Treatment with Natalizumab in Patients with Multiple Sclerosis Is Associated with Increased Numbers of Circulating CD34+ Cells in the  Peripheral Blood.

Introduction:

Under physiological condition there is a smallproportion of CD34+ hematopoietic stem and progenitors cellspresent in the peripheral blood.  The underlying mechanisms ofblood stem cell mobilisation and trafficking are only partiallyunderstood. It is apparently a multistep process involving cytokinesand chemoki nes as well as endothelial cells and compounds ofthe bone marrow’s extracellular matrix. Here, we analysedthe role of the adhesion molecule very late activation antigen4 (VLA-4), an a4/b1-integrin (CD49d), on CD34+ cells for bloodstem and progenitor cell trafficking. For this purpose, patientswith Multiple Sclerosis (MS) were examined who received thehumanized anti-VLA-4 monoclonal antibody Natalizumab, whichis directed against the a4 chain of the integrin.

Patients and Methods:

A total of 15 MS patients (11 females/ 4 males) with a median age of 31 years (range: 21–42)were included in the study. At the time of examination patientshad received a median number of 4 infusions (range: 1–9)of Natalizumab at a standard dose of 300 mg i.v. monthly.

Inall 15 patients the number of CD34+ cells and the immunophenotypewere analysed in the peripheral blood using flow-cytometry.The samples were taken four weeks following the last Natalizumabinfusion. For comparison, peripheral blood samples from 5 healthyvolunteers (4 females / 1 male) were also analysed. In additionsequential analysis, including colony-forming unit assays, wereperformed in 3 patients before and at 1, 24, 48 and 72 hoursafter initial administration of Natalizumab.

Results:

With a median proportion of 0.07% CD34+ cells (range:0.03 – 0.3) and a corresponding median concentration of6.8 CD34+ cells/µl blood (range: 2.2 – 32.4) theNatalizumab treated MS patients showed significantly higherCD34+ cell-counts compared to the 5 healthy volunteers who hada median proportion of 0.03% CD34+ cells (range: 0.01–0.03)and a median concentration of 1.4 CD34+ cells/µl blood(range: 0.6 – 2.5) (p=0.019).

In all 15 patients a secondCD34+ cell measurement was performed 1h after Natalizumab infusion,without showing a significant change in the number of circulatingCD34+ cells which argues against an immediate release.  Dualcolour phenotyping showed that the vast majority (>85%) ofcirculating CD34+ cells belonged to the subset of more committedprogenitors co-expressing CD38. Sequential analysis in 3 patientsshowed, that a single-dose administration of Natalizumab at300 mg iv caused a 4-fold increase in circulating CD34+ cells,representing pluripotent hematopoietic progenitors in vitrocolony-forming unit assays, with a peak value at 48 to 72 hourswithout declining to baseline levels within 31 days.