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 small proportion of CD34+ hematopoietic stem and progenitors cells present in the peripheral blood. The underlying mechanisms of blood stem cell mobilisation and trafficking are only partially understood. It is apparently a multistep process involving cytokines and chemokines as well as endothelial cells and compounds of the bone marrow’s extracellular matrix. Here, we analysed the role of the adhesion molecule very late activation antigen 4 (VLA-4), an a4/b1-integrin (CD49d), on CD34+ cells for blood stem and progenitor cell trafficking. For this purpose, patients with Multiple Sclerosis (MS) were examined who received the humanized anti-VLA-4 monoclonal antibody Natalizumab, which is 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 patients had received a median number of 4 infusions (range: 1–9) of Natalizumab at a standard dose of 300 mg i.v. monthly. In all 15 patients the number of CD34+ cells and the immunophenotype were analysed in the peripheral blood using flow-cytometry. The samples were taken four weeks following the last Natalizumab infusion. For comparison, peripheral blood samples from 5 healthy volunteers (4 females / 1 male) were also analysed. In addition sequential analysis, including colony-forming unit assays, were performed in 3 patients before and at 1, 24, 48 and 72 hours after initial administration of Natalizumab.

Results: With a median proportion of 0.07% CD34+ cells (range: 0.03 – 0.3) and a corresponding median concentration of 6.8 CD34+ cells/μl blood (range: 2.2 – 32.4) the Natalizumab treated MS patients showed significantly higher CD34+ cell-counts compared to the 5 healthy volunteers who had a 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 second CD34+ cell measurement was performed 1h after Natalizumab infusion, without showing a significant change in the number of circulating CD34+ cells which argues against an immediate release. Dual colour phenotyping showed that the vast majority (>85%) of circulating CD34+ cells belonged to the subset of more committed progenitors coexpressing CD38. Sequential analysis in 3 patients showed, that a single-dose administration of Natalizumab at 300 mg iv caused a 4-fold increase in circulating CD34+ cells, representing pluripotent hematopoietic progenitors in in vitro colony-forming unit assays, with a peak value at 48 to 72 hours without declining to baseline levels within 31 days.

Conclusion: Natalizumab treatment is associated with an increased number of circulating CD34+ cells in the peripheral blood in patients with MS. This effect of Natalizumab might be useful for patients with hematological malignancies responding poorly to G-CSF based mobilisation protocols.