Technological advances have enabled us to formulate, and answer, questions about our immune system that were never thought possible previously. We can now observe the actions of single immune cells in lymphoid tissues, close up and in three dimensions — a concept that has inspired our cover this month. As discussed by Michael D. Cahalan and colleagues on page 872, the new biophotonic technique of two-photon laser microscopy promises to revolutionize our understanding of the cellular cooperations that underlie an immune response, and it has enabled us to see the immune system in a new light.
On page 859, J. Andrew Bradley, Eleanor M. Bolton and Roger A. Pedersen discuss how progress of another kind — the ability to derive human embryonic stem cells in culture — has led researchers to ask whether stem cells could become a source of replacement cells for damaged or diseased tissues. Before this potential can be realized, many questions need to be addressed regarding how the immunological barriers to the transplantation of these cells can be overcome, including ways to induce tolerance in the host and to reduce the immunogenicity of the donor cells.
