SkinTE and the FDA's 361 Pathway

Doctors who perform wound treatments have limited options for skin repair. A new entrant into the wound treatment space is SkinTE, a product sold by PolarityTE. SkinTE has already been used to treat a first group of patients and has received early plaudits. The company describes SkinTE as a patient-specific, single application product created from a small piece of the patient’s own skin. As described in PolarityTE’s 2017 10K SEC filing, SkinTE is available for:

the repair, reconstruction, replacement and regeneration of skin (i.e., homologous uses) for patients who have suffered from wounds, burns or injuries that require skin coverage over both small and large areas of the body.
— from 2017 Form 10K

SkinTE is described as an impressive, all-encompassing product. The technology behind this product appears to be the company’s “TE” platform based on:

… our ability to create minimally polarized functional units, or MPFUs, which contain polarizing multi-cellular aggregates capable of expanding, proliferating and synthesizing those cells, materials, factors and/or systems we believe are necessary for integrative full-thickness three-dimensional tissue regeneration, not simply two-dimensional cell sheets. Instead of starting with artificial materials, synthetic factors and/or altered cell suspensions, our platform begins with the patient’s own (autologous) tissue and those components, appendages and substrates we believe are necessary for the development of an expandable and self-propagating complete system.
— From 2017 Form 10K

More specifically to SkinTE, the company describes the procedure and strategy:

With SkinTE, often within 24-48 hours of the initial skin harvest, our product is applied to the patient, whose body then provides a receptive environment and nutrients for controlled healing. By both preserving the tissue’s natural microenvironment and using the patient’s body as an intrinsic bioreactor—which means using the body’s own natural biological healing process rather than a manufactured or engineered environment to support the regenerative process—we believe a patient’s own tissue can be regenerated, along with its natural coloring and texture, layers and structure, hair and appendages.
— From 2017 Form 10K

This description is accompanied with a graphic overview of the SkinTE procedure that, admittedly, appears very simple to perform (right).

The company asserts that the TE platform has potential to transform tissue regeneration in multiple tissue types such as bone, muscle, fat, cartilage, nerves, and blood vessels in addition to skin. Given these strong claims, the technology behind SkinTE is certainly of interest. However, finding a detailed protocol for the technology and preparation behind SkinTE is not a trivial task.

Fortunately, Dr. Denver Lough, Chairman of the Board, President, Chief Executive Officer, and Chief Scientific Officer of PolarityTE has filed patent applications numbered 14/954,335 and 15/650,656 both titled “Methods for development and use of minimally polarized function cell micro-aggregate units in tissue applications using LGR4, LGR5 and LGR6 expressing epithelial stem cells.” This invention is largely summarized as:

[0014] The invention provides in a first embodiment a minimally polarized micro-aggregate multi-cellular composition including isolated living LGR expressing cells and a multi-dimensional support selected from the group consisting of scaffolding, collagen, matrix, particle, and fiber.
[0015] The invention provides in a further embodiment to the previous embodiment a minimally polarized micro-aggregate multi-cellular composition including isolated living LGR expressing cells and a multi-dimensional support selected from the group consisting of scaffolding, collagen, matrix, particle, and fiber where the LGR expressing cells are supplemented with growth factors and where the LGR expressing cells are selected from the group consisting of LGR4, LGR5 and LGR6.
[0016] The invention provides in a further embodiment to any of the previous embodiments a minimally polarized micro-aggregate multi-cellular composition including isolated living LGR expressing cells and a multi-dimensional support selected from the group consisting of scaffolding, collagen, matrix, particle, and fiber where the LGR expressing cells are supplemented with migratory/recruiting analytes and the LGR expressing cells being selected from the group consisting of LGR4, LGR5 and LGR6.

