DNA amount and quality are very critical for Nucleofection™ of Dendritic Cells (recommended 0.5-1µg; maximal 2 µg). LPS (lipopolysaccharides) have a strong negative effect on cell viability. Please make sure that all components you use for dendritic cell culture and transfection, e.g. PBS, FCS and especially DNA, are Endotoxin free. We additionally recommend purifying your DNA by precipitating it twice with 20% PEG/2.5 M NaCl. Viability is usually not an issue when working with mRNA or siRNA.