Teresa Lozano

A Peptide Inhibitor of FOXP3 Impairs Regulatory T Cell Activity and Improves Vaccine Efficacy in Mice

Immunosuppressive activity of regulatory T cells (Treg) may contribute to the progression of cancer or infectious diseases by preventing the induction of specific immune responses. Using a phage-displayed random peptide library, we identified a 15-mer synthetic peptide, P60, able to bind to forkhead/winged helix transcription factor 3 (FOXP3), a factor required for development and function of Treg. P60 enters the cells, inhibits FOXP3 nuclear translocation, and reduces its ability to suppress the transcription factors NF-κB and NFAT. In vitro, P60 inhibited murine and human-derived Treg and improved effector T cell stimulation. P60 administration to newborn mice induced a lymphoproliferative autoimmune syndrome resembling the reported pathology in scurfy mice lacking functional Foxp3. However, P60 did not cause toxic effects in adult mice and, when given to BALB/c mice immunized with the cytotoxic T cell epitope AH1 from CT26 tumor cells, it induced protection against tumor implantation. Similarly, P60 improved the antiviral efficacy of a recombinant adenovirus expressing NS3 protein from hepatitis C virus. Functional inhibition of Treg by the FOXP3-inhibitory peptide P60 constitutes a strategy to enhance antitumor and antiviral immunotherapies.

Eradication of large tumors expressing human papillomavirus E7 protein by therapeutic vaccination with E7 fused to the extra domain a from fibronectin.

Cervical carcinoma is one of the most common cancers in women worldwide. It is well established that chronic infection of the genital tract by various mucosatropic human papillomavirus (HPV) types causes cervical cancer. Cellular immunity to E7 protein from HPV (HPVE7) has been associated with clinical and cytologic resolution of HPV‐induced lesions. Thus, we decided to test if targeting of HPVE7 to dendritic cells using a fusion protein containing the extra domain A (EDA) from fibronectin, a natural ligand for TLR4, and HPVE7 (EDA‐HPVE7) might be an efficient vaccine for the treatment of cervical carcinoma. We found that EDA‐HPVE7 fusion protein was efficiently captured by bone marrow derived dendritic cells in vitro and induced their maturation, with the upregulation of maturation markers and the production of IL‐12. Immunization of mice with EDA‐HPVE7 fusion protein induced antitumor CD8+ T cell responses in the absence of additional adjuvants. Repeated intratumoral administration of EDA‐HPVE7 in saline was able to cure established TC‐1 tumors of 5–7 mm in diameter. More importantly, intravenous injection with EDA‐HPVE7 in combination with the TLR ligand polyinosinic‐polycytidylic acid (pIC), or with low doses of cyclophosphamide and the TLR9 ligand CpG‐B complexed in cationic lipids, were able to eradicate large established TC‐1 tumors (1.2 cm in diameter). Thus, therapeutic vaccination with EDA‐HPVE7 fusion protein may be effective in the treatment of human cervical carcinoma.

A Combined PD-1/C5a Blockade Synergistically Protects Against Lung Cancer Growth and Metastasis

Disruption of the programmed cell death protein 1 (PD-1) pathway with immune checkpoint inhibitors represents a major breakthrough in the treatment of non-small cell lung cancer. We hypothesized that combined inhibition of C5a/C5aR1 and PD-1 signaling may have a synergistic antitumor effect. The RMP1-14 antibody was used to block PD-1, and an L-aptamer was used to inhibit signaling of complement C5a with its receptors. Using syngeneic models of lung cancer, we demonstrate that the combination of C5a and PD-1 blockade markedly reduces tumor growth and metastasis and leads to prolonged survival. This effect is accompanied by a negative association between the frequency of CD8 T cells and myeloid-derived suppressor cells within tumors, which may result in a more complete reversal of CD8 T-cell exhaustion. Our study provides support for the clinical evaluation of anti-PD-1 and anti-C5a drugs as a novel combination therapeutic strategy for lung cancer.Significance: Using a variety of preclinical models of lung cancer, we demonstrate that the blockade of C5a results in a substantial improvement in the efficacy of anti-PD-1 antibodies against lung cancer growth and metastasis. This study provides the preclinical rationale for the combined blockade of PD-1/PD-L1 and C5a to restore antitumor immune responses, inhibit tumor cell growth, and improve outcomes of patients with lung cancer. Cancer Discov; 7(7); 694-703. ©2017 AACR.This article is highlighted in the In This Issue feature, p. 653.