In effect, the invention appears to focus on a special population of LGR4, LGR5 and LGR6 expressing cells potentially supported by a matrix and supplemented with growth factors. Data behind these claims is contained in two papers:

Lough et al, 2013 Plast Reconstr Surg 132: 1159-1171 (link)
Lough et al, 2016 Plast Reconstr Surg 137: 495-507 (link)

This can be verified by side-to-side comparisons of sample figures in the above two papers and figures presented in the patent application. For example, in the first comparison below, Figures 12A and 12B from the patent application are the data published in Figure 6 of Lough et al (2013). In the second comparison, the data in Figures 5A-D of the patent application are the data published in Figure 5 of Lough et al (2016).

Patent Application 14/954,335 Figures 12A, B

Patent Application 14/954,335 Figures 5A-D

Lough et al (2013) Figure 6

Lough et al (2016) Figure 5

In Lough et al (2016), the isolation procedure for the cell population is described as generally following the protocol of Snippert et al (2010 Cell 143: 134-144), specifically maintained in:

Dulbecco’s Modified Eagle Medium/F12 (Sigma Chemical Co., St. Louis, Mo.), 10% fetal bovine serum (Atlas Biologicals, Fort Collins, Colo.), 10 ng/ml epidermal growth factor (Invitrogen, Waltham, Mass.), 20 ng/ml basic fibroblast growth factor (Invitrogen), 20 nM hydrocortisone (Sigma), 5 μg/ml insulin (Sigma), and 100 U/ml penicillin/streptomycin (Hyclone Laboratories, Logan, Utah) at 37°C in 5% carbon dioxide until passage 1.

The cells were validated for LGR6 mRNA expression, and further cultured as described prior to testing in preclinical wound models:

The scaffold/matrices were cut into 1-mm^2 pieces and transferred aseptically to 12 × 75-mm polystyrene tubes (BD Falcon, Franklin Lakes, N.J.) and 500 μl of the cells was added (1 × 10^6 total cells). The caps on the tubes were loosened to allow for gas exchange and were placed in a 37°C, 5% carbon dioxide incubator for 3 hours. The matrices were agitated every 15 minutes by gentle shaking of the tube to resuspend any cells that may have settled out. After 3 hours, the matrices were removed aseptically from the tubes and placed individually into wells of a 24-well plate containing growth media. After 24 hours, the matrices were examined under fluorescent microscopy for the adherence of the cells to the matrices. Culture medium was changed every 3 days.

In short, the procedure described by Lough et al (2016) calls for isolation of an LRG6 expressing epithelial cell population that is then cultured in a growth hormone containing medium and allowed to adhere to a matrix prior to placement in the murine wound model. As a result, the authors conclude:

In this article, we present a new method of providing skin to those wound beds that are intrinsically incapable of healing themselves.

FDA Registration Pathway

Typically, new treatments for use in the clinic must go through the FDA and be assessed for their safety and efficacy in clinical trials. However, pathways do exist to market products without safety or efficacy data in humans. One such pathway is to register with the FDA as a 361 HCT/P (Human Cells, Tissues, and Cellular And Tissue-Based Products) designation as described in Section 361 of the Public Health Service Act and 21 CFR Part 1271 (link to pdf). This is indeed the pathway used by PolarityTE. In the 2017 10K filing, PolarityTE describes SkinTE as a registered 361 HCT/P with the FDA:


This can further be confirmed via the FDA’s Human Cell and Tissue Establishment Registration portal wherein SkinTE is confirmed as an HCT/P under 21 CFR 1271.10 (screenshot right):

 

 

 

As described by the FDA, an HCT/P is regulated solely under section 361 of the PHS Act and 21 CFR Part 1271 if it meets all of the following criteria (21 CFR 1271.10(a)):

 1) The HCT/P is minimally manipulated;

 2) The HCT/P is intended for homologous use only, as reflected by the labeling, advertising, or other indications of the manufacturer’s objective intent;

 3) The manufacture of the HCT/P does not involve the combination of the cells or tissues with another article, except for water, crystalloids, or a sterilizing, preserving, or storage agent, provided that the addition of water, crystalloids, or the sterilizing, preserving, or storage agent     does not raise new clinical safety concerns with respect to the HCT/P; and

4) Either:

  1. The HCT/P does not have a systemic effect and is not dependent upon the metabolic activity of living cells for its primary function; or
  2. The HCT/P has a systemic effect or is dependent upon the metabolic activity of living cells for its primary function, and a) Is for autologous use; b) Is for allogeneic use in a first-degree or second-degree blood relative; or c) Is for reproductive use.

