Tumor immunotherapy using adenovirus vaccines in combination with intratumoral doses of CpG ODN

Heterologous prime-boost vaccine using antigen-loaded microparticles and adenovirus (encoding antigen) enhances cellular immune responses and antitumor activity

Heterologous prime-boost vaccines have the potential to promote higher immune responses than homologous prime-boost vaccines and were used in this murine study to investigate the effect on the magnitude of the cellular (and humoral) antigen-specific immune responses and antitumor efficacy when a microparticle formulation (prime) is combined with an adenoviral vaccine (boost). Specifically, the prime comprised chick egg ovalbumin (OVA; 25 µg/dose), used here as a model tumor antigen (TA), encapsulated in microparticles (∼700 nm diameter) made from the biodegradable polymer, 50:50 poly(lactic-co-glycolic acid) (PLGA); while attenuated adenovirus (type 5) encoding OVA (Ad5OVA; 108 PFU/dose) was employed as the boost. The ability of OVA-loaded microparticles to enhance OVA-specific antibody responses, OVA-specific CD3 + CD8 + T cell responses and antitumor activity (i.e., protection against OVA-expressing tumor-challenge) to the heterologous prime-boost vaccine was investigated; and it was found that this prime-boost combination could significantly enhance OVA-specific cellular responses compared to all other vaccination groups and was the only group to confer a significant survival advantage over the unvaccinated group (naïve) in a prophylactic animal tumor model. This finding illustrates the potential for combining TA-loaded PLGA-based microparticles with other vaccine formats to improve tumor-specific cellular immune responses.

Cationic nanoparticles enhance T cell tumor infiltration and antitumor immune responses to a melanoma vaccine

In clinical settings, cancer vaccines as monotherapies have displayed limited success compared to other cancer immunotherapeutic treatments. Nanoscale formulations have the ability to increase the efficacy of cancer vaccines by combatting the immunosuppressive nature of the tumor microenvironment. Here, we have synthesized a previously unexplored cationic polymeric nanoparticle formulation using polyamidoamine dendrimers and poly(d,l-lactic-co-glycolic acid) that demonstrate adjuvant properties in vivo. Tumor-challenged mice vaccinated with an adenovirus-based cancer vaccine [encoding tumor-associated antigen (TAA)] and subsequently treated with this nanoparticulate formulation showed significant increases in TAA-specific T cells in the peripheral blood, reduced tumor burden, protection against tumor rechallenge, and a significant increase in median survival. An investigation into cell-based pathways suggests that administration of the nanoformulation at the site of the developing tumor may have created an inflammatory environment that attracted activated TAA-specific CD8⁺ T cells to the vicinity of the tumor, thus enhancing the efficacy of the vaccine.

Effects of CpG oligodeoxynucleotides on the differentiation of Treg/Th17 cells

AIM

The balance between Th17 cells and T regulatory (Treg) cells has emerged as a prominent factor in regulating cancer development. However, the effect of CpG oligodeoxynucleotides (ODNs) on the differentiation of Treg/Th17 cells has not been well studied. We sought here to explore the function of CpG ODNs in the differentiation of Tregs and Th17 cells in vitro and in vivo.

METHODS

Mouse spleen cells were cultured with anti-CD3 monoclonal antibodies in vitro. Tregs and Th17 cell differentiation was induced by transforming growth factor (TGF)-β and interleukin (IL)-2, or TGF-β, IL-6, and IL-23, respectively. Then cells were treated with two CpG ODNs, CpG 1982, or CpG 1826. FBL-3-inoculated C57Bl/6 mice were treated with CpG 1826, tumor vaccine, or combination of CpG 1826 and tumor vaccine. After treatment, spleen cells and serum were isolated, and Tregs/Th17 cells were detected by flow cytometry. The expression of forkhead box P3 (Foxp3), retinoid-related orphan receptor gamma-t (RORγt), IL-10, and IL-17 mRNA was measured by real-time PCR, and protein levels were measured by Western blot and enzyme-linked immunosorbent assay.

