Cytotoxic T lymphocytes responding to low dose TRP2 antigen are induced against B16 melanoma by liposome-encapsulated TRP2 peptide and CpG DNA adjuvant

Recent advances in lipid-based long-acting injectable depot formulations

Long-acting injectable (LAIs) delivery systems sustain the drug therapeutic action in the body, resulting in reduced dosage regimen, toxicity, and improved patient compliance. Lipid-based depots are biocompatible, provide extended drug release, and improve drug stability, making them suitable for systemic and localized treatment of various chronic ailments, including psychosis, diabetes, hormonal disorders, arthritis, ocular diseases, and cancer. These depots include oil solutions, suspensions, oleogels, liquid crystalline systems, liposomes, solid lipid nanoparticles, nanostructured lipid carriers, phospholipid phase separation gel, vesicular phospholipid gel etc. This review summarizes recent advancements in lipid-based LAIs for delivering small and macromolecules, and their potential in managing chronic diseases. It also provides an overview of the lipid depots available in market or clinical phase, as well as patents for lipid-based LAIs. Furthermore, this review critically discusses the current scenario of using in vitro release methods to establish IVIVC and highlights the challenges involved in developing lipid-based LAIs.

Synthesis and Evaluation of a Self-Adjuvanting Pseudomonal Vaccine Based on Major Outer Membrane Porin OprF Epitopes Formulated with Low-Toxicity QS-21-Containing Liposomes

Pseudomonas aeruginosa (PA) is a Gram-negative pathogen that the World Health Organization has ranked as a priority 1 (critical) threat. One potential prophylactic approach to preventing or reducing the incidence of PA would be development of a long sought-after vaccine. Both antibody and CD4+ T-cell responses have been noted as playing key roles in protection against infection. In these studies, we have designed a prototype vaccine consisting of several known linear B-cell epitopes derived from an outer membrane porin F (OprF). The resulting thiol-containing protein was conjugated to a version of the lipopeptide-based Toll-like receptor agonist Pam3CysSK4Mal (10) containing a maleimide moiety and formulated into dipalmitoylphosphatidylcholine (DPPC)/cholesterol (Chol) liposomes. Mice immunized with the resulting vaccine generated antibodies that bound PA14 (serotype O10) in vitro and induced opsonization in the presence of rabbit complement and murine macrophage RAW264.7 cells. The liposome was optimized to contain 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dimyristoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DMPG), Chol, Pam3CysSK4-OprF (12) and the Quillaja saponaria-derived saponin adjuvant QS-21. The resulting vaccine formulation produced significantly higher antibody titers, increased the IgG2a antibody isotype, and increased the number of IgG-producing B-cells as well as splenic primed T-cells. In summary, the liposomal vaccine platform was found highly useful for the generation of a robust and balanced TH1/TH2 response.

Complexing CpG adjuvants with cationic liposomes enhances vaccine-induced formation of liver TRM cells

Tissue resident memory T cells (T_RM cells) can provide effective tissue surveillance and can respond rapidly to infection. Vaccination strategies aimed at generating T_RM cells have shown promise against a range of pathogens. We have previously shown that the choice of adjuvant critically influences CD8⁺ T_RM cell formation in the liver. However, the range of adjuvants tested was limited. Here, we assessed the ability of a broad range of adjuvants stimulating membrane (TLR4), endosomal (TLR3, TLR7 and TLR9) and cytosolic (cGAS, RIG-I) pathogen recognition receptors for their capacity to induce CD8⁺ T_RM formation in a subunit vaccination model. We show that CpG oligodeoxynucleotides (ODN) remain the most efficient inducers of liver T_RM cells among all adjuvants tested. Moreover, their combination with the cationic liposome DOTAP further enhances the potency, particularly of the class B ODN CpG 1668 and the human TLR9 ligand CpG 2006 (CpG 7909). This study informs the design of efficient liver T_RM-based vaccines for their potential translation.

Hybrid red blood cell membrane coated porous silicon nanoparticles functionalized with cancer antigen induce depletion of T cells

Erythrocyte-based drug delivery systems have been investigated for their biocompatibility, long circulation time, and capability to transport cargo all around the body, thus presenting enormous potential in medical applications. In this study, we investigated hybrid nanoparticles consisting of nano-sized autologous or allogeneic red blood cell (RBC) membranes encapsulating porous silicon nanoparticles (PSi NPs). These NPs were functionalized with a model cancer antigen TRP2, which was either expressed on the surface of the RBCs by a cell membrane-mimicking block copolymer polydimethylsiloxane-b-poly-2-methyl-2-oxazoline, or attached on the PSi NPs, thus hidden within the encapsulation. When in the presence of peripheral blood immune cells, these NPs resulted in apoptotic cell death of T cells, where the NPs having TRP2 within the encapsulation led to a stronger T cell deletion. The deletion of the T cells did not change the relative proportion of CD4⁺ and cytotoxic CD8⁺ T cells. Overall, this work shows the combination of nano-sized RBCs, PSi, and antigenic peptides may have use in the treatment of autoimmune diseases.

We report a study on the effect of red blood cell membrane based cancer antigen-functionalized nanoparticles on peripheral blood T cells. These nanoparticles induce apoptosis of T cells and they may have use in treating autoimmune diseases.

