Double-filtered leukoreduction as a method for risk reduction of transfusion-associated graft-versus-host disease

Pathophysiology and preclinical relevance of experimental graft-versus-host disease in humanized mice

Graft-versus-host disease (GVHD) is a life-threatening complication of allogeneic hematopoietic cell transplantations (allo-HCT) used for the treatment of hematological malignancies and other blood-related disorders. Until recently, the discovery of actionable molecular targets to treat GVHD and their preclinical testing was almost exclusively based on modeling allo-HCT in mice by transplanting bone marrow and splenocytes from donor mice into MHC-mismatched recipient animals. However, due to fundamental differences between human and mouse immunology, the translation of these molecular targets into the clinic can be limited. Therefore, humanized mouse models of GVHD were developed to circumvent this limitation. In these models, following the transplantation of human peripheral blood mononuclear cells (PBMCs) into immunodeficient mice, T cells recognize and attack mouse organs, inducing GVHD. Thereby, humanized mice provide a platform for the evaluation of the effects of candidate therapies on GVHD mediated by human immune cells in vivo. Understanding the pathophysiology of this xenogeneic GVHD is therefore crucial for the design and interpretation of experiments performed with this model. In this article, we comprehensively review the cellular and molecular mechanisms governing GVHD in the most commonly used model of xenogeneic GVHD: PBMC-engrafted NOD/LtSz-PrkdcscidIL2rγtm1Wjl (NSG) mice. By re-analyzing public sequencing data, we also show that the clonal expansion and the transcriptional program of T cells in humanized mice closely reflect those in humans. Finally, we highlight the strengths and limitations of this model, as well as arguments in favor of its biological relevance for studying T-cell reactions against healthy tissues or cancer cells.

Bacterial contamination of autologous blood salvaged during deceased donor liver transplantation: a prospective observational study

Decompensated cirrhotic patients experience severely increased intestinal permeability and bacterial translocation. Thus, autologous blood salvaged during deceased donor liver transplantation (DDLT) may be contaminated with enteric bacteria. We aimed to evaluate bacterial contamination of autologous blood salvaged during DDLT and its association with post-transplant bacteremia. In 30 patients undergoing DDLT, bacterial culture was performed in salvaged autologous blood samples: one before graft reperfusion (non-leukoreduced) and two after graft reperfusion (non-leukoreduced and leukoreduced). The primary outcome was bacterial contamination of salvaged autologous blood. Seven of 30 patients (23.3%) were positive for bacteria (3 enteric/4 non-enteric) before graft reperfusion while 11 patients (36.7%) were positive (5 enteric/6 non-enteric) after graft reperfusion. Six of 7 patients who were positive for bacteria before graft reperfusion were positive after graft reperfusion with the same bacteria. Only 4 of 11 contaminated blood samples were converted to negative after leukoreduction. Post-transplant bacteremia risk was insignificantly greater in patients who received autologous blood with bacteria than in patients without bacteria (30.0% vs. 5.0%, P = 0.06). We found contamination of salvaged autologous blood with enteric bacteria throughout DDLT and incomplete performance of leukoreduction, indicating high bacterial load. The potential association between contaminated autotransfusion and post-transplant bacteremia warrants further validation in a larger prospective study.Clinical trial notation: This study was registered at the Clinical Research Information Service (CRiS; https://cris.nih.go.kr ; No. KCT0007223; principal registration investigator: Sangbin Han, date of registration: April 25, 2022).

X-ray irradiation effectively inactivated lymphocytes in transfusion in vivo monitored by the bioluminescence transfusion-associated graft-versus-host disease model

BACKGROUND AND OBJECTIVES

Transfusion of cold-stored whole blood is the preferred resuscitation method for trauma patients but may cause transfusion-associated graft-versus-host disease (TA-GVHD). Standard clinical practice to prevent this is to irradiate blood components with gamma-rays. X-ray irradiations are also a safe and effective alternative to gamma-ray irradiation. We established a visual mouse model of TA-GVHD to compare the viability and function of lymphocytes exposed to gamma- and x-ray irradiation.

MATERIALS AND METHODS

A haploidentical transplantation mouse model was established to simulate TA-GVHD with Balb/c mice as donors and hybrid F1 CB6 mice (Balb/c × C57) as recipients. Spleen cells from Tg-Fluc+ Balb/c mice were isolated and irradiated with gamma-rays and x-rays. Lymphocyte activation, apoptosis and proliferation post phorbol 1 2-myristate 1 3-acetate (PMA) stimulation were evaluated. After transfusion, we monitored Fluc+ lymphocytes daily by bioluminescence imaging. Recipients were euthanized on day 21, and tissues were examined pathologically and for inflammatory cytokines.

RESULTS

The viability of gamma- or x-ray irradiated lymphocytes decreased significantly with slight changes in proliferation in vivo after transfusion. Compared with the non-irradiated group, both the gamma- and x-ray irradiated groups showed significantly decreased clinical scoring and inflammatory cytokine levels. The fluorescence intensity of the body and target organs was reduced after irradiation.

CONCLUSION

No recipients acquired TA-GVHD after lymphocyte transfusion subjected to gamma- or x-rays, showing that x-rays inactivate as well as gamma rays and are suitable for irradiating whole blood.

Irradiation is not sufficient to eradicate residual immortalized erythroid cells in in vitro-generated red blood cell products

BACKGROUND

The generation of immortalized erythroid progenitor cell lines capable of producing enough red blood cells (RBCs) for blood transfusion typically requires the overexpression of oncogenes in stem cells or progenitor cells to permanently proliferate immature cells. It is essential that any live oncogene-expressing cells are eliminated from the final RBC products for clinical use.

