Lupus Science & Medicine
Figure 3 Mezagitamab decreased type 1 interferon responsive genes. A subset of placebo and 135 mg patients had available samples analysed for inflammation-associated RNA gene expression by Nanostring. Data from selected type 1 interferon genes are presented as heatmaps normalised to the baseline expression of each gene for each patient. CLASI, Cutaneous Lupus Erythematosus Disease Area and Severity Index; SLEDAI-2K, SLE Disease Activity Index 2000.
Downstream pharmacology of targeting CD38 Since plasma cells reside predominantly in tissues (particularly in bone marrow), 19 potential effects of mezagitamab were assessed indirectly by using serum IgG as a surrogate biomarker. Multiple administrations of either 45 mg or 90 mg doses of mezagitamab resulted in modest reductions in IgG of less than 10% mean decrease from baseline at any given time point and did not show substantial differences compared with the placebo group, which had approximately 5% maximum mean decrease from baseline during the dosing period (figure 1C). In the 135 mg dose group, mezagitamab treatment resulted in 18.8% maximum mean decrease from baseline in IgG. Reductions in immunoglobulins generally did not return to baseline levels by day 85, which was the last time point of the study. In addition to changes in serum immunoglobulin concentrations, the effects of mezagitamab were assessed for changes in serum concentrations of autoantibodies in patients positive for a given autoantibody at baseline. There were six autoantibodies for which patients were positive: anti-dsDNA, anti-SmD p , beta-2 glycoprotein IgM, ribonucleoprotein-70, SS-A and SS-B. Many patients were positive for anti-dsDNA (9 of 22 patients) or SS-A (14 of total 22 patients). Changes in autoantibody concentra- tions did not appear to be dose dependent and generally did not show strong concordance with changes in total immunoglobulins or clinical response (online supple- mental figure 4). Maximum reductions in autoantibody concentrations were approximately 20% mean decrease from baseline for all evaluated autoantibodies (data not shown). Cytometry by time of flight To gain further insight into the broad immune land- scape changes induced by mezagitamab, CyTOF anal- ysis was performed on PBMCs. These results showed a general trend of CD38 expression being correlated with the extent of cell depletion (figure 2A). Plasma cells, regulatory B cells (Bregs), NK cells and plasmablasts
were among the most impacted populations, in align- ment with the receptor occupancy data for a subset of these cells. Additionally, the unsorted CyTOF data were subjected to FlowSOM clustering and TSNE visualisation (figure 2B,C, online supplemental figure 5). These data showed changes in cluster size specifically around clus- ters expressing high levels of CD38. To obtain more information on specific clusters undergoing substantial alteration, cluster number was increased from 20 to 50 (online supplemental figure 6A). This more granular analysis revealed two clusters of CD8+ and CD4+ (32 and 34, online supplemental figure 6B,C) that express gran- zyme, are CCR7−, and are CD45rAlo/−. Assessing treat- ment effect on this population revealed an increase in the prevalence of these populations, which appeared to dependent on time on treatment and/or dose (online supplemental figure 6B,C). Taken together, data showed that mezagitamab targets high CD38-expressing cells, resulting in their depletion and overall reduction of the CD38 signal in immune cells. IFN gene signature Whole blood RNA samples were collected at discrete time- points throughout the treatment course and subjected to Nanostring’s autoimmune profiling panel. All available data are presented in figure 3. Viable RNA samples for analysis were available for only a subset of patients in placebo and 135 mg groups and only at indicated time points. Based on the limited data available from placebo (n=4) and 135 mg (n=5), genes associated with a type 1 IFN response appeared to be downregulated in patients in the 135 mg cohort but not in placebo patients (figure 3). This response was most pronounced in the patients with the largest changes in CLASI scoring from baseline. DISCUSSION Mezagitamab was well tolerated, with no safety concerns and no observable differences in safety events across treat- ment groups identified in this study. The mezagitamab
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McDonnell SRP, et al . Lupus Science & Medicine 2024; 11 :e001112. doi:10.1136/lupus-2023-001112
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