Proliferation conditions promote intrinsic changes in NK cells for an IL-10 response.

Constitutively found at high frequencies, the role for NK cell proliferation remains unclear. In this study, a shift in NK cell function from predominantly producing IFN-γ, a cytokine with proinflammatory and antimicrobial functions, to producing the immunoregulatory cytokine IL-10 was defined during extended murine CMV infection. The response occurred at times subsequent to IL-12 production, but the NK cells elicited acquired responsiveness to IL-12 and IL-21 for IL-10 production. Because neither IL-12 nor IL-21 was required in vivo, however, additional pathways appeared to be available to promote NK cell IL-10 expression. In vitro studies with IL-2 to support proliferation and in vivo adoptive transfers into murine CMV-infected mice demonstrated that NK cell proliferation and further division enhanced the change. In contrast to the sustained open profile of the IFN-γ gene, NK cells responding to infection acquired histone modifications in the IL-10 gene indicative of changing from a closed to an open state. The IL-10 response to IL-12 was proliferation dependent ex vivo if the NK cells had not yet expanded in vivo but independent if they had. Thus, a novel role for proliferation in supporting changing innate cell function is reported.

Cutting edge: a novel mechanism bridging innate and adaptive immunity: IL-12 induction of CD25 to form high-affinity IL-2 receptors on NK cells.

NK cell expression and use of the IL-2Rα-chain (CD25), required for the high-affinity IL-2R, remain poorly understood. The studies reported in this article demonstrate that infections with murine CMV (MCMV), but not with lymphocytic choriomeningitis virus, induce CD25 on NK cells, along with high levels of IL-12 and IL-18. The cytokines act ex vivo to increase CD25 levels, and IL-12, IL-12R, and STAT4, but not the NK activating receptor Ly49H, are required for peak induction in vivo. All examined NK cell populations are driven into proliferation and incorporate BrdU in response to high ex vivo concentrations of IL-2, but only those from MCMV infection respond to low ex vivo concentrations of IL-2. The numbers of NK cells elicited during MCMV infection are reduced by IL-2 neutralization. Thus, a link between innate and adaptive immunity is established by which composition of innate cytokine responses sets up to promote NK cell use of a factor supporting adaptive responses.

Mesenchymal stem cells secreting angiopoietin-like-5 support efficient expansion of human hematopoietic stem cells without compromising their repopulating potential.

Clinical and preclinical applications of human hematopoietic stem cells (HSCs) are often limited by scarcity of cells. Expanding human HSCs to increase their numbers while maintaining their stem cell properties has therefore become an important area of research. Here, we report a robust HSC coculture system wherein cord blood CD34(+) CD133(+) cells were cocultured with mesenchymal stem cells engineered to express angiopoietin-like-5 in a defined medium. After 11 days of culture, SCID repopulating cells were expanded ~60-fold by limiting dilution assay in NOD-scid Il2rg(-/-) (NSG) mice. The cultured CD34(+) CD133(+) cells had similar engraftment potential to uncultured CD34(+) CD133(+) cells in competitive repopulation assays and were capable of efficient secondary reconstitution. Further, the expanded cells supported a robust multilineage reconstitution of human blood cells in NSG recipient mice, including a more efficient T-cell reconstitution. These results demonstrate that the expanded CD34(+) CD133(+) cells maintain both short-term and long-term HSC activities. To our knowledge, this ~60-fold expansion of SCID repopulating cells is the best expansion of human HSCs reported to date. Further development of this coculture method for expanding human HSCs for clinical and preclinical applications is therefore warranted.

Block of T cell development in P53-deficient mice accelerates development of lymphomas with characteristic RAG-dependent cytogenetic alterations.

Mice deficient in the DNA damage sensor P53 display normal T cell development but eventually succumb to thymic lymphomas. Here, we show that inactivation of the TCR beta gene enhancer (E beta) results in a block of T cell development at stages where recombination-activating genes (RAG) are expressed. Introduction of the E beta mutation into p53-/- mice dramatically accelerates the onset of lethal thymic lymphomas that harbor RAG-dependent aberrant rearrangements, chromosome 14 and 12 translocations, and amplification of the chromosomal region 9A1-A5.3. Phenotypic and genetic analyses suggest that lymphomas emerge through a normal thymocyte development pathway. These findings provide genetic evidence that block of lymphocyte development at stages with RAG endonuclease activity can provoke lymphomagenesis on a background with deficient DNA damage responses.