CD28 Blockade Ex Vivo Induces Alloantigen-Specific Immune Tolerance but Preserves T-Cell Pathogen Reactivity.

Donor T-cells contribute to reconstitution of protective immunity after allogeneic hematopoietic stem cell transplantation (HSCT) but must acquire specific tolerance against recipient alloantigens to avoid life-threatening graft-versus-host disease (GvHD). Systemic immunosuppressive drugs may abrogate severe GvHD, but this also impedes memory responses to invading pathogens. Here, we tested whether ex vivo blockade of CD28 co-stimulation can enable selective T-cell tolerization to alloantigens by facilitating CD80/86-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) signaling. Treatment of human allogeneic dendritic cell/T-cell co-cultures with a human CD28 blocking antibody fragment (α-huCD28) significantly abrogated subsequent allospecific immune responses, seen by decreased T-cell proliferation and of type 1 cytokine (IFN-γ and IL-2) expression. Allo-tolerization persisted after discontinuation of CD28 blockade and secondary alloantigen stimulation, as confirmed by enhanced CTLA-4 and PD-1 immune checkpoint signaling. However, T-cells retained reactivity to pathogens, supported by clonotyping of neo-primed and cross-reactive T-cells specific for Candida albicans or third-party antigens using deep sequencing analysis. In an MHC-mismatched murine model, we tolerized C57BL/6 T-cells by ex vivo exposure to a murine single chain Fv specific for CD28 (α-muCD28). Infusion of these cells, after α-muCD28 washout, into bone marrow-transplanted BALB/c mice caused allo-tolerance and did not induce GvHD-associated hepatic pathology. We conclude that selective CD28 blockade ex vivo can allow the generation of stably allo-tolerized T-cells that in turn do not induce graft-versus-host reactions while maintaining pathogen reactivity. Hence, CD28 co-stimulation blockade of donor T-cells may be a useful therapeutic approach to support the immune system after HSCT.

Comparative evaluation of techniques for the manufacturing of dendritic cell-based cancer vaccines.

Manufacturing procedures for cellular therapies are continuously improved with particular emphasis on product safety. We previously developed a dendritic cell (DC) cancer vaccine technology platform that uses clinical grade lipopolysaccharide (LPS) and interferon (IFN)-y for the maturation of monocyte derived DCs. DCs are frozen after 6 hrs exposure at a semi-mature stage (smDCs) retaining the capacity to secret interleukin (IL)-12 and thus support cytolytic T-cell responses, which is lost at full maturation. We compared closed systems for monocyte enrichment from leucocyte apheresis products from healthy individuals using plastic adherence, CD14 selection, or CD2/19 depletion with magnetic beads, or counter flow centrifugation (elutriation) using a clinical grade in comparison to a research grade culture medium for the following DC generation. We found that elutriation was superior compared to the other methods showing 36 +/- 4% recovery, which was approximately 5-fold higher as the most frequently used adherence protocol (8 +/- 1%), and a very good purity (92 +/- 5%) of smDCs. Immune phenotype and IL-12 secretion (adherence: 1.4 +/- 0.4; selection: 20 +/- 0.6; depletion: 1 +/-0.5; elutriation: 3.6 +/- 1.5 ng/ml) as well as the potency of all DCs to stimulate T cells in an allogeneic mixed leucocyte reaction did not show statistically significant differences. Research grade and clinical grade DC culture media were equally potent and freezing did not impair the functions of smDCs. Finally, we assessed the functional capacity of DC cancer vaccines manufactured for three patients using this optimized procedure thereby demonstrating the feasibility of manufacturing DC cancer vaccines that secret IL-12 (9.4 +/- 6.4 ng/ml). We conclude that significant steps were taken here towards clinical grade DC cancer vaccine manufacturing.

Leukemia-associated antigenic isoforms induce a specific immune response in children with T-ALL.

The potential immunogenicity of acute lymphoblastic leukemia of the T cell (T-ALL), a small subgroup of childhood leukemia with increased risk for treatment failure and early relapse, was addressed by serological identification of leukemia-derived antigens by recombinant expression cloning (SEREX). Thirteen antigens with homology to known genes that are involved in critical cellular processes were detected. Further characterization of the 4 novel isoforms revealed that 3 (HECTD1Delta, CX-ORF-15Delta and hCAP-EDelta) had restricted mRNA expression in more than 70% of T-ALLs (n = 22) and that specific antibodies against these isoforms were detected in up to 30% of patients (n = 16), with the highest frequency for HECTD1Delta. The latter protein was present at high abundance in T-ALLs but not in normal hematopoietic tissues. Given that the leukemia-associated antigens detected in this study have an intracellular localization, the generation of immune effector responses most likely requires antigen presentation. To test this assumption, dendritic cells were loaded with HECTD1Delta protein and used for T cell stimulation. A specific T cell response was induced in vitro in all 3 healthy donors studied, including a former T-ALL patient. These data suggest that T-ALL may induce a specific cellular and humoral antileukemia immune response in children, thereby supporting new approaches for immunotherapy.