# Mesenchymal stem cells alleviate experimental cerebral malaria disease severity by inducing RoRγt+ Foxp3+ T regulatory (Tr 17) cells and modulating the dysregulated Th17/Treg axis

## TL;DR

Mesenchymal stem cells reduce cerebral malaria severity by balancing immune responses and inducing a specific regulatory T cell subset.

## Contribution

MSCs induce a novel Tr17 cell subset that suppresses harmful immune responses in cerebral malaria for the first time.

## Key findings

- MSCs reduced parasitemia, improved survival, and decreased spleen hemozoin accumulation in infected mice.
- MSCs modulated Th17/Treg imbalance by downregulating IL-6 and IL-17 and upregulating IL-10.
- MSCs induced RoRγt+ Foxp3+ Tr17 cells that suppressed pathogenic Th17 cells by downregulating IL-17.

## Abstract

Cerebral malaria (CM) is associated with dysregulated immune response against the blood stage of malaria parasite that often leads to serious organ damage, ultimately causing fatal pathological complications. Conventional treatments, although effective in controlling the parasite, often fail to address the severe immunopathology associated with the disease. Herein, we investigated the therapeutic potential of Mesenchymal stem cells (MSCs) in managing the excess proinflammatory response and maintaining immune homeostasis in Plasmodium berghei ANKA (PbA) infected C57BL/6 mice, an experimental cerebral malaria (ECM) disease model. Parasitemia and survival were monitored regularly, along with the neurological complications associated with the disease. Immunophenotyping, along with programmed cell death analysis of splenocytes, was also done via flow cytometry, and cytokine levels were analyzed at different time points in serum, as well as spleen, through bioplex assay and qRT-PCR. It was found that MSC effectively reduced parasitemia, increased survival, and decreased hemozoin accumulation in spleens of PbA-infected mice, along with improving brain pathology by preventing vascular leakage and protecting the blood–brain barrier (BBB). MSCs not only rescued the lymphocytes from apoptosis by downregulating PD-1/PD-L1 and ROS levels but also effectively modulated the Th17/Treg imbalance and maintained immune homeostasis by downregulating Interleukin-6 (IL-6) and Interleukin-17 (IL-17) cytokines and upregulating Interleukin-10 (IL-10) cytokine in infected mice. For the first time, we reported that MSCs were able to induce a dual phenotype effector Treg cell subset (Tr17), which are known to express both RoRγt and Foxp3 transcription factors, which were highly suppressive against pathogenic Th17 cells as they significantly downregulated IL-17 expression in Th17 cells. In conclusion, our findings offer insight into how the infusion of MSCs reduces the severity of experimental CM by modulating Th17/Treg balance and inducing Tr17 effector Treg response against Th17 cells. Thus, MSCs could potentially be used as an adjunct therapy for addressing the immunopathological complications of CM.