When neuroprotective factors, such as nerve growth factor, brain-derived neurotrophic factor (BDNF), neurotrophin 3 (NT-3), and neurotrophin 4/5 (NT-4/5) are deficient in MS patients, the influx of PBMC cells to the CNS can make up for this, slowing the rate of cerebral atrophy. This evidence concerns the gene BDNF and myeloid sarcoma.