UM171A-induced ROS promote antigen cross-presentation of immunogenic peptides by bone marrow-derived mesenchymal stromal cells

Abstract

Background Mesenchymal stromal cells (MSCs) have been extensively used in the clinic due to their exquisite tissue repair capacity. However, they also hold promise in the field of cellular vaccination as they can behave as conditional antigen presenting cells in response to interferon (IFN)-gamma treatment under a specific treatment regimen. This suggests that the immune function of MSCs can be pharmacologically modulated. Given the capacity of the agonist pyrimido-indole derivative UM171a to trigger the expression of various antigen presentation-related genes in human hematopoietic progenitor cells, we explored the potential use of UM171a as a means to pharmacologically instill and/or promote antigen presentation by MSCs. Methods Besides completing a series of flow-cytometry-based phenotypic analyses, several functional antigen presentation assays were conducted using the SIINFEKL-specific T-cell clone B3Z. Anti-oxidants and electron transport chain inhibitors were also used to decipher UM171a’s mode of action in MSCs. Finally, the potency of UM171a-treated MSCs was evaluated in the context of therapeutic vaccination using immunocompetent C57BL/6 mice with pre-established syngeneic EG.7T-cell lymphoma. Results Treatment of MSCs with UM171a triggered potent increase in H2-Kb cell surface levels along with the acquisition of antigen cross-presentation abilities. Mechanistically, such effects occurred in response to UM171a-mediated production of mitochondrial-derived reactive oxygen species as their neutralization using anti-oxidants or Antimycin-A mitigated MSCs’ ability to cross-present antigens. Processing and presentation of the immunogenic ovalbumin-derived SIINFEKL peptide was caused by de novo expression of the Psmb8 gene in response to UM171a-triggered oxidative stress. When evaluated for their anti-tumoral properties in the context of therapeutic vaccination, UM171a-treated MSC administration to immunocompetent mice with pre-established T-cell lymphoma controlled tumor growth resulting in 40% survival without the need of additional supportive therapy and/or standard-of-care. Conclusions Altogether, our findings reveal a new immune-related function for UM171a and clearly allude to a direct link between UM171a-mediated ROS induction and antigen cross-presentation by MSCs. The fact that UM171a treatment modulates MSCs to become antigen-presenting cells without the use of IFN-gamma opens-up a new line of investigation to search for additional agents capable of converting immune-suppressive MSCs to a cellular tool easily adaptable to vaccination. Graphical abstract

Humoral Immunity to Allogeneic Immunoproteasome-Expressing Mesenchymal Stromal Cells Requires Efferocytosis by Endogenous Phagocytes

“…MSCs are generally used in regenerative medicine or as an immune-modulating therapy for the treatment of several autoimmune diseases or catastrophic illnesses such as graft-versus-host disease [ 35 , 36 , 37 , 38 , 39 ]. However, our group has demonstrated that MSCs can be converted to potent APCs following pharmacological treatment with the agonist pyrimido-indole derivative UM171a or by modulating the proteasomal machinery [ 19 , 21 , 40 ]. One example of the latter approach consists of engineering MSCs to express the IPr complex.…”

LSD1 Inhibition Enhances the Immunogenicity of Mesenchymal Stromal Cells by Eliciting a dsRNA Stress Response

“…Mesenchymal stromal cells (MSCs) were long perceived to be potent immune-suppressive cells mediating their effects via two distinct mechanisms: (i) the secretion of paracrine-acting soluble factors, and/or (ii) the activation/reprogramming of endogenous suppressive myeloid cells following MSC uptake by efferocytosis [ 1 , 2 , 3 , 4 ]. MSCs can, however, be reprogrammed to behave as antigen presenting cells (APCs) that are capable of capturing and cross-presenting extracellular antigens [ 5 , 6 ]. These new functions can be instilled through the de novo expression of specific proteasomal subunits, or in response to pharmacological stimulation [ 5 , 6 , 7 , 8 ].…”

“…MSCs can, however, be reprogrammed to behave as antigen presenting cells (APCs) that are capable of capturing and cross-presenting extracellular antigens [ 5 , 6 ]. These new functions can be instilled through the de novo expression of specific proteasomal subunits, or in response to pharmacological stimulation [ 5 , 6 , 7 , 8 ]. The latter strategy is particularly interesting as it entails the use of small molecules other than interferon (IFN)γ to elicit a selective rather than wider activation of gene expression [ 5 , 7 , 8 ].…”

“…These new functions can be instilled through the de novo expression of specific proteasomal subunits, or in response to pharmacological stimulation [ 5 , 6 , 7 , 8 ]. The latter strategy is particularly interesting as it entails the use of small molecules other than interferon (IFN)γ to elicit a selective rather than wider activation of gene expression [ 5 , 7 , 8 ]. An example of such an approach uses UM171a, a pyrimido-indole derivative that was originally identified for its ability to ex vivo stimulate hematopoietic stem cell (HSC) expansion [ 5 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ].…”

“…The latter strategy is particularly interesting as it entails the use of small molecules other than interferon (IFN)γ to elicit a selective rather than wider activation of gene expression [ 5 , 7 , 8 ]. An example of such an approach uses UM171a, a pyrimido-indole derivative that was originally identified for its ability to ex vivo stimulate hematopoietic stem cell (HSC) expansion [ 5 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ]. The idea of treating MSCs with UM171a stems from the ability of this chemotype to trigger the expression of the co-stimulatory molecule CD86 on the surface of UM171a-treated HSCs [ 14 ].…”