Polycarbonate-based ultra-pH sensitive nanoparticles improve therapeutic window

Stimuli-sensitive nanomaterials with cooperative response are capable of converting subtle and gradual biological variations into robust outputs to improve the precision of diagnostic or therapeutic outcomes. In this study, we report the design, synthesis and characterization of a series of degradable ultra-pH sensitive (dUPS) polymers that amplify small acidic pH changes to efficacious therapeutic outputs. A hydrolytically active polycarbonate backbone is used to construct the polymer with pH-dependent degradation kinetics. One dUPS polymer, PSC7A, can achieve activation of the stimulator of interferon genes and antigen delivery upon endosomal pH activation, leading to T cell-mediated antitumor immunity. While a non-degradable UPS polymer induces granulomatous inflammation that persists over months at the injection site, degradable PSC7A primes a transient acute inflammatory response followed by polymer degradation and complete tissue healing. The improved therapeutic window of the dUPS polymers opens up opportunities in pH-targeted drug and protein therapy.

Multimodal stratified imaging of nanovaccines in lymph nodes for improving cancer immunotherapy

Vaccines hold enormous potential in cancer immunotherapy by stimulating the body's immune response; unfortunately, the clinical response rates of cancer vaccines are less than 30%. Nanovaccines show the potential to enhance the treatment efficacy of conventional vaccines due to their unique properties, such as efficient co-delivery of cocktail to the secondary lymphatic system, high tumor accumulation and penetration, and customizable delivery of antigens and adjuvants. Meanwhile, the non-invasive visualization of vaccines after their delivery can yield information about in vivo distribution and performance, and aid in their subsequent optimization and translational studies. In this review, we summarize the strategies for the spatiotemporal visualization of nanovaccines in lymph nodes, including whole-body in vivo imaging, intravital organ/cell imaging, and ex vivo tissue/cell imaging. The application of imaging modalities in nanovaccine development is discussed. Moreover, strategies to achieve different combinations of imaging modalities are proposed.

Tumor growth inhibition by mSTEAP peptide nanovaccine inducing augmented CD8+ T cell immune responses

Poly(lactic-co-glycolic) acid (PLGA) has been successfully used in drug delivery and biomaterial applications, but very little attention has been directed towards the potential in vivo effects of peptide-loaded PLGA nanoparticles (NPs), specifically the potency of intravenous (IV) STEAP peptide-loaded PLGA-NP (nanovaccine) dosing and whether STEAP-specific CD8⁺ T cells directly play a key role in tumor inhibition. To address these concerns, syngeneic prostate cancer mouse models were established and treated with either mSTEAP peptide emulsified in incomplete Freund's adjuvant (IFA) via subcutaneous (SC) injection or mSTEAP peptide nanovaccine containing the same amount of peptide via IV or SC injection. Meanwhile, mice were treated with either CD8b mAb followed by nanovaccine treatment, free mSTEAP peptide, or empty PLGA-NPs. Immune responses in these mice were examined using cytotoxicity assays at 14 days after treatment. Tumor size and survival in various treatment groups were measured and monitored. The results demonstrated that mSTEAP peptide nanovaccine resulted in tumor inhibition by eliciting a significantly stronger CD8⁺ T cell immune response when compared with the controls. Moreover, the survival periods of mice treated with mSTEAP nanovaccine were significantly longer than those of mice treated with mSTEAP peptide emulsified in IFA or the treatment controls. Additionally, it was observed that the peptide nanovaccine was mainly distributed in the mouse liver and lungs after IV injection. These findings suggest that the peptide nanovaccine is a promising immunotherapeutic approach and offers a new opportunity for prostate cancer therapies.

