2005 Donor Eligibility Requirements: Unintended Consequences for Stem Cell Development

Several human embryonic stem cell (hESC)-derived cell therapeutics have entered clinical testing or are in various stages of preclinical development. Ambiguity in the guidelines and the redundant testing requirements have unintentionally created a burdensome regulatory paradigm. A simple solution is proposed to address FDA safety concerns, eliminate regulatory uncertainty and risk, and provide flexibility for the FDA in the regulation of hESC-derived cell therapies.

Summary

Several human embryonic stem cell (hESC)-derived cell therapeutics have entered clinical testing and more are in various stages of preclinical development. The U.S. Food and Drug Administration (FDA) regulates these products under existing regulations and has stated that these products do not constitute a new class of biologic. However, as human tissue, hESCs are subject to regulations that were developed before hESCs were first described. The regulations have not been revised since 2005, well before the first hESC-derived product entered clinical studies. The current regulations require donors of hESCs to be tested in the same manner as donors of tissues intended for transplantation. However, because hESC-derived cell products are more than minimally manipulated, they are also subject to the same end-of-production release testing as most other biologic agents. In effect, this makes hESC products subject to redundant testing. No other biologic is subject to a similar testing requirement. Furthermore, the regulations that require donor testing are specifically applicable to hESC cells harvested from donors after a date in 2005. It is unclear which regulations cover hESCs harvested before 2005. Ambiguity in the guidelines and redundant testing requirements have unintentionally created a burdensome regulatory paradigm for these products and reluctance on the part of developers to invest in these promising therapeutics. We propose a simple solution that would address FDA safety concerns, eliminate regulatory uncertainty and risk, and provide flexibility for the FDA in the regulation of hESC-derived cell therapies.

Significance

Regulatory ambiguity concerning donor eligibility screening and testing requirements for human embryonic stem cell lines, in particular those lines created before 2005, are causing significant concern for drug developers. Technically, most of these lines fail to meet eligibility under U.S. Food and Drug Administration (FDA) rules for product licensure, and many developers are unaware that FDA approval to begin trials under an exemption is not an assurance that the FDA will grant licensure of the product. This Perspective outlines the ambiguity and the problem it has caused and proposes a workable solution. The intent is to generate stakeholder and FDA discussion on this issue.

Introduction

The U.S. Food and Drug Administration (FDA) regulates biologics under the authority of the Public Health Service (PHS) Act and Food, Drug, and Cosmetic Act under regulations outlined in the Code of Federal Regulations (CFR). These regulations are often supplemented with nonbinding guidance documents published by the FDA that assist the drug development community in understanding how reviewers within the FDA will interpret and apply the various regulations to Investigational New Drug (IND) and Biologic License Application submissions. Drug developers around the world depend on these documents to guide development of preclinical and clinical plans that have a reasonable likelihood of leading to a licensable product in the United States. Inadequate or ambiguous regulations create uncertainty in the development of new product types that can result in reluctance on the part of developers to move promising new therapies into the clinic. The FDA periodically amends the existing CFR or issues new regulations to (a) address ambiguities, (b) address new technologies that render older technologies inadequate, or (c) address safety concerns that arise after clinical experience with new product types. In addition, regulations are amended when it is discovered that certain product types might not have been adequately contemplated, if at all, during the drafting of existing regulations. Human embryonic stem cell (hESC)-derived products are one such new product type that have been the subject of much discussion among regulators and drug developers [1, 2]. Reports of promising results in preclinical models with hESC products underscore their considerable promise as novel therapeutics for a number of indications with unmet clinical need, such as Parkinson’s disease, stroke, heart disease, spinal cord injury, macular degeneration, and amyotrophic lateral sclerosis [3–7]. However, regulations applicable to all human tissue-derived products were established years before hESC-derived products were envisioned. This has inadvertently created ambiguity in the regulatory pathways for these products, which has resulted in uncertainty for drug developers. With an unclear path to approval in the United States, this ambiguity increases the perceived risk for investors and could be causing unnecessary delays in the field’s ability to generate the capital required to move these products forward. A summary of the current regulatory framework for hESC products, a historical perspective of the evolving regulations and guidance documents, their inadvertent negative impact on the field, and a proposed solution that will allow for a predictable regulatory path that accommodates advances in product testing for these products will be discussed.

