Recombinant lipidated FLIPr effectively enhances mucosal and systemic immune responses for various vaccine types.

Formyl peptide receptor-like 1 inhibitor protein (FLIPr) is an immune evasion protein produced by Staphylococcus aureus, and FLIPr is a potential vaccine candidate for reducing Staphylococcus aureus virulence and biofilm formation. We produced recombinant lipidated FLIPr (rLF) to increase the immunogenicity of FLIPr and showed that rLF alone elicited potent anti-FLIPr antibody responses to overcome the FLIPr-mediated inhibition of phagocytosis. In addition, rLF has potent immunostimulatory properties. We demonstrated that rLF is an effective adjuvant. When an antigen is formulated with rLF, it can induce long-lasting antigen-specific immune responses and enhance mucosal and systemic antibody responses as well as broad-spectrum T-cell responses in mice. These findings support further exploration of rLF in the clinic as an adjuvant for various vaccine types with extra benefits to abolish FLIPr-mediated immunosuppressive effects.

Intranasal Vaccination With Recombinant Antigen-FLIPr Fusion Protein Alone Induces Long-Lasting Systemic Antibody Responses and Broad T Cell Responses.

A simple formulation is urgently needed for mucosal vaccine development. We employed formyl peptide receptor-like 1 inhibitory protein (FLIPr), an FcγR antagonist secreted by Staphylococcus aureus, as a vector to target ovalbumin (OVA) to dendritic cells (DCs) via intranasal administration. Our results demonstrate that intranasal administration of recombinant OVA-FLIPr fusion protein (rOVA-FLIPr) alone efficiently delivers OVA to DCs in nasal lymphoid tissue. Subsequently, OVA-specific IgG and IgA antibodies in the circulatory system and IgA antibodies in mucosal tissue were detected. Importantly, activation of OVA-specific CD4+ and CD8+ T cells and induction of a broad-spectrum cytokine secretion profile were detected after intranasal administration of rOVA-FLIPr alone in immunocompetent C57BL/6 mice. Furthermore, we employed immunodeficient AG129 mice as a Zika virus infection model and demonstrated that intranasal administration of recombinant Zika virus envelope protein domain III-FLIPr fusion protein induced protective immune responses against the Zika virus. These results suggest that antigen-FLIPr fusion protein alone via intranasal administration can be applied to mucosal vaccine development.

Activation of GM-CSF and TLR2 signaling synergistically enhances antigen-specific antitumor immunity and modulates the tumor microenvironment.

BACKGROUND: The major challenge of antitumor immunotherapy is dealing with the immunosuppressive tumor microenvironment, which involves immature myeloid cell accumulation that results in T cell dysfunction. Myeloid cell activation is induced by Toll-like receptor agonists. Additionally, granulocyte/macrophage colony stimulating factor (GM-CSF) promotes myelopoiesis and recruits myeloid cells. Here, we combined the Toll-like receptor 2 (TLR2) agonist lipoprotein and GM-CSF to assess whether this bifunctional immunotherapy has synergistic effects on myeloid cells and could be further developed as a therapeutic intervention that enhances the antitumor response. METHODS: We investigated the synergistic effects of biadjuvanted tumor antigen on antigen-presenting cell (APC) activation in bone marrow-derived dendritic cells. Furthermore, therapeutic efficacy was monitored in different tumor models treated via intratumoral or subcutaneous administration routes. The immune effects of the bifunctional fusion protein on myeloid cells in the tumor mass and draining lymph nodes were analyzed by flow cytometry. The induction of cytotoxic T lymphocytes was evaluated via intracellular cytokine levels, perforin/granzyme B staining and an in vivo killing assay. RESULTS: The TLR2 agonist lipoprotein combined with GM-CSF synergistically induced DC maturation, which subsequently enhanced antitumor immunity. In addition, rlipoE7m-MoGM modulated tumor-infiltrating myeloid cell populations. Vaccination with rlipoE7m-MoGM therapy increased the number of CCR7+CD103+ cDC1s, whereas the number of suppressive tumor-associated macrophages was reduced in the tumor lesions. Consistent with this observation, proliferating antigen-specific CD8+ T cells are highly infiltrated within the tumor, and the expression of IFN-r and perforin was most pronounced within antigen-specific CD8+ T cells in mice administered rlipoE7m-MoGM therapy. This finding corresponded with observation that the combination of a TLR2 agonist and GM-CSF provides increased antitumor activity by inhibiting established tumor outgrowth and protecting against metastatic cancer compared with a TLR2 agonist alone. Importantly, tumor growth inhibition was not due to the direct effects of the TLR2 agonist or GM-CSF but was instead due to the induction of antigen-specific immunity. CONCLUSIONS: The combination of a TLR2 agonist and GM-CSF has synergistic effects that inhibit tumor growth and modulate tumor-infiltrating APCs. This therapeutic approach could be applied to other tumor antigens to treat different cancers.