Hybrid nanovaccine for the co-delivery of the mRNA antigen and adjuvant

For efficient cancer vaccines, the antitumor function largely relies on cytotoxic T cells, whose activation can be effectively induced via antigen-encoding mRNA, making mRNA-based cancer vaccines an attractive approach for personalized cancer therapy. While the liposome-based delivery system enables the systemic delivery and transfection of mRNA, incorporating an adjuvant that is non-lipid like remains challenging, although the co-delivery of mRNA (antigen) and effective adjuvant is key to the activation of the cytotoxic T cells. This is because the presence of an adjuvant is important for dendritic cell maturation-another necessity for cytotoxic T cell activation. In the present work, we designed a poly (lactic-co-glycolic acid) (PLGA)-core/lipid-shell hybrid nanoparticle carrier for the co-delivery of mRNA and gardiquimod (adjuvant that cannot be incorporated into the lipid shell). We demonstrated in the present work that the co-delivery of mRNA and gardiquimod led to the effective antigen expression and DC maturation in vitro. The intravenous administration of the hybrid nanovaccine resulted in the enrichment of mRNA expression in the spleen and a strong immune response in vivo. The simultaneous delivery of the antigen and adjuvant both spatially and temporally via the core/shell nanoparticle carrier is found to be beneficial for tumor growth inhibition.

Targeted Codelivery of an Antigen and Dual Agonists by Hybrid Nanoparticles for Enhanced Cancer Immunotherapy

Among approaches of current cancer immunotherapy, a dendritic cell (DC)-targeted vaccine based on nanotechnology could be a promising way to efficiently induce potent immune responses. To enhance DC targeting and vaccine efficiency, we included imiquimod (IMQ), a toll-like receptor 7/8 (TLR 7/8) agonist, and monophosphoryl lipid A (MPLA), a TLR4 agonist, to synthesize lipid-polymer hybrid nanoparticles using PCL-PEG-PCL and DOTAP (IMNPs) as well as DSPE-PEG-mannose (MAN-IMNPS). The spatiotemporal delivery of MPLA (within the outer lipid layer) to extracellular TLR4 and IMQ (in the hydrophobic core of NPs) to intracellular TLR7/8 can activate DCs synergistically to improve vaccine efficacy. Ovalbumin (OVA) as a model antigen was readily absorbed by positively charged DOTAP and showed a quick release in vitro. Our results demonstrated that this novel nanovaccine enhanced cellular uptake, cytokine production, and maturation of DCs. Compared with the quick metabolism of free OVA-agonists, the depot effect of OVA-IMNPs was observed, whereas MAN-OVA-IMNPs promoted trafficking to secondary lymphoid organs. After immunization with a subcutaneous injection, the nanovaccine, especially MAN-OVA-IMNPs, induced more antigen-specific CD8⁺ T cells, greater lymphocyte activation, stronger cross-presentation, and more generation of memory T cells, antibody, IFN-γ, and granzyme B. Prophylactic vaccination of MAN-OVA-IMNPs significantly delayed tumor development and prolonged the survival in mice. The therapeutic tumor challenge indicated that MAN-OVA-IMNPs prohibited tumor progression more efficiently than other formulations, and the combination with an immune checkpoint blockade further enhanced antitumor effects. Hence, the DC-targeted vaccine codelivery with IMQ and MPLA adjuvants by hybrid cationic nanoparticles in a spatiotemporal manner is a promising multifunctional antigen delivery system in cancer immunotherapy.

Immunostimulatory nanomedicines synergize with checkpoint blockade immunotherapy to eradicate colorectal tumors

Nanoparticles can potentially stimulate tumour microenvironments to elicit antitumour immunity. Herein, we demonstrate effective immunotherapy of colorectal cancer via systemic delivery of an immunostimulatory chemotherapeutic combination in nanoscale coordination polymer (NCP) core-shell particles. Oxaliplatin and dihydroartemesinin have contrasting physicochemical properties but strong synergy in reactive oxygen species (ROS) generation and anticancer activity. The combined ROS generation is harnessed for immune activation to synergize with an anti-PD-L1 antibody for the treatment of murine colorectal cancer tumours. The favourable biodistribution and tumour uptake of NCPs and the absence of peripheral neuropathy allow for repeated dosing to afford 100% tumour eradication. The involvement of innate and adaptive immune systems elicit strong and long lasting antitumour immunity which prevents tumour formation when cured mice are challenged with cancer cells. The intrinsically biodegradable, well tolerated, and systemically available immunostimulatory NCP promises to enter clinical testing as an immunotherapy against colorectal cancer.

