Eradication of large tumors in mice by a tritherapy targeting the innate, adaptive, and regulatory components of the immune system

Modeling tumor response after combined administration of different immune-stimulatory agents

The aims of this work were as follows: 1) to develop a semimechanistic pharmacodynamic model describing tumor shrinkage after administration of a previously developed antitumor vaccine (CyaA-E7) in combination with CpG (a TLR9 ligand) and/or cyclophosphamide (CTX), and 2) to assess the translational capability of the model to describe tumor effects of different immune-based treatments. Population approach with NONMEM version 7.2 was used to analyze the previously published data. These data were generated by injecting 5 × 10(5) tumor cells expressing human papillomavirus (HPV)-E7 proteins into C57BL/6 mice. Large and established tumors were treated with CpG and/or CTX administered alone or in combination with CyaA-E7. Applications of the model were assessed by comparing model-based simulations with preclinical and clinical outcomes obtained from literature. CpG effects were modeled: 1) as an amplification of the immune signal triggered by the vaccine and 2) by shortening the delayed response of the vaccine. CTX effects were included through a direct decrease of the tumor-induced inhibition of vaccine efficacy over time, along with a delayed induction of tumor cell death. A pharmacodynamic model, built based on plausible biologic mechanisms known for the coadjuvants, successfully characterized tumor response in all experimental scenarios. The model developed was satisfactory applied to reproduce clinical outcomes when CpG or CTX was used in combination with different vaccines. The results found after simulation exercise indicated that the contribution of the coadjuvants to the tumor response elicited by vaccines can be predicted for other immune-based treatments.

Mucosal imprinting of vaccine-induced CD8⁺ T cells is crucial to inhibit the growth of mucosal tumors

Although many human cancers are located in mucosal sites, most cancer vaccines are tested against subcutaneous tumors in preclinical models. We therefore wondered whether mucosa-specific homing instructions to the immune system might influence mucosal tumor outgrowth. We showed that the growth of orthotopic head and neck or lung cancers was inhibited when a cancer vaccine was delivered by the intranasal mucosal route but not the intramuscular route. This antitumor effect was dependent on CD8⁺ T cells. Indeed, only intranasal vaccination elicited mucosal-specific CD8⁺ T cells expressing the mucosal integrin CD49a. Blockade of CD49a decreased intratumoral CD8⁺ T cell infiltration and the efficacy of cancer vaccine on mucosal tumor. We then showed that after intranasal vaccination, dendritic cells from lung parenchyma, but not those from spleen, induced the expression of CD49a on cocultured specific CD8⁺ T cells. Tumor-infiltrating lymphocytes from human mucosal lung cancer also expressed CD49a, which supports the relevance and possible extrapolation of these results in humans. We thus identified a link between the route of vaccination and the induction of a mucosal homing program on induced CD8⁺ T cells that controlled their trafficking. Immunization route directly affected the efficacy of the cancer vaccine to control mucosal tumors.

Efficacy of DNA vaccines forming e7 recombinant retroviral virus-like particles for the treatment of human papillomavirus-induced cancers

Human papillomavirus (HPV) is involved in the development of anogenital tumors and also in the development of oropharyngeal head and neck carcinomas, where HPV-16, expressing the E6 and E7 oncoproteins, is the most frequent serotype. Although vaccines encoding L1 and L2 capsid HPV proteins are efficient for the prevention of HPV infection, they are inadequate for treating established tumors. Hence, development of innovative vaccine therapies targeting E6/E7 is important for controlling HPV-induced cancers. We have engineered a nononcogenic mutated E7-specific plasmo-retroVLP vaccine (pVLP-E7), consisting of plasmid DNA, that is able to form recombinant retrovirus-based virus-like particles (VLPs) that display E7 antigen into murine leukemia virus Gag proteins pseudotyped with vesicular stomatitis virus envelope glycoprotein (VSV-G). pVLP-E7 vaccinations were studied for their ability to generate specific immune responses and for induction of protective immunity against tumor cell challenge in preventive and therapeutic models. The produced VLPs induce the maturation of human dendritic cells in vitro and mount specific E7 T cell responses. Intradermic vaccinations of mice with pVLP-E7 show their efficacy to generate antigen-specific T cell responses, to prevent and protect animals from early TC-1 tumor development compared with standard DNA or VLP immunizations. The vaccine efficacy was also evaluated for advanced tumors in mice vaccinated at various time after the injection of TC-1 cells. Data show that pVLP-E7 vaccination can cure mice with already established tumors only when combined with Toll-like receptor-7 (TLR7) and TLR9 agonists. Our findings provide evidence that pVLPs, combining the advantages of DNA and VLP vaccines, appear to be a promising strategy for the treatment of HPV-induced cancers.

