The goal of this observational study is to study the long-term effects of autologous hematopoietic stem cell transplantation (aHSCT) in people with highly active relapsing-remitting multiple sclerosis. The study will evaluate the following items: 1. Disease activity 2. Safety and tolerability of aHSCT 3. Changes in the immune system Participants will be subjected to frequent visits for five years after treatment with aHSCT. During these visits, clinical testing, evaluation by questionnaires, MRI scans and blood sampling will be performed.