DNA-based immunization by in vivo transfection of dendritic cells

Tumour cell/dendritic cell fusions as a vaccination strategy for multiple myeloma

Multiple myeloma (MM) cells express certain tumour-associated antigens (TAAs) that could serve as targets for active-specific immunotherapy. The aim of the present study was to test the MM/dendritic cell (DC) fusion as a vaccination strategy. We fused MM cells with DC to generate fusion cells (FCs) and tested their antigen presenting cell (APC) function in mixed lymphocyte reactions and cytotoxicity assays. First, the HS Sultan and SK0-007 HAT sensitive human MM cell lines and DCs generated from peripheral blood of normal donors were fused in the presence of 50% polyethylene glycol to form FCs. Next, tumour cells freshly isolated from patients were similarly fused with autologous DCs to generate FCs. The FCs demonstrated a biphenotypic profile, confirmed both by flow-cytometry and dual immunofluorescence microscopy. These FCs induced MM-specific cytotoxicity. FCs, but not MM cells or DCs alone, were potent stimulators of autologous patient T cells. More importantly, FC-primed autologous peripheral blood mononuclear cells demonstrated major histocompatibility complex-restricted MM-specific cytolysis. These studies therefore demonstrated that MM/DC FC can trigger an autologous immune response to MM cells and formed the framework for a clinical trial currently underway.

Enhancement of DNA vaccine potency by coadministration of a tumor antigen gene and DNA encoding serine protease inhibitor-6

Serine protease inhibitor 6 (SPI-6), also called Serpinb9, inhibits granzyme B and thus may provide a method for delaying apoptotic cell death in dendritic cells. We have previously enhanced DNA vaccine potency by targeting antigen to MHC antigen presentation pathways, using proteins such as Mycobacterium tuberculosis heat shock protein 70, calreticulin, domain II of Pseudomonas aeruginosa exotoxin A, or the sorting signal of the lysosome-associated membrane protein type 1. In this study, we explored intradermal coadministration of DNA encoding SPI-6 with DNA constructs encoding human papillomavirus type 16 E7 linked to these intracellular targeting molecules for its ability to generate E7-specific CD8+ T-cell immune responses and E7-specific antitumor effects. This combination of strategies resulted in significantly increased E7-specific CD8+ T-cell and CD4+ Th1-cell responses, enhanced tumor treatment ability, and stronger tumor protection when compared with vaccination without SPI-6. Among these targeting strategies tested, mice vaccinated with Sig/E7/lysosome-associated membrane protein type 1 mixed with SPI-6 showed the greatest fold increase in E7-specific CD8+ T cells ( approximately 5-fold). Vaccination with a nonfunctional mutant of SPI-6 did not result in immune enhancement, indicating that enhancement was dependent on the antiapoptotic function of SPI-6. Our results suggest that DNA vaccines combining strategies that enhance MHC class I and II antigen processing with SPI-6 have potential clinical implications for control of viral infection and neoplasia.

Enhancement of suicidal DNA vaccine potency by delaying suicidal DNA-induced cell death

DNA-based alphaviral RNA replicon vectors, also called suicidal DNA vectors, alleviate the concerns of integration or transformation related to conventional DNA vectors since suicidal DNA vectors eventually cause apoptosis of transfected cells. However, the expression of inserted genes in these vectors is transient and the potency of suicidal DNA vaccines may be compromised because of apoptotic cell death. Therefore, to enhance the immune response to the human papillomavirus type 16 (HPV-16) E7 antigen, we generated a DNA-based Semliki Forest virus vector, pSCA1, encoding E7 fused with BCL-xL, an antiapoptotic member of the BCL-2 family. Our results indicated that pSCA1 encoding E7/BCL-xL fusion protein delayed cell death in the pSCA1-transfected dendritic cell line and generated significantly higher E7-specific CD8(+) T-cell-mediated immune responses and better antitumor effects than pSCA1 encoding wild-type E7 gene in vaccinated mice. The antiapoptotic function of BCL-xL is important for the enhancement of antigen-specific CD8(+) T-cell responses in vaccinated mice, because a point mutant of BCL-xL lacking antiapoptotic function was ineffective. These results suggest that strategies to delay suicidal DNA-induced cell death using antiapoptotic proteins may greatly enhance the potency of suicidal DNA.

GM-CSF enhances protective immunity to cottontail rabbit papillomavirus E8 genetic vaccination in rabbits

We have reported previously that cottontail rabbit papillomavirus (CRPV) E8 gene immunization induced strong protection against virus challenge. In this study, we primed E8 gene vaccination with mouse granulocyte-macrophage colony-stimulating factor (mGM-CSF), a cytokine that induces differentiation and local recruitment of professional antigen-presenting cells. EIII/JC inbred rabbits were divided into four groups receiving vaccinations with the following constructs: mGM-CSF plus E8, mGM-CSF only, E8 only and vector only. After three immunizations at intervals of 3 weeks, rabbits were challenged with viral DNA at six scarified sites. Papillomas grew on all vaccinated rabbits 4 weeks after inoculation. At week 5, papillomas on four rabbits of mGM-CSF plus E8 and one of E8 only rabbits began to regress. At week 11, all the papillomas on rabbits in the GM-CSF plus E8 vaccination group regressed (regression rate = 100%); regression rates of the mGM-CSF only and E8 only vaccination groups were 50 and 25%, respectively. All papillomas on the vector immunized rabbits remained persistent until the end of the experiment (0%). Antibodies to mGM-CSF were detected in rabbit serum by Western blot. Rabbits vaccinated with E8 plus mGM-CSF or E8 only group had positive Delayed-type hypersensitivity (DTH) skin test to different E8 peptides. These results demonstrated that mGM-CSF could enhance the effects of E8 immunization in rabbits to CRPV infection through cell-mediated immune responses.

Comparison of HPV DNA vaccines employing intracellular targeting strategies

Intradermal vaccination via gene gun efficiently delivers DNA vaccines into dendritic cells (DCs) of the skin, resulting in the activation and priming of antigen-specific T cells in vivo. In the context of DNA vaccines, we previously used the gene gun approach to test several intracellular targeting strategies that are able to route a model antigen, such as the human papillomavirus type-16 (HPV-16) E7, to desired subcellular compartments in order to enhance antigen processing and presentation to T cells. These strategies include the use of the sorting signal of lysosome-associated membrane protein (LAMP-1), Mycobacterium tuberculosis heat-shock protein 70 (HSP70), calreticulin (CRT) and the translocation domain (dII) of Pseudomonas aeruginosa exotoxin A (ETA). Vaccination with DNA vaccines encoding E7 antigen linked to any of these molecules all led to a significant enhancement of E7-specific CD8(+) T-cell immune responses and strong antitumor effects against an E7-expressing tumor, TC-1. However, we were interested in identifying the most potent DNA vaccine for our future clinical trials. Thus, we performed a series of experiments to directly compare the potency of the various DNA vaccines. Among the DNA vaccines we tested, we found that vaccination with pcDNA3-CRT/E7 generated the highest number of E7-specific CD8(+) T cells and potent long-term protection and treatment effects against E7-expressing tumors in mice. Interestingly, we observed that pcDNA3-CRT/E7 is also capable of protecting against an E7-expressing tumor with downregulated MHC class I expression, a common feature associated with most HPV-associated cervical cancers. Our data suggest that the DNA vaccine linking CRT to E7 (CRT/E7) may be a suitable candidate for human trials for the control of HPV infections and HPV-associated lesions.

