Priming CD8+ T cells with dendritic cells matured using TLR4 and TLR7/8 ligands together enhances generation of CD8+ T cells retaining CD28.

TLRs expressed on dendritic cells (DCs) differentially activate DCs when activated alone or in combination, inducing distinct cytokines and costimulatory molecules that influence T-cell responses. Defining the requirements of DCs to program T cells during priming to become memory rather than effector cells could enhance vaccine development. We used an in vitro system to assess the influence of DC maturation signals on priming naive human CD8+ T cells. Maturation of DCs with lipopolysaccharide (LPS; TLR4) concurrently with R848 (TLR7/8) induced a heterogeneous population of DCs that produced high levels of IL12 p70. Compared with DCs matured with LPS or R848 alone, the DC population matured with both adjuvants primed CD8+ T-cell responses containing an increased proportion of antigen-specific T cells retaining CD28 expression. Priming with a homogenous subpopulation of LPS/R848-matured DCs that were CD83(Hi)/CD80+/CD86+ reduced this CD28+ subpopulation and induced T cells with an effector cytokine signature, whereas priming with the less mature subpopulations of DCs resulted in minimal T-cell expansion. These results suggest that TLR4 and TLR7/8 signals together induce DCs with fully mature and less mature phenotypes that are both required to more efficiently prime CD8+ T cells with qualities associated with memory T cells.

HIV-specific CD8+ T cells from HIV+ individuals receiving HAART can be expanded ex vivo to augment systemic and mucosal immunity in vivo.

Most HIV+ individuals require lifelong highly active antiretroviral therapy (HAART) to suppress HIV replication, but fail to eliminate the virus in part because of residual replication in gut-associated lymphoid tissues (GALT). Naturally elicited HIV-specific CD8+ T cells generated in the acute and chronic infectious phases exhibit antiviral activity, but decrease in number after HAART. Therapeutic vaccines represent a potential strategy to expand cellular responses, although previous efforts have been largely unsuccessful, conceivably because of a lack of responding HIV-specific central-memory CD8+ T cells (Tcm). To determine whether patients receiving HAART possess CD8+ T cells with Tcm qualities that are amenable to augmentation, HIV-specific CD8+ T-cell clones were derived from HIV-reactive CD28+CD8+ T-cell lines isolated from 7 HIV+ HAART-treated patients, expanded ex vivo, and reinfused into their autologous host. Tracking of the cells in vivo revealed that clones could persist for ≥ 84 days, maintain expression and/or re-express CD28, up-regulate CD62L, secrete IL-2, proliferate on cognate Ag encounter and localize to the rectal mucosa. These results suggest some infused cells exhibited phenotypic and functional characteristics shared with Tcm in vivo, and imply that more effective therapeutic vaccination strategies targeting CD8+ Tcm in patients on HAART might provide hosts with expanded, long-lasting immune responses not only systemically but also in GALT.

Tumor skewing of CD34+ cell differentiation from a dendritic cell pathway into endothelial cells.

Patients and animals bearing tumors have increased levels of CD34(+) progenitor cells, which are capable of developing into dendritic cells. However, addition of medium conditioned by murine Lewis lung carcinoma cells increases the cellularity of the CD34(+) cell cultures and redirects their differentiation into endothelial cells. The resulting cells resemble endothelial cells phenotypically as well as functionally by their capacity to reorganize into cord structures. Mechanisms by which tumors induced the increased cellularity and skewing toward endothelial cells were examined. Tumor-derived VEGF contributed to the increase in cellularity, but not to the redirection of differentiation. Differentiation into endothelial cells was blocked with sTie-2, suggesting tumor-derived angiopoietins in skewing differentiation. These studies show the capacity of tumors to skew progenitor cell development toward endothelial cells and define the mediators that contribute to endothelial cell development.