A Novel Recombinant Fcγ Receptor-Targeted Survivin Combines with Chemotherapy for Efficient Cancer Treatment.

Formyl peptide receptor-like 1 inhibitor (FLIPr), an Fcγ receptor (FcγR) antagonist, can be used as a carrier to guide antigen-FLIPr fusion protein to FcγR then enhances antigen-specific immune responses. Survivin, a tumor-associated antigen, is over-expressed in various types of human cancer. In this study, we demonstrate that recombinant survivin-FLIPr fusion protein (rSur-FLIPr) binds to FcγRs, and efficient uptake by dendritic cells in vivo. In addition, rSur-FLIPr alone stimulates survivin-specific immune responses, which effectively suppresses the tumor growth. The antitumor immunities are through TAP-mediated and CD8-dependent pathways. Furthermore, preexisting anti-FLIPr antibody does not abolish antitumor responses induced by rSur-FLIPr immunization. These results suggest that FLIPr is an effective antigen delivery vector and can be repeatedly used. Combination of chemotherapy with rSur-FLIPr treatment reveals a great benefit to tumor-bearing mice. Altogether, these findings suggest that rSur-FLIPr is a potential candidate for efficient cancer therapy.

Liposomal TLR9 Agonist Combined with TLR2 Agonist-Fused Antigen Can Modulate Tumor Microenvironment through Dendritic Cells.

Dendritic cells (DCs) are antigen-presenting cells involved in T cell activation and differentiation to regulate immune responses. Lipoimmunogens can be developed as pharmaceutical lipoproteins for cancer immunotherapy to target DCs via toll-like receptor 2 (TLR2) signaling. Previously, we constructed a lipoimmunogen, a lipidated human papillomavirus (HPV) E7 inactive mutant (rlipoE7m), to inhibit the growth of HPV16 E7-expressing tumor cells in a murine model. Moreover, this antitumor effect could be enhanced by a combinatory treatment with CpG oligodeoxynucleotides (ODN). To improve safety, we developed a rlipoE7m plus DOTAP liposome-encapsulated native phosphodiester CpG (POCpG/DOTAP) treatment to target DCs to enhance antitumor immunity. We optimized the formulation of rlipoE7m and POCpG/DOTAP liposomes to promote conventional DC and plasmacytoid DC maturation in vitro and in vivo. Combination of rlipoE7m plus POCpG/DOTAP could activate conventional DCs and plasmacytoid DCs to augment IL-12 production to promote antitumor responses by intravenous injection. In addition, the combination of rlipoE7m plus POCpG/DOTAP could elicit robust cytotoxic T lymphocytes (CTLs) by intravenous immunization. Interestingly, the combination of rlipoE7m plus POCpG/DOTAP could efficiently inhibit tumor growth via intravenous immunization. Moreover, rlipoE7m plus POCpG/DOTAP combined reduced the number of tumor-infiltrating regulatory T cells dramatically due to downregulation of IL-10 production by DCs. These results showed that the combination of rlipoE7m plus POCpG/DOTAP could target DCs via intravenous delivery to enhance antitumor immunity and reduce the number of immunosuppressive cells in the tumor microenvironment.

Recombinant lipidated Zika virus envelope protein domain III elicits durable neutralizing antibody responses against Zika virus in mice.

BACKGROUND: The emergence of Zika virus (ZV) in tropical and subtropical areas of the world has created an urgent need for vaccines against ZV. However, approved vaccines that prevent ZV infection are not available. To develop an effective vaccine against ZV infection, a lipidated form of ZV envelope protein domain III that possesses an intrinsic adjuvant property was rationally designed. Our goal was to examine the immunogenicity of recombinant lipidated ZV envelope protein domain III (rLZE3) and evaluate its potential as a vaccine candidate against ZV. METHODS: Recombinant ZV envelope protein domain III (rZE3) and rLZE3 were prepared with an Escherichia coli-based system. Dendritic cell surface marker expression and cytokine production upon stimulation were analyzed to evaluate the function of rLZE3. Neutralizing antibody capacities were evaluated using focus reduction neutralization tests after immunization. To investigate the protective immunity in immunized mice, serum samples collected from immunized mice were adoptively transferred into AG129 mice, and then viremia levels and survival times were examined after ZV challenge. RESULTS: rLZE3 alone but not rZE3 alone efficiently activated dendritic cells in vitro and was taken up by dendritic cells in vivo. Immunization of C57BL/6 mice with rLZE3 alone (without exogenous adjuvant) could induce ZV-specific neutralizing antibody responses. Furthermore, serum samples obtained from rLZE3-immunized mice provided protection as indicated by a reduction in viremia levels and prolongation of survival times after ZV challenge. CONCLUSION: These results indicate that rLZE3 is an excellent vaccine candidate and has great potential that should be evaluated in further preclinical studies.

