Cell recruitment and collection yields in autologous MNC apheresis

Abstract

Background & Aim Autologous MNC apheresis is applied for the preparation of various advanced therapy medicinal products (ATMPs) for immunotherapy of cancer. The recruitment of cells during leukapheresis results in unexpectedly high yields in some patients. It is further characterized by an algorithm for calculation of CD34+ HPC yield in stem cell collection (see: Humpe et al, Transfusion 2000; 40: 1363-70). Methods, Results & Conclusion Methods 9 patients were subjected to autologous MNC leukapheresis procedures on a cell separator (Spectra Optia, V11.0, CMNC programme, TerumoBCT). Blood counts and quantification of lymphocyte subpopulations were done before and after leukapheresis as well as in the apheresis product on a hematology analyzer (Sysmex K21) and a flow cytometer (FACS Verse, BD). From the results and the apheresis key data cell yields, collection efficiency (CE2) and recruitment as well as the predicted yields by the above mentioned algorithm were calculated. Results The yields in 9 procedures averaged to vital TNC s 1.4*10E10, monocytes (MC) 3.8 *10E9, lymphocytes (LY) 6.7*10E9, CD3+ T cells (TC) 5.5 *10E9, NK cells (NKs) 11.5*10E8, platelets (PLT) 23.3 *10E10, respectively. Though CD34+ HPCs in the blood of 6/9 patients were below 1/µl, they were detected in all apheresis products (average 4.4*10E7 CD34+ HPCs). CE2 was independent of counts in peripheral blood and amounted to 0.61 for MC, 0.65 for LY and TC, respectively, 0.60 for NKs and 0.11 for PLT. In the model for the prediction of CD34+ HPC yields decribed by Humpe et al, the calculated amounts overestimated PLT yields (4.5fold), but underscored the harvests of NK, TC and MC 0.5fold, 0.4fold and 0.6fold, respectively. Predicted and measured cell contents were highly correlated as for NK and PLT (R2 >0.8), moderately for MC and TC (R2∼0.6). Only with TC, a significant, but negative correlation was found between the percentage of cells recruited into the product and the ratio of predicted to recorded yield. Despite a high interindividual variance, the portion of cells recruited into the product were similar for MC, LY, TC and NK (0.41, 0.46, 0.48, 0.37), except for PLT (-2.10). Conclusion Yields in MNC leukapheresis cannot be predicted using the same algorithm as in CD34+ HPC collection. We speculate that this is due to a considerable recruitment of cells into the apheresis product, resulting in unexpectedly high yields despite low blood counts. Hence, an apheresis collection may serve as liquid biopsy.