Cell-based therapies are rapidly changing the way the medical industry is treating a wide range of diseases. As the development of these therapies continues to advance, effective planning and selection of appropriate source material to ensure successful manufacture of cell-based therapy, is critical.
The rundown on off-the-shelf and patient-specific cell-based therapy source materials
With many possible types of source materials, how exactly do you choose the right one? Selection is typically based on nature of the manufacturing process, the targeted cell you are looking for and the number of cells that are needed.
Selecting source material for patient-specific cell-based therapy manufacturing and development must consider the disease state of the patient, as this introduces input variation that must be controlled by a robust process. In contrast, source material for off-the-shelf cell-based therapies can utilize material from healthy patients, typically as “super donors”, individuals that have been pre-screened to ensure that their donated material contains the desired quality attributes for the cell-based therapy.
Currently, there are a number of types of source materials that are used in cell-based therapy manufacture and development:
1. Whole blood collection: This collection is essentially a standard blood donation and is the least invasive and most tolerable of the collections. Cell types in whole blood will include white blood cells, red blood cells, plasma, and platelets. As a result, when working with whole blood, more steps are necessary to separate components such as red blood cells, platelets, granulocytes, and plasma. Thus, whole blood is not typically used as a starting material for subjects receiving cell-based therapies. It is, however, a source material of last resort, and is used primarily when it is the only tolerable collection for the patient, such as pediatric cases.
2. Bone marrow: This process involves removing bone marrow using a needle and syringe, from the soft center of the bone. Bone marrow will be extracted from the hip bone or the sternum at the time of harvest. The procedure is quite painful, and thus anesthesia is used, to help ease the pain. Bone marrow is commonly used as a starting material for cell-based therapy products. However, large collections run into the issue of having impurities such as red blood cells, platelets, and granulocytes, which will add complexity to the manufacturing process, as these cell types typically have to be removed.
3. Non-mobilized apheresis: This process requires a laboratory procedure in which white blood cells are separated from a sample of blood. The samples received are called LeukoPaks, which provide a concentrated number of mononuclear cells (MNCs), which are the lymphocytes and monocytes. Apheresis collections will have much fewer red blood cells, plasma, granulocytes and platelets, since these cell types are not typically used in cell-based therapy applications, making them much simpler to work with as compared to whole blood or bone marrow.
4. Mobilized apheresis: The process is the same regarding collection of apheresis, but in this case the patient is administered granulocyte colony-stimulating factor (G-CSF) approximately 100 hours before the collection. G-CSF mobilizes the CD34+ stem cells from the patient’s bone marrow into the blood stream so that they can be collected and used in the cell-based therapy product without having to harvest the cells directly from the bone marrow.
5. Other tissue sources: There are many alternative tissue sources (e.g. adipose, skeletal, umbilical cord, neural and skin) and various methods for extracting cell types from these adult tissues sources. The isolation of these cell types typically involves removal of the tissue from the patient (occasionally diseased or even cadaveric), a tissue digestion and extraction step, followed by a culture step to expand the cells.
6. Immortalized: In addition to primary cell types for cell-based therapy manufacturing and development, there are a number of immortalized and/or genetically modified cell types such as embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs) and immortalized primary cells. These cell types have the ability to continuously expand in culture and in the case of ESCs and iPSCs, also have the ability, under the required conditions, to differentiate into all cell types.
Effective manufacturing development for patient-specific cell-based therapies: A robust process is a must
Given that each situation is unique in terms of patient health and cellular therapy product, the choice of starting materials is dictated by what the patient can tolerate, as well as what type of manufacturing process is required. In conjunction with the choice of starting materials, an efficient yet reliable manufacturing process must be developed to warrant the cellular therapy for disease state patients.
During early product development, healthy donor material is primarily used due to ethical concerns associated with collection from already disease-burdened patients. In most cases, the manufacturing process is developed using healthy material as a stand-in, which can have significant phenotypical differences from healthy apheresis, such as reduced target cell numbers, increased impurities and/or genetic changes to the cell populations. Therefore, it is necessary to be prepared for any changes that come along once the transition to patient material begins, which is often during late process qualification runs or the initiation of the clinical trial.
It is imperative that your manufacturing process be designed robustly -- to withstand the expected potential lot-to-lot variability. This can be achieved in part by assessing the level of potential input variation to the manufacturing process and breaking the process down into multiple unit operations, so that each unit operation can be developed to ensure the required flexibility is present during manufacture. For example, when working with patient material, the purity of your target cell (e.g., T-cells) could be a lot lower than what it was during development work. If a robust enrichment process was not developed, there is the likelihood that a less than optimal purity will be obtained during this crucial unit operation.
For instance, this can be significant during a viral transduction step, which is the key step when your target cells are converted into the cell-based therapy product. You want a pure target cell enrichment, to ensure that when the virus is added, you are infecting just those target cells. If the enrichment is impure, your virus is going to be allocated to not only your target cells, but also the other cells in the mixture - ultimately causing your cell-based therapy product to be much less potent.
Navigating cell therapy can be challenging. At PCT, it is our goal to help clients develop a robust process that will get their cellular therapies to clinic safer and faster.
