Sensitized recipients are defined by the presence of pre-transplant donor-specific antibodies and have significantly poorer graft outcomes compared to unsensitized recipients despite efforts to desensitize. Thus there is an urgent need for better therapeutic strategies for this group of transplant recipients. Here, we report on a new experimental model of sensitization that utilizes C57BL/6 recipient mice previously challenged with BALB/c splenocytes to study recall alloantibody responses and to identify effective therapeutic strategies. When challenged with BALB/c spleen cells or heart grafts 10 weeks later, a rapid and high-titer IgG response was observed. This recall response was confirmed to be B cell intrinsic using adoptive transfer experimental approaches. To identify the fate and activity of alloreactive memory B cells in these sensitized recipients, we identified alloreactive B cells that specifically bound MHC Class I tetramers (H-2Kd) within the switched IgG+ population using flow cytometry and ELISpot assay. At 10 weeks post-immunization, IgG+ memory alloreactive B cells exhibited a quiescent post-GC phenotype characterized by CD73+CD273+CD38hiCD80lowCD138-GL7- expression. Upon rechallenging with BALB/c heart allografts, the memory B cells rapidly expanded and differentiated into plasma cells without differentiating into germinal center B cells. This was in contrast to non-sensitized recipients, where the alloreactive B cells differentiated preferentially into germinal center B cells. Despite the striking differences in the differentiation of naïve and memory alloreactive B cells, CTLA-4Ig (500 ¯o;g/mouse, 2X/week) was remarkably effective at inhibiting both the naïve and the recall B cell response. CTLA-4Ig was also effective at extending allograft survival in sensitized recipients; 6 of 7 allografts survived >30 days post-transplantation. This observation is in striking contrast to the lack of efficacy of CTLA-4Ig at inducing tolerance in sensitized recipients. In aggregate, our observations identify a model for investigating sensitized T and B cell responses to allografts, and underscore the unexpected potency of CTLA-4Ig at inhibiting memory B cell responses

« Back to 2015 American Transplant Congress