RESULTS

The frequency of Treg cells increased significantly (p < 0.05) in the FBL-3-inoculated leukemia mouse model compared with control mice, whereas the frequency of Th17 cells did not change. Median survival of mice after treatment with CpG 1826 and tumor vaccine was significantly prolonged compared with that of control mice (p < 0.05). The frequency of induced Treg cells decreased after treatment with CpG 1826, whereas the frequency of Th17 cells induced by cytokines in vitro and in the murine leukemia model increased following treatment with CpG 1826. Furthermore, after treatment with CpG 1826, the mRNA and protein levels of Foxp3 and IL-10 decreased significantly both in vitro and in vivo (p < 0.05), whereas those of RORγt and IL-17 increased significantly (p < 0.05).

CONCLUSION

CpG 1826 may inhibit the differentiation of Treg cells induced by cytokines, promote the differentiation of Th17 cells in vitro and in murine leukemia models, and prolong the median survival of mice with leukemia.

Modulating the Tumour Microenvironment by Intratumoural Injection of Pattern Recognition Receptor Agonists

Signalling through pattern recognition receptors (PRRs) leads to strong proinflammatory responses, enhancing the activity of antigen presenting cells and shaping adaptive immune responses against tumour associated antigens. Unfortunately, toxicities associated with systemic administration of these agonists have limited their clinical use to date. Direct injection of PRR agonists into the tumour can enhance immune responses by directly modulating the cells present in the tumour microenvironment. This can improve local antitumour activity, but importantly, also facilitates systemic responses that limit tumour growth at distant sites. As such, this form of therapy could be used clinically where metastatic tumour lesions are accessible, or as neoadjuvant therapy. In this review, we summarise current preclinical data on intratumoural administration of PRR agonists, including new strategies to optimise delivery and impact, and combination studies with current and promising new cancer therapies.

Advances in engineering local drug delivery systems for cancer immunotherapy

Cancer immunotherapy aims to leverage the immune system to suppress the growth of tumors and to inhibit metastasis. The recent promising clinical outcomes associated with cancer immunotherapy have prompted research and development efforts towards enhancing the efficacy of immune checkpoint blockade, cancer vaccines, cytokine therapy, and adoptive T cell therapy. Advancements in biomaterials, nanomedicine, and micro-/nano-technology have facilitated the development of enhanced local delivery systems for cancer immunotherapy, which can enhance treatment efficacy while minimizing toxicity. Furthermore, locally administered cancer therapies that combine immunotherapy with chemotherapy, radiotherapy, or phototherapy have the potential to achieve synergistic antitumor effects. Herein, the latest studies on local delivery systems for cancer immunotherapy are surveyed, with an emphasis on the therapeutic benefits associated with the design of biomaterials and nanomedicines. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Immune-based therapies for metastatic prostate cancer: an update

Prostate cancer (PC) is a common malignancy among elderly males and is noncurable once it becomes metastatic. In recent years, a number of antigen-delivery systems have emerged as viable and promising immunotherapeutic agents against PC. The approval of sipuleucel-T by the US FDA for the treatment of males with asymptomatic or minimally symptomatic castrate resistant PC was a landmark in cancer immunotherapy, making this the first approved immunotherapeutic. A number of vaccines are under clinical investigation, each having its own set of advantages and disadvantages. Here, we discuss the basic technologies underlying these different delivery modes, we discuss the completed and current human clinical trials, as well as the use of vaccines in combination with immune checkpoint inhibitors.

Induction of necrotic cell death and activation of STING in the tumor microenvironment via cationic silica nanoparticles leading to enhanced antitumor immunity