   
The descriptions in the patent application and published papers regarding PolarityTE’s technology raise the question of how SkinTE meets the first, second, and third criteria listed above.


Minimally Manipulated

Under the FDA guidance, skin is considered a structural tissue and serves to “physically support or serve as a barrier or conduit, or connect, cover, or cushion in the donor.” This refines the minimally manipulated criterion to ask if the processing of the tissue “alters an original relevant characteristic of the tissue relating to the tissue’s utility for reconstruction, repair, or replacement as structural tissue.”

As noted in a previous PolarityTE presentation and shown in their overview of the procedure, the SkinTE product starts as a piece of excised, full thickness skin and is then processed to yield an applied paste. This processing would appear to exceed the description of minimally manipulated, and an analogous method is specifically described as such in the FDA guidance under Example 10-4b in 21 CFR 1271.10 (right; pdf link)

Further to this point, Example 11-3 in the FDA guidance makes further clarification (right). As described in PolarityTE’s presentations and in the relevant literature, the procedure behind SkinTE no longer allows the product to maintain the “original relevant characteristics of skin related to its utility as a protective covering.” It is no longer a protective covering but rather a paste due to the processing, nor does the product retain its “dense, strong, and flexible connective tissue layer.”

As described in PolarityTE’s presentations and in the relevant literature, the procedure behind SkinTE no longer allows the product to maintain the “original relevant characteristics of skin related to its utility as a protective covering.” It is no longer a protective covering but rather a paste due to the processing, nor does the product retain its “dense, strong, and flexible connective tissue layer.”


Homologous Use

The FDA also mandates that products registered under section 361 meet the definition of homologous use. This generally requires the product to adequately perform its same basic function:

Under this guideline, SkinTE would have to be a product wherein its “basic” function to regenerate full thickness skin in the recipient is obvious and commonly understood, and should not require any laboratory, preclinical or clinical studies. This does not apply to the SkinTE product. In effect, if the biological function of SkinTE to regenerate full thickness skin (footnote 1) was well understood and did not require any preclinical or clinical examination, scientific papers attempting to explain and demonstrate this effect would be unnecessary. In effect, in the publication by Lough et al (2016) the authors clearly acknowledge that the group “seeks to determine” whether the LGR6 cell population isolated by fluorescent-activated cell sorting is effective for translational use (caption right). If the function of SkinTE were “basic” as described under FDA guidelines, such experiments to clarify the function of this cell population would be unnecessary.


As it stands, PolarityTE’s description that SkinTE “regenerates full-thickness hair-bearing skin” is a claim quite beyond a basic function under homologous use but rather a putatively significant treatment advancement in need of clinical validation.


Combination of Another Article

The FDA further notes that products registered under 361 may not involve “the combination of the cells or tissues with another article, except for water, crystalloids, or a sterilizing, preserving, or storage agent, provided that the addition of water, crystalloids, or the sterilizing, preserving, or storage agent does not raise new clinical safety concerns with respect to the HCT/P.” Under this guidance, products are not allowed to be mixed with a carrier during manufacture, nor are they allowed to be treated with supplements such as growth hormones during manufacture.

As shown below, both previously referenced publications by Lough in 2013 and 2016 clearly note that the fundamental research behind the PolarityTE patents involves culturing with fetal bovine serum (which contains a collection of growth factors) as well as endothelial growth factor and basic fibroblast growth factor. The conditions also call for the addition of insulin and hydrocortisone, two additional factors that would lie outside of the FDA’s guidance.

