Immune response to killed-whole cell cholera vaccines and development of immuno-monitoring method

Abstract

Vaccine is a cost-effective and prophylactic tool to defend host from infectious diseases. There are mainly three types of vaccines, inactivated whole cells, live attenuated whole cells, and purified or recombinant microbial components. Of these, inactivated whole cell vaccines are widely used due to convenience and low cost for preparation with high immunogenecity. Specific aims of in this work are (1) to characterize unique immunological properties to killed-whole cell cholera vaccines as a model system, (2) to develop a reliable serologic assay to evaluate vaccine efficacy for use in clinical trials, (3) to examine pokeweed mitogen (PWM) which has been used as a laboratory reagent in the evaluation of lymphocytes of vaccinees because of its human T or B-cell mitogenic potential. First, cholera vaccine showed different Toll-like receptor (TLR) response, TLR2 was a major receptor for killed V. cholerae rather than TLR4 unlike other gram-negative bacteria in chinese hamster ovary cell (CHO) system and human monocyte. Moreover, we demonstrated that LPS is not the major immuno-stimulating cell-wall component since the LPS purified from V. cholerae is less potent to induce inflammatory cytokines than membrane proteins or heat killed V. cholerae (HKVC). Secondly, we developed an improved assay for reliable serological assay of cholera vaccine. Through testing 30 pairs of clinical samples, we compared microtiter-plate format, which is normally used in clinical trials, to semi-automated assay a newly developed method in terms of correlations of the vibriocidal titers and fold increases in titers between pre- and post-vaccinated sera., Notably, the newly developed semi-automated assay demonstrated that serum samples with the same endpoint titers turned out to have distinct vibriocidal kinetics which were not distinguishable by the microtiter-plate assay. The semi-automated assay provides better sensitivity, accuracy, and stability of the assay results with minimized e...