Granulocytes

Granulocyte transfusions are among the least common blood components used, reserved for very specific, life-threatening situations. They represent a concentrated dose of white blood cells, primarily neutrophils, aimed at helping patients fight off severe infections when their own neutrophil count is dangerously low

What Are Granulocytes?

• Definition: Granulocytes are a category of white blood cells characterized by the presence of granules in their cytoplasm. This category includes Neutrophils, Eosinophils, and Basophils. For transfusion purposes, the focus is almost entirely on Neutrophils, which are the primary phagocytic cells responsible for engulfing and destroying bacteria and fungi
• Function: The goal of granulocyte transfusion is to provide a temporary boost of functional neutrophils to patients unable to mount their own adequate response to severe infection

Preparation Method

Granulocytes cannot be effectively prepared from standard whole blood donations due to the low numbers present. Collection requires Apheresis, and involves several specialized steps:

1. Donor Stimulation (Mobilization) Donors typically receive agents beforehand to significantly increase the number of circulating neutrophils:
   • G-CSF (Granulocyte Colony-Stimulating Factor): A cytokine administered by injection for several days or hours before donation, stimulating the bone marrow to produce and release more neutrophils
   • Corticosteroids (e.g., Dexamethasone): Often given orally a few hours before donation. They cause neutrophils marginated along blood vessel walls to enter the circulation and prevent their egress, further boosting the circulating count
   • Donor Consideration: Requires specific informed consent regarding the side effects of these medications (e.g., bone pain, headache with G-CSF; usual steroid effects)
2. Apheresis Collection Whole blood is drawn into the apheresis machine. Often, a sedimenting agent (like Hydroxyethyl Starch - HES, though its use is decreasing due to safety concerns) is added to enhance the separation of WBCs from RBCs by causing RBC rouleaux formation
3. Separation & Collection The machine uses centrifugation to separate and collect the granulocyte layer (often appearing as a “buffy coat”)
4. Resulting Product A granulocyte concentrate typically has a volume of 200-300 mL and contains:
   • A high number of granulocytes (mostly neutrophils) - target dose often >1.0 x 10¹⁰ per unit
   • Significant numbers of lymphocytes (requiring irradiation - see below)
   • Variable numbers of platelets
   • Significant numbers of Red Blood Cells (often >20-30 mL, requiring crossmatch compatibility)
   • Plasma and anticoagulant (usually citrate)

Indications for Transfusion

Granulocyte transfusion is rarely indicated and considered a supportive therapy of last resort. Stringent criteria usually apply:

• Severe Neutropenia: Absolute Neutrophil Count (ANC) typically < 500/µL
• Documented Infection: Evidence of a severe bacterial or fungal infection (e.g., positive cultures, imaging)
• Lack of Response: Infection is progressing despite appropriate, high-dose antimicrobial therapy
• Potential for Marrow Recovery: There should be a reasonable expectation that the patient’s own bone marrow function will eventually recover (granulocytes are a temporary bridge, not a cure)
• Specific Situations
  • Neonatal sepsis with neutropenia
  • Patients with chronic granulomatous disease (CGD) experiencing severe infections

Contraindications Generally not useful if marrow recovery is not anticipated or if the infection is well-controlled by antibiotics alone

Storage and Expiration

Storage conditions are critical and differ from other components:

• Storage Temperature: 20°C to 24°C (Controlled Room Temperature)
  • Rationale: Neutrophil function (phagocytosis, chemotaxis) is significantly impaired by refrigeration
• Agitation: DO NOT AGITATE. Store undisturbed
  • Rationale: Agitation can damage fragile neutrophils
• Expiration: Extremely short - 24 hours from the end of collection
  • Rationale: Rapid loss of neutrophil function in vitro and the high risk of bacterial proliferation at room temperature

Quality Control / Specifications

• Granulocyte Content: Target dose usually > 1.0 x 10¹⁰ per adult unit (actual content varies)
• Volume: Typically 200-300 mL
• RBC Content: Usually significant enough to require crossmatching
• Bacterial Testing: Standard protocols apply due to room temperature storage

Administration

Administration requires careful planning and monitoring due to high reaction rates and specific requirements:

• Irradiation: MANDATORY. Granulocyte concentrates contain viable T-lymphocytes and must be irradiated (25-50 Gy) shortly before infusion to prevent TA-GVHD. Irradiation does not change the 24-hour expiration time
• Compatibility
  • ABO: Plasma must be ABO compatible with recipient red cells
  • Rh: Must be Rh compatible due to significant RBC content. Rh-negative recipients should receive Rh-negative granulocytes if possible. Consider RhIG for Rh-negative females of childbearing age receiving Rh-positive units
  • Crossmatch: An RBC crossmatch is required due to the volume of contaminating RBCs
  • HLA: HLA matching is desirable (especially if the patient is alloimmunized or expected to receive multiple transfusions) but often not feasible due to the urgency and short shelf life. HLA antibodies in the recipient can cause reactions and neutralize the transfused granulocytes. Antibodies in the donor plasma can contribute to TRALI
• Filtration: Use a standard blood filter (170-260 microns). DO NOT use a leukocyte-reduction filter – it will remove the therapeutic granulocytes!
• Infusion Time: Infuse slowly, typically over 2-4 hours, to minimize reactions
• Pre-medication: Often recommended (e.g., antihistamines, acetaminophen, corticosteroids) due to the high frequency of transfusion reactions
• Timing with Amphotericin B: Controversial. Some older data suggested increased pulmonary reactions when given concurrently. Many institutions separate administration times by several hours as a precaution

Potential Risks / Adverse Reactions

Granulocyte transfusions have a higher rate of adverse reactions compared to other components:

• Febrile Non-Hemolytic Reactions (FNHTRs): Very common due to cytokines and alloantigens
• Pulmonary Reactions: A significant concern. Can range from mild dyspnea and hypoxia to severe TRALI-like reactions. May be related to neutrophil activation, sequestration in the lungs, or underlying infection/inflammation
• Alloimmunization: To HLA and neutrophil-specific antigens, potentially hindering effectiveness of future transfusions
• CMV Transmission: Risk if donor is CMV positive and recipient is negative/at risk. Finding CMV-seronegative granulocyte donors can be challenging
• TA-GVHD: Prevented by mandatory irradiation
• Allergic Reactions
• Septic Reactions (Bacterial Contamination): Risk due to room temperature storage
• Hemolytic Transfusion Reactions: Possible if RBC incompatibility occurs

Key Terms

• Granulocyte: Type of WBC including neutrophils, eosinophils, basophils. Transfusions primarily provide neutrophils
• Neutrophil: Primary phagocytic cell fighting bacterial/fungal infections
• Apheresis: Method used to collect granulocytes from a donor
• G-CSF (Granulocyte Colony-Stimulating Factor): Medication to stimulate neutrophil production
• Corticosteroids: Medications used to mobilize neutrophils into circulation
• Neutropenia: Low neutrophil count (ANC < 500/µL is severe)
• Irradiation: Mandatory treatment to prevent TA-GVHD
• TA-GVHD (Transfusion-Associated Graft-versus-Host Disease): Complication where donor lymphocytes attack recipient tissues
• Crossmatch: Required due to significant RBC content in granulocyte concentrates
• Alloimmunization: Development of antibodies against foreign antigens (e.g., HLA, neutrophil antigens)