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Therapeutic Leukocytapheresis and Adsorptive Cytapheresis
Therapeutic leukocytapheresis (or leukapheresis) is a procedure in which white blood cells (WBCs) are selectively removed from patient’s circulation, generally with the aim of treating hyperleukocytosis and/or hyperviscosity. Additionally, leukocytapheresis has been performed prophylactically, such as to prevent tumor lysis syndrome before initiation of chemotherapy. Unfortunately, neither therapeutic nor prophylactic leukocytapheresis appear to effect long-term survival in leukemic patients.
Selective leukocyte apheresis incorporates adsorptive columns into extracorporeal stage of apheresis procedure with the goal of removing circulating leukocytes and immune system modulation. This procedure has been used for the treatment of inflammatory bowel disease (IBD), systemic lupus erythematosus, psoriasis, Behçet's disease, rheumatoid arthritis, and exacerbations of idiopathic interstitial pneumonias.
Processing Volume
Therapeutic leukocytapheresis processes between 1.5 and 2 total blood volumes (TBVs) resulting in 30%–60% reduction in WBC count. Postprocedure WBC count is often difficult to predict, as leukocytes are mobilized from extramedullary sites into intravascular space during procedure. Procedural efficacy may be improved through use of erythrocyte-sedimenting agent, such as 6% hydroxyethyl starch (HES). HES enhances separation of WBCs from other blood components, thereby, improving leukocyte removal efficiency. Addition of HES is recommended when treatment is intended for removal of mature myeloid cells. However, each patient’s renal and cardiovascular status must be assessed before use of HES due its renal excretion and function as volume expander.
Replacement Fluid
If leukocytapheresis procedures result in <15% of TBV removal, then it is sufficient to use normal saline as needed to maintain patient’s blood pressure. When volume removal >15% of TBV, then replacement with colloid solution, such as 5% albumin, is recommended. Furthermore, apheresis circuit may be primed with irradiated RBCs for selected anemic patients. This is often preferable to RBC transfusion, which can result in increase in viscosity.
Leukocyte Adsorption Devices
There are currently two methods of selective apheresis available in Europe and Japan, leukocytapheresis (LCAP) using the Cellsorba (Asahi Medical, Japan) or granulocyte/monocyte apheresis (GMA) using the Adacolumn (JIMRO, Japan). The Adacolumn consists of a column containing cellulose acetate beads in isotonic saline. It selectively retains monocytes and granulocytes through binding of FCγR. Meanwhile, the Cellsorba column consists of cylindrical nonwoven polyester fibers, which removes leukocytes through filtration and adhesion. In addition to effectively removing 90%–100% of monocytes and granulocytes, it eliminates 30%–60% of circulating lymphocytes.
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