Development of a Bioconjugate Platform for Modifying the Immune Response of Autoreactive Cytotoxic T Lymphocytes Involved in Type 1 Diabetes

Type 1 diabetes (T1D) is an autoimmune disorder characterized by autoimmune cell mediated destruction of pancreatic beta cells. Pancreatic beta cells are the only source of insulin in the body. T1D patients then have to depend on insulin injections for their lifetime. Insulin injection can modulate the blood sugar levels, but insulin has little effect on the autoimmune process. Altered peptide ligands (APL) derived from known autoantigens in T1D are able to induce tolerance in autoreactive cells in T1D animal models, but are currently unable to elicit this protection in humans. There is a need to improve immunogenicity of the APLs, as these short peptides can be easily degraded by enzymes in the blood. GAD546-554 is a dominant epitope recognized by autoreactive T cells in the nonobese diabetic (NOD) mouse model that can cause destruction of beta cells. Alanine substitution at the eighth position of GAD546-554 peptide (APL9) induced tolerance in a GAD546-554 specific cytotoxic T lymphocyte clone. To improve the antigen presentation and endosomal escape of APL9, we developed a bioconjugate platform that consists of a liposome containing a bioconjugate of APL9 and toll-like receptor 2 ligand Pam₃CysSK₄ as well as an antibody against macrophage protein F4/80. APL9 bioconjugate liposome with F4/80 antibody was able to induce tolerance in a GAD 546-554 specific clone. Diabetic NOD splenocytes pretreated with APL9 bioconjugate were also not able to transfer diabetes into prediabetic NOD recipient mice. This work is beneficial to prevent T1D as an immunotherapy strategy to render autoreactive immune cells more tolerant of beta cells.

Efficient Delivery of Tyrosinase Related Protein-2 (TRP2) Peptides to Lymph Nodes using Serum-Derived Exosomes

Exosomes (EXO) are considered to be versatile carriers for biomolecules; however, the delivery of therapeutic peptides using EXOs poses several challenges. In this study, the efficiency of serum-derived EXOs in delivering tyrosinase-related protein-2 (TRP2) peptides to lymph nodes is determined. TRP2 peptides are successfully incorporated into EXOs, which show a uniform and narrow size distribution of around 45 nm. The TRP2-incorporated exosomes (EXO-TRP2) are efficiently internalized into macrophages and dendritic cells, and are seen to display a punctate distribution. EXOs loaded with TRP2 together with MPLA, (EXO-MPLA-TRP2) result in a strong release of proinflammatory cytokines (TNF-α and IL-6) from both RAW264.7 and DC2.4 cells. Finally, subcutaneous injection of fluorescently labeled EXO-TRP2 followed by ex vivo imaging using in vivo imaging system (IVIS) show a strong fluorescent signal in the lymph nodes after only 1 h, which is maintained until at least 4 h after injection. Taken together, the findings suggest that serum-derived EXOs can serve as promising carriers to deliver therapeutic peptides to lymph nodes for immunotherapy.

Optimized Gemcitabine Therapy in Combination with E7 Peptide Immunization Elicits Tumor Cure by Preventing Ag-Specific CTL Inhibition in Animals with Large Established Tumors

The role of chemotherapeutic agents in tumor immunotherapy is still controversial. In this study, we test using a TC-1 tumor model whether gemcitabine plus E7 peptide vaccine regimens (E7 peptides+CpG-ODN+anti-4-1BB Abs) may result in tumor cure in mice with large established tumors, with a focus on their effects on Ag-specific cytotoxic T lymphocyte (CTL) and myeloid-derived suppressor cell levels. Gemcitabine inhibited tumor growth by its direct cytotoxicity to tumor cells in vivo. E7 peptide vaccine regimens enhanced Ag-specific CTL lytic and antitumor therapeutic activity. Initial combination therapy using gemcitabine and E7 peptide vaccine regimens resulted in tumor regression with tumor relapse in animals with large established tumors, which appeared to result from the suppression of Ag-specific CTL activity by gemcitabine treatment. However, optimization of gemcitabine therapy by reducing its dose and frequency led to complete tumor regression without any recurring tumors in all tested mice even after discontinuation of therapy, possibly due to Ag-specific CTL responses. Thus, this study shows that the optimal dose and therapy frequency of gemcitabine are critical for achieving tumor cure in tumor-bearing animals undergoing E7 peptide vaccine regimen therapy, mainly by preventing CTL suppression. These findings may have implications for designing peptide-based therapeutic vaccines in cancer patients undergoing chemotherapy.

CpG-based immunotherapy impairs antitumor activity of BRAF inhibitors in a B-cell-dependent manner

Combining immunotherapy with targeted therapy has increasingly become an appealing therapeutic paradigm for cancer treatment due to its great potential for generating durable and synergistic antitumor response. In this study, however, we unexpectedly found that two types of CpG-based tumor peptide vaccine treatments consistently negated the antitumor activity of a selective BRAF inhibitor in tumors with BRAF mutation rather than showing a synergistic antitumor effect. Our further studies demonstrated that CpG alone was sufficient to dampen BRAF inhibitor-induced antitumor responses, suggesting that the impaired antitumor activity of the BRAF inhibitor observed in mice receiving CpG-based peptide vaccine is mainly dependent upon the use of CpG. Mechanistically, CpG increased the number of circulating B cells, which produced elevated amounts of tumor necrosis factor-α (TNFα) that contributed to the increased tumor resistance to BRAF inhibitors. More importantly, B-cell depletion or TNFα neutralization can restore the antitumor effect of BRAF inhibition in mice receiving CpG treatment, indicating that TNFα-secreting B cells play an indispensable role in BRAF inhibitor resistance induced by CpG. Taken together, our results strongly suggest that precautions must be implemented when designing combinatorial approaches for cancer treatment, because distinct regimens, despite their respective therapeutic benefit as monotherapy, may together provide antagonistic clinical outcomes.

