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CD8 T-cell immunity is thought to require helper activity derived from CD4 T cells. Nevertheless, under some circumstances, effective CD8-dependent T-cell responses occur in vivo without CD4 T-cell help. Several recent papers help to explain this paradox and lead to a refined view concerning the role of T helper cells and interleukin-2 receptor signaling in the production of cytotoxic T lymphocytes. [ABSTRACT FROM AUTHOR]