Briefly . . .

Gene therapy hits a snag

Using gene therapy to combat cancer depends on delivering the genes to the tumour on a "vector" — usually an adenovirus thought to be harmless to the host. But long-term follow-up of survivors of gene therapy for brain glioblastoma shows that the therapy causes chronic brain inflammation (Nat Med 1999;5:1256-63). Three months after glioma growth was inhibited through gene therapy, researchers found activated macrophages/microglia and astrocytes, positive T cells, secondary demyelination, widespread immunoreactivity to a herpes simplex virus 1 enzyme, and the genome of the adenovirus vector throughout large areas of the brain. This could pose an important stumbling block for the future use of gene therapy.

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Our understanding of the immune response to infection, and of immunization, may be revolutionized by recent research into T cells. The immune response after vaccination results from the property of "memory," which is established in appropriate lymphocytes. It was thought that these "memory T cells" are activated when they "see" the offending antigen, together with a major histocompatibility protein, and that there was a continuing requirement for antigen stimulation for memory T cells to work. Now 2 studies in mice show that memory T cells — both CD4 and CD8 cells — never forget (Science 1999;286:1377-81,1381-3). Even in mice genetically altered to lack major histocompatibility complex proteins and never exposed to the antigen before, memory T cells launched an immune response to invading pathogens.

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