Targeted Programming of the Lymph Node Environment Causes Evolution of Local and Systemic Immunity

Biomaterial vaccines offer cargo protection, targeting, and co-delivery of signals to immune organs such as lymph nodes (LNs), tissues that coordinate adaptive immunity. Understanding how individual vaccine components impact immune response has been difficult owing to the systemic nature of delivery. Direct intra-lymph node (i.LN.) injection offers a unique opportunity to dissect how the doses, kinetics, and combinations of signals reaching LNs influence the LN environment. Here, i.LN. injection was used as a tool to study the local and systemic responses to vaccines comprised of soluble antigen and degradable polymer particles encapsulating toll-like receptor agonists as adjuvants. Microparticle vaccines increased antigen presenting cells and lymphocytes in LNs, enhancing activation of these cells. Enumeration of antigen-specific CD8⁺ T cells in blood revealed expansion over 7 days, followed by a contraction period over 1 month as memory developed. Extending this strategy to conserved mouse and human tumor antigens resulted in tumor antigen-specific primary and recall responses by CD8⁺ T cells. During challenge with an aggressive metastatic melanoma model, i.LN. delivery of depots slowed tumor growth more than a potent human vaccine adjuvant, demonstrating local treatment of a target immunological site can promote responses that are potent, systemic, and antigen-specific.

Synthesis of a Liposomal MUC1 Glycopeptide-Based Immunotherapeutic and Evaluation of the Effect of l-Rhamnose Targeting on Cellular Immune Responses

Generation of a CD8(+) response to extracellular antigen requires processing of the antigen by antigen presenting cells (APC) and cross-presentation to CD8(+) T cell receptors via MHC class I molecules. Cross-presentation is facilitated by efficient antigen uptake followed by immune-complex-mediated maturation of the APCs. We hypothesize that improved antigen uptake of a glycopeptide sequence containing a CD8(+) T cell epitope could be achieved by delivering it on a liposome surface decorated with an immune complex-targeting ligand, an l-Rhamnose (Rha) epitope. We synthesized a 20-amino-acid glycopeptide TSAPDT(GalNAc)RPAPGSTAPPAHGV from the variable number tandem repeat region of the tumor marker MUC1 containing an N-terminal azido moiety and a tumor-associated α-N-acetyl galactosamine (GalNAc) at the immunogenic DTR motif. The MUC1 antigen was attached to Pam3Cys, a Toll-like receptor-2 ligand via copper(I)-catalyzed azido-alkyne cycloaddition (CuAAc) chemistry. The Rha-decorated liposomal Pam3Cys-MUC1-Tn 4 vaccine was evaluated in groups of C57BL/6 mice. Some groups were previously immunized to generate anti-Rha antibodies. Anti-Rha antibody expressing mice that received the Rha liposomal vaccine showed higher cellular immunogenicity compared to the control group while maintaining a strong humoral response.

Combinatorial prospects of nano-targeted chemoimmunotherapy

Despite the significant increase in our knowledge on cancer initiation and progression, and the development of novel cancer treatments, overall patient survival rates have thus far only marginally improved. However, it can be expected that lasting tumor control will be attainable for an increasing number of cancer patients in the foreseeable future, which is likely to be achieved by combining cancer chemotherapy with anticancer immunotherapy. A plethora of new cancer chemotherapy reagents are expected to become accessible to the clinic in the coming years which can then be used for efficient tumor debulking and aid in antigen exposure to the immune system. Durable remission and the eradication of micrometastases are likely to be achieved with specialized monoclonal antibodies and therapeutic cancer vaccines that modulate the immune system to overcome immunosuppression and kill distant cancer cells. Moreover, the method of drug delivery to tumors, stromal and immune cells is expected to shift largely from conventional 'free' drug molecules to encapsulated in targeted nano-vehicles, therapeutics often referred to or considered part of "nanomedicine". Several biocompatible nano-vehicles, such as metal-nanoparticles, biodegradable-nanoparticles, liposomes or dendrimers are potential candidates for targeted drug delivery but may also serve additional purposes. A dexterous combination of nanomedicine, cancer immunotherapy and chemotherapeutic engineering are likely to become the basis for new hope in the form of targeted cancer therapies that could attack tumors early in their development. One can envision nano-vehicles that would selectively deliver effective doses of chemotherapeutic agents to cancer cells while leaving healthy cells untouched. Furthermore, given that after chemotherapeutic treatment there often remains a limited number of chemo-resistant tumor cells, which go on to drive tumor progression, nano-vehicles could also be engineered to provoke an appropriate immune response to destroy these cells. Here, we discuss the potential of the combinatorial role of cancer chemotherapy, cancer immunotherapy and the prospective of nanotechnology for the targeted delivery of chemoimmunotherapeutic agents.