Nanotechnology has demonstrated tremendous clinical utility, with potential applications in cancer immunotherapy. Although nanoparticles with intrinsic cytotoxicity are often considered unsuitable for clinical applications, such toxicity may be harnessed in the fight against cancer. Nanoparticle-associated toxicity can induce acute necrotic cell death, releasing tumor-associated antigens which may be captured by antigen-presenting cells to initiate or amplify tumor immunity. To test this hypothesis, cytotoxic cationic silica nanoparticles (CSiNPs) were directly administered into B16F10 melanoma implanted in C57BL/6 mice. CSiNPs caused plasma membrane rupture and oxidative stress of tumor cells, inducing local inflammation, tumor cell death and the release of tumor-associated antigens. The CSiNPs were further complexed with bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP), a molecular adjuvant which activates the stimulator of interferon genes (STING) in antigen-presenting cells. Compared with unformulated c-di-GMP, the delivery of c-di-GMP with CSiNPs markedly prolonged its local retention within the tumor microenvironment and activated tumor-infiltrating antigen-presenting cells. The combination of CSiNPs and a STING agonist showed dramatically increased expansion of antigen-specific CD8+ T cells, and potent tumor growth inhibition in murine melanoma. These results demonstrate that cationic nanoparticles can be used as an effective in situ vaccine platform which simultaneously causes tumor destruction and immune activation.

Intratumoral CpG-B Promotes Antitumoral Neutrophil, cDC, and T-cell Cooperation without Reprograming Tolerogenic pDC

Cancer immunotherapies utilize distinct mechanisms to harness the power of the immune system to eradicate cancer cells. Therapeutic vaccines, aimed at inducing active immune responses against an existing cancer, are highly dependent on the immunological microenvironment, where many immune cell types display high levels of plasticity and, depending on the context, promote very different immunologic outcomes. Among them, plasmacytoid dendritic cells (pDC), known to be highly immunogenic upon inflammation, are maintained in a tolerogenic state by the tumor microenvironment. Here, we report that intratumoral (i.t.) injection of established solid tumors with CpG oligonucleotides-B (CpG-B) inhibits tumor growth. Interestingly, control of tumor growth was independent of tumor-associated pDC, which remained refractory to CpG-B stimulation and whose depletion did not alter the efficacy of the treatment. Instead, tumor growth inhibition subsequent to i.t. CpG-B injection depended on the recruitment of neutrophils into the milieu, resulting in the activation of conventional dendritic cells, subsequent increased antitumor T-cell priming in draining lymph nodes, and enhanced effector T-cell infiltration in the tumor microenvironment. These results reinforce the concept that i.t. delivery of TLR9 agonists alters the tumor microenvironment by improving the antitumor activity of both innate and adaptive immune cells.Significance: Intratumoral delivery of CpG-B disrupts the tolerogenic tumor microenvironment and inhibits tumor growth. Cancer Res; 78(12); 3280-92. ©2018 AACR.

Development and Evaluation of Biodegradable Particles Coloaded With Antigen and the Toll-Like Receptor Agonist, Pentaerythritol Lipid A, as a Cancer Vaccine

Immune adjuvants are important components of current and prospective cancer vaccines. In this study, we aimed at evaluating the use of a synthetic lipid A derivative, pentaerythritol lipid A (PET lipid A), loaded into poly(lactic-co-glycolic acid) particles, as a potential cancer vaccine adjuvant. Poly(lactic-co-glycolic acid) particles (size range: 250-600 nm) were successfully formulated to include PET lipid A and/or the model tumor antigen, chicken ovalbumin (OVA). It was shown that particulated PET lipid A had a distinct advantage at promoting secretion of the immune potentiating cytokine, IL-12p70, and upregulating key costimulatory surface proteins, CD86 and CD40, in murine dendritic cells in vitro. In a murine tumor model, involving prophylactic vaccination with various permutations of soluble versus particulated formulations of OVA with or without PET lipid A, modest benefit was observed in terms of OVA-specific cell-mediated immune responses when PET lipid A was delivered in particles. These findings translated into a corresponding trend toward increased survival of mice challenged with OVA-expressing tumor cells (E.G7). In terms of translation of safe adjuvants into the clinic, these results promote the concept of delivering toll-like receptor-4 agonists in particles because doing so improves their adjuvant properties, while decreasing the chances of adverse effects due to off-target uptake by nonphagocytic cells.

