Validating -80 "dump freezing" of PBPC

[bmarotto]

My hospital blood bank supports our small autologous-only peripheral blood stem cell program. My techs do both the collection (15-25 liters processed) and cryopreservation. The entire process runs into 2nd shift and involves calling in techs if a procedure has to be done on a weekend. In an attempt to reduce tech time, I would like to switch from control-rate freezing (CRF) to dump freezing. The product would be put in -80 immediately after processing and then moved to LN2 vapor storage the next day. For validation, I have multiple references comparing the two methods showing similar engraftment. I have also monitored the dump freeze cooling rate. I thawed product scheduled for discard and refroze them by the dump method, recording the product temperature at one minute intervals. I used the same sample probe used to record product temperature during CRF. I made adjustments on how the canisters were placed/insulated in the -80 until I found an arrangement that consistenly yielded an average cooling rate in the 1.00-1.75 degree/minute range until a temperature of -60 degrees was reached. I also compared the sample warm-up during the heat of fusion phase from several CRF tracings and found them to be comparable to what I recorded during the dump freeze procedures.

I would appreciate any comments on the adequacy of this validation. Our program director suggested doing a double collection on our next patient and freeze half by CRF and half by dump method. He would then infuse the dump freeze cells, keeping the CRF cells in reserve should there be a problem. We would also check post thaw viability for each method.

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[Bonni Hazelton]

I think your program director is requesting the correct follow up. Although you have multiple references re: the engraftment, the final piece of your validation should be engraftment using cells manufactured and frozen under YOUR conditions.
I assume you are freezing aliquots of the products along with the units in both freeze conditions. Although these will never completely and accurately represent the product in the bag, they are a good monitor of the quality of the product. In the situation where you freeze using both methods, they can be checked for viability and compared subsequent to cryopreservation but prior to infusion. You may have done this already, but if not it would add to your validation.
The ultimate end point for using cells frozen in this fashion is acceptable time to engraftment. The plan to infuse the "dump" frozen product and monitor the patient's engraftment is great, but due to the possibility of patient/HPC differences you may want to extend that to 2 or 3 patients. (Just a thought)
Bonni

[bmarotto]

We were able to get a double collection on our last patient and we infused the "dump" frozen product. Engraftment was right on schedule for both WBC, granulocytes, and platelets. We did add a second patient to this phase of the validation. Infusion is scheduled for next week. We are keeping our fingers crossed.

[kate murphy]

You've done much more validation than we did when we implemented dump freezing 10 years ago. Split products were compared for viability and progenitor cell assays. We then monitored engraftment rates.
For the past 9 years, dump freeze is our SOP.
We are FACT accredited.

[bmarotto]

Thanks everyone. We now have three patients who have received dump freeze products. Engraftment has been right on schedule for each of them.