In this phase I clinical trial of autologous BM-MSCs, which use a three-stage dose escalation scheme, we confirmed the safety and tolerability of the intra-arterial administration of BM-MSCs at a single dose of 9.0 × 105 cells/kg in patients with MSA-C. Although we did not observe significantly favorable motor outcomes because the sample size was small, the medium- and high-dose groups tended to have a slow rate of increase in USMARS score. Additionally, the plasma levels of some pro-inflammatory cytokines tended to be decreased after BM-MSC administration in the medium- and high-dose groups. These findings suggest that intra-arterial administration of autologous BM-MSCs is a safe and promising neuroprotective strategy in patients with MSA-C. Further studies with a larger sample size and multiple administration schedules are required to confirm the clinical efficacy of MSC treatment.
MSA is a rapidly progressive and fatal neurodegenerative disorder. Although no therapies have been proven to cure the disease or slow its progression [22], a growing body of evidence has suggested that cell therapy using MSCs is a promising therapeutic strategy for MSA [12–14, 23]. It is well established that MSCs can migrate to injury sites and secrete various neurotrophic factors that exert neuroprotective effects [15, 24], via anti-apoptotic [25], supportive (i.e., stimulation of mitosis, proliferation, and differentiation) [26], and angiogenic effects [25]. In our previous experimental studies, we have demonstrated the therapeutic potential of MSCs in animal models of parkinsonian disorders through anti-inflammatory action [27], autophagy modulation [28], stabilization of axonal transport [18], control of microglia M2 polarization [29], proteolysis of α-synuclein aggregates [17], and inhibition of α-synuclein transmission [16], which might modulate α-synuclein-related microenvironments. Furthermore, in two previous clinical trials [12, 13], we demonstrated the safety and clinical efficacy of intra-arterial and intravenous administration of autologous BM-MSCs in patients with MSA-C. However, our previous protocols were criticized for the barrier to the delivery of MSCs [14, 30]: although intravenous injection is the least invasive procedure, it may lead to the majority of MSCs being trapped in the lung, liver, and spleen [14, 31]. Intra-arterial administration allows a larger number of MSCs to reach the brain [31], although the BBB likely still comprises a major hurdle to MSC access [14]. For this reason, we slightly modified the protocol of BM-MSC administration (i.e., simply via intra-arterial routes) in the present trial. Additionally, we adjusted the dose of BM-MSCs based on a preclinical study and then estimated the maximum tolerated dose of BM-MSCs using a three-stage dose escalation schedule.
In the present study, we observed no SAEs corresponding to DLT. As a moderate level SUSAR, we saw one case of leptomeningeal enhancement in the cerebellar folia, along with enhancement in the right superior colliculus and right thalamus 1 day after the intra-arterial administration of MSCs. Clinically, these MRI findings might be attributed to BBB breakdown with increased permeability. We previously provided clinical and radiological evidence of increased BBB permeability in patients with MSA, [32] although it remains unclear whether this was due to a compensatory response to the neurodegenerative process or as a direct consequence of disease progression. MSCs can also penetrate the BBB [33, 34] either through transiently formed inter-endothelial gaps [35] or via interaction with adhesion molecules and activation of matrix metalloproteinases [36]. Therefore, the early-stage patient with MS in the present study who showed leptomeningeal enhancement in the cerebellar folia likely had a more efficient delivery of MSCs to the brain through the porous BBB [37–39]. Additionally, the reversible hyperintensity in the right superior colliculus and thalamus may have been related to a reactive implantation response to MSCs. A similar abnormal MRI finding was observed in a recently reported clinical trial of intrathecal administration of autologous MSCs in patients with MSA [14]. Taken together, this case demonstrated that the BBB penetrance of intra-arterially administrated MSCs is not associated with serious adverse effects in patients with MSA. Furthermore, none of the patients from the present study showed acute cerebral ischemic lesions on brain MRI after the procedure in this study. In a previous study, 28.6% of MSC-treated patients had ischemic spots [13]. This discrepancy may be due to the small number of patients in the present trial; it is less likely that the spotty ischemic lesions on diffusion-weighted images were secondary to the MSCs themselves or related to the MSC concentrations used in the present trial.
The present study failed to reveal whether MSC treatment was associated with slower disease progression assessed using the UMSARS scores. However, it is not surprising that statistically significant results could not be obtained because the number of patients was small in each treatment group. In fact, there was a dose-dependent trend, with the medium- and high-dose groups tending to have a slower rate of increase in UMSARS scores than the low-dose group. Moreover, these negative results may have arisen because the observation periods were insufficient to investigate disease progression. In our previous study, a significant treatment effect was observed at day 240 after initial MSCs treatment, implying that there is a considerable time lag until the neuroprotective effect of MSCs is clinically evident [13]. Additional studies with a large sample size and high-dose MSC therapy are required to investigate the clinical efficacy of MSCs. Meanwhile, we found that the plasma levels of pro-inflammatory cytokines, including IL-1β, TNF-α, and MCP-1, tended to be decreased after MSC treatment in the medium- and high-dose groups. These findings suggest that MSCs have a neuroprotective effect in patients with MSA, although the clinical benefits and changes in plasma cytokine levels did not reach statistical significance.
Our study had some limitations. First, it was designed as a single-center study because the procedures such as harvest and intra-arterial administration of MSCs required skilled and experienced experts. Secondly, the number of study participants was too small to draw significant results. Additionally, a single injection of MSCs may not be sufficient to exert an effect [13], so the safety and optimal timing of repeated injections should be further investigated. Thirdly, the study was confined to patients with MSA-C, whereas the European and North American MSA Study Groups reported a predominance of the MSA-parkinsonian (MSA-P) subtype over the MSA-C subtype [40, 41]. In fact, patients with MSA-P appear to have a distinct clinical course from patients with MSA-C [42, 43], and additional studies are required to validate the safety and tolerability of MSCs in patients with MSA-P.