Hematopoietic stem cell transplantation (HSCT) is a potentially curative treatment for multiple sclerosis (MS) with now more than 600 documented cases in the medical literature. Long-term remission can be achieved with this therapy, but when is it justified to claim that a patient is cured from MS? In attempt to answer this question, the outcome of the Swedish patients is described, mechanisms behind the therapeutic effect are discussed and new tools for demonstration of absence of disease have been developed.

In Swedish patients treated with HSCT for aggressive MS, disease free survival was 68 % at five years, and no patient progressed after three years of stable disease. Presence of gadolinium enhancing lesions prior to HSCT was associated with a favorable outcome (disease free survival 79 % vs 46 %, p=0.028). There was no mortality and no patient required intensive care.

The immune system of twelve of these patients was investigated further. In most respects HSCT-treated patients were similar to healthy controls, demonstrating normalization. In the presence of a potential antigen, leukocytes from HSCT-treated patients ceased producing pro-inflammatory IL-17 and increased production of the inhibitory cytokine TGF-β1 suggesting restoration of tolerance.

Cytokine levels and biomarkers of tissue damage were investigated in cerebrospinal fluid from a cohort of MS patients. The levels were related to clinical and imaging findings. A cytokine signature of patients with relapsing-remitting MS could be identified, characterized by increased levels of CCL22, CXCL10, sCD40L, CXCL1 and CCL5 as well as down-regulation of CCL2. Further, we could demonstrate that active inflammation in relapsing-remitting MS is a tissue damaging process, with increased levels of myelin basic protein and neurofilament light. Importantly, relapsing-remitting MS patients in remission displayed no tissue damage. In secondary progressive MS, moderate tissue damage was present without signs of active inflammation.

From a clinical vantage point, it seems that we confidently can claim cure of relapsing-remitting MS patients after five years absence of disease activity. The new tools for evaluation of disease can strengthen this assertion and may enable earlier prediction of outcome.