Cross-dressing of CD8α+ Dendritic Cells with Antigens from Live Mouse Tumor Cells Is a Major Mechanism of Cross-priming.

Live cells are the most abundant sources of antigen in a tumor-bearing host. Here, we used live tumor cells as source of antigens to investigate the mechanism underlying their immunogenicity in murine tumor models. The live tumor cells were significantly more immunogenic than irradiated or apoptotic tumor cells. We examined the interaction of live and apoptotic tumor cells with major subsets of antigen-presenting cells, i.e., CD8α+ dendritic cells (DC), CD8α- DCs, plasmacytoid DCs, and CD169+ macrophages at skin draining lymph nodes. The CD8α+ DCs captured cell-associated antigens from both live and apoptotic tumor cells, whereas CD169+ macrophages picked up cell-associated antigens mostly from apoptotic tumor cells. Trogocytosis and cross-dressing of membrane-associated antigenic material from live tumor cells to CD8α+ DCs was the primary mechanism for cross-priming of tumor antigens upon immunization with live cells. Phagocytosis of apoptotic tumor cells was the primary mechanism for cross-priming of tumor antigens upon immunization with apoptotic or irradiated cells. These findings clarify the mechanism of cross-priming of cancer antigens by DCs, allowing for a greater understanding of antitumor immune responses.

YZGD from Paenibacillus thiaminolyticus, a pyridoxal phosphatase of the HAD (haloacid dehalogenase) superfamily and a versatile member of the Nudix (nucleoside diphosphate x) hydrolase superfamily.

YZGD from Paenibacillus thiaminolyticus is a novel bifunctional enzyme with both PLPase (pyridoxal phosphatase) and Nudix (nucleoside diphosphate x) hydrolase activities. The PLPase activity is catalysed by the HAD (haloacid dehalogenase) superfamily motif of the enzyme, and the Nudix hydrolase activity is catalysed by the conserved Nudix signature sequence within a separate portion of the enzyme, as confirmed by site-directed mutagenesis. YZGD's phosphatase activity is very specific, with pyridoxal phosphate being the only natural substrate, while YZGD's Nudix activity is just the opposite, with YZGD being the most versatile Nudix hydrolase characterized to date. YZGD's Nudix substrates include the CDP-alcohols (CDP-ethanol, CDP-choline and CDP-glycerol), the ADP-coenzymes (NADH, NAD and FAD), ADP-sugars, TDP-glucose and, to a lesser extent, UDP- and GDP-sugars. Regardless of the Nudix substrate, one of the products is always a nucleoside monophosphate, suggesting a role in nucleotide salvage. Both the PLPase and Nudix hydrolase activities require a bivalent metal cation, but while PLPase activity is supported by Co2+, Mg2+, Zn2+ and Mn2+, the Nudix hydrolase activity is Mn2+-specific. YZGD's phosphatase activity is optimal at an acidic pH (pH 5), while YZGD's Nudix activities are optimal at an alkaline pH (pH 8.5). YZGD is the first enzyme reported to be a member of both the HAD and Nudix hydrolase superfamilies, the first PLPase to be recognized as a member of the HAD superfamily and the first Nudix hydrolase capable of hydrolysing ADP-x, CDP-x and TDP-x substrates with comparable substrate specificity.