Topical TLR9 agonists induce more efficient cross-presentation of injected protein antigen than parenteral TLR9 agonists do

Topically Applied Resiquimod versus Imiquimod as a Potential Adjuvant in Melanoma Treatment

Melanoma is the most lethal form of skin cancer and surgery remains the preferred and most effective treatment. Nevertheless, there are cases where surgery is not a viable method and alternative treatments are therefore adopted. One such treatment that has been tested is topical 5% imiquimod (IMQ) cream, which, although showing promise as a treatment for melanoma, has been found to have undesirable off-target effects. Resiquimod (RSQ) is an immunomodulatory molecule that can activate immune responses by binding to Toll-like receptors (TLR) 7 and 8 and may be more effective than IMQ in the context of melanoma treatment. RSQ can cross the stratum corneum (SC) easily without requiring pretreatment of the skin. In a gel formulation, RSQ has been studied as a monotherapy and adjuvant for melanoma treatment in pre-clinical studies and as an adjuvant in clinical settings. Although side effects of RSQ in gel formulation were also reported, they were never severe enough for the treatment to be suspended. In this review, we discuss the potential use of RSQ as an adjuvant for melanoma treatment.

Cutaneous CpG adjuvant conditioning to enhance vaccine responses

Adjuvant activity of the Toll receptor 9 agonist CpG 1826 was compared when given subcutaneously (s.c.) together with ovalbumin (s.c.[CpG + Ova]), or when given by either s.c. or intradermally (i.d.) routes two days prior to s.c. ovalbumin. Frequencies of CD8 + effector (T_EFF) and central memory (T_CM) T cells along with total IgG, IgG2c, and IgG1 titres were measured to ascertain how timing and location of CpG conditioning influenced vaccination outcome. Prior treatment with CpG enhanced T_EFF, T_CM, as well as total IgG responses. T_EFF and T_CM responses were greatest when CpG was given intradermally and prior to s.c. ovalbumin, conditions that eliminated the fraction of T_CM 'non-responders' observed after s.c.[CpG + Ova] vaccination. IgG responses were polarized toward IgG2c after early s.c. CpG but toward IgG1 after early i.d. CpG. Separating CpG adjuvant and antigen application in time and space can improve vaccination outcome.

Topical Adjuvant Application during Subcutaneous Vaccination Promotes Resident Memory T Cell Generation

Skin tissue resident memory T cells (T_RM) provide superior protection to a second infection. In this study, we evaluated the use of topical CpG oligodeoxynucleotide (ODN) as adjuvant to generate skin T_RM in mice. Topical or s.c. CpG ODN adjuvant administration at the time of a s.c. Ag injection led to an accumulation of CD103^- CD8 T cells in the epidermis. However, only mice with CpG ODN administered topically had significant numbers of CD103⁺ Ag-specific CD8 T cells persisting in the local epidermal skin, enhanced circulating memory cells in the blood, and showed protection from intradermal challenge with melanoma cells. Generation of Ag-specific CD8 T cells was dependent on TLR9 expression on hematopoietic cells and partially dependent on receptor expression on stromal cells. Topical challenge of immunized mice at a distal site led to significant expansion of Ag-specific T cells in the blood and accumulation in the challenged skin. We demonstrate that local and systemic T cell memory can be generated with topical CpG ODN at the time of s.c. immunization, suggesting a new method of enhancing current vaccine formulations to generate tissue T_RM.

Topical CpG Oligodeoxynucleotide Adjuvant Enhances the Adaptive Immune Response against Influenza A Infections

Current influenza vaccines generate humoral immunity, targeting highly variable epitopes and thus fail to achieve long-term protection. T cells recognize and respond to several highly conserved epitopes across influenza serotypes. A strategy of raising strong cytotoxic T cell memory responses to epitopes conserved across serotypes would provide cross serotype protection, eliminating the need for annual vaccination. We explored the adjuvant potential of epicutaneous (ec) and subcutaneous (sc) delivery of CpG oligodeoxynucleotide in conjunction with sc protein immunization to improve protection against influenza A virus (IAV) infections using a mouse model. We found enhanced long-term protection with epicutaneous CpG ODN (ecCpG) compared to subcutaneous CpG ODN (scCpG) as demonstrated by reduced viral titers in the lungs. This correlated with increased antigen-specific CD8 T cells in the airways and the lungs. The memory T cell response after immunization with ecCpG adjuvant was comparable to memory response by priming with IAV infection in the lungs. In addition, ecCpG was more efficient than scCpG in inducing the generation of IFN-γ producing CD4 T cells. The adjuvant effect of ecCpG was accompanied with its ability to modulate tissue-homing molecules on T cells that may direct them to the site of infection. Together, this work provides evidence for using ecCpG to induce strong antibody and memory T cell responses to confer protection against IAV infection.

