Effect of heat-labile factors on the neutralization of vaccinia virus by human

Phase 1 Study of Intravenous Oncolytic Poxvirus (vvDD) in Patients With Advanced Solid Cancers

We have conducted a phase 1 study of intravenous vvDD, a Western Reserve strain oncolytic vaccinia virus, on 11 patients with standard treatment-refractory advanced colorectal or other solid cancers. The primary endpoints were maximum tolerated dose and associated toxicity while secondary endpoints were pharmacokinetics, pharmacodynamics, immune responses, and antitumor activity. No dose-limiting toxicities and treatment related severe adverse events were observed. The most common adverse events were grades 1/2 flu-like symptoms. Virus genomes were detectable in the blood 15–30 minutes after virus administration in a dose-dependent manner. There was evidence of a prolonged virus replication in tumor tissues in two patients, but no evidence of virus replication in non-tumor tissues, except a healed injury site and an oral thrush. Over 100-fold of anti-viral antibodies were induced in patients' sera. A strong induction of inflammatory and Th1, but not Th2 cytokines, suggested a potent Th1-mediated immunity against the virus and possibly the cancer. One patient showed a mixed response on PET-CT with resolution of some liver metastases, and another patient with cutaneous melanoma demonstrated clinical regression of some lesions. Given the confirmed safety, further trials evaluating intravenous vvDD in combination with therapeutic transgenes, immune checkpoint blockade or complement inhibitors, are warranted.

Complement inhibition prevents oncolytic vaccinia virus neutralization in immune humans and cynomolgus macaques

Oncolytic viruses (OVs) have shown promising clinical activity when administered by direct intratumoral injection. However, natural barriers in the blood, including antibodies and complement, are likely to limit the ability to repeatedly administer OVs by the intravenous route. We demonstrate here that for a prototype of the clinical vaccinia virus based product Pexa-Vec, the neutralizing activity of antibodies elicited by smallpox vaccination, as well as the anamnestic response in hyperimmune virus treated cancer patients, is strictly dependent on the activation of complement. In immunized rats, complement depletion stabilized vaccinia virus in the blood and led to improved delivery to tumors. Complement depletion also enhanced tumor infection when virus was directly injected into tumors in immunized animals. The feasibility and safety of using a complement inhibitor, CP40, in combination with vaccinia virus was tested in cynomolgus macaques. CP40 pretreatment elicited an average 10-fold increase in infectious titer in the blood early after the infusion and prolonged the time during which infectious virus was detectable in the blood of animals with preexisting immunity. Capitalizing on the complement dependence of antivaccinia antibody with adjunct complement inhibitors may increase the infectious dose of oncolytic vaccinia virus delivered to tumors in virus in immune hosts.

Synergistic neutralizing activities of antibodies to outer membrane proteins of the two infectious forms of vaccinia virus in the presence of complement

The two forms of infectious vaccinia virus particles, known as intracellular mature virions and extracellular enveloped virions, are liberated by cell lysis and exocytosis, respectively. The extracellular enveloped form, which is highly resistant to antibody neutralization, contains an outer membrane surrounding an intracellular mature form. We provide evidence that complement mediates antibody-dependent lysis of the outer membrane of extracellular virus, exposing the inner infectious virus to neutralization by a second antibody. These results can help explain the disparity between the in vitro neutralizing and in vivo protective effects of antibodies to extracellular envelope proteins as well as the enhanced protection afforded by specific combinations of antibodies.

Sensitivity of the standardized pseudorabies virus neutralization test varies with the test strain used

The effect of altering the strain of the test virus used in the standardized pseudorabies virus neutralization (VN) test on the sensitivity of the assay was evaluated. Comparative VN tests were performed using 4 different strains: the avirulent Bartha parental, the avirulent recombinant Bartha gIIIKa, the moderately virulent Shope (currently used for the VN test at the National Veterinary Services Laboratory, Ames, IA), and the highly virulent P2208 (Funkhauser). A radioimmunoassay and a Western immunoblotting technique were employed to verify the presence of anti-pseudorabies virus (PrV) antibodies in sera. Statistical analysis indicated that replacement of the Shope strain by the Bartha gIIIKa or the P2208 strain resulted in VN titers that were 4.23- and 2.00-fold higher, respectively. Despite these differences, specificity with regard to PrV diagnosis was unaltered. This apparent enhancement of the sensitivity of the PrV VN test would be beneficial for the serologic identification of PrV-infected animals during an eradication effort.

