Co-Stimulatory Blockade Prevents Intragraft Accrual of Class-Switched, Activated B Cells Despite Failing to Prevent T-Cell Mediated Rejection

Previously, we defined the transcriptomes and clonality of intragraft CD8 ⁺ T cell during renal allograft rejection. Here, using single cell RNA sequencing (scRNAseq), we investigated non-CD8 ⁺ immune cells during T-cell-mediated rejection (TCMR) under different maintenance immunosuppression (mIS) regimens: tacrolimus, and co-stimulatory blockade (CoB) with belatacept (CTLA4-Ig) or iscalimab (anti−CD40). Myeloid cells comprised of DCs, monocytes and macrophages whose proportion and gene expression were similar between mIS regimens. Given their transcriptiomic similarities, we analyzed publicly-available scRNAseq/CITEseq datasets as well as immunofluorescence staining to resolve independent subpopulations of γ/δ T cells and NK cells. Intragraft B cells consisted of clusters of naïve, plasmablast, and class-switched B (B _CS ) cells, with the latter being diminished in CoB mIS. Intragraft CD4 ⁺ T cells consisted of FoxP3 ⁺ regulatory (Treg), exhausted, Th17, and CXCL13 ⁺ peripheral helper (Tph) cells whose proportions differed based in mIS, and the latter two had increased clonal expansion. Notably, cell-cell communication analysis indicated Th17 and Tph cell interactions with B _CS cells in tacrolimus, but not CoB, samples. Thus, although failing to prevent TCMR, CoB mIS modulates the accrual of CD4 ⁺ T cells and inhibits the intragraft accrual of B _CS cells, possibly reflective of clinical observations of less chronic antibody-mediated rejection under CoB mIS.