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New Treatments for Traumatic Brain Injury

Can a combination of regulatory T-cells and mesenchymal stromal cells modulate microglial responses?

Traumatic brain injury (TBI) is a leading cause of death and disability worldwide. And physical damage it causes is only the beginning; a chain reaction of inflammation within the brain can lead to even more significant harm, often resulting in lifelong impairments. Existing treatments have been largely ineffective in reducing this secondary injury. However, a promising new treatment for traumatic brain injury using a new combination therapy of regulatory T-cells (Treg) and mesenchymal stromal cells (MSCs) to modulate microglial responses may offer hope.

The Inflammatory Response to TBI

Microglia  – the so-called immune cells of the brain – are crucial in the inflammatory response to TBI. These cells become activated and contribute to secondary brain injury and pathology that can last for years. That response involves a complex interaction of cells within the central nervous system (CNS) and systemic immune systems. One way cell therapies tackle this response is via Treg.

The authors of this new study have previously explored the use of human MSCs and human cord blood-derived Treg therapy to reduce inflammation after TBI, and both therapies have shown potential in decreasing the neuroinflammatory response by interacting with the host immune system. However, to build on this work, they speculated that a combination of both therapies might offer greater benefits than either treatment alone. After all, two’s better than one, right?

Treg+MSC Combination Therapy: Modulating the Microglia Response

The team set out to establish the efficacy of human MSC+Treg combination therapy and Treg and MSC monotherapies on the inflammatory response after TBI as potential new treatments for traumatic brain injury. They started by establishing a suitable population of cells by immunophenotyping live microglia using a mix of antibodies suited to live cell flow cytometry (Figure 1), including the anti-P2Y12 receptor antibody conjugated directly to FITC from Alomone Labs.

Gating Microglia

Figure 1. Microglia gating strategy and multicolor flow cytometry panel. (A): Representative samples from both sham and CCI groups are shown. The single cell population was identified based on SSC and FSC. Live cells were identified as negative for the 7-AAD. Microglia were identified using a two-step method. First, CD11b/c+ cells (PE-Cy7) were selected to identify all myeloid cells. The CD11b/c+ cells were then gated on P2Y12 (FITC) and CD45 (APC-Cy7). Microglia were identified as triple positive cells. SSC, side scatter; FSC, forward scatter. (B): The multiple color flow cytometry panel used to identify and immunophenotype microglia and peripheral myeloid cells. Image and legend from Caplan, H. W., et al. Stem Cells. 2021;39(3):358-370.

From here, their in vitro work examined the immunomodulatory effects of this MSC+Treg combination therapy on rat splenocytes and then on the sorted rat microglia as a possible new TBI treatment. In splenocytes, Treg+MSC combination therapy significantly reduced the production of key pro-inflammatory cytokines, such as TNFα and IFNγ, more effectively than either Treg or MSC monotherapies. This effect was particularly pronounced in the reduction of IFNγ and several other cytokines such as MCP-1, GM-CSF, IL-17A, and IL-6. When they looked at primary cultures of rat microglia, the combined therapy also consistently inhibited the inflammatory response and showed differential effects on activated microglia concerning cytokine production and surface phenotypes.

The in vitro work was off to a good start. Finally, the researchers moved to in vivo work to see if this Treg+MSC combination therapy would modulate microglia response after TBI as it had done in vitro. By using specific timing for the infusions of Treg and MSC, they demonstrated that the treatment was indeed successful in reducing microgliosis in the brain after 14 days – a critical phase in the inflammatory response. The results were not only in line with the in vitro studies, but also suggested the importance of timing and multiple infusions in achieving therapeutic efficacy, possibly leading to a new treatment for traumatic brain injury.

Overall, they found that all therapies reduced markers of microglia activation, and that combination therapy significantly decreased the systemic inflammatory response compared to monotherapy. Furthermore, the timing of therapy emerged as an important factor: staggered Treg+MSC therapy, where the treatments were administered at different times, proved more effective both in laboratory tests and animal models.

The Future is Combination

Based on early phase results here, combination therapy of Treg+MSC could offer a new direction in the quest to discover new treatments for traumatic brain injury. By attenuating microgliosis and the inflammatory response, this combined approach delivers superior results compared to monotherapies in both laboratory and animal models.

Crucially, the study’s insights into the timing of therapy have important implications for any new TBI treatments. Treg+MSC combination therapy represents a significant step forward in our understanding and treatment of TBI’s inflammatory response, with real potential for therapeutic development of new treatments for traumatic brain injury as we pursue this research further.


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