Effect of schistosome egg antigens on a Listeria vector HIV-1 vaccine
Bui, Cac Thanh
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Vaccines are an important public health measure for prevention and treatment of diseases. In addition to the vaccine immunogen, many vaccines incorporate adjuvants, to stimulate the recipient’s immune system and enhance vaccine-specific responses. While vaccine development has advanced from attenuated organism to recombinant protein or use of plasmid DNA, the development of new adjuvants that safely increase immune responses has not kept pace. Previous studies have shown the complex mixture of molecules that comprise saline soluble egg antigens (SEA) from Schistosoma mansoni eggs functions to promote CD4+ T helper 2 (Th2) responses. Therefore, we hypothesized that co-administration of SEA with a Listeria vector HIV-1 Gag (Lm-Gag) vaccine would suppress host cytotoxic T lymphocyte (CTL) and T helper 1 (Th1) responses to HIV-1 Gag epitopes. Surprisingly, instead of driving HIV-1 Gag-specific responses towards Th2-type, we found that co-administration of SEA with Lm-Gag vaccine significantly increased the frequency of IFNγ producing Gag-specific Th1 and CTL responses over that seen in mice administered Lm-Gag only. Analysis on the functionality and durability of vaccine responses suggested that SEA not only enlarged different memory T cell compartments but induced functional and long-lasting vaccine-specific responses as well. These results suggest there are components in SEA that can synergize with potent inducers of strong and durable Th1-type responses such as Listeria. We hypothesize SEA contains moietie(s) that if defined, can be used to expand type 1, pro-inflammatory responses for use in vaccines.