Human Dendritic Cells Mitigate NK-Cell Dysfunction Mediated by Nonselective JAK1/2 Blockade.

Janus kinase (JAK) inhibitors have achieved positive responses in myeloproliferative neoplasms, but at the expense of decreased natural killer (NK) cell numbers and compromised function. Selective JAK2 inhibition may also have a role in preventing and treating graft-versus-host disease after allogeneic hematopoietic stem cell transplantation. Although JAK inhibitors can impair monocyte-derived dendritic cell (moDC) activation and function and suppress effector T-cell responses, the effects on NK cells and the relevant mechanisms remain undefined. Using common γc cytokines and distinct human dendritic cell (DC) subtypes, we compared the effects of a JAK2-specific (TG101348) with a less selective JAK1/2 (ruxolitinib) inhibitor on NK-cell activation and function. Ruxolitinib treatment completely blocked IL2, IL15, and DC-mediated STAT5 phosphorylation, along with the capacity of NK cells to secrete IFNγ or lyse NK cell-sensitive targets. Only NK-cell proliferation stimulated by moDCs resisted ruxolitinib treatment. In contrast, TG101348 treatment of stimulated NK cells resulted in far less functional compromise. TG101348 completely inhibited only soluble IL15-mediated STAT5 phosphorylation, which Langerhans-type DCs (LCs), presenting membrane-bound IL15 in trans, could salvage. These results demonstrate that ruxolitinib's nonselective inhibition of JAK1/2 results in profound NK-cell dysfunction by blocking downstream pSTAT5, hence providing a persuasive rationale for the development of selective JAK2 inhibitors for immunotherapeutic applications. Cancer Immunol Res; 5(1); 52-60. ©2016 AACR.

Langerhans-type and monocyte-derived human dendritic cells have different susceptibilities to mRNA electroporation with distinct effects on maturation and activation: implications for immunogenicity in dendritic cell-based immunotherapy.

BACKGROUND: mRNA electroporation of dendritic cells (DCs) facilitates processing and presentation of multiple peptides derived from whole antigen, tailored to different HLA molecules. Clinical responses to electroporated moDC vaccines, however, have been suboptimal. Human Langerhans-type DCs (LCs) are the most potent conventional DC subtype for inducing CD8+ cytotoxic T lymphocytes (CTLs) in vitro. We recently demonstrated that Wilms' tumor 1 (WT1) mRNA-electroporated LCs are superior to moDCs as stimulators of tumor antigen-specific CD8+ CTLs, even though they are comparable stimulators of allogeneic T cell proliferative responses. A detailed comparative evaluation of the effects of mRNA electroporation on LCs versus moDCs, however, is needed. METHODS: Immature and partially-matured human moDCs and LCs electroporated with mRNA were compared for transfection efficiency, phenotypic changes, viability, retention of transgene expression after cryopreservation, and immunogenicity. Student t test was used for each pairwise comparison. One-way analysis of variance was used for multiple group comparisons. RESULTS: Transfection efficiency after electroporation with enhanced green fluorescent protein (eGFP) mRNA was higher for immature than for partially-matured moDCs. In contrast, transfection efficiency was higher for partially-matured than for immature LCs, with the additional benefit that electroporation itself increased maturation and activation of CD83+HLA-DRbright LCs but not moDCs. Electroporation did not impair final maturation and activation of either DC subtype, after which both mRNA-electroporated LCs and moDCs were functionally similar in stimulating allogeneic T cell proliferation, a standard assay of DC immunogenicity. CONCLUSIONS: These findings support mRNA electroporation of DCs, and in particular LCs, as an effective non-viral method to stimulate specific, potent CD8+ CTL responses. The differences between LCs and moDCs regarding this form of antigen-loading have important implications for DC-based immunotherapies.

Human Langerhans cells use an IL-15R-α/IL-15/pSTAT5-dependent mechanism to break T-cell tolerance against the self-differentiation tumor antigen WT1.

