By Lisa Seachrist
Nexell Therapeutics Inc. received marketing clearance from the FDA to begin selling its stem cell selection systems, Isolex 300 and the fully automated Isolex 300i, as a means to remove tumor cells and select hematopoietic stem cells from peripheral blood used in bone marrow transplantation following aggressive chemotherapy.
The approval marks the final days for the Ceprate SC system, which was developed by the now-bankrupt CellPro Inc., of Bothell, Wash. Irvine, Calif.-based Nexell will place a high priority on phasing out the Ceprate SC Systems, which were found to be in "willful infringement" of stem cell sorting patents in August 1998.
"There are two priorities: the first is replacing the defunct Ceprate SC System and the second will be transforming the investigational sites using Isolex 300 into commercial sites," company spokesman Ted Heitmann said. "Because we will need to place instruments and train people, replacing the Ceprate systems will take more time."
Stem cells, which are located in the peripheral blood and bone marrow, are rare, immature, undifferentiated cells that can reproduce themselves and differentiate in order to produce all the different cells that make up the blood and immune systems. Autologous stem cell transplantation involves removing some blood or bone marrow from a patient prior to high-dose chemotherapy and returning those cells in an effort to restore the blood and immune system.
The problem with that procedure is that some tumor cells likely will be given back to the patient with the stem cells. Stem cell selection allows physicians to select the CD34 positive stem cells away from tumor cells.
Nexell's products use antibodies linked to magnetic beads that recognize the CD34 antigen on stem cells. The now defunct Ceprate SC used columns rather than magnetic beads to remove stem cells, but the end result was similar.
Nexell was formed by its former parent company, Vimrx Pharmaceuticals Co., and Baxter, the principal operating subsidiary of Baxter International Inc., of Deerfield, Ill. Early this year Vimrx acquired Baxter's interest in the venture, and then merged all its operations into Nexell.
Last September, Nexell bought CellPro's assets including intellectual property, patents, antibodies and related cell banks, research and licensed rights for $3 million. Nexell has continued to supply the Ceprate SC System kits to the facilities using the system. However, that supply is now running low. (See BioWorld Today, Sept. 30, 1998, p.1; and Aug. 13, 1998, p.1.)
"We tried to estimate what we would need and it looks like we got it just right," Heitmann said.
Switching to the Isolex system from the Ceprate system will be relatively straightforward for institutions using the system solely for therapeutic endeavors. Nexell will place the Isolex 300 or Isolex 300i equipment on site and the laboratory staff will participate in 2.5 days of training. The company also will be present for treatment of the first patient.
For institutions using the Ceprate system in an investigational manner, the company will not only have to train the laboratory staff, but also will need to help the institutions navigate all protocol changes with the FDA and the institutional review board. The FDA may decide to simply accept the change as a protocol modification but will review each change on a case-by-case basis.
"This approval will allow us to get the system into more clinicians' and researchers' hands and allow them to have access to state-of-the-art transplantation techniques and the opportunity to explore new areas of cell therapy," Heitmann said.
Heitmann pointed out that intuitively, it makes sense that giving tumor cells back to patients is a bad idea. However, that assertion never has been proven. The company intends to further establish that stem cell selection provides benefit to patients in either disease-free survival or survival alone.
In addition, the U.S. Isolex systems only provide a positive selection system in which CD34+ stem cells are identified and kept. In Europe, the systems also provide a negative selection following the positive selection that rids the product of any tumor cells that slipped through the first positive selection. The company is working to get approval for the second negative selection step in the U.S.
Nexell's stock (NASDAQ:NEXL) closed unchanged Tuesday at $2.187.