CD28 and hydrops fetalis: Similarly to CD28, CD27 and its ligand CD70 control B- and T-cell function.45 Higher CD27/CD70 activity favours helper T-cell survival and induces apoptosis in Tregs.46 Interestingly, CD27−CD70+ Tregs paradoxically have pro-inflammatory effects, while CD27+CD70− Tregs show strong inhibitory potential.46,47 Thus, modulation of CD27/CD70 signalling, particularly by selective inhibition of CD70 might be an attractive approach in HF.