Natalie Schub

Enhanced ADCC activity of affinity maturated and Fc-engineered mini-antibodies directed against the AML stem cell antigen CD96.

CD96, a cell surface antigen recently described to be preferentially expressed on acute myeloid leukemia (AML) leukemic stem cells (LSC) may represent an interesting target structure for the development of antibody-based therapeutic approaches. The v-regions from the CD96-specific hybridoma TH-111 were isolated and used to generate a CD96-specific single chain fragment of the variable regions (scFv). An affinity maturated variant resulting in 4-fold enhanced CD96-binding was generated by random mutagenesis and stringent selection using phage display. The affinity maturated scFv CD96-S32F was used to generate bivalent mini-antibodies by genetically fusing an IgG1 wild type Fc region or a variant with enhanced CD16a binding. Antibody dependent cell-mediated cytotoxicity (ADCC) experiments revealed that Fc engineering was essential to trigger significant effector cell-mediated lysis when the wild type scFv was used. The mini-antibody variant generated by fusing the affinity-maturated scFv with the optimized Fc variant demonstrated the highest ADCC activity (2.3-fold enhancement in efficacy). In conclusion, our data provide proof of concept that CD96 could serve as a target structure for effector cell-mediated lysis and demonstrate that both enhancing affinity for CD96 and for CD16a resulted in mini-antibodies with the highest cytolytic potential.

Successful Mobilization, Intra-Apheresis Recruitment, and Harvest of Hematopoietic Progenitor Cells by Addition of Plerixafor and Subsequent Large-Volume Leukapheresis

Background: In patients failing successful conventional mobilization of hematopoietic progenitor cells (HPC) plerixafor (Mozobil®) seems to be an alternative. We report a series of 14 patients with multiple myeloma or NHL successfully mobilized and harvested by plerixafor together with large-volume leukaphereses (LVL). Methods: In a first series (GI), 5 patients were mobilized with G-CSF and plerixafor. In the second series (GII), 9 patients were mobilized by chemotherapy, G-CSF, and plerixafor. Results: In GI and GII, addition of plerixafor led to a significant (p < 0.01) increase of leukocytes and CD34+ cells in peripheral blood (PB). In GII, the median number of CD34+ cells in PB before and after addition of plerixafor was significantly (p = 0.019) higher compared to GI (9 vs. 5 and 50 vs. 24 cells/µl, respectively). In GI and GII, a median number of three or one aphereses was performed. In GII, the median yield (6.7 × 106 CD34+ cells/kg) of the first apheresis and the median intra-apheresis recruitment of CD34+ cells were significantly (p < 0.05) higher compared to GI (2.94 × 106 CD34+ cells/kg). All patients transplanted, 5 in GI and 8 in GII, exhibited successful engraftment. Conclusions: Plerixafor and G-CSF mobilization or the addition of plerixafor during non-optimal chemotherapy and G-CSF mobilization together with LVL enabled, independent of leukocyte count and even without detectable CD34+ cells before addition of plerixafor, sufficient harvest of HPC numbers for transplantation. Addition of plerixafor during chemotherapy and G-CSF mobilization led to an increased intra-apheresis recruitment and a significantly higher yield of CD34+ cells compared to plerixafor and G-CSF steady-state mobilized patients.