Vaccination with a DNA Vaccine Encoding Herpes Simplex Virus Type 1 VP22 Linked to Antigen Generates Long-Term Antigen-Specific CD8-Positive Memory T Cells and Protective Immunity

Intradermal vaccination with DNA encoding herpes simplex virus type 1 (HSV-1) VP22 linked to antigen leads to spread of antigen within the epithelium and results in enhanced antigen-specific CD8+ T cell immune responses in vaccinated mice. In this study, we characterized the number of antigen-expressing dendritic cells (DCs) in the draining lymph nodes of vaccinated mice and determined whether the linkage of VP22 to antigen would influence the ability of antigen-expressing DCs to activate antigen-specific CD8+ T cells in vivo. Vaccination with DNA encoding HSV-1 VP22 linked to human papillomavirus type 16 E7 antigen generated more antigen-expressing DCs in the draining lymph nodes of vaccinated mice than E7 alone. In addition, the linkage of VP22 to E7 improved the MHC class I presentation of E7 in transfected DCs and led to enhanced activation of E7-specific CD8+ T cells. We also observed that vaccination with DNA encoding VP22 linked to E7 generated more E7-specific CD8+ memory T cells, and enhanced long-term protective antitumor immunity against an E7-expressing tumor in vaccinated mice compared with vaccination with DNA encoding E7 alone. Thus, administration of DNA encoding VP22 linked to antigen represents a plausible approach for the development of protective DNA vaccines.

Tracking the ‘General’: tagging skin-derived dendritic cells

Dendritic cells (DCs) are the sentinels of the immune system; their migration, maturation and mobilization are fundamental to immunity and tolerance. The recent tracking of DCs from the skin to lymph node (LN) and their enumeration using a Cre/loxP system demonstrate the recruitment of a higher than expected number of DCs to the draining LN after cutaneous administration of DNA-coated gold particles. The longevity of the migrated DCs was also longer than previously reported.

Uptake and trafficking of DNA in keratinocytes: evidence for DNA-binding proteins

The skin is an interesting organ for human gene therapy due to accessibility, immunologic potential and synthesis capabilities. In this study, we attempted to visualize and measure the uptake of naked FITC-labeled plasmid by FACS analysis detecting up to 15% internalization in a dose- and time-dependent manner. Cycloheximide treatment inhibited the uptake by >90%, suggesting a protein-mediated uptake. The inhibition of different internalization pathways demonstrated that blocking macropinocytosis (by amiloride and N,N-dimethylamylorid) reduced DNA uptake by >85%, while the inhibition of clathrin-coated pits (by chlorpromazine) and caveolae (by nystatin/filipin III) did not limit the uptake. Colocalization studies using confocal laser microscopy revealed a time-dependent accumulation of plasmid DNA in endosomes and lysosomes. When a green fluorescent protein (GFP) expression vector was used, specific GFP-RNA became detectable by reverse transcriptase-PCR, whereas measurable amounts of protein could not be identified in FACS experiments. To detect the potential DNA receptors on the keratinocyte surface, membrane proteins were extracted and subjected to South-Western blotting using digoxigenin-labeled calf thymus and lambda-phage DNA. Two DNA-binding proteins, ezrin and moesin, known as plasma membrane-actin linkers, were identified by one- and two-dimensional-South-Western blots and matrix-assisted laser desorption and ionization-mass spectrometry. Ezrin and moesin are functionally associated with a number of transmembrane receptors such as the EGF, CD44 or ICAM-1 receptor. Taken together, naked plasmid DNA seems to enter human keratinocytes through different pathways, mainly by macropinocytosis. Two DNA-binding proteins were identified that seemed to be involved in binding/trafficking of internalized DNA.

Unexpectedly, induction of cytotoxic T lymphocytes enhances the humoral response after DNA immunization

Although there are many examples (eg, immune deviation) in which enhanced cellular responses correspond with lower humoral responses, here we demonstrate for the first time 2 models in which cytotoxic T-lymphocyte (CTL) activity is associated with an enhanced antibody response. First, C57BL/6 mice generate a stronger antibody response to ovalbumin DNA immunization than congenic bm1 mice. The latter differ from C57BL/6 mice in that the H-2Kb molecule is mutated so that the immunodominant CTL epitope of ovalbumin is no longer presented. Second, pre-existing CTLs (induced by ovalbumin peptide-priming) increased the antibody response to a second unrelated antigen (beta-galactosidase) co-immunized with ovalbumin. One possible mechanism is that CTLs may release antigen from DNA-transfected cells by killing or damaging them, and this freed antigen is then accessible to dendritic cells and B cells. Our finding of CTL-mediated antibody enhancement has important implications for tumor and viral immunobiology and vaccination.

DNA immunisation: altering the cellular localisation of expressed protein and the immunisation route allows manipulation of the immune response

DNA immunisation by intramuscular (IM) injection induces Th1 responses, whereas gene gun (GG) immunisation into the skin stimulates Th2 responses. Three ovalbumin (OVA) cDNA constructs, in which OVA is cytoplasmic (CYT), secreted (SECR), or transmembrane (TM), were compared in immunisation studies using intramuscular injection or biolistic bombardment of the skin. Gene gun immunisation with OVA-CYT or OVA-TM led to strong OVA-specific CTL responses, but not following OVA-SECR immunisation. In contrast, intramuscular immunisation with OVA-SECR or OVA-TM led to potent CTL while immunisation with OVA-CYT was ineffective. OVA-specific antibodies were detected following gene gun immunisation with all three constructs, whereas only the OVA-SECR construct induced antibody production following intramuscular immunisation. These results demonstrate the capacity to manipulate the nature of the immune response by altering the cellular localization of expressed proteins and the route of DNA immunisation.

Efficient delivery of DNA to dendritic cells mediated by influenza virosomes

In an attempt to enhance the immunological efficacy of DNA-based vaccines, we have investigated a new biological means for delivering target gene DNA directly to professional antigen presenting cells (APC), such as the dendritic cells (DC), which are ultimately responsible for the antigen presentation and the primary activation of the immune system. For this purpose we investigated influenza virosomes (IRIV) with assembled DNA as a possible biological carrier for targeting the APC in vivo and in vitro. By cytofluorimetric analysis of the draining lymph nodes of Balb/c mice which had received (by intranasal (in.) administration) FITC-labeled DNA assembled with IRIV, we detected a significant labeled DNA uptake in a subset of lymph node deriving cells expressing DC surface markers. Subsequent mRNA analysis of these lymph nodes showed that the trans-gene delivered by the virosomes was effectively expressed as mRNA. Finally, a further cytofluorimetric analysis performed on human DC-enriched-PMBC, infected in vitro with labeled DNA/IRIV lead to the conclusion that the majority of APC (DC, B lymphocytes and CD16+ cells) are able to incorporate the labeled DNA transported by the construct. These findings suggest that the virosome is an efficient delivery system for testing infectious, as well as anti-cancer, DNA-based vaccine research.

