Immunomodulatory potential of human umbilical cord tissue-derived mesenchymal stromal cell (UCX®) exosomes in combination with immunosuppressive “A151” oligodeoxynucleotide

Abstract

Mesenchymal stromal or stem cells (MSCs) modulate immune responses apart from their regenerative capacities. Accumulating evidence suggests that MSCs exert their paracrine effects through extracellular vesicles known as exosomes. In this study, we utilized a particular human umbilical cord tissue-derived MSC type termed as UCX®. UCX® is superior to the gold-standard bone marrow-derived MSCs in terms of immunosuppressive properties. We aimed to characterize and employ UCX® exosomes as cell-free immunosuppressive therapeutic agents. Another aim was to compare the functionalities of exosomes either isolated from 2-dimensional (2D) cultures or isolated from 3-dimensional (3D) spheroid cultures. 3D culture provides better cell-to-cell and cell-to-matrix interactions thereby mimics the in vivo environment better. A synthetic oligodeoxynucleotide called A151 ODN, which consists of 4 repeats of the mammalian telomeric TTAGGG motif, has broad immunosuppressive effects. Delivery of A151 ODN within liposomes or exosomes protects it from degradation by nucleases and improve the desired outcome. We also aimed to combine the immunomodulatory potentials of UCX® exosomes and A151 ODN through direct loading of A151 ODN into exosomes with ~95% efficiency via a dehydration-rehydration-based lyophilization method. First, we determined the binding and internalization kinetics of exosomes with different immune cells. 3D-exosomes interacted with the target cells much faster and more efficiently. Next, we investigated how UCX® exosomes influence Toll-like receptor (TLR) signaling in mouse splenocytes and bone marrow-derived macrophages (BMDMs). 3D-exosomes compared to 2D-exosomes were more potent to suppress IFNγ, IL6, IL12, and to a lesser extent TNFα production mediated by TLR1/2, TLR4, TLR7/8 and TLR9 but not by TLR3 triggering. A151 ODN-loading to either 2D- or 3D-exosomes improved the inhibition of all the above mentioned pro-inflammatory cytokines. Especially 3D-exosomes downregulated co-stimulatory molecules CD80 and CD86 along with MHC-II on BMDMs following TLR stimulation. Macrophage polarization experiments revealed that UCX® exosomes reprogram BMDMs to produce high amounts of nitric oxide and arginase-1 which are the key immunomodulatory factors induced by myeloid-derived suppressor cells (MDSCs) to inhibit T- and NK-cell activity. Besides shifting macrophages to an MDSC-like suppressive phenotype, exosomes also supported expansion of MDSC populations in vivo upon intraperitoneal injection. Next, we tested the therapeutic efficiency of UCX® exosomes with or without A151 ODN in zymosan-induced peritonitis and dextran sodium sulfate (DSS)-induced colitis models in mice. Exosomes could not alleviate zymosan-induced peritonitis which is an acute and severe inflammation. However, 3D-exosomes and A151 ODN-loaded versions of both 2D- and 3D-exosomes remarkably prevented DSS-induced colitis progression. A151 ODN itself was also therapeutic, albeit to a lesser degree. Standalone 3D-exosomes and A151 ODN-loaded exosomes prevented weight loss and colon shortening. All treatments except for 2D-exosomes could restore DSS-induced loss of T-cell numbers and cytokine-producing capacities in mesenteric lymph nodes and spleen. All treatments except for A151 ODN prevented DSS-induced macrophage accumulation in the lymph nodes. 3D-exosomes and A151 ODN-loaded versions of both exosomes normalized serum IL6 levels while only A151 ODN-loaded 3D-exosomes could impact the cytokine production capacities of macrophages. Finally, we tested the effects of UCX® exosomes with or without A151 ODN on wound healing. In vitro, 2D- and 3D-exosomes differentially upregulated the productions of wound healing-related cytokines and growth factors such as IL1α, TGFβ and VEGFα from fibroblast and keratinocyte cell lines. In vivo, in an excisional wound healing model, free or A151 ODN-loaded exosomes did not accelerate wound closure. However, they caused systemic immunosuppression at the late stages of wound healing. Systemic outcomes include reduced inflammatory capacity of macrophages and higher granulocytic MDSC numbers in spleen. A151 ODN-loaded 3D-exosomes also reduced T-cell numbers in spleen and pro-inflammatory cytokine levels in circulation. Taken together, this study revealed that 2D- but more importantly 3D-culturing of umbilical cord MSCs result in functionally different exosomes, 3D culture-derived exosomes display higher immunosuppressive potential, A151 ODN-loading into these exosomes improves immunosuppressive capacity and A151 ODN-loaded UCX® exosomes could be a valuable therapeutic agent for inflammatory and autoimmune disorders.