There are no mucosal adjuvant formulations licensed for human use, despite protection against many mucosally-transmitted infections probably requiring immunity at the site of pathogen entry1. Polyethyleneimines (PEI) are organic polycations used as nucleic acid transfection reagents in vitro, and gene and DNA vaccine delivery vehicles in vivo2, 3. Here we show that PEI has unexpected and unusually potent mucosal adjuvant activity in conjunction with viral subunit glycoprotein antigens. Single intranasal administration of influenza HA or HSV-2 gD with PEI elicited robust protection from otherwise lethal infection, and was superior to existing experimental mucosal adjuvants. PEI formed nanoscale complexes with antigen that were taken up by antigen presenting cells in vitro and in vivo, promoted DC trafficking to draining lymph nodes and induced non-proinflammatory cytokine responses. PEI adjuvanticity required release of host dsDNA that triggered Irf-3-dependent signaling. PEI therefore merits further investigation as a mucosal adjuvant for human use.

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Type-1 regulatory T (TR1) cells are Foxp3-negative IL-10-producing CD4+ T cells with potent immune suppressive properties but their requirements for lineage development have remained elusive. Here we show that TR1 cells constitute the most abundant regulatory population after allogeneic bone marrow transplantation (BMT), express the transcription factor Eomesodermin (Eomes) and are critical for the prevention of graft-versus-host disease (GVHD). We demonstrate that Eomes is required for TR1 cell differentiation during which it acts in concert with the transcription factor B-lymphocyte-induced maturation protein-1 (Blimp-1) by transcriptionally activating IL-10 expression and repressing differentiation into other Th lineages. We further show that Eomes induction in TR1 cells requires T-bet and donor macrophage-derived IL-27. We thus define the cellular and transcriptional control of TR1 cell differentiation during bone marrow transplantation, opening new avenues to therapeutic manipulation.

Autologous stem cell transplantation (SCT) remains a standard of care for multiple myeloma (MM) patients and prolongs progression-free survival. A small cohort of patients achieve long-term control of disease, but the majority of patients ultimately relapse, and the mechanisms permitting disease progression remain unclear. In this study, we used a preclinical model of autologous SCT for myeloma where the disease either progressed (MM relapsed) or was controlled. In the bone marrow (BM), inhibitory receptor expression on CD8 T cells correlated strongly with myeloma progression after transplant. In conjunction, the costimulatory/adhesion receptor CD226 (DNAM-1) was markedly downregulated. Interestingly, DNAM-1 CD8 T cells in MM-relapsed mice had an exhausted phenotype, characterized by upregulation of multiple inhibitory receptors, including T-cell immunoglobulin and ITIM domains (TIGIT) and programmed cell death protein 1 (PD-1) with decreased T-bet and increased eomesodermin expression. Immune checkpoint blockade using monoclonal antibodies against PD-1 or TIGIT significantly prolonged myeloma control after SCT. Furthermore, CD8 T cells from MM-relapsed mice exhibited high interleukin-10 (IL-10) secretion that was associated with increased TIGIT and PD-1 expression. However, while donor-derived IL-10 inhibited myeloma control post-SCT, this was independent of IL-10 secretion by or signaling to T cells. Instead, the donor myeloid compartment, including colony-stimulating factor 1 receptor-dependent macrophages and an IL-10-secreting dendritic cell population in the BM, promoted myeloma progression. Our findings highlight PD-1 or TIGIT blockade in conjunction with SCT as a potent combination therapy in the treatment of myeloma.

Key Points Donor-derived Tc17 cells differentiate early after allogeneic transplant in response to IL-6 and alloantigen presentation by host DCs. Tc17 are highly proinflammatory and pathogenic posttransplant, but exert limited or no GVL activity.

A normalized subtracted gene expression library was generated from freshly isolated mouse dendritic cells (DC) of all subtypes, then used to construct cDNA microarrays. The gene expression profiles of the three splenic conventional DC (cDC) subsets were compared by microarray hybridization and two genes encoding signal regulatory protein β (Sirpβ1 and Sirpβ4) molecules were identified as differentially expressed in CD8− cDC. Genomic sequence analysis revealed a third Sirpβ member localized in the same gene cluster. These Sirpβ genes encode cell surface molecules containing extracellular Ig domains and short intracytoplasmic domains that have a charged amino acid in the transmembrane region which can potentially interact with ITAM-bearing molecules to mediate signaling. Indeed, we demonstrated interactions between Sirpβ1 and β2 with the ITAM-bearing signaling molecule Dap12. Real-time PCR analysis showed that all three Sirpβ genes were expressed by CD8− cDC, but not by CD8+ cDC or plasmacytoid pre-DC. The related Sirpα gene showed a similar expression profile on cDC subtypes but was also expressed by plasmacytoid pre-DC. The differential expression of Sirpα and Sirpβ1 molecules on DC was confirmed by staining with mAbs, including a new mAb recognizing Sirpβ1. Cross-linking of Sirpβ1 on DC resulted in a reduction in phagocytosis of Leishmania major parasites, but did not affect phagocytosis of latex beads, perhaps indicating that the regulation of phagocytosis by Sirpβ1 is a ligand-dependent interaction. Thus, we postulate that the differential expression of these molecules may confer the ability to regulate the phagocytosis of particular ligands to CD8− cDC.

Signaling by the serine and threonine kinase Akt (also known as protein kinase B), a pathway that is common to all eukaryotic cells, is central to cell survival, proliferation, and gene induction. We sought to elucidate the mechanisms underlying regulation of the kinase activity of Akt in the immune system. We found that the four-transmembrane protein CD37 was essential for B cell survival and long-lived protective immunity. CD37-deficient (Cd37(-/-)) mice had reduced numbers of immunoglobulin G (IgG)-secreting plasma cells in lymphoid organs compared to those in wild-type mice, which we attributed to increased apoptosis of plasma cells in the germinal centers of the spleen, areas in which B cells proliferate and are selected. CD37 was required for the survival of IgG-secreting plasma cells in response to binding of vascular cell adhesion molecule 1 to the α(4)β(1) integrin. Impaired α(4)β(1) integrin-dependent Akt signaling in Cd37(-/-) IgG-secreting plasma cells was the underlying cause responsible for impaired cell survival. CD37 was required for the mobility and clustering of α(4)β(1) integrins in the plasma membrane, thus regulating the membrane distribution of α(4)β(1) integrin necessary for activation of the Akt survival pathway in the immune system.

Koyama et al. show that GVHD markedly enhances alloantigen presentation within the mesenteric lymph nodes, mediated by donor CD103+CD11b− DCs that migrate from the colon under the influence of CCR7. This antigen presentation imprints gut-homing integrin signatures on donor T cells, leading to their migration to the GI tract where they mediate fulminant disease.