Enhanced endoplasmic reticulum entry of tumor antigen is crucial for cross-presentation induced by dendritic cell-targeted vaccination

Efficient cross-presentation of protein Ags to CTLs by dendritic cells (DCs) is essential for the success of prophylactic and therapeutic vaccines. In this study, we report a previously underappreciated pathway involving Ag entry into the endoplasmic reticulum (ER) critically needed for T cell cross-priming induced by a DC-targeted vaccine. Directing the clinically relevant, melanoma Ag gp100 to mouse-derived DCs by molecular adjuvant and chaperone Grp170 substantially facilitates Ag access to the ER. Grp170 also strengthens the interaction of internalized protein Ag with molecular components involved in ER-associated protein dislocation and/or degradation, which culminates in cytosolic translocation for proteasome-dependent degradation and processing. Targeted disruption of protein retrotranslocation causes exclusive ER retention of tumor Ag in mouse bone marrow-derived DCs and splenic CD8(+) DCs. This results in the blockade of Ag ubiquitination and processing, which abrogates the priming of Ag-specific CD8(+) T cells in vitro and in vivo. Therefore, the improved ER entry of tumor Ag serves as a molecular basis for the superior cross-presenting capacity of Grp170-based vaccine platform. The ER access and retrotranslocation represents a distinct pathway that operates within DCs for cross-presentation and is required for the activation of Ag-specific CTLs by certain vaccines. These results also reinforce the importance of the ER-associated protein quality control machinery and the mode of the Ag delivery in regulating DC-elicited immune outcomes.

Phase I study utilizing a novel antigen-presenting cell-targeted vaccine with Toll-like receptor stimulation to induce immunity to self-antigens in cancer patients

PURPOSE

The use of tumor-derived proteins as cancer vaccines is complicated by tolerance to these self-antigens. Tolerance may be broken by immunization with activated, autologous, ex vivo generated and antigen-loaded, antigen-presenting cells (APC); however, targeting tumor antigen directly to APC in vivo would be a less complicated strategy. We wished to test whether targeted delivery of an otherwise poorly immunogenic, soluble antigen to APC through their mannose receptors (MR) would induce clinically relevant immunity.

EXPERIMENTAL DESIGN

Two phase I studies were conducted with CDX-1307, a vaccine composed of human chorionic gonadotropin beta-chain (hCG-β) fused to an MR-specific monoclonal antibody, administered either locally (intradermally) or systemically (intravenously) in patients with advanced epithelial malignancies. An initial dose escalation of single-agent CDX-1307 was followed by additional cohorts of CDX-1307 combined with granulocyte-macrophage colony-stimulating factor (GM-CSF) and the Toll-like receptor (TLR) 3 agonist polyinosinic-polycytidylic acid (poly-ICLC) and TLR7/8 agonist resiquimod to activate the APC.

RESULTS

CDX-1307 induced consistent humoral and T-cell responses to hCG-β when coadministered with TLR agonists. Greater immune responses and clinical benefit, including the longest duration of stable disease, were observed with immunization combined with local TLR agonists. Immune responses were induced equally efficiently in patients with elevated and nonelevated levels of serum hCG-β. Antibodies within the serum of vaccinated participants had tumor suppressive function in vitro. Toxicity consisted chiefly of mild injection site reactions.

CONCLUSIONS

APC targeting and activation induce adaptive immunity against poorly immunogenic self-antigens which has implications for enhancing the efficacy of cancer immunotherapy.

[Preparation and antitumor immunity of long circulating nano-liposome encapsulated tumor specific antigen]

AIM

To prepare Nano-Liposome encapsulated MAGE3/HSP70(NL M3H) and study its character and antitumor immunity in mouse.

METHODS

NL M3H was prepared by the thin film-dispersion ultrasonic. The shape and size of NL M3H were detected by electron microscope. The encapsulation rate, drug-carrying capacity, stability and the releasing character were tested by Sephedex-G100 gel filtration. The mouse was immunized by NL M3H, and the antitumor immunity was detected by ELISPOT and LDH release assay.