Inhibition of spontaneous development of liver tumors by inoculation with dendritic cells loaded with hepatocellular carcinoma cells in C3H/HeNCRJ mice

We attempted to prevent spontaneous development of liver tumors by s.c. inoculation with DCs loaded with syngeneic HCC cells in C3H/HeNCrj mice. A new cell line, MIH-2, was established from an HCC that had developed spontaneously in a C3H/HeNCrj mouse. Bone marrow-derived DCs were loaded with irradiated MIH-2 cells by treatment with PEG. Fluorescence microscopy and flow-cytometric analysis showed that about 45% of PEG-treated DCs and MIH-2 cells (DC/MIH-2) were DCs loaded with MIH-2 cells. Thirteen-month-old mice received inoculations of DC/MIH-2 (9 x 10(5)/mouse) 4 times at 6-day intervals and were killed at 16 months of age to assess liver tumors. The incidence of liver tumors in these mice was significantly lower than that in mice not receiving inoculations (p < 0.05) but similar to that in 13-month-old mice (the age at which inoculation started), indicating that inoculation inhibited the development of new tumors. Splenocytes from inoculated mice, but not those from uninoculated mice, showed cytotoxic activity against MIH-2 cells. Cytotoxic activity was not elicited by CD4(+) T cells, CD8(+) T cells, or DX5(+) cells isolated from splenocytes but was elicited by adherent cells, identified as CD11b(+) macrophages. CD4(+) T cells, but not CD8(+) T cells, from inoculated mice produced IFN-gamma by incubation with DC/MIH-2. Cytotoxicity by splenocytes was attenuated by anti-IFN-gamma antibody. Immunization with DCs loaded with syngeneic HCC cells induces CD4(+) T cells that produce IFN-gamma by response to antigen of HCC, which would lead to macrophage activation to kill liver tumor cells at an early stage.

Enhancement of gp120-specific immune responses by genetic vaccination with the human immunodeficiency virus type 1 envelope gene fused to the gene coding for soluble CTLA4

DNA vaccines exploit the inherent abilities of professional antigen-presenting cells to prime the immune system and to elicit immunity against diverse pathogens. In this study, we explored the possibility of augmenting human immunodeficiency virus type 1 gp120-specific immune responses by a DNA vaccine coding for a fusion protein, CTLA4:gp120, in mice. In vitro binding studies revealed that secreted CTLA4:gp120 protein induced a mean florescence intensity shift, when incubated with Raji B cells, indicating its binding to B7 proteins on Raji B cells. Importantly, we instituted three different vaccination regimens to test the efficacy of DNA vaccines encoding gp120 and CTLA4:gp120 in the induction of both cellular (CD8(+)) and antibody responses. Each of the vaccination regimens incorporated a single intramuscular (i.m.) injection of the DNA vaccines to prime the immune system, followed by two booster injections. The i.m.-i.m.-i.m. regimen induced only modest levels of gp120-specific CD8(+) T cells, but the antibody response by CTLA4:gp120 DNA was nearly 16-fold higher than that induced by gp120 DNA. In contrast, using the i.m.-subcutaneous (s.c.)-i.m. regimen, it was found that gp120 and CTLA4:gp120 DNAs were capable of inducing significant levels of gp120-specific CD8(+) T cells (3.5 and 11%), with antibody titers showing a modest twofold increase for CTLA4:gp120 DNA. In the i.m.-gene gun (g.g.)-g.g. regimen, the mice immunized with gp120 and CTLA4:gp120 harbored gp120-specific CD8(+) T cells at frequencies of 0.9 and 2.9%, with the latter showing an eightfold increase in antibody titers. Thus, covalent antigen modification and the routes of genetic vaccination have the potential to modulate antigen-specific immune responses in mice.

Transcriptional targeting of dendritic cells in gene gun-mediated DNA immunization favors the induction of type 1 immune responses

Cutaneous dendritic cells (DC) are pivotal for the elicitation of antigen-specific immune responses following gene gun-mediated biolistic transfection of the skin. We transcriptionally targeted transgene expression to DC using vectors containing the murine fascin promoter (pFascin) to control antigen production and compared the immune response elicited with conventional DNA immunization using plasmid constructs with the ubiquitously active CMV promoter (pCMV). Biolistic transfection with pFascin initiated a marked type 1 immune response characterized by the occurrence of a large population of IFN-gamma-producing T helper (Th) cells in spleen and draining lymph nodes. Consistently, immunoglobulin production was dominated by IgG2a antibodies. In contrast, the humoral response after repeated administration of pCMV was strongly enhanced and characterized by a type 2-like isotype pattern (IgG1 > IgG2a). Cytokine production analysis in vitro indicated compartmentalization of the immune response, revealing large numbers of IL-4-producing Th cells in the lymph nodes and dominant presence of IFN-gamma-producing Th cells in the spleen. Biolistic transfection with pFascin, like immunization with pCMV, led to potent induction of cytotoxic T cells as was assessed by JAM test. Thus gene gun immunization with plasmids that focus transgene expression and antigen production specifically to DC propagates type 1-biased cellular immune responses.

Powder and particle-mediated approaches for delivery of DNA and protein vaccines into the epidermis

The epidermis of the skin is both a sensitive immune organ and a practical target site for vaccine administration. However, administration of vaccines into the epidermis is difficult to achieve using conventional vaccine delivery methods employing a needle and syringe. A needle-free vaccine delivery system has been developed that efficiently delivers powdered or particulate DNA and protein vaccines into the epidermal tissue. The delivery system can be used to directly transfect antigen presenting cells (APCs) by formulating DNA or protein vaccines onto gold particles (particle-mediated immunization). Antigen can be directly presented to the immune system by the transfected APCs. Antigen can also be expressed and secreted by transfected keratinocytes and picked up by resident APCs through the exogenous antigen presentation pathway. Alternatively, protein antigens can be formulated into a powder and delivered into the extracellular environment where they are picked up by APCs (epidermal powder immunization). Using any of these formulations, epidermal immunization offers the advantage of efficiently delivering vaccines into the APC-rich epidermis. Recent studies demonstrate that epidermal vaccine delivery induces humoral, cellular, and protective immune responses against infectious diseases in both laboratory animals and man.

