Is Promoting a 361 HCT/P for Its Clinical Effects Compatible with a Homologous Intended Use?August 16, 2019
The Food and Drug Administration (FDA) regulates human cell, tissue, and cellular and tissue-based products, or HCT/Ps, under a unique regulatory regime set forth in 21 C.F.R. Part 1271 (Part 1271). An HCT/P that meets certain requirements is eligible for regulation as a “361 HCT/P.” This term is a shorthand way to designate a product that is regulated solely under section 361 of the Public Health Service Act (PHSA) and Part 1271, both of which are aimed at preventing the transmission of communicable disease. Such a product is not subject to additional regulation by FDA as a device, drug, or biologic under the Food, Drug, and Cosmetic Act (FDCA).
This discussion will focus on the requirement that a 361 HCT/P be labeled and advertised only for homologous use. We will look first at the basic regulatory definition and guidance. Then, we will ask the specific question of whether advertising the clinical effects (performance characteristics) of an HCT/P 361 is compatible with meeting the homologous use requirement.
The regulation defines homologous use to mean “the repair, reconstruction, replacement, or supplementation of a recipient’s cells or tissues with an HCT/P that performs the same basic function or functions in the recipient as in the donor.” In determining whether a product is “intended” for homologous use, FDA considers only “the labeling, advertising, or other indications of the manufacturer’s objective intent.” 21 C.F.R. § 1271.10(a)(2).
In the preamble to the regulation, FDA clarified that homologous use does not require use of tissue in its native anatomic location: “a use of a structural tissue may be homologous even when it does not occur in the same location as it occurred in the donor. For example, the use of bone for repair, replacement, or reconstruction anywhere in the skeleton of the recipient (including the vertebral column) would be considered homologous use.” 66 Fed. Reg. 5447, 5457 (Jan. 19, 2001).
In addition, as a general matter, FDA indicated that the homologous use test merely would be a coarse screen for unproven uses: “We intend to interpret ‘nonhomologous’ narrowly. Examples of uses that would be considered nonhomologous include: The use of dermis as a replacement for dura mater . . . and the use of cartilage in the bladder.” Id. And: “For example, promotion of an HCT/P for an unproven therapeutic use, such as curing cancer, would clearly make it inappropriate to regulate the HCT/P [as a 361 HCT/P].” Id. Instead, an HCT/P intended for an unproven therapeutic use would be regulated under both Part 1271 (to prevent disease transmission) and the Federal Food, Drug, and Cosmetic Act as a drug, device or biologic. These preamble statements are legally entitled to great weight in interpreting and applying the regulation.
In a recent guidance, FDA elaborated on the concept of the “same basic function or functions” of an HCT/P:
The basic function of an HCT/P is what it does from a biological/physiological point of view, or is capable of doing when in its native state. By “basic” we mean the function or functions that are commonly attributed to the HCT/P as it exists in the donor. Basic functions are well understood; it should not be necessary to perform laboratory, pre-clinical, or clinical studies to demonstrate a basic function or functions for the purpose of applying the HCT/P regulatory framework.
FDA, Guidance for Industry, Regulatory Considerations for Human Cells, Tissues, and Cellular and Tissue-Based Products: Minimal Manipulation and Homologous Use, 16 (Dec. 2017) (footnotes omitted) (2017 Guidance).
FDA adds: “Also, clinical effects of the HCT/P in the recipient that are not basic function or functions of the HCT/P in the donor would generally not be considered basic function or functions of the HCT/P for the purpose of applying the definition of homologous use.” Id. at 16‑17.
As an example, FDA cites different uses of amniotic membrane. The basic functions of amniotic membrane “include serving as a selective barrier for the movement of nutrients between the external and in utero environment, protecting the fetus from the surrounding maternal environment, and serving as a covering to enclose the fetus and retain fluid in utero.” Id. at 18. Accordingly, FDA concludes that when “an amniotic membrane product is used for wound healing and/or to reduce scarring and inflammation,” this intended use “is not homologous use because wound healing and reduction of scarring and inflammation are not basic functions of amniotic membrane.” Id. at 18. In contrast, amniotic fluid as a covering is homologous. For instance:
amniotic membrane product is applied to the surface of the eye to cover or offer protection from the surrounding environment in ocular repair and reconstruction procedures. This is homologous use because serving as a covering and offering protection from the surrounding environment are basic functions of amniotic membrane. [Id.]
