Nanobody-based targeting of the macrophage mannose receptor for effective in vivo imaging of tumor-associated macrophages.
Tumor-associated macrophages (TAM) are an important component of the tumor stroma and exert several tumor-promoting activities. Strongly pro-angiogenic TAMs that reside in hypoxic tumor areas highly express macrophage mannose receptor (MMR, CD206). In this study, we targeted MMR+ TAMs using nanobodies, which are single-domain antigen-binding fragments derived from Camelidae heavy-chain antibodies. MMR-specific nanobodies stained TAMs in lung and breast tumor single-cell suspensions in vitro, and intravenous injection of 99mTc-labeled anti-MMR nanobodies successfully targeted tumor in vivo. Retention of the nanobody was receptor-specific and absent in MMR-deficient mice. Importantly, co-injection of excess unlabeled, bivalent anti-MMR nanobodies reduced nanobody accumulation in extratumoral organs to background levels, without compromising tumor uptake. Within tumors, the 99mTc-labeled nanobodies specifically labeled MMR+ TAMs, as CCR2-deficient mice that contain fewer TAMs showed significantly reduced tumor uptake. Further, anti-MMR nanobodies accumulated in hypoxic regions, thus targeting pro-angiogenic MMR+ TAMs. Taken together, our findings provide preclinical proof of concept that anti-MMR nanobodies can be used to selectively target and image TAM subpopulations in vivo.
VIB Laboratory of Myeloid Cell Immunology, Cell Differentiation Unit, Diabetes Research Centre, Department of Immunology-Physiology, Vrije Universiteit Brussel, Brussels, Belgium.
Kiavash
K
Movahedi
Steve
S
Schoonooghe
Damya
D
Laoui
Isabelle
I
Houbracken
Wim
W
Waelput
Karine
K
Breckpot
Luc
L
Bouwens
Tony
T
Lahoutte
Patrick
P
De Baetselier
Geert
G
Raes
Nick
N
Devoogdt
Jo A
JA
Van Ginderachter
D000595:Amino Acid Sequence; D000818:Animals; D018827:Carcinoma, Lewis Lung / Q000000981:diagnostic imaging* / Q000276:immunology / Q000378:metabolism; D015687:Cell Hypoxia / Q000502:physiology; D005260:Female; D037181:Lectins, C-Type / Q000737:chemistry* / Q000276:immunology; D008264:Macrophages / Q000737:chemistry / Q000000981:diagnostic imaging* / Q000276:immunology; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins / Q000737:chemistry* / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D011956:Receptors, Cell Surface / Q000737:chemistry* / Q000276:immunology; D061905:Single-Domain Antibodies / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D013667:Technetium / Q000737:chemistry*; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods
D037181:Lectins, C-Type; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins; D011956:Receptors, Cell Surface; D061905:Single-Domain Antibodies; D013667:Technetium