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Tracy Hampton, PhD
No vaccine currently exists to protect against infection with the sexually transmitted bacterium Chlamydia trachomatis, which can cause female infertility and ectopic pregnancies and is the leading cause of preventable blindness in developing countries. Now, however, investigators at Harvard Medical School, in Boston, present a promising candidate vaccine consisting of UV light–inactivated C trachomatis tightly conjugated to charged nanoparticles carrying an adjuvant to boost the immune response (Stary G et al.Science. 2015;348:aaa8205).
The vaccine protected against C trachomatis infection in female conventional mice and mice engineered with human immune cells, although only when delivered through mucosal routes. Experiments revealed that protection relied on targeting a particular population of immunogenic dendritic cells and inducing mucosal memory T cells that reside in the uterus. Without these resident memory T cells, mice were suboptimally protected, even when circulating memory T cells were abundant. Optimal clearance of infection required 2 waves of immune protection, first seeding resident mucosal T cells and then circulating memory T cells.
Efforts to develop a chlamydia vaccine have been limited after failed trials in the 1960s, involving an injected inactivated form of chlamydia, paradoxically increased the susceptibility to infection among some women. The results of this latest study suggest that mucosal delivery and precise packaging of a vaccine are critical to its effectiveness against C trachomatis.