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

BACKGROUND: 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). OBJECTIVE: The objective of this study was to investigate the effect of OCR on lymphocyte subtypes in MS patients with and without lymphopenia. METHODS: 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. RESULTS: 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. CONCLUSION: 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.