This study aims to immunophenotype PBMC subsets in CIS and RRMS patients not under disease modifying therapy; identify biomarkers that predict progression to RRMS; examine changes in PBMC subpopulations in RRMS over time; and examine the effect of cryopreservation and recovery on cell populations.

Clinically isolated syndrome (CIS) is the prodromal phase of multiple sclerosis (MS) disease course, with patients having experienced one neurological episode. Since up to 70% of CIS patients are subsequently diagnosed with MS, it is important to determine who will convert to RRMS later.

Multi-colour flow cytometry panels were used to identify up to 50 peripheral blood lymphocyte subpopulations. Samples from two sites were used, with one done on fresh blood and the other on cryopreserved cells after recovery. We compared patients with CIS who do (CIS-C) or don’t (CIS-N) covert to RRMS later with relapsing remitting multiple sclerosis (RRMS) patients, further divided into early (RRMS-E) and late (RRMS-L). Comparisons were also done between the two sites.

In the fresh samples, naïve/transitional B cells are significantly higher in RRMS-L than RRMS-E, which is similar to CIS-C. In the T cell compartment, the CD4-to-CD8 ratio and Th1 cells are both higher in RRMS than CIS-N. A lower percentage of CD27+ cells were found in recovered frozen samples across different subtypes, with the CD45RA expressing cells not showing the same change. Some NK cell populations are only significantly different in the cryopreserved samples.

Later conversion status to RRMS plays a role in immune subpopulations, with converters being more like RRMS patients in some. Cryopreservation of cells results in changes in immune subpopulations, decreasing CD27+ cells in CD45RA- cells and changing NK cell subpopulations. These results support the view that the immune system of CIS patients who convert to RRMS is similar to early stage RRMS patients.