The main aim is to quantify the changes in alemtuzumab antibody-anti-alemtuzumab over a 24 months period

Primary To quantify the longitudinal changes in alemtuzumab ADAs over a 24 month period.

Secondary

1. Relative occurrence of infusion-related reactions based on high alemtuzumab ADA levels prior to course 2.
2. Relative change in lymphocyte counts after the second infusion of alemtuzumab in ADA positive patients to assess the health economic impact of infusion-related reactions.
3. Relative change in relapses or EDSS score based on alemtuzumab ADA levels to assess the health economic impact of disease activity.
4. Relative change in relapses or EDSS score based on alemtuzumab ADA levels.
5. Relative change in T2 lesion number or Gd-enhancing lesions, and serum NfL based on alemtuzumab ADA levels to assess the health economic impact of disease activity.

Inclusion Criteria:

1. Patients with RRMS who are being treated with alemtuzumab at Barts Health NHS Trust will be approached to participate in the study.
2. Patients must be willing and able to undergo blood tests.

Exclusion Criteria:

1. Ineligible for alemtuzumab under NHS England prescribing guidelines.
2. Those unable to comply with study requirements, including frequency of visits. Abnormal baseline investigations (WBC<3 x 10*9/l, lymphocytes <1.0 x 10*9/l, neutrophil count <1.5 x 10*9/l, platelet count <100 x 10*9/l, haemoglobin <110 g/l, LFT >/3x upper limit of normal of site reference ranges, potassium <2.8 mmol/l or >5.5 mmol/l, sodium /,125 mmol/l, creatinine >130 umol/l).

Relapsing-remitting MS