Dysregulation of NGF signaling has also been linked to Alzheimer's disease. Connective tissue cells genetically engineered to synthesize and secrete NGF and implanted in patients' basal forebrains reliably pumped out NGF, which enhanced the cells’ size and their ability to sprout new neural fibers. The treatment also rescued vulnerable cells, even if they already showed the trademark signs of Alzheimer's pathology. In some patients, these beneficial effects lasted almost 10 years after the treatment. Even patients who died responded positively to the therapy. Even pathological cells with protein clumps in their cell bodies and surroundings extended their fibers toward the NGF source, maintained a healthy size and activated pro-survival signals that boosted their stress resilience. Two other patients received direct injections of modified viruses containing the NGF gene directly to their basal forebrains. This allowed the gene to express longer in the brain.