HIV-1 p55Gag encoded in the lysosome-associated membrane protein-1 as a DNA plasmid vaccine chimera is highly expressed, traffics to the major histocompatibility class II compartment, and elicits enhanced immune responses

Several genetic vaccines encoding antigen chimeras containing the lysosome-associated membrane protein (LAMP) translocon, transmembrane, and cytoplasmic domain sequences have elicited strong mouse antigen-specific immune responses. The increased immune response is attributed to trafficking of the antigen chimera to the major histocompatibility class II (MHC II) compartment where LAMP is colocalized with MHC II. In this report, we describe a new form of an HIV-1 p55gag DNA vaccine, with the gag sequence incorporated into the complete LAMP cDNA sequence. Gag encoded with the translocon, transmembrane and cytoplasmic lysosomal membrane targeting sequences of LAMP, without the luminal domain, was poorly expressed, did not traffic to lysosomes or MHC II compartments of transfected cells, and elicited a limited immune response from DNA immunized mice. In contrast, addition of the LAMP luminal domain sequence to the construct resulted in a high level of expression of the LAMP/Gag protein chimera in transfected cells that was further increased by including the inverted terminal repeat sequences of the adeno-associated virus to the plasmid vector. This LAMP/Gag chimera with the complete LAMP protein colocalized with endogenous MHC II of transfected cells and elicited strong cellular and humoral immune responses of immunized mice as compared with the response to DNA-encoding native Gag, with a 10-fold increase in CD4+ responses, a 4- to 5-fold increase in CD8+ T-cell responses, and antibody titers of >100,000. These results reveal novel roles of the LAMP luminal domain as a determinant of Gag protein expression, lysosomal trafficking, and possibly of the immune response to Gag.

Enhancing DNA vaccine potency by combining a strategy to prolong dendritic cell life with intracellular targeting strategies

We have recently shown that intradermal coadministration of DNA encoding Ag with DNA encoding inhibitors of apoptosis, including Bcl-x(L), prolongs dendritic cell (DC) life and thereby enhances the potency of DNA vaccines in vivo. We have also demonstrated that DNA vaccines targeting Ag to subcellular compartments, using proteins such as Mycobacterium tuberculosis heat shock protein 70, calreticulin, or the sorting signal of the lysosome-associated membrane protein type 1 (LAMP-1), enhanced DNA vaccine potency. In this study, we reasoned that the combination of a strategy to prolong DC life with intracellular targeting strategies might produce a more effective DNA vaccine against human papillomavirus E7. We showed that coadministration of DNA encoding Bcl-x(L) with DNA encoding E7/heat shock protein 70, calreticulin/E7, or Sig/E7/LAMP-1 resulted in further enhancement of the E7-specific CD8(+) T cell response for all three constructs. Of these strategies, mice vaccinated with Sig/E7/LAMP-1 DNA mixed with Bcl-x(L) DNA showed the greatest increase in E7-specific CD8(+) T cells ( approximately 13-fold increase). This combination of strategies resulted in increased CD8(+) T cell functional avidity, an increased E7-specific CD4(+) Th1 cell response, enhanced tumor treatment ability, and stronger long-term tumor protection when compared with mice vaccinated without Bcl-x(L) DNA. Therefore, DNA vaccines that combine strategies to enhance intracellular Ag processing and prolong DC life have potential clinical implications for control of viral infection and neoplasia.

Comparison of the CD8+ T cell responses and antitumor effects generated by DNA vaccine administered through gene gun, biojector, and syringe

DNA vaccines have emerged as an attractive approach for antigen-specific cancer immunotherapy. We have previously linked Mycobacterium tuberculosis heat shock protein 70 (HSP70) to human papillomavirus type 16 (HPV-16) E7 in the context of a DNA vaccine. Vaccination with DNA encoding E7/HSP70 has generated a dramatic increase of E7-specific CD8+ T cell precursors and a strong antitumor effect against E7-expressing tumor (TC-1) in vaccinated mice. The success of our strategy has led to two phases I/II clinical trial proposals in patients with HPV-16 associated high-grade squamous intraepithelial lesion (HSIL) of the cervix and in patients with advanced HPV-associated head and neck squamous cell carcinoma (HNSCC). To translate our HPV DNA vaccines into the clinical domain, the efficacy of pNGVL4a-Sig/E7(detox)/HSP70 DNA vaccine and of various routes of administrations were assessed in mice. Our results indicated that pNGVL4a-Sig/E7(detox)/HSP70 DNA vaccine administered via gene gun generated the highest number of E7-specific CD8+ T cells. In addition, DNA vaccination via gene gun required the least dose to generate similar or slightly better antitumor effects compared to needle intramuscular (i.m.) and biojector administrations. Thus, our data suggest that DNA vaccination via gene gun represents the most potent regimen for DNA administration.

Enhancement of antigen-presenting capacity and antitumor immunity of dendritic cells pulsed with autologous tumor-derived RNA in mice

Dendritic cells (DCs) are antigen-presenting cells that play an important role in antitumor immunity. Several studies have reported that DCs pulsed with RNA from tumor cells have the ability to suppress tumors, but the details regarding the function and the immune-mechanism of DCs transfected with RNA remain to be elucidated. In this study, we investigated the transfection efficiency of RNA into DCs, and the functional modification and the antitumor efficacy of DCs pulsed with tumor-derived RNA. After the transfection of tumor-derived RNA into DCs cultured from the bone marrow of mice, pulsed DCs exhibited a high expression of both MHC antigens and CD86 on the cell surface as well as cultured DCs, and had a stronger ability both to present antigen on the MHC antigens and to stimulate T cells compared with DCs without transfection. DCs could sufficiently translate luciferase encoding RNA into luciferase proteins, and luciferase protein was expressed up to 12 hours in pulsed DCs. The DCs pulsed with tumor-derived RNA could elite a potent induction of cytotoxic T lymphocytes against autologous tumors, but not lysis against syngeneic normal cells. RNA-pulsed DCs exhibited a significant antitumor immunity in animal model. In conclusion, DCs could sufficiently uptake exogenous tumor-derived RNA, and consequently grow to be an intermediate maturate type, and induce potent T-cell stimulation and fully cause an antitumor effect in vivo. Therapy with DCs pulsed with tumor-derived RNA is sufficiently effective and safe, and thus it is considered to be clinically useful for tumor-immunotherapy.

B-lymphocytes in bone marrow or lymph nodes can take up plasmid DNA after intramuscular delivery

Nucleic acid vaccines are an attractive alternative to conventional protein vaccines because of their ability to induce de novo production of antigens in a given tissue after DNA delivery. Although DNA vaccines are highly effective in inducing both cell-mediated and humoral immunity, little is known about the many cell types involved in plasmid DNA uptake in vivo. Here we demonstrate, for the first time, that plasmid DNA can be taken up by both bone marrow and lymph node B cells after intramuscular immunization. Plasmid DNA was also detected in CD11b+ and CD11c+ cells. This phenomenon was not restricted to plasmid DNA encoding mycobacterial 65-kd heat shock protein (pcDNA3-hsp65) because we observed similar results with plasmid-encoding green fluorescent protein (GFP-pEGFP-2C). In addition to plasmid DNA uptake, B cells also express the encoded protein, suggesting that B cells play a role in the immune response after DNA immunization. The biodistribution of plasmid DNA in B cells opens a new perspective in B-cell gene therapy for the in vivo use of plasmid DNA.

