The site of allergen expression in hematopoietic cells determines the degree and quality of tolerance induced through molecular chimerism

Abstract

The transplantation of allergens (e.g. Phl p 5 or Bet v 1) expressed on BM cells as membrane-anchored full-length proteins leads to permanent tolerance at the T-cell, B-cell, and effector-cell levels. Since the exposure of complete allergens bears the risk of inducing anaphylaxis, we investigated here whether expression of Phl p 5 in the cytoplasm (rather than on the cell surface) is sufficient for tolerance induction. Transplantation of BALB/c BM retrovirally transduced to express Phl p 5 in the cytoplasm led to stable and durable molecular chimerism in syngeneic recipients (∼20% chimerism at 6 months). Chimeras showed allergen-specific T-cell hyporesponsiveness. Further, Phl p 5-specific TH1-dependent humoral responses were tolerized in several chimeras. Surprisingly, Phl p 5-specific IgE and IgG1 levels were significantly reduced but still detectable in sera of chimeric mice, indicating incomplete B-cell tolerance. No Phl p 5-specific sIgM developed in cytoplasmic chimeras, which is in marked contrast to mice transplanted with BM expressing membrane-anchored Phl p 5. Thus, the expression site of the allergen substantially influences the degree and quality of tolerance achieved with molecular chimerism in IgE-mediated allergy.

Coupling of a Major Allergen to the Surface of Immune Cells for Use in Prophylactic Cell Therapy for the Prevention of IgE-Mediated Allergy

“…The allergen was retained only for a limited time on the cell surface due to internalization, and we hypothesize that this period of time was not sufficient for tolerance induction. Internalized Phl p 5 is probably less potent in tolerization, as we observed in a previous study that cytoplasmic Phl p 5 led to less robust tolerance [16]. We attempted to circumvent this issue by repeatedly injecting coupled cells.…”

“…In proof-of-concept studies, we have shown that irradiated BALB/c mice infused with autologous bone marrow cells (BM), that have either been transfected with a gene encoding the major grass pollen allergen, Phl p 5, or that have been retrieved from a transgenic mouse ubiquitously expressing Phl p 5, do not develop Phl p 5-specific IgE despite repetitive allergen immunizations [ 14 , 15 , 16 ]. The treatment also fully prevented Phl p 5-specific T cell responses and allergic airway inflammation, whereas immune responses towards the control allergen Bet v 1 remained unaffected.…”

Development of gene transfer for induction of antigen-specific tolerance

“…Using specific regulatory elements such as tissue-specific promoters and microRNA targets, it is possible to strictly control transgene to a particular cell lineage. 93–97 As platelets, lymphocytes (B and T cells), and most of our professional APC are derived from HSC, it is possible to direct the expression of a transgene product to promote the generation of nTreg from antigen presentation in the thymus or peripheral induction of CD4 + effector T cells to iTreg. Later sections will discuss approaches of direct gene modification of differentiated B and T cells and professional APCs.…”

“… 109 HSC gene modification has also been reported to control allergic responses in a mouse model. 95 , 111 , 119 Several small and large animal disease models have shown long-term correction and tolerance using HSC gene transfer protocols including hemophilia A, 120–125 hemophilia B, 126–129 and Pompe disease. 130 , 131 The recently reported safety and efficacy of LV gene transfer to HSCs in two clinical trials for Wiskott–Aldrich syndrome 132 and metachromatic leukodystrophy 133 provide optimism for the translation of some of the above studies into new clinical trials.…”

Deletional and regulatory mechanisms coalesce to drive transplantation tolerance through mixed chimerism

“…Therefore, immunological tolerance -i.e., a state of specific nonresponsiveness to donor antigens -remains the "Holy Grail" in clinical organ transplantation. Among the Correspondence: Dr. Thomas Wekerle e-mail: Thomas.Wekerle@meduniwien.ac.at numerous strategies that have been tested over time, chimerismbased tolerance induction appears particularly promising [3,4]. This concept is based on the cotransplantation of donor hematopoietic stem cells (HSCs) (contained in bone marrow (BM) or mobilized peripheral blood stem cells (mPBSCs)) into the organ transplant recipient who has been sufficiently preconditioned, either with radiation or cytotoxic drugs, to permit HSC engraftment.…”