Hi, I am an American Board Certified Neurologist and I am very glad to help you with your health concerns.
With JC virus antibodies now being detected in your serum, and since you are on Tysabri I can fully understand your concerns related to the continuation of Tysabri due to the risk of PML. Since JC+ there is some increased risk to develop PML. The risk is overall quite small in the first 2 years of treatment, but if used for more than 2 years then there is a quite significant risk of developing PML. So your Dr is considering to continue on Tysabri for total 2 years and then switch to some other treatments. But with JC+ there is some risk of PML with treatment duration for less than 2 years too. But considering that there are not many very effective treatment options for SPMS it is really a tough decision to make regarding what to do next. There is some initial evidence to show that stem cell treatment can be useful in SPMS too. But it is still being used on research/experimental basis. If you could get into an institute where they are currently conducting stem cells for SPMS and also if they are actively recruiting patients then you may consider this treatment option. They will first evaluate you for inclusion & exclusion criteria and if you fulfil the inclusion criteria then you can get recruited. And you can specifically look for centres offering HSCT (Hematopoietic stem cell transplantation).
I have provided few relevant studies/articles below here and I hope you may find them helpful in making a final decision;
Tysabri related risk;
Stem cell treatment related;
Since stem cell treatment is still experimental for SPMS, and also there may be difficulties in finding a proper center to get recruited for these studies, and there could be some issues of adverse effects related to the stem cell treatment too (for example initially they seem to produce immunosuppression before conducting the stem cell implantation, this additional immunosuppression can further slightly increase the risk for PML) - so looking at all these issues it may be somewhat justifiable to stay on Tysabri until 2 years, however since there is some risk of PML even below 2 years of treatment because you are positive for JC virus so switching over to HSCT is not an imprudent decision, also considering the effectiveness of stem cells for SPMS – so may be worth considering HSCT treatment in your case.
Please let me know if you have any further questions; and if you feel you have received the answer to your question please rate me so that I can receive credit for the time and effort put by me in answering your question.