Post-thaw viability of cryopreserved peripheral blood stem cells: what are we actually looking at?

Autologous stem cell transplant is a standard of care for a variety of hematological malignant and non-malignant diseases, and the process of stem cell collection, cryo-preservation, thawing and rein fusion, defined as "stem cell processing" has evolved Thoroughly in recent years. The enumeration of CD34+ cells within the graft represents a surrogate of its clonogenic potential and is today widely recognized as the main param-eter capable of predicting hematopoietic recovery. Post-thaw viability assay is routinely performed as a measure of graft quality for autologous transplant. However, quality control measures are challenging as there is not standardized assay for such test, little is known on the correlation between viable CD34+ count and graft clonogenic potential, and progenitor cells responsible for hematopoietic recovery are actually only a minority of the hematopoietic stem cells infused within the peripheral blood graft. We will herein briefly review the main issues on post-thaw hematopoietic stem cell viability test, with the aim to provide practical answers to some of the main open questions on this topic.