Scientists are One Step Closer to a Vaccine for Chlamydia

In the past, efforts to develop a safe and effective vaccine for chlamydia proved fruitless.

However, the findings of a team of Canadian researchers may be the first step in the formulation of a viable prophylactic strategy for the troubling sexually transmitted infection (STI). Using mice models, scientists from McMaster University and St. Joseph’s Healthcare have identified a possible role for a multi-component vaccine consisting of the N-terminal 100 amino acids of chlamydia trachomatis (CopB, CopD, and full length CT584), although many questions about how it works remain unanswered. Their findings were published on July 25th in the journal Vaccine.

“Despite decades of research on chlamydia immunobiology, limited success has been achieved in vaccine development,” they write in the Vaccine paper. “Given the success of vaccines derived from T3SS proteins in other bacterial species, we developed a novel trivalent antigen consisting of three T3S chlamydia proteins… The highly conserved nature of T3SS proteins across different bacterial species suggests that immunization with T3S antigens could produce an effective pan-serovar Chlamydia vaccine.”

Chlamydia has posed a healthcare challenge for clinicians due to the serious complications associated with it. The World Health Organization reports that more than 100 million cases of the STI are diagnosed each year, in both developed and developing countries. Though often asymptomatic, the infection, if left untreated, can lead to pelvic inflammatory disease and even tubal factor infertility.

The researchers, working in the laboratory of James B. Mahony, BSc, PhD, experimented with the novel vaccine, called BD584, in 10 mice infected with chlamydia. Five of the mice received the vaccine intranasally, delivered with a vehicle solution of phosphate buffered saline, and 5 control mice received phosphate buffered saline alone.

They found that intranasal immunization with BD584 elicited serum neutralizing antibodies that inhibited chlamydia trachomatis infection in vitro. Following intravaginal challenge with chlamydia muridarum, immunized mice had a 95% reduction in chlamydial shedding (P<0.05) from the vagina at the peak of infection. They also cleared the infection sooner than control mice. Interestingly, the authors also noted that immunization with BD584 reduced the rate of hydrosalpinx by 87.5% compared to control mice (P<0.05). As a follow-up to this research, the authors are currently investigating BD584’s immune mechanism of protection.

The authors of the Vaccine paper did not respond to requests for comment at press time.

However, in their concluding remarks, they write, “We show here for the first time that T3SS antigens from chlamydia represent a good vaccine candidate. Intranasal immunization of mice with BD584 antigen plus CpG adjuvant elicited serum antibodies against BD584 [that] were capable of neutralizing chlamydia infection in vitro. Mice vaccinated with BD584 and challenged with [chlamydia] muridarum had a reduction in both bacterial shedding and chlamydia-induced fallopian tube pathology. Together, this data suggests that BD584 represents a good chlamydial vaccine candidate.”

Brian P. Dunleavy is a medical writer and editor based in New York. His work has appeared in numerous healthcare-related publications. He is the former editor of Infectious Disease Special Edition.