Mathematical model approach to describe tumour response in mice after vaccine administration and its applicability to immune-stimulatory cytokine-based strategies

Immunotherapy is a growing therapeutic strategy in oncology based on the stimulation of innate and adaptive immune systems to induce the death of tumour cells. In this paper, we have developed a population semi-mechanistic model able to characterize the mechanisms implied in tumour growth dynamic after the administration of CyaA-E7, a vaccine able to target antigen to dendritic cells, thus triggering a potent immune response. The mathematical model developed presented the following main components: (1) tumour progression in the animals without treatment was described with a linear model, (2) vaccine effects were modelled assuming that vaccine triggers a non-instantaneous immune response inducing cell death. Delayed response was described with a series of two transit compartments, (3) a resistance effect decreasing vaccine efficiency was also incorporated through a regulator compartment dependent upon tumour size, and (4) a mixture model at the level of the elimination of the induced signal vaccine (k 2) to model tumour relapse after treatment, observed in a small percentage of animals (15.6%). The proposed model structure was successfully applied to describe antitumor effect of IL-12, suggesting its applicability to different immune-stimulatory therapies. In addition, a simulation exercise to evaluate in silico the impact on tumour size of possible combination therapies has been shown. This type of mathematical approaches may be helpful to maximize the information obtained from experiments in mice, reducing the number of animals and the cost of developing new antitumor immunotherapies.

[Cancers of the upper aerodigestive tract associated with human papillomavirus]

Carcinomas of the aerodigestive tract are most often secondary to alcohol and tobacco intoxication. However, it is shown that the oncogenic human papillomavirus (HPV) have an increasing role in the carcinogenesis of these cancers. Patients with HPV+ carcinoma are generally younger and not alcohol and tobacco users. These carcinomas are mainly localized in the oropharynx and in particular at the tonsil. HPV is found in 40 to 90 % of the cancers in the oropharynx, depending on the country. These HPV+ carcinomas have a better prognosis with better radio or chemosensitivity. To date, no change of treatment is recommended, however, several trials are underway. Preventive vaccination of boys is a real public health issue, especially since it is recommended in some countries. Moreover, a better understanding of the tumor microenvironment will ultimately offer therapeutic vaccination.

Complexes of streptavidin-fused antigens with biotinylated antibodies targeting receptors on dendritic cell surface: a novel tool for induction of specific T-cell immune responses

The choice of tools that enable efficient targeting of exogenous antigens (Ag) for processing and presentation by professional Ag-presenting cells (APC) remains limited. This represents, indeed, a bottleneck in development of vaccines inducing specific T-cell responses. Here, we describe a novel strategy of Ag delivery into APCs. The Ag of choice is fused to the N- or C-terminus of streptavidin (SA) and tetrameric Ag-SA or SA-Ag fusion proteins are produced in E. coli and purified by 2-Iminobiotin-Agarose affinity chromatography. Alternatively, Ag-SA proteins are purified from urea extracts of E. coli inclusion bodies and refolded in vitro into functional tetramers. Complexes with biotinylated antibodies targeting cell surface receptors are formed and used to deliver the Ags of choice for processing and presentation by APCs and induction of Ag-specific CD4+ and CD8+ T-cell responses in vitro and in vivo.

Heterosubtypic protection against influenza A induced by adenylate cyclase toxoids delivering conserved HA2 subunit of hemagglutinin

The protective efficacy of currently available influenza vaccines is restricted to vaccine strains and their close antigenic variants. A new strategy to obtain cross-protection against influenza is based on conserved antigens of influenza A viruses (IAV), which are able to elicit a protective immune response. Here we describe a vaccination approach involving the conserved stem part of hemagglutinin, the HA2 subunit, shared by different HA subtypes of IAV. To increase its immunogenicity, a novel strategy of antigen delivery to antigen presenting cells (APCs) has been used. The HA2 segment (residues 23-185) was inserted into a genetically detoxified adenylate cyclase toxoid (CyaA-E5) which specifically targets and penetrates CD11b-expressing dendritic cells. The CyaA-E5-HA2 toxoid induced HA2(93-102), HA2(96-104) and HA2(170-178)-specific and Th1 polarized T-cell responses, and also elicited strong broadly cross-reactive HA2-specific antibody response. BALB/c mice immunized with three doses of purified CyaA-E5-HA2 without any adjuvant recovered from influenza infection 2days earlier than the control mock-immunized mice. More importantly, immunized mice were protected against a lethal challenge with 2LD(50) dose of a homologous virus (H3 subtype), as well as against the infection with a heterologous (H7 subtype) influenza A virus. This is the first report on heterosubtypic protection against influenza A infection mediated by an HA2-based vaccine that can induce both humoral and cellular immune responses without the need of adjuvant.