Generation of antibodies to the urokinase receptor (uPAR) by DNA immunization of uPAR knockout mice: membrane-bound uPAR is not required for an antibody response

The urokinase receptor (uPAR) is a glycolipid-anchored cell surface glycoprotein that plays a central role in extracellular proteolysis during tissue remodeling processes including cancer invasion. Furthermore, uPAR is found on the surface of both dendritic cells (DCs) and T cells, and has been proposed to play a role in DC-induced T-cell activation and, therefore, in the induction of an immune response. In order to investigate the possibility of using DNA immunization for the generation of poly- and monoclonal antibodies to uPAR, we injected wild-type mice and mice deficient in uPAR (uPAR knockouts) intramuscularly with plasmid DNA encoding a carboxy-terminal truncated soluble form of the human uPAR. Multiple injections of 100 micro g of DNA resulted in a strong and specific antibody response in all mice irrespective of genotype. Antisera with a maximum titre of 32,000 were obtained, comparable with that obtained after immunization with recombinant uPAR. The subclass distribution of uPAR-specific antibodies in the sera demonstrated the induction of a mixed TH1/TH2 response, irrespective of the genotype of the mice. Our results demonstrate the possibility of generating high titre antibodies to uPAR by DNA immunization of wild-type as well as uPAR knockout mice, and that cell surface uPAR is not indispensable for the generation of a humoral immune response.

Genetic tagging shows increased frequency and longevity of antigen-presenting, skin-derived dendritic cells in vivo

Dendritic cells (DCs) are key regulators of immune responses that activate naive antigen-specific T lymphocytes. In draining lymph nodes, antigen-bearing DCs are reported to be rare and short-lived. How such small numbers of short-lived DCs can activate rare antigen-specific T cells is unclear. Here we show that after immunization of mouse skins by gene gun, the number of antigen-bearing DCs that migrate to draining lymph node is 100-fold higher than previously estimated and that they persist for approximately 2 weeks. The substantial frequency and longevity of DCs in situ ensures ample antigen presentation and stimulation for the rare antigen-specific T cells in draining lymph nodes.

Cancer vaccines: between the idea and the reality

Whether vaccines are designed to prepare the immune system for the encounter with a pathogen or with cancer, certain common challenges need to be faced, such as what antigen and what adjuvant to use, what type of immune response to generate and how to make it long lasting. Cancer, additionally, presents several unique hurdles. Cancer vaccines must overcome immune suppression exerted by the tumour, by previous therapy or by the effects of advanced age of the patient. If used for cancer prevention, vaccines must elicit effective long-term memory without the potential of causing autoimmunity. This article addresses the common and the unique challenges to cancer vaccines and the progress that has been made in meeting them. Considering how refractory cancer has been to standard therapy, efforts to achieve immune control of this disease are well justified.

CD8+ T cells, NK cells and IFN-gamma are important for control of tumor with downregulated MHC class I expression by DNA vaccination

One of the major hurdles facing cancer immunotherapy is that cancers may downregulate expression of MHC class I molecules. The development of a suitable tumor model with downregulated MHC class I expression is critical for designing vaccines and immunotherapeutic strategies to control such tumors. We developed an E7-expressing murine tumor model with downregulated MHC class I expression, TC-1 P3 (A15). Using this model, we tested DNA and vaccinia vaccines for their ability to control tumors with downregulated MHC class I expression. We found that vaccination with DNA encoding E7 linked to Mycobacterial heat shock protein 70 (HSP70) generated a significant antitumor effect against TC-1 P3 (A15), while vaccination with E7/HSP70 vaccinia did not generate an appreciable antitumor effect. Lymphocyte depletion experiments revealed that both CD8+ T cells and NK cells were essential for the antitumor effect generated by E7/HSP70 DNA against TC-1 P3 (A15). Furthermore, tumor protection experiments using IFN-gamma knockout mice revealed that IFN-gamma was essential for the antitumor effect generated by E7/HSP70 DNA against TC-1 P3 (A15). Our results demonstrate that vaccination with E7/HSP70 DNA results in a significant antitumor effect against a neoplasm with downregulated MHC class I expression and the importance of CD8+ T cells, NK cells, and IFN-gamma in generating this antitumor effect.

A complicated relationship: fulfilling the interactive needs of the T lymphocyte and the dendritic cell

T cells recognize antigenic peptides displayed on the surface of MHC-bearing antigen-presenting cells (APCs), and with sufficient costimulation become activated. However, the ability of an APC (even bearing the correct peptide) to initiate and fulfill the requirements for T cell activation is not easily achieved. Naive T cells use multiple copies of a single receptor to survey the vast array of peptides presented on an APC, and require multiple receptor engagements to initiate T cell activation. Dendritic cells (DCs) are specialized cells with optimal capabilities for priming naive CD4+ T cells. Activation occurs, after initial antigen recognition by T cells, followed by a rapid dialogue between the T cells and the DCs. The resulting changes in both the cytoskeleton and the expression or regulation of cell-surface molecules on both cell types act to further strengthen engagement. In this report, we review the fundamentals of CD4+ T helper cell : DC interactions and discuss recent data concerning the molecular characteristics of this engagement.

Dendritic cell vaccination and viral infection--animal models

Dendritic cells (DCs) play a pivotal role in the initiation and maintenance of immune responses against viruses and other microbial pathogens. Adoptively transferred, in vitro manipulated DCs presenting antigen derived from different viruses have been shown to elicit cytotoxic T cell (CTL) and T helper (Th) cell responses and to induce protective antiviral immunity. Furthermore, DC-based adoptive immunotherapies have the potential to specifically (re)activate antiviral immunity in chronic viral diseases such as HIV or hepatitis virus infections. Cellular dendritic cell vaccines, however, are not suitable for large-scale prophylactic immunization. Strategies for vaccine development should therefore aim at the specific delivery of microbial antigens to DCs in situ. Furthermore, appropriate mobilization and activation of DCs by the vaccine is important for the generation of optimal antimicrobial immune responses. Here, we discuss recent data on induction of antiviral immunity with various DC-vaccination approaches and outline future directions for the development of specific antigen targeting to DCs.

Enhancing DNA vaccine potency by coadministration of DNA encoding antiapoptotic proteins

Intradermal vaccination by gene gun efficiently delivers DNA vaccines into DCs of the skin, resulting in the activation and priming of antigen-specific T cells in vivo. DCs, however, have a limited life span, hindering their long-term ability to prime antigen-specific T cells. We reason that a strategy that prolongs the survival of DNA-transduced DCs will enhance priming of antigen-specific T cells and DNA vaccine potency. Here we show that codelivery of DNA encoding inhibitors of apoptosis (BCL-xL, BCL-2, XIAP, dominant negative caspase-9, or dominant negative caspase-8) with DNA encoding model antigens prolongs the survival of transduced DCs. More importantly, vaccinated mice exhibited significant enhancement in antigen-specific CD8+ T cell immune responses, resulting in a potent antitumor effect against antigen-expressing tumors. Among these antiapoptotic factors, BCL-xL demonstrated the greatest enhancement in antigen-specific immune responses and antitumor effects. Thus, coadministration of DNA vaccines with DNA encoding antiapoptotic proteins represents an innovative approach to enhance DNA vaccine potency.

