ALBERT

Description: NK cell immunotherapy as a cancer treatment shows promise, but methods for consistent expansion of NK cells from a small fraction (~5%) of peripheral blood mononuclear cells (PBMCs) to therapeutically effective amounts are not widely accessible. Strategies that promote in vivo expansion rely on high-dose IL-2 in combination with lymphodepletion and suffer from severe treatment related toxicities as well as limited expansion. On the other hand, in vitro methods are available for robust NK cell expansion, but rely on prolonged in vitro co-culture with feeder cells that is costly and complex and requires high dose IL-2 (25,000-35,000 U) for persistence after injection into mice. An optimal NK cell expansion method would rely on off the shelf reagents, would not require long-term complex cultures, and would induce a rapid, sustained in vivo expansion of NK cells from unsorted PBMCs under low concentration of IL-2. We have developed a method to prepare particles from K562 cells engineered to express specific cytokines, and such particles stimulate NK cell expansion. Particles prepared using K562 cells expressing IL-21 and 41BBL (PM21 particles) cause highly specific expansion of cytotoxic NK cells from unsorted PBMCs that achieves 95% NK cells in ~14 days and ~10,000 fold expansion of NK in about 21 days. NK cell expansion is consistent using different preparations of PM-particles or leukocyte sources, and the PM-particles retain expansion efficacy with storage. The PM-mb21-41BBL particles were also used to stimulate in vivo NK cell expansion in NSG mice under ultralow IL-2 (1,000 units per injection, 3 injections per week, per mouse). Unsorted human PBMCs, either shortly pre-activated in culture for two days or not pre-activated, were injected (2 x 106 PBMCs per mice by i.p.) and human CD56+CD3- NK cells and other relevant hCD45+ lymphocytes were monitored in the peripheral blood over time and in tissues and fluids at the time of euthanization. In vivo NK cell expansion was observed in mice injected with PBMCs that were pre-activated with PM21 particles. The extent of NK cell expansion observed in the peripheral blood was in levels that would be relevant for clinical cancer treatment (〉50,000 NK cells/mL of mouse blood 14 days post injection). In vivo NK cell expansion was further confirmed with analogous experiments using PBMCs that were stained with CellTrace Violet to monitor proliferation. Notably, NK cells were also found in spleen, bone marrow, lung, liver and brain. These results taken together provide proof of principle that PM-particle technology is effective for direct in vivo NK cell expansion from unsorted PBMCs under low dose IL-2. Disclosures No relevant conflicts of interest to declare.