Prophylactic and therapeutic efficacy of an attenuated Listeria monocytogenes-based vaccine delivering HPV16 E7 in a mouse model

Listeria monocytogenes (L. monocytogenes) has been developed as a cancer vaccine vector due to its ability to elicit strong innate and adaptive immune responses. For clinical application, it is necessary to exploit a Listeria platform strain that is safe and that also retains its immunogenicity to develop vaccine candidates against cancer. In this study, a highly attenuated strain with a deletion of actA/plcB was employed as a vector to deliver the human papillomavirus type 16 (HPV16) E7 antigen, which was stably inserted into the chromosome of L. monocytogenes. The prophylactic and therapeutic efficacy of the recombinant L. monocytogenes strain expressing E7 (LM1-2-E7) were evaluated in C57BL/6 mice. In prophylactic tumor challenge assays, immunization with the recombinant strain LM1-2-E7 was able to protect against tumor formation in 87.5% of the mice, even after a second challenge, suggesting that this prophylactic immunization can provide long-lasting immunity. In the therapeutic setting, immunization with LM1-2-E7 led to tumor regression in 50% of the mice and suppressed tumor growth in the remaining mice. The results showed that the recombinant strain was cleared by the immune system within 5 days after immunization and induced a Th1 immune response against E7 peptide and E7-specific cytotoxic T-lymphocyte (CTL) killing activity without severe inflammatory responses in the spleen and liver. Markedly, recombinant Listeria strain resulted in preferential accumulation within tumor tissues and induced higher numbers of CD8+ T cells that infiltrated into the tumor, which were associated with retardation of tumor growth. Collectively, these data indicate that LM1-2-E7 is a possible vaccine candidate against cervical cancer.

Low-dose cyclophosphamide administered as daily or single dose enhances the antitumor effects of a therapeutic HPV vaccine

Although therapeutic HPV vaccines are able to elicit systemic HPV-specific immunity, clinical responses have not always correlated with levels of vaccine-induced CD8(+) T cells in human clinical trials. This observed discrepancy may be attributable to an immunosuppressive tumor microenvironment in which the CD8(+) T cells are recruited. Regulatory T cells (Tregs) are cells that can dampen cytotoxic CD8(+) T-cell function. Cyclophosphamide (CTX) is a systemic chemotherapeutic agent, which can eradicate immune cells, including inhibitory Tregs. The optimal dose and schedule of CTX administration in combination with immunotherapy to eliminate the Treg population without adversely affecting vaccine-induced T-cell responses is unknown. Therefore, we investigated various dosing and administration schedules of CTX in combination with a therapeutic HPV vaccine in a preclinical tumor model. HPV tumor-bearing mice received either a single preconditioning dose or a daily dose of CTX in combination with the pNGVL4a-CRT/E7(detox) DNA vaccine. Both single and daily dosing of CTX in combination with vaccine had a synergistic antitumor effect as compared to monotherapy alone. The potent antitumor responses were attributed to the reduction in Treg frequency and increased infiltration of HPV16 E7-specific CD8(+) T cells, which led to higher ratios of CD8(+)/Treg and CD8(+)/CD11b(+)Gr-1(+) myeloid-derived suppressor cells (MDSCs). There was an observed trend toward decreased vaccine-induced CD8(+) T-cell frequency with daily dosing of CTX. We recommend a single, preconditioning dose of CTX prior to vaccination due to its efficacy, ease of administration, and reduced cumulative adverse effect on vaccine-induced T cells.

The T-cell receptor repertoire of tumor-infiltrating regulatory T lymphocytes is skewed toward public sequences

The accumulation of CD4(+) T regulatory cells (Treg) in tumor tissue is a widely described phenomenon in mouse models and in human cancer patients. Understanding the mechanisms by which Treg migrate and accumulate in tumors is important because they strongly influence the potential efficacy of many immunotherapies. In this study, we used immunoscope technology to analyze the T-cell receptor (TCR) repertoire of tumor-infiltrating T cells in non-TCR transgenic mice. Both tumor-infiltrating Tregs and T effector cells (Teff) displayed sequence profiles in the CDR3 region that were characteristic of biased repertoires seen during clonal cell expansions, implying that strong T-cell responses have occurred within the tumor tissue. By comparing the TCR sequences of tumor-infiltrating Tregs, we obtained evidence of the presence of so-called public TCR sequences that are common to many individuals yet were tumor-specific in nature. Such comparisons also suggested that the Treg-Teff conversion process is not an active process at the tumor site or tumor-draining lymph nodes. Our findings strongly suggest that Treg infiltration of tumor tissue is followed by marked proliferation of a few dominant T-cell clones in the tumor.

Immunotherapeutic synergy between anti-CD137 mAb and intratumoral administration of a cytopathic Semliki Forest virus encoding IL-12

Intratumoral injection of Semliki Forest virus encoding interleukin-12 (SFV-IL-12) combines acute expression of IL-12 and stressful apoptosis of infected malignant cells. Agonist antibodies directed to costimulatory receptor CD137 (4-1BB) strongly amplify pre-existing cellular immune responses toward weak tumor antigens. In this study, we provide evidence for powerful synergistic effects of a combined strategy consisting of intratumoral injection of SFV-IL-12 and systemic delivery of agonist anti-CD137 monoclonal antibodies (mAbs), which was substantiated against poorly immunogenic B16 melanomas (B16-OVA and B16.F10) and TC-1 lung carcinomas. Effector CD8(β)(+) T cells were sufficient to mediate complete tumor eradications. Accordingly, there was an intensely synergistic in vivo enhancement of cytotoxic T lymphocytes (CTL)-mediated immunity against the tumor antigens OVA and tyrosine-related protein-2 (TRP-2). This train of phenomena led to long-lasting tumor-specific immunity against rechallenge, attained transient control of the progression of concomitant tumor lesions that were not directly treated with SFV-IL-12 and caused autoimmune vitiligo. Importantly, we found that SFV-IL-12 intratumoral injection induces bright expression of CD137 on most tumor-infiltrating CD8(+) T lymphocytes, thereby providing more abundant targets for the action of the agonist antibody. This efficacious combinatorial immunotherapy strategy offers feasibility for clinical translation since anti-CD137 mAbs are already undergoing clinical trials and development of clinical-grade SFV-IL-12 vectors is in progress.

