Cooperation of TNF family members CD40 ligand, receptor activator of NF-kappa B ligand, and TNF-alpha in the activation of dendritic cells and the expansion of viral specific CD8+ T cell memory responses in HIV-1-infected and HIV-1-uninfected individuals.

Members of the TNF superfamily have been shown to be instrumental in enhancing cell-mediated immune responses, primarily through their interactions with dendritic cells (DCs). We systematically evaluated the ability of three TNF superfamily molecules, CD40 ligand (CD40L), receptor activator of NF-kappaB ligand (RANKL), and TNF-alpha, to expand ex vivo EBV-specific CTL responses in healthy human individuals and ex vivo HIV-1-specific CTL responses in HIV-1-infected individuals. In both groups of individuals, we found that all three TNF family molecules could expand CTL responses, albeit at differing degrees. CD40L treatment alone was better than RANKL or TNF-alpha alone to mature DCs and to expand CTL. In healthy volunteers, TNF-alpha or RANKL could cooperate with CD40L to maximize the ability of DCs to expand virus-specific CTL responses. In HIV-1 infection, cooperative effects between TNF-alpha or RANKL in combination with CD40L were variable. TNF-alpha and RANKL cooperated with CD40L via differing mechanisms, i.e., TNF-alpha enhanced IL-12 production, whereas RANKL enhanced survival of CD40L-stimulated DCs. These findings demonstrate that optimal maturation of DCs requires multiple signals by TNF superfamily members that include CD40L. In HIV-1 infection, DCs may only require CD40L to maximally expand CTL. Finally, CTL responses were higher in CD4(+) T cell-containing conditions even in the presence of TNF family molecules, suggesting that CD4(+) T cells can provide help to CD8(+) T cells independently of CD40L, RANKL, or TNF-alpha.