Commercially available immunoglobulins contain virus neutralizing antibodies against all major genotypes of polyomavirus BK.

Neutralizing antibodies (NAbs) form the basis of immunotherapeutic strategies against many important human viral infections. Accordingly, we studied the prevalence, titer, genotype-specificity, and mechanism of action of anti-polyomavirus BK (BKV) NAbs in commercially available human immune globulin (IG) preparations designed for intravenous (IV) use. Pseudovirions (PsV) of genotypes Ia, Ib2, Ic, II, III, and IV were generated by co-transfecting a reporter plasmid encoding luciferase and expression plasmids containing synthetic codon-modified VP1, VP2, and VP3 capsid protein genes into 293TT cells. NAbs were measured using luminometry. All IG preparations neutralized all BKV genotypes, with mean EC50 titers as high as 254 899 for genotype Ia and 6,666 for genotype IV. Neutralizing titers against genotypes II and III were higher than expected, adding to growing evidence that infections with these genotypes are more common than currently appreciated. Batch to batch variation in different lots of IG was within the limits of experimental error. Antibody mediated virus neutralizing was dose dependent, modestly enhanced by complement, genotype-specific, and achieved without effect on viral aggregation, capsid morphology, elution, or host cell release. IG contains potent NAbs capable of neutralizing all major BKV genotypes. Clinical trials based on sound pharmacokinetic principles are needed to explore prophylactic and therapeutic applications of these anti-viral effects, until effective small molecule inhibitors of BKV replication can be developed.

NHPV16 VLP vaccine induces human antibodies that neutralize divergent variants of HPV16.

Genital HPV genotypes are generally distinct serotypes, but whether variants within a genotype can represent serologic subtypes is unclear. In this study we used serum from human volunteers vaccinated with HPV16 L1 VLPs from variant 114K, to examine cross-neutralization of variants from each of the five major phylogenetic branches of HPV16. Recombinant Semliki Forest virus-derived pseudovirions for each variant were generated and combined with serum from vaccines, and the mixture was monitored for infectivity in a standard C127 cell focal transformation assay. Sera from all 10 VLP-immunized individuals had neutralizing activity against each of the variant pseudovirions. For each of the sera, variant titers differed by only fourfold or less from the median titer. Therefore, from a vaccine perspective, HPV16 variants belong to a single serotype. Vaccination with HPV16 114K L1 VLPs generates antibodies that should confer a similar degree of protection against all known phylogenetic branches of HPV16.

Effect of preexisting neutralizing antibodies on the anti-tumor immune response induced by chimeric human papillomavirus virus-like particle vaccines.

Chimeric human papillomavirus virus-like particles (HPV cVLPs) carrying HPV16 E7 protein are potent vaccines for inducing cell-mediated immunity (CMI) against HPV-induced tumors in animal models. We tested the hypothesis that virion-neutralizing antibodies generated during an initial vaccination might prevent effective boosting of CMI to the cVLPs. Mice with circulating HPV16-neutralizing antibodies, generated by direct immunization with wild-type VLPs or by passive transfer of hyperimmune anti-HPV16 VLP mouse sera, were subsequently vaccinated with HPV16 E7-containing cVLPs. Mice with preexisting neutralizing antibodies were not protected from HPV16 E7-positive TC-1 tumor challenge, compared to the protection seen in mice lacking these antibodies. Antibody-coated VLPs bound very inefficiently to receptor-positive cell lines, suggesting that one of the mechanisms of antibody interference is blocking of VLP binding to its receptor and thereby uptake of VLPs by antigen-presenting cells. Our results suggest that repetitive vaccination with a cVLP for induction of cellular immune responses to an incorporated antigen may be of limited effectiveness due to the presence of neutralizing antibodies against the capsid proteins induced after the first application. This limitation could potentially be overcome by boosting with cVLPs containing the same target antigen incorporated into other papillomavirus-type VLPs.

Filarial nematode parasites secrete a homologue of the human cytokine macrophage migration inhibitory factor.

Filarial nematode parasites establish long-term chronic infections in the context of an antiparasite immunity that is strongly biased toward a Th2 response. The mechanisms that lead to this Th2 bias toward filarial antigens are not clear, but one possibility is that the parasites produce molecules that have the capacity to proactively modify their immunological environment. Here we report that filarial parasites of humans secrete a homologue of the human proinflammatory cytokine macrophage migration inhibitory factor (MIF) that has the capability of modifying the activity of human monocytes/macrophages. A cDNA clone isolated from a Brugia malayi infective-stage larva expression library encoded a 12.5-kDa protein product (Bm-MIF) with 42% identity to human and murine MIF. MIF homologues were also found to be expressed in the related filarial species Wuchereria bancrofti and Onchocerca volvulus. Bm-mif was transcribed by adult and larval parasites, and the protein product was found in somatic extracts and in the parasite's excretory-secretory products. Immunohistocytochemistry revealed that Bm-MIF was localized to cells of the hypodermis/lateral chord, the uterine wall, and larvae developing in utero. Unexpectedly, the activities of recombinant Bm-MIF and human MIF on human monocytes/macrophages were found to be similar. When placed with monocytes/macrophages in a cell migration assay, Bm-MIF inhibited random migration. When placed away from cells, Bm-MIF induced an increase in monocyte/macrophage migration that was specifically inhibited by neutralizing anti-Bm-MIF antibodies. Bm-MIF is the first demonstration that helminth parasites produce cytokine homologues that have the potential to modify host immune responses to promote parasite survival.