[Cancer immunotherapy: recent breakthroughs and perspectives]

Immunotherapy of cancer has long been considered as an attractive therapeutic approach but with no impact on clinical practice. Two clinical protocols of immunotherapy, one based on a cancer vaccine in patients with prostate cancer or melanoma and the other using an immunomodulator targeting T cells (anti-CTLA4 mAb) in melanoma patients, have demonstrated clinical efficacy in two phase III clinical trials. To improve these encouraging clinical results, biomarkers to better select patients which may benefit from this therapy are actively searched. In addition, immunosuppression associated with cancer has to be overcome to allow a better immunostimulation. In contrast to chemotherapy, clinical variables to monitor the efficacy of immunotherapy has to be revisited and overall survival appears to be a better endpoint than clinical response defined by the RECIST criteria. Combination of immunotherapy with conventional treatments (chemotherapy, anti-angiogenic, etc.) should further improve this approach both in its effectiveness and in its clinical indications.

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

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

Innate immune cells in breast cancer--from villains to heroes?

The innate immune system ensures effective protection against foreign pathogens and plays important roles in tissue remodeling. There are many types of innate immune cells, including monocytes, macrophages, dendritic cells, and granulocytes. Interestingly, these cells accumulate in most solid tumors, including those of the breast. There, they play a tumor-promoting role through secretion of growth and angiogenic factors, as well as immunosuppressive molecules. This is in strong contrast to the tumor-suppressing effects that innate immune cells exert in vitro upon proper activation. Therapeutic approaches have been developed with the aim of achieving similar suppressive activities in vivo. However, multiple factors in the tumor microenvironment, many of which are immunosuppressive, represent a major obstacle to effective treatment. Here, we discuss the potential of combating breast cancer through activation of the innate immune system, including possible strategies to enhance the success of immunotherapy.

A novel, broad spectrum therapeutic HPV vaccine targeting the E7 proteins of HPV16, 18, 31, 45 and 52 that elicits potent E7-specific CD8T cell immunity and regression of large, established, E7-expressing TC-1 tumors

Persistent infection by high risk genotypes of human papillomavirus (HPV) is the cause of cervical cancer, which remains one of the most common cancers among women worldwide. In addition, there is a growing appreciation that high risk HPVs are associated with a number of other cancers including anogenital cancers as well as a subset of head and neck cancers. Recently, prophylactic HPV vaccines targeting the two most prevalent high risk HPVs (HPV16 and HPV18) have been deployed in large-scale vaccination campaigns. However, the extent to which these prophylactic vaccines confer protection against other high risk HPV genotypes is largely unknown and prophylactic vaccines have been shown to be ineffective against pre-existing infection. Thus there continues to be an urgent need for effective therapeutic vaccines against HPV. The E7 protein of HPV16 has been widely studied as a target for therapeutic vaccines in HPV-associated cancer settings because HPV16 is the most prevalent of the high risk HPV genotypes. However, HPV16 accounts for only about 50% of cervical cancers and there are at least 15 other high risk HPVs that are known to be oncogenic. We have developed a novel, broad-spectrum, therapeutic vaccine (Pentarix) directed at the E7 proteins from five of the most prevalent high-risk genotypes of HPV worldwide (HPV16, 18, 31, 45 and 52) that together account for more than 80% of all HPV-associated cancers. Pentarix is a recombinant protein-based vaccine that elicits strong, multi-genotype specific CD8 T cell immunity when administered to mice in combination with adjuvants comprised of agonists of the TLR3 or TLR9 family of innate immune receptors. Furthermore, large, established E7-expressing TC-1 tumors undergo rapid and complete regression after therapeutic vaccination of mice with Pentarix. Together, these data suggest that Pentarix may be of clinical value for patients with E7-positive, HPV-associated precancerous lesions or malignant disease.

Parenteral is more efficient than mucosal immunization to induce regression of human papillomavirus-associated genital tumors

Cervical cancer is a public health concern as it represents the second cause of cancer death in women worldwide. High-risk human papillomaviruses (HPV) are the etiologic agents, and HPV E6 and/or E7 oncogene-specific therapeutic vaccines are under development to treat HPV-related lesions in women. Whether the use of mucosal routes of immunization may be preferable for inducing cell-mediated immune responses able to eradicate genital tumors is still debated because of the uniqueness of the female genital mucosa (GM) and the limited experimentation. Here, we compared the protective activity resulting from immunization of mice via intranasal (i.n.), intravaginal (IVAG) or subcutaneous (s.c.) routes with an adjuvanted HPV type 16 E7 polypeptide vaccine. Our data show that s.c. and i.n. immunizations elicited similar frequencies and avidity of TetE71CD81 and E7-specific Interferon-gamma-secreting cells in the GM, whereas slightly lower immune responses were induced by IVAG immunization. In a novel orthotopic murine model, both s.c. and i.n. immunizations allowed for complete long-term protection against genital E7-expressing tumor challenge. However, only s.c. immunization induced complete regression of already established genital tumors. This suggests that the higher E7-specific systemic response observed after s.c. immunization may contribute to the regression of growing genital tumors, whereas local immune responses may be sufficient to impede genital challenges. Thus, our data show that for an efficiently adjuvanted protein-based vaccine, parenteral vaccination route is superior to mucosal vaccination route for inducing regression of established genital tumors in a murine model of HPV-associated genital cancer.

