He made significant contributions to the clonal selection theory.

It has been suggested that the phenomena that the theory describes in terms of networks are also explained by clonal selection theory.

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 1969 he published Cellular Immunology, considered his magnum opus on immunity, attempted to show how various phenomena could be predicted by the clonal selection theory.

In 1958 Gustav Nossal and Lederberg showed that one B cell always produces only one antibody, which was the first evidence for clonal selection theory.

Australian immunologist Frank Macfarlane Burnet with input from David W. Talmage worked on this model, and was the first to name it "clonal selection theory."

Jerne was awarded the Nobel Prize for Medicine or Physiology in 1984 partly for his work towards the clonal selection theory, as well as his proposal of the immune network concept.

According to the clonal selection theory, at birth, an animal will randomly generate a vast diversity of lymphocytes (each bearing a unique antigen receptor) from information encoded in a small family of genes.

Clonal Selection Algorithm: A class of algorithms inspired by the clonal selection theory of acquired immunity that explains how B and T lymphocytes improve their response to antigens over time called affinity maturation.

The theory is now sometimes known as Burnet's clonal selection theory, which overlooks the contributions of Ehrlich, Jerne, Talmage, and the contributions of Lederberg, who conceptualised the genetics of clonal selection.

Throughout this time the journal published the research of eminent Australian scientists, including Sir Douglas Mawson and Sir Frank Macfarlane Burnet, whose groundbreaking clonal selection theory was published in the journal in 1957.

Immunology in particular became linked with molecular biology, with innovation flowing both ways: the clonal selection theory developed by Niels Jerne and Frank Macfarlane Burnet in the mid-1950s helped shed light on the general mechanisms of protein synthesis.

The clonal selection theory became one of the central concepts of immunology, and Burnet regarded his contributions to the theoretical understanding of the immune system as his greatest contribution to science, writing that he and Jerne should have received the Nobel for this work.

Mitchison's contributions to immunology include the discovery of both low dose and high dose tolerance for a single antigen, a surprising result in the context of basic clonal selection theory, but which can be understood in the context of immune network theory.