It is known that progenitor cells (CD34+) in the bone marrow may express Fas in response to tumor necrosis factor-alpha (TNF-α) and interferon-gamma (INF-γ) in vitro [41] and cytotoxic T lymphocytes in T-LGL leukemia may spontaneously produce INF-γ and TNF-α after stimulation [42]. The gene discussed is FAS; the disease is leukemia.