Stimulation of rotavirus IgA, IgG and neutralising antibodies in baboon milk by parenteral vaccination

Perspectives on immunoglobulins in colostrum and milk

Immunoglobulins form an important component of the immunological activity found in milk and colostrum. They are central to the immunological link that occurs when the mother transfers passive immunity to the offspring. The mechanism of transfer varies among mammalian species. Cattle provide a readily available immune rich colostrum and milk in large quantities, making those secretions important potential sources of immune products that may benefit humans. Immune milk is a term used to describe a range of products of the bovine mammary gland that have been tested against several human diseases. The use of colostrum or milk as a source of immunoglobulins, whether intended for the neonate of the species producing the secretion or for a different species, can be viewed in the context of the types of immunoglobulins in the secretion, the mechanisms by which the immunoglobulins are secreted, and the mechanisms by which the neonate or adult consuming the milk then gains immunological benefit. The stability of immunoglobulins as they undergo processing in the milk, or undergo digestion in the intestine, is an additional consideration for evaluating the value of milk immunoglobulins. This review summarizes the fundamental knowledge of immunoglobulins found in colostrum, milk, and immune milk.

Prevention of the murine model of biliary atresia after live rotavirus vaccination of dams

PURPOSE

Biliary atresia (BA) is a neonatal disease that results in the obliteration of the biliary tree. The murine model of BA has been established where rhesus rotavirus (RRV) infection of newborn mice leads to an obstructive cholangiopathy. We determined whether maternal postconception rotavirus vaccination could prevent the murine model of BA.

MATERIALS AND METHODS

Female mice were mated and injected intraperitoneally with one of the following materials: purified rotavirus strains RRV or Wa, high or low-dose Rotateq (Merck and Co Inc, Whitehouse Station, NJ) (a pentavalent rotavirus vaccine [PRV]), purified recombinant viral antigens of rotavirus (VP6) or influenza (NP), or saline. B-cell-deficient females also underwent postconception PRV injection.

RESULTS

Maternal vaccination with PRV improves survival of pups infected with RRV. Serum rotavirus IgG, but not IgA, levels were increased in pups delivered from dams who received RRV, Wa, PRV, or VP6, but in the case of the Wa, PRV, and VP6 groups, these antibodies were not neutralizing. Postconception injection of high-dose PRV did not improve survival of pups born to B-cell-deficient dams.

CONCLUSION

Maternal vaccination against RRV can prevent the rotavirus-induced murine model of BA in newborn mouse pups.

Experimental infection of non-human primates with a human rotavirus isolate

Several rotavirus candidate vaccines have been developed and are at various stages of evaluation. In order to assess the safety and efficacy of these candidate vaccines, an appropriate non-human primate model is desirable. In earlier studies, we reported the presence of naturally occurring anti-rotavirus antibodies in monkeys and demonstrated that parenteral vaccination of baboons led to production of specific rotavirus antibodies in their milk. In the present study, we assessed the possibility of developing the baboon and the vervet monkey as an animal model for rotavirus studies by inoculating them with a pathogenic human rotavirus isolate prepared from the fresh faeces obtained from a child suffering from rotavirus diarrhoea. Preliminary studies have showed excretion of rotavirus in the faeces of 5 of 5 vervets monkeys and 1 of 2 baboons, by antigen ELISA and SDS-PAGE. These results were confirmed by RT-PCR and electron microscopy. The animals also showed elevation of IgG and high titres of virus neutralising antibodies. These data indicate that baboon and vervet monkeys may be useful models for human rotavirus infection and for pre-clinical evaluation of rotavirus candidate vaccines.

Serum IgG mediates mucosal immunity against rotavirus infection

We evaluated the protective role of passively transferred circulating antibodies in protecting non-human primates against experimental rotavirus infection. Pooled sera with rotavirus-specific IgG titers that were either high (1:10,000), intermediate (1:300), or negative (< 1:25) were infused i.v. into naive pigtailed macaques (ages 3-6 months). Rotavirus-specific IgG could be detected in the sera at 18 h in all animals infused with antibody-containing serum, and fecal IgG titers could be detected only in animals given high-titer pooled sera. When orally challenged with 10(6) fluorescent-forming units of a simian rotavirus strain, YK-1, at 18 h after serum transfer, control animals shed virus starting 1-3 days after challenge and continued to shed virus at high titers for 6-8 days, whereas passively immunized macaques did not shed virus or had delayed shedding at low titers for only a limited time. The observation that passively transferred antibodies can suppress or delay viral infection in rotavirus-challenged pigtailed macaques has important implications for the design and testing of parenteral candidate rotavirus vaccines.