Poxvirus pathogenesis

Poxviruses are a highly successful family of pathogens, with variola virus, the causative agent of smallpox, being the most notable member. Poxviruses are unique among animal viruses in several respects. First, owing to the cytoplasmic site of virus replication, the virus encodes many enzymes required either for macromolecular precursor pool regulation or for biosynthetic processes. Second, these viruses have a very complex morphogenesis, which involves the de novo synthesis of virus-specific membranes and inclusion bodies. Third, and perhaps most surprising of all, the genomes of these viruses encode many proteins which interact with host processes at both the cellular and systemic levels. For example, a viral homolog of epidermal growth factor is active in vaccinia virus infections of cultured cells, rabbits, and mice. At least five virus proteins with homology to the serine protease inhibitor family have been identified and one, a 38-kDa protein encoded by cowpox virus, is thought to block a host pathway for generating a chemotactic substance. Finally, a protein which has homology with complement components interferes with the activation of the classical complement pathway. Poxviruses infect their hosts by all possible routes: through the skin by mechanical means (e.g., molluscum contagiosum infections of humans), via the respiratory tract (e.g., variola virus infections of humans), or by the oral route (e.g., ectromelia virus infection of the mouse). Poxvirus infections, in general, are acute, with no strong evidence for latent, persistent, or chronic infections. They can be localized or systemic. Ectromelia virus infection of the laboratory mouse can be systemic but inapparent with no mortality and little morbidity, or highly lethal with death in 10 days. On the other hand, molluscum contagiosum virus replicates only in the stratum spinosum of the human epidermis, with little or no involvement of the dermis, and does not spread systemically from the site of infection. The host response to infection is progressive and multifactorial. Early in the infection process, interferons, the alternative pathway of complement activation, inflammatory cells, and natural killer cells may contribute to slowing the spread of the infection. The cell-mediated response involving learned cytotoxic T lymphocytes and delayed-type hypersensitivity components appears to be the most important in recovery from infection. A significant role for specific antiviral antibody and antibody-dependent cell-mediated cytotoxicity has yet to be demonstrated in recovery from a primary infection, but these responses are thought to be important in preventing reinfection.

Poxvirus pathogenesis

Poxviruses are a highly successful family of pathogens, with variola virus, the causative agent of smallpox, being the most notable member. Poxviruses are unique among animal viruses in several respects. First, owing to the cytoplasmic site of virus replication, the virus encodes many enzymes required either for macromolecular precursor pool regulation or for biosynthetic processes. Second, these viruses have a very complex morphogenesis, which involves the de novo synthesis of virus-specific membranes and inclusion bodies. Third, and perhaps most surprising of all, the genomes of these viruses encode many proteins which interact with host processes at both the cellular and systemic levels. For example, a viral homolog of epidermal growth factor is active in vaccinia virus infections of cultured cells, rabbits, and mice. At least five virus proteins with homology to the serine protease inhibitor family have been identified and one, a 38-kDa protein encoded by cowpox virus, is thought to block a host pathway for generating a chemotactic substance. Finally, a protein which has homology with complement components interferes with the activation of the classical complement pathway. Poxviruses infect their hosts by all possible routes: through the skin by mechanical means (e.g., molluscum contagiosum infections of humans), via the respiratory tract (e.g., variola virus infections of humans), or by the oral route (e.g., ectromelia virus infection of the mouse). Poxvirus infections, in general, are acute, with no strong evidence for latent, persistent, or chronic infections. They can be localized or systemic. Ectromelia virus infection of the laboratory mouse can be systemic but inapparent with no mortality and little morbidity, or highly lethal with death in 10 days. On the other hand, molluscum contagiosum virus replicates only in the stratum spinosum of the human epidermis, with little or no involvement of the dermis, and does not spread systemically from the site of infection. The host response to infection is progressive and multifactorial. Early in the infection process, interferons, the alternative pathway of complement activation, inflammatory cells, and natural killer cells may contribute to slowing the spread of the infection. The cell-mediated response involving learned cytotoxic T lymphocytes and delayed-type hypersensitivity components appears to be the most important in recovery from infection. A significant role for specific antiviral antibody and antibody-dependent cell-mediated cytotoxicity has yet to be demonstrated in recovery from a primary infection, but these responses are thought to be important in preventing reinfection.

