Storage-Induced Platelet Apoptosis Is a Potential Risk Factor for Alloimmunization Upon Platelet Transfusion

Abstract

Platelet transfusion can elicit alloimmune responses leading to alloantibody formation against donor-specific polymorphic residues, ultimately resulting in platelet transfusion refractoriness. Universal leukoreduction significantly reduced the frequency of alloimmunization after platelet transfusion, thereby showing the importance of white blood cells (WBCs) in inducing this alloresponse. It is, however, unknown if the residual risk for alloimmunization is caused by WBCs remaining after leukoreduction or if alloimmunization can be induced by platelets themselves. This study investigated the capacity of platelets to induce alloimmunization and identified potential product-related risk factors for alloimmunization. First, internalization of allogeneic platelets by dendritic cells (DCs) was demonstrated by confocal microscopy. Second, after internalization, presentation of platelet-derived peptides was shown by mass spectrometry analysis of human leukocytes antigen (HLA)-DR eluted peptides. Third, platelet-loaded DCs induced platelet-specific CD4 T cell responses. Altogether, this indicates a platelet-specific ability to induce alloimmunization. Therefore, factors enhancing platelet internalization may be identified as risk factor for alloimmunization by platelet concentrates. To investigate if storage of platelets is such a risk factor, internalization of stored platelets was compared with fresh platelets and showed enhanced internalization of stored platelets. Storage-induced apoptosis and accompanied phosphatidylserine exposure seemed to be instrumental for this. Indeed, DCs pre-incubated with apoptotic platelets induced the strongest IFN-γ production by CD4 T cells compared with pre-incubation with untreated or activated platelets. In conclusion, this study shows the capacity of platelets to induce platelet-specific alloimmune responses. Furthermore, storage-induced apoptosis of platelets is identified as potential risk factor for alloimmunization after platelet transfusions.

Pathogen-reduced PRP blocks T-cell activation, induces Treg cells, and promotes TGF-β expression by cDCs and monocytes in mice

“…Prior studies have shown UV1R-treated WBCs take on apoptotic characteristics, and processing of these apoptotic-like cells may drive the tolerogenic phenotype we observed. 22,[82][83][84] Our findings are consistent with studies demonstrating that allogeneic platelets can give rise to T-cell responses [50][51][52][53][54] but clarify the kinetics and quality of the alloimmune response. We demonstrate that the primary alloresponse includes CD4 1 T cells with both T helper type 1 (Th1) and Th2 phenotypes, 26 whereas the recall response skews toward a Th1 phenotype.…”

“…Recipient cDCs, Mfs, and B cells were activated, however, suggesting a role for indirect presentation of alloantigens, in line with other work. [50][51][52][53] Others have shown platelets can directly activate cDCs, 31,34,35,46,47,49,50 but this work specifically highlights recipient CD8 1 cDCs as the critical subset in PRP alloimmunization, further supporting a role for CTL in platelet clearance. 54,73 Although the response to untreated PRP showed similar effect sizes among CD11b 1 CD4 1 cDCs, only UV1R-treated PRP induced significantly elevated TGF-b expression among CD11b 1 CD4 1 cDCs and monocytes.…”

“…31,[39][40][41][42] Similarly, platelets and platelet-secreted products can directly affect human APCs in vitro. 34,35,[42][43][44][45][46][47][48][49][50] While studies have identified roles for APCs or T cells in the immune response to allogeneic platelets, 34,[50][51][52][53][54] a comprehensive understanding of how the recipient immune system responds to allogeneic platelet transfusions in vivo is lacking. Furthermore, while the effect of PRT or UV light on blood components has been evaluated in vitro, 21,[55][56][57][58][59][60] in vivo studies have focused predominantly on alloantibody outcomes, with little known about cellular responses.…”

The role of pathogen‐reduced platelet transfusions on HLA alloimmunization in hemato‐oncological patients

“…In these studies, PCs were administered immediately or within 2 days after illumination, whereas our study used PCs stored up to 7 days, which results in development of platelet storage lesion . The enhanced HLA Class I alloimmunization associated with Mirasol pathogen inactivation in our study could be explained by our recent in vitro finding that storage‐mediated apoptosis and concomitant phosphatidylserine exposure, which are enhanced after pathogen inactivation, significantly enhances platelet internalization and presentation and subsequent platelet‐specific alloimmune responses . In line with this, patients who received PCs stored for at least 4 days seem to be at increased risk for alloimmunization as compared to patients receiving fresh PCs.…”

Immunological Features in the Process of Blood Platelet-Induced Alloimmunisation, with a Focus on Platelet Component Transfusion

“…Further, in a recent and very elegant study, Saris et al evidenced that platelets endocytosed by dendritic cells—through likely apoptotic mechanisms (apoptotic platelets)—have the potential of eliciting strong IFN-γ production by alloreactive CD4+ T-cells. This further suggests that not only HLA from residual leukocytes but also HLA class I from foreign platelets themselves can be immunising [48]. This tends to demonstrate that the outcome is complex and multifocal.…”