Regulatory Issues: Down to the Bare Bones - Engineered Bone: Tissue Engineering Intelligence Unit - page 217

Quality Controls for the Final Product 19
Purity Quantity and Biological Activiy
It is necessary to define the required dose of the manufactured product to obtain the bio-
logical/therapeutic effects. Doses (for example the average cell concentration in a given com-
posite product) may be derived from preclinical experiments or may vary according to each
donor's cell responsiveness to culturing conditions (typically cell response depends on the do-
nor/patient's age/health condition).
Culture conditions may also influence the cell(s) properties or responsivness to the ex-vivo
expansion; it is therefore necessary to assess the quality of the cell product by means of appro-
priate markers. In the case of cultured chondrocytes, for example, a certified counting method
would ensure proper delivery of a correct amount of expanded cells for reimplantation pur-
poses. At the same time, as already mentionned for the control of the cell identity of possible
phenotype loss, culturing conditions must ensure the maintenance of a collagen type II pro-
ducing phenotype in the manufactured chondrocytes. 18 The determination of this typical car-
tilage marker can be assumed as one of the possible standard assessments to be included for the
validation of the manufacturing procedures. Clearly it would not be wise to consume the final
product (i.e., manufactured chondrocytes) to demonstrate their collagen type II expression,
leaving none to reimplant in the donor/patient. Therefore down-scaled tests should be demon-
strated as proper and applied when feasible. Alternatively, the quality assessment procedure
must be validated. Obviously proper markers must be identified for each specific product.
The biological activity of the final product can also depend upon the site of the therapeutic
application with respect to the location of the tissue of origin of the cell component. In this
respect the FDA operates a distinction between homologous and nonhomologous function
whether or not the product is a structural tissue. 8 A structural tissue engineered product is
exerting an homologous function when used to replace an analogous tissue that has been dam-
aged: examples include bone allograft obtained from long bones but used in a vertebra; skin
allograft from the arm but used on the face and so on.
An example of nonhomologous use is cartilage placed under the sub-mucosa layer of the
urinary bladder to change the angle of the uretra and thus preventing the backflow of urine: the
cartilage would be acting as a structural support in a district where that support does not
normally exist. Another example of nonhomologous use of a cellular product would be the
treatment of metabolic disfunctions with stem cells, intended to perform a different function
other than the hematopoietic reconstitution. It is evident the need of increased quality controls
either for the manufacturing process or for the final products in case of tissue-based products
that are used for nonhomologous functions.
Toxicity Studies 11,20
Toxicity studies must be performed, as for pharmaceutical drugs. In certain cases the use of
human cells in living experimental animals may induce toxic/immuno response due to the
inter-specie differences. Therefore proper toxicity studies on the final product must be con-
ducted in immunodeficient animals. Proper species must be selected to give an experimental
answer as close as possible to that of humans. For example if the new therapy is based on the
effects of a cytokine secreted by transplanted cells, tests should be performed with animal cells
that possess receptors for that molecule and where that molecule induces the same biological
effects. Undesired toxic effects in body districts other than the ones subjected to the therapy
must be clearly reported.
Biological Product Stability
A detailed description should be provided of the storage conditions, along with study pro-
tocols and results supporting the stability of the lot/batch of the final product. Stability data
must be submitted for the final product as packaged in the container in which it is to be
shipped/marketed. If the product is to be shipped under conditions in which cell viability is to