Catch Me If You Can--The Race Between HIV and Neutralizing Antibodies.

Broadly neutralizing antibodies represent the major protective mechanism of vaccines targeting pathogenic microbes in humans and animals. For HIV, broadly neutralizing antibodies have also been shown to be protective in experimental animal models. However, despite the identification of a respectable number of broadly neutralizing antibodies from chronically infected HIV-positive persons in recent years, attempts to induce such antibodies by vaccines have generally failed over the last decades. Though unsuccessful in view of achieving a protective vaccine against HIV, many of these studies have contributed significantly to the understanding of the generation of broadly neutralizing antibodies against HIV-1 as well as to the vulnerable sites they target on the surface of the virus. Here we review the most important features of patient-derived broadly neutralizing antibodies, the long and complex B-cell maturation pathways required for their production, and the resulting consequences for vaccine development. We further address characteristics of the epitopes targeted by broadly neutralizing antibodies on the virus surface as well as mechanisms of viral escape. Taken together, the identification of vaccine candidates able to induce broadly neutralizing antibodies against HIV-1 is the major challenge in HIV vaccine development. Mutual coevolution of rationally designed HIV vaccine candidates, with affinity maturation pathways of antibodies they induce upon vaccination, may best mimic the natural situation of chronically HIV-infected patients who are able to generate broadly neutralizing antibodies.

Re-engineering vesicular stomatitis virus to abrogate neurotoxicity, circumvent humoral immunity, and enhance oncolytic potency.

As cancer treatment tools, oncolytic viruses (OV) have yet to realize what some see as their ultimate clinical potential. In this study, we have engineered a chimeric vesicular stomatitis virus (VSV) that is devoid of its natural neurotoxicity while retaining potent oncolytic activity. The envelope glycoprotein (G) of VSV was replaced with a variant glycoprotein of the lymphocytic choriomeningitis virus (LCMV-GP), creating a replicating therapeutic, rVSV(GP), that is benign in normal brain but can effectively eliminate brain cancer in multiple preclinical tumor models in vivo. Furthermore, it can be safely administered systemically to mice and displays greater potency against a spectrum of human cancer cell lines than current OV candidates. Remarkably, rVSV(GP) escapes humoral immunity, thus, for the first time, allowing repeated systemic OV application without loss of therapeutic efficacy. Taken together, rVSV(GP) offers a considerably improved OV platform that lacks several of the major drawbacks that have limited the clinical potential of this technology to date.

Comparison of three humanized mouse models for adoptive T cell transfer.

BACKGROUND: Humanized mouse models for adoptive T cell transfer are important for preclinical efficacy and toxicity studies. However, common xenograft models using immunodeficient mice have so far failed to efficiently support the homing of human T cells to secondary lymphoid tissues. METHODS: We established a new mouse model for the adoptive transfer of genetically-modified (gm) T cells using conditioned BALB/c mice. Conditioning involved cyclophosphamide injections, lethal irradiation and radioprotection with bone marrow from immunodeficient mice. We compared repopulation kinetics and the quality of grafts in these modified Trimera (mT3) mice with immunodeficient BALB/c Rag2(-/-) interleukin (IL)2 receptor gamma (rg) knockout (DKO) and NOD/LtSz-scid IL2rg(-/-) (NSG) recipient mouse strains. RESULTS: DKO mice showed only marginal engraftment until onset of graft-versus-host disease, whereas mT3 and NSG were repopulated with comparable kinetics. However, T cell repertoire and human cytokine profiles suggest a xenoreactivity-driven gm T cell expansion in mT3 mice, whereas NSG mice were characterized by an initial homeostatic proliferation. Morphological analysis revealed high levels of human gm T cell infiltration in the spleen and liver of all three mouse strains. However, mT3 mice provided the strongest homing of human gm T cells to mucosal sites. Additionally, mT3 mice were the only model with macroscopically visible superficial inguinal lymph nodes. These lymph nodes strongly supported the homing of gm T cells. CONCLUSIONS: In the present study, we give proof-of-concept that wild-type mice can accept gm T cell grafts while providing secondary lymphoid structures. Despite limitations, mT3 mice are a valid alternative for applications that specifically rely on improved secondary lymphoid structures.

Semireplication-competent vesicular stomatitis virus as a novel platform for oncolytic virotherapy.

Among oncolytic viruses, the vesicular stomatitis virus (VSV) is especially potent and a highly promising agent for the treatment of cancer. But, even though effective against multiple tumor entities in preclinical animal models, replication-competent VSV exhibits inherent neurovirulence, which has so far hindered clinical development. To overcome this limitation, replication-defective VSV vectors for cancer gene therapy have been tested and proven to be safe. However, gene delivery was inefficient and only minor antitumor efficacy was observed. Here, we present semireplication-competent vector systems for VSV (srVSV), composed of two trans-complementing, propagation-deficient VSV vectors. The de novo generated deletion mutants of the two VSV polymerase proteins P (phosphoprotein) and L (large catalytic subunit), VSVΔP and VSVΔL respectively, were used mutually or in combination with VSVΔG vectors. These srVSV systems copropagated in vitro and in vivo without recombinatory reversion to replication-competent virus. The srVSV systems were highly lytic for human glioblastoma cell lines, spheroids, and subcutaneous xenografts. Especially the combination of VSVΔG/VSVΔL vectors was as potent as wild-type VSV (VSV-WT) in vitro and induced long-term tumor regression in vivo without any associated adverse effects. In contrast, 90% of VSV-WT-treated animals succumbed to neurological disease shortly after tumor clearance. Most importantly, even when injected into the brain, VSVΔG/VSVΔL did not show any neurotoxicity. In conclusion, srVSV is a promising platform for virotherapeutic approaches and also for VSV-based vector vaccines, combining improved safety with an increased coding capacity for therapeutic transgenes, potentially allowing for multipronged approaches.