RESULTS

The mean size of NL M3H was lower than 100 nm. The encapsulation rate was 38%.The drug content was 0.038 g/L. NL M3H has good stability after stored in 4 degrees C for 6 months. The releasing profile showed that 74 percent of proteins was released during the first 24 hours in saline. The results of ELISPOT and LDH release assay showed that NL M3H generated tumor specific cytotoxic T lymphocyte(CTL)to damage tumor cell.

CONCLUSION

NL M3H has novel characters, it can generate specific CTL to kill tumor cell, and can be used as new kind of vaccine against tumor.

Use of radiolabeled monoclonal antibody to enhance vaccine-mediated antitumor effects

Radiolabeled monoclonal antibodies (mAb) have demonstrated measurable antitumor effects in hematologic malignancies. This outcome has been more difficult to achieve for solid tumors due, for the most part, to difficulties in delivering sufficient quantities of mAb to the tumor mass. Previous studies have shown that nonlytic levels of external beam radiation can render tumor cells more susceptible to T cell-mediated killing. The goal of these studies was to determine if the selective delivery of a radiolabeled mAb to tumors would modulate tumor cell phenotype so as to enhance vaccine-mediated T-cell killing. Here, mice transgenic for human carcinoembryonic antigen (CEA) were transplanted with a CEA expressing murine carcinoma cell line. Radioimmunotherapy consisted of yttrium-90 (Y-90)-labeled anti-CEA mAb, used either alone or in combination with vaccine therapy. A single dose of Y-90-labeled anti-CEA mAb, in combination with vaccine therapy, resulted in a statistically significant increase in survival in tumor-bearing mice over vaccine or mAb alone; this was shown to be mediated by engagement of the Fas/Fas ligand pathway. Mice receiving the combination therapy also showed a significant increase in the percentage of viable tumor-infiltrating CEA-specific CD8(+) T cells compared to vaccine alone. Mice cured of tumors demonstrated an antigen cascade resulting in CD4(+) and CD8(+) T-cell responses not only for CEA, but for p53 and gp70. These results show that systemic radiotherapy in the form of radiolabeled mAb, in combination with vaccine, promotes effective antitumor response, which may have implications in the design of future clinical trials.

Longitudinal microSPECt/CT imaging and pharmacokinetics of synthetic luteinizing hormone-releasing hormone (LHRH) vaccine in rats

BACKGROUND

Luteinizing hormone-releasing hormone (LHRH)-derived decapeptide-based vaccines have been used in studies of immunocastration and immunotherapy of prostate cancer, but no image data are available on the kinetics of vaccines post injection (p.i.). Therefore, an 131I radiolabeled LHRH-derived immunogen was developed to visualize and evaluate the retention of LHRH-derived vaccines in rats.

MATERIALS AND METHODS

The LHRH immunogens, which contained equal moles of 131I-p607E, p667 and p500, were formulated with an equal volume of an adjuvant, Montanide ISA50. MicroSPECT/CT imaging was performed to visualize the retention of the radiolabeled immunogen up to 30 days after intramuscular inoculation of 25 microg immunogens. The pharmacokinetics, distribution and excretion were also evaluated.

RESULTS

The radiochemical purity of 131I-p607E was 97.85+/-2.12%. The longitudinal microSPECT/CT imaging revealed that most 131I-p607E was retained at the injected muscle site until 30 days p.i.. Biodistribution showed that 34.56+/-4.27% of radioactivity remained at the injected muscle site at 28 days p.i.. The cumulative radioactivity excreted via urine was 30.02+/-3.82% up to day 28 p.i.. The elimination half-life (t1/2), Tmax and Cmax were 158.67 h, 24 h, and 0.026 percentage of injected dose per gram (%ID/g), respectively.

CONCLUSION

The LHRH immunogen, 131I-p607E, was mainly retained at the intramuscular injection site during the whole study period. The microSPECTICT imaging modality can be used to monitor the location and distribution of the LHRH immunogen, 131I-p607E, in a rat model.

