By Mary Welch

Nexell Therapeutics Inc. received an approvable letter from the FDA for its Isolex Cell Selection System, contingent on more information from the company regarding labeling and manufacture of the product. Laura Mastrangelo, spokeswoman for Irvine, Calif.,-based Nexell, said the agency has "very specific questions about data, such as wanting more information about one patient at one site." She said the company expects to respond by the end of the first quarter, or sooner.

The questions pertain to the premarket approval application for the Isolex 300, and the supplement to the Isolex 300i. Both systems are used to select and purify cells from cancer patients to replenish their bone marrow, which is ravaged by chemotherapy and radiation. The only difference between the two systems, Mastrangelo said, is that the latter is fully automatic. "Some companies want more control of the process than others," she said.

Stem cells, located in the bone marrow and blood, are extremely rare, immature, undifferentiated cells that can reproduce themselves or differentiate in order to produce all the different cells that make up the blood and immune systems. Stem-cell transplantation, using bone marrow or peripheral blood, is performed following high-dose chemotherapy in an effort to restore a patient's blood and immune cell production.

The procedure carries the risk that some tumor cells will be given back to the patient with the stem cells. In transplantation with cell selection, a patient's stem cells are isolated further from the other components of bone marrow and blood, to reduce tumor cells.

Nexell's products use magnetism and antibodies to select cells. The products consist of a device (magnetic beads) and a drug (antibodies), used for either positive selection of a desired target cell population, or negative selection and removal of cells that are potentially harmful to the patient, such as T cells.

The Isolex system is currently marketed in Europe as a component of cancer treatment, and is available in Hungary, Israel, New Zealand, Poland and Slovenia. Worldwide sales in 1997 totaled $15 million and are expected to double by 1999. Analysts say U.S. sales could reach about $200 million.

Although the Isolex system, if approved, would be the only such product available in the U.S., it would not be the first. That distinction went to CellPro Inc., of Bothell, Wash., which marketed a Ceprate SC Stem Cell Concentration System from 1996 to 1998. In a bitter 1997 patent dispute, CellPro was found to have willfully infringed on two patents covering CD34 monoclonal antibodies and purified stem cells. CellPro was ordered to pay $7 million in damages and stop selling the system in the U.S. whenever an alternative system licensed under the patents wins FDA approval.

The trio found by the courts to possess the valid patents were John Hopkins University, of Baltimore, Md.; Becton Dickinson Co., of Franklin Lakes, N.J. (to whom Johns Hopkins licensed the patents); and Baxter Healthcare Corp., the principal U.S. operating subsidiary of Deerfield, Ill,-based Baxter International Inc. Becton licensed the technology for therapeutic uses to Baxter. Last year, a U.S. Court of Appeals upheld the ruling. (See BioWorld Today, Aug. 13, 1998, p. 1)

In September 1998, Nexell Therapeutics, a majority-owned subsidiary of Vimrx Pharmaceuticals Inc., of Wilmington, Del., acquired all of CellPro's intangible assets, including intellectual property, patents, antibodies and related cell banks, research and licensed rights, in exchange for $3 million in Vimrx securities. CellPro has declared bankruptcy. Baxter owns 20 percent of Nexell. (See BioWorld Today, Sept. 30, 1998, p. 1.)

Baxter is the exclusive worldwide distributor for a specific quantity of Ceprate kits based on market needs. With Nexell and CellPro, Baxter is providing product support and customer service on CellPro's products for a limited time.

Vimrx's stock (NASDAQ:VMRX) closed Friday at $1.687, up $0.406. n