B cell and T cell immunity in the female genital tract: potential of distinct mucosal routes of vaccination and role of tissue-associated dendritic cells and natural killer cells.

The female genital mucosa constitutes the major port of entry of sexually transmitted infections. Most genital microbial pathogens represent an enormous challenge for developing vaccines that can induce genital immunity that will prevent their transmission. It is now established that long-lasting protective immunity at mucosal surfaces has to involve local B-cell and T-cell effectors as well as local memory cells. Mucosal immunization constitutes an attractive way to generate systemic and genital B-cell and T-cell immune responses that can control early infection by sexually transmitted pathogens. Nevertheless, no mucosal vaccines against sexually transmitted infections are approved for human use. The mucosa-associated immune system is highly compartmentalized and the selection of any particular route or combinations of routes of immunization is critical when defining vaccine strategies against genital infections. Furthermore, mucosal surfaces are complex immunocompetent tissues that comprise antigen-presenting cells and also innate immune effectors and non-immune cells that can act as 'natural adjuvants' or negative immune modulators. The functions of these cells have to be taken into account when designing tissue-specific antigen-delivery systems and adjuvants. Here, we will discuss data that compare different mucosal routes of immunization to generate B-cell and T-cell responses in the genital tract, with a special emphasis on the newly described sublingual route of immunization. We will also summarize data on the understanding of the effector and induction mechanisms of genital immunity that may influence the development of vaccine strategies against genital infections.

Mucosal delivery of human papillomavirus pseudovirus-encapsidated plasmids improves the potency of DNA vaccination.

Mucosal immunization may be important for protection against pathogens whose transmission and pathogenesis target the mucosal tissue. The capsid proteins of human papillomavirus (HPV) confer tropism for the basal epithelium and can encapsidate DNA during self-assembly to form pseudovirions (PsVs). Therefore, we produced mucosal vaccine vectors by HPV PsV encapsidation of DNA plasmids expressing an experimental antigen derived from the M and M2 proteins of respiratory syncytial virus (RSV). Intravaginal (IVag) delivery elicited local and systemic M-M2-specific CD8+ T-cell and antibody responses in mice that were comparable to an approximately 10,000-fold higher dose of naked DNA. A single HPV PsV IVag immunization primed for M-M2-specific-IgA in nasal and vaginal secretions. Based on light emission and immunofluorescent microscopy, immunization with HPV PsV-encapsidated luciferase- and red fluorescent protein (RFP)-expressing plasmids resulted in transient antigen expression (<5 days), which was restricted to the vaginal epithelium. HPV PsV encapsidation of plasmid DNA is a novel strategy for mucosal immunization that could provide new vaccine options for selected mucosal pathogens.

Sublingual tolerance induction with antigen conjugated to cholera toxin B subunit induces Foxp3+CD25+CD4+ regulatory T cells and suppresses delayed-type hypersensitivity reactions.

Although sublingual (s.l.) immunotherapy with selected allergens is safe and often effective for treating patients with allergies, knowledge of the immunological mechanisms involved remains limited. Can s.l. administration of antigen (Ag) induce peripheral immunological tolerance and also suppress delayed-type hypersensitivity (DTH) responses? To what extent can s.l.-induced tolerance be explained by the generation of Foxp3+CD25+CD4+ regulatory T cells (T(reg))? This study addressed these questions in mice and compared the relative efficacy of administering ovalbumin (OVA) conjugated to cholera toxin B (CTB) subunit with administration of the same Ag alone. We found that s.l. administration of a single or even more efficiently three repeated 40-mug doses of OVA/CTB conjugate suppressed T-cell proliferative responses to OVA by cervical lymph node (CLN), mesenteric lymph node (MLN) and spleen cells and concurrently strongly increased the frequency of Ag-specific T(reg) in CLN, MLN and spleen and also transforming growth factor-beta (TGF-beta) levels in serum. The CLN and splenic cells from OVA/CTB-treated BALB/c mice efficiently suppressed OVA-specific T-cell receptor (TCR) transgenic (DO11.10) CD25-CD4+ effector T-cell proliferation in vitro. Further, s.l. treatment with OVA/CTB completely suppressed OVA-specific DTH responses in vivo and T-cell proliferative responses in mice immunized subcutaneously with OVA in Freund's complete adjuvant. The intracellular expression of Foxp3 was strongly increased in OVA-specific (KJ1-26+) CD4+ T cells from OVA/CTB-treated mice. Thus, s.l. administration of CTB-conjugated Ag can efficiently induce peripheral T-cell tolerance associated with strong increases in serum TGF-beta levels and in Ag-specific Foxp3+CD25+CD4+ T(reg) cells.