By Toni Clarke

Washington, July 30 (Reuters) - Advisors to the U.S. Food and Drug Administration will meet on Thursday to discuss the relative risks and benefits of Baxter International Inc's experimental treatment for certain hereditary disorders of the immune system.

The FDA on Wednesday posted its preliminary assessment of the data on its website. The agency is seeking guidance from a panel of outside experts on whether the benefits of the product outweigh the risks. The FDA is not obligated to follow the recommendations of its advisors, but typically does so.

Baxter's therapy, HyQvia, is designed to treat primary immunodeficiency diseases. These are genetic disorders in which certain cells of the immune system are missing, leading to a infections, recurrent pneumonia and abscesses of the organs.

HyQvia combines immune globulin (IG), a substance made from human blood plasma, and one vial of recombinant human hyaluronidase, or rHuPH20, a genetically engineered enzyme that increases absorption of the IG and allows it to be used less frequently than traditional products.

The FDA declined to approve the product in 2012, and asked for more information about its possible impact after some patients in a clinical trial developed antibodies against rHuPH20, which Baxter licensed from Halozyme Therapeutics Inc . HyQvia was approved in Europe in 2013.

Baxter's data showed the elevated antibodies, which the immune system produces to fight foreign bodies, had no clinical impact on patients. However, the FDA was concerned about the theoretical potential of long-term exposure to the product to cause inflammation of the brain and bowel, as well as fertility problems.

"The risk-benefit considerations are very different for HyQvia compared to other IG products because the main immunogenetic component of concern (rHuPH20) is not a life-saving therapeutic," the FDA's report noted. The benefit of the product is primarily one of convenience.

Eun Yang, an analyst at Jefferies LLC, said in a research note that without therapeutic advantages in a well-supplied market, the "FDA does not have to take risks of approving HyQvia."

Even if approved, Yang added, its commercial potential would likely be very limited given the concerns about male fertility. He estimated that peak U.S. and European sales would reach $740 million, translating into royalty revenue for Halozyme of $37 million.

Existing immune globulin therapies are given intravenously once every three to four weeks in a hospital, or by injection at home once every one to two weeks. HyQvia is designed to be injected at home once every three to four weeks.

(Reporting by Toni Clarke in Washington. Editing by Andre Grenon)