Development of DNA vaccines against hemolytic-uremic syndrome in a murine model

Shiga toxin type 2 (Stx2) produced by Escherichia coli O:157H7 can cause hemolytic-uremic syndrome in children, a disease for which there is neither a vaccine nor an effective treatment. This toxin consists of an enzymatically active A subunit and a pentameric B subunit responsible for the toxin binding to host cells, and also found to be immunogenic in rabbits. In this study we developed eukaryotic plasmids expressing the B subunit gene of Stx2 (pStx2B) and the B subunit plus the gene coding for the A subunit with an active-site deletion (pStx2 Delta A). Transfection of eukaryotic cells with these plasmids produced proteins of the expected molecular weight which reacted with specific monoclonal antibodies. Newborn and adult BALB/c mice immunized with two intramuscular injections of each plasmid, either alone or together with the same vector expressing the granulocyte and monocyte colony-stimulating factor (pGM-CSF), elicited a specific Th1-biased humoral response. The effect of pGM-CSF as an adjuvant plasmid was particularly notable in newborn mice and in pStx2B-vaccinated adult mice. Stx2-neutralizing activity, evaluated in vitro on VERO cell monolayers, correlated with in vivo protection. This is the first report using plasmids to induce a neutralizing humoral immune response against the Stx2.

Gene gun immunization in a preclinical model is enhanced by B7 targeting

DNA vaccines have great potential but despite the promise shown in rodent models, responses in large animals, including humans, have been disappointing. Furthermore, gene gun delivery of DNA has been used to improve these responses. However, most cells that are transfected are not the professional antigen presenting cells (APC) which are critical for generating the primary immune response. Here, we show that in the large animal model of the pig, the combination of the use of gene gun delivery and a DNA vector that targets antigen presenting cells by expressing a CTLA4-ovalbumin (OVA) fusion antigen, leads to enhanced ovalbumin specific serum IgG, IgA, IgG1 and IgG2 immune responses.

Transcriptional targeting of dendritic cells for gene therapy using the promoter of the cytoskeletal protein fascin

Strong cell-type-specific promoters are basic tools in gene therapy allowing for novel applications and focused strategies by transcriptionally targeting gene expression to selected cells. In immunotherapy, dendritic cells (DC) are of central importance, since they represent the principal inducers of immune responses. Here we describe isolation and use of the promoter of the murine actin-bundling protein fascin to target transcriptionally gene expression to cutaneous DC. Using the reporter gene enhanced green fluorescent protein (EGFP), we demonstrate that the fascin promoter mediates a strong antigen expression that is restricted to mature DC. DNA vaccination with antigen-encoding expression vectors under control of the fascin promoter using a gene gun resulted, consistently, in limited antigen expression by few directly transfected DC. Nevertheless, nearly as many antigen-specific CD8+ T cells directed against the encoded antigens EGFP and beta-galactosidase, respectively, were induced as with expression constructs under control of the ubiquitously expressed CMV promoter. This result impressively underlines the pivotal role of directly transfected DC in DNA vaccination. Immunization using the fascin promoter induced markedly lower levels of antigen-specific antibodies following single or repeated immunization. Thus, our DC-targeted DNA vaccination approach induces qualitatively distinct, predominantly cellular immune responses and provides new opportunities for immunotherapy.

Drug-inducible, dendritic cell-based genetic immunization

Determining the mechanism of Ag loading of Langerhans cells (LC) for genetic immunization (GI) is complicated by the inability to distinguish between the response generated by direct transfection of LC from that due to exogenous uptake. To unravel this mechanism, we examined the impact of gene gun treatment on LC with respect to their activation and migration from skin, transgene expression, and ability to initiate humoral and cellular immune responses upon transfer to naive mice. To assess responses generated by direct LC transfection, an RU486-inducible expression system was used as a GI vector. In vitro skin organ cultures were developed from gene gun immunized mouse ear specimens to obtain LC. Gene gun treatment markedly augmented (3-fold) LC migration from ear skin, and these LC expressed the transgene at RNA and protein levels. Transfer of 2 x 10(5) migratory cells resulted in identical cellular responses to, but 10-fold lower humoral responses than, standard GI. Using an RU486-inducible system, we were able to measure responses generated by directly transfected LC. Our results indicate that direct transfection is a predominant pathway for LC Ag loading. The ability to regulate transgene expression with inducible DC-based vaccines demonstrates a new level of immunological control.

Lipid-protamine-DNA-mediated antigen delivery to antigen-presenting cells results in enhanced anti-tumor immune responses

Vaccination with antigenic peptides encoding tumor antigens has the potential to be an effective treatment for cancer. To induce tumor-specific cellular immune responses, a peptide antigen must be presented by antigen-presenting cells (APCs) to T-cells in the lymphatic tissues. Effective in vivo delivery of peptide antigens to APCs has been problematic. Here we use a model antigen from the HPV16 E7 protein to formulate LPD/E7 particles that upon iv administration are internalized by CD11c(+) and CD11b(+) cells in the marginal zone of the spleen. Either iv or sc vaccination with LPD/E7 particles induces E7-specific CTL responses stronger than those obtained using previously described liposome/peptide strategies and prevents the establishment of E7-expressing tumors. Furthermore, the administration of LPD/E7 particles to tumor-bearing mice caused complete tumor regression in 100% of the treated animals. Based on these studies, the entrapment of peptide antigens inside LPD particles may be an effective and generally applicable strategy for the enhancement of peptide vaccine potency.

Two major histocompatibility complex class I-restricted epitopes of the Borna disease virus p10 protein identified by cytotoxic T lymphocytes induced by DNA-based immunization

Borna disease virus (BDV) infection of Lewis rats is the most studied animal model of Borna disease, an often fatal encephalomyelitis. In this experimental model, BDV-specific CD8(+) cytotoxic T lymphocytes (CTLs) play a prominent role in the immunopathogenesis of infection by the noncytolytic, persistent BDV. Of the six open reading frames of BDV, CTLs to BDV X (p10) and the L-polymerase have never been studied. In this study, we used plasmid immunization to investigate the CTL response to BDV X and N. Plasmid-based immunization was a potent CTL inducer in Lewis rats. Anti-X CTLs were primed by a single injection of the p10 cDNA. Two codominant p10 epitopes, M(1)SSDLRLTLL(10) and T(8)LLELVRRL(16), associated with the RT1.A(l) major histocompatibility complex class I molecules of the Lewis rats, were identified. In addition, immunization with a BDV p40-expressing plasmid confirmed the previously reported RT1.A(l)-restricted A(230)SYAQMTTY(238) peptide as the CTL target for BDV N. In contrast to the CTL responses, plasmid vaccination was a poor inducer of an antibody response to p10. Three injections of a recombinant eukaryotic expression plasmid of BDV p10 were needed to generate a weak anti-p10 immunoglobulin M response. However, the antibody response could be optimized by a protein boost after priming with cDNA.

