Reversibility of the effects of natalizumab on peripheral immune cell dynamics in MS patients

Abstract

Objective: To characterize the reversibility of natalizumab-mediated changes in pharmacokinetics/pharmacodynamics in patients with multiple sclerosis (MS) following therapy interruption.

Methods: Pharmacokinetic/pharmacodynamic data were collected in the Safety and Efficacy of Natalizumab in the Treatment of Multiple Sclerosis (AFFIRM) (every 12 weeks for 116 weeks) and Randomized Treatment Interruption of Natalizumab (RESTORE) (every 4 weeks for 28 weeks) studies. Serum natalizumab and soluble vascular cell adhesion molecule-1 (sVCAM-1) were measured using immunoassays. Lymphocyte subsets, α4-integrin expression/saturation, and vascular cell adhesion molecule-1 (VCAM-1) binding were assessed using flow cytometry.

Results: Blood lymphocyte counts (cells/L) in natalizumab-treated patients increased from 2.1 × 10⁹ to 3.5 × 10⁹. Starting 8 weeks post last natalizumab dose, lymphocyte counts became significantly lower in patients interrupting treatment than in those continuing treatment (3.1 × 10⁹ vs 3.5 × 10⁹; p = 0.031), plateauing at prenatalizumab levels from week 16 onward. All measured cell subpopulation, α4-integrin expression/saturation, and sVCAM changes demonstrated similar reversibility. Lymphocyte counts remained within the normal range. Ex vivo VCAM-1 binding to lymphocytes increased until ≈16 weeks after the last natalizumab dose, then plateaued, suggesting reversibility of immune cell functionality. The temporal appearance of gadolinium-enhancing lesions was consistent with pharmacodynamic marker reversal.

Conclusions: Natalizumab's effects on peripheral immune cells and pharmacodynamic markers were reversible, with changes starting 8 weeks post last natalizumab dose; levels returned to those observed/expected in untreated patients ≈16 weeks post last dose. This reversibility differentiates natalizumab from MS treatments that require longer reconstitution times. Characterization of the time course of natalizumab's biological effects may help clinicians make treatment sequencing decisions.

Classification of evidence: This study provides Class III evidence that the pharmacodynamic markers of natalizumab are reversed ≈16 weeks after stopping natalizumab.

Figure 1. Pharmacokinetic and pharmacodynamic assessments over the 28 weeks of randomized treatment in RESTORE

Least squares means estimates ± 95% confidence interval for (A) natalizumab concentration, (B) leukocyte percentage α4-integrin saturation, (C) leukocyte α4-integrin (CD49d) expression, and (D) serum vascular cell adhesion molecule (sVCAM) expression in patients continuing natalizumab or with a treatment interruption. The arrow represents the last dose before the 24-week interruption period. For percentage α4-integrin saturation (B), the gray dashed line indicates saturation prior to natalizumab treatment in the Safety and Efficacy of Natalizumab in the Treatment of Multiple Sclerosis (AFFIRM) natalizumab treatment arm (2.8%), as shown in figure e-1B. MFI = mean fluorescence intensity; RESTORE = Randomized Treatment Interruption of Natalizumab. *p < 0.001. ^aMean natalizumab levels were not analyzed once ≥33% of patients had values below the lower limit of quantification.

Figure 2. Total lymphocyte, lymphocyte subset, and hematopoietic progenitor counts over the 28 weeks in RESTORE

Least squares (LS) mean estimated counts ± 95% confidence interval (CI) for (A) total lymphocytes, (B) CD4+ T cells, (C) CD8+ T cells, (D) CD19+ B cells, (E) CD3−/CD16+/CD56+ natural killer (NK) cells, and (F) CD34+/CD45+ hematopoietic progenitor cells. Total lymphocyte counts in RESTORE patients stratified by demographics and disease activity. LS mean estimates ± 95% CI are shown for patients continuing and discontinuing natalizumab classified by (G) age, (H) disease activity, and (I) sex. The arrow represents the last dose before the 24-week interruption period. The shaded area shows the range of normal lymphocyte counts (total lymphocyte counts: 0.91–4.28 × 10⁹ cells/L [Safety and Efficacy of Natalizumab in the Treatment of Multiple Sclerosis (AFFIRM)]; CD4+ T cells¹⁴: 491–2,000 cells/mm³; CD8+ T cells¹⁴: 314–2,087 cells/mm³; CD19+ B cells¹⁴: 64–800 cells/mm³; CD3−/CD16+/CD56+ NK cells¹⁴: 27–693 cells/mm³; CD34+/CD45+ hematopoietic progenitor cells¹¹: 1.4–2.2 cells/mm³). For total lymphocytes (A, G, H, I), the gray dashed line indicates total lymphocyte counts prior to natalizumab treatment in the AFFIRM natalizumab treatment arm (2.08 × 10⁹ cells/L), as shown in figure e-1C. Lymphocyte subsets were not assessed in AFFIRM. RESTORE = Randomized Treatment Interruption of Natalizumab. *p < 0.05. **p < 0.001.

Figure 3. Functional activity of CD3+ T cells, CD19+ B cells, and monocytes from RESTORE patients

Least squares mean estimates ± 95% confidence interval are shown for ex vivo binding of cells to vascular cell adhesion molecule–1 (VCAM-1). The arrow represents the last dose before the 24-week interruption period. MESF = molecules of equivalent soluble fluorochrome; RESTORE = Randomized Treatment Interruption of Natalizumab. *p = 0.001 for T cells; p < 0.001 for B cells and monocytes. **p < 0.001 for T cells, B cells, and monocytes.

Figure 4. Relationship of α4-integrin saturation and the incidence of gadolinium-enhancing (Gd+) lesions over time after the last natalizumab dose

The median α4-integrin saturation level and the cumulative percentage of patients with a natalizumab treatment interruption developing Gd+ lesions are shown. The last natalizumab dose was administered on day 0. Patients with >1 Gd + lesion, %, represents the cumulative percentage of study patients with Gd + lesions out of all patients not treated with natalizumab who remained in the study at that time point.