Diaminosulfide based polymer microparticles as cancer vaccine delivery systems

The aim of the research presented here was to determine the characteristics and immunostimulatory capacity, in vivo, of antigen and adjuvant co-loaded into microparticles made from a novel diaminosulfide polymer, poly(4,4'-trimethylenedipiperdyl sulfide) (PNSN), and to assess their potential as cancer vaccine vectors. PNSN microparticles co-loaded with the antigen, ovalbumin (OVA), and adjuvant, CpG 1826, (PNSN(OVA + CpG)) were fabricated and characterized for size (1.64 μm diameter; PDI=0.62), charge (-23.1 ± 0.3), and loading efficiencies of antigen (7.32 μg/mg particles) and adjuvant (0.95 μg/mg particles). The ability of PNSN(OVA + CpG) to stimulate cellular and humoral immune responses in vivo was compared with other PNSN microparticle formulations as well as with poly(lactic-co-glycolic acid)(PLGA)-based microparticles, co-loaded with OVA and CpG (PLGA(OVA + CpG)), an adenovirus encoding OVA (Ad5-OVA), and OVA delivered with incomplete Freund's adjuvant (IFA(OVA)). In vivo OVA-specific IgG1 responses, after subcutaneous prime/boosts in mice, were similar when PNSN(OVA + CpG) and PLGA(OVA + CpG) were compared and the presence of CpG 1826 within the PNSN microparticles demonstrated significantly improved responses when compared to PNSN microparticles loaded with OVA alone (PNSN(OVA)), plus or minus soluble CpG 1826. Cellular immune responses to all particle-based vaccine formulations ranged from being negligible to modest with PNSN(OVA + CpG) generating the greatest responses, displaying significantly increased levels of OVA-specific CD8+ T lymphocytes compared to controls and IFA(OVA) treated mice. Finally, it was shown that of all vaccination formulations tested PNSN(OVA + CpG) was the most protective against subsequent challenge with an OVA-expressing tumor cell line, E.G7. Thus, microparticles made from poly(diaminosulfide)-based macromolecules possess promising potential as vaccine vectors and, as demonstrated here, may have impact as cancer vaccines in particular.

Vaccine immunotherapy for prostate cancer: from mice to men

Preclinical studies demonstrated the ability of an adenovirus/PSA (Ad/PSA) vaccine to induce strong anti-PSA immune responses, and these responses were capable of destroying prostate-specific antigen (PSA)-secreting mouse prostate tumors. A series of preclinical studies have demonstrated the superiority of the Ad/PSA vaccine to other PSA vaccines for the induction of anti-PSA immune responses, the ability of Ad/PSA vaccination combined with cytokine gene therapy and the TLR9 agonist CpG to enhance the anti-prostate tumor immunotherapy, and the reduction of negative regulatory elements when the vaccine was combined with 5-fluoruracil administration. A phase I clinical trial of the Ad/PSA vaccine in men with metastatic castrate-resistant prostate cancer demonstrated the safety of the vaccine even at the highest single dose permitted by the FDA. Currently, a phase II trial of the Ad/PSA vaccine is underway treating patients in two protocols. Thus far 81 patients have been enrolled and vaccinated. Early results from the patients evaluated to date demonstrated the induction of anti-PSA T cell responses, and the majority of patients evaluated at this time had demonstrated an increase in PSA doubling times.

Applying biodegradable particles to enhance cancer vaccine efficacy

One of the primary goals of our group and our collaborators here at the University of Iowa is to develop therapeutic cancer vaccines using biodegradable and biocompatible polymer-based vectors. A major advantage of using discretely packaged immunogenic cargo over non-encapsulated vaccines is that they promote enhanced cellular immunity, a key requirement in achieving antitumor activity. We discuss the importance of co-encapsulation of tumor antigen and adjuvant, with specific focus on the synthetic oligonucleotide adjuvant, cytosine-phosphate-guanine oligodeoxynucleotides. We also discuss our research using a variety of polymers including poly(α-hydroxy acids) and polyanhydrides, with the aim of determining the effect that parameters, such as size and polymer type, can have on prophylactic and therapeutic tumor vaccine formulation efficacy. Aside from their role as vaccine vectors per se, we also address the research currently underway in our group that utilizes more novel applications of biodegradable polymer-based particles in facilitating other types of immune-based therapies.

