Single-cell sequencing of bone marrow cells and peripheral mononuclear cells reveals immune features of paraneoplastic pemphigus in a FL patient

Abstract Objective：To elucidate the cellular and molecular mechanisms underlying paraneoplastic pemphigus (PNP), a fatal autoimmune blistering disease associated with benign/malignant neoplasms, particularly when occurring secondary to lymphoma.Methods：Single-cell transcriptional profiling and T cell receptor (TCR) analysis were performed on peripheral blood mononuclear cells (PBMCs) and bone marrow cells (BMCs) from a follicular lymphoma (FL) patient with PNP. Samples were collected before, during, and after successful treatment to map immune dynamics.Results：Before the treatment, the specific enrichment of ITGAL+ T cells, abnormal γδT cell subtypes and BCL2+ B cells were observed in PBMCs. And especially, the naïve T cells and abnormal B cell subtype were enriched in BMCs. Specifically, in our FL patient with PNP, the single-cell analysis revealed the enrichment of ITGAL+ T cells and two abnormal γδT cell subtypes (TRDV1+ KLRD1+ and TRDV1+ KLRB1+). In PNP, ITGAL+ T cells may contribute to tissue damage by enhancing cytotoxic T cell recruitment to mucocutaneous sites. The abnormal γδT cell subtypes, characterized by TRDV1 and NK receptor expression (KLRD1/KLRB1), diverged from healthy controls expressing TRDV2. γδT cells are known to bridge innate and adaptive immunity, and their dysregulation in PNP may drive aberrant cytokine production (e.g., IFN-γ) and direct epithelial cytotoxicity. These subsets likely exacerbate mucosal injury and perpetuate autoimmunity, aligning with reports of γδT cell involvement in PNP-associated bronchiolitis obliterans. The decline in CD4+ naïve T cells and Tregs, coupled with the expansion of CD8+ Tte and Tem cells post-treatment, underscores the dominance of cytotoxic T cell responses in disease resolution. CD8+ Tte cells, marked by GZMB expression, likely mediate tumor cell clearance and suppression of autoantibody-producing B cells. In contrast, the depletion of Tregs may reflect impaired immune regulation during active disease, permitting unchecked T and B cell activation. This imbalance highlights the dual role of CD8+ T cells in both antitumor immunity and immunopathology in PNP. The identification of BCL2+ B cells in both peripheral blood and bone marrow aligns with their role as follicular lymphoma cells. BCL2 overexpression confers apoptosis resistance, enabling malignant B cell survival and shaping an immunosuppressive TME. These cells may directly interact with T cells, promoting Treg differentiation and CD8+ T cell exhaustion via cytokine secretion (e.g., IL10). Furthermore, BCL2+ B cells could serve as a reservoir for autoantibody production, perpetuating humoral autoimmunity in PNP19. The near-complete depletion of B cells post-obinutuzumab treatment correlates with clinical improvement, emphasizing the centrality of B cell targeting in PNP management. These single-cell transcriptome results mapped a sketch of lymphoma-associated tumor microenvironment, and showed that the immune reconstitution post-treatment involving activated DNA damage and T cell immune responses, which were also indicated by the gradually expanded TCR clone as treatment progresses.Conclusions：This study provides novel insights into PNP pathogenesis, highlighting lymphoma-specific immune dysregulation (e.g., aberrant B/T-cell subsets) .