Topical CpG adjuvantation of a protein-based vaccine induces protective immunity to Listeria monocytogenes

Robust CD8(+) T cell responses are essential for immune protection against intracellular pathogens. Using parenteral administration of ovalbumin (OVA) protein as a model antigen, the effect of the Toll-like receptor 9 (TLR9) agonist, CpG oligodeoxynucleotide (ODN) 1826, as an adjuvant delivered either topically, subcutaneously, or intramuscularly on antigen-specific CD8(+) T cell responses in a mouse model was evaluated. Topical CpG adjuvant increased the frequency of OVA-specific CD8(+) T cells in the peripheral blood and in the spleen. The more effective strategy to administer topical CpG adjuvant to enhance CD8(+) T cell responses was single-dose administration at the time of antigen injection with a prime-boost regimen. Topical CpG adjuvant conferred both rapid and long-lasting protection against systemic challenge with recombinant Listeria monocytogenes expressing the cytotoxic T lymphocyte (CTL) epitope of OVA(257-264) (strain Lm-OVA) in a TLR9-dependent manner. Topical CpG adjuvant induced a higher proportion of CD8(+) effector memory T cells than parenteral administration of the adjuvant. Although traditional vaccination strategies involve coformulation of antigen and adjuvant, split administration using topical adjuvant is effective and has advantages of safety and flexibility. Split administration of topical CpG ODN 1826 with parenteral protein antigen is superior to other administration strategies in enhancing both acute and memory protective CD8(+) T cell immune responses to subcutaneous protein vaccines. This vaccination strategy induces rapid and persistent protective immune responses against the intracellular organism L. monocytogenes.

Adaptor protein 1 promotes cross-presentation through the same tyrosine signal in major histocompatibility complex class I as that targeted by HIV-1

Certain antigen-presenting cells (APCs) process and present extracellular antigen with major histocompatibility complex class I (MHC-I) molecules to activate naive CD8(+) T cells in a process termed cross-presentation. We used insights gained from HIV immune evasion strategies to demonstrate that the clathrin adaptor protein adaptor protein 1 (AP-1) is necessary for cross-presentation by MHC-I molecules containing a cytoplasmic tail tyrosine signal (murine MHC-I molecules, human MHC-I HLA-A and HLA-B allotypes). In contrast, AP-1 activity was not needed for cross-presentation by MHC-I molecules containing a human MHC-I HLA-C cytoplasmic tail, which does not contain a tyrosine signal. AP-1 activity was also dispensable for presentation of endogenous antigens by MHC-I via the classical pathway. In APCs, we show that HIV Nef disrupts cross-presentation by MHC-I containing the tyrosine signal but does not affect cross-presentation by MHC-I containing the HLA-C cytoplasmic tail. Thus, we provide evidence for two separable cross-presentation pathways, only one of which is targeted by HIV.

The role of heat shock proteins in antigen cross presentation

Heat shock proteins (HSPs) are molecular chaperones that bind tumor antigens and mediate their uptake into antigen presenting cells. HSP–antigen complexes are then directed toward either the MHC class I pathway through antigen cross presentation or the conventional class II pathway, leading to activation of T cell subsets. Uptake of HSP-chaperoned polypeptides can involve both receptor-mediated and receptor-independent routes, and mechanisms of antigen sorting between the Class I and II pathways after uptake are currently under investigation. The processes involved in internalization of HSP–antigen complexes differ somewhat from the mechanisms previously determined for (unchaperoned) particulate and free soluble antigens. A number of studies show that HSP-facilitated antigen cross presentation requires uptake of the complexes by scavenger receptors (SR) followed by processing in the proteasome, and loading onto MHC class I molecules. In this review we have examined the roles of HSPs and SR in antigen uptake, sorting, processing, cell signaling, and activation of innate and adaptive immunity.

