To the best of my knowledge there is not a scientifically proven method of clearing the feline leukemia virus from infected cats using immunotherapy. We have a number of cats who live reasonably long and healthy lives despite infection with feline leukemia virus. I count the treatment of them as successful, despite the fact that in the end they may die from complications of the disease. There have been conflicting studies on a couple of therapies for feline leukemia virus using Staph protein A (one claimed benefit, one didn't), Immunoregulin (at this point, I think that the studies overwhelmingly support no success in treatment) and interferon. There have been good anecdotal reports of the helpfulness of interferon in treatment of cats ill with this disease but no reports of it actually clearing the virus under controlled conditions, at least to the best of my knowledge. We generally try to use good supportive care -- good quality diet, reduction of as much stress as possible, early aggressive treatment of any illness and keeping the cats indoors (both for their benefit and the benefit of cats they might expose to the virus). Many cats live reasonably normal lives for quite some time despite infection with this virus under these conditions. The vaccines are about 85% effective in preventing infection with feline leukemia virus.