using human embryonic stem cell media, their goal is to select and study tumor cells that have stem cell properties.

"Our long term goal is to define the microenvironment within malignant lesions, like matrix and stromal cells, that is responsible for self-renewal and differentiation, and that likely also controls proliferation and invasion," according to Meenhard Herlyn D.V.M., D.Sc., professor and chairman of the program of molecular and cellular oncogenesis, Wistar Institute in Philadelphia, Pa., speaking at the Third International Melanoma Research Congress, here.

It is known that human embryonic stem cells readily differentiate into melanocytes.

Human hair follicle stem cells have properties similar to human embryonic stem cell-derived multi-potential progenitor cells.

Dr. Herlyn and his fellow researchers were able to isolate and characterize a multi-potent progenitor cell from the human hair follicle and maintain it in "hair spheres" that can differentiate not only into melanocytes, but also into neuronal and muscle cells. He cultured these cells as hair spheres using media conditions developed for human embryonic stem cells.

In his research study, Dr. Herlyn cultured cells from 35 metastatic melanoma lesions using the same media as for human embryonic stem cells and succeeded in obtaining 16 cases in which cells formed spheres of similar morphology as embryoid bodies.

Melanoma marker expression

When Dr. Herlyn tested these melanoma spheres for antigenic markers, he found that they did not express the T cell markers CD3, CD4 or CD8.

However, a small population expressed the CD20 B cell marker and the pan-lymphocyte marker CD45. The cells also expressed the melanoma markers GD2, CSPG, Beta3, MCAM (Mel-CAM/CD146) and P70 NGFR, as well as E-cadherin, but not N-cadherin.

According to Dr. Herlyn, there is a possibility that there is a single stem cell in melanoma, perhaps a CD20 positive cell, a side population/drug resistance cell or a label-retaining cell.

He found that the CD20 positive cells from the melanoma spheres that grew stably over eight months:

Stem cell qualities in melanoma lesions

"We saw that the CD20 positive cells differentiated not only into pigmented melanoma cells, but we were able to induce their differentiation into mesenchymal cells, namely adipocytes, osteoblasts as well as chondrocytes.

"We could characterize an adipogenic lineage by staining with Oil Red, chondrogenic by staining for collagen type II and osteogenic by staining for alkaline phosphatase.

"The importance of this data is that it indicates that melanoma lesions contain a population with stem cell-like characteristics (CD20 positive cells), which are tumorigenic. However, expression of CD20 is not always stable and we are currently developing optimal growth conditions for stable 'high' expression of at least one percent to two percent," Dr. Herlyn tells Dermatology Times.

Dr. Herlyn says that these studies are challenging because the melanoma stem cell population comprises only 0.1 percent to one percent of the total population.

In exceptional cell lines, the stem cell population can reach up to 10 percent of the total population. This higher percentage can allow further studies on tumor dormancy, self-renewal, differentiation, growth and drug resistance.