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McKee, TD, Grandi, P, Mok, W, Alexandrakis, G, Insin, N, Zimmer, JP et al. (2006). Degradation of fibrillar collagen in a human melanoma xenograft improves the efficacy of an oncolytic herpes simplex virus vector. Cancer Res 66: 2509–2513. 7. Wang, Y, Hallden, G, Hill, R, Anand, A, Liu, TC, Francis, J et al. (2003). E3 gene manipulations affect oncolytic adenovirus activity in immunocompetent tumor models. Nat Biotechnol 21: 1328–1335. 8. Gaggar, A, Shayakhmetov, DM and Lieber, A (2003). CD46 is a cellular receptor for group B adenoviruses. Nat Med 9: 1408–1412. 9. Kambara, H, Saeki, Y and Chiocca, EA (2005). Cyclophosphamide allows for in vivo dose reduction of a potent oncolytic virus. Cancer Res 65: 11255–11258. 10. Power, AT and Bell, JC (2007). Cell-based delivery of oncolytic viruses: a new strategic alliance for a biological strike against cancer. Mol Ther 15: 660–665. 11. Laurie, SA, Bell, JC, Atkins, HL, Roach, J, Bamat, MK, O’Neil, JD et al. (2006). A phase 1 clinical study of intravenous administration of PV701, an oncolytic
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virus, using two-step desensitization. Clin Cancer Res 12: 2555–2562. Thorne, SH, Hwang, TH, O’Gorman, WE, Bartlett, DL, Sei, S, Kanji, F et al. (2007). Rational strain selection and engineering creates a broad-spectrum, systemically effective oncolytic poxvirus, JX-963. J Clin Invest 117: 3350–3358. Wang, Y, Thorne, S, Hannock, J, Francis, J, Au, T, Reid, T et al. (2005). A novel assay to assess primary human cancer infectibility by replication-selective oncolytic adenoviruses. Clin Cancer Res 11: 351–360. Rots, MG, Elferink, MG, Gommans, WM, Oosterhuis, D, Schalk, JA, Curiel, DT et al. (2006). An ex vivo human model system to evaluate specificity of replicating and non-replicating gene therapy agents. J Gene Med 8: 35–41. Wein, LM, Wu, JT and Kirn, DH (2003). Validation and analysis of a mathematical model of a replicationcompetent oncolytic virus for cancer treatment: implications for virus design and delivery. Cancer Res 63: 1317–1324.
Lentivector Targeting to Dendritic Cells Alexander Ageichik1, Mary K Collins1 and Marie Dewannieux1 doi:10.1038/mt.2008.95
D
evelopment of effective vaccines for the immunotherapy of cancer or persistent infectious disease will require the reactivation of a suboptimal immune response; in the case of cancer immunotherapy this often involves breaking immunologic tolerance to selfantigens expressed by the tumor cells. Dendritic cells (DCs) are the most potent antigen-presenting cells of the immune system, and much effort has therefore been devoted to methods for delivering appropriate antigen to DCs to induce immunization. Initial DC therapies tested in clinical trials used autologous DCs cultured in the laboratory, loaded with antigen, and then re-injected.1 However, more cost-effective and efficient protocols will involve direct delivery of antigens to DCs in vivo.2 Targeting of antigens to DCs can be achieved by linking antigens to antibodies that recognize DC surface molecules (e.g., Bonifaz et al.3) or by targeting viral vectors to DCs 1
Division of Infection and Immunity, University College London, London, UK Correspondence: Mary K Collins, Division of Infection and Immunity, University College London, Windeyer Building, 46 Cleveland Street, London W1T 4JF, UK. E-mail:
[email protected]
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so that they then express antigens within the antigen-presenting cell. DCs residing in the skin and lymph nodes constitute the natural detection system for external pathogens and are thus relevant for vaccination. Viral vector targeting to DCs can potentially avoid antigen expression in other tissues, and DCs may recognize the viral vectors as pathogens and become activated, increasing the potency of immunization. Adenoviral vectors are potent immunogens, and it has recently proved possible to engineer adenovirus serotype 5 to improve DC specificity and maintain immunogenicity.4 Targeting of enveloped viruses—for example, using single-chain antibodies fused to murine leukemia virus envelope—has often resulted in relatively inefficient infection because the function of the chimeric envelope protein was compromised to some extent (e.g., Martin et al.5). As an alternative solution to this problem, binding-deficient but fusion-competent mutants were isolated from Sindbis and measles viruses and used to retarget binding without affecting the efficiency of fusion.6,7 In these viruses the binding and fusion functions could be separated because they reside on different envelope glycoproteins. The
