Researchers report a safe vaccine candidate to combat a chronic skin condition in Sudan

In 2021, researchers showed that a new vaccine candidate is safe for patients with post-kala-azar dermal leishmaniasis (PKDL), a chronic skin condition.

Leishmania is a disease that kills over 20 000 people a year, and is spread by the bite of a female sand fly called phlebotomine. The disease can affect internal organs of the body, such as the spleen, liver, and bone marrow - this is called visceral leishmaniasis. 

Post-kala-azar dermal leishmaniasis (PKDL), is a chronic skin disease that may develop in patients who have suffered from this visceral form of leishmaniasis. 

The World Health Organisation (WHO) says leishmaniases is one of the most neglected diseases and is linked with poverty. 

This study was part of a clinical trial to test the safety and effectiveness of the ChAd63-KH vaccine in Sudanese patients with chronic PKDL. Researchers hope to use the vaccine to  prevent PKDL.

They tested the vaccine on a group of PKDL patients made up of 16 adults and 8 adolescents. They used several clinical and laboratory tests to measure the safety and efficacy of the vaccine. 

They confirmed that the vaccine is safe and effective to treat PKDL patients, and it can also be used to prevent PKDL.

This was the first study to use this type of vaccine in patients with leishmaniasis, highlighting an important opportunity to further test and develop the ChAd63-KH vaccine in patients with chronic PKDL.

This study was limited by a lack of complete understanding about Sudanese PKDL. More research is needed, but the researchers are confident that the results of this study are an important step in developing a vaccine for PKDL.

This study was done by Sudanese researchers in collaboration with researchers in the United Kingdom, Italy, and Germany.

Abstract

Post-kala-azar dermal leishmaniasis (PKDL) is a chronic, stigmatizing skin condition occurring frequently after apparent clinical cure from visceral leishmaniasis. Given an urgent need for new treatments, we conducted a phase IIa safety and immunogenicity trial of ChAd63-KH vaccine in Sudanese patients with persistent PKDL. LEISH2a (ClinicalTrials.gov: NCT02894008) was an open-label three-phase clinical trial involving sixteen adult and eight adolescent patients with persistent PKDL (median duration, 30 months; range, 6– 180 months). Patients received a single intramuscular vaccination of 1 X 1010 viral particles (v.p.; adults only) or 7.5 X 1010 v.p. (adults and adolescents), with primary (safety) and secondary (clinical response and immunogenicity) endpoints evaluated over 42–120 days follow-up. AmBisome was provided to patients with significant remaining disease at their last visit. ChAd63-KH vaccine showed minimal adverse reactions in PKDL patients and induced potent innate and cell-mediated immune responses measured by whole-blood transcriptomics and ELISpot. 7/23 patients (30.4%) monitored to study completion showed >90% clinical improvement, and 5/23 (21.7%) showed partial improvement. A logistic regression model applied to blood transcriptomic data identified immune modules predictive of patients with >90% clinical improvement. A randomized controlled trial to determine whether these clinical responses were vaccine-related and whether ChAd63-KH vaccine has clinical utility is underway.

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