Vaccines: new approaches and concepts

Gene therapy for tolerance: high-level expression of donor major histocompatibility complex in the liver overcomes naive and memory alloresponses to skin grafts

BACKGROUND

The liver has long been recognized as having tolerogenic properties. We investigated whether recombinant adenoassociated virus (rAAV)-mediated expression of donor major histocompatibility complex in recipient livers could induce tolerance to donor-strain grafts.

METHODS

Naive B10.BR (H-2) or B10.BR recipients primed with a H-2K-expressing (K) skin graft were injected with rAAV-expressing H-2K (rAAV-K) to induce K expression on hepatocytes 7 days before challenge with a K skin graft. K-specific responses were measured by interferon (IFN)-γ ELISpot and flow cytometric assessment of directly H-2K reactive cells. Fully allogeneic grafts from C57BL/6 (H-2) donors were transplanted onto longstanding B10.BR recipients of K skin to test for linked epitope suppression.

RESULTS

rAAV-K-treated B10.BR mice accepted K skin grafts with increased median survival time (MST) more than 169 days compared to uninoculated (MST=18.5 days) and rAAV-K-treated controls (MST=19 days). rAAV-K-treated B10.BR animals primed with K skin grafts also accepted secondary K skin grafts in the long term (MST>100 days) compared to accelerated rejection in primed, uninoculated mice (MST=12 days). Treatments did not induce liver pathology, assessed by serum alanine aminotransferase levels and histology. IFN-γ ELISpot analysis of splenocytes from rAAV-K-treated mice indicated reduced responses to donor K antigen, but protection was not extended to fully allogeneic C57BL/6 skin or heart grafts, even in recipients that had accepted K skin grafts in the long term.

CONCLUSIONS

High-level expression of donor major histocompatibility complex in recipient livers promotes tolerance to skin allografts, even in animals primed to produce a memory response. This provides proof of concept for an approach using liver-targeted gene delivery for tolerance induction to donor antigen.

O ensino e a saúde: um olhar biológico

Os seres vivos são sistemas determinados por suas estruturas. O ensino é impossível, mas a aprendizagem é inevitável, um comentário de um observador sobre algum aspecto das mudanças constantes que ocorrem durante o viver. Professor é aquele que abre um espaço de convivência. Não existem interações instrutivas na natureza. A saúde e a biologia dos seres vivos são fenômenos estudados em domínios distintos, a primeira sendo definida pela cultura. Como um fenômeno biológico, a saúde ou a doença são configurações relacionais do organismo com seu meio e, como tais, são fenômenos descritos no domínio das interações do organismo. Por esse entendimento, a saúde individual é um fenômeno social.

Lymphocyte proliferative response in brown bears: cytokine role and glucocorticoid effect

Lymphocyte stimulation and proliferation play a pivotal role in the immune response to soluble as well as to cellular, bacterial, and viral antigens. In this study, peripheral blood mononuclear cells (PBMC), mainly composed of lymphocytes, were separated by Ficoll-Hypaque density gradient centrifugation from 50-ml jugular vein blood samples drawn from six captive and five wild-caught brown bears (Ursus arctos) (eight Apennine brown bears from the Italian population; three of undetermined origin). Stimulation of cultured bear PBMC with the two classical T lymphocyte mitogens phytohemagglutinin (PHA) and Concanavalin A (ConA) was followed by a significantly greater proliferative response than that shown by human PBMC (n = 11) (PHA: T = 4.03, d.f. = 20, P = 0.001; ConA: T = 4.25, d.f. = 20, P < 0.0005; Student's t-test, oneway ANOVA). As in humans, the PBMC proliferative response in bears was markedly (> 50%) inhibited by addition of transforming growth factor beta (TGF beta) human recombinant cytokine to the culture. Further fractionation provided a cell preparation extremely rich in peripheral blood lymphocytes (PBL) (mean +/- SD = 96.1 +/- 1.7%). Addition of interleukin 1 (IL1) or interleukin 2 (IL2) human recombinant cytokines to cultured PBL stimulated with a suboptimal concentration of mitogens resulted in a ninefold increase in the lymphocyte proliferative response. Dexamethasone (DEX, a synthetic analog of hydrocortisone) inhibited the bear PBMC proliferative response by 22.2 +/- 4.3% (mean +/- SD), compared with 46.2 +/- 6.9% and 91.8 +/- 8.1% (mean +/- SD) in humans and mice (n = 11) (Mus domesticus), respectively. Inhibition of the brown bear and human PBMC responses was markedly (> 60%) reduced by the addition of IL2. The finding that IL1 and IL2 augment and that DEX inhibits bear lymphocyte proliferative response suggests that these cytokines can be used to increase the immune response in vaccinations, and that DEX may hamper several immunologically mediated diseases.

Biochemical and immunological characterization of recombinant allergen Lol p 1

Pollen from perennial rye grass (Lolium perenne), a major cause of type-I allergy worldwide, contains a complex mixture of allergenic proteins among which Lol p 1 is one of the most important. We describe the expression, purification and characterization of a recombinant Lol p 1 overproduced in Escherichia coli. The recombinant allergen, expressed in high yields and purified in milligram amounts, bound to specific IgE antibodies from human sera, induced histamine release from sensitized human basophils, and elicited rabbit antisera that recognize specifically recombinant Lol p 1 and natural Lol p 1 of pollen extract. Recombinant Lol p 1 was used to develop ImmunoCAP assays for analysis of 150 sera that were Radioallergosorbent test positive to L. perenne pollen. In 130 of them (87%) the assay detected a significant level of IgE antibodies to Lol p 1, reaching on average 37% of the level obtained with a test for IgE to the whole grass pollen extract. To map epitopes on Lol p 1, we produced three deletion mutants [des-(116-240)-Lol p 1, des-(1-88)-Lol p 1 and des-(133-189)-Lol p 1], which were efficiently expressed in bacteria. These all showed a strong reactivity with the specific rabbit IgG antibodies, but lacked most or all the allergenic properties of recombinant Lol p 1. A study of the antigenic structure of Lol p 1 was performed using the three deletion mutants and a set of 17-18-residue overlapping synthetic peptides covering the whole allergen sequence. The results indicate that human IgE and rabbit IgG antibodies bind to distinct regions of Lol p 1, and that at least some important IgE epitopes are mainly conformational. The findings suggest that recombinant allergens constitute useful reagents for further development of serological diagnosis of allergy, and that it should be possible to produce immunogenic fragments of allergenic proteins without allergenic properties.