Autologous peripheral blood stem cell harvesting and utilization in multiple myeloma patients in LUHS Kaunas Clinics, Lithuania 2015-2022

Background: The optimal number of CD34+ cells needed for repetitive autologous hematopoietic stem cell transplantation (auto-HSCT) in multiple myeloma (MM) patients remains unclear. As effective novel therapies for MM emerge, the use of salvage autologous hematopoietic stem cell transplantation (auto-HSCT) for relapse/refractory MM is questionable. Methods: We conducted a retrospective single center study using the clinical and laboratory databases. The study included 158 MM patients, 384 apheresis, 536 products and 211 auto-HSCT in the hospital of Lithuanian University of Health Sciences Kaunas Clinics from 2015 to 2022. Peripheral blood hematopoietic stem cells (PBHSC) were harvested after mobilization Cyclo+G-CSF (10 µg/kg) or an additional mobilizing agent such as plerixafor (0.24 mg/kg) if needed. PBHSC harvesting was done via apheresis. In our center the goal is to collect enough CD34+ cells for 3 auto-HSCT, which would equate to at least 10 x106 CD34+/kg. After each apheresis session, CD34+ counts were calculated. If the goal was achieved or if further mobilization was not possible, the harvesting was stopped. We calculated collected cells and divided patients in to 2 groups: A – if the goal is reached, B – goal is not reached. Descriptive statistics were performed on the variables of interest. We report frequencies and percentages as well as mean and ranges where applicable. Results: In total 158 MM patients were mobilized via 384 apheresis, that harvested 536 products, and transplanted at least 1 time. For 100 (63.3%) of the patients the CD34+ goal was achieved (A group), for 58 (36.7%) was not (B group). Mean collected CD34+ cell count for both groups were 12.45 x106/kg (range 2.0 x106 – 31.4 x106 /kg). To reach the CD34+ cell goal, 3 (3%) patients needed only 1 apheresis, most of them 67 (67%) needed 2 procedures, 28 (28%) – 3 apheresis procedures, and 2 (2%) patients needed 4 procedures. In comparison, in the B group more than half of the patients 35 (60.3%) needed 3 or more apheresis procedures. There is a correlation between CD34+ yield and number of apheresis procedures: patients yielding higher CD34+ counts required fewer apheresis procedures compared to those yielding lower CD34+ counts (p<0.01). Out of the patients that reached the targeted CD34+ goal (A group) transplanted in tandem 37 (37%) patients and 5 (5%) received as salvage auto-HSCT. Out of the B group 6 (10.2%) patients received tandem auto-HSCT, but no one received auto-HSCT as salvage. Conclusions: Our analysis evaluated the use of stored cryopreserved PBHSC for a salvage auto-HSCT in patients with MM. We showed that we could collect enough PBHSC for third auto-HSCT in most patients and usually they required 2 or 3 apheresis procedures. A third auto-HSCT was performed in just 5% of the included cohort. The increased survival rates offered by new cellular and immunotherapies, alongside the decreasing frequency of conducting salvage auto-HSCT warrant reconsideration of PBHSC collection goals.