Virus-like particles (VLPs) have increasingly attracted attention as DNA-free and safe antigen carriers in tumor immunotherapy, requiring only minute amounts of antigens. Previously, we have immunized with murine polyomavirus (MPyV) VLPs carrying human Her2/neu and prevented the outgrowth of a human Her2/ neu expressing tumor in a transplantable tumor model as well as outgrowth of spontaneous rat Her2/neu carcinomas in BALBneuT mice. Here, we examine if prophylactic and therapeutic protection could be obtained with murine pneumotropic virus (MPtV) VLPs, and study the cross-reactivity between human and rat Her2/neu. VLPs from MPyV and MPtV carrying human or rat Her2/neu were tested in two transplantable tumor models against a human Her2/neu positive (D2F2/E2) and a rat Her2/neu positive tumor cell line (TUBO). Rat Her2/neu-VLPs were also tested in BALB-neuT mice. Her2/neu-MPtVLPs were as efficient as prophylactic vaccines against D2F2/E2 and TUBO as those from MPyV. Homologous Her2/neu was better than heterologous, i.e. human Her2/neu-VLPs were better than rat Her2/neu-VLPs against D2F2/E2 and vice versa. Moreover, therapeutic immunization with human Her2/neu-VLPs together with CpG given up to 6 days after challenge protected against D2F2/E2. In BALB-neuT mice, rat Her2/neu-VLPs were less efficient than human Her2/ neu-VLPs used in our previous study, implying that protection seen in that study was partly due to the use of human rather than rat Her2/neu. In conclusion, Her2/neu-MPtVLPs are effective both as prophylactic and therapeutic tumor vaccines. Homologous Her2/neu-VLPs are superior to heterologous in transplantable tumor models, while the opposite is true in BALB-neuT mice. ' 2008 Wiley-Liss, Inc.Key words: Her2; neu; virus-like particle; polyomavirus; immunotherapy Breast cancer is the most common cancer among women in the Western world. In about 20% of all cases, the proto-oncogene Her2/neu is overexpressed. Her2/neu is a tyrosine kinase receptor belonging to the epidermal growth factor receptor family and is composed of extracellular, transmembrane and intracellular domains. 1 On the one hand, overexpression of Her2/neu is associated with poor prognosis 2 ; on the other, it renders novel therapies directed against Her2/neu possible, of which the monoclonal antibody trastuzumab is the best known. 3 Unfortunately, however, most women sooner or later develop resistance against trastuzumab, warranting the search for other treatments. 4 Several immunotherapeutic strategies against Her2/neu have therefore been evaluated both in humans 5,6 and in mouse models. 7-9 Her2/neu is an attractive tumor antigen for several reasons. First of all, it is selectively overexpressed in malignant cells. Second, the transformed phenotype is dependent on the expression of Her2/neu, making antigen-negative variants less likely. Third, and very important, immune responses to Her2/neu are frequently found in patients with Her2/neu positive breast cancer, 10,11 demonstrating that tolerance to Her2/neu can be broken in humans.Caps...

Virus-like particles (VLPs) consist of capsid proteins from viruses and have been shown to be usable as carriers of protein and peptide antigens for immune therapy. In this study, we have produced and assayed murine polyomavirus (MPyV) VLPs carrying the entire human Prostate Specific Antigen (PSA) (PSA-MPyVLPs) for their potential use for immune therapy in a mouse model system. BALB/c mice immunized with PSA-MPyVLPs were only marginally protected against outgrowth of a PSA-expressing tumor. To improve protection, PSA-MPyVLPs were co-injected with adjuvant CpG, either alone or loaded onto murine dendritic cells (DCs). Immunization with PSA-MPyVLPs loaded onto DCs in the presence of CpG was shown to efficiently protect mice from tumor outgrowth. In addition, cellular and humoral immune responses after immunization were examined. PSA-specific CD4+ and CD8+ cells were demonstrated, but no PSA-specific IgG antibodies. Vaccination with DCs loaded with PSA-MPyVLPs induced an eight-fold lower titre of anti-VLP antibodies than vaccination with PSA-MPyVLPs alone. In conclusion, immunization of BALB/c mice with PSA-MPyVLPs, loaded onto DCs and co-injected with CpG, induces an efficient PSA-specific tumor protective immune response, including both CD4+ and CD8+ cells with a low induction of anti-VLP antibodies.

BackgroundImmunization with murine pneumotropic virus virus-like particles carrying Her2/neu (Her2MPtVLPs) prevents tumour outgrowth in mice when given prophylactically, and therapeutically if combined with the adjuvant CpG. We investigated which components of the immune system are involved in tumour rejection, and whether long-term immunological memory can be obtained.Methodology and ResultsDuring the effector phase in BALB/c mice, only depletion of CD4+ and CD8+ in combination, with or without NK cells, completely abrogated tumour protection. Depletion of single CD4+, CD8+ or NK cell populations only had minor effects. During the immunization/induction phase, combined depletion of CD4+ and CD8+ cells abolished protection, while depletion of each individual subset had no or negligible effect. When tumour rejection was studied in knock-out mice with a C57Bl/6 background, protection was lost in CD4−/−CD8−/− and CD4−/−, but not in CD8−/− mice. In contrast, when normal C57Bl/6 mice were depleted of different cell types, protection was lost irrespective of whether only CD4+, only CD8+, or CD4+ and CD8+ cells in combination were eradicated. No anti-Her2/neu antibodies were detected but a Her2/neu-specific IFNγ response was seen. Studies of long-term memory showed that BALB/c mice could be protected against tumour development when immunized together with CpG as long as ten weeks before challenge.ConclusionHer2MPtVLP immunization is efficient in stimulating several compartments of the immune system, and induces an efficient immune response including long-term memory. In addition, when depleting mice of isolated cellular compartments, tumour protection is not as efficiently abolished as when depleting several immune compartments together.

We consider the comparatively restrictive Swedish recommendations to be safe and recommend that palivizumab should also be used very restrictively in the future. In our opinion, palivizumab in preterm children could be recommended only for those with chronic lung disease younger than 1 y of age, and with active treatment for their disease.