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Oral Abstract

Cell Biology, Immunology and Biochemistry (Basic and Preclinical Research)

Oral Abstract Spotlight Session - Discoveries in the Science of Immunohematology

#OA1-AM25-ST-28 - Transfusion Induced Alloantigen-Specific CD8+ T Cells Cause Platelet Refractoriness in Mice.

Saturday, October 25, 2025

10:45 AM - 12:15 PM PT

Room: SDCC 30AB

Presenting Author(s)

Elizabeth L. Frost, PhD (she/her/hers)

Senior Research Scientist
University of Virginia
Charlottesville, Virginia

Disclosure information not submitted.

Background/Case Studies: Refractoriness to platelet (PLT) transfusions is a significant clinical obstacle with multiple causes, including alloantibodies (allo-abs) to HLA class I expressed on PLTs. 50% of patients who develop PLT refractoriness with ongoing transfusion have no detectable allo-abs. This is attributed to non-immune causes as a diagnosis of exclusion, assuming allo-abs are the only immune mechanism of PLT clearance. It has been reported in mice that CD8⁺ T cells have the capacity to clear allo-PLTs, but the ability of transfusion to induce CD8⁺ T cell mediated PLT destruction has not been explored, nor has it been tested if CD8⁺ T cells recognize PLTs as targets.

Study

Design/Methods: C57BL/6 [B6; (MHC haplotype b)] recipients (n=5/group) were transfused weekly for 4 weeks with whole blood (WB) from allogeneic B6.d donor mice (MHC haplotype d) or control B6 donors. Additional donor mice that only express MHC-I haplotype d intracellularly (IC) with no surface expression (IC.d mice), were used to isolate cellular immunity in the absence of allo-abs. Serum allo-abs and post-transfusion PLT clearance were both quantified by flow cytometry. Alloantigen-specific CD8⁺ T cells were detected by measuring IFNg induction after ex vivo stimulation with splenocytes or PLTs from B6.d mice. CD8⁺ T cells were depleted in some mice using anti-CD8 IgG.

Results/Findings: Transfusions from B6.d and IC.d donors induced a 12% and 38% decrease (p=0.18 and p < 0.0001), respectively, in post-transfusion PLT circulation compared to control B6 donors. A 15-fold increase (p < 0.0001) in anti-d allo-abs was induced by transfusion from B6.d donors compared to a 3.7-fold increase (p=0.0009) from IC.d donors. Transfusions from B6.d and IC.d donors induced a 58% and 77% increase (p=0.007 and p=0.002), respectively, in the frequency of CD8⁺ T cells expressing IFNg in spleens. Increased CD8⁺ T cells expressing IFNg were also detectable in peripheral blood. Depletion of CD8⁺ T cells with anti-CD8 IgG restored normal post-transfusion PLT circulation in recipients transfused with IC.d.

Conclusions: These data demonstrate transfusion-induced alloimmune refractoriness independent of allo-abs due to CD8⁺ T cells and the ability to detect alloreactive CD8⁺ T cells in recipient peripheral blood using donor leukocytes (and potentially PLTs) as stimulation. These studies lay the conceptual and technical basis to test the hypothesis that joint characterization of alloantibodies and alloreactive CD8⁺ T cells will improve diagnosis and management of alloimmune refractoriness in patients.