Role of regulatory T-cells in immunization strategies involving a recombinant alphavirus vector system

BACKGROUND

Regulatory T-cells (Treg) hamper immune responses elicited by cancer vaccines. Therefore, depletion of Treg is being used to improve the outcome of vaccinations.

METHODS

We studied whether an alphavirus vector-based immunotherapeutic vaccine changes the number and/or activity of Treg and if Treg depletion improves the efficacy of this vaccine against tumours. The vaccine is based on a Semliki Forest virus (SFV). The recombinant SFV replicon particles encode a fusion protein of E6 and E7 from human papillomavirus (HPV) type 16 (SFVeE6,7).

RESULTS

We demonstrated that SFVeE6,7 immunization did not change Treg levels and their suppressive activity. Depletion of Treg in mice, using the novel anti-folate receptor 4 antibody, did not enhance the immune response induced by SFVeE6,7 immunization. Both the priming and the proliferation phases of the HPV-specific response elicited with SFVeE6,7 were not affected by the immune-suppressive activity of Treg. Moreover, Treg depletion did not improve the therapeutic antitumour response of SFVeE6,7 in a murine tumour model.

CONCLUSIONS

The efficacy of the SFVeE6,7 vaccine was not hampered by Treg. Therefore, SFVeE6,7 seems a very promising candidate for the treatment of HPV-induced disease, as it may not require additional immune interventions to modulate Treg activity.

A Semliki forest virus vector engineered to express IFNα induces efficient elimination of established tumors

Semliki Forest virus (SFV) represents a promising gene therapy vector for tumor treatment, because it produces high levels of recombinant therapeutic proteins while inducing apoptosis in infected cells. In this study, we constructed a SFV vector expressing murine interferon alpha (IFNα). IFNα displays antitumor activity mainly by enhancing an antitumor immune response, as well as by a direct antiproliferative effect. In spite of the antiviral activity of IFNα, SFV-IFN could be produced in BHK cells at high titers. This vector was able to infect TC-1 cells, a tumor cell line expressing E6 and E7 proteins of human papillomavirus, leading to high production of IFNα both in vitro and in vivo. When injected into subcutaneous TC-1 tumors implanted in mice, SFV-IFN was able to induce an E7-specific cytotoxic T lymphocyte response, and to modify tumor infiltrating immune cells, reducing the percentage of T regulatory cells and activating myeloid cells. As a consequence, SFV-IFN was able to eradicate 58% of established tumors treated 21 days after implantation with long-term tumor-free survival and very low toxicity. SFV-IFN was also able to induce significant antitumor responses in a subcutaneous tumor model of murine colon adenocarcimoma. These data suggest that local production of IFNα by intratumoral injection of recombinant SFV-IFN could represent a potent new strategy to treat tumors in patients.

The adjuvant effect of TLR agonists on CD4(+) effector T cells is under the indirect control of regulatory T cells

TLR agonists have been suggested to directly impact Tregs, thereby enhancing or reversing their suppressive function. Here, in order to select TLR agonists leading to potent effector T-cell responses, while minimizing Treg inhibitory function, we used a model antigen, covalently linked to an inert delivery system, combined with a large panel of TLR agonists, for the immunization of mice with an attenuated/depleted or intact Treg subset. We observed that the negative modulation of effector CD4(+) T cells exerted by Tregs cannot be circumvented, whatever the TLR agonist used as adjuvant. To better understand the impact of TLR agonists on Tregs, we investigated (i) the TLR expression profile of highly purified CD4(+) Foxp3(+) Tregs, at steady state or subsequent to in vivo activation by TLR agonists and (ii) the Treg phenotype after in vivo and in vitro activation by TLR agonists. Our results demonstrate that TLR agonists, as single signal inducers, are not able to directly activate Tregs. The phenotypic Treg activation observed in vivo, following TLR administration, does not result from cross-talk with conventional T cells but is rather a consequence of the interaction with other immune cell type(s).

Clinical development of combination strategies in immunotherapy: are we ready for more than one investigational product in an early clinical trial?