MPLA incorporation into DC-targeting glycoliposomes favours anti-tumour T cell responses

Dendritic cells (DC) are attractive targets for cancer immunotherapy as they initiate strong and long-lived tumour-specific T cell responses. DC can be effectively targeted in vivo with tumour antigens by using nanocarriers such as liposomes. Cross-presentation of tumour antigens is enhanced with strong adjuvants such as TLR ligands. However, often these adjuvants have off-target effects, and would benefit from a DC-specific targeting strategy, similar to the tumour antigen. The goal of this study was to develop a strategy for specifically targeting DC with tumour antigen and adjuvant by using glycoliposomes. We have generated liposomes containing the glycan Lewis(Le)(X) which is highly specific for the C-type lectin receptor DC-SIGN expressed by DC. Le(X)-modified liposomes were taken up by human monocyte-derived DC in a DC-SIGN-specific manner. As adjuvants we incorporated the TLR ligands Pam3CySK4, Poly I:C, MPLA and R848 into liposomes and compared their adjuvant capacity on DC. Incorporation of the TLR4 ligand MPLA into glycoliposomes induced DC maturation and production of pro-inflammatory cytokines, in a DC-SIGN-specific manner, and DC activation was comparable to administration of soluble MPLA. Incorporation of MPLA into glycoliposomes significantly enhanced antigen cross-presentation of the melanoma tumour antigen gp100280-288 peptide to CD8(+) T cells compared to non-glycosylated MPLA liposomes. Importantly, antigen cross-presentation of the gp100280-288 peptide was significantly higher using MPLA glycoliposomes compared to the co-administration of soluble MPLA with glycoliposomes. Taken together, our data demonstrates that specific targeting of a gp100 tumour antigen and the adjuvant MPLA to DC-SIGN-expressing DC enhances the uptake of peptide-containing liposomes, the activation of DC, and induces tumour antigen-specific CD8(+) T cell responses. These data demonstrate that adjuvant-containing glycoliposome-based vaccines targeting DC-SIGN(+) DC represent a powerful new approach for CD8(+) T cell activation.

Nanoparticle-delivered transforming growth factor-β siRNA enhances vaccination against advanced melanoma by modifying tumor microenvironment

Achievement of potent immunoresponses against self/tumor antigens and effective therapeutic outcome against advanced tumors remain major challenges in cancer immunotherapy. The specificity and efficiency of two nanoparticle-based delivery systems, lipid-calcium-phosphate (LCP) nanoparticle (NP) and liposome-protamine-hyaluronic acid (LPH) NP, provide us an opportunity to address both challenges. A mannose-modified LCP NP delivered both tumor antigen (Trp 2 peptide) and adjuvant (CpG oligonucleotide) to the dendritic cells and elicited a potent, systemic immune response regardless of the existence or the stage of tumors in the host. This vaccine was less effective, however, against later stage B16F10 melanoma in a subcutaneous syngeneic model. Mechanistic follow-up studies suggest that elevated levels of immune-suppressive cytokines within the tumor microenvironment, such as TGF-β, might be responsible. We strategically augment the efficacy of LCP vaccine on an advanced tumor by silencing TGF-β in tumor cells. The delivery of siRNA using LPH NP resulted in about 50% knockdown of TGF-β in the late stage tumor microenvironment. TGF-β down-regulation boosted the vaccine efficacy and inhibited tumor growth by 52% compared with vaccine treatment alone, as a result of increased levels of tumor infiltrating CD8+ T cells and decreased level of regulatory T cells. Combination of systemic induction of antigen-specific immune response with LCP vaccine and targeted modification of tumor microenvironment with LPH NP offers a flexible and powerful platform for both mechanism study and immunotherapeutic strategy development.

Enhancing efficacy of anticancer vaccines by targeted delivery to tumor-draining lymph nodes

The sentinel or tumor-draining lymph node (tdLN) serves as a metastatic niche for many solid tumors and is altered via tumor-derived factors that support tumor progression and metastasis. tdLNs are often removed surgically, and therapeutic vaccines against tumor antigens are typically administered systemically or in non-tumor-associated sites. Although the tdLN is immune-suppressed, it is also antigen experienced through drainage of tumor-associated antigens (TAA), so we asked whether therapeutic vaccines targeting the tdLN would be more or less effective than those targeting the non-tdLN. Using LN-targeting nanoparticle (NP)-conjugate vaccines consisting of TAA-NP and CpG-NP, we compared delivery to the tdLN versus non-tdLN in two different cancer models, E.G7-OVA lymphoma (expressing the nonendogenous TAA ovalbumin) and B16-F10 melanoma. Surprisingly, despite the immune-suppressed state of the tdLN, tdLN-targeting vaccination induced substantially stronger cytotoxic CD8+ T-cell responses, both locally and systemically, than non-tdLN-targeting vaccination, leading to enhanced tumor regression and host survival. This improved tumor regression correlated with a shift in the tumor-infiltrating leukocyte repertoire toward a less suppressive and more immunogenic balance. Nanoparticle coupling of adjuvant and antigen was required for effective tdLN targeting, as nanoparticle coupling dramatically increased the delivery of antigen and adjuvant to LN-resident antigen-presenting cells, thereby increasing therapeutic efficacy. This work highlights the tdLN as a target for cancer immunotherapy and shows how its antigen-experienced but immune-suppressed state can be reprogrammed with a targeted vaccine yielding antitumor immunity.