Drug evaluation: Therion's rV-PSA-TRICOM + rF-PSA-TRICOM prime-boost prostate cancer vaccine

Therion Biologics Corp is developing PROSTVAC-VF-TRICOM, a prime-boost vaccine regimen that consists of a priming injection with a recombinant attenuated vaccinia virus expressing PSA and TRICOM (the company's proprietary triad of costimulatory molecules: ICAM-1, B7.1 and lymphocyte function-associated antigen-3), and a booster injection with a fowlpox virus expressing the same combination, for the potential treatment of prostate cancer. Phase II clinical trials are underway.

Preclinical safety and biodistribution of adenovirus-based cancer vaccines after intradermal delivery

The recombinant adenoviral (Ad) vector is being considered as a cancer vaccine platform because it efficiently induces immune responses to tumor antigens by intradermal immunization. The aims of this study were to evaluate the potential toxicities and biodistribution after a single dose or six weekly intradermal doses of Ad2/gp100v2 and Ad2/MART-1v2, which encode tumor-associated antigens gp100 and MelanA/MART-1, respectively. The only dose-related toxicities associated with intradermal administration of these Ad vectors were inflammatory cell infiltrates in the draining lymph nodes and injection sites that persisted 83 days after administration. The biodistribution of Ad DNA as detected by real-time polymerase chain reaction was largely confined to the injection sites and draining lymph nodes of mice treated with either a single dose or multiple doses of Ad vector and in the spleens of mice treated with multiple doses of Ad vector. Adenoviral DNA was transiently detected in the bone marrow, lung, or blood of only one animal for each site and was below the limit of assay quantification (<10 copies/microg DNA). The vector persisted in the skin and lymph nodes as long as 92 days after the last dose. We conclude that Ad vectors delivered by intradermal administration provide a safe, genetic vaccine delivery platform that induces desirable immune responses at the immunization sites and the lymph nodes that, ultimately, result in immune responses specific to the tumor antigens.

Polyarginine-Mediated Protein Delivery to Dendritic Cells Presents Antigen More Efficiently onto MHC Class I and Class II and Elicits Superior Antitumor Immunity

Protein transduction domains (PTDs) have been used increasingly to deliver reagents to a variety of cell types in vitro and in vivo. We have previously shown that HIV TAT-PTD-containing whole protein antigens (Ags)-transduced dendritic cells (DCs) stimulated Ag-specific CD8+ and CD4+ T cells. Although the cytotoxic T lymphocytes (CTL) activity generated was sufficient to prevent engraftment of mice with Ag-expressing tumors, treatment of tumor-bearing mice with TAT-PTD Ag-transduced DCs resulted in tumor regression in some animals. Recently, several other PTDs were reported to promote higher transduction efficiencies than TAT-PTD. To evaluate the role of individual PTDs in induction of immune responses in tumor vaccination studies, we engineered recombinant fusion Ovalbumin (OVA) that contained three differrent PTDs, including the most efficacious known PTD (polyarginine (R9)-PTD). Our results demonstrated that R9-PTD-containing OVA transduced DCs most efficiently, and that transduction efficacy was closely correlated with the extent of Ag-specific CD4+ and CD8+ T-cell activation in vitro and in vivo. Repeated vaccination with R9-PTD-OVA-transduced DC in (OVA-expressing) tumor-bearing mice induced enhanced antitumor immunity, and elicited complete rejection of tumors when DC was co-injected with adjuvants. This vaccination strategy may be clinically applicable, and offers theoretical and practical advantages to those that are in current use.

Drug evaluation: IGN-101--an anti-EpCAM murine antibody vaccine for cancer

Igeneon GmbH, a wholly owned subsidiary of Aphton Corp, is developing IGN-101, an anticancer vaccine containing the EpCAM-targeting aluminum-adsorbed munrine monoclonal antibody 17-1A (edrecolomab), for the potential subcutaneous treatment of epithelial cancers such as colorectal and rectal tumors. By February 2004, Igeneon was seeking to outlicense the drug.

