Nanobodies As Tools to Understand, Diagnose, and Treat African Trypanosomiasis

Abstract

African trypanosomes are strictly extracellular protozoan parasites that cause diseases in humans and livestock and significantly affect the economic development of sub-Saharan Africa. Due to an elaborate and efficient (vector)–parasite–host interplay, required to complete their life cycle/transmission, trypanosomes have evolved efficient immune escape mechanisms that manipulate the entire host immune response. So far, not a single field applicable vaccine exists, and chemotherapy is the only strategy available to treat the disease. Current therapies, however, exhibit high drug toxicity and an increased drug resistance is being reported. In addition, diagnosis is often hampered due to the inadequacy of current diagnostic procedures. In the context of tackling the shortcomings of current treatment and diagnostic approaches, nanobodies (Nbs, derived from the heavy chain-only antibodies of camels and llamas) might represent unmet advantages compared to conventional tools. Indeed, the combination of their small size, high stability, high affinity, and specificity for their target and tailorability represents a unique advantage, which is reflected by their broad use in basic and clinical research to date. In this article, we will review and discuss (i) diagnostic and therapeutic applications of Nbs that are being evaluated in the context of African trypanosomiasis, (ii) summarize new strategies that are being developed to optimize their potency for advancing their use, and (iii) document on unexpected properties of Nbs, such as inherent trypanolytic activities, that besides opening new therapeutic avenues, might offer new insight in hidden biological activities of conventional antibodies.

Use of camel single-domain antibodies for the diagnosis and treatment of zoonotic diseases

“…Multiple VHHs have already been generated against the parasite (for a review, [60]). Trypanolytic VHH An46 disturbs the endocytic machinery of the parasite in the flagellar pocket of the parasite.…”

Evolution of protein trafficking in kinetoplastid parasites: Complexity and pathogenesis

“…Exploitation of the unique aspects of the trypanosome surface and trafficking has underpinned much of the classical therapeutic arsenal, and recent applications of nanobodies (Nbs) have the potential to extend this in a rational manner. Nbs are derived from heavy chain‐only antibodies of camelids (see recent review), and can be utilized for delivery of drugs and toxins with high efficiency and specificity owing to their biochemical and physical features. An immunotoxin consisting of a nanobody coupled to serum trypanolytic factor Apolipoprotein L‐1 (ApoL‐1) circumvented resistance dependent on the ApoL‐I‐neutralizing serum resistance‐associated (SRA) protein in T. b. rhodesiense, while Nbs coupled to pentamidine not only enhanced the potency of pentamidine but also overcome resistance to pentamidine dependent on aquaglyceroporin‐2 (AQP2) .…”

Adaptation and Therapeutic Exploitation of the Plasma Membrane of African Trypanosomes

“…Moreover, a plethora of drugs have been developed through target-based strategies, and which fail against intact cells, likely due to difficulty in crossing biological membranes. In this regard, the development of nanobodies (Nbs), small (~15 kDa) antibody fragments derived from camelid heavy chains, has recently proved to provide an unparalleled opportunity to test this concept [99,100].…”

“…Nbs possess several key features that make them attractive candidates for therapeutic applications; apart from small size, they can bind to their target with nanomolar affinity and are highly soluble [99]. More importantly, given their small size they can recognize epitopes that are otherwise inaccessible to IgG or IgM, and can penetrate the blood-brain barrier, providing an opportunity to deliver compounds to parasites in the CNS during late stage disease [99].…”

“…Nbs possess several key features that make them attractive candidates for therapeutic applications; apart from small size, they can bind to their target with nanomolar affinity and are highly soluble [99]. More importantly, given their small size they can recognize epitopes that are otherwise inaccessible to IgG or IgM, and can penetrate the blood-brain barrier, providing an opportunity to deliver compounds to parasites in the CNS during late stage disease [99]. A recent report demonstrated that nanoparticles loaded with pentamidine, coated with the Nb-33 against a variable region of VSG reduced the IC50 by 7-fold in vitro, and cured infected mice with ~10-fold lower dose than free pentamidine [101].…”