VLPs and particle strategies for cancer vaccines

Effective delivery of tumor antigens to APCs is one of the key steps for eliciting a strong and durable immune response to tumors. Several cancer vaccines have been evaluated in clinical trials, based on soluble peptides, but results have not been fully satisfactory. To improve immunogenicity particles provide a valid strategy to display and/or incorporate epitopes which can be efficiently targeted to APCs for effective induction of adaptive immunity. In the present review, we report some leading technologies for developing particulate vaccines employed in cancer immunotherapy, highlighting the key parameters for a rational design to elicit both humoral and cellular responses.

Multifunctional nanoparticles co-delivering Trp2 peptide and CpG adjuvant induce potent cytotoxic T-lymphocyte response against melanoma and its lung metastasis

Immunotherapy has shown the potential to become an essential component of the successful treatment of various malignancies. In many cases, such as in melanoma, however, induction of a potent and specific T-cell response against the endogenous antigen or self-antigen still remains a major challenge. To induce a potent MHC I-restricted cytotoxic T-lymphocyte (CTL) response, cytosol delivery of an exogenous antigen into dendritic cells is preferred, if not required. Lipid-calcium-phosphate (LCP) nanoparticles represent a new class of intracellular delivery systems for impermeable drugs. We are interested in exploring the potential of LCP NPs for use as a peptide vaccine delivery system for cancer therapy. To increase the encapsulation of Trp2 peptide into the calcium phosphate precipitate core of LCP, two phosphor-serine residues were added to the N-terminal of the peptide (p-Trp2). CpG ODN was also co-encapsulated with p-Trp2 as an adjuvant. The NPs were further modified with mannose to enhance and prolong the cargo deposit into the lymph nodes (LNs), which ensured persistent antigen loading and stimulation. Compared with free Trp2 peptide/CpG, vaccination with LCP encapsulating p-Trp2 and CpG resulted in superior inhibition of tumor growth in both B16F10 subcutaneous and lung metastasis models. An IFN-γ production assay and in vivo CTL response study revealed that the improved efficacy was a result of a Trp2-specific immune response. Thus, encapsulation of phospho-peptide antigens into LCP may be a promising strategy for enhancing the immunogenicity of poorly immunogenic self-antigens for cancer therapy.

Dendritic cell-based nanovaccines for cancer immunotherapy

Cancer immunotherapy critically relies on the efficient presentation of tumor antigens to T-cells to elicit a potent anti-tumor immune response aimed at life-long protection against cancer recurrence. Recent advances in the nanovaccine field have now resulted in formulations that trigger strong anti-tumor responses. Nanovaccines are assemblies that are able to present tumor antigens and appropriate immune-stimulatory signals either directly to T-cells or indirectly via antigen-presenting dendritic cells. This review focuses on important aspects of nanovaccine design for dendritic cells, including the synergistic and cytosolic delivery of immunogenic compounds, as well as their passive and active targeting to dendritic cells. In addition, nanoparticles for direct T-cell activation are discussed, addressing features necessary to effectively mimic dendritic cell/T-cell interactions.

Synthesis and immunological evaluation of a MUC1 glycopeptide incorporated into l-rhamnose displaying liposomes

MUC1 variable number tandem repeats (VNTRs) conjugated to tumor-associated carbohydrate antigens (TACAs) have been shown to break self-tolerance in humanized MUC1 transgenic mice. Therefore, we hypothesize that a MUC1 VNTR TACA-conjugate can be successfully formulated into a liposome-based anticancer vaccine. The immunogenicity of the vaccine should be further augmented by incorporating surface-displayed l-rhamnose (Rha) epitopes onto the liposomes to take advantage of a natural antibody-dependent antigen uptake mechanism. To validate our hypothesis, we synthesized a 20-amino-acid MUC1 glycopeptide containing a GalNAc-O-Thr (Tn) TACA by SPPS and conjugated it to a functionalized Toll-like receptor ligand (TLRL). An l-Rha-cholesterol conjugate was prepared using tetra(ethylene glycol) (TEG) as a linker. The liposome-based anticancer vaccine was formulated by the extrusion method using TLRL-MUC1-Tn conjugate, Rha-TEG-cholesterol, and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) in a total lipid concentration of 30 mM. The stability, homogeneity, and size characterization of the liposomes was evaluated by SEM and DLS measurements. The formulated liposomes demonstrated positive binding with both anti-Rha and mouse anti-human MUC1 antibodies. Groups of female BALB/c mice were immunized and boosted with a rhamnose-Ficoll (Rha-Ficoll) conjugate formulated with alum as adjuvant to generate the appropriate concentration of anti-Rha antibodies in the mice. Anti-Rha antibody titers were >25-fold higher in the groups of mice immunized with the Rha-Ficoll conjugate than the nonimmunized control groups. The mice were then immunized with the TLRL-MUC1-Tn liposomal vaccine formulated either with or without the surface displaying Rha epitopes. Sera collected from the groups of mice initially immunized with Rha-Ficoll and later vaccinated with the Rha-displaying TLRL-MUC1-Tn liposomes showed a >8-fold increase in both anti-MUC1-Tn and anti-Tn antibody titers in comparison to the groups of mice that did not receive Rha-Ficoll. T-cells from BALB/c mice primed with a MUC1-Tn peptide demonstrated increased proliferation to the Rha-liposomal vaccine in the presence of antibodies isolated from Rha-Ficoll immunized mice compared to nonimmune mice, supporting the proposed effect on antigen presentation. The anti-MUC1-Tn antibodies in the vaccinated mice serum recognized MUC1 on human leukemia U266 cells. Because this vaccine uses separate rhamnose and antigenic epitope components, the vaccine can easily be targeted to different antigens or epitopes by changing the peptide without having to change the other components.

