 From 1962 he focused on immune reactions, demonstrating that antigens are not present in antibody-producing cells, in support of Burnet's clonal selection theory.In 1968 Ada was appointed head of the Microbiology Department at the John Curtin School of Medical Research at the Australian National University, taking over from Frank Fenner.He held the position for 20 years; during his period of leadership the school became an international centre for the analysis of T cell-mediated immunity.