We also tested whether introduction of exogenous p21waf1/cip1 would reverse the SP-B resistance of NALM-6/SP-B cells, or enhance the susceptibility of the K562 human erythroleukemia leukemia cell line, which is less susceptible to SP-B than NALM-6 cells, to SP-B-induced apoptosis. The gene discussed is SFTPB; the disease is leukemia.