BACKGROUND Cellular therapies could play a role in cancer treatment and regenerative medicine if it were possible to quickly eliminate the infused cells in case of adverse events. We devised an inducible T-cell safety switch that is based on the fusion of human caspase 9 to a modified human FK-binding protein, allowing conditional dimerization. When exposed to a synthetic dimerizing drug, the inducible caspase 9 (iCasp9) becomes activated and leads to the rapid death of cells expressing this construct. METHODS We tested the activity of our safety switch by introducing the gene into donor T cells given to enhance immune reconstitution in recipients of haploidentical stem-cell transplants. Patients received AP1903, an otherwise bioinert small-molecule dimerizing drug, if graft-versus-host disease (GVHD) developed. We measured the effects of AP1903 on GVHD and on the function and persistence of the cells containing the iCasp9 safety switch. RESULTS Five patients between the ages of 3 and 17 years who had undergone stem-cell transplantation for relapsed acute leukemia were treated with the genetically modified T cells. The cells were detected in peripheral blood from all five patients and increased in number over time, despite their constitutive transgene expression. A single dose of dimerizing drug, given to four patients in whom GVHD developed, eliminated more than 90% of the modified T cells within 30 minutes after administration and ended the GVHD without recurrence. CONCLUSIONS The iCasp9 cell-suicide system may increase the safety of cellular therapies and expand their clinical applications. (Funded by the National Heart, Lung, and Blood Institute and the National Cancer Institute; ClinicalTrials.gov number, NCT00710892.)

Key Points The frequency of CD8+CD45RA+CCR7+ cells, a subset closest to T-memory stem cells, correlates with CAR–T-cell expansion in lymphoma patients. IL-7 and IL-15 increase the frequency of CD8+CD45RA+CCR7+ cells during the ex vivo expansion of CAR+ T cells.

Targeting disialoganglioside (GD2) on neuroblastoma (NB) with T cells expressing a first-generation chimeric antigen receptor (CAR) was safe, but the cells had poor expansion and long-term persistence. We developed a third-generation GD2-CAR (GD2-CAR3) and hypothesized that GD2-CAR3 T cells (CARTs) would be safe and effective. This phase 1 study enrolled relapsed or refractory NB patients in three cohorts. Cohort 1 received CART alone, cohort 2 received CARTs plus cyclophosphamide and fludarabine (Cy/Flu), and cohort 3 was treated with CARTs, Cy/Flu, and a programmed death-1 (PD-1) inhibitor. Eleven patients were treated with CARTs. The infusions were safe, and no dose-limiting toxicities occurred. CARTs were detectable in cohort 1, but the lymphodepletion induced by Cy/Flu increased circulating levels of the homeostatic cytokine interleukin (IL)-15 (p = 0.003) and increased CART expansion by up to 3 logs (p = 0.03). PD-1 inhibition did not further enhance expansion or persistence. Antitumor responses at 6 weeks were modest. We observed a striking expansion of CD45/CD33/CD11b/CD163 myeloid cells (change from baseline, p = 0.0126) in all patients, which may have contributed to the modest early antitumor responses; the effect of these cells merits further study. Thus, CARTs are safe, and Cy/Flu can further increase their expansion.

• Alloreplete iC9-T cells can promote immune recovery posttransplant and protect patients against viral infections.• iC9-T cells can be eliminated from both peripheral blood and CNS by administration of AP1903 leading to a rapid resolution of GVHD.To test the feasibility of a single T-cell manipulation to eliminate alloreactivity while sparing antiviral and antitumor T cells, we infused 12 haploidentical hematopoietic stem cell transplant patients with increasing numbers of alloreplete haploidentical T cells expressing the inducible caspase 9 suicide gene (iC9-T cells). We determined whether the iC9-T cells produced immune reconstitution and if any resultant graft-versus-host disease (GVHD) could be controlled by administration of a chemical inducer of dimerization (CID; AP1903/ Rimiducid). All patients receiving >10 4 alloreplete iC9-T lymphocytes per kilogram achieved rapid reconstitution of immune responses toward 5 major pathogenic viruses and concomitant control of active infections. Four patients received a single AP1903 dose. CID infusion eliminated 85% to 95% of circulating CD3 1 CD19 1 T cells within 30 minutes, with no recurrence of GVHD within 90 days. In one patient, symptoms and signs of GVHDassociated cytokine release syndrome (CRS-hyperpyrexia, high levels of proinflammatory cytokines, and rash) resolved within 2 hours of AP1903 infusion. One patient with varicella zoster virus meningitis and acute GVHD had iC9-T cells present in the cerebrospinal fluid, which were reduced by >90% after CID. Notably, virus-specific T cells recovered even after AP1903 administration and continued to protect against infection. Hence, alloreplete iC9-T cells can reconstitute immunity posttransplant and administration of CID can eliminate them from both peripheral blood and the central nervous system (CNS), leading to rapid resolution of GVHD and CRS. The approach may therefore be useful for the rapid and effective treatment of toxicities associated with infusion of engineered T lymphocytes. This trial was registered at www.clinicaltrials.gov as #NCT01494103. (Blood. 2015;125(26):4103-4113)