CpG ODN nanorings induce IFNα from plasmacytoid dendritic cells and demonstrate potent vaccine adjuvant activity

CpG oligodeoxynucleotides (ODN) are short single-stranded synthetic DNA molecules that activate the immune system and have been found to be effective for preventing and treating infectious diseases, allergies, and cancers. Structurally distinct classes of synthetic ODN expressing CpG motifs differentially activate human immune cells. K-type ODN (K-ODN), which have progressed into human clinical trials as vaccine adjuvants and immunotherapeutic agents, are strong activators of B cells and trigger plasmacytoid dendritic cells (pDCs) to differentiate and produce tumor necrosis factor-α (TNFα). In contrast, D-type ODN (D-ODN) stimulate large amounts of interferon-α (IFNα) secretion from pDCs. This activity depends on the ability of D-ODN to adopt nanometer-sized G quadruplex-based structures, complicating their manufacturing and hampering their progress into the clinic. In search of a D-ODN substitute, we attempted to multimerize K-ODN into stable nanostructures using cationic peptides. We show that short ODN with a rigid secondary structure form nuclease-resistant nanorings after condensation with the HIV-derived peptide Tat(47-57). The nanorings enhanced cellular internalization, targeted the ODN to early endosomes, and induced a robust IFNα response from human pDCs. Compared to the conventional K-ODN, nanorings boosted T helper 1-mediated immune responses in mice immunized with the inactivated foot and mouth disease virus vaccine and generated superior antitumor immunity when used as a therapeutic tumor vaccine adjuvant in C57BL/6 mice bearing ovalbumin-expressing EG.7 thymoma tumors. These results suggest that the nanorings can act as D-ODN surrogates and may find a niche for further clinical applications.

CpG oligodeoxynucleotide inhibits HBV replication in a hydrodynamic injection murine model

BACKGROUND

Chronic HBV infection is a significant public health problem and one major cause of liver cirrhosis and hepatocellular carcinoma (HCC). HBV impairs the host immune system and results in immunotolerance, which is a major obstacle to HBV therapy. CpG oligodeoxynucleotide (ODN) is a strong immunostimulant which activates the innate immune response rapidly and has been shown to be an efficient therapy agent in viral infection treatment. Here, we report the anti-HBV activity of CpG-1826 in a hydrodynamic injection murine model.

METHODS

CpG-1826 was administrated intraperitoneally every other day in HBV carrier mice established by tail vein hydrodynamic injection of HBV plasmids. The serum concentrations of HBV surface antigen (HBsAg), HBV e antigen (HBeAg), HBV surface antibody (HBsAb), HBV core antibody (HBcAb), interferon-α (IFN-α) and interferon-γ (IFN-γ) were measured by enzyme-linked immunosorbent assay (ELISA). The activities of alanine aminotransferase (ALT) were determined by ALT kit using a Spectramax Plus spectrophotometer. Hepatic HBV DNA was quantified by quantitative real-time PCR. The expression of HBV core antigen (HBcAg) in liver was detected by immunohistochemistry. Drug toxicity of CpG-1826 was evaluated by body weighting and liver histopathology confirmation.

RESULTS

CpG-1826 administration inhibited HBV replication efficiently with significant reduction of serum HBsAg and HBeAg, hepatic HBcAg and HBV DNA levels. The serum levels of IFN-α, IFN-γ and HBsAb increased but the HBcAb level declined in the CpG-1826 group compared to CpG-1982 and PBS control groups. Results of ALT activity indicated no significant difference among CpG-1826 group, CpG-1982 and PBS control groups. Body weighting and histopathology examination showed no obvious toxicity.

CONCLUSIONS

Given the stimulation activity of a host immune system, CpG ODN is a promising strategy for HBV therapy with more relevant research needed.

Evaluation of protective efficacy of the synthetic peptide vaccine containing the T-helper 1 epitope with CpG oligodeoxynucleotide against feline infectious peritonitis virus infection in cats

BACKGROUND

Feline infectious peritonitis (FIP) is a feline coronavirus-induced fatal disease in domestic and wild cats. Cellular immunity is considered to play an important role in the prevention of FIP. Thus, induction of the cellular immune response is essential in vaccines against FIP virus (FIPV) infection.

