Graft versus host disease (GvHD) is the clinical condition in which bone marrow-derived mesenchymal stromal cells (MSCs) have been most frequently studied. In this review, we summarize the experience from clinical trials that have paved the way to translation. While MSC-based therapy has shown an exceptional safety profile, identifying potency assays and disease biomarkers that reliably predict the capacity of a specific MSC batch to alleviate GvHD has been difficult. As GvHD diagnosis and staging are based solely on clinical criteria, individual patients recruited in the same clinical trial may have vastly different underlying biology, obscuring trial outcomes and making it difficult to determine the benefit of MSCs in subgroups of patients. An accumulating body of evidence indicates the importance of considering not only the cell product but also patient-specific biomarkers and/or immune characteristics in determining MSC responsiveness. A mode of action where intravascular MSC destruction is followed by monocyte-efferocytosis-mediated skewing of the immune repertoire in a permissive inflammatory environment would both explain why cell engraftment is irrelevant for MSC efficacy and stress the importance of biologic differences between responding and nonresponding patients. We recommend a combined analysis of clinical outcomes and both biomarkers of disease activity and MSC potency assays to identify patients with GvHD who are likely to benefit from MSC therapy.

Steroid-refractory chronic graft-vs-host disease (cGvHD) contributes to morbidity after allogeneic hematopoietic stem cell transplantation. Here, we report on 11 patients with severe, refractory cGvHD treated with repeated infusions of allogeneic bone marrow-derived mesenchymal stromal cells (MSC) over a 6- to 12-month period. Six patients responded to MSC treatment following National Institutes of Health response criteria, accompanied by improvement in GvHD-related symptoms and quality of life. This response was durable, with systemic immunosuppressive therapy withdrawn from two responders, and a further two free from steroids and tapering calcineurin inhibitors. All responders displayed a distinct immune phenotype characterized by higher levels of naïve T cells and B cells before treatment compared with the nonresponders, and a significantly higher fraction of CD31+ naïve CD4+ T cells. MSC treatment was associated with significant increases in naïve T cells, B cells, and Tregs 7 days after each infusion. Skin biopsies showed resolution of epidermal pathology. CXCL9 and CXCL10 showed differential responses in responder and nonresponder patients. Our data support the use of MSC infusions as treatment for steroid-refractory cGvHD with durable responses. We propose CXCL9 and CXCL10 as early biomarkers for responsiveness to MSC treatment. Our results highlight the importance of the MSC recipient immune phenotype in promoting treatment response. This trial was registered at www.ClinicalTrials.gov as #NCT01522716.

Bone marrow derived mesenchymal stromal cells (BM-MSCs) have emerged as a possible new therapy for Multiple Sclerosis (MS), however studies regarding efficacy and in vivo immune response have been limited and inconclusive. We conducted a phase I clinical study assessing safety and clinical and peripheral immune responses after MSC therapy in MS. Seven patients with progressive MS were intravenously infused with a single dose of autologous MSC (1–2 × 10⁶ MSCs/kg body weight). The infusions were safe and well tolerated when given during clinical remission. Five out of seven patients completed the follow up of 48 weeks post-infusion. Brain magnetic resonance imaging (MRI) showed the absence of new T2 lesions at 12 weeks in 5/6 patients, while 3/5 had accumulated new T2 lesions at 48 weeks. Patient expanded disability status scales (EDSS) were stable in 6/6 at 12 weeks but declined in 3/5 patients at 48 weeks. Early changes of circulating microRNA levels (2 h) and increased proportion of FOXP3⁺ Tregs were detected at 7 days post-infusion compared to baseline levels. In conclusion, MSC therapy was safe and well tolerated and is associated with possible transient beneficial clinical and peripheral immunotolerogenic effects.

Murine studies indicate that, after allogeneic haematopoietic stem cell transplantation (aHSCT), donor-derived macrophages replace damaged microglia and alloreactive T-cells invade the central nervous system (CNS). The clinical relevance of this is unknown. We assessed CNS immune surveillance and metabolic activity involved in neuronal survival, in relation to fatigue and cognitive dysfunction in 25 long-term survivors after aHSCT. Patients with cognitive dysfunction exhibited increased proportions of activated T-cells and CD16 + NK-cells in the cerebrospinal fluid (CSF). Immune cell activation was paralleled with reduced levels of anti-inflammatory factors involved in T-cell suppression (transforming growth factor-β, programmed death ligand-1), NK-cell regulation (poliovirus receptor, nectin-2), and macrophage and microglia activation (CD200, chemokine [C-X3-C motif] ligand-1). Additionally, the CSF mRNA expression pattern was associated with neuroinflammation and oxidative stress. Furthermore, proteomic, and transcriptomic studies demonstrated decreased levels of neuroprotective factors, and an upregulation of apoptosis pathway genes. The kynurenine pathway of tryptophan metabolism was activated in the CNS of all aHSCT patients, resulting in accumulation of neurotoxic and pro-inflammatory metabolites. Cognitive decline and fatigue are overlooked but frequent complications of aHSCT. This study links post-transplant CNS inflammation and neurotoxicity to our previously reported hypoactivation in the prefrontal cortex during cognitive testing, suggesting novel treatment targets.

Long-term fatigue and cognitive dysfunction affects 35% of allogeneic haematopoietic stem cell transplantation (aHSCT) survivors, suggesting a dysfunctional prefrontal cortex. In this study, we assessed prefrontal cortex and sympathetic nervous system activity in aHSCT patients with fatigue (n = 12), non-fatigued patients (n = 12) and healthy controls (n = 27). Measurement of near-infrared spectroscopy and electrodermal activity was carried out at rest and during cognitive performance (Stroop, verbal fluency and emotion regulation tasks). Prefrontal cortex and sympathetic nervous system activity were also analyzed in response to dopamine and noradrenaline increase after a single dose of methylphenidate. Baseline cognitive performance was similar in the two patient groups. However, after methylphenidate, only non-fatigued patients improved in Stroop accuracy and had better verbal fluency task performance compared to the fatigued group. Task-related activation of prefrontal cortex in fatigued patients was lower compared to non-fatigued patients during all cognitive tests, both before and after methylphenidate administration. During the Stroop task, reaction time, prefrontal cortex activation, and sympathetic nervous system activity were all lower in fatigued patients compared to healthy controls, but similar in non-fatigued patients and healthy controls. Reduced prefrontal cortex activity and sympathetic arousal suggests novel treatment targets to improve fatigue after aHSCT.