Human CD34(+) progenitor-derived Langerhans-type dendritic cells (LCs) are more potent stimulators of T-cell immunity against tumor and viral antigens in vitro than are monocyte-derived DCs (moDCs). The exact mechanisms have remained elusive until now, however. LCs synthesize the highest amounts of IL-15R-α mRNA and protein, which binds IL-15 for presentation to responder lymphocytes, thereby signaling the phosphorylation of signal transducer and activator of transcription 5 (pSTAT5). LCs electroporated with Wilms tumor 1 (WT1) mRNA achieve sufficiently sustained presentation of antigenic peptides, which together with IL-15R-α/IL-15, break tolerance against WT1 by stimulating robust autologous, WT1-specific cytolytic T-lymphocytes (CTLs). These CTLs develop from healthy persons after only 7 days' stimulation without exogenous cytokines and lyse MHC-restricted tumor targets, which include primary WT1(+) leukemic blasts. In contrast, moDCs require exogenous rhuIL-15 to phosphorylate STAT5 and attain stimulatory capacity comparable to LCs. LCs therefore provide a more potent costimulatory cytokine milieu for T-cell activation than do moDCs, thus accounting for their superior stimulation of MHC-restricted Ag-specific CTLs without need for exogenous cytokines. These data support the use of mRNA-electroporated LCs, or moDCs supplemented with exogenous rhuIL-15, as vaccines for cancer immunotherapy to break tolerance against self-differentiation antigens shared by tumors.

Janus kinase-2 inhibition induces durable tolerance to alloantigen by human dendritic cell-stimulated T cells yet preserves immunity to recall antigen.

Janus kinase-2 (JAK2) conveys receptor-binding signals by several inflammatory cytokines, including IL-6, via phosphorylation of signal transducer and activator of transcription 3 (STAT3). We demonstrate that selective JAK2 inhibition by TG101348 during initial encounters between human T cells and allogeneic monocyte-derived dendritic cells induces durable, profound, and specific T-cell tolerance upon reexposure to the same alloantigens. Subsequent responses by nonalloreactive T cells to stimulation de novo by a pathogenic nominal antigen remain intact. TG101348 also suppresses primed T-cell responses when present only during alloantigen restimulation. TG101348 ablates IL-6/JAK2-mediated phosphorylation of STAT3, but has no off-target effects on IL-2 or IL-15/JAK3/pSTAT5-dependent signaling, which sustain the responses of regulatory T cells (Tregs) and other effector T cells. JAK2 inhibition preserves Treg numbers and thereby enhances the ratio of CD4(+) Tregs to CD8(+)CD25(+) effector T cells in favor of Tregs. JAK2 inhibition also reduces the production of IL-6 and TNF-α in allogeneic MLRs, impairing the activation of central and effector memory T cells as well as the expansion of responder Th1 and Th17 cells. While we have reported the limitations of isolated IL-6R-α inhibition on dendritic cell-stimulated alloreactivity, we demonstrate here that JAK2 represents a relevant biologic target for controlling GVHD or allograft rejection without broader immune impairment.

Anti-IL6-receptor-alpha (tocilizumab) does not inhibit human monocyte-derived dendritic cell maturation or alloreactive T-cell responses.

Significant comorbidites and lethality complicate GVHD and its treatment. Targeting the cytokine milieu may improve GVHD control; and IL6 is an attractive candidate, given its role in dendritic cell activation and T-cell differentiation. Tocilizumab is a humanized mAb to IL6-receptor-α (IL6R-α), which is Food and Drug Administration-approved for treatment of rheumatoid arthritis. Mouse transplant models have demonstrated that IL6 blockade also improves GVHD scores and survival. Definitive immunologic effects of IL6 inhibition have not emerged given inconsistent alterations in regulatory T cells (Tregs) and suppression of T-cell proliferation. Despite on-target suppression of IL6R-α signaling in human monocyte-derived dendritic cells (moDCs) and T cells, our data show no effect on moDC maturation/activation, alloreactive T-cell proliferation, Treg expansion, or allogeneic Th1/Th17 responses in vitro. These findings merit attention in any clinical trials of tocilizumab for GVHD prevention or treatment and provide a rationale for evaluating more specific inhibitors of downstream JAK2/STAT3 signaling as well.