Fortunately mechanisms exist for alternative test methods.⁶ Overall, confirming that the final product meets specifications for release is a key component of ensuring product quality and biosafety for biological products. For example, a variety of cell-based therapies are being investigated for various types of cardiac disease. One approach involves the use of bone marrow to stimulate angiogenesis in ischemic heart tissue. Unfractionated bone marrow contains a complex mixture of cells including T cells, B cells, NK cells, monocytes, macrophages, stromal cells, and neutrophils, which makes it difficult to determine which cells may contain therapeutic vs. non-therapeutic contaminating elements. This raises biosafety concerns since these cells produce a variety of cytokines that could lead to deleterious effects such as inflammation, fever, acute phase response, lymphocyte activation, and proliferation. In vitro and in vivo studies are needed to determine the significance of these concerns.¹⁴ Once information becomes available regarding these issues, it may be necessary to establish release specifications for the purity of the final product to avoid the possibility of adverse clinical events. Thus, the ability to characterize the final product by the purity-impurity profile can have important biosafety implications.

Preclinical pharmacology and toxicology

Undesirable pharmacological activity or unrecognized toxicities are unlikely to be detected through in vitro testing, and generally must be evaluated in a relevant animal model. This is, of course, due to the unique aspects of CBTs.

Table 4. Preclinical Biosafety Considerations for Engineered Cell-Biomaterial Constructs

The principles involved in designing and developing appropriate preclinical testing to determine the safety of cell-based products are similar to those encountered for other biological products. Key components of protocol design for preclinical studies include:

• discerning activity and toxicity of the product (mechanism of action)
• recommendation of an initial safe dose and dose escalation scheme in humans
• identification of potential toxicity or activity target organs
• identification of parameters that should be monitored clinically
• identification of patient eligibility criteria.¹³

When available, relevant animal species and animal models of disease should be utilized in preclinical studies. We all recognize that no single species will be representative or predictive for all patients. Ideally, the animal disease model chosen should have a similar pathophysiology and anatomy to humans, which should improve predictability of human risks as well as facilitate modeling of route of administration and dose exploration. Standard animal models of disease are frequently modified to generate the preclinical toxicity data. For example, immunological reactions to human cells in animals often necessitate that preclinical toxicology studies be performed with autologous animal cellular products (animal products that are analogous to the intended clinical product), rather than the actual human product.¹⁴ Follow good laboratory practices (GLP) for preclinical safety studies. However, given the unique design requirements of preclinical assessments of CBTs, regulatory authorities recognize that this is not always possible. In these cases the "spirit of GLP" should be followed.

Performing preclinical safety studies in an animal model of the disease depends onthe existence of such a model. Where models do exist, recognize their limitations, such as whether the model is relevant to the pathophysiology of the disease in humans, the physical size of the animal, and potential technical limits on feasibility. Other important considerations are the availability of the animal model, including age, gender, and numbers needed for statistical considerations; the need for specialized housing; animal welfare concerns; costs; and the availability of historical data to support the animal model.