Several gene-deficiency models promote the development of innate CD8 + T cells that have diverse T cell antigen receptors (TCRs) but have a memory phenotype and rapidly produce cytokines. We demonstrate here that similar cells developed in mice deficient in the transcription factor KLF2. However, this was not due to intrinsic deficiency in KLF2 but instead was due to interleukin 4 (IL-4) produced by an expanded population of T cells expressing the transcription factor PLZF. The development of innate CD8+ T cells in mice deficient in the tyrosine kinase Itk and coactivator CBP was also attributable to this IL-4-dependent mechanism. Finally, we show that the same mechanism drove the differentiation of innate CD8+ T cells in BALB/c mice. Our findings identify a previously unknown mechanism of regulation of CD8+ T cells via the production of IL-4 by PLZF + T cells.