This sounds like a fair distinction – an amniotic membrane intended as a wound cover in the recipient is essentially performing its native covering function. On the other hand, the same amniotic membrane when “intended” to reduce scarring or inflammation is likely not performing the same function as it did in utero.
But what exactly does it mean for the amniotic membrane to be “intended” to reduce scarring or inflammation? Is it not possible for an amniotic membrane to be intended as wound cover (a homologous use) and, as such, have the clinical effect of reducing scarring and inflammation compared to other wound covers?
There are at least two ways one could establish this proposition. One way is to claim that the biological/physiological composition of amniotic tissue (e.g., presence of cytokines) is such that it is likely to have anti‑scarring and anti‑inflammatory effects in a skin wound. This approach may be what FDA implicitly meant to convey in the example above. It is not homologous because, says FDA, preventing scars or inflammation is not a well understood biological/physiological function of native amniotic membrane. On this view, it is an unproven functional claim.
A second way to establish the proposition is to conduct a well‑controlled randomized clinical trial to substantiate it. Imagine a clinical trial showing that an amniotic membrane used as a skin wound cover provides a 10% statistically significant reduction in scarring as compared to a synthetic wound cover.
The question is whether presenting this study in labeling or advertising would generate a new, non‑homologous “intended use.” This question has important ramifications. Increasingly, manufacturers seek to study 361 HCT/Ps and quantify their clinical effects. These studies help advance the science of medicine and benefit patients. Such studies, however, may never be undertaken if the results cannot be disseminated without exposing a 361 HCT/P to regulation as a drug, device or biologic under the FDCA or PHSA.
As discussed above, the concept of homologous use does not derive from the treatment intent of an HCT/P. Rather, it is based upon the biological or physiological functioning of an HCT/P. For instance, if an HCT/P is being used to perform a covering function, the definition of homologous use is satisfied, regardless of where the covering is applied. That is why FDA agrees that homologous use is not dependent upon an HCT/P being used in the same location as the native tissue. It also why FDA correctly asserts (as quoted above) that clinical effects in a recipient are not to be considered in determining homologous use.
This principle logically cut both ways. If clinical effects in the recipient cannot contribute to a determination that an intended use is homologous, then providing information about such clinical effects cannot contribute to a determination that an intended use is non‑homologous. The homologous use test is not a general inquiry into the objectively intended therapeutic effects of an HCT/P. Rather, it is a limited inquiry into the biological or physiological functioning that is objectively claimed for the HCT/P. If this limited intent meets the requirement of homologous use, the inquiry should be over. Claims as to clinical effects, of course, require adequate substantiation and must be presented in a truthful and non‑misleading manner. But they are not properly part of a homologous use analysis.
To return to the amniotic membrane example, a white paper describing the results of a study comparing the two types of wound coverings (amniotic membrane and synthetic) is not relevant to whether the amniotic membrane covering is intended for homologous use. That is because the study results are based upon observed clinical effects in the recipient; they do not address the putative biological or physiological function involved, which is the basis of a homologous intended use determination. On the other hand, if the white paper also discusses the role of native cytokines in the amniotic membrane in inhibiting scar formation as an explanation for the study results, that would properly be considered in determining whether the intended use is homologous. If FDA finds that native cytokines in the donor are not commonly understood to prevent scarring, then it potentially could find that the amniotic membrane has a non‑homologous intended use.
None of this is to say that FDA has accepted this approach. Frankly, the discussion around homologous use has not proceeded in these terms. Yet, the framing here seems implicit in the logic of FDA’s regulatory definitions and guidance. It would certainly be helpful to have more explicit guidance from FDA, because this confusion around homologous use may inhibit sponsors from initiating valuable clinical studies of 361 HCT/Ps. Any clarity FDA could provide around its position on this issue would be very welcome.