Delivery of Antigen to CD8+ Dendritic Cells by Fusing Antigen With Formyl Peptide Receptor-Like 1 Inhibitor Protein Induces Antitumor Immunity.

A major challenge for vaccine development is targeting antigens to dendritic cells (DCs) in vivo, enabling cross-presentation, and inducing the memory responses. Fcγ receptors (FcγRs) are expressed on many cell types including DCs. Therefore, targeting of antigen to DCs via FcγRs is an attractive strategy for vaccine development. This study employ formyl peptide receptor-like 1 inhibitory protein (FLIPr), an FcγR binding protein secreted by Staphylococcus aureus, to deliver antigen to DCs. Our results show that FLIPr is a competent vehicle in delivering antigen to CD8+ DCs for induction of potent immunities without extra adjuvant formulation. Fusion antigen with FLIPr enables effective antigen presentation on both MHC class II and class I to induce memory T cell responses. Altogether, using FLIPr as an antigen delivery vector has great potential to apply antigens for cancer immunotherapy as well as other infectious disease vaccines.

Efficient Uptake of Recombinant Lipidated Survivin by Antigen-Presenting Cells Initiates Antigen Cross-Presentation and Antitumor Immunity.

Survivin is overexpressed in various types of human cancer, but rarely expressed in terminally differentiated adult tissues. Thus, survivin is a potential target antigen for a cancer vaccine. However, self-tumor-associated antigens are not highly immunogenic. Bacteria-derived lipoproteins can activate antigen-presenting cells through their toll-like receptors to enhance immune responses. In this context, lipidated survivin is an attractive candidate for cancer immunotherapy. In the present study, recombinant lipidated human survivin (LSur) was prepared from an Escherichia coli-based system. We investigated whether LSur is efficiently captured by antigen-presenting cells then facilitating effective induction of survivin cross-presentation and generation of immunity against cancer cells. Our results demonstrate that LSur, but not its non-lipidated counterpart, can activate mouse bone-marrow-derived-dendritic cells (BMDCs) to enhance cytokine (IL-6, TNF-α, and IL-12) secretion and costimulatory molecules (CD40, CD80, CD86, and MHC II) expression. However, the pathways involved in the capture of the recombinant lipidated antigen by antigen-presenting cells have not yet been elucidated. To this end, we employ various endocytosis inhibitors to study the effect on LSur internalization. We show that the internalization of LSur is suppressed by the inhibition of various routes of endocytosis. These results suggest that endocytosis of LSur by BMDCs can be mediated by multiple mechanisms. Furthermore, LSur is trafficked to the early endosome after internalization by BMDCs. These features of LSur are advantageous for cross-presentation and the induction of antitumor immunity. We demonstrate that immunization of C57BL/6 mice with LSur under treatment with exogenous adjuvant-free formulation induce survivin-specific CD8+ T-cell responses and suppress tumor growth. The antitumor responses are mediated by CD8+ cells. Our findings indicate that LSur is a potential candidate for stimulating protective antitumor immunity. This study suggests that lipidated tumor antigens may be a promising approach for raising a robust antitumor response in cancer immunotherapy.

A novel liposomal recombinant lipoimmunogen enhances anti-tumor immunity.