Searching for the Achilles Heel of FOXP3

FOXP3 is a multifaceted transcription factor with a major role in the control of immune homeostasis mediated by T regulatory cells (Treg). The immunoregulatory function of FOXP3 may hinder the induction of immune responses against cancer and infectious agents, and thus, development of inhibitors of its functions might give new therapeutic opportunities for these diseases. But also, FOXP3 is an important tumor suppressor factor in some types of cancers, and therefore, understanding the structure and function of FOXP3 is crucial to gaining insights into the development of FOXP3-targeted therapeutic strategies. FOXP3 homodimerize and likely form supramolecular complexes which might include hundreds of proteins which constitute the FOXP3 interactome. Many of the functions of FOXP3 are clearly regulated by the interactions with these cofactors contributing importantly on the establishment of Treg-cell signature. We summarize here the structural/functional information on this FOXP3 complex, to identify potential opportunities for the development of new strategies to modulate FOXP3 activity.

Targeting inhibition of Foxp3 by a CD28 2'-Fluro oligonucleotide aptamer conjugated to P60-peptide enhances active cancer immunotherapy.

The specific inhibition of Treg function has long been a major technical challenge in cancer immunotherapy. So far no single cell-surface marker has been identified that could be used to distinguish Treg cells from other lymphocytes. The only available specific marker mostly expressed in Treg is Foxp3, which is an intracellular transcription factor. A targeting molecule able to penetrate the membrane and inhibit Foxp3 within the cell is needed. P60-peptide is able to do that, but due to lack of target specificity, the doses are extremely high. In this study we have shown as a proof of concept that P60 Foxp3 inhibitor peptide can be conjugated with a CD28 targeting aptamer to deliver the peptide to CD28-expressing cells. The AptCD28-P60 construct is a clinically feasible reagent that improves the efficacy of the unconjugated P60 peptide very significantly. This approach was used to inhibit Treg function in a vaccination context, and it has shown a significant improvement in the induced immune response, entailing a lower tumor load in an antigen-specific cancer vaccine protocol.

Inhibition of FOXP3/NFAT Interaction Enhances T Cell Function after TCR Stimulation

Regulatory T cell (Treg) activity is modulated by a cooperative complex between the transcription factor NFAT and FOXP3, a lineage specification factor for Tregs. FOXP3/NFAT interaction is required to repress expression of IL-2, upregulate expression of the Treg markers CTLA4 and CD25, and confer suppressor function to Tregs. However, FOXP3 is expressed transiently in conventional CD4+ T cells upon TCR stimulation and may lead to T cell hyporesponsiveness. We found that a short synthetic peptide able to inhibit FOXP3/NFAT interaction impaired suppressor activity of conventional Tregs in vitro. Specific inhibition of FOXP3/NFAT interaction with this inhibitory peptide revealed that FOXP3 downregulates NFAT-driven promoter activity of CD40L and IL-17. Inhibition of FOXP3/NFAT interaction upregulated CD40L expression on effector T cells and enhanced T cell proliferation and IL-2, IFN-γ, IL-6, or IL-17 production in response to TCR stimulation. The inhibitory peptide impaired effector T cell conversion into induced Tregs in the presence of TGF-β. Moreover, in vivo peptide administration showed antitumor efficacy in mice bearing Hepa129 or TC1 tumor cells when combined with sorafenib or with an antitumor vaccine, respectively. Our results suggest that inhibition of NFAT/FOXP3 interaction might improve antitumor immunotherapies.

A core of kinase-regulated interactomes defines the neoplastic MDSC lineage

Myeloid-derived suppressor cells (MDSCs) differentiate from bone marrow precursors, expand in cancer-bearing hosts and accelerate tumor progression. MDSCs have become attractive therapeutic targets, as their elimination strongly enhances anti-neoplastic treatments. Here, immature myeloid dendritic cells (DCs), MDSCs modeling tumor-infiltrating subsets or modeling non-cancerous (NC)-MDSCs were compared by in-depth quantitative proteomics. We found that neoplastic MDSCs differentially expressed a core of kinases which controlled lineage-specific (PI3K-AKT and SRC kinases) and cancer-induced (ERK and PKC kinases) protein interaction networks (interactomes). These kinases contributed to some extent to myeloid differentiation. However, only AKT and ERK specifically drove MDSC differentiation from myeloid precursors. Interfering with AKT and ERK with selective small molecule inhibitors or shRNAs selectively hampered MDSC differentiation and viability. Thus, we provide compelling evidence that MDSCs constitute a distinct myeloid lineage distinguished by a “kinase signature” and well-defined interactomes. Our results define new opportunities for the development of anti-cancer treatments targeting these tumor-promoting immune cells.