Technical and regulatory hurdles for DNA vaccines

DNA vaccines have been widely used in laboratory animals and non-human primates over the last decade to induce antibody and cellular immune responses. This approach has shown some promise, in models of infectious diseases of both bacterial and viral origin as well as in tumour models. Clinical trials have shown that DNA vaccines appear safe and well tolerated, but need to be made much more potent to be candidates for preventive immunisation of humans. This review describes recent work to improve the delivery of plasmid DNA vaccines and also to increase the immunogenicity of antigens expressed from the DNA vaccine plasmids, including various formulations and molecular adjuvants. Because DNA vaccines are relatively new and represent a novel vaccine technology, certain safety issues, such as the potential for induction of autoimmune disease and integration into the host genome, must be examined carefully. If potency can be improved and safety established, plasmid DNA vaccines offer advantages in speed, simplicity, and breadth of immune response that may be useful for the immunisation of humans against infectious diseases and cancers.

DNA immunization via intramuscular and intradermal routes using a gene gun provides different magnitudes and durations on immune response

We investigated the antibody (Ab) and cytotoxic T lymphocyte (CTL) responses to gene gun (GG)-mediated DNA immunization via the intramuscular (i.m.) and intradermal (i.d.) routes. BALB/c mice were immunized five times at weekly intervals with plasmid DNA encoding enhanced green fluorescent protein (EGFP). EGFP production was rapidly detected in the target tissues after injection via either delivery route. There were significant differences in the magnitude and duration of the Ab and CTL responses according to the route employed. Intradermal injection elicited higher Ab and CTL responses to EGFP than i.m. injection 1 week after the last immunization. However, both immune responses were reduced rapidly 5 weeks after the last immunization via i.d. injection. In contrast, in mice injected via the i.m. routes, Ab and CTL responses 5 weeks after the last immunization remained at levels similar to those detected after 1 week. All mice generated a predominantly IgG1 Ab response via either route. These findings suggest that a combination of these two routes of DNA immunization would provide optimal conditions for induction of a broad immune response, and this information is expected to be very important for future applications of DNA vaccination.

Induction of protective immunity to Listeria monocytogenes with dendritic cells retrovirally transduced with a cytotoxic T lymphocyte epitope minigene

In the present study, we developed a cytotoxic T lymphocyte (CTL) epitope minigene-transduced dendritic cell (DC)-based vaccine against Listeria monocytogenes. Murine bone marrow-derived DCs were retrovirally transduced with a minigene for listeriolysin O (LLO) 91-99, a dominant CTL epitope of L. monocytogenes, and were injected into BALB/c mice intravenously. We found that the DC vaccine was capable of generating peptide-specific CD8+ T cells exhibiting LLO 91-99-specific cytotoxic activity and gamma interferon production, leading to induction of protective immunity to the bacterium. Furthermore, we demonstrated that the retrovirally transduced DC vaccine was more effective than a CTL epitope peptide-pulsed DC vaccine and a minigene DNA vaccine for eliciting antilisterial immunity. These results provide an alternative strategy in which retrovirally transduced DCs are used to design vaccines against intracellular pathogens.

Long-term maintenance of gp120-specific immune responses by genetic vaccination with the HIV-1 envelope genes linked to the gene encoding Flt-3 ligand

DNA vaccines target dendritic cells (DC) to induce Ag-specific immune responses in animals. Potent HIV-specific immunity could be achieved by efficient priming of the immune system by DNA vaccines. We investigated a novel DNA vaccine approach based on the role of growth factors in DC expansion and differentiation. To this end, we constructed chimeric genes encoding the HIV envelope glycoproteins physically linked to the extracellular domain of Fms-like tyrosine kinase receptor-3 ligand (FLex; a DC growth factor; both mouse (m)FLex and human (h)FLex). These chimeric gene constructs synthesized biologically active, oligomeric FLex:gp120 fusion proteins and induced DC expansion (CD11c(+)CD11b(+)) when injected i.v. into mice. This DC expansion is comparable to that achieved by FLex DNA encoding native FLex protein. When delivered intramuscularly as DNA vaccines, hFLex:gp120 induced high frequencies of gp120-specific CD8(+) T cells in the presence or absence of FLex DNA-induced DC expansion, but gp120 and mFLex:gp120 elicited only low to moderate levels of Ag-specific CD8(+) T cells. In contrast, mFLex:gp120 induced high levels of anti-gp120 Abs under identical conditions of DNA vaccination. However, the Ab levels in mice immunized with DNA vaccines encoding hFLex:gp120 and gp120 proteins were low without DC expansion, but reached high levels comparable to that elicited by mFLex:gp120 only after the second boost in the presence of DC expansion. Importantly, the gp120-specific CD8(+) T cells persisted at high frequency for 114 days (16 wk) after a booster injection. These experiments provide insight into the importance of modulating DC function in vivo for effective genetic vaccination in animals.

Delivery of tumor-derived RNA for the induction of cytotoxic T-lymphocytes

Dendritic cells (DC) are professional antigen-presenting cells playing a central role in the induction of antigen-specific cytotoxic T-lymphocytes (CTL). We analyzed the efficiency of tumor RNA transfection into DC using different sources of RNA as well as delivery strategies including electroporation, lipofection and CD71-receptor-based delivery. To evaluate the sensitivity of these approaches, we utilized in vitro transcribed enhanced green fluorescence protein (EGFP)-RNA and whole tumor RNA from EGFP-transfected renal cell carcinoma cell line N43. We demonstrate that electroporation was the most effective way yielding about 30% EGFP positive cells while less than 1% of DC expressed EGFP using the transferrin receptor transfection system. Delivery of RNA with liposomes resulted in 17.5% of EGFP positive cells depending on the RNA amount. However, when these approaches were applied to transduce DC with RNA derived from the A498 cell line for T-cell priming, tumor-specific CTL could be induced using all delivery strategies suggesting that this technology has the potential to induce cytotoxic T-cell response even when low level of antigen is delivered. Furthermore, we demonstrate that amplification of whole tumor messenger RNA (mRNA) as well as the use of total instead of purified mRNA can be utilized for stimulating tumor-specific CTL responses.

In vitro analysis of the antileukemic effect of tumor necrosis factor-alpha gene therapy with myeloid progenitor cells: the role of dendritic cells

We have previously demonstrated that tumor necrosis factor-alpha (TNF-alpha) gene therapy with transgene-expressing myeloid progenitor cells (32DTNF-alpha) is effective in inhibiting the progression of leukemia with a lethal dose of murine 32Dp210 myeloid leukemia cells. Because TNF-alpha has been shown to induce the activation and maturation of dendritic cells (DCs), we investigated the effect of TNF-alpha secreted by transduced cells (32DTNF-alpha cells) on the activation of DCs and their role in the production of antileukemic cytotoxic T lymphocytes (CTLs). We demonstrate that administration of 32DTNF-alpha cells to the mice enhances the allo-stimulatory capacity of the splenic (CD11c+) and bone marrow-derived DCs in both mixed leukocyte response and CTL development. The enhanced allo-stimulatory capacity of splenic DCs from mice injected with 32DTNF-alpha cells correlated with increase in the cell-surface expression of the costimulatory molecules CD40, CD80, CD86, and major histocompatibility complex (MHC) class II molecules (I-Ak), and production of interleukin-12 (IL-12). Furthermore, administration of 32DTNF-alpha cells during immunization with irradiated 32Dp210 leukemia cells augmented the capacity of splenic DCs to stimulate antileukemic CTL response in spleen cells. Collectively, these data suggest that in vivo production of TNF-alpha by transduced cells enhances the phenotypic and functional activation of DCs, resulting in induction of a stronger antileukemic cytotoxic T-cell immune response.

