Factors Influencing Lymphocyte Collection Efficiency for the Manufacture of CAR-T Cells in Adults with B Cell Malignancies , a Single Center Experience

Aim:

During leukapheresis, accurate estimation of the proportion of T cells that are removed from peripheral blood (collection efficiency, CE) is essential to minimise apheresis time, reduce lab storage requirements and prevent excess product collection. Based on historical precedent from autologous HPC donors, many centres estimate a CE of 40% for autologous T cell donors, although data are lacking. We aimed to identify patient characteristics and collection parameters that might influence leukapheresis CE in order to maximise efficiency and minimize waste during CAR T manufacture.

Methods:

We reviewed data from 33 consecutive patients who underwent leukapheresis for CAR-T cell treatment at our centre from March 2020 to October 2022. Apheresis was performed on the Spectra Optia, using the CMNC collection protocol.

Apheresis were performed on the Spectra Optia, using the CMNC collection protocol. peripheral collection was used if patients had adequate venous access, otherwise central venous access was used. Peripheral blood flow cytometry was done prior to apheresis.

Results:

33 apheresis procedures were documented from patients with 3% acute lymphocytic leukemia (ALL) (n=1), 82% non-Hodgkin lymphoma (NHL) (n=27) and 15% Multiple myeloma (n=5). Median age was 62 (18 -76 ) , Male to Female ratio was 1.38 , the median weight was 75 kg (45-136) the median of prior lines of therapy was 2 (1-7) with 33% of pts receiving prior autologous HCT and 3% Prior allogeneic HCT. The median time from diagnosis to collection was 15 months (3-109) The median WBC value was 6× 10 ⁹/L (2-24), median Hematocrit was 0,34% (0,25-0,45), Median Neutrophil was 4,43×10 ⁹/L (1-21), Monocytes 0,62 ×10 ⁹/L (0,36-1,43), Platelets 185× 10 ⁹/L (94-385), and median absolute Lymphocytes count was 0.8 (0.21-2,4). With median CD3 value was 560×10 ⁹/L and a median percentage of ALC of 76%. CD4 and CD8 absolute median values were 276 and 309 respectively. The median CRP, LDH and Ferritinemia were 29,238 and 252 respectively.

The collection was successful in all patients with 32 (97%) having a high CE of >40%. The median CD3 lymphocyte count in the apheresis product was 4,3 × 10 ⁹ with an overall viability of 99% . The median collection efficiency was 71% (31-96) . Median Run time was 210 minutes, total blood volume and apheresis product volume were 9750 and 278ml.

In the apheresis product, median CD3 value was 15415 ×10 ⁶ and the median CD3 value per kg was 58×10 ⁶ /kg.

In multivariate analysis, baseline characteristics did not significantly impact the collection efficiency. ALC and CD3 pre-apheresis strongly predicted the CD3 yield after apheresis (p< 0,001). No major adverse events were recorded.

Conclusion:

High efficiency leukapheresis is safe and feasible in autologous T-cell donors. Our data also confirms that high ALC and peripheral blood CD3 counts pre-apheresis are strongly correlated to the CD3 yield in the product. Our centre now uses a CE estimate of 60% for collection of CAR T starting material.