Stimulating the innate and adaptive immunity against cancer necessitates the tricking of a system evolved to fight microbial pathogens and directing its activity towards transformed self-tissue. Efficacious interventions to start and sustain the response will probably require a number of agents to tamper simultaneously or sequentially with several immune mechanisms. Although master switches controlling various functions may exist, the goal of a curative immune response will probably demand the combined actions of several therapeutic components. Synergy occurs when drugs interact in ways that enhance or magnify one or more effects or side effects. In cancer immunotherapy, two agents that have minor or no therapeutic effects as single agents can be powerful when combined. Mouse experimentation provides multiple examples of synergistic combinations. Elements to be combined include chiefly: tumor vaccines, adoptive T-cell therapies, cytokines, costimulatory molecules, molecular deactivation of immunosuppressive or tolerogenic pathways and immunostimulatory monoclonal antibodies. These novel therapies, even as single agents, are extremely complex products to be developed owing to the associated biomolecules, cell therapies or gene therapies. At present, drug-development programs are run individually for each immunotherapeutic agent and combinations are considered only at a later stage in clinical development, even in the absence of formal compulsory regulations to prevent clinical trials with combinations. As a result, instead of the search for maximal efficacy, ease of combination with standard treatments, intellectual property management, regulations and business-based decisions often guide the way. Even though the maximal effort must be made in order to prevent adverse effects in patients, it seems reasonable that combination pilot trials should be performed at an early stage, following safe completion of Phase I trials. These trials should be performed based on evidence for synergy in animal models and be simplified in terms of regulatory requirements. Such 'short-cut' combination immunotherapy trials can bring much needed efficacy earlier to the bedside.

A tritherapy combination of a fusion protein vaccine with immune-modulating doses of sequential chemotherapies in an optimized regimen completely eradicates large tumors in mice

Tumor-induced immunosuppression plays a critical role in both impeding tumor-specific immune responses and limiting the effects of cancer immunotherapy. Analyses of regulatory cells recruited during the growth of the E7-expressing tumor, TC-1, revealed a high percentage of regulatory T cells (Tregs) as well as myeloid-derived suppressor cells (MDSCs) in spleens and tumors. In this study, we proposed that treatment with immune-modulating doses of cyclophosphamide (CTX) and all-trans retinoic acid (ATRA) would result in a beneficial tumor microenvironment with the suppression of Tregs and MDSCs and, thus, enhance the effect of a human papillomavirus protein vaccine. Our results showed that CTX preconditioning and persistent ATRA treatment along with the vaccine achieved long-term survival and induced long-term memory responses. However, the effect of the antitumor response sharply declined when the tritherapy was initiated after the optimal therapeutic time. The more intensive regimen could rescue the effect of the tritherapy accompanied by the decreased percentage of Tregs and MDSCs in spleens and tumors. Besides, a favorable host environment was created by the reduced secretion of interleukin-10 and 6 and vascular endothelial growth factor (VEGF) in the tumor niche and decreased the expression of phosphorylation-signal transducer and activator of transcription 3 of TC-1 tumors. Our data shed light on the immune-modulating doses of sequential chemoimmunotherapeutic strategy targeting not only the tumor but also its microenvironment, which suggests a potential clinical benefit for the immunotherapy of HPV-associated malignancies.

Intratumoral injection of interferon-α and systemic delivery of agonist anti-CD137 monoclonal antibodies synergize for immunotherapy

CD137 artificial costimulation results in complete tumor rejection in several mouse models. Type I interferons (IFN) exert antitumor effects through an array of molecular functions on malignant cells, tumor stroma and immune system cells. The fact that agonist anti-CD137 mAb induce tumor regressions in mice deficient in the unique receptor for Type I IFNs (IFNAR(-/-) ) indicated potential for treatment combinations. Indeed, combination of intratumor injections of mouse IFN-α and intraperitoneal injections of anti-CD137 mAb synergized as seen on subcutaneous lesions derived from the MC38 colon carcinoma, which is resistant to each treatment if given separately. Therapeutic activity was achieved both against lesions directly injected with IFN-α and against distant concomitant tumors. Experiments in bone marrow chimeras prepared with IFNAR(-/-) and WT mice concluded that expression of the receptor for Type I interferons is mainly required on cells of the hematopoietic compartment. Synergistic effects correlated with a remarkable cellular hyperplasia of the tumor draining lymph nodes (TDLNs). Enlarged TDLNs contained more plasmacytoid and conventional dendritic cells (DC) that more readily cross-presented. Importantly, numbers of both DC subtypes inversely correlated with the tumor size. Numbers of CD8 T cells specific for a dominant tumor antigen were increased at TDLNs by each separate treatment but only with slight augments due to the combination. Combined antitumor effects of the therapeutic strategy were also seen on subcutaneous TC-1 tumors established for 24 days before treatment onset. The described strategy is realistic because (i) agents of each kind are clinically available and (ii) equivalent procedures in humans are feasible.

Better understanding tumor-host interaction in head and neck cancer to improve the design and development of immunotherapeutic strategies

Head and neck cancers are heavily infiltrated by immune cells, the significance of which is complex. The natural immune response against head and neck tumors, including anti-human papillomavirus (HPV) T cells, and humoral responses has been clearly documented. However, during the course of tumor progression, co-option of the immune system by tumor cells for their own advantage and increased resistance of tumor cells to immune attack also occur. Inflammation and immune subversion to support angiogenesis are key factors promoting tumor growth. Only a better understanding of this tumor-host interaction will permit a rational design of new immunotherapeutic approaches combining immunostimulation with drugs endowed with the ability to counteract immunoevasion mechanisms.

