0124: Single-cell atlas reveals the central-and-peripheral immune remodeling mechanism and clinical benefits of talitacicept therapy in patients with primary antiphospholipid syndrome

Background/Purpose: To elucidate the molecular and cellular mechanisms underlying Talitacicept therapy in primary antiphospholipid syndrome (PAPS) patients using integrated single-cell RNA and TCR/BCR profiling of paired bone marrow (BM) and peripheral blood (PB) samples.

Methods: 8 PAPS patients were recruited to receive standard Talitacicept treatment for 12 months. Clinical data were recorded every 3 months during treatment. Paired BM and PB samples were collected pre-treatment and after the 12-month treatment is completed. In 3 patients scRNA and BCR/TCR sequencing were performed on BMMCs and PBMCs to reveal the global changes in immune landscape; and for the other 5 patients, BM and PB B cells were sequenced to reveal intrinsic change in B cell subpopulations.

Results: 12 months of standard talitacicept treatment effectively reduced the number of B cells and plasma cells in both BM and PB. The number of neutrophils increased in all 3 patients after treatment, while CD4 T, CD8 T and NK cell showed a coordinated decrease in both BM and PB. However, a male patient with a poor treatment response (defined as no significant decrease in pan-aPL antibodies after treatment) showed an opposite increase in BM B cells. We also confirmed that most aPLs were effectively reduced, but the decline in aCL IgG and aβ2GPI IgG was relatively insignificant in male patients (Figure 1). The differential states of overall transcriptional characteristics revealed that B cells and plasma cells were the most significantly different cell subpopulations. Additionally, DEG (differential expressed gene) analysis showed each celltype presented significant downregulation of abundant interferon and inflammation-related genes. A B cell blueprint was constructed and confirmed that talitacicept effectively cleared most B cell subpopulations. Cellchat analysis indicated that the interactions from B cells and plasma cells toward other immune cells generally decreased after treatment, and UCell scoring also confirmed that the interferon, JAK-STAT pathway and apoptosis levels among global immune landscape were effectively reduced (Figure 2). For intrinsic changes in B cell lineage, naive B cells and plasma cells were the main subpopulations that decreased in BM and PB, while the relative proportions of pro-, pre-, and memory B cells increased. Additionally, B cell subpopulations presented similar downregulation of interferon and inflammation-related genes after treatment. Features potentially related with autoimmunity were evaluated, and the V-D-J rearrangement activity was reduced in pro/pre B cells, the activation level of naive B cells and the SHM level in memory B cell stage was reduced, while the autoantibody-related signature in plasma cells decreased as well (Figure 3).

Conclusion: Our study revealed the mechanism of talitacicept in treating PAPS patients, including reducing the level of pathogenic antibodies by eliminating mature B cells and plasma cells, inhibiting the interferon and inflammatory pathways among the global immune landscape, and reprogramming autoreactivity-related functions alongside B cell development trajectory. These findings provide important theoretical basis for optimizing the targeted treatment strategy of PAPS.