Cured but not well : long term survivorship after allogeneic haematopoietic stem cell transplantation

Abstract

Improved donor matching and supportive care have reduced short term complications after allogeneic haematopoietic stem cell transplantation (HSCT), leading to a growing number of survivors. However, despite being cured of leukemia many patients struggle to return to a normal life due to persistent chronic graft versus host disease (cGvHD), fatigue and cognitive dysfunction. Failure to develop tolerance to the grafted immune system underlies cGvHD and we thus hypothesized that MSC treatment may be effective when the first lines of treatment has failed. Further, a similar mechanism in the brain may disrupt neural communication and underlie persistent fatigue and cognitive symptoms. Consequently, this thesis aimed to study MSC treatment of cGvHD, as well as central nervous system (CNS) function, neurobiology, and immunology in patients with fatigue after HSCT.

In study I, 11 patients that were refractory to or did not tolerate first-line treatment for cGvHD were administered repeated infusions of allogeneic MSC. Responses were seen in six patients according to the National Institutes of Health scale. Responding patients had a pre- treatment immune phenotype with increased naïve lymphocytes and infusion triggered short- term increases in naïve T-cells and regulatory T-cells. Further, CXC-motif Chemokine Ligand 9 and 10 are potential biomarkers of response, as they decreased in responders and increased in non-responders during the study.

Study II, III and IV recruited 27 patients in haematological remission with (n=14) or without (n=13) self-reported fatigue confirmed with validated questionnaires, 1-5 years after HSCT. Metabolic, neurological, and psychiatric diseases were excluded. Fatigue associated with worse quality of life and reduced employment. Further, computerized testing focusing on memory and executive function demonstrated cognitive impairments. Subsequent functional near infra-red spectroscopy showed reduced prefrontal cortex activity during cognitive challenges, and impaired responses to a single dose of methylphenidate, compared to the non-fatigued patients. Lumbar punctures were performed and immune activity in the cerebrospinal fluid was assessed by proteomic analyses, mRNA sequencing and flow cytometry. Cognitive dysfunction was associated with reduced factors involved in immune regulation, neurogenesis, and synapse function, supported by mRNA-expression suggestive of reduced cell-cell adhesion and noradrenergic neuron differentiation. Flow cytometry demonstrated increased activated T-cells in patients with fatigue and cognitive dysfunction.

In summary, cGvHD is the manifestation of an imbalance between inflammatory and regulatory factors after HSCT, where the stroma plays a major role. MSC treatment can restore this balance by inducing regulatory phenotypes in innate and adaptive immune cells, as demonstrated by the clinical responses seen in study I. We show that dysregulated immune activation after HSCT also occur in the CNS. Deficits in stromal-derived, reparative, and trophic factors in liquor, characterized patients with fatigue and cognitive dysfunction, perhaps by impairing cortical activity. This thesis emphasizes the need to understand the stroma-immune crosstalk, to design targeted therapies for debilitating, currently untreatable inflammatory conditions.