Peroxynitrite in the tumor microenvironment changes the profile of antigens allowing escape from cancer immunotherapy

Cancer immunotherapy often depends on recognition of peptide epitopes by cytotoxic T lymphocytes (CTLs). The tumor microenvironment (TME) is enriched for peroxynitrite (PNT), a potent oxidant produced by infiltrating myeloid cells and some tumor cells. We demonstrate that PNT alters the profile of MHC class I bound peptides presented on tumor cells. Only CTLs specific for PNT-resistant peptides have a strong antitumor effect in vivo, whereas CTLs specific for PNT-sensitive peptides are not effective. Therapeutic targeting of PNT in mice reduces resistance of tumor cells to CTLs. Melanoma patients with low PNT activity in their tumors demonstrate a better clinical response to immunotherapy than patients with high PNT activity. Our data suggest that intratumoral PNT activity should be considered for the design of neoantigen-based therapy and also may be an important immunotherapeutic target.

Cancer-Associated Fibroblasts Neutralize the Anti-tumor Effect of CSF1 Receptor Blockade by Inducing PMN-MDSC Infiltration of Tumors

Tumor-associated macrophages (TAM) contribute to all aspects of tumor progression. Use of CSF1R inhibitors to target TAM is therapeutically appealing, but has had very limited anti-tumor effects. Here, we have identified the mechanism that limited the effect of CSF1R targeted therapy. We demonstrated that carcinoma-associated fibroblasts (CAF) are major sources of chemokines that recruit granulocytes to tumors. CSF1 produced by tumor cells caused HDAC2-mediated downregulation of granulocyte-specific chemokine expression in CAF, which limited migration of these cells to tumors. Treatment with CSF1R inhibitors disrupted this crosstalk and triggered a profound increase in granulocyte recruitment to tumors. Combining CSF1R inhibitor with a CXCR2 antagonist blocked granulocyte infiltration of tumors and showed strong anti-tumor effects.

Myeloid-derived suppressor cells in the tumor microenvironment: expect the unexpected

Our understanding of the role of myeloid-derived suppressor cells (MDSCs) in cancer is becoming increasingly complex. In addition to their eponymous role in suppressing immune responses, they directly support tumor growth, differentiation, and metastasis in a number of ways that are only now beginning to be appreciated. It is because of this increasingly complex role that these cells may become an important factor in the treatment of human cancer. In this Review, we discuss the most pertinent and controversial issues of MDSC biology and their role in promoting cancer progression and highlight how these cells may be used in the clinic, both as prognostic factors and as therapeutic targets.

Antigen-specific Treg and IL-10 influence DC immunogenicity hours following vaccination with a self versus a foreign antigen (P4232)

Mice transgenic for the human tumor antigen MUC1 (MUC1.Tg) are hyporesponsive to MUC1 peptide relative to WT mice. A recently identified biomarker of this hyporesponsiveness is suppression in splenic dendritic cells (DC) of a family of pancreatic enzymes, represented by several trypsin isoforms and carboxypeptidase B1. These enzymes are upregulated following vaccination of WT mice with MUC1 peptide (foreign antigen) or MUC1.Tg mice with ovalbumin (foreign antigen), but are suppressed following vaccination of MUC1.Tg mice with MUC1 peptide (self antigen). This suppression can be alleviated by eliminating Tregs or by blocking signaling through the IL-10 receptor. This enzyme profile marking suppression or activation of DC could be identified as early as 4 hours post MUC1 peptide vaccination of WT and MUC1.Tg mice. Differences in enzyme expression also correlated with differential NK cell activation at the same early timepoint as measured by IFNγ and IL-10 secretion. This work shows that the decision for tolerance or immunity is established in multiple cell types no more than 4 hours post vaccination and that these enzymes are an early biomarker of this decision.

