Increased numbers of circulating hematopoietic stem/progenitor cells are chronically maintained in patients treated with the CD49d blocking antibody natalizumab

Abstract

Blockade of CD49d-mediated lymphocyte trafficking has been used therapeutically for certain autoimmune diseases, such as multiple sclerosis (MS). In addition to negative effects on the trafficking of mature lymphocytes to sites of inflammation, CD49d blockade in mice and monkeys rapidly mobilizes hematopoietic stem/progenitor cells (HSPCs) capable of short- and long-term engraftment. Here we aimed to ascertain the effects of treatment with antifunctional anti-CD49d antibody in humans (MS patients receiving infusions of the CD49d-blocking antibody natalizumab) on levels of circulating HSPCs after a single dose of antibody or after long-term treatment. On average, 6-fold elevated levels of circulating CD34+ cells and colony-forming unit-culture (CFU-C) were achieved within 1 day of the first dose of natalizumab, and similar levels were continuously maintained under monthly natalizumab infusions. The blood of natalizumab-treated subjects also contained SCID-repopulating cells. The fate of these circulating HSPCs and their clinical relevance for MS patients remains to be determined.

Figure 1

Elevated numbers of circulating HSPCs in the blood of natalizumab-treated MS patients. (A,D) Circulating HSPCs in healthy controls, not natalizumab-treated MS patients and long-term natalizumab-treated MS patients: Circulating CD34⁺ cells (1.8 ± 0.4/μL, P = .36 vs control) and CFU-C (638 ± 128/mL, P = .4 vs control) were normal in MS patients before the first natalizumab infusion (“untreated”) and significantly elevated in patients who had received at least 5 prior doses of natalizumab, measured immediately before application of the next dose (“chronic”; 9.0 ± 1.2/μL CD34⁺ cells, 3243 ± 332/mL CFU-C, P < .005 vs control). (Normal controls [“nl. ctrl.”]: 1.3 ± 0.1/μL CD34⁺ cells, 608 ± 129/mL CFU-C, on the left.) (B,E) First-dose natalizumab patients: After the first natalizumab infusion (“after”), peripheral blood CD34⁺ cells and CFU-C were significantly increased over pretreatment values (“before”; 1.6 ± 0.2/μL vs 8.0 ± 2.1/μL CD34⁺ cells, 414 ± 161/mL vs 2560 ± 726/mL CFU-C, P < .005). (C,F) Chronic natalizumab patients: Renewed natalizumab infusion (“after”) in “chronic” natalizumab recipients did not result in additional mobilization, compared with CD34⁺ cell and CFU-C values just before that infusion (7.9 ± 1.7/μL vs 7.9 ± 0.9/μL CD34⁺ cells, P = .99; 3133 ± 335/mL vs 3525 ± 305/mL CFU-C, P = .27). CD34⁺ cells/μL (A-C) or CFU-C/mL (D-F) are plotted on the y-axis. Each diamond represents values from one patient (for CFU-C: mean values from replicates from one patient); bars and whiskers indicate mean values plus or minus SEM. (G) CFU-C migration. In contrast to normal BM HSPCs, peripheral blood CFU-C from natalizumab recipients did not migrate toward SDF-1 in in vitro transwell assays (P < .001). (H) Cell-cycle status of natalizumab-mobilized HSPCs. natalizumab-mobilized CD34⁺ cells were almost exclusively quiescent and overwhelmingly in G₀ phase of cell cycle (flow cytometric histogram; RNA displayed on the x-axis, DNA on the y-axis).