FDA Regulations

The FDA’s Center for Biologics Evaluation and Research regulates human cells, tissues, and cellular- and tissue-based products (HCT/Ps) under Section 361 of the PHS Act, depending on their intended medical use. HCT/Ps include transplantable tissues and cells and expanded and manipulated cell products derived from human cells or tissues. Current HCT/Ps regulations evolved from regulations originally issued in 1993 as an interim rule to address the immediate need to protect tissue transplant patients from virus infection through tissues obtained from HIV-, hepatitis B virus-, and hepatitis C virus-infected donors. With some clarifications and modifications, the interim rules were made final in 1997 as 21 CFR Part 1270 (“1270 rules”) [8]. A guidance document pertaining to the new rules was published later that same year [9].

The derivation of hESCs was announced in 1998, 1 year after the 1270 rules became final [10]. The scientific and medical community immediately understood the potential value of these cells for regenerative medicine applications. The rapid development of hESC technologies resulted in the initiation of the first clinical trial using hESC-derived cells in 2010, some 12 years after the 1270 regulations were finalized. Given this timing, the generation of the 21 CFR Part 1270 rules could not have contemplated the development of such unique cell therapies.

Although the 1270 rules adequately covered transplantable human tissues in use at the time, novel transplantable human tissue and cell products began to emerge that were not specifically or clearly covered by the regulations. The FDA responded by issuing new regulations in 2001, as an expansion of the scope of the 1270 rules, with an expanded list of infectious agents of concern, and with increased screening and testing requirements: 21 CFR Part 1271: Human Cells, Tissues, and Cellular and Tissue-based Products (“1271 rules”) [11]. The new rules were further modified, effective May 25, 2005, to include “Subpart C,” outlining specific donor eligibility requirements [12]. This later revision has become known in the industry as the “2005 donor eligibility rules.” A corresponding guidance document was published in August 2007 [13]. Importantly, in January 2001, just 3 months before the effective date of the first sections of the new 1271 rules, the FDA outlined their intention to revoke the original 1270 rules and make all human cells, tissues, and cell and tissue products subject to the new 1271 rules [10]. However, the FDA never revoked the 1270 rules, and they remain effective today. Also, the 1271 rules were amended by the enactment of the 2005 donor eligibility rules to be effective for cells and tissues recovered after May 25, 2005. However, no guidance is provided in the 1271 rules for hESC-derived products made from human cells or tissues derived or recovered before May 25, 2005. Because hESC-derived products could not have been contemplated in the earlier 1270 rules, and many of the hESC lines currently in development were isolated well before May 25, 2005, it is not clear which regulations, particularly those regarding donor eligibility and screening requirements, should apply to products derived from these lines.

In practice, the FDA regulates HCT/Ps using a tiered, risk-based approach, and these products are defined in 21 CFR 1271 as falling into 2 distinct categories that are subject to different regulatory and registration processes. Cells and tissues intended to be transplanted directly following donor harvest that meet specific criteria for transplantable tissues as defined in 21 CFR 1271 are regulated solely by Section 361 of the PHS Act. These products are commonly referred to as “361 products,” and because they are considered to have lower risk are not subject to premarket review through an IND application. Examples of 361 products include skin, ligaments, pericardium, ocular tissues, and tissue intended for reproductive use, such as embryos and semen. Products that do not meet the criteria for regulation under 361 are regulated as biologic drugs under Section 351 of the PHS Act and are referred to as “351 products.” As described in the following paragraphs, these products are considered to have more risk and require investigation under an IND and compliance with Current Good Manufacturing Practices and end-of-production testing requirements. Examples of 351 products include cultured cartilage cells, lymphocyte immune therapy, gene therapy products, unrelated donor lymphocytes for infusion, and most stem cell therapies.