A Fusion Protein between Streptavidin and the Endogenous TLR4 Ligand EDA Targets Biotinylated Antigens to Dendritic Cells and Induces T Cell Responses In Vivo

The development of tools for efficient targeting of antigens to antigen presenting cells is of great importance for vaccine development. We have previously shown that fusion proteins containing antigens fused to the extra domain A from fibronectin (EDA), an endogenous TLR4 ligand, which targets antigens to TLR4-expressing dendritic cells (DC), are highly immunogenic. To facilitate the procedure of joining EDA to any antigen of choice, we have prepared the fusion protein EDAvidin by linking EDA to the N terminus of streptavidin, allowing its conjugation with biotinylated antigens. We found that EDAvidin, as streptavidin, forms tetramers and binds biotin or biotinylated proteins with a K d ~ 2.6 × 10−14 mol/L. EDAvidin favours the uptake of biotinylated green fluorescent protein by DC. Moreover, EDAvidin retains the proinflammatory properties of EDA, inducing NF-κ β by TLR4-expressing cells, as well as the production of TNF-α by the human monocyte cell line THP1 and IL-12 by DC. More importantly, immunization of mice with EDAvidin conjugated with the biotinylated nonstructural NS3 protein from hepatitis C virus induces a strong anti-NS3 T cell immune response. These results open a new way to use the EDA-based delivery tool to target any antigen of choice to DC for vaccination against infectious diseases and cancer.

Combination of a TLR4 ligand and anaphylatoxin C5a for the induction of antigen-specific cytotoxic T cell responses☆

The complement system and Toll-like receptors (TLR) are key innate defense systems which might interact synergistically on dendritic cells (DC) to reinforce adaptive immunity. In a previous work, we found that the extra domain A from fibronectin EDA (an endogenous ligand for TLR4) can favour antigen delivery to DC and induce their maturation. Given the potential of anaphylatoxins to cause inflammation and activation of myeloid cells, we hypothesized that a fusion protein between EDA, and anaphylatoxins C3a, C4a or C5a together with an antigen might improve the immunogenicity of the antigen. Naked DNA immunization with a construct expressing the fusion protein between C5a, EDA and the cytotoxic T cell epitope SIINFEKL from ovalbumin, induced strong antigen specific T cell responses. The purified recombinant fusion protein EDA-SIINFEKL-C5a induced activation of dendritic cells, the production of proinflammatory cytokines/chemokines and stimulated antigen presenting cell migration and NK cell activation. As compared to EDA-SIINFEKL, the fusion protein EDA-SIINFEKL-C5a did not induce the production of the immunosuppressive molecules IL-10, CCL17, CCL1, CXCL12 or XCL1 by DC. Moreover, EDA-SIINFEKL-C5a induced strong specific T cell responses in vivo and protected mice against E.G7-OVA tumor growth more efficiently than EDA-SIINFEKL or SIINFEKL-C5a recombinant proteins. Our results suggest that fusion proteins containing EDA, the anaphylatoxin C5a and the antigen may serve as a suitable strategy for the development of anti-tumor or anti-viral vaccines.

Identification of small-molecule inhibitors of calcineurin-NFATc signaling that mimic the PxIxIT motif of calcineurin binding partners

Finding compounds that target a specific phosphatase-substrate interaction may yield immunosuppressive drugs with fewer side effects. Finding better immunosuppressants The immunosuppressant cyclosporin A (CsA) prevents organ rejection in transplant patients. CsA binds to and inhibits the phosphatase calcineurin, thereby preventing the dephosphorylation and activation of the NFAT transcription factors, which are required for T cell proliferation. However, CsA also prevents calcineurin from interacting with its other targets, leading to numerous side effects. Matsoukas et al. performed a virtual screen of a chemical database to identify compounds predicted to interact with the NFAT-binding region of calcineurin. In vitro, some of the compounds displaced NFAT from calcineurin-NFAT complexes without inhibiting the activity of the phosphatase. Experiments with primary human CD4+ T cells further narrowed the pool of candidate compounds to four that blocked the expression of NFAT-dependent genes and inhibited cellular proliferation, suggesting that these may be good leads for further testing as immunosuppressants. Calcineurin (CN), a serine and threonine protein phosphatase that depends on Ca2+ and calmodulin for its activity, is the target of the immunosuppressant drugs cyclosporin A (CsA) and tacrolimus (FK506). CN dephosphorylates and activates members of the NFATc (nuclear factor of activated T cells) family of transcription factors in T cells by binding to their conserved PxIxIT motif. Upon dephosphorylation, NFATc proteins translocate to the nucleus, where they stimulate the expression of genes encoding cytokines and chemokines that are required for T cell proliferation and the immune response. We performed a pharmacophore-based virtual screening of ~5.5 million commercially available, “drug-like” compounds to identify nonpeptidic compounds that inhibited the CN-dependent activation of NFATc signaling and that could serve as potential drug candidates for immunosuppressive therapy. Of 32 compounds that mimicked the PxIxIT motif, 7 competed with NFATc for binding to CN in vitro without interfering with the phosphatase activity of CN. Furthermore, in activated human CD4+ T cells, four of the seven compounds inhibited the expression of NFATc-dependent genes, cytokine production, and cell proliferation, suggesting that these may have therapeutic potential as immunosuppressive agents.