361 vs 351: Understanding Stem Cell Regulation and Cell Therapy Rules

Two numbers come up again and again in U.S. stem cell discussions: 361 and 351. They sound like shorthand for a technical argument, and in many ways they are. But they point to a real question with real consequences: when is a human cell or tissue product regulated mainly to prevent the spread of communicable disease, and when is it regulated more like a drug or biologic that needs premarket review?

That question sits at the center of many debates about regenerative medicine, stem cell clinics, tissue products, and cell therapy development. It also explains why simple claims like “it is your own cells” or “it is just injected differently” rarely answer the regulatory question by themselves.

This article is informational only. It is not legal advice, medical advice, or a substitute for guidance from regulatory counsel, FDA, or qualified clinical experts.

What 361 and 351 refer to

The numbers come from sections of the Public Health Service Act.

Section 361 gives FDA authority to issue regulations aimed at preventing the introduction, transmission, or spread of communicable disease. In the cell and tissue world, products regulated only under this pathway are often called 361 HCT/Ps.

Section 351 covers biological products. If a product falls under this pathway, it is generally treated as a biologic, drug, or device, depending on the product. A 351 biological product usually needs more extensive FDA oversight, which may include an Investigational New Drug application, clinical studies, and a Biologics License Application before marketing.

The key term here is HCT/P, short for human cells, tissues, and cellular and tissue-based products. These include articles containing or consisting of human cells or tissues that are intended for implantation, transplantation, infusion, or transfer into a human recipient.

Examples can include bone, skin, corneas, ligaments, tendons, reproductive tissue, and some cellular products. Some products are clearly traditional tissue grafts. Others are more complex, especially when cells are isolated, processed, expanded, combined with other substances, or used for a function that differs from their original role in the body.

That is where the 361 vs 351 question begins.

The basic FDA framework for HCT/Ps

FDA’s HCT/P framework appears mainly in 21 CFR Part 1271. The rules do not treat every human tissue product the same way. Instead, they ask whether a product meets specific criteria.

If an HCT/P meets all of the main criteria in 21 CFR 1271.10(a), it may be regulated solely under section 361 and the tissue regulations in Part 1271. If it does not meet those criteria, it is typically regulated more broadly under section 351 and other applicable laws, including the Food, Drug, and Cosmetic Act.

The main criteria are:

These criteria work together. A product does not become a 361 HCT/P by satisfying one factor. It must meet the relevant criteria as a whole.

This is one reason classification can feel confusing. A product may sound simple in ordinary language but become complex under FDA’s framework. For example, “stem cells from fat” does not answer the regulatory question. The analysis may need to consider the source tissue, the processing steps, the intended use, the product’s biological activity, whether it is combined with other materials, and how it is described in labeling or marketing.

Minimal manipulation asks what processing changes

Minimal manipulation is one of the most discussed parts of the framework.

FDA looks at minimal manipulation differently depending on whether the tissue is structural tissue or cells or nonstructural tissue.

For structural tissue, the question is whether processing alters the original relevant characteristics of the tissue relating to its utility for reconstruction, repair, or replacement. Structural tissues include tissue types that provide physical support, cushioning, covering, or connection.

For cells or nonstructural tissues, the question is whether processing alters the relevant biological characteristics of the cells or tissues.

That difference matters. A process that seems modest from a laboratory viewpoint may still be more than minimal manipulation if it changes the relevant characteristics FDA focuses on.

Examples help, but they can also oversimplify.

A traditional bone graft that is cleaned, shaped, and preserved may pose a different regulatory question than cells that are separated from a tissue, enzymatically digested, concentrated, cultured, or otherwise processed. Some steps may be considered compatible with minimal manipulation in one context and not in another. The product’s original characteristics and intended function matter.

The word “minimal” can also be misleading. It does not simply mean “not much time,” “same-day,” or “not expanded in culture.” Those facts may matter, but they do not decide the issue by themselves. The question is regulatory and biological: what changed, and are the changed characteristics relevant to how the product is meant to work?

Homologous use asks what the product is intended to do

The second major concept is homologous use. In plain terms, FDA asks whether the HCT/P is intended to perform the same basic function in the recipient as it performed in the donor.

This is not just about where the product came from. It is about what it is being used for.

A tissue that provides cushioning or support in the body may raise questions if it is promoted to treat an unrelated disease through a different biological effect. A product taken from one tissue source and marketed to address neurologic, orthopedic, immune, or systemic conditions may require a close look at whether the intended use is truly homologous.

FDA considers the manufacturer’s objective intent. That can be shown through:

• Labeling

• Advertising

• Instructions for use

• Website claims

• Patient brochures

• Training materials

• The circumstances surrounding distribution

  
  

This means the same physical product could face different regulatory analysis if it is promoted for different uses. A claim that a product supports, replaces, or repairs a function similar to its original role may be viewed differently from a claim that it treats a disease through a broad therapeutic effect.

Homologous use is often one of the most fact-specific parts of HCT/P classification. It may turn on close questions about tissue function, clinical claims, and the way the product is presented.

Why “it is autologous” does not end the analysis

Autologous use means the product comes from and returns to the same person. This fact can matter, especially under the criterion dealing with systemic effects and metabolic activity.

But autologous use does not automatically make a product a 361 HCT/P.

A product still has to satisfy the other criteria, including minimal manipulation and homologous use. If processing is more than minimal, or if the intended use is non-homologous, the product may fall outside the 361 pathway even when the cells came from the patient.

This point is central to many misunderstandings. The phrase “your own cells” sounds reassuring, and it may be clinically relevant in some ways. But from a regulatory standpoint, autologous status is only one part of the analysis.

