 In earlier work, he and his colleagues introduced Bacillus Calmette-Guérin (BCG) to tumor immunotherapy; discovered the first link between the major histocompatibility complex (MHC) and disease (leukemia); found the unexpected association between Epstein-Barr virus (EBV) and nasopharyngeal carcinoma; discovered Tumor necrosis factors (TNF); defined the concept of cell-surface differentiation antigens with the discovery of TL, Lyt (CD8), and a range of other mouse antigenic systems; discovered p53, independently with two other groups; and identified the tumor immunogenicity of heat shock proteins.Old is the author or co-author of more than 800 research publications.He was also a teacher helping young scientist as they began their career.