Key Points Removal of αβ+ T and CD19+ B cells is an effective strategy for successful HLA-haploidentical hematopoietic stem cell transplantation. The high probability of disease-free survival renders this transplant option attractive for any child with a nonmalignant disorder.

Key Points• Children with AL given haplo-HSCT after ab T-and B-cell depletion are exposed to a low risk of acute and chronic GVHD and NRM.• The leukemia-free, GVHDfree survival of patients given this type of allograft is comparable to that of HLAmatched donor HSCT recipients.Allogeneic hematopoietic stem cell transplantation (HSCT) from an HLA-haploidentical relative (haplo-HSCT) is a suitable option for children with acute leukemia (AL) either relapsed or at high-risk of treatment failure. We developed a novel method of graft manipulation based on negative depletion of ab T and B cells and conducted a prospective trial evaluating the outcome of children with AL transplanted with this approach. Eighty AL children, transplanted between September 2011 and September 2014, were enrolled in the trial. All children were given a fully myeloablative preparative regimen. Anti-T-lymphocyte globulin from day 25 to 23 was used for preventing graft rejection and graft-versus-host disease (GVHD); no patient received any posttransplantation GVHD prophylaxis. Two children experienced primary graft failure. The cumulative incidence of skin-only, grade 1-2 acute GVHD was 30%; no patient developed extensive chronic GVHD. Four patients died, the cumulative incidence of nonrelapse mortality being 5%, whereas 19 relapsed, resulting in a 24% cumulative incidence of relapse. With a median follow-up of 46 months for surviving patients, the 5-year probability of chronic GVHD-free, relapsefree survival (GRFS) is 71%. Total body irradiation-containing preparative regimen was the only variable favorably influencing relapse incidence and GRFS. The outcomes of these 80 patients are comparable to those of 41 and 51 children given transplantation from an HLA-identical sibling or a 10/10 allelic-matched unrelated donor in the same period. These data indicate that haplo-HSCT after ab T-and B-cell depletion represents a competitive alternative for children with AL in need of urgent allograft. This trial was registered at www.clinicaltrials.gov as #NCT01810120. (Blood. 2017;130(5):677-685)

SummaryActivation of a galactosidase-specific murine T hybridoma clone and of a human tetanus toxoid-specific T clone by antigen-presenting cells (APC) was used to evaluate the regulatory function ofantibodies complexed with the relevant antigen . Complexed antigen, in fact, is taken up with high efficiency thanks to Fc receptors borne by APC . Antibody/antigen ratio in the complexes proved to be a critical parameter in enhancing antigen presentation . Complexes in moderate antibody excess provided optimal T cell activation independently of the physical state of the complexes {precipitated by a second antibody or solubilized by complement) . Complexes in extreme antibody excess, on the contrary, did not yield T cell activation although taken up by APC efficiently. The effect of antibodies at extreme excess was observed with substimulatory dose of antigen (loss of potentiation) and with optimal dose of antigen (loss of stimulation). An excess of specific polyclonal antibodies hampers proteolytic degradation of antigen in vitro, supporting the view that a similar mechanism may operate within the APC that have internalized immune complexes in extreme antibody excess. The possibility that immune complex forming in extreme antibody excess may turn off the T cell response is proposed as a regulatory mechanism .

We developed an innovative and efficient, feeder-free culture method to genetically modify and expand peripheral blood-derived NK cells with high proliferative capacity, while preserving the responsiveness of their native activating receptors. Activated peripheral blood NK cells were efficiently transduced by a retroviral vector carrying a second-generation CAR targeting CD19. CAR expression was demonstrated across the different NK subsets. CAR.CD19-NK cells display higher anti-leukemic activity towards CD19 + cell lines and primary blasts obtained from patients with B-cell precursor ALL compared to unmodified NK cells. In vivo animal model data showed that the anti-leukemia activity of CAR.CD19-NK cell is superimposable to that of CAR-T cells, with a lower toxicity profile. These data support the feasibility of generating feeder-free expanded, genetically-modified peripheral blood NK cells for effective 'off-the-shelf' immuno-gene-therapy, while their innate alloreactivity can be safely harnessed to potentiate allogeneic cell therapy.