Description: Method of Mobilization: Implication on Cell Subsets in The Graft and Immune Reconstitution post Autologous Hematopoietic Cell Transplantation (AHCT) The optimal mobilization method for either myeloma or lymphoma patients undergoing AHCT is still debatable and strategies for graft collection vary between different institutions. Plerixafor, a CXCR4 antagonist is used for peripheral blood stem cell mobilization in multiple myeloma and non-Hodgkins lymphoma patients requiring AHCT. The effect of plerixafor on graft composition has scarce data that are based mostly on cryopreserved samples. Moreover; the effect of plerixafor on immune reconstitution and hematologic recovery post AHCT has not been well evaluated. The goal of our study was to compare graft composition, hematologic and immune reconstitution recovery among patients mobilized with plerixafor plus G-CSF to those mobilized with G-CSF alone. Methods: 49 patients eligible for AHCT were enrolled on a single arm prospective trial at a single transplant center. All patients were mobilized with G-CSF 10µg/kg/day for 4 consecutive days. A peripheral blood CD34 level of 2x106 cells/Kg was obtained after 3 collection days. Samples from the freshly collected graft and patients' peripheral blood on days +30 and +60 were analyzed by flow cytometry (BD FACSCanto II) . A single platform assay was used (Beckman-Coulter Stem kit) via a ISHAGE protocol. The antibody cocktail contained the following pre-conjugated monoclonal antibodies: CD56-PE (Miltenyi Biotech, Auburn, CA), CD3-APC, CD16-FITC, (Beckman Coulter, Brea, CA), CD19-PE-CY7 (BD Biosciences, San Jose, CA). Data were acquired using BD FACSCanto II (BD Biosciences) and analyzed with the FACSDiva software (BD Biosciences) to quantify CD3+ T cells, CD3+ CD56+ NK-like T cells, CD56+ CD16+ and CD56+ CD16- NK cells as well as CD19+ B cells. Results: 49 patients with a median age of 58 years (range 21-75) were mobilized with either G-CSF alone (N=16) or plerixafor +G-CSF (G+P)(N=33).The median number of collection days was 1.42 and 1.81 (p=0.2) and the median collected CD34+ dose was 8.28x106/kg and 5.24x106 /kg (p=022) in the G+P and G-CSF alone groups respectively. Both groups had similar times to neutrophil and platelet engraftment. The graft analysis showed a white blood count of 309x109/l and 262x109/l (p=0.38), median percentage of CD34+ cells of 0.75% and 0.73% (p=0.81), percentage of CD3+ T cells of 25.6% and 22% (p=0.6) in the G+P and G-CSF alone groups resepectively. Both groups had similar proportions of CD3+, CD4+,CD8+, NK, NKT and iNKT cells in the mobilized grafts. Peripheral blood samples at day +30 and day +60 were analyzed for T cell markers and hematologic recovery (table 1). There was no significant difference between absolute lymphocyte counts, NK cell counts, T cells and absolute neutrophil count. Conclusion: Plerixafor when combined with G-CSF helps in achieving mobilization goals in patients predicted to be poor mobilizers based on peripheral CD34 levels. The addition of plerixafor doesn't not seem to affect T cell composition of the graft and yields similar hematologic and immune recovery when compared to mobilization with G-CSF alone. Table 1: Immune Reconstitution at Day 30 and Day 60 post Autologous Transplantation Treatment Group G-CSF (N=16) Plerixafor + G-CSF (N=33) P-value G-CSF (N=16) Plerixafor + G-CSF (N=33) P-value Day 30 Day 60 WBC 5.08 5.41 0.873 4.94 5.38 0.654 HGB 10.86 11.19 0.353 11.22 11.17 0.757 HCT 32.35 33.66 0.321 33.36 33.53 0.565 PLT 119.88 161.42 0.068 166.94 173.73 0.949 Abs Lymph 1.09 1.44 0.296 1.41 1.50 0.974 % NK 26.14 30.38 0.277 11.53 20.09 0.095 Abs NK 0.31 0.35 0.186 0.17 0.21 0.470 % T cell 67 60 0.183 76.15 67.39 0.340 Abs T cell 0.72 0.96 0.717 1.35 .82 0.095 NKT%* 5.28 3.33 8.25 3.38 B cell % 2.38 1.52 0.922 2.63 5.58 0.424 Abs. Neut count 2.99 2.64 0.488 2.85 3.01 0.848 Disclosures No relevant conflicts of interest to declare.

Description: Lack of a matched sibling or unrelated donor can be a significant barrier to allogeneic hematopoietic cell transplantation (HCT). Haploidentical (haplo) donors are readily available for nearly all such patients. However, donor selection criteria to determine the optimal haplo donor are not readily available. In order to determine which donor characteristics are most important in predicting transplant success, we retrospectively analyzed 208 consecutive donor-recipient pairs receiving haplo HCT with post-transplant cyclophosphamide for hematologic malignancy. Donor characteristics were evaluated by multivariate Cox analysis and correlated with overall survival (OS), disease-free survival (DFS), relapse/progression, and non-relapse mortality (NRM), while controlling for significant patient and transplant-related factors. Donor variables analyzed included age, sex, relationship to recipient, CMV status, ABO compatibility, HLA disparity and several NK alloreactivity models (KIR receptor-ligand, ligand-ligand, haplotype, B content, activating KIR-based education systems, Sekine donor licensing model). Median (range) recipient and donor age was 52 (19-75) and 38 (15-73) years respectively, and 41% of donor-recipient pairs were non-Caucasian. Patients were transplanted for AML (34%), MDS/MPS/CML (20%), ALL (17%), NHL/HD/CLL (25%). PBSC was used as the stem cell source in 66% of patients, and conditioning intensity was myeloablative in 41%. The donor was a child, sibling, or parent in 47%, 38%, and 14% respectively. Median (range) follow-up for surviving patients was 33 (7-130) months. In multivariate Cox analysis, patient/transplant characteristics associated with improved OS and DFS included recipient age