Background aims Interest in natural killer (NK) cell-based immunotherapy has resurged since new protocols for the purification and expansion of large numbers of clinical-grade cells have become available. Methods We have successfully adapted a previously described NK expansion method that uses K562 cells expressing interleukin (IL)-15 and 4-1 BB Ligand (BBL) (K562-mb15-41BBL) to grow NK cells in novel gas-permeable static cell culture flasks (G-Rex). Results Using this system we produced up to 19 × 109 functional NK cells from unseparated apheresis products, starting with 15 × 107 CD3− CD56+ NK cells, within 8–10 days of culture. The G-Rex yielded a higher fold expansion of NK cells than conventional gas-permeable bags and required no cell manipulation or feeding during the culture period. We also showed that K562-mb15-41BBL cells up-regulated surface HLA class I antigen expression upon stimulation with the supernatants from NK cultures and stimulated alloreactive CD8+ T cells within the NK cultures. However, these CD3+ T cells could be removed successfully using the CliniMACS system. We describe our optimized NK cell cryopreservation method and show that the NK cells are viable and functional even after 12 months of cryopreservation. Conclusions We have successfully developed a static culture protocol for large-scale expansion of NK cells in the gas permeable G-Rex system under good manufacturing practice (GMP) conditions. This strategy is currently being used to produce NK cells for cancer immunotherapy.

and Epstein-Barr virus (EBV)-specific responses in 4 of 6 evaluable patients at dose level 2 as early as 2 to 4 months after transplantation, whereas such responses were not observed until 6 to 12 months in dose-level 1 patients. The incidence of significant acute (2 of 16) and chronic graft-versus-host disease (GVHD; 2 of 15) was low. These data demonstrate that allodepleted donor T cells can be safely used to improve T-cell recovery after haploidentical SCT and may broaden the applicability of this approach.

Key Points Allodepleted-T-cells containing the iC9 safety gene persist long-term in vivo, promote immune recovery, and protect against infections. GvHD caused by iC9-T cells can be permanently controlled by a single administration of AP1903 without abrogating immune reconstitution.

Apheresis-derived hematopoietic progenitor cells have recently been used for allogeneic transplantation. Forty-one normal donors were studied to assess the effects of recombinant human granulocyte colony-stimulating factor (rhG-CSF) (12 micrograms/kg/d) on the peripheralization of hematopoietic progenitor cells and lymphoid subsets. The white blood cell, polymorphonuclear cell (PMNC), and lymphocyte concentrations at the peak of rhG-CSF effect in the donor's peripheral blood (PB) exceeded baseline by 6.4-, 8.0-, and 2.2-fold, respectively. Corresponding concentrations of PB CD34+ cells and primitive subsets such as CD34+ Thy-1dim, and CD34+ Thy-1dim CD38- cells increased by 16.3-fold, 24.2-fold, and 23.2-fold, respectively in eight normal donors. The percentage of CD34+ Thy-1dim and CD34+ Thy- 1dim CD38- cells among CD34+ cells increased as well, suggesting an additional peripheralization effect of rhG-CSF on primitive CD34+ subsets. The preapheresis PB CD34+ and CD34+ Thy-1dim cell concentrations were predictive of their corresponding apheresis yield per liter of donor blood processed PB lymphoid subsets were not significantly affected by rhG-CSF treatment. The mean apheresis-derived yield of CD34+, CD34+ Thy-1dim, and CD34+ Thy-1dim CD38- cells per kilogram of recipient body weight and per liter of donor blood processed was 48.9 x 10(4) (n = 41), 27.2 x 10(4) (n = 10), and 1.9 x 10(4) (n = 10), respectively. As compared with 43 single bone marrow (BM) harvest, the CD34+ cell yield of peripheral blood progenitor cell allografts of 41 normal donors exceeded that of BM allografts by 3.7- fold and that of lymphoid subsets by 16.1-fold (CD3+), 13.3-fold (CD4+), 27.4-fold (CD8+), 11.0-fold (CD19+), and 19.4-fold (CD56+CD3-). All PBPC allografts were cryopreserved before transplantation. The mean recovery of CD34+ cells after freezing, thawing, and washing out dimethylsulfoxide was 86.6% (n = 31) and the recovery of lymphoid subsets was 115.5% (CD3+), 121.4% (CD4+), 105.6% (CD8+), 118.1% (CD19+), and 102.4% (CD56+CD3-). All donors were related to patients: 39 sibling-to-sibling, 1 parent-to-child, and 1 child-to-parent transplant. Thirty-eight transplants were HLA fully identical, two transplants differed in one and two antigens. Engraftment occurred in 38 recipients; two patients died too early to be evaluated, and one patient did not engraft. The lowest CD34+ cell dose transplanted and resulting in complete and sustained engraftment was 2.5 x 10(6)/kg of recipient body weight.(ABSTRACT TRUNCATED AT 400 WORDS)