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 {gamma}/{delta} T cells and NK cells. Intragraft B cells consisted of clusters of naive, plasmablast, and class-switched B (BCS) 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 BCS 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 BCS cells, possibly reflective of clinical observations of less chronic antibody-mediated rejection under CoB mIS.