Sindbis virus envelope has also been used for retargeting lentiviral vectors (lentivectors).8 Lentivectors are attractive vaccine vector candidates because they can transduce DCs in vivo without interfering with their function and then induce both cellular and humoral immune responses.9–11 In a recent article, Yang and collaborators presented an elegant piece of work in which they achieved high targeting specificity in vivo using a lentivectorbased vaccine.12 Instead of trying to add a new module to the glycoprotein so as to target the vector, they decided to take advantage of the in vivo tropism of Sindbis virus, which naturally shows preference for DCs. They further restricted infection by inactivating its binding to broadly expressed heparan sulfate molecules. This strategy enabled them to show infection of DCs in culture via DC-SIGN, the other natural receptor of Sindbis virus, which is expressed mainly by DCs. Interestingly, this modified glycoprotein works equally well with mouse and human DC-SIGN molecules, making it an interesting candidate for human therapeutic applications. The in vivo studies in mice showed infection of DCs, with substantially fewer offtarget transduction events than with the more commonly used vesicular stomatitis virus G (VSV-G)–pseudotyped lentivectors. Despite reducing the number of in vivo–infected cells, this protocol still resulted in strong immunization against the model antigen ovalbumin, with the induction of both specific CD8+ T cells and an antibody response. In this respect, the authors’ results resemble those from our group using a specific promoter to target lentivector-driven antigen expression to DCs in vivo.13 From a functional point of view, the surface-targeted in vivo vaccination was strong enough to protect mice against challenge with a tumor expressing ovalbumin, and it also proved efficient in tumor-therapy experiments. These results are highly encouraging for the future of lentivector-based vaccination strategies. However, before they can be used with patients for whom alternative therapies exist, there are safety considerations that must be tackled, such as the possibility of insertional mutagenesis. The reduction in in vivo–transduced cells that can be achieved by efficient targeting www.moleculartherapy.org vol. 16 no. 6 june 2008
© The American Society of Gene Therapy
of DCs is an important step; however, the in vivo tropism of the targeted Sindbis virus must be further assessed with more sensitive methods than the luciferasebased system used in the present study. It is possible that the background infection of cells lacking DC-SIGN still shown by this system may be improved by further mutagenesis. Furthermore, persistence of transduced DCs or other antigen-presenting cells following vector integration may result in prolonged antigen presentation, the consequences of which are not yet fully understood. The ability of DCs to capture viruses via DC-SIGN and transmit them to other cells must also be evaluated in this system. In the case of HIV, this mechanism results in viral spreading far from the site of initial infection.14 Despite these technical issues, Yang and collaborators provide a proof-ofprinciple study of lentivector targeting to DCs, which can lead to improved human vaccination. A strength of their strategy may be that, compared with other lentiviral pseudotypes that have been tested in mice, the targeting via DC-SIGN results in both antigen presentation and concomitant DC activation,
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demonstrated in mouse DC cultures. We have reported that VSV-G–pseudotyped lentivectors do not activate such mouse DCs unless an intracellular activator of the p38 MAP kinase pathway is coexpressed with the antigen.15 The reason for the difference between Sindbis- and VSV-G–pseudotyped lentivectors in the induction of DC maturation is unknown; it may be hypothesized that attachment of Sindbis glycoproteins to DC-SIGN provides DCs with the maturation signals they require. This could allow initiation of a strong immune response despite low transduction efficiency.
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Steinman, RM and Banchereau, J (2007). Taking dendritic cells into medicine. Nature 449: 419–426. Tacken, PJ, de Vries, IJ, Torensma, R and Figdor, CG (2007). Dendritic-cell immunotherapy: from ex vivo loading to in vivo targeting. Nat Rev Immunol 7: 790–802. Bonifaz, LC, Bonnyay, DP, Charalambous, A, Darguste, DI, Fujii, S, Soares, H et al. (2004). In vivo targeting of antigens to maturing dendritic cells via the DEC-205 receptor improves T cell vaccination. J Exp Med 199: 815–824. Cheng, C, Gall, JG, Kong, WP, Sheets, RL, Gomez, PL, King, CR et al. (2007). Mechanism of ad5 vaccine immunity and toxicity: fiber shaft targeting of dendritic cells. PLoS Pathog 3: e25. Martin, F, Neil, S, Kupsch, J, Maurice, M, Cosset, F and Collins, M (1999). Retrovirus targeting by tropism restriction to melanoma cells. J Virol 73: 6923–6929.
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