METHODS

We immunized cats with peptides containing T-helper (Th)1 epitopes derived from the nucleocapsid (N) protein of the type I FIPV KU-2 strain (NP7 and NP8) with feline CpG-oligodeoxynucleotides (fCpG-ODNs) as a vaccine adjuvant.

RESULTS

Prevention against type II FIPV 79-1146 strain-induced FIP was slightly better in specific pathogen-free cats treated with NP7 and NP8 with fCpG-ODNs. However, immune tolerance was suggested to be induced by the high dose and frequency of NP7 and NP8 with fCpG-ODNs.

CONCLUSIONS

Further investigations on the combination and concentrations of the peptides and fCpG-ODNs, dose, frequency and route of administration are needed.

Biodegradable particles as vaccine antigen delivery systems for stimulating cellular immune responses

There is a need for both new and improved vaccination formulations for a range of diseases for which current vaccines are either inadequate or non-existent. Biodegradable polymer-based vaccines fulfill many of the desired properties in achieving effective long-term protection in a manner that is safe, economical, and potentially more practicable on a global scale. Here we discuss some of the work performed with micro/nanoparticles made from either synthetic (poly[lactic-co-glycolic acid] [PLGA] and polyanhydrides) or natural (chitosan) biodegradable polymers. Our attention is focused on, but not limited to, the generation of antitumor immunity where we stress the importance of particle size and co-delivery of antigen and adjuvant.

The combination of a low-dose chemotherapeutic agent, 5-fluorouracil, and an adenoviral tumor vaccine has a synergistic benefit on survival in a tumor model system

Standard cancer therapies, particularly those involving chemotherapy, are in need of modifications that both reduce short-term and long-term side effects as well as improve the overall survival of cancer patients. Here we show that combining low-dose chemotherapy with a therapeutic vaccination using an adenovirus encoding a model tumor-associated antigen, ovalbumin (Ad5-OVA), had a synergistic impact on survival in tumor-challenged mice. Mice that received the combinatorial treatment of Ad5-OVA plus low-dose 5-fluorouracil (5-FU) had a 95% survival rate compared to 7% and 30% survival rates for Ad5-OVA alone and 5-FU alone respectively. The presence of 5-FU enhanced the levels of OVA-specific CD8⁺ T lymphocytes in the spleens and draining lymph nodes of Ad5-OVA-treated mice, a phenomenon that was dependent on the mice having been tumor-challenged. Thus 5-FU may have enhanced survival of Ad5-OVA-treated mice by enhancing the tumor-specific immune response combined with eliminating tumor bulk. We also investigated the possibility that the observed therapeutic benefit may have been derived from the capacity of 5-FU to deplete MDSC populations. The findings presented here promote the concept of combining adenoviral cancer vaccines with low-dose chemotherapy.

Intravaginal TLR agonists increase local vaccine-specific CD8 T cells and human papillomavirus-associated genital-tumor regression in mice

Human papillomaviruses (HPV)-related cervical cancer is the second leading cause of cancer death in women worldwide. Despite active development, HPV E6/E7 oncogene-specific therapeutic vaccines have had limited clinical efficacy to date. Here, we report that intravaginal (IVAG) instillation of CpG-ODN (TLR9 agonist) or poly-(I:C) (TLR3 agonist) after subcutaneous E7 vaccination increased ~fivefold the number of vaccine-specific interferon-γ-secreting CD8 T cells in the genital mucosa (GM) of mice, without affecting the E7-specific systemic response. The IVAG treatment locally increased both E7-specific and total CD8 T cells, but not CD4 T cells. This previously unreported selective recruitment of CD8 T cells from the periphery by IVAG CpG-ODN or poly-(I:C) was mediated by TLR9 and TLR3/melanoma differentiation-associated gene 5 signaling pathways, respectively. For CpG, this recruitment was associated with a higher proportion of GM-localized CD8 T cells expressing both CCR5 and CXCR3 chemokine receptors and E-selectin ligands. Most interestingly, IVAG CpG-ODN following vaccination led to complete regression of large genital HPV tumors in 75% of mice, instead of 20% with vaccination alone. These findings suggest that mucosal application of immunostimulatory molecules might substantially increase the effectiveness of parenterally administered vaccines.

