Antigen Choice Determines Vaccine-Induced Generation of Immunogenic versus Tolerogenic Dendritic Cells That Are Marked by Differential Expression of Pancreatic Enzymes

Abstract

Dendritic cells (DC) elicit immunity to pathogens and tumors while simultaneously preserving tolerance to self. Efficacious cancer vaccines have been a challenge because they are based on tumor antigens, some of which are self-antigens and thus subject to self-tolerance. One such antigen is the tumor-associated mucin MUC1. Preclinical testing of MUC1 vaccines revealed existence of peripheral tolerance to MUC1 that compromises their efficacy. To identify mechanisms that act early post-vaccination and might predict vaccine outcome, we immunized human MUC1 transgenic mice (MUC1.Tg) i.v. with a MUC1 peptide vaccine against which they generate weak immunity, and WT mice that respond strongly to the same peptide. We analyzed differences in splenic DC phenotype and function between the two mouse strains at 24 and 72 hours post-vaccination, and also performed unbiased total gene expression analysis of the spleen. Compared to WT, MUC1.Tg spleens had significantly fewer DC and they exhibited significantly lower expression of co-stimulatory molecules, decreased motility and preferential priming of antigen-specific Foxp3+ regulatory T cells (Treg). This tolerogenic DC phenotype and function was marked by a new putative biomarker revealed by the microarray: a cohort of pancreatic enzymes (trypsin, carboxypeptidase, elastase and others) not previously reported in DC. These enzymes were strongly upregulated in the splenic DC from vaccinated WT mice and suppressed in the splenic DC of vaccinated MUC1.Tg mice. Suppression of the enzymes was dependent on Treg and on signaling through the IL-10 receptor and correlated with global down-regulation of DC immunostimulatory phenotype and function.

Novel Mechanisms Underlying the Immediate and Transient Global Tolerization of Splenic Dendritic Cells after Vaccination with a Self-Antigen

“…Fig. 2) and (10, 12). We explored the potential function of these enzymes, focusing on CBP1 and trypsin as representatives of two main families of enzymes, metallopeptidases (represented by CBP1) and serine proteases (represented by trypsin).…”

“…They also preferentially prime naïve CD4 + T cells into Treg versus IFNγ-producing effector T cells. Additionally, there are fewer DC 24h post-immunization in the spleens of MUC1.Tg mice compared to WT (12). Low costimulatory molecule expression and priming of Treg are hallmarks of immature DC (iDC) (2, 17, 18).…”

“…We previously showed that immunization with a self Ag inhibits, within the first 24 hours, the maturation and immunogenicity of all splenic DC in the target lymphoid organ and not just the relatively few DC that present the Ag (12). This rapid tolerization of all DC is likely due to the increased frequency of pre-existing self Ag-specific Treg (12, 35).…”

“…This rapid tolerization of all DC is likely due to the increased frequency of pre-existing self Ag-specific Treg (12, 35). Here we report that early and transiently tolerized DC have a less inflammatory cytokine/chemokine profile that results in impaired DC-mediated inflammation and chemotaxis.…”

“…immunization of human MUC1 transgenic mice (MUC1.Tg) with an unglycosylated human MUC1 peptide (MUC1p) resulted in the transient tolerization (between 24h–72h) of the entire splenic DC population that failed to upregulate costimulatory molecules, lacked motility, and preferentially primed Foxp3 + Treg. These vaccine-tolerized DC also differed in their gene expression profile from vaccine-activated (immunogenic) DC by suppressed expression of a group of “pancreatic” enzymes, specifically trypsin and carboxypeptidase B1 (CPB1) (12), which we proposed as predictive biomarkers of vaccine outcome. These results were consistent with the previously observed low level of vaccine-induced immunity against MUC1p in MUC1.Tg mice (10, 13, 14).…”