There are several important distinctions between 361 and 351 products, including that 361 products are not manipulated and are intended to provide functions that reflect their inherent biologic characteristics. Although all HCT/Ps carry a risk of transmission of infectious agents, limitations in the amount of available material or the time between harvest and transplantation of 361 products restricts our ability to test these human donor-derived tissues. Accordingly, the regulations for these transplant products emphasize screening and testing of donors rather than the products themselves. Importantly, compliance with donor screening and eligibility requirements requires that testing must be performed within a short period after the cell or tissue has been recovered from the donor. However, the FDA frequently grants exemptions to the donor eligibility and screening rules for 361 products in cases of medical need for which it is not possible to complete donor screening and other tissue is not available. In contrast, one of the defining characteristics of 351 products is that they are more than minimally manipulated and typically use manufacturing processes that include extended cell culture and cryopreservation. Therefore, often sufficient material and adequate time for testing of the final product are available before administration, although exceptions exist to this generalization, particularly with novel product types for which manufacturing and cryopreservation processes have not been established. The 351 products are typically subject to the same extensive testing for a broad array of infectious agents after their manufacture as are most other biologic products such as recombinant proteins, gene therapy cell products, and viral vectors. Unlike the narrow time window permitted for screening donors of 361 products, 351 products, which might be manufactured years after acquisition of the starting donor cell or tissue, can be tested at any time before clinical use, facilitating the use of the most contemporary assay technologies to assess for the most current infectious agents of concern to public safety.

By regulating all HCT/Ps initially through 21 CFR Part 1271 and then through either Section 351 or 361 of the PHS Act, the FDA established a unified registration and listing program for all cell and tissue products with a tiered, risk-based approach to their regulation. In principle, HCT/Ps that are defined as 351 products would be subject to biologic drug regulations and testing of final products, and 361 products would depend on donor screening and eligibility determination and be exempt from extensive final product testing. In practice, however, this has not been how the regulations have been constructed or interpreted. The 351 HCT/Ps, notably hESC-derived cell products, are currently subject to donor screening as human-derived tissue, as well as final product testing as biologics—effectively for the same infectious agents. An inadvertent effect of the current regulations is that expanded, banked, and cryopreserved hESC-derived products that could be fully tested for relevant infectious agents and shown to be safe in preclinical testing would not be eligible for licensure if any aspect of donor eligibility screening and testing had not been performed. Although FDA has granted exemptions for hESC products that do not meet 361 donor eligibility requirements to enter clinical trials, no assurance exists that such exemptions will be granted for licensure of these products or for additional hESC-derived products for early clinical trials, making investments of time and resources into the development of these promising therapeutics risky.

Nearly a decade after the issuance of the 2005 donor eligibility rules, the 1271 rules remain in effect largely unmodified and remain applicable to all HCT/Ps derived or recovered after May 25, 2005. No further FDA guidance has been provided on the regulation of hESC-derived products derived or recovered before May 25, 2005. However, regardless of the prevailing regulation, the donor screening and testing requirements are intended to minimize the risk of transmission of a range of infectious agents after transplantation of 361 products for which testing of the final products is impractical or not possible. The purpose of donor eligibility screening is to identify and exclude potential donors who are in, or are closely associated with persons in, high-risk groups or who engage in high-risk lifestyles. In addition, eligibility screening is intended to identify and exclude prospective donors who might have been exposed to transmissible spongiform encephalopathy (TSE) or bovine spongiform encephalopathy (BSE). Currently, all but one of the pathogens listed in HCT/P regulations, TSE/BSE, can be directly tested for in final products using FDA accepted tests. Furthermore, although yet to be validated or accepted by the FDA, tests for TSE are in development [14, 15]. However, the current regulations provide no exemption to the donor testing and screening requirements for hESC-derived 351 products that could be adequately tested at end-of-manufacture as biologics before administration to patients, and no allowance is made for the FDA to assess the adequacy of developing analytical technology.

