Lymphopenia in Multiple Sclerosis patients treated with Ocrelizumab is associated with an effect on CD8 T cells

In the phase III, OPERA I and OPERA II, clinical trial lymphopenia was reported in 20.7% of relapsing-remitting multiple sclerosis (RRMS) patients taking Ocrelizumab (OCR).

The objective of this study was to investigate the effect of OCR on lymphocyte subtypes in MS patients with and without lymphopenia.

Retrospective study comparing lymphocyte subtypes in OCR-treated MS patients with low (G1) and normal (G2) absolute lymphocyte count (ALC) at the six-month follow-up (cut-off: 1000 × 10⁶/L). Mann Whitney U test was used to compare ALC, CD19, CD4 T, CD8 T and NK cell counts at baseline and at the six-month follow up between the two groups. A linear mixed model was applied to compare changes in ALC, and subset counts and proportions between patients with and without lymphopenia. We performed the same analyses in a subpopulation of naïve to treatment patients to exclude the possible influence of the previous disease modifying therapy (DMT) in the different kinetics observed between the two groups.

One hundred sixty-seven patients were included (G1, n = 34; G2, n = 133). At the six-month follow-up, compared with baseline, in the whole population we observed a significant reduction in ALC (p<0.0001), CD19 (p<0.0001) and CD8 T (p<0.0288) lymphocytes. We also found and increase in CD4/CD8 ratio after six months of treatment (p = 0.0098). G1 showed a lower ALC than G2 at baseline. At six months, mean ALC was 896.41 ± 156.25 × 10⁶/L in G1 and 1909.9 ± 629.07 × 10⁶/L in G2. CD4 and CD8 T cell mean counts were lower (p < 0.0001) in G1 than G2. At the linear mixed model analysis, we found a more pronounced increase in CD8 T percentage in G2 than G1 (p = 0.008). In the naïve to treatment group fifty patients were included. CD4 and CD8 T cell mean counts at six months were lower (p = 0.0074 and p = 0.0032, respectively) in G1 than G2. At the linear mixed model analysis, we found a more pronounced decrease of CD8 T cell count in G1 than G2 (p = 0.0103). Furthermore, we found an increase in CD8 T percentage in G2 whereas a profound decrease of CD8 T percentage was observed in G1 (p = 0.0052). After adjusting for confounders, significantly positive correlations were noted between ALC and both CD4 and CD8 T cell counts. Negative correlation was observed between ALC and CD4/CD8 ratio driven by low CD8 T cell counts.

OCR decreases ALC. Among T cells, the treatment predominantly impacts CD8 cells. However, CD8 T cell decrease was more pronounced in patients with lymphopenia. Further studies are needed to establish the relationship between the effect of OCR on ALC and CD8 T cells and its potential implication in the early clinical response and risk for viral infections.