Poly(methyl vinyl ether-co-maleic anhydride) nanoparticles as innate immune system activators

Adjuvant research is being oriented to TLR-agonists, but complement activation has been relatively unexplored. In previous studies it was demonstrated that poly(methyl vinyl ether-co-maleic anhydride) nanoparticles (PVMA NPs) used as adjuvant differentially activate dendritic cells through toll like receptors (TLR) stimulation, however, a high dose of these NPs was used. Now, we demonstrated a dose-response effect, with a concentration as low as 20μg/mL able to stimulate TLR2 and TLR4 transfected dendritic cells. In addition, we investigated whether PVMA NPs are able to exploit also the immunomodulatory benefits of complement activation. Results indicated that the hydroxylated surface of these NPs highly activated the complement cascade, as measured by adsorption studies and a complement fixation bioassay. Stable binding of C3b to NPs was confirmed as indicated by lability to SDS treatment after washing resistance. Complement consumption was confirmed as the lytic capacity of complement exposed to NPs was abolished against antibody-sensitized sheep erythrocytes, with a minimal inhibitory concentration of 50μg NPs, equivalent to a surface of 1cm(2). On the contrary, nanoparticles prepared with poly(lactic-co-glycolic acid) (PLGA), used as a reference, did not consume complement at a concentration ≥3mg NPs (≥40cm(2)). Complement consumption was inhibited when PVMA NPs were cross-linked with diamino groups (1,3-diaminopropane), indicating the role of hydroxyl groups as responsible of the phenomenon. These results favour a model whereby PVMA NPs adjuvant activate complement on site to attract immature antigen presenting cells that are activated through TLR2 and TLR4.

CpG oligodeoxynucleotides as TLR9 agonists: therapeutic applications in cancer

Toll-like receptors (TLRs) are part of the innate immune system, and they belong to the pattern recognition receptors (PRR) family. The PRR family is designed to recognize and bind conserved pathogen-associated molecular patterns, which are not generated by the host and are restricted and essential to micro-organisms. TLR9, which recognizes unmethylated CpG (cytosine guanosine dinucleotide), is a very promising target for therapeutic activation. Stimulation of TLR9 activates human plasmacytoid dendritic cells and B cells, and results in potent T helper-1 (T(h)1)-type immune responses and antitumor responses in mouse tumor models and in patients. Several pharmaceutical companies, such as Pfizer, Idera, and Dynavax, are developing CpG oligodeoxynucleotides (ODNs) for the treatment of cancer, along with other conditions, such as infections and allergy. CpG ODNs have shown promising results as vaccine adjuvants and in combination with cancer immunotherapy. Several TLR9 agonists are being developed and have entered clinical trials to evaluate their safety and efficacy for the treatment of several hematopoietic and solid tumors. In this review, we discuss the use of CpG ODNs in several phase I and II clinical trials for the treatment of NHL, renal cell carcinoma, melanoma, and non-small cell lung cancer, either alone or in combination with other agents.

CD4+ and CD8+ T cells can act separately in tumour rejection after immunization with murine pneumotropic virus chimeric Her2/neu virus-like particles

Background

Immunization with murine pneumotropic virus virus-like particles carrying Her2/neu (Her2MPtVLPs) prevents tumour outgrowth in mice when given prophylactically, and therapeutically if combined with the adjuvant CpG. We investigated which components of the immune system are involved in tumour rejection, and whether long-term immunological memory can be obtained.

Methodology and Results

During the effector phase in BALB/c mice, only depletion of CD4⁺ and CD8⁺ in combination, with or without NK cells, completely abrogated tumour protection. Depletion of single CD4⁺, CD8⁺ or NK cell populations only had minor effects. During the immunization/induction phase, combined depletion of CD4⁺ and CD8⁺ cells abolished protection, while depletion of each individual subset had no or negligible effect. When tumour rejection was studied in knock-out mice with a C57Bl/6 background, protection was lost in CD4^−/−CD8^−/− and CD4^−/−, but not in CD8^−/− mice. In contrast, when normal C57Bl/6 mice were depleted of different cell types, protection was lost irrespective of whether only CD4⁺, only CD8⁺, or CD4⁺ and CD8⁺ cells in combination were eradicated. No anti-Her2/neu antibodies were detected but a Her2/neu-specific IFNγ response was seen. Studies of long-term memory showed that BALB/c mice could be protected against tumour development when immunized together with CpG as long as ten weeks before challenge.

Conclusion

Her2MPtVLP immunization is efficient in stimulating several compartments of the immune system, and induces an efficient immune response including long-term memory. In addition, when depleting mice of isolated cellular compartments, tumour protection is not as efficiently abolished as when depleting several immune compartments together.

