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We previously developed an innovative strategy to induce CD8+T lymphocyte-immunity through in vivo engineering of extracellular vesicles (EVs). This approach relies on intramuscular injection of DNA expressing antigens of interest fused at a biologically-inactive HIV-1 Nef protein mutant (Nefmut). Nefmutis very efficiently incorporated into EVs, thus conveying large amounts of fusion proteins into EVs released by transfected cells. This platform proved successful against highly immunogenic tumor-specific antigens. Here, we tested whether antigen-specific CD8+T cell immune responses induced by engineered EVs can counteract the growth of tumors expressing two “self” tumor-associated antigens (TAAs): HOXB7 and Her2/neu. FVB/N mice were injected with DNA vectors expressing Nefmutfused to HOXB7 or Her2/neu, singly and in combination, before subcutaneous implantation of breast carcinoma cells co-expressing HOXB7 and Her2/neu. All mice immunized with the combination vaccine remained tumor-free, whereas groups vaccinated with single Nefmut-fused antigens were only partly protected, with stronger antitumor effects in Her2/neu-immunized mice. Double-vaccinated mice also controlled tumor growth upon a later tumor cell re-challenge. Importantly, co-vaccination also contained tumors in a therapeutic immunization setting. These results showed the efficacy of EV-based vaccination against two TAAs, and represent the first demonstration that HOXB7 may be targeted in multi-antigen immunotherapy strategies.

Expression of the human immunodeficiency virus type 1 (HIV-1) Nef triple mutant F12Nef strongly inhibits HIV-1 replication. We exploited such a unique feature in a novel anti-HIV-1 gene therapy design by constructing an HIV-1 Tat-defective lentivirus vector expressing the product of fusion between the low-affinity human nerve growth factor receptor truncated in its intracytoplasmic domain (ΔNGFr, NH2 moiety), and F12Nef (COOH moiety), under the control of the HIV-1 long terminal repeats. In this manner, both the selection marker (ΔNGFr) and the anti-HIV-1 effector are comprised in the same fusion protein, the expression of which is targetable by HIV-1 infection. Such a vector was proved to transduce human cells efficiently and, on HIV-1 infection, it expressed high levels of the fusion protein. In addition, strong antiviral activity of the ΔNGFr/F12Nef-expressing vector was demonstrated in cell lines as well as in primary cell cultures challenged with T- or M-tropic HIV-1 isolates. Thus, the HIV-1-targetable expression of the ΔNGFr/F12Nef fusion protein represents a novel and powerful tool for an effective anti-HIV-1 gene therapy strategy.

ABSTRACTF12 human immunodeficiency virus type 1 (HIV-1) nefis a naturally occurring nefmutant cloned from the provirus of a nonproductive, nondefective, and interfering HIV-1 variant (F12-HIV). We have already shown that cells stably transfected with a vector expressing the F12-HIV nefallele do not downregulate CD4 receptors and, more peculiarly, become resistant to the replication of wild type (wt) HIV. In order to investigate the mechanism of action of such an HIV inhibition, the F12-HIVnefgene was expressed in the context of the NL4-3 HIV-1 infectious molecular clone by replacing the wt nefgene (NL4-3/chi). Through this experimental approach we established the following. First, NL4-3/chi and nef-defective (?nef) NL4-3 viral particles behave very similarly in terms of viral entry and HIV protein production during the first replicative cycle. Second, no viral particles were produced from cells infected with NL4-3/chi virions, whatever the multiplicity of infection used. The viral inhibition apparently occurs at level of viral assembling and/or release. Third, this block could not be relieved by in-transexpression of wt nef. Finally, NL4-3/chi reverts to a producer HIV strain when F12-HIV Nef is deprived of its myristoyl residue. Through a CD4 downregulation competition assay, we demonstrated that F12-HIV Nef protein potently inhibits the CD4 downregulation induced by wt Nef. Moreover, we observed a redistribution of CD4 receptors at the cell margin induced by F12-HIV Nef. These observations strongly suggest that F12-HIV Nef maintains the ability to interact with the intracytoplasmic tail of the CD4 receptor molecule. Remarkably, we distinguished the intracytoplasmic tails of Env gp41 and CD4 as, respectively, viral and cellular targets of the F12-HIV Nef-induced viral retention. For the first time, the inhibition of the viral life cycle by means of in-cisexpression of a Nef mutant is here reported. Delineation of the F12-HIV Nef mechanism of action may offer additional approaches to interference with the propagation of HIV infection.

ABSTRACTWe previously demonstrated that expression of the nonproducer F12-human immunodeficiency virus type 1 (HIV-1) variant induces a block in the replication of superinfecting HIV that does not depend on the down-regulation of CD4 HIV receptors. In order to individuate the gene(s) involved in F12-HIV-induced interference, vectors expressing each of the nine F12-HIV proteins were transfected in HIV-susceptible HeLa CD4 cells. Pools of cell clones stably producing each viral protein were infected with HIV-1, and virus release was measured in terms of reverse transcriptase activity in supernatants. We hereby demonstrate that HeLa CD4 cells expressing the F12-HIV gag, vif, ornefgene were resistant, to different degrees, to infection with T-cell-line-adapted HIV-1 strains. Conversely, expression of either the tat, rev, or vpuF12-HIV gene increased the rate of HIV release, and no apparent effects on HIV replication were observed in cells expressing either the F12-HIVvpr, pol, or envgene. No variation of CD4 exposure was detected in any of the uninfected HeLa CD4 pools. These data indicate that F12-HIV homologous viral interference is the consequence of the synergistic anti-HIV effects of Gag, Vif, and Nef proteins. Retrovirus vectors expressing F12-HIV vifornefallowed us to further establish that the expression of each mutated protein (i) inhibits the replication of clinical HIV-1 isolates as well, (ii) impairs the infectivity of the virus released by cells chronically infected with HIV-1, and (iii) limitedly to F12-HIV Vif protein, induces HIV resistance in both vif-permissive and vif-nonpermissive cells. The levels of action of F12-HIV vifand nefanti-HIV effects were also determined. We observed that HIV virions emerging from the first viral cycle on F12-HIV vif-expressing cells, although released in unaltered amounts, had a strongly reduced ability to initiate the retrotranscription process when they reinfected parental HeLa CD4 cells. Differently, we observed that expression of F12-HIV Nef protein affects the HIV life cycle at the level of viral assembling and/or release. For the first time, an inhibitory effect on the HIV life cycle in both acutely and chronically infected cells induced by mutated Vif and Nef HIV-1 proteins is described. These genes could thus be proposed as new useful reagents for anti-HIV gene therapy.