Immunological and antitumor effects of IL-23 as a cancer vaccine adjuvant

The promising, but modest, clinical results of many human cancer vaccines indicate a need for vaccine adjuvants that can increase both the quantity and the quality of vaccine-induced, tumor-specific T cells. In this study we tested the immunological and antitumor effects of the proinflammatory cytokine, IL-23, in gp100 peptide vaccine therapy of established murine melanoma. Neither systemic nor local IL-23 alone had any impact on tumor growth or tumor-specific T cell numbers. Upon specific vaccination, however, systemic IL-23 greatly increased the relative and absolute numbers of vaccine-induced CD8(+) T cells and enhanced their effector function at the tumor site. Although IL-23 specifically increased IFN-gamma production by tumor-specific T cells, IFN-gamma itself was not a primary mediator of the vaccine adjuvant effect. The IL-23-induced antitumor effect and accompanying reversible weight loss were both partially mediated by TNF-alpha. In contrast, local expression of IL-23 at the tumor site maintained antitumor activity in the absence of weight loss. Under these conditions, it was also clear that enhanced effector function of vaccine-induced CD8(+) T cells, rather than increased T cell number, is a primary mechanism underlying the antitumor effect of IL-23. Collectively, these results suggest that IL-23 is a potent vaccine adjuvant for the induction of therapeutic, tumor-specific CD8(+) T cell responses.

Migration of dendritic cell based cancer vaccines: in vivo veritas?

Ex vivo generated cancer vaccines based on dendritic cells (DCs) are currently applied in the clinic. The migration of DCs from the tissues to the lymph nodes is tightly controlled and involves many different mediators and their receptors. A recent study demonstrated that the rate of migration of antigen-bearing DCs in situ from the skin to the lymph node is 100-fold higher than previously estimated. The migration of ex vivo generated DCs is rather inefficient but can be improved by pre-conditioning of the vaccine injection site with inflammatory cytokines. An alternative approach that is currently being explored is to target tumor antigens directly to DCs in situ, thereby exploiting the intricate migratory capacity of DCs in vivo. Recent advances have been made in understanding DC migration in the context of DC-based vaccines.

Enhancing antitumor immune responses: intracellular peptide delivery and identification of MHC class II-restricted tumor antigens

The importance of T-cell-mediated antitumor immunity has been demonstrated in both animal models and human cancer therapy. The identification of major histocompatibility complex (MHC) class I-restricted tumor antigens has generated a resurgence of interest in immunotherapy for cancer. However, recent studies suggest that therapeutic strategies that have mainly focused on the use of CD8+ T cells (and MHC class I-restricted tumor antigens) may not be effective in eliminating cancer cells in patients. Novel strategies have been developed for enhancing T-cell responses against cancer by prolonging antigen presentation of dendritic cells to T cells and the inclusion of MHC class II-restricted tumor antigens. identification of MHC class II-restricted tumor antigens, which are capable of stimulating CD4+ T cells, not only aids our understanding of the host immune responses against cancer antigens, but also provides opportunities for developing effective cancer vaccines.

GVAX (Cell Genesys)

Cell Genesys (formerly Somatix Therapy Corp) is developing GVAX as a potential cancer vaccine for various tumor types. Clinical trials have commenced for melanoma, renal tumor, lung tumor, pancreatic tumor, prostate tumor and multiple myeloma [191143], [287470], [298308], [367408], [401114]; trials are planned for 2001 in leukemia (phase I) and pancreatic cancer (phase II) [366918], [388814]. A worldwide collaboration was signed with Japan Tobacco in December 1998, covering the application of GVAX in prostate cancer trials [312213]. This collaboration may be extended to lung cancer and melanoma, depending on the clinical trial results for prostate cancer [309873], [311835]. The Japanese clinical trials were put on hold on 21 September 2000 due to problems with the mass production of cells by Cell Genesys [384885]. Somatix was developing GVAX until its merger with Cell Genesys in June 1997 [248422]. In April 2001, Cell Genesys initiated the first in a series of trials of a high-potency version of GVAX prostate cancer vaccine following encouraging phase II data reported for its first-generation product. The high-potency form of GVAX is similar to the first-generation product except that it releases an increased quantity of immune system stimulant [405932].

