Peripheral blood stem cell mobilisation and harvesting

Properties of stem cells

• Stem cells are defined as the most primitive haemopoietic precursor cell.

• Unique property is capability of both infinite self-renewal and differentiation to form all mature cells of the haemopoietic and immune systems.

• In the resting state almost all stem cells reside in the bone marrow although a tiny minority circulate in peripheral blood.

• Stem cells in marrow can migrate into the blood after treatment with chemotherapy and/or haemopoietic growth factors.

• Once circulating, they can easily be harvested using a cell separator machine.

• Stem cell levels in peripheral blood can be assessed by CD34 immuno-phenotype analysis.

• More than one day of apheresis may be necessary to achieve required

306 yield.

• The yield can be assessed for engraftment potential.

Protocols

Mobilisation and harvesting protocols differ between diseases. The following illustrate the principal types of schedule:

1. Mobilisation after standard chemotherapy

• No specific additional stimulus given.

• Harvest times determined by WBC and platelet recovery, and CD34 count.

• Yields variable. Improved by addition of G-CSF. Suitable for

• NHL post DHAP chemotherapy.

• AML post ADE/DAT chemotherapy.

• ALL post high dose methotrexate.

2. Mobilisation with chemotherapy and haemopoietic growth factors

The commonest schedule and the best evaluated. Harvest timing and yields more predictable.

Typical protocol for NHL

Day 0 cyclophosphamide 1.5g/m2 IVI with Mesna. Day +4 to day + 10 G-CSF 5|jg/kg/d SC continued until last day of harvesting.

Harvest ~day +10 when CD34 >10 x 106/L and/or WBC >10 x 109/L

Typical protocol for myeloma

Day 0 cyclophosphamide 4g/m2 IVI with Mesna.

Harvest day +10 to14 when CD34 > 10 x 106/L and/or WBC >10 x 109/L

Mobilisation with haemopoietic growth factor alone

Suitable for normal volunteers e.g. allograft donors.

Yield evaluation

Common parameters are mononuclear cell counts (MNC); CD34 numbers and haemopoietic colony forming unit assays e.g. CFU-GM. All are a quantitative or functional assessment of engraftment potential expressed per kg of recipient weight.

Typical target yields

Daily apheresis and daily G-CSF continue until the collection exceeds:

(i) 4 x 108/kg mononuclear cells or

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