Alloprimed Antibody-Suppressor CD8(+) T Cells Preferentially Kill Alloprimed Germinal Center B Cells.

Abstract Antibody-mediated rejection is a significant contributor to transplant rejection. Our prior work identified a novel subset of CXCR5+CD8+ T cells (CD8+ TAb-supp cells) that suppresses alloantibody production by mediating cytotoxic killing of IgG+ alloantibody-producing B cells. The purpose of these studies was to investigate which B cell subsets are susceptible to CD8+ TAb-supp cell-mediated cytotoxicity. Alloprimed CXCR5+CD8+ T cells were isolated from splenocytes of C57BL/6 mice on day 7 following allo-lysate stimulation. Various target cells (alloprimed B cell subsets, macrophages, and dendritic cells) were isolated from CD8 KO mice on day 7 following allo-lysate stimulation. Alloprimed CD8 KO mice are known to be high alloantibody producers from our prior studies. Target cells were tested in co-cultures to evaluate their susceptibility to CXCR5+CD8+ T cell-mediated in vitro cytotoxicity. Alloprimed CXCR5+CD8+ T cells exhibited significantly higher in vitro cytotoxicity towards alloprimed GC B cells (IgG+GL-7+Fas+; 11.4±1.0%) than towards other antibody producing B cell subsets, including alloprimed extrafollicular plasmablasts (IgG+CD138+; 0.9±0.3%) and plasma cells (IgG−CD138+; 1.6±0.5%; p<0.0001 for both). In addition, CXCR5+CD8+ T cells did not kill alloprimed dendritic cells (MHCII+CD11c+; 1.5±0.7) or macrophages (F4/80+; 1.7±0.4) in co-culture. No significant cytotoxicity was observed in control co-cultures using third party-primed CXCR5+CD8+ T cells (1.1±0.2), naïve CD8+ T cells (1.2±0.3%), or alloprimed CXCR5-negative CD8+ T cells (0.6±0.3%). These data show that alloprimed antibody-suppressor CXCR5+CD8+ T cells preferentially mediate cytotoxic killing of alloprimed GC B cells. This work was supported by a National Institutes of Health R01 grant AI083456 (to GLB), CA016058, UL1TR002733, the OSU Division of Transplant Surgery, and the OSU College of Medicine.