How safe are leukocyte-depleted (leukoreduced) blood products in avoiding alloimmunization?

Leukocyte-Depleted Blood Products for Preventing Alloimmunization

Leukocyte-depleted (leukoreduced) blood products are highly effective and safe in preventing HLA alloimmunization, reducing the risk from 45% with standard platelets to 17-21% with leukoreduced products. 1

Efficacy of Leukoreduction in Preventing Alloimmunization

Evidence Base

• The Trial to Reduce Alloimmunization to Platelets (TRAP) provides Level I evidence supporting leukoreduction, demonstrating significant reduction in:

  • Formation of lymphocytotoxic antibodies (17-21% vs 45% in controls)
  • Immune-mediated platelet refractoriness (3-5% vs 13% in controls) 2

• Target leukocyte count for effective prevention of alloimmunization:

  • <5 × 10^6 leukocytes per transfusion 1
  • This level of leukoreduction can be reliably achieved through modern filtration methods

Methods of Leukoreduction

• Pre-storage leukoreduction (performed at blood collection facilities) is preferred over bedside filtration due to:

  • Better quality control
  • Prevention of cytokine accumulation during storage
  • Reduced transfusion reactions 2

• Both filtered pooled platelet concentrates and single-donor apheresis platelets show equal efficacy in preventing alloimmunization when properly leukoreduced 1

Patient Populations Benefiting from Leukoreduction

Highest Benefit Groups

• Patients with acute myeloid leukemia (AML) receiving induction chemotherapy 2
• Patients with other leukemias requiring multiple transfusions
• Patients requiring long-term platelet support due to:
  • Aplastic anemia
  • Myelodysplastic syndromes 2

Moderate Benefit Groups

• Previously untransfused patients benefit more than those with prior transfusion exposure
• Patients without prior pregnancies 2

Limited Benefit Groups

• Patients requiring only short-term platelet support (e.g., peripheral blood stem-cell transplantation) 2
• Only 10-15% of newly diagnosed AML patients might actually benefit clinically from leukoreduction 2

Additional Benefits of Leukoreduction

Beyond preventing alloimmunization, leukoreduced blood products offer:

• Reduction in febrile non-hemolytic transfusion reactions
• Prevention of transmission of leukotropic viruses (CMV, EBV)
• Decreased platelet refractoriness in multitransfused patients 3

Implementation Considerations

Timing

• Antibody formation typically occurs 3-4 weeks after initial exposure
• The major impact of prevention may be noted during intensive consolidation therapy rather than during induction 2

Potential Drawbacks

• Leukoreduction adds cost to transfusion therapy
• Filtration can cause platelet loss (up to 25-35%) 2
• Cost-benefit ratio is most favorable for patients requiring multiple transfusions

Current Practice

In the United States and many other countries, universal prestorage leukoreduction is now standard practice, eliminating the need for additional filtration at the time of transfusion 2

Conclusion

For patients requiring multiple platelet transfusions, particularly those with hematologic malignancies, leukoreduced blood products should be used from the time of diagnosis to prevent HLA alloimmunization and its associated complications. The evidence strongly supports this approach with a Grade A recommendation based on Level I evidence. 2