Navigating Market Authorization: The Path Holoclar Took to Become the First Stem Cell Product Approved in the European Union

Abstract

Gene therapy, cell therapy, and tissue engineering have the potential to revolutionize the treatment of disease and injury. Attaining marketing authorization for such advanced therapy medicinal products (ATMPs) requires a rigorous scientific evaluation by the European Medicines Agency-authorization is only granted if the product can fulfil stringent requirements for quality, safety, and efficacy. However, many ATMPs are being provided to patients under alternative means, such as "hospital exemption" schemes. Holoclar (ex vivo expanded autologous human corneal epithelial cells containing stem cells), a novel treatment for eye burns, is one of the few ATMPs to have been granted marketing authorization and is the first containing stem cells. This review highlights the differences in standards between an authorized and unauthorized medicinal product, and specifically discusses how the manufacture of Holoclar had to be updated to achieve authorization. The result is that patients will have access to a therapy that is manufactured to high commercial standards, and is supported by robust clinical safety and efficacy data. Stem Cells Translational Medicine 2018;7:146-154.

Keywords: Adult stem cells; Autologous stem cell transplantation; Cellular therapy; Stem/progenitor cell; Tissue regeneration; Tissue-specific stem cells.

Figure 1

The role of clonogenic keratinocytes in generation and renewal of the corneal epithelium. (A): The holoclone differentiation process from highly proliferative self‐renewing holoclones to transiently amplifying cells (meroclones and paraclones). A confocal microscopy image of holoclone stem cells is on the left showing high expression of ΔNp63α, an isoform of the p63 transcription factor. Due to this characteristic, these cells are also referred to as p63bright cells. (B): Stem cells from (A) in their ocular context. Holoclones, meroclones, and paraclones are found in the basal layer of the limbus with holoclones having the least abundance (10%–15%). The basal layer of the cornea is populated by meroclones and paraclones at the periphery, and only paraclones in the central cornea. All suprabasal layers of the limbus and corneal surface contain terminally differentiated cells which have no capacity for self‐renewal or proliferation (shown in gray). The conjunctival surface is composed of epithelial cells (yellow) and a low proportion of goblet cells (magenta) that are interspersed throughout.

Figure 2

Key steps in the manufacture of Holoclar. The figure shows a simplified flow chart of the manufacture of Holoclar. The term “drug Substance” is used to denote the cell suspension of epithelial cells obtained after thawing from the frozen primary culture, and which is ready to be plated on the fibrin matrix, which will yield the final material for transplant (the “drug product”).

Figure 3

Comparison of human fibroblast or mouse 3T3‐J2 cells as feeder layers to support human keratinocyte proliferation. Both types of feeder layer cells were seeded at equal density (∼700,000 cells per plate) in duplicate after lethal irradiation. Equal numbers of human keratinocytes (1,000 cells) were then added to each plate. Following 12 days of keratinocyte culturing, plates were stained and the colonies counted. Whole plate staining allowed macroscopic comparison of total keratinocyte proliferation between the two conditions. After 6 days in culture, the parallel mass cultures were labeled and analyzed in parallel by fluorescent microscopy to determine the percentage of p63^bright cells (holoclones).