First Phase 1 Trial of Chlamydia Vaccine Candidate Shows Promising Results

The US Centers for Disease Control and Prevention (CDC) estimates that the rate of sexually transmitted infections (STI) are on the rise with an estimated 1.7 million cases documented in 2017 in the United States.

Although chlamydia can typically be successfully treated with antibiotics, if left untreated it can cause serious health issues. Untreated chlamydia in women can cause severe damage to the uterus and fallopian tubes and lead to and ectopic pregnancy in women or even infertility.

With the rate of cases on the rise, it is clear that screening programs and antibiotic treatment alone have fallen short in decreasing incidence. Furthermore, there are no vaccines available to prevent against the infection.

But now, for the first time, investigators have conducted a phase 1 clinical trial in humans to assess the safety and immunogenicity of a novel vaccine candidate for chlamydia. The results of the study were published in The Lancet Infectious Diseases.

"Given the impact of the chlamydia epidemic on women's health, reproductive health, infant health through vertical transmission, and increased susceptibility to other sexually transmitted diseases, a global unmet medical need exists for a vaccine against genital chlamydia," said study author Peter Andersen, DVM, DMSc, from Statens Serum Institut, Denmark, in a statement.

The double-blind, parallel, randomized, placebo-controlled trial was conducted at Hammersmith Hospital in London, United Kingdom. The vaccine is based on a recombinant protein subunit (CTH522) and evaluated in a prime—boost immunization schedule.

The study enrolled 35 female participants aged 19-45 years. The participants were randomized 3:3:1 to receive either: CTH522 adjuvanted with CAF01 liposomes (CTH522:CAF01), CTH522 adjuvanted with aluminum hydroxide (CTH522:AH), or placebo.

Study participants received 3 intramuscular injections of 85 μg vaccine or placebo to the deltoid region of the arm at 0, 1, and 4 months, followed by 2 intranasal administrations of 30 μg at months 4.5 and 5.0. The primary outcome of the study was safety and the secondary outcome was anti-CTH522 IgG seroconversion.

The study was conducted between August 15, 2016, and February 13, 2017. During this time, 32 of the 35 enrolled participants received all 5 doses. The most frequent adverse events were mild local injection-site reactions, which were reported in all participants in the 2 vaccine groups and in 3 of the 5 participants in the placebo group (p = 0.0526 for both comparisons). According to the investigators, no serious adverse reactions related to the vaccine were reported.

“Intranasal vaccination was not associated with a higher frequency of related local reactions (reported in 7 [47%] of 15 participants in the active treatment groups vs 3 [60%] of 5 in the placebo group; p = 1.000),” the authors wrote.

The team observed that both CTH522:CAF01 and CTH522:AH induced anti-CTH522 IgG seroconversion in 100% of participants after 5 immunizations, although no participants in the placebo group seroconverted. However, CTH522:CAF01 showed accelerated seroconversion, as well as increased IgG titers, enhanced mucosal antibody profile, and a more consistent cell-mediated immune response profile when compared with CTH522:AH.

“Both vaccines were immunogenic, although CTH522:CAF01 had a better immunogenicity profile, holding promise for further clinical development,” the authors conclude.