The same is true for “same-day” procedures. Timing may matter in some contexts, including questions about whether a procedure falls under certain establishment exceptions. But same-day use does not automatically decide whether the product is minimally manipulated, homologous, or outside section 351.

Some practices also raise the same surgical procedure exception, which appears in FDA’s regulations. In general terms, that exception can apply where an establishment removes HCT/Ps from an individual and implants them into the same individual during the same surgical procedure, with limits. The scope of that exception can be nuanced, and FDA has addressed it in guidance. Small factual differences in handling, processing, or storage can matter.

Why the route of administration does not decide everything

A common shortcut is to focus on how the product enters the body. People may ask whether an injection into a joint, an intravenous infusion, or another route automatically makes the product 351 or 361.

The answer is no. The route of administration alone does not determine regulatory status.

Route can still be relevant. It may help show intended use. It may affect safety questions. It may relate to whether the product has a systemic effect. It can also inform FDA’s view of how the product is expected to act in the body.

But route is not the whole test.

For example, a local injection does not automatically mean homologous use. If the product is promoted to treat a condition through a function it did not perform in the donor tissue, homologous use may still be in question.

By contrast, a route that seems more complex, such as infusion, does not by itself answer every classification issue either. The facts still matter. What is the product? How was it processed? What function is claimed? Does it act systemically? Does it depend on living cells’ metabolic activity? Is it autologous or allogeneic? Is it combined with other substances?

FDA’s framework looks at the product and its intended use as a whole. Route is one piece of evidence, not the rulebook.

Why classification gets complicated in real life

The framework sounds tidy on paper. Real products are not always tidy.

Classification can become complicated because cell and tissue products sit at the intersection of biology, medicine, manufacturing, and law. A small change in one area can shift the analysis.

Several factors often make the answer nuanced:

• Source tissue

  Cells from adipose tissue, bone marrow, birth tissue, blood, or another source may raise different questions because those tissues have different relevant characteristics and functions.

  
  

• Processing steps

  Washing, cutting, grinding, centrifuging, enzymatic digestion, cell selection, expansion, cryopreservation, and other steps may have different regulatory significance depending on the product.

  
  

• Intended clinical use

  Using tissue to replace or support the same basic function differs from using it to treat a disease through a new biological mechanism.

  
  

• Product claims

  Marketing language can influence how FDA understands objective intent. Broad claims about treating systemic diseases may change the analysis.

  
  

• Combination with other substances

  Adding drugs, biologics, devices, scaffolds, or other materials can move a product outside the simpler 361 framework.

  
  

• Systemic effect and metabolic activity

  Living cell products may act through metabolic activity. If they have systemic effects or depend on that activity for their primary function, the regulation asks further questions about whether an exception applies.

  
  

This is why two products that sound similar may end up in different regulatory categories. It is also why two uses of the same product may not be treated the same way.

A short description such as “umbilical cord cells,” “exosomes,” “stromal vascular fraction,” or “bone marrow stem cells” does not provide enough information by itself. Each term can cover different collection methods, processing methods, intended uses, and claims.

Another source of confusion is that clinical risk and regulatory classification are related but not identical. A product may raise safety concerns even if it uses familiar materials. A product may also require FDA premarket review even if a clinic describes it as natural, autologous, or minimally processed.

What the 351 pathway generally means

When an HCT/P does not meet the criteria for regulation solely under section 361, it may be regulated as a 351 biological product. That usually means a more demanding development and review pathway.

A 351 product may require:

• Preclinical testing

• Manufacturing controls

• An Investigational New Drug application before clinical studies

• FDA-reviewed clinical trials

• Evidence of safety, purity, and potency

• A Biologics License Application before commercial marketing

  
  

This pathway is not a punishment. It is the system used for products that make therapeutic claims and may pose risks that require more evidence before widespread use.

For developers, the 351 pathway can be longer and more expensive. For patients and clinicians, it can mean that a marketed product has gone through a formal FDA review process for a specific indication. For researchers, it creates a structure for studying potential benefits and risks.

Some products in regenerative medicine have received FDA approval through appropriate pathways. Many others remain investigational. When evaluating claims, the key question is not whether something is called “stem cell therapy” in general, but whether that specific product is FDA-approved for that specific use.

How to read claims about stem cell regulation

A careful reading of regulatory claims can prevent confusion. Watch for broad statements that treat one fact as decisive.

Claims that deserve closer scrutiny include:

• “No FDA approval is needed because the cells are autologous.”

• “It is legal because it is performed the same day.”

• “It is 361 because it is minimally processed.”

• “The injection route makes it local, so it is not a drug.”

• “Human tissue products are never regulated like biologics.”

  
  

Each of these statements may leave out key facts. Some may be partly true in a narrow setting but misleading when stated broadly.

A more reliable regulatory discussion will identify the product, the processing, the intended use, and the claimed mechanism of action. It will also acknowledge uncertainty where the facts are incomplete.

The terms 361 and 351 are useful, but they are not labels that can be applied casually. They are conclusions reached after working through the regulatory criteria.

The practical takeaway

The 361 vs 351 distinction is best understood as a framework, not a slogan. Section 361 is generally tied to controlling communicable disease risks for HCT/Ps that meet specific criteria. Section 351 applies when a product is regulated more like a biologic, often because it is more than minimally manipulated, intended for non-homologous use, combined in ways that fall outside the rule, or has systemic or metabolic activity that does not fit an exception.

The hard part is that real products do not always fit neatly into simple categories. Minimal manipulation is technical. Homologous use depends on function and claims. Autologous use helps in some analyses but does not answer every question. Route of administration can matter, but it does not decide regulatory status on its own.

When the facts are specific, the answer is specific too. That is why serious discussions of stem cell regulation should avoid shortcuts and focus on the full product, the full process, and the full intended use.