What type of platelets should be used to minimize human leukocyte (HLA) antibody formation?

Leukoreduced Platelets Are Most Effective for Minimizing HLA Antibody Formation

Leukoreduced platelets (filtered platelets) are the most effective type of platelet transfusion for minimizing human leukocyte antigen (HLA) antibody formation, regardless of whether they come from single donors or pooled sources. Based on high-quality evidence from the Trial to Reduce Alloimmunization to Platelets (TRAP) study, leukoreduction significantly reduces HLA alloimmunization compared to standard platelets 1.

Evidence on Different Platelet Types for Minimizing HLA Antibody Formation

Leukoreduced Platelets (Filtered Platelets)

• The TRAP study, a large randomized multi-institutional trial with 603 patients, demonstrated that leukoreduction through filtration reduced HLA antibody formation from 45% (with standard platelets) to 17-21% 1
• Leukoreduction also reduced immune-mediated platelet refractoriness from 13% to 3-5% 1
• The target level of leukoreduction was <5 × 10^6 leukocytes per transfusion 1

Single Donor vs. Pooled Platelets

• The TRAP study specifically compared filtered pooled platelets with filtered single-donor platelets and found no additional advantage from single-donor platelets when both were properly leukoreduced 1
• Both filtered single-donor and filtered pooled platelets showed similar post-transfusion increments and similar rates of HLA antibody formation 1
• This contradicts earlier studies suggesting single-donor platelets might be superior 2

UVB-Irradiated Platelets

• UVB irradiation of platelets also showed similar effectiveness to filtration in reducing HLA antibody formation (17-21% vs. 45% in controls) 1
• UVB irradiation works by inactivating contaminating mononuclear leukocytes 3
• However, there is no FDA-approved UVB irradiation device available for routine clinical use 1

Radiated Platelets (Gamma Irradiation)

• Standard gamma irradiation (not to be confused with UVB irradiation) is primarily used to prevent transfusion-associated graft-versus-host disease, not to prevent HLA alloimmunization
• Gamma irradiation does not significantly reduce HLA antibody formation

Clinical Application

Patient Selection for Leukoreduced Platelets

• Most beneficial for patients requiring long-term platelet support, particularly:
  • Patients with acute leukemia receiving intensive chemotherapy 1
  • Patients with inherited platelet disorders requiring frequent transfusions 4
• Less critical for patients requiring only short-term platelet support (e.g., those undergoing peripheral blood stem-cell transplantation) 1

Important Considerations

• Leukoreduction can cause some platelet loss (25-35%) during processing 1
• Filtration can be performed at the blood bank rather than bedside for better quality control 1
• Patients with prior pregnancies or transfusions have higher risk of alloimmunization and may particularly benefit from leukoreduced products 1

Potential Pitfalls

• Relying solely on single-donor platelets without leukoreduction is insufficient to prevent HLA alloimmunization 1, 5
• A study specifically examining leukoreduction of single-donor platelets in high-risk patients (females with prior pregnancies) found that leukoreduction to <5 × 10^6 leukocytes was insufficient to prevent secondary HLA-alloimmunization 5
• The timing of alloimmunization is important - antibodies often develop 3-4 weeks after initial exposure, which may be after the immediate need for transfusions has passed 1

In conclusion, the evidence strongly supports using leukoreduced platelets (whether from single donors or pooled sources) as the most effective approach to minimize HLA antibody formation in patients requiring platelet transfusions. The key factor is adequate leukoreduction rather than the source of platelets.