Novel allogeneic granulocyte-macrophage colony-stimulating factor-secreting tumor vaccine for pancreatic cancer: a phase I trial of safety and immune activation

PURPOSE

Allogeneic granulocyte-macrophage colony-stimulating factor (GM-CSF)-secreting tumor vaccines can cure established tumors in the mouse, but their efficacy against human tumors is uncertain. We have developed a novel GM-CSF-secreting pancreatic tumor vaccine. To determine its safety and ability to induce antitumor immune responses, we conducted a phase I trial in patients with surgically resected adenocarcinoma of the pancreas.

PATIENTS AND METHODS

Fourteen patients with stage 1, 2, or 3 pancreatic adenocarcinoma were enrolled. Eight weeks after pancreaticoduodenectomy, three patients received 1 x 10(7) vaccine cells, three patients received 5 x 10(7) vaccine cells, three patients received 10 x 10(7) vaccine cells, and five patients received 50 x 10(7) vaccine cells. Twelve of 14 patients then went on to receive a 6-month course of adjuvant radiation and chemotherapy. One month after completing adjuvant treatment, six patients still in remission received up to three additional monthly vaccinations with the same vaccine dose that they had received originally.

RESULTS

No dose-limiting toxicities were encountered. Vaccination induced increased delayed-type hypersensitivity (DTH) responses to autologous tumor cells in three patients who had received >or= 10 x 10(7) vaccine cells. These three patients also seemed to have had an increased disease-free survival time, remaining disease-free at least 25 months after diagnosis.

CONCLUSION

Allogeneic GM-CSF-secreting tumor vaccines are safe in patients with pancreatic adenocarcinoma. This vaccine approach seems to induce dose-dependent systemic antitumor immunity as measured by increased postvaccination DTH responses against autologous tumors. Further clinical evaluation of this approach in patients with pancreatic cancer is warranted.

Bispecific tandem diabody for tumor therapy with improved antigen binding and pharmacokinetics

To increase the valency, stability and therapeutic potential of bispecific antibodies, we designed a novel recombinant molecule that is bispecific and tetravalent. It was constructed by linking four antibody variable domains (VHand VL) with specificities for human CD3 (T cell antigen) or CD19 (B cell marker) into a single chain construct. After expression in Escherichia coli, intramolecularly folded bivalent bispecific antibodies with a mass of 57 kDa (single chain diabodies) and tetravalent bispecific dimers with a molecular mass of 114 kDa (tandem diabodies) could be isolated from the soluble periplasmic extracts. The relative amount of tandem diabodies proved to be dependent on the length of the linker in the middle of the chain and bacterial growth conditions. Compared to a previously constructed heterodimeric CD3xCD19 diabody, the tandem diabodies exhibited a higher apparent affinity and slower dissociation from both CD3(+)and CD19(+)cells. They were also more effective than diabodies in inducing T cell proliferation in the presence of tumor cells and in inducing the lysis of CD19(+)cells in the presence of activated human PBL. Incubated in human serum at 37 degrees C, the tandem diabody retained 90 % of its antigen binding activity after 24 hours and 40 % after one week. In vivo experiments indicated a higher stability and longer blood retention of tandem diabodies compared to single chain Fv fragments and diabodies, properties that are particularly important for potential clinical applications.