Synthetic liposomes provide a biocompatible and biodegradable approach for delivering drugs and antigens. In addition, self-adjuvanting recombinant lipoproteins (rlipoproteins) can enhance Th1 anti-tumor immune responses via the TLR2 signaling pathway. To generate a liposomal rlipoprotein for a cancer immunotherapeutic vaccine, we assessed 3 types of synthetic liposomes for use with the rlipoproteins rlipoE7m and rlipoOVA. We determined that the cationic liposome DOTAP could stabilize anionic rlipoproteins and delay rlipoprotein release. Surprisingly, rlipoproteins and DOTAP could synergistically up-regulate CD83 expression in bone marrow-derived dendritic cells (BMDCs). Compared with other liposome formulations, the rlipoprotein/DOTAP formulation elicited higher cytotoxic T-lymphocyte (CTL) responses. To explore the mechanism of BMDC activation by rlipoprotein/DOTAP, we assessed the production of reactive oxygen species (ROS) and the TNF-α secretion of BMDCs. We observed that rlipoprotein/DOTAP induced ROS to the same extent as DOTAP did. In addition, TLR2 signaling was also required for the TNF-α secretion of rlipoprotein/DOTAP-treated BMDCs. Moreover, compared with rlipoOVA-treated BMDCs, rlipoOVA/DOTAP-treated BMDCs increased the levels of IFN-γ produced by OVA-specific T cells. We also observed that rlipoE7m/DOTAP treatment but not rlipoE7m treatment delayed tumor growth. These results indicate that the rlipoprotein/DOTAP formulation can synergistically activate BMDCs via ROS and the TLR2 signaling pathway. In summary, rlipoprotein/DOTAP is a novel and stable formulation for cancer immunotherapy.

A Toll-like receptor 2 agonist-fused antigen enhanced antitumor immunity by increasing antigen presentation and the CD8 memory T cells population.

The induction of long-lived effector CD8+ T cells is key to the development of efficient cancer vaccines. In this study, we demonstrated that a Toll-like receptor 2 (TLR2) agonist-fused antigen increased antigen presentation via TLR2 signaling and induced effector memory-like CD8+ T cells against cancer after immunization. The N-terminus of ovalbumin (OVA) was biologically fused with a bacterial lipid moiety TLR2 agonist to produce a recombinant lipidated ovalbumin (rlipo-OVA). We demonstrated that rlipo-OVA activated bone marrow-derived dendritic cells (BM-DCs) maturation and increased antigen presentation by major histocompatibility complex (MHC) class I via TLR2. After immunization, rlipo-OVA skewed the immune response towards T helper (Th) 1 and induced OVA-specific cytotoxic T lymphocyte (CTL) responses. Moreover, immunization with rlipo-OVA induced higher numbers of effector memory (CD44+CD62L-) CD8+ T cells compared with recombinant ovalbumin (rOVA) alone or rOVA mixed with the TLR2 agonist Pam3CSK4. Accordingly, the CD27+CD43+ effector memory CD8+ T cells expressed high levels of the long-lived CD127 marker. The administration of rlipo-OVA could inhibit tumor growth, but the anti-tumor effects were lost after the depletion of CD8 or CD127 cells in vivo. These findings suggested that the TLR2 agonist-fused antigen induced long-lived memory CD8+ T cells for efficient cancer therapy.

Toll-like receptor 9 agonist enhances anti-tumor immunity and inhibits tumor-associated immunosuppressive cells numbers in a mouse cervical cancer model following recombinant lipoprotein therapy.

BACKGROUND: Although cytotoxic T lymphocytes (CTLs) play a major role in eradicating cancer cells during immunotherapy, the cancer-associated immunosuppressive microenvironment often limits the success of such therapies. Therefore, the simultaneous induction of cancer-specific CTLs and reversal of the immunosuppressive tumor microenvironment may be more effectively achieved through a single therapeutic vaccine. A recombinant lipoprotein with intrinsic Toll-like receptor 2 (TLR2) agonist activity containing a mutant form of E7 (E7m) and a bacterial lipid moiety (rlipo-E7m) has been demonstrated to induce robust CTL responses against small tumors. This treatment in combination with other TLR agonists is able to eliminate large tumors. METHODS: Mouse bone marrow-derived dendritic cells (DCs) were employed to determine the synergistic production of pro-inflammatory cytokines upon combination of rlipo-E7m and other TLR agonists. Antigen-specific CTL responses were investigated using immunospots or in vivo cytolytic assays after immunization in mice. Mice bearing various tumor sizes were used to evaluate the anti-tumor effects of the formulation. Specific subpopulations of immunosuppressive cells in the tumor infiltrate were quantitatively determined by flow cytometry. RESULTS: We demonstrate that a TLR9 agonist (unmethylated CpG oligodeoxynucleotide, CpG ODN) enhances CTL responses and eradicates large tumors when combined with rlipo-E7m. Moreover, combined treatment with rlipo-E7m and CpG ODN effectively increases tumor infiltration by CTLs and reduces the numbers of myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages (TAMs) and regulatory T cells (Tregs) in the tumor microenvironment. CONCLUSION: These findings suggest that the dramatic anti-tumor effects of the recombinant lipoprotein together with CpG ODN may reflect the amplification of CTL responses and the repression of the immunosuppressive environment. This promising approach could be applied for the development of additional therapeutic cancer vaccines.