Characterizing the antitumor response in mice treated with antigen-loaded polyanhydride microparticles

Delivery of vaccine antigens with an appropriate adjuvant can trigger potential immune responses against cancer leading to reduced tumor growth and improved survival. In this study, various formulations of a bioerodible amphiphilic polyanhydride copolymer based on 1,8-bis(p-carboxyphenoxy)-3,6-dioxaoctane (CPTEG) and 1,6-bis(p-carboxyphenoxy) hexane (CPH) with inherent adjuvant properties were evaluated for antigen-loading properties, immunogenicity and antitumor activity. Mice were vaccinated with 50:50 CPTEG:CPH microparticles encapsulating a model tumor antigen, ovalbumin (OVA), in combination with the Toll-like receptor-9 agonist, CpG oligonucleotide 1826 (CpG ODN). Mice treated with OVA-encapsulated CPTEG:CPH particles elicited the highest CD8(+) T cell responses on days 14 and 20 when compared to other treatment groups. This treatment group also displayed the most delayed tumor progression and the most extended survival times. Particles encapsulating OVA and CpG ODN generated the highest anti-OVA IgG(1) antibody responses in mice but these mice did not show significant tumor protection. These results suggest that antigen-loaded CPTEG:CPH microparticles can stimulate antigen-specific cellular responses and could therefore potentially be used to promote antitumor responses in cancer patients.

Proposed mechanisms of action for prostate cancer vaccines

Prostate cancer is responsible for the deaths of more than 33,000 American men every year. Once this disease has become metastatic, there is no curative treatment. Alternative therapies to chemotherapy and radical prostatectomy are being increasingly explored. Prostate cancer vaccines--which trigger a tumour-specific cytotoxic-T-lymphocyte-mediated immune attack by the patient's immune system--have been investigated in clinical trials with modest, yet encouraging, results. When developing and administering prostate cancer vaccines, it is critical to consider how vital parameters, such as the stage of disease progression and the nature of adjuvant therapies, could influence treatment outcome. Of particular interest are current and future strategies for diminishing the activity of regulatory T lymphocytes.

Antigen-coated poly α-hydroxy acid based microparticles for heterologous prime-boost adenovirus based vaccinations

Adenoviruses show promising potential as vectors for cancer vaccines, however, their high immunogenicity can be problematic when it comes to homologous prime-boost strategies. In the studies presented here we show that heterologous prime-boost vaccinations involving ovalbumin (OVA)-antigen-coated microparticles as a prime, and adenovirus encoding OVA (AdOVA) as a boost, were equally as effective as homologous AdOVA prime-boosts at generating OVA-specific CD8(+) T-cell responses, which translated into effective tumor protection. OVA-coated biodegradable poly α-hydroxy acid-based microparticles of varying chemistries, when used as primes in heterologous prime-boost vaccinations, were comparable in terms of promoting OVA-specific CD8(+) T cells as well as providing protection against subsequent tumor challenge. These findings auger well for using poly α-hydroxy acid-based microparticles in prime-boost viral vaccination strategies geared toward the safer, and potentially more efficient, generation of anti-tumor immunity.

Immunotherapy for castration-resistant prostate cancer

The improved survival with sipuleucel-T, an autologous antigen-presenting cell-based agent, for the treatment of patients with metastatic asymptomatic and minimally symptomatic castration-resistant prostate cancer supports immunotherapy as a valid approach. Also, multiple novel immunotherapeutic approaches are undergoing vigorous investigation. T-lymphocyte checkpoint blockade and poxvirus-based prime-boost approaches are in phase III evaluation. Other immunotherapeutic platforms undergoing early investigation include radioimmunoconjugates and adenovirus-based, DNA-based, and Listeria-based approaches. The development of predictive markers for immune response that translate into improved long-term outcomes is important. This article reviews the emerging data and the unique strengths and weaknesses of these approaches.