STUDY DESIGN AND METHODS

It is believed that safety issues may be resolved by using a leukoreduction filter or by irradiating the final products, as is conventionally done in blood banks; however, this has never been proven to be effective. Therefore, to investigate whether immortalized erythroblasts can be completely removed using γ-ray irradiation, we irradiated the erythroblast cell line, HiDEP, and the erythroleukemic cell line, K562 that overexpress HPV16 E6/E7. We then analyzed the extent of cell death using flow cytometry and polymerase chain reaction (PCR). The cells were also subjected to leukoreduction filters.

RESULTS

Using γ-ray irradiation at 25 Gy, 90.4% of HiDEP cells, 91.6% of K562-HPV16 E6/E7 cells, and 93.5% of non-transduced K562 cells were dead. In addition, 5.58 × 10⁷ HiDEP cells were passed through a leukoreduction filter, and 38 intact cells were harvested, revealing a filter removal efficiency of 99.9999%. However, both intact cells and oncogene DNA were still detected.

DISCUSSION

Irradiation cannot induce total cell death of oncogene-expressing erythroblasts and leukocyte filter efficiency is not 100%. Therefore, our findings imply that for clinical applications, safer methods should be developed to completely remove residual nucleated cells from cell line-derived RBC products.

Insights into mechanisms of graft-versus-host disease through humanised mouse models

Graft-versus-host disease (GVHD) is a major complication that occurs following allogeneic haematopoietic stem cell transplantation (HSCT) for the treatment of haematological cancers and other blood-related disorders. GVHD is an inflammatory disorder, where the transplanted donor immune cells can mediate an immune response against the recipient and attack host tissues. Despite over 60 years of research, broad-range immune suppression is still used to prevent or treat GVHD, leading to an increased risk of cancer relapse and infection. Therefore, further insights into the disease mechanisms and development of predictive and prognostic biomarkers are key to improving outcomes and reducing GVHD development following allogeneic HSCT. An important preclinical tool to examine the pathophysiology of GVHD and to understand the key mechanisms that lead to GVHD development are preclinical humanised mouse models. Such models of GVHD are now well-established and can provide valuable insights into disease development. This review will focus on models where human peripheral blood mononuclear cells are injected into immune-deficient non-obese diabetic (NOD)-scid-interleukin-2(IL-2)Rγ mutant (NOD-scid-IL2Rγ^null) mice. Humanised mouse models of GVHD can mimic the clinical setting for GVHD development, with disease progression and tissues impacted like that observed in humans. This review will highlight key findings from preclinical humanised mouse models regarding the role of donor human immune cells, the function of cytokines and cell signalling molecules and their impact on specific target tissues and GVHD development. Further, specific therapeutic strategies tested in these preclinical models reveal key molecular pathways important in reducing the burden of GVHD following allogeneic HSCT.

Adverse transfusion reactions and what we can do

INTRODUCTION

Transfusions of blood and blood components have inherent risks and the ensuing adverse reactions. It is very important to understand the adverse reactions of blood transfusion comprehensively for ensuring the safety of any future transfusions.

AREAS COVERED

According to the time of onset, adverse reactions of blood transfusion are divided into immediate and delayed transfusion reactions. In acute transfusion reactions, timely identification and immediate cessation of transfusion is critical. Vigilance is required to distinguish delayed responses or reactions that present non-specific signs and symptoms. In this review, we present the progress of mechanism, clinical characteristics and management of commonly encountered transfusion reactions.

EXPERT OPINION

The incidence of many transfusion-related adverse events is decreasing, but threats to transfusion safety are always emerging. It is particularly important for clinicians and blood transfusion staff to recognize the causes, symptoms and treatment methods of adverse blood transfusion reactions to improve the safety. In the future, at-risk patients will be better identified and can benefit from more closely matched blood components.

Hypothermic storage of leukoreduced red blood cells for greater than 21 days is a safe alternative to irradiation

BACKGROUND

Irradiation of red blood cells (RBCs) inactivates residual donor T lymphocytes to prevent transfusion-associated graft-vs-host disease (TA-GVHD) but can have adverse effects on recipients and inventory management. Reported incidence of TA-GVHD is lower when leukoreduced RBCs and older blood products are transfused; therefore, the impact of leukoreduction and storage was evaluated as an alternative prevention strategy.

STUDY DESIGN AND METHODS

Effectiveness of leukoreduction filters on white blood cell (WBC) proliferation was evaluated by filtering buffy coat (BC) products and isolating residual WBCs. Additionally, leukoreduced RBCs were spiked with 5 × 10⁶ WBCs on Day 21 of hypothermic storage, then stored and processed on Days 7, 14, and 21 to obtain residual WBCs to investigate the impact of hypothermic storage on their viability and proliferative ability. Viability of residual WBCs was assessed by staining with annexin V and an antibody cocktail for flow cytometry analysis. Proliferative ability was assessed by placing carboxyfluorescein diacetate succinimidyl ester-labeled residual WBCs into culture for 6 days with phytohemagglutinin before flow cytometry assessment.

RESULTS

Filtration of BC units depleted WBCs, particularly T lymphocytes, to 0.001% ± 0.003% cells/unit, although proliferative activity remained consistent with prefiltration levels of WBCs. WBCs in stored RBCs remained viable even on Day 21 of storage; however, the proliferative activity decreased to 0.24% ± 0.41%.

CONCLUSIONS

Hypothermic storage of RBCs for 21 days or more is sufficient to inactivate T lymphocytes, which may help prevent TA-GVHD when irradiated RBCs are not available.