Optimizing 3-dimensional human skin models to facilitate long-term development ofOnchocerca volvulus, a debilitating obligatory human parasite
Authors: Malkmus Christoph , Jawahar Shabnam , Tricoche Nancy , Lustigman Sara , Hansmann Jan 
Published: June 2020

Onchocerciasis also known as river blindness is a neglected tropical disease and the world’s second-leading infectious cause of blindness in humans; it is caused byOnchocerca volvulus. Current therapies kill microfilariae but fail to kill the adult parasites, which reside within subcutaneous nodules. To support a more target-driven drug development that can also cure and thus support the elimination of this disease, an in-depth understanding ofO. volvulusbiology especially the factors that support the longevity of these worms in the human host (>10 years) is required. However, research is hampered by a lack of access to adult worms.O. volvulusis an obligatory human parasite and no small animal models that can propagate this parasite were successfully developed. The current optimized 2-dimensional (2-D)in vitroculturing method starting withO. volvulusinfective larvae does not yet support the development of mature adult worms. To overcome these limitations, we have developed 3-dimensional (3-D) culture systems that simulated the humanin vivoniche usingin vitroengineered skin and adipose tissue. We show that an optimized indirect co-culture ofin vitroskin tissue with fourth-stage larvae supported a significant increase in growth until the pre-adult stage with a median length of 816 – 831 μm as compared to 767 μm of 2-D cultured larvae. Notably, when larvae were co-cultured directly with adipose tissue models, a significant improvement for larval motility and thus fitness was observed; 95 % compared to 26 % in the 2-D system. These promising co-culture concepts are a first step to further improve the long-term development of adult wormsin vitro, and thus provide the filarial research community with a valuable source ofO. volvulusworms at various developmental stages, which may accelerate innovative unsolved biomedical inquiries into the parasite’s biology.

Author summary

The filarial nematodeOnchocerca volvulusis an obligatory human parasite and the causative agent of onchocerciasis, better known as river blindness. In 2017, more than 20 million infections withO. volvuluswere estimated worldwide, 99 % of the patients live in Africa. Current international control programs focus on the reduction of microfilaridermia by mass drug administration of ivermectin. However, to meet the elimination goals, additional therapy strategies are needed that also target the adult worms. As this parasite is obliged to humans, there are no small animal models that sustain the full life cycle of the parasite, thus greatly impeding the research on this filarial nematode. To overcome these drawbacks, we developed co-culture systems based on engineered human skin and adipose tissue that represent thein vivoniche ofO. volvulusin which we were able to establish improved conditions of culturing to the pre-adult stages of the parasite. Furthermore, our new culture approach could significantly reduce the use of animal models currently used for drug testing of surrogate larvae.