The ability to study the properties and functions of individual cells is a major
goal of cell biologists. Nowhere is this more true than in studies of the immune
system, in which the complexity is such that results obtained at the population
level often obscure critical aspects of the function and diversity of the component
cells. The study of individual cells per se is still technically difficult and
of necessity limited in scope, leading to the compromise in which populations
of cells derived from a single parent cell (clones) are studied. Considerable
valuable information can be obtained from even relatively small clones of limited
life span (ref. 1, Chapter 2), but the ultimate aim is to produce clonal populations
of cells that show indefinite growth and retain normal physiological
properties, thereby permitting large-scale and long-term studies. The discovery
of methods for cloning mouse and human T cells led directly to major advances
in our understanding of the recognition mechanisms and functional capabilities
of “individual” T cells. More recently, the development of procedures for the
cloning of human NK cells was instrumental in the discovery of killer cell immunoglobulin-like
inhibitory (KIR) receptors (2,3; and Chapter 1).