Compliance with the donor eligibility requirements of the 2005 rules for hESC-derived products is further complicated by the reality that many existing lines were acquired from tissue donated well before the creation of the 1271 rules. Efforts to meet the prescribed donor eligibility and screening requirements are confounded by the requirement for the testing to be performed within 7–30 days of tissue recovery in a Clinical Laboratory Improvement Amendments (CLIA)-certified laboratory or equivalent, using FDA-approved tests. The logistics of generating hESC lines are often not compatible with these requirements. For instance, generation of hESC lines uses human embryos that are created in in vitro fertilization (IVF) clinics. The IVF process includes the acquisition of gametes, fertilization, culture of the embryo, and implantation of selected embryos. The remaining embryos are then either discarded or cryopreserved. After the patients have completed the IVF process, the patient’s preference for dispensation of the remaining frozen embryos is determined. This decision is usually separated in time from the IVF process, usually for as long as 5 years. The current regulations do not require donor testing for gamete donors from sexually intimate couples; thus, in many cases, by the time a couple chooses to donate their embryos to research it is too late to perform the required donor testing, even in cases in which the couple is willing to be tested. Compliance with the 2005 rules is not possible in these cases. An additional complicating factor is the use of third-party donation gametes. In such cases, the oocyte or sperm are anonymously donated, and the “ownership” of the embryo is transferred to the couple. Once again, it is impossible to comply with the donor testing and screening requirements. In addition, when using anonymized third-party gamete donations, it is not possible to retroactively acquire informed consent for the development and commercialization of hESC therapies.

Despite the ambiguities and seemingly redundant requirements imposed on hESC-derived 351 products, donor eligibility screening and testing of prospective donors, through the 1270 and 1271 rules, were well aligned with the risks and requirements of transplantable 361 tissue and cell products established or in development at the time the regulations were established. These regulations have certainly helped to protect the public from transmissible infectious agents in transplantable donor cells and tissues. However, because the 1271 rules elaborated on the 1270 rules to address regulatory inadequacies and ambiguities that became apparent owing to the emergence of human donor-derived products in the mid- to late 1990s, it has become clear after nearly a decade since the issuance of 1271 that additional opportunities exist for continued evolution of the regulations to accommodate hESC-derived products. Notably, three important issues have emerged in the development of these new therapies.

The first issue is that it is unclear which regulations, particularly those addressing donor screening and testing, specifically cover HCT/Ps isolated and recovered before May 25, 2005. The 1271 rules clearly state that they are applicable specifically to cells and tissues procured on or after the 2005 date. The document makes no reference to the applicable regulations for cells and tissues recovered before the 2005 date. In addition, an apparent objective of the 1271 rules was to expand on the very limited scope of “tissues” of the 1270 rules by specifically adding “cells and cell and tissue-derived products” to the limited scope of “tissues” described in the 1270 rules. That cells and cell- and tissue-derived products are not defined or described in the 1270 rules could lead to the interpretation that hESC-derived products obtained and recovered before May 25, 2005 are not covered under either regulation.

The lack of clear regulation or guidance concerning the applicable regulations for pre-May 25, 2005 cell- and tissue-derived products creates a second important issue. The ambiguity creates considerable uncertainty for drug developers in predicting the regulatory process for these products as they move toward licensure. For HCT/Ps created before the advent of the 1271 rules, and in particular the Subpart C donor eligibility criteria, it is likely that few, if any, products derived from these early lines could meet the 2005 criteria that determine suitability of these products for licensure. One might assume that because no specific regulations cover these cells, they might be regulated under a “grandfather clause” and subject only to the regulations in place at the time of their procurement and not subject to the 2005 criteria. However, although it would effectively eliminate the current regulatory ambiguity, grandfathering pre-2005 hESC lines under the 1270 rules intended for transplantable tissues would result in reduced requirements for testing, and eliminate the testing requirement for important infectious agents listed in the 1271 rules. In contrast, establishing these products as subject to the 1271 rules, while also eliminating the ambiguity, would make it very unlikely that promising products based on hESC lines procured and created before 2005 would be licensable, regardless of their clinical efficacy. Although clarifying the relevant regulations for pre-2005 hESC-derived products would eliminate some ambiguity, it would not address the general problems in establishing donor eligibility for hESC lines derived from embryos generated in IVF clinics.

