In my last post, I introduced the use of clinical stem cell therapy in treating multiple myelomas and lymphomas. The treatment focuses blood stem cells, known as hematopoietic progenitor cells (HPCs). By transplanting healthy HPCs into patients, nearly normal white blood cell counts can be restored after cell-destroying cancer treatment.
The process begins not in the lab, but in the hospital, with a procedure called apheresis. In this procedure, the patient’s or donor’s blood passes through a cell-separator which uses a centrifuge to separate the whole blood into layers. The HPC and plasma layers are skimmed into a sterile collection bag and this “blood product” is speedily brought to the lab for processing. The remaining layers are returned to the donor’s circulation.
Back in the lab, several technicians are required to complete the processing. A sealed-off “clean” area is dedicated to processing the patient sample. Unlike a research lab, a lab working with patient samples must carefully track all materials used. Each item, from pipettes to PVC tubing to plastic disposal bags, are labelled with tracking numbers and (for sterile items) expiry dates.
Preparing HPCs for storage is a three stage procedure. The initial stage is cell recovery. The technician checks the quantity and quality of the sample by taking a small sample of blood and determining the number of nucleated cells. If within reason, the blood product is transferred from the collection bag to a centrifuge bag and spun down. This separates the plasma layer from the HPC-rich layer and also reduces the volume of product to freeze.
The plasma is carefully siphoned off into a separate bag and discarded, while the remaining blood product is weighed and a cell count taken. If the cell count is approximately 90% or better of the original count, then it is considered a good recovery and the procedure can continue.
Now the blood product is rich in HPCs but not yet in a form that is appropriate for long term storage. Left as is, the cells would die. Here, we enter the second stage of the process, preparation for storage.
From the centrifuge bag, the blood product is again transferred, this time to a sterile freezing bag. Separately, a preparation of 20% dimethyl sulfoxide (DMSO) is made in isotonic solution, equal to the volume of cells. Both bags are pre-cooled and the DMSO solution is added to the freezing bag. The final solution is 10% DMSO by volume, which protects the cells from the effects of freezing – the final stage of the process.
Slowly, the HPC-DMSO mixture is frozen in a specialized freezer before being transferred to liquid nitrogen tanks. It is here that the pouches of HPC-rich product reside, at a numbing -195°C, until the day that the patient requires a transplant.
(Photo by Dale Tidy)