Intrauterine vaccination induces a dose-sensitive primary humoral response with limited evidence of recall potential

Intrauterine immunizations trigger antigen-specific mucosal and systemic immunity in pigs and passive protection in suckling piglets

We assessed whether vaccines administered to the uterus at breeding can lead to sufficient colostral antibodies to protect suckling piglets against Porcine Endemic Diarrhea Virus (PEDV). An antigen from Lawsonia intracellularis, a disease that impacts weanling intestinal health, was also included because we have extensive knowledge on the pig immune response to this antigen. Gilts were mock-bred at 2nd estrus with killed sperm including an intrauterine (i.u.) vaccine comprised of recombinant (r) PEDV Spike protein (rPEDVS1) and L. intracellularis flagellin (rFliC) formulated with poly I:C, host defense peptide, and polyphosphazene (TriAdj). Gilts returned to estrus within 3 weeks and they were inseminated with killed sperm (3rd estrus) or live sperm (4th estrus) with rPEDVS1-TriAdj vaccine. They also received an i.m. injection of rFliC-TriAdj at 3rd and 4th estrus to establish whether i.u. vaccination primes systemic immunity without inducing mucosal tolerance. Control gilts were administered semen alone at 2nd estrus which allowed us to compare litter weights and sizes to industry standards. Colostrum from gilts challenged with low dose PEDV plus alum was used as positive reference samples for neutralizing antibodies and passive protection. Thirteen weeks later, the i.u.-vaccinated gilts showed significant PEDVS1-specific serum, colostral, and uterine antibody titers and colostral PEDVS1-neutralizing antibodies but poor cell-mediated immunity. Piglets born to i.u. vaccinated gilts received partial passive protection from PEDV infection 3 days after birth but eventually succumbed to the disease. Immunization by the i.u./i.m. route triggered significant anti-FliC cell-mediated immunity and colostral FliC antibodies that remained high in weaned piglet serum. This trial and a repeat trial wherein gilts were immunized at 1st estrus without semen and at 2nd estrus with live semen showed that intrauterine immunization did not impact fertility, number of live births or piglet growth kinetics. Further optimization is needed to promote robust passive protection in suckling offspring.

Polyphosphazene immunoadjuvants: Historical perspective and recent advances

The development of successful vaccines has been increasingly reliant on the use of immunoadjuvants - additives, which can enhance and modulate immune responses to vaccine antigens. Immunoadjuvants of the polyphosphazene family encompass synthetic biodegradable macromolecules, which attain in vivo activity via antigen delivery and immunostimulation mechanisms. Over the last decades, the technology has witnessed evolvement of next generation members, expansion to include various antigens and routes of administration, and progression to clinical phase. This was accompanied by gaining important insights into the mechanism of action and the development of a novel class of virus-mimicking nano-assemblies for antigen delivery. The present review evaluates in vitro and in vivo data generated to date in the context of latest advances in understanding the primary function and biophysical behavior of these macromolecules. It also provides an overview of relevant synthetic and characterization methods, macromolecular biodegradation pathways, and polyphosphazene-based multi-component, nanoparticulate, and microfabricated formulations.

Assessment of Immunological Response and Impacts on Fertility Following Intrauterine Vaccination Delivered to Swine in an Artificial Insemination Dose

To protect the health of sows and gilts, significant investments are directed toward the development of vaccines against infectious agents that impact reproduction. We developed an intrauterine vaccine that can be delivered with semen during artificial insemination to induce mucosal immunity in the reproductive tract. An in vitro culture of uterine epithelial cells was used to select an adjuvant combination capable of recruiting antigen-presenting cells into the uterus. Adjuvant polyinosinic:polycytidylic acid (poly I:C), alone or in combination, induced expression of interferon gamma, tumor necrosis factor alpha, and select chemokines. A combination adjuvant consisting of poly I:C, host defense peptide and polyphosphazene (Triple Adjuvant; TriAdj), which previously was shown to induce robust mucosal and systemic humoral immunity when administered to the uterus in rabbits, was combined with boar semen to evaluate changes in localized gene expression and cellular recruitment, in vivo. Sows bred with semen plus TriAdj had decreased γδ T cells and monocytes in blood, however, no corresponding increase in the number of monocytes and macrophages was detected in the endometrium. Compared to sows bred with semen alone, sows bred with semen plus TriAdj showed increased CCL2 gene expression in the epithelial layer. These data suggest that the adjuvants may further augment a local immune response and, therefore, may be suitable for use in an intrauterine vaccine. When inactivated porcine parvovirus (PPV) formulated with the TriAdj was administered to the pig uterus during estrus along with semen, we observed induction of PPV antibodies in serum but only when the pigs were already primed with parenteral PPV vaccines. Recombinant protein vaccines and inactivated PPV vaccines administered to the pig uterus during breeding as a primary vaccine alone failed to induce significant humoral immunity. More trials need to be performed to clarify whether repeated intrauterine vaccination can trigger strong humoral immunity or whether the primary vaccine needs to be administered via a systemic route to promote a mucosal and systemic immune response.

Recent advances in experimental polyphosphazene adjuvants and their mechanisms of action

Vaccination continues to be a very important public health intervention to control infectious diseases in the world. Subunit vaccines are generally poorly immunogenic and require the addition of adjuvants to induce protective immune responses. Despite their critical role in vaccines, adjuvant mechanism of action remains poorly understood, which is a barrier to the development of new, safe and effective vaccines. In the present review, we focus on recent progress in understanding the mechanisms of action of the experimental adjuvants poly[di(carboxylatophenoxy)phosphazene] (PCPP) and poly[di(sodiumcarboxylatoethyl-phenoxy)phosphazene] (PCEP) (in this review, adjuvants PCPP and PCEP are collectively referred to as PZ denoting polyphosphazenes). PZs are high molecular weight, water-soluble, synthetic polymers that have been shown to regulate innate immune response genes, induce cytokines and chemokines secretion at the site of injection and, also, induce immune cell recruitment to the site of injection to create a local immune-competent environment. There is an evidence that as well as its role as an immunoadjuvant (that activate innate immune responses), PZ can also act as a vaccine carrier. The mechanism of action that explains how PZ leads to these effects is not known and is a barrier to the development of designer vaccines.