Induction of anti-Tat neutralizing antibodies by the CyaA vector targeting dendritic cells: influence of the insertion site and of the delivery of multicopies of the dominant Tat B-cell epitope

HIV-Tat based vaccines have been proposed as an attractive option to prevent or treat AIDS. A vaccine to induce optimal anti-Tat neutralizing antibody responses was designed by inserting this protein, or its dominant B-cell epitope, into the CyaA vector, which targets dendritic cells (DC). Tat was inserted into various sites of CyaA, including regions that do not translocate into the cytosol of the targeted DC. The presentation of the Tat CD4(+) T-cell epitope delivered by the CyaA-Tat proteins was observed with a recombinant CyaA in which the entire AC domain was replaced by the entire Tat protein (Tat-Δ373 CyaA) but was abolished with large deletions of the N-terminal region. Moreover, CyaA carrying multiple copies of the dominant Tat: 1-21 B-cell epitope were shown to induce high titers of anti-Tat antibodies, even after a single immunization, that persisted up to 10 weeks post-immunization.

Induction of human papillomavirus oncogene-specific CD8 T-cell effector responses in the genital mucosa of vaccinated mice

Cervical cancer, the second leading cause of cancer mortality in women worldwide, results from infection with a subset of human papillomaviruses (HPV), HPV-16 being the most prevalent type. The available prophylactic vaccines are an effective strategy to prevent this cancer in the long term. However, they only target 70-80% of all cervical cancers and cannot control existing HPV infections and associated lesions. Therapeutic vaccines are thus necessary for women who cannot benefit from prophylactic vaccination. Induction of protective immune responses in the genital mucosa (GM) may be crucial for efficacy of HPV therapeutic vaccines. We report here that mice that received a single subcutaneous (s.c.) vaccination of an adjuvanted long synthetic HPV16 E7(1-98) polypeptide showed induction of 100% tumor protection against s.c. TC-1 tumors and that tumor regression was mainly provided by CD8 T cells. In vivo cytotoxic assay revealed high E7-specific cytolytic T lymphocytes activity in spleen and in genital draining lymph nodes (LN), and E7-specific CD8 T cells could be detected in GM by tetramer staining. More importantly, high-avidity E7-specific INF-gamma secreting CD8 T cells were induced not only in blood, spleen and LN but also in GM of vaccinated mice, thus providing evidence that a parenteral vaccination may be sufficient to provide regression of genital tumors. In addition, there was no correlation between the responses measured in blood with those measured in GM, highlighting the necessity and relevance to determine the immune responses in the mucosa where HPV-tumors reside.

Dendritic cell recovery post-lymphodepletion: a potential mechanism for anti-cancer adoptive T cell therapy and vaccination

Adoptive transfer of autologous tumor-reactive T cells holds promise as a cancer immunotherapy. In this approach, T cells are harvested from a tumor-bearing host, expanded in vitro and infused back to the same host. Conditioning of the recipient host with a lymphodepletion regimen of chemotherapy or radiotherapy before adoptive T cell transfer has been shown to substantially improve survival and anti-tumor responses of the transferred cells. These effects are further enhanced when the adoptive T cell transfer is followed by vaccination with tumor antigens in combination with a potent immune adjuvant. Although significant progress has been made toward an understanding of the reasons underlying the beneficial effects of lymphodepletion to T cell adoptive therapy, the precise mechanisms remain poorly understood. Recent studies, including ours, would indicate a more central role for antigen presenting cells, in particular dendritic cells. Unraveling the exact role of these important cells in mediation of the beneficial effects of lymphodepletion could provide novel pathways toward the rational design of more effective anti-cancer immunotherapy. This article focuses on how the frequency, phenotype, and functions of dendritic cells are altered during the lymphopenic and recovery phases post-induction of lymphodepletion, and how they affect the anti-tumor responses of adoptively transferred T cells.

Consecutive low doses of cyclophosphamide preferentially target Tregs and potentiate T cell responses induced by DNA PLG microparticle immunization

Cyclophosphamide in combination with immunotherapeutic approaches preferentially impinges on T(reg) activity and allows for robust generation of T cell effectors. Reduced dosages of cyclophosphamide are necessary to restrict its cytotoxic effects to the negative regulatory cell populations while sparing effector lymphocytes. We investigated cyclophosphamide dosing in combination with ZYC300, a PLG-encapsulated plasmid DNA vaccine which encodes the cytochrome P450 family member, CYP1B1, a known human tumor-associated antigen. In mice, three consecutive, low doses of cyclophosphamide comprised a superior regimen in enhancing the magnitude, diversity of epitopes, and avidity to individual epitopes of specific T cell responses when compared to regimens that used either a single low or a single high dose. Consecutive low doses of cyclophosphamide predominantly targeted T(regs) while sparing overall T lymphocyte counts. Thus, we report the synergistic activity of pharmacologic T(reg) depletion with cyclophosphamide on quantitatively and qualitatively increasing T cell responses to a known human tumor-associated antigen.