Lough et al (2013)

Lough et al (2016)

Lough et al (2016)

It’s important to note that these additives  are not limited to growth factors, nor is citation of their use confined to the published literature. For example, Lough et al (2016; caption right) as well as the cited patent filing (excerpt below) mention the use of a scaffold to support the cells in addition to the aforementioned growth factors.

 

In fact, relevant excerpts from a PolarityTE patent filing run counter to the FDA’s guidance:

  • [0014] The invention provides in a first embodiment a minimally polarized micro-aggregate multi-cellular composition including isolated living LGR expressing cells and a multi-dimensional support selected from the group consisting of scaffolding, collagen, matrix, particle, and fiber.
  • [0015] The invention provides in a further embodiment to the previous embodiment a minimally polarized micro-aggregate multi-cellular composition including isolated living LGR expressing cells and a multi-dimensional support selected from the group consisting of scaffolding, collagen, matrix, particle, and fiber where the LGR expressing cells are supplemented with growth factors and where the LGR expressing cells are selected from the group consisting of LGR4, LGR5 and LGR6.
  • [0016] The invention provides in a further embodiment to any of the previous embodiments a minimally polarized micro-aggregate multi-cellular composition including isolated living LGR expressing cells and a multi-dimensional support selected from the group consisting of scaffolding, collagen, matrix, particle, and fiber where the LGR expressing cells are supplemented with migratory/recruiting analytes and the LGR expressing cells being selected from the group consisting of LGR4, LGR5 and LGR6.
  • [0017] The invention provides in a further embodiment to any of the previous embodiments a minimally polarized micro-aggregate multi-cellular composition including isolated living LGR expressing cells and a multi-dimensional support selected from the group consisting of scaffolding, collagen, matrix, particle, and fiber where the LGR expressing cells are supplemented with LGR specific binding elements selected from the group consisting of ligand families, R-spondin, EDGF, PDGF, Wnt, VEGF, and antimicrobial peptides and where the LGR expressing cells are selected from the group consisting of LGR4, LGR5 and LGR6.

As clearly described in the bolded segments, the patent filing by PolarityTE consists of claims which include combinations with other components such as scaffolding and growth factor receptor ligands. These additives are not allowed for products registered under the 361 pathway. It remains possible that PolarityTE intentionally removed both the scaffold and growth factors from the marketed version of SkinTE. At a recent investor conference, the company mentions the use of “crystalloids” as a carrier rather than scaffolds. But if they have removed both scaffolds and growth factors, does the product used to treat patients meet the company’s own efficacy claims as published in the scientific literature and related patent filings? What is the final SkinTE product?

 

In sum, PolarityTE’s registration of SkinTE as a 361 HCT/P has allowed the company to rapidly bring their product to market for sale and use in the clinical setting. However, the FDA guidelines regarding the standards for a 361 HCT/P designation and the SkinTE product as described in whole or in part through PolarityTE presentations, patent filings, and scientific publications authored by the CEO raises questions. Are the production methods behind SkinTE and the final product offered by PolarityTE compliant with the FDA’s 361 standards? Have the scaffolds and growth factors described in the scientific publications and patent filings been omitted from SkinTE? Absent appropriate growth factors and culturing conditions, how do the cells in the excised skin maintain their differentiated state and pattern of LGR receptor expression? Are specific LGR receptor expressing cells isolated via fluorescent-activated cell sorting for use in SkinTE? Has the FDA effectively examined products like SkinTE to assure the public that the standards outlined by 21 CFR 1271 are met and adhered to? In this specific case, PolarityTE is marketing a product that has not been tested in randomized controlled clinical trials. Whether this treatment choice meets the FDA guidelines under section 361, and whether this choice is clinically safe and efficacious are questions in the public’s interest that should be further examined.

 

 


Footnote 1: PolarityTE makes a clear claim that “SkinTE Regenerates Full-Thickness Hair-Bearing Skin.” Screenshot below taken from the PolarityTE website.