Combined stimulation of TLR9 and 4.1BB augments Trp2 peptide vaccine-mediated melanoma rejection by increasing Ag-specific CTL activity and infiltration into tumor sites

Peptide vaccines are a clinically applicable therapy shown to be effective in tumor control. In this study, Trp2 peptides plus CpG-oligodeoxynucleotide treatment was found to induce Ag-specific IFN-γ and CD8+CTL responses, and antitumor activity against large established melanoma (tumor size, 7mm). A combination of anti-4.1BB antibodies with Trp2 peptides+CpG-oligodeoxynucleotide increased the antitumor cure rate from 0% to 75%. This effect was concomitant with greater induction of Ag-specific CD8+CTLs and their infiltration into the tumor sites, highlighting the importance of combined stimulation of TLR9 and 4.1BB for achieving tumor eradication. These findings may have implications for designing peptide-based therapeutic vaccines for cancer-patients.

Trp2 peptide vaccine adjuvanted with (R)-DOTAP inhibits tumor growth in an advanced melanoma model

Previously we have shown cationic lipid (R)-DOTAP as the immunologically active enantiomer of the DOTAP racemic mixture, initiating complete tumor regression in an exogenous antigen model (murine cervical cancer model). Here, we investigate the use of (R)-DOTAP as an efficacious adjuvant delivering an endogenous antigen in an aggressive murine solid tumor melanoma model. (R)-DOTAP/Trp2 peptide complexes showed decreasing size and charge with increasing peptide concentration, taking a rod shape at highest concentrations. The particles were stable for 2 weeks at 4 °C. A dose of 75 nmol of Trp2 (formulated in (R)-DOTAP) was able to show statistically significant tumor growth delay compared to lower doses of 5 and 25 nmol, which were no different than untreated tumors. (R)-DOTAP/Trp2 (75 nmol) treated mice also showed increased T cell IFN-γ secretion after restimulation with Trp2, as well as CTL activity in vivo. This vaccination group also showed the highest population of functionally active tumor-infiltrating lymphocytes, indicated by IFN-γ secretion after restimulation with Trp2. Thus, (R)-DOTAP has shown the ability to break tolerance as an adjuvant. Its activity to enhance immunogenicity of other tumor associated antigens should be studied further.

Quantitative determination of the composition of multi-shell calcium phosphate-oligonucleotide nanoparticles and their application for the activation of dendritic cells

Biodegradable calcium phosphate nanoparticles as carriers for the immunoactive toll-like receptor ligands CpG and polyinosinic-polycytidylic acid for the activation of dendritic cells (DC) combined with the viral antigen hemagglutinin (HA) were prepared. A purification method based on ultracentrifugation and ultrasonication was developed to separate the nanoparticles from dissolved biomolecules. The number of biomolecules, i.e., oligonucleotides and peptide, incorporated into the nanoparticles was quantitatively determined by UV-spectroscopy, using fluorescent derivatives of the biomolecules. The immunostimulatory effects of purified calcium phosphate nanoparticles on DC were studied, i.e., cytokine production and activation of the cells in terms of the upregulation of surface molecules. Purified calcium phosphate nanoparticles, i.e., without dissolved biomolecules, are capable of inducing adaptive immunity by activation of DC. Immunostimulatory effects of purified calcium phosphate nanoparticles on DC were demonstrated by increased expression of co-stimulatory molecules and MHC II and by cytokine secretion. In addition, DC treated with purified functionalized calcium phosphate nanoparticles induced an antigen-specific T-cell response in vitro.

Peptide-conjugated PAMAM dendrimer as a universal DNA vaccine platform to target antigen-presenting cells

DNA-based vaccines hold promise to outperform conventional antigen-based vaccines by virtue of many unique features. However, DNA vaccines have thus far fallen short of expectations, due in part to poor targeting of professional antigen-presenting cells (APC) and low immunogenicity. In this study, we describe a new platform for effective and selective delivery of DNA to APCs in vivo that offers intrinsic immune-enhancing characteristics. This platform is based on conjugation of fifth generation polyamidoamine (G5-PAMAM) dendrimers, a DNA-loading surface, with MHC class II-targeting peptides that can selectively deliver these dendrimers to APCs under conditions that enhance their immune stimulatory potency. DNA conjugated with this platform efficiently transfected murine and human APCs in vitro. Subcutaneous administration of DNA-peptide-dendrimer complexes in vivo preferentially transfected dendritic cells (DC) in the draining lymph nodes, promoted generation of high affinity T cells, and elicited rejection of established tumors. Taken together, our findings show how PAMAM dendrimer complexes can be used for high transfection efficiency and effective targeting of APCs in vivo, conferring properties essential to generate effective DNA vaccines.

