IMMUNE REGULATION AND TOLERANCE II

E.A.M. Giets, V. Carlier, L. Vander elst, M. Jacquemin, J. Saint-remy
Cmvb, KU Leuven, Leuven/BELGIUM

Body: Chronic graft rejection depends primarily on indirect presentation of donor-derived antigens by host antigen presenting cells (APC). Specific elimination of such APC could represent a strategy toabort chronic rejection.

We observed that naïve CD4⁺ T cells can be converted to cytolytic cells when activated by cognate interaction of class II-restricted peptides encompassing a thio-disulfideoxidoreductase motif (CxxC motif) in epitope flanking residues. Such cytolytic CD4⁺ T cells (cCD4⁺ T cells) induce apoptosis of APC by Fas-FasL- and granzyme B-dependentmechanism.

We tested the hypothesis that elicitation of cCD4⁺ T cells by active immunization with a CxxC-containing peptide leads to long-term tolerance of skin graft, using the H-Y mHC model.

Female C57BL/6 (H-2b) mice mount a CD4⁺ T cell response towards the H2^b-restricted NAGFNSNRASSRSS epitope of male mHAg, Dby. Pre-immunization of such mice with the Dby epitopeincluding the CxxC motif was carried out with 4 SC injections of 50 ug in alum. Full-thickness trunk male skin (circa 1 cm²) was grafted on the back of such pre-immunized mice or onnaïve female mice as control. The figure shows full acceptance of graft in pre-immunized animals whilst all naïve mice rejected it. Minimal or no graft necrosis was observed in thepre-treated group. Accepted grafts show no retraction and evidence of hair re-growth.

Mice tolerating the graft retained immunocompetence as shown by their capacity to mount immune responses towards unrelated antigens such as tetanus toxoid. Histology showed healthy epidermis intolerated grafts, whilst extensive cellular infiltration as well as apoptotic bodies were observed in rejected grafts. CD4⁺ T cells isolated from pre-immunized mice proliferated uponcognate-peptide interaction and induced apoptosis of male APC.
We next evaluated whether induction of cCD4⁺ T cells to another antigen would also lead to long-term graft tolerance. We took advantage of the immunogenicity of GFP shed by graft anddemonstrated that active immunization with a class II-restricted GFP epitope encompassing a CxxC motif led to full graft tolerance in a sex-matched setting.

We conclude that tolerance to skin graft could be obtained by inducing cCD4⁺ T cells specific to alloantigens shed by the graft by active immunization with a class II epitope including aCxxC motif within flanking residues.

Disclosure: All authors have declared no conflicts of interest.