Gene and cell therapies for diabetes mellitus: strategies and clinical potential

The last 5 years have witnessed an explosion in the use of genes and cells as biomedicines. While primarily aimed at cancer, gene engineering and cell therapy strategies have additionally been used for Mendelian, neurodegenerative and metabolic disorders. The main focus of gene and cell therapy strategies in metabolism has been diabetes mellitus. This disease is a disorder of glucose homeostasis, either due to the immune-mediated eradication of pancreatic beta cells in the islets of Langerhans (type 1 diabetes) or resulting from insulin resistance and obesity syndromes where the insulin-producing capability of the beta cell is ultimately exhausted in the face of insensitivity to the effects of insulin in the peripheral glucose-utilising tissues (type 2 diabetes). A significant number of animal studies have demonstrated the potential in restoring normoglycaemia by islet transplantation in the context of immunoregulation achieved by gene transfer of immunoregulatory genes to allo- and xenogeneic islets ex vivo. Additionally, gene and cell therapy has also been used to induce tolerance to auto- and alloantigens and to generate the tolerant state in autoimmune rodent animal models of type 1 diabetes or rodent recipients of allogeneic/xenogeneic islet transplants. The achievements of gene and cell therapy in type 2 diabetes are less evident, but seminal studies promise that this modality can be relevant to treat and perhaps prevent the underlying causes of the disease. Here we present an overview of the current status of gene and cell therapy for type 1 and 2 diabetes and we propose potential therapeutic options that could be clinically useful. For type 1 diabetes, transplantation of islets engineered to evade or suppress the recipient immune response is the most readily-available technology today. A number of gene delivery vectors encoding proteins that impair a variety of immune cells have already been examined and proven versatile. More challenging but, nonetheless, just over the horizon are attempts to promote tolerance to islet allografts. Type 2 diabetes will likely require a better understanding of the processes that determine insulin sensitivity in the periphery. Targeting tissues such as muscle and fat with vectors encoding genes whose products promote insulin sensitivity and glucose uptake is an approach that does not carry with it the side-effects often associated with pharmacologic agents currently in use. In the end, progress in vector design, elucidation of antigen-specific immunity and insulin sensitivity will provide the framework for gene drug use in the treatment of type 1 and type 2 diabetes.

Vaccination of mice with MUC1 cDNA suppresses the development of lung metastases

C57BL/6 mice were immunized intradermally with various doses of purified pCEP4 plasmid DNA containing full-length MUC1 cDNA (22 tandem repeats). Mice immunized with MUC1 DNA three times at weekly intervals had serum antibodies to a synthetic peptide corresponding to the tandem repeats of MUC1. The antibody titer correlated with the plasmid DNA dose. After the third immunization mice were injected intravenously with 5 x 10(5) 16-F10 melanoma cells that had been stably transfected with MUC1 cDNA (F10-MUC1-C8 clone cells). The number of lung metastatic nodules three weeks after inoculation of F10-MUC1-C8 cells was significantly lower in mice immunized with MUC1 plasmid DNA than in mice immunized with the vector DNA alone. Thus, the suppression of lung metastasis was antigen-specific. In vivo depletion of lymphocyte subpopulations by specific antibodies revealed that natural killer cells are the major effector cells responsible for the suppression of lung metastasis. CD4+ cells and CD8+ cells apparently played some roles too.

Stabilization of alum-adjuvanted vaccine dry powder formulations: mechanism and application

Studies were performed to elucidate the mechanism of alum gel coagulation upon freezing and drying and its relationship to vaccine potency loss and to develop a novel freeze-drying process for the production of stable alum-adjuvanted vaccine formulations suitable for conventional needle injection and epidermal powder immunization (EPI). The alum hydroxide-adjuvanted hepatitis-B surface antigen (Alum-HBsAg) and the alum phosphate-adjuvanted diphtheria and tetanus toxoids (Alum-DT) were dehydrated by freeze drying (FD), spray drying (SD), air drying (AD), or spray freeze drying (SFD). After drying by FD, SD, or AD, alum gels coagulated when examined by optical microscopy and particle size analysis. In addition, desorption of antigen molecules from the coagulated when examined by optical microscopy and particle size analysis. In addition, desorption of antigen molecules from the coagulated alum gel upon reconstitution appeared to be difficult, as indicated by attenuated band intensity on SDS-PAGE. In contrast, SFD alum gels turned a homogenous suspension upon reconstitution, suggesting minimal alum coagulation. In the mouse model, the in vivo immunogenicity of SFD Alum-HBsAg was preserved, whereas the FD Alum-HBsAg suffered significant immunogenicity loss. Grinding of coagulated FD Alum-HBsAg into smaller particles could partially recover the immunogenicity. In a guinea pig study using EPI, the SD Alum-DT formulation was not immunogenic, but the SFD Alum-DT formulations had a vaccine potency comparable to that of the untreated DT administered by I.M. injection. Overall, the relationship of coagulation of alum gel upon reconstitution and the loss of vaccine potency was established in this study. Alum gels became highly coagulated after dehydration by spray drying and traditional freeze-drying processes. However, freezing rate played a critical role in preserving the adjuvant effect of alum and fast freezing decreased the tendency of alum coagulation. Spraying the alum gel into liquid nitrogen represents the fastest freezing rate achievable and resulted in no discernible alum coagulation. Therefore, SFD presents a novel and effective drying process for alum-adjuvanted vaccine formulations and is particularly valuable for dry powder applications such as EPI.

Vascular complications and gene therapy

For gene therapy, the last few years have been an exciting period. Encouraging results from several successful gene therapy trials were reported. Children born with a life-threatening immune system disorder, severe combined immune deficiency (SCID), were cured after receiving gene therapy for replacement of their defective adenosine deaminase (ADA) gene. Gene therapy successes related to vascular complications were also reported. The first human gene therapy trial for a blood-vessel disorder was performed successfully, in which copies of an angiogenic gene, the vascular endothelial growth factor (VEGF) gene, were directly delivered to the area surrounding the diseased artery of the leg of a patient with peripheral artery disease. Within a few days, this stimulated the growth of new blood vessels around the blockage in the ailing blood vessel and helped avoid amputation. In 1998, a patient with genetically small arteries became the first to receive VEGF gene therapy in the heart. Multiple copies of a plasmid with the VEGF gene were delivered into the damaged area of the heart, and a few days later angiogenesis ensued that helped bypass the blocked vessel, with markedly reduced chest pain in the patient. Gene therapy is becoming a reality and, more importantly, it appears to be safe and does not require supplementary immuno-suppressing drugs. Gene therapy seems to have begun delivering on its promises.