DC enzymes as early biomarkers of an effective vaccine (46.7)

Previous work by our lab and others has shown that human MUC1 transgenic mice (MUC1.tg) are hyporesponsive to vaccination with some forms of MUC1 and fail to mount a spontaneous immune response against MUC1 positive tumors. An interesting correlate of hyporesponsiveness to MUC1 vaccination is that as early as 24 hours post vaccination, splenic dendritic cells (DC) in wild type (WT) mice upregulate expression of a group of proteolytic enzymes previously characterized as functioning primarily in pancreatic catabolism (e.g. Trypsin-1, Trypsin-4, Carboxypeptidase B1). This upregulation does not occur in the MUC1.tg animals. Using an in vitro co-culture system and in vivo antibody depletion, we show that regulation of enzyme expression in DC is dependent on their interaction with CD4 T cells such that CD4 effector T cells (Teff) up-regulate these enzymes, whereas the presence of activated CD4 regulatory T cells (Treg) actively suppress this activity in an IL-10 dependent manner. TLR agonists do not upregulate enzyme expression, suggesting differences are due to alternative DC activation pathways following their interaction with T cells. We propose that one or more of these enzymes, which appear to be co-regulated, could serve as early markers of, and most likely also as contributors to, DC activation by helper T cells. In contrast, lack of their expression marks insufficient activation or active suppression by Tregs.

A Novel Transgenic Animal Model for HPV-Associated Cancer

Objective: The incidence of HPV-associated tumors is rising at a rapid pace. In order to develop novel therapies with high efficacy but low toxicity, it is crucial to have an animal model in which HPV-associated oral lesions spontaneously develop. Our objective was to develop such a model.

Method: A transgene was created to target expression of E7 to the oral cavity by cloning HPV-16 E7 downstream of the L2 promoter. Transgenic mice which carry this gene were created on the C57Bl6 background. Then, these mice were backcrossed with a strain of mice heterozygous for p53.

Results: Mice were bred to create the desired genotype, E7 +/+, p53 -/-. Because of the short life span and limited breeding potential of mice with a homozygous p53 deletion, breeding was performed with p53 heterozygous mice. In accordance with Mendelian genetics, we found the majority of offspring were heterozygous for p53, and did not form spontaneous tumors. Of the offspring with homozygous p53 deletions, few lived longer than 25 weeks. However, one mouse lived long enough to develop an HPV-associated oral tumor. E7 transcript was detected in the tumor by RT-PCR, and E7 protein was detected via Western blot.

Conclusion: We report the development of a transgenic mouse which spontaneously expressed an HPV-associated oral tumor. Additional genetic manipulation may be required to enhance the longevity and stability of this mouse strain. This strain has the potential to serve as a platform to investigate novel therapeutic strategies for HPV-associated tumors.

Transcriptional regulation of proteolytic enzymes in dendritic cells by effector versus regulatory T cells: a new mechanism of maintaining peripheral tolerance (52.15)

MUC1.Tg mice express the human tumor associated antigen MUC1 in a physiological pattern that is analogous to its expression on normal human epithelial cells and tumors. Vaccine-induced responses to MUC1 peptide in these animals are weak compared to WT mice. Gene expression profiling post vaccination revealed differential regulation in spleen dendritic cells (DC) of several proteolytic enzymes that were previously thought to function exclusively in pancreatic catabolism (i.e. Trypsin-1, Trypsin-4, Carboxypeptidase B1). These enzymes were upregulated in DC when WT mice were vaccinated with the MUC1 peptide (more foreign) and highly downregulated after the same vaccination in MUC1.Tg mice (more self). Using an in vitro co-culture system, we show that this regulation is dependent on CD4 T cell interactions with DC, such that activated effector T cells (Teff), but not TLR agonists, upregulate these enzymes, whereas activated regulatory T cells (Treg) actively suppress their expression. Cell-cell contact appears to be necessary. The Treg mediated suppression is dominant and it occurs even when DC are cultured simultaneously with Treg and Teff. We propose a new mechanism of maintaining peripheral tolerance whereby self-antigen specific Treg recognize the presence of antigen on a few DC and temporarily shut down antigen processing by all DC to avoid efficient priming of effector T cells.