Poly(anhydride) nanoparticles act as active Th1 adjuvants through Toll-like receptor exploitation

The mechanisms that underlie the potent Th1-adjuvant capacity of poly(methyl vinyl ether-co-maleic anhydride) nanoparticles (NPs) were investigated. Traditionally, polymer NPs have been considered delivery systems that promote a closer interaction between antigen and antigen-presenting cells (APCs). Our results revealed that poly(anhydride) NPs also act as agonists of various Toll-like receptors (TLRs) (TLR2, -4, and -5), triggering a Th1-profile cytokine release (gamma interferon [IFN-gamma], 478 pg/ml versus 39.6 pg/ml from negative control; interleukin-12 [IL-12], 40 pg/ml versus 7.2 pg/ml from negative control) and, after incubation with dendritic cells, inducing a 2.5- to 3.5-fold increase of CD54 and CD86 costimulatory molecule expression. Furthermore, in vivo studies suggest that NPs actively elicit a CD8(+) T-cell response. Immunization with empty NPs resulted in a significant delay in the mean survival date (from day 7 until day 23 postchallenge) and a protection level of 30% after challenge against a lethal dose of Salmonella enterica serovar Enteritidis. Taken together, our results provide a better understanding of how NPs act as active Th1 adjuvants in immunoprophylaxis and immunotherapy through TLR exploitation.

Conditioning of the injection site with CpG enhances the migration of adoptively transferred dendritic cells and endogenous CD8+ T-cell responses

The efficiency of immunotherapy using tumor-antigen-loaded dendritic cells (DCs) is severely limited by the impaired migration of injected cells from the application site to the draining lymph nodes. As described earlier, pretreatment of the injection site with inflammatory cytokines enhances DC migration. We wanted to test whether toll-like receptor (TLR) ligands can improve migration of murine bone marrow-derived DC (BMDC) and the subsequent T-cell responses. For this purpose, we established an experimental setup closely resembling human vaccination protocols that served to investigate DC migration from the skin to the draining lymph nodes. We observed that BMDC, matured with a cytokine cocktail (tumor necrosis factor-alpha, interleukin-beta, interleukin-6, prostaglandin E2), strongly expressed CCR7. The migration efficiency of adoptively transferred mature BMDCs was determined by the number of cells injected and the application site. We decided to inject DC intradermally into the ear skin and investigated the effects of pretreatment of the injection site with various TLR ligands. Conditioning of the skin site with the TLR ligands CpG and Peptidoglycan increased the number of DCs arriving in the lymph node. Mechanical stress applied to the skin, such as tape stripping of the skin was equally effective. Importantly, only pretreatment with CpG enhanced responses of endogenous CD8 T cells. Thus, conditioning of the injection site with the TLR ligand CpG could be a new promising way to improve the outcome of DC immunotherapy.

Topical resiquimod promotes priming of CTL to parenteral antigens

We explored the topical use of resiquimod (R-848), a Toll-like receptor (TLR) 7/8 agonist, in gel formulation, to enhance cross-priming to subcutaneously administered protein antigen in a murine model. Resiquimod application at the time of subcutaneous administration of ovalbumin generated robust antigen-specific CTL as detected by tetramers, IFN-gamma ELISPOT assays and standard cytotoxicity assays. Induced CTL were capable of mediating antigen-specific killing in vivo as measured by in vivo cytotoxicity assays and an ability to protect against B16-OVA tumor challenge. Multiple serial applications of topical resiquimod increased the frequency of antigen-specific CTL when compared to single application. This enhanced frequency was noted despite a marked inhibition of adjuvant mediated pro-inflammatory cytokine release following repeated administration. Topical resiquimod is a potent adjuvant for locally administered subcutaneous vaccines, inducing clinically relevant CTL responses following single application at the time of subcutaneous vaccination.

Topical CpG enhances the response of murine malignant melanoma to dacarbazine

Malignant melanoma is a potentially fatal skin cancer that is increasing in incidence. Standard chemoimmunotherapy consisting of dacarbazine (DTIC) given with IFN-alpha has had disappointing results. We describe a chemoimmunotherapy protocol for cutaneous melanoma that combines the administration of DTIC with the topical application of CpG oligodinucleotide (ODN). Subcutaneous B16 melanoma tumors in C57BL/6 mice were treated with intraperitoneal injections of DTIC followed by the topical application of CpG-ODN over the tumors. This therapeutic approach abrogated the growth of established tumors and significantly enhanced survival. Topical CpG application was more effective than intratumoral CpG. Cell depletion studies indicated that the antitumor effect was dependent on both CD4(+) and CD8(+) cells but not on natural killer (NK) cells. Tumor-specific cytotoxic T-lymphocyte activity was generated in treated animals and was highest in topically treated animals. Immunohistochemical analysis revealed that DTIC, but not CpG, enhanced tumor cell apoptosis. Further, topical CpG induced an expansion of a B220(+)CD8(+) subset of dendritic cells and a subset of NK1.1(+) CD11c(+) cells within the tumors. By enhancing both tumor cell death and local immune activation, DTIC/topical CpG chemoimmunotherapy induced an effective T-cell-dependent host-immune response against melanoma.