Harnessing dendritic cells for immunotherapy

Dendritic cells (DC) are the antigen presenting cells that initiate and direct adaptive immune responses, capable of inducing protective adaptive immune responses and tolerance. They sample their surroundings, internalizing, processing and presenting antigens to T cells. They distinguish between self and foreign antigens with a wide array of microbial sensors, and induce immunity when antigen is captured in the presence of microbial products or inflammatory stimuli, but tolerance in the absence of these signals. However, not all DCs are identical. There are distinct DC subsets spread throughout the body, and although they share common features, they also have specialized functions. As a consequence, the outcome of the immune response is determined by the context in which the antigen is acquired, and also by the DC subset(s) involved. Here we discuss the features of the DC subsets, their handling of antigens for MHCI- and MHCII-restricted presentation, how their functions are regulated by foreign and endogenous signals, the consequences on the type of immune response induced, and how they provide insights on the design of immunotherapy.

In vivo studies on the effect of co-encapsulation of CpG DNA and antigen in acid-degradable microparticle vaccines

Protein-based vaccines have been explored as a safer alternative to traditional weakened or killed whole organism based vaccination strategies and have been investigated for their ability to activate the immune system against certain cancers. For optimal stimulation of T lymphocytes, protein-based vaccines should deliver protein antigens to antigen presenting cells in the context of appropriate immunostimulatory signals, thus mimicking actual pathogens. In this report, we describe the synthesis, characterization, and biological evaluation of immunostimulatory acid-degradable microparticles, which are suitable delivery vehicles for use in protein-based vaccines and cancer immunotherapy. Using a 3' conjugation strategy, we optimized the attachment of immunostimulatory CpG DNA to our vaccine carriers and demonstrated that under acidic conditions similar to those found in endosomal compartments, these new particles were capable of simultaneously releasing a model protein antigen and a CpG DNA adjuvant. We found in an in vivo cytotoxicity assay that the co-encapsulation of ovalbumin, a model antigen, and immunostimulatory agent in the same particle led to superior cytotoxic T lymphocyte activity compared to particles coadministered with adjuvant in an unbound form. In addition, we investigated the ability of these acid-degradable particles to induce protective immunity in the MO5 murine melanoma model and found that they were effective until tumor escape, which appeared to result from a loss of antigen expression by the cancer cells due to in vivo selection pressure.

Lipid-based delivery of CpG oligonucleotides enhances immunotherapeutic efficacy

There has been significant interest in the potential of cytosine-guanine (CpG) containing oligodeoxynucleotides (ODN) as an immunotherapy for malignant, infectious and allergic diseases. While human trials have yielded promising results, clinical use of free CpG ODN still faces several challenges which limit their effectiveness. These include suboptimal in vivo stability, toxicity, unfavorable pharmacokinetic/biodistribution characteristics, lack of specificity for target cells and the requirement for intracellular uptake. To overcome these challenges, optimized lipid-based delivery systems have been developed to protect the CpG ODN payload, modify their circulation/distribution so as to enhance immune cell targeting and facilitate intracellular uptake. Ultimately, lipid-mediated delivery has the capacity to increase the immunopotency of CpG ODN and enhance their prophylactic or therapeutic efficacy in a range of diseases. Lipid-encapsulation provides a feasible strategy to optimize the immunostimulatory activity and immunotherapeutic efficacy of CpG ODN, thereby allowing their full clinical potential to be realized.

CpG oligonucleotide as an adjuvant for the treatment of prostate cancer

The use of an adenovirus transduced to express a prostate cancer antigen (PSA) as a vaccine for the treatment of prostate cancer has been shown to be active in the destruction of antigen-expressing prostate tumor cells in a pre-clinical model, using Balb/C or PSA transgenic mice. The destruction of PSA-secreting mouse prostate tumors was observed in Ad/PSA immunized mice in a prophylaxis study with 70% of the mice surviving long term tumor free. This successful immunotherapy was not observed in therapeutic studies in which tumors were established before vaccination and the development of anti-PSA immune response was not as easily generated in PSA transgenic mice. Immunization of conventional and transgenic animals was enhanced by incorporating a collagen matrix into the immunizing injection. Therefore the need to strengthen anti-PSA and anti-prostate cancer immunity was an obvious next step in developing a successful prostate cancer immunotherapy. Because the use of immunostimulatory CpG motifs was shown to enhance immune responses to a wide variety of antigens, our studies incorporated CpG into the Ad/PSA vaccine experimental plans. The results of the subsequent studies demonstrated a dichotomy where Ad/PSA plus CpG enhanced the in vivo destruction of PSA-secreting tumors and the survival of experimental animals, but revealed that the number and in vitro activities of antigen specific CD8+ T cells was decreased as compared to the values observed when the vaccine alone was used for immunization. The dichotomous observations were confirmed using another antigen system, OVA also incorporated into a replication defective adenovirus. Despite the reduction in antigen-specific CD8+ cells after vaccine plus CpG immunization the enhanced destruction of sc and systemic tumors was shown to be mediated entirely by CD8+ T cells. Finally, the reduction of the CD8+ T cells was the result of an observed decrease in the proliferation of the antigen specific cell population.

