Circulating B cell and T cell activation states predict clinical outcomes in melanoma and reveal dynamic immune reinvigoration with checkpoint inhibitor immunotherapy.

backgroundNearly half of patients with melanoma do not respond to immune checkpoint inhibitors (CPIs) and many develop immune-related adverse events (irAEs), often forcing treatment discontinuation, and underscoring the need to predict and monitor outcomes. Responses may depend on both B cell and T cell activity.

methodsWe performed high-dimensional mass cytometry profiling of coexisting peripheral B cell and key T cell states in treatment-naïve patients and healthy individuals, and paired longitudinal samples from CPI-treated patients, with clinical annotations to define immune correlates of outcomes.

resultsCPI-naive patients exhibited reduced CD19+ B cells, reduced B cell (CD21, IL-2, CXCR5) and T cell (CD38, CD27) activation markers, alongside enriched naïve (CD21lo) and double-negative (DN2)-like B cells, CD95+IL-10+plasmablasts, consistent with extrafollicular responses. Concurrently, programmed cell death protein 1 (PD-1)+ and proliferation marker protein-67 (Ki67)+ T cell expansion indicates ongoing activation with features of proliferative exhaustion. Active disease featured increased regulatory CD95 expression on B cells and expanded T follicular helper-like and activated DN (CD4-CD8-) T cells, indicating sustained antigen stimulation. Pretreatment, elevated PD-1+ T cells predicted irAEs, whereas VEGF (vascular endothelial growth factor)+TGF-β (transforming growth factor-β)+ DN T cells were enriched in patients without subsequent toxicity. Pretreatment, plasmablasts, transitional B cells, Forkhead box protein P3 (FoxP3)+ and central memory-like CD8+ T cells correlated with worse overall survival; naïve CD21lo B cells, PD-1+CD8+ T cells and CD4+follicular helper-like T cells predicted shorter event-free survival; CD4+ memory T cells predicted better prognosis, implicating dysregulated differentiation and sustained activation in adverse outcomes. On-treatment, naïve CD21hi B cells, plasmablasts, activated CD8+ and central memory-like CD4+ T cells expanded, indicating de novo humoral responses and cytotoxic T cell invigoration. On-treatment, increased class-switched memory (IgG2+) B and activated T cells predicted improved survival, while persistent naïve and DN B cells were associated with poorer outcomes. Anti-PD-1 monotherapy expanded naïve (CD21hi) B cells and global T cells. Anti-PD-1/anti-LAG-3 (lymphocyte-activation gene 3) combination contracted memory B cells.

conclusionsMelanoma displays aberrant peripheral B and T cell activation, maturation and exhaustion, prominent in active disease. Treatment-induced class-switched B cells and T cell invigoration predict clinical benefit and naïve/DN B cells signify resistance. Coordinated B and T cell responses, especially recurrent extrafollicular B cell and exhausted/regulatory T cell states emerge as candidate indicators of outcome.