The third issue involves the lack of distinction in the regulations between (a) minimally manipulated transplantation tissues for which the donor material or time to test for human infectious agents is often inadequate, and (b) extensively cultured, expanded, and cryopreserved products, such as hESC-derived products, for which direct product testing is both practical and reliable. For directly transplanted donor-derived cells and tissues, or for cases in which there is insufficient material to directly test products before infusion, such as those contemplated in the 1270 rules, focusing on the testing and screening donors makes sense and might be the only practical approach to minimizing the spread of infectious agents. However, tests for all the infectious agents listed as being of concern in either the 1270 or 1271 rules are either established as validated assays or are, in the case of TSE/BSE, in development [14, 15]. Cultured and cryopreserved cells and tissue-derived products are readily testable using methodologies otherwise accepted by the FDA for other 351 biologic products. Furthermore, the current requirement for testing by CLIA-approved laboratories or equivalent, which are typically oriented toward the testing of clinical samples and not biologic products, ignores the suitability of Good Laboratory Practices-compliant testing that laboratories commonly used for product characterization and release testing of biologics. The FDA currently addresses the ambiguity concerning the regulations for pre-2005 HCT/Ps that were not tested according to the 2005 rules by granting limited exemptions. The FDA will consider the granting of an exemption based on the attributes of the cell product, the disease application, and the specific stage of clinical development. However, the granting of an exemption for an initial clinical trial does not ensure that the FDA will grant an exemption for later phase trials or, more importantly, product licensure, further emphasizing the ambiguity and risk associated with investing in these types of products. The lack of clarity in the regulations and the ambiguity concerning the granting of exemptions could be imposing an unnecessary burden and financial risk on drug developers.

Several possible steps could be taken by the FDA to address these concerns and eliminate the ambiguity concerning the regulation of promising hESCs and other HCT/Ps that are either not clearly covered under the 1270 or 1271 rules or for which compliance with the 2005 donor eligibility rules is impractical or impossible. The first step is to clarify the governing regulations for HCT/Ps, in particular, hESC-based products derived before May 25, 2005. The second step is to distinguish between minimally manipulated products for which donor testing and screening is the most, or only, practical method of ensuring safety and products for which final product testing using existing or developing methodologies is practical. With this step, the intent of the existing regulations to protect patients against the transmission of communicable diseases is maintained and the development of these much-needed therapies is expedited.

Conclusion

For the purposes of patient safety and elimination of the existing regulatory ambiguity and to foster the development of the promising HCT/Ps alluded to in the present report, the FDA could amend the 1271 rules in two ways. First, the FDA could clarify that all HCT/Ps not specifically covered under the 1270 rules are subject to the 1271 rules. Second, the FDA could amend the 1271 rules to include an exclusion for HCT/Ps that can be adequately tested for all relevant adventitious agents by conventional biologic product methods and laboratories. These two steps would permit the FDA to regulate hESC-derived products equivalently using a tiered, risk-based approach as originally intended and would clarify the regulatory process for these cell products, in terms of both clinical entry and for licensure. This would have a profound effect on the ability of HCT/P developers to raise the necessary capital to move promising therapeutics into, and through, clinical testing.

Author Contributions

L.A.C., M.K.C.: conception and design, manuscript writing, final approval of manuscript.

Disclosure of Potential Conflicts of Interest

The authors indicated no potential conflicts of interest.