Delivery strategies of melanoma vaccines: an overview

For many years, various cancer vaccines have been widely evaluated, however clinical responses remain rare. In this review, we attempt to address the question of which delivery strategies and platforms are feasible to produce clinical response and define the characteristics of the strategy that will induce long-lasting antitumor response. We limit our analysis and discussion to microparticles/nanoparticles, liposomes, heat-shock proteins, viral vectors and different types of adjuvants. This review aims to provide an overview of the specific characteristics, strengths and limitations of these delivery systems, focusing on their impacts on the development of melanoma vaccine. To date, only adoptive T-cell transfer has shown promising clinical outcomes compared to other treatments.

Immunostimulatory DNA as a vaccine adjuvant

Immunostimulatory DNA containing unmethylated CpG motifs is recognized by Toll-like receptor 9, resulting in the activation of innate immune responses that subsequently amplify the adaptive-immune response. Advances in the characterization of Toll-like receptor 9 signaling have identified immunostimulatory sequences (ISS) with distinct biological activities. Numerous animal models have demonstrated that synthetic ISS are effective adjuvants that enhance both humoral and cellular immune responses in diverse indications, ranging from infectious disease to cancer and allergy. An added benefit supporting the use of ISS as a vaccine adjuvant is that the specific activation of a pathway critical to the regulation of the immune response results in minimal toxicity. To date, clinical testing has largely affirmed the potency and safety of ISS-adjuvanted vaccines.

Functional Up-regulation of Human Leukocyte Antigen Class I Antigens Expression by 5-aza-2′-deoxycytidine in Cutaneous Melanoma: Immunotherapeutic Implications

PURPOSE

To investigate the potential of the DNA hypomethylating agent 5-aza-2'-deoxycytidine (5-aza-CdR) to improve the effectiveness of immunotherapeutic approaches against melanocyte differentiation antigens.

EXPERIMENTAL DESIGN

The effect of 5-aza-CdR on the constitutive expression of gp100 was investigated in 11 human melanoma cell lines by real-time reverse transcription-PCR and indirect immunofluorescence (IIF) analyses. 5-aza-CdR-mediated changes in the levels of expression of human leukocyte antigen (HLA) class I antigens and HLA-A2 allospecificity, intercellular adhesion molecule-1 (ICAM-1), and leukocyte-function-associated antigen-3 were investigated by IIF analysis on melanoma cells under study. The recognition of gp100-positive Mel 275 melanoma cells, treated or not with 5-aza-CdR, by HLA-A2-restricted gp100((209-217))-specific CTL was investigated by (51)Cr-release assays, IFN-gamma release and IFN-gamma ELISPOT assays.

RESULTS

The constitutive expression of gp100 was not affected by 5-aza-CdR on all melanoma cells investigated. Compared with untreated cells, the exposure of Mel 275 melanoma cells to 5-aza-CdR significantly (P < 0.05) up-regulated their expression of HLA class I antigens and of ICAM-1. These phenotypic changes significantly (P < 0.05) increased the lysis of 5-aza-CdR-treated Mel 275 melanoma cells by gp100-specific CTL and increased their IFN-gamma release. 5-aza-CdR treatment of Mel 275 cells also induced a higher number of gp100-specific CTL to secrete IFN-gamma.

CONCLUSIONS

Treatment with 5-aza-CdR improves the recognition of melanoma cells by gp100-specific CTL through the up-regulation of HLA class I antigens expression; ICAM-1 also contributes to this phenomenon. These findings highlight a broader range of therapeutic implications of 5-aza-CdR when used in association with active or adoptive immunotherapeutic approaches against a variety of melanoma-associated antigens.

Therapy of established B16-F10 melanoma tumors by a single vaccination of CTL/T helper peptides in VacciMax

BACKGROUND

Melanoma tumors are known to express antigens that usually induce weak immune responses of short duration. Expression of both tumor-associated antigens p53 and TRP2 by melanoma cells raises the possibility of simultaneously targeting more than one antigen in a therapeutic vaccine. In this report, we show that VacciMax (VM), a novel liposome-based vaccine delivery platform, can increase the immunogenicity of melanoma associated antigens, resulting in tumor elimination.

METHODS

C57BL/6 mice bearing B16-F10 melanoma tumors were vaccinated subcutaneously 6 days post tumor implantation with a mixture of synthetic peptides (modified p53: 232-240, TRP-2: 181-188 and PADRE) and CpG. Tumor growth was monitored and antigen-specific splenocyte responses were assayed by ELISPOT.

RESULTS

Vaccine formulated in VM increased the number of both TRP2- and p53-specific IFN-gamma producing splenocytes following a single vaccination. Vaccine formulated without VM resulted only in enhanced IFN-gamma producing splenocytes to one CTL epitopes (TRP2:180-188), suggesting that VM overcomes antigen dominance and enhances immunogenicity of multiple epitopes. Vaccination of mice bearing 6-day old B16-F10 tumors with both TRP2 and p53-peptides formulated in VM successfully eradicated tumors in all mice. A control vaccine which contained all ingredients except liposomes resulted in eradication of tumors in no more than 20% of mice.

CONCLUSION

A single administration of VM is capable of inducing an effective CTL response to multiple tumor-associated antigens. The responses generated were able to reject 6-day old B16-F10 tumors.