Immunological activities associated with milk

Milk contains a multitude of components that can, or may, provide immune protection to the suckling offspring and that also may promote development of neonatal immune competence. In addition, these specialized factors are essential for the protection of the mammary gland, the offspring's food source, from pathogen colonization and lactation failure. Breast milk also facilitates the establishment of a gut flora that inhibits colonization by many pathogens and stimulates the growth of beneficial microorganisms. Maternal immunity can be transferred to the infant via antibodies, primarily of the sIgA type in humans, as well as by leukocytes including effector and memory T lymphocytes. In this way, protection is provided passively against the pathogens to which the mother has been exposed. Currently, there is much interest in determining the protective efficacy of oral supplementation with immunoglobulins from the milk of lactating animals hyperimmunized against specific pathogens. An array of immunostimulatory components in milk, notably cytokines, may be protected against intestinal proteolysis, thereby providing the offspring with a prepackaged immune response system. These components may help to boost the infant's immature immune system. At the same time, anti-inflammatory factors in breast milk help to modulate cytokine responses to infection, thereby facilitating defense while minimizing tissue damage such as that which occurs in infants with necrotizing enterocolitis. Undoubtedly, the many components constituting the repertoire of immune and immunomodulating agents in milk interact synergistically to protect both the mammary gland and the offspring from invading pathogenic microorganisms.

Immunomodulation by iscoms, immune stimulating complexes

The iscom is a uniform stable complex consisting of cholesterol, phospholipid, adjuvant-active saponin, and antigen. The iscom matrix is a particulate complex with identical composition, shape, and morphology, but lacking the incorporated antigen. The assembly of the complex is based on hydrophobic interactions, but antigens that are not hydrophobic can be conjugated with a hydrophobic tail or hidden hydrophobic regions can be exposed, e.g., by acid treatment, to facilitate the incorporation into iscoms. The functional aspects of iscoms are described emphasizing immunomodulation in mouse models. Iscoms prominently enhance the antigen targeting, uptake, and activity of antigen presenting cells including dendritic and B cells and macrophages resulting in the production of proinflammatory cytokines, above all interleukin (IL)-1, IL-6, and IL-12. The expression of costimulatory molecules major histocompatibility complex (MHC) class II, B7.1 and B7.2, is also enhanced. The latter partly explains why the iscom is an efficient adjuvant for elderly mice. Iscoms enhance the Th1 type of response with increased production of IL-2 and interferon gamma. However, with some antigens and particularly in monkeys immunized with HIV iscoms, the production of IL-4 was enhanced. IL-4, IL-2, and interferon gamma (IFNgamma) together with the beta chemokines MIP-1alpha and MIP-1beta correlated with protection against challenge infection with a chimeric virus (simian immunodeficiency virus-human immunodeficiency virus). Iscoms were also shown to induce a potent immune response in the newborn and to be an efficient delivery system for mucosal administration. Technical information is given about formulation of iscoms and about handling of antigens to optimize their incorporation into iscoms.

Stimulation of local immunity and protection in mice by intramuscular immunization with triple- or double-layered rotavirus particles and QS-21

Based on studies in animal models, parenteral immunization has become recognized as a potential vaccination strategy against rotavirus. Using an adult mouse model, the effects of the saponin adjuvant QS-21 on protection against murine rotavirus (strain EDIM) infection was determined following two intramuscular (i.m.) immunizations with purified EDIM particles including triple-layered (tl) infectious particles, tl particles inactivated with psoralen/UV, and double-layered (dl) inactivated particles. All three particles stimulated large serum rotavirus IgG responses and small amounts of serum rotavirus IgA, but undetectable stool rotavirus IgA. Inclusion of QS-21 during immunization increased the serum responses approximately 2- to 10-fold and also stimulated low levels of stool rotavirus IgA. Protection based on reduced shedding of rotavirus following EDIM challenge was significant (P < 0.001) with each immunized group and was enhanced (P < 0.001) by inclusion of QS-21 during immunization. Mice immunized with either live or inactivated tl particles and QS-21 were almost fully protected. Furthermore, animals inoculated with dl particles and the adjuvant shed significantly (P = .02) less virus following challenge than mice immunized with inactivated tl particles even though the latter induced measurable titers of neutralizing antibody to EDIM. These results demonstrate significant protection against rotavirus following i.m. immunization with both dl and tl EDIM particles which is consistently enhanced with QS-21.

ISCOMs (immunostimulating complexes): the first decade

A little over a decade ago, novel immunostimulating complexes (ISCOMs) were described. This review examines the position and progress that ISCOM technology has achieved in the fields of vaccine research and medicine over this period. Much of the work on ISCOMs has remained in the area of vaccine research where there is still an urgent need for improved adjuvants to help combat important diseases such as AIDS, malaria and influenza. Currently the only widely licensed adjuvants for human use are the aluminium salts, but with the trend towards highly purified subunit vaccines, which are inherently less immunogenic than some of the older vaccines, potent adjuvants capable of promoting specific immune responses are required. ISCOMs are one such technology that offers many of these requirements and as their use in vaccines enters its second decade clinical trials are commencing that will establish whether these submicron, non-living particles composed of saponin, cholesterol, phospholipid and in many cases protein, are useful components for a range of human vaccines.