Targeting tumor-associated myeloid cells

Samenvatting

Tumor cells produce soluble factors that favor the establishment of a myeloid cell compartment in the tumor microenvironment (TME). Many cancers are therefore characterized by a high infiltration of macrophages (MFs), myeloid-derived suppressor cells (MDSCs) and dendritic cells (DCs), albeit to a lesser extent. Most of these myeloid cells are found in an immature state in the TME. Consequently, they play an immunoregulatory role rather than an immunostimulatory role. Therefore, tumor- infiltrating myeloid cells (TIMs) have emerged as therapeutic targets.
The tumor-promoting activity of TIMs is often redundant. Consequently, it is contended that one should rather manipulate various TIMs instead of one subset, in order to control tumor development. Therefore, the aim of this study was to develop a novel strategy that acts on multiple TIMs. In this thesis, we studied nanobody drug conjugates (NDCs) as a tool to deplete tumor-promoting TIMs. Two NDCs were developed at the Laboratory of Molecular and Cellular Therapy. These consist of a nanobody specific for CD206 (macrophage mannose receptor) coupled to the protein wasabi green (WG) or truncated second mitochondria derived activator of caspases (tSMAC). These NDCs were used to study the binding and depletion of myeloid cells, respectively.
Flow cytometry was used to study the expression of CD206 on MFs, DCs and MDSCs, either generated in vitro or isolated from in vivo grown MO4 (melanoma) tumors. In vitro, expression of CD206 was observed on MFs and DCs, while MDSCs did not express CD206. In vivo, expression of CD206 was shown on MFs, DCs and MDSCs, suggesting that CD206 is a suitable marker for the targeting of TIMs. To deliver a proof-of-concept on the targeting ability of the NDCs, we used in vitro generated MFs that were treated with interferon-gamma (resulting in type 1 MFs) or interleukin-4 (resulting in type 2 MFs) as these are phenotypically characterized by low and high CD206 expression, respectively. As hoped, NDCs containing WG targeted the type 2 MFs, high in CD206, which was confirmed using flow cytometry. Two types of SMAC mimetics were used in addition to NDCs that contain tSMAC to evaluate upregulation of caspase 3/7, the downstream effector molecules of tSMAC. We showed that type 2 MFs show upregulation of caspase 3/7 followed by the loss of cell viability after incubation with both SMAC mimetics and that tSMAC containing NDCs exert similar effects. In contrast, type 1 MFs did not show caspase 3/7 upregulation nor cell death.
In conclusion, these preliminary data suggest that NDCs containing nanobodies specific for CD206 can be used to target CD206 expressing cells. Moreover, these data suggest that delivery of the pro- apoptotic protein tSMAC might be useful to deplete myeloid cells with pro-tumor activity, while it leaves myeloid cells with anti-tumor activity unharmed. How tSMAC mediates these opposing effects in myeloid cell subsets remains to be addressed. Solving this paradox will shed light on the usability of nanobody CD206 and tSMAC containing NDCs as a strategy to manipulate the TIM compartment, and thereby aid in resolving cancer.

Datum prijs	2018
Originele taal	English
Begeleider	Karine Breckpot (Promotor) & Yannick De Vlaeminck (Co-promotor)