Comparison of fluorescent-antibody, neutralizing-antibody, and complement-enhanced neutralizing-antibody assays for detection of serum antibody to respiratory syncytial virus

A comparison of three assays for the detection of serum antibody to respiratory syncytial virus (RSV) was carried out on 47 serum samples obtained sequentially from infants and young children with RSV infection. Neutralizing-antibody (NA) activity was determined by a semimicromethod of plaque reduction. Complement-enhanced NA activity was determined by the addition of guinea pig complement to NA assays. RSV antibody responses in immunoglobulin G, immunoglobulin M, and immunoglobulin A classes were determined by using indirect immunofluorescence techniques for fluorescent-antibody (FAb) assay. Antibody to RSV was detectable by all three techniques as early as 4 days after the onset of illness. At all phases of illness, titers obtained by complement-enhanced NA assays were significantly greater than those obtained by NA or FAb assays (P less than 0.01). RSV-FAb titers determined in the immunoglobulin G class correlated well with those determined by complement-enhanced NA or NA assays. The data suggest that the FAb assay for detection of RSV antibody in serum is somewhat less sensitive but also less laborious and more rapid than NA assays.

Studies on the neutralization of herpes simplex virus. X. Demonstration of complement-requiring neutralizing (CRN) and slow-reacting CRN (s-CRN) antibodies in late IgG

A sample of late IgG from a rabbit hyperimmunized with herpes simplex virus was analyzed for neutralizing (N) and complement-requiring neutralizing (CRN) antibodies. In a usual endpoint test, N and CRN titers were 1: 40 and 1: 160, respectively, but when virus-IgG mixtures were incubated at 0 C overnight before addition of complement (C), an endpoint of 1:1280 was obtained. Virus sensitized at 0 C overnight required more C for inactivation than did sensitized virus formed earlier. Sensitization kinetic curve experiments employing a proper initial virus concentration, which permitted differentiation of sensitized viruses requiring different amounts of C, indicated that formation of sensitized virus detectable only with a relatively large amount of C proceeded slowly at IgG dilutions where the ordinary CRN antibody requiring a smaller amount of C was negligible. The results strongly suggested that the IgG sample contained slow-reacting CRN (s-CRN) antibody in excess of the hitherto known CRN antibody. As to the mechanism of formation of s-CRN complexes, experiments failed to prove the occurrence of complexes initially insensitive to C, and it appears more likely that s-CRN antibody has a comparatively low avidity for virus.

Viral antibodies in cerebrospinal fluid of multiple sclerosis and control patients: comparison between radioimmunoassay and conventional techniques

Cerebrospinal fluid antibodies to measles, rubella, vaccinia, herpes simplex, and varicella-zoster viruses in four patient study groups (clinically definite multiple sclerosis [MS], early probable MS, optic neuritis, and control patients with other neurological diseases) were assayed by radioimmunoassay, complement fixation, hemagglutination-inhibition, or complement-enhanced plaque reduction methods. Antibodies were more frequently found and at higher dilutions by radioimmunoassay than by other techniques. Measles virus antibody, the most frequently found antibody, was present in the cerebrospinal fluid of 72% of MS patients and 5% of control patients. The differences between the numbers of MS patients and control patients with antibodies to other viruses were not as marked. Thus, 58% of MS patients versus 21% of control patients had antibody to rubella virus, 20 versus 3% had antibody to vaccinia virus, 50 versus 33% had antibody to herpes simplex virus, and 25 versus 8% had antibody to varicella virus. Sixty-seven percent of MS patients and 26% of control patients had antibodies to two or more viruses in their cerebrospinal fluid.

Neutralization kinetics studies with type SAT2 foot-and-mouth disease virus strains. 1. Factors that influence the rate and pattern of neutralization

A study of the kinetics of inactivation of foot-and-mouth disease virus type SAT 2 strains revealed that in most cases the rate of neutralization was not rectilinear. Deviations from first-order kinetics observed represented biphasic or parabolic and stepwise reactions. The initial rate was rapid and showed no lag phase or shoulder. The effects of deviations from linearity could be minimized by dilution of antiserum to a suitable extent. Treatment of virus-antibody mixtures with anti-species globulin resulted in enhancement of the rate of neutralization of homologous and heterologous reactions without significantly altering the relation between the two. This treatment also considerably reduced the amount of the persistent fraction. In attempt to disaggregate virus it was observed that sodium dodecyl sulphate inhibited neutralization of virus by specific antiserum.