Biodistribution and vaccine efficiency of murine dendritic cells are dependent on the route of administration

Dendritic cells (DCs) are professional antigen-presenting cells, well equipped to initiate an immune response. Currently, tumor antigen-derived peptide loaded DCs are used in clinical vaccination in cancer patients. However, the optimal dose and route of administration of a DC vaccine still remain to be determined. Using indium-111-labeled DCs, we investigated whether the route of administration does affect the biodistribution of DCs in lymphoid organs and whether it influences the outcome of DC vaccination in the B16 mouse melanoma tumor model. The results demonstrate that i.v. injected DCs mainly accumulate in the spleen, whereas s.c. injected DCs preferentially home to the T-cell areas of the draining lymph nodes. Using tyrosinase-related protein-2-derived peptide-loaded DC vaccination in a fully autologous B16 melanoma tumor model, we observed a delay in tumor growth, improved survival as well as increased antitumor cytotoxic T-cell reactivity after s.c. vaccination as compared to i.v. vaccination. These data demonstrate that optimal induction of antitumor reactivity against the autologous melanocyte differentiation antigen tyrosinase-related protein-2-derived peptide occurs after s.c. vaccination and correlates with the preferential accumulation of DCs in the T-cell areas of lymph nodes.

Immunization of patients with melanoma peptide vaccines: immunologic assessment using the ELISPOT assay

PURPOSE

Interest in the development of antimelanoma peptide vaccines has been renewed by the identification of specific epitopes recognized by tumor-infiltrating lymphocytes that mediate tumor regression after adoptive transfer. The human leukocyte antigen (HLA)-A2*0201-restricted, nonmutated melanocyte differentiation antigen gp100 has multiple T-cell epitopes, of which three are recognized by most gp100-reactive tumor infiltrating lymphocytes. Synthetic peptides based on two of these epitopes, or modifications to improve HLA binding affinity, were used individually to vaccinate patients with metastatic melanoma. The purpose of this study was to evaluate the success of the vaccinations, as determined by the results of enzyme-linked immunospot (ELISPOT) tests of individual immune cells.

PATIENTS AND METHODS

The ELISPOT assay was used to measure the immunologic reactivity of peripheral blood lymphocytes from patients with metastatic melanoma before and after vaccination with gp100 peptides mixed with incomplete Freund's adjuvant. The peptides were g209 (ITDQVPFSV), g280 (YLEPGPVTA), modified g209 (g209-2M: IMDQVPFSV) or modified g280 (g280-9V: YLEPGPVTV) peptide. The patients' lymphocytes were tested by use of an ELISPOT assay for their ability to secrete interferon gamma with and without 12 days of in vitro sensitization with peptide.

RESULTS

Patients were successfully vaccinated by gp100 peptides, as judged by the ELISPOT assays. Restimulation of the patients' lymphocytes in vitro with peptide for 12 days before the ELISPOT assay significantly amplified the immune activity. Increased immune activity after vaccination was specific for the immunizing peptide or its altered form, was major histocompatibility complex restricted, and was apparent against HLA-A2+, gp100+ melanoma cell lines and against T2 cells pulsed with the appropriate synthetic peptides. In general, the frequency of immune T cells was 10 to 100-fold higher in ELISPOT assays against peptide-pulsed T2 cells than against melanoma cell lines. Judged by the ELISPOT assays, vaccination was successful in six of seven patients injected with g209-2M when tested against g209-2M peptide and in five of these seven patients when tested against the native g209 peptide. Vaccination was also successful in five of six patients injected with g209, one of three patients injected with g280-9V, and four of seven patients injected with g280. Even without peptide restimulation in vitro before the ELISPOT assay, the frequency of immune T cells among fresh peripheral blood mononuclear cells tested 3 weeks after a second vaccination with g209-2M peptide was elevated in four of six patients and was about 1/1000 of cells tested against the same peptide pulsed onto T2 cells.

DISCUSSION

Gp100 peptides were selected for vaccine development because they are epitopes recognized by tumor-infiltrating lymphocytes that are associated with tumor regression after adoptive immunotherapy in patients with metastatic melanoma. In the present study, most of the patients vaccinated with the gp209-2M peptide in incomplete Freund's adjuvant generated circulating antigen-specific immune T cells that could be detected by restimulation in vitro followed by an ELISPOT assay for individual cells secreting interferon gamma. The immune T cells reacted not only with the HLA-A2 restricted modified peptide but also with the native peptide and with melanoma cells that express gp100 and HLA-A2. Analysis of T-cell responses at the single cell level will be a valuable aid in assessing the effectiveness of melanoma vaccines and in determining optimal vaccine formulations and delivery.