Cyclophosphamide induces bone marrow to yield higher numbers of precursor dendritic cells in vitro capable of functional antigen presentation to T cells in vivo

We have shown recently that cyclophosphamide (CTX) treatment induced a marked increase in the numbers of immature dendritic cells (DCs) in blood, coinciding with enhanced antigen-specific responses of the adoptively transferred CD8(+) T cells. Because this DC expansion was preceded by DC proliferation in bone marrow (BM), we tested whether BM post CTX treatment can generate higher numbers of functional DCs. BM was harvested three days after treatment of C57BL/6 mice with PBS or CTX and cultured with GM-CSF/IL-4 in vitro. Compared with control, BM from CTX-treated mice showed faster generation and yielded higher numbers of DCs with superior activation in response to toll-like receptor (TLR) agonists. Vaccination with peptide-pulsed DCs generated from BM from CTX-treated mice induced comparable adjuvant effects to those induced by control DCs. Taken together, post CTX BM harbors higher numbers of DC precursors capable of differentiating into functional DCs, which be targeted to create host microenvironment riches in activated DCs upon treatment with TLR agonists.

Improving administration regimens of CyaA-based vaccines using TRAP assays to detect antigen-specific CD8(+) T cells directly ex vivo

Vaccination with recombinant adenylate cyclase of Bordetella pertussis (CyaA) carrying antigen is a promising approach to target antigen-presenting cells. We have used Trogocytosis Analysis Protocol (TRAP) assays to monitor immune responses raised by different vaccination regimens with recombinant CyaA carrying the ovalbumin antigen. We find that the intradermal, intramuscular or subcutaneous routes are all superior to intravenous injections, and actually lead to a sufficiently high frequency of reactive CTL to be detected and characterized directly ex vivo by TRAP assay or other standard assays. Finally, for all routes, we find a clear boosting effect upon re-injection of the vaccine.

Costimulation as a platform for the development of vaccines: a peptide-based vaccine containing a novel form of 4-1BB ligand eradicates established tumors

Vaccines represent an attractive treatment modality for the management of cancer primarily because of their specificity and generation of immunologic memory important for controlling recurrences. However, the efficacy of therapeutic vaccines may require formulations that not only generate effective immune responses but also overcome immune evasion mechanisms employed by progressing tumor. Costimulatory molecules play critical roles in modulating innate, adaptive, and regulatory immunity and have potential to serve as effective immunomodulatory components of therapeutic vaccines. In this study, we tested the function of a novel soluble form of 4-1BB ligand (4-1BBL) costimulatory molecule in modulating innate, adaptive, and regulatory immunity and assessed its therapeutic efficacy in the HPV-16 E7-expressing TC-1 cervical cancer and survivin-expressing 3LL lung carcinoma mouse models. Vaccination with 4-1BBL activated dendritic cells and enhanced antigen uptake, generated CD8(+) T-cell effector/memory responses, and endowed T effector cells refractory to suppression by CD4(+)CD25(+)FoxP3(+) T regulatory cells. Immunization with 4-1BBL in combination with an E7 peptide or survivin protein resulted in eradication of TC-1 and 3LL tumors, respectively. 4-1BBL was more effective than TLR agonists LPS, MPL, and CpG and an agonistic 4-1BB antibody as a component of E7 peptide-based therapeutic vaccine for the generation of immune responses and eradication of TC-1 established tumors in the absence of detectable toxicity. Therapeutic efficacy was associated with reversal of tumor-mediated nonresponsiveness/anergy as well as establishment of long-term CD8(+) T-cell memory. Potent pleiotropic immunomodulatory activities combined with lack of toxicity highlight the potential of 4-1BBL molecule as an effective component of therapeutic cancer vaccines.

Evaluation of bioluminescent imaging for noninvasive monitoring of colorectal cancer progression in the liver and its response to immunogene therapy

Background

Bioluminescent imaging (BLI) is based on the detection of light emitted by living cells expressing a luciferase gene. Stable transfection of luciferase in cancer cells and their inoculation into permissive animals allows the noninvasive monitorization of tumor progression inside internal organs. We have applied this technology for the development of a murine model of colorectal cancer involving the liver, with the aim of improving the pre-clinical evaluation of new anticancer therapies.

Results

A murine colon cancer cell line stably transfected with the luciferase gene (MC38Luc1) retains tumorigenicity in immunocompetent C57BL/6 animals. Intrahepatic inoculation of MC38Luc1 causes progressive liver infiltration that can be monitored by BLI. Compared with ultrasonography (US), BLI is more sensitive, but accurate estimation of tumor mass is impaired in advanced stages. We applied BLI to evaluate the efficacy of an immunogene therapy approach based on the liver-specific expression of the proinflammatory cytokine interleukin-12 (IL-12). Individualized quantification of light emission was able to determine the extent and duration of antitumor responses and to predict long-term disease-free survival.

Conclusion

We show that BLI is a rapid, convenient and safe technique for the individual monitorization of tumor progression in the liver. Evaluation of experimental treatments with complex mechanisms of action such as immunotherapy is possible using this technology.