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Nanobodies as molecular probes for targeting of dendritic cells

Thursday, 8 July, 2010 - 10:45
Campus: Brussels Humanities, Sciences & Engineering campus
Faculty: Science and Bio-engineering Sciences
Kurt De Groeve
phd defence

Dendritic cells are professional antigen presenting cells that play an important role in the
control of immunity. The availability of “vehicles” to target these receptors in vivo is also a
key issue in the challenge to manipulate the effector functions of DCs in vivo. Nanobodies
are single‐domain antigen‐binding fragments derived from naturally occurring heavy‐chain
antibodies in Camelidae, constituting exquisite targeting moieties for therapeutic and
diagnostic applications. In the present study, we have evaluated Nanobodies as molecular
probes to target dendritic cells. Immunisation of llamas with bone marrow‐derived dendritic
cells resulted in the retrieval of a panel of anti‐DC Nanobodies after whole cell panning. The
generated anti‐DC Nanobodies displayed distinct binding profiles on in vitro and ex vivo cell
populations defining at least two groups of cellular specificity i.e. DC‐specific and myeloid
cell‐specific. To evaluate the application of anti‐DC Nanobodies as targeting moieties for
delivery of antigens to DCs, we have genetically fused a model Ag, with selected Nbs.
Nanobody‐mediated targeting to DCs could enhance antigen presentation of the truncated
OVA by the DCs, but so far the observed antigen presentation was restricted to the MHC
class I pathway. In order to explore the role of anti‐DC Nanobodies as imaging agents, the
biodistribution of radionuclide labelled Nanobodies was evaluated by single photon emission
computed tomography after intravenous injection in naïve mice. The observed in vivo
biodistribution for the selected Nanobodies with different cellular specificities nicely reflects
the main in vivo locations of the cells that have been determined in vitro to be recognized by
the Nanobodies. We verified the observed biodistributions of the Nanobodies by grafting the
antigen recognition loops upon a universal scaffold and re‐evaluated their biodistributions.
These experiments have indicated that the observed biodistribution of these Nanobodies is
determined by their antigen‐binding loops. In addition to the ‘classical’ Nanobodies, we
exploited for the first time a novel class of Nanobodies, in essence Nanobodies of the family
IV which expand the known repertoire.

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