TRANSVIVO ANALYSIS OF HUMAN DELAYED TYPE HYPERSENSITIVITY

Abstract

157 Introduction: In a murine model of cardiac transplantation, we have observed that acute rejection is associated with allosensitization and the expression of donor-reactive delayed type hypersensitivity (DTH) responses. In contrast, allograft acceptance is associated with a loss of donor-reactive DTH, due to an active, antigen-induced inhibition of donor-reactive DTH responses. If similar mechanisms operate in humans, it would be advantageous to monitor post-transplant donor-reactive DTH responses in transplant patients. However, skin tests with donor alloantigen on transplant patients is not advised, due to the possibility of allosensitization. Methods: We developed a transvivo method of human DTH testing for which human peripheral blood mononuclear cells plus specific antigen are transferred into the pinnae of naive mice. Degree of ear swelling, measured 24 hours post-injection, serves as an index of human DTH. The transvivo human DTH system was field tested using two common antigens, tetanus toxoid (TT) and cytomegalovirus (CMV). Results: We have observed that (1) human TT-induced DTH responses can be observed in C57BL/6 SCID mice, normal C57BL/6 mice, or normal DBA/2 mice; (2) murine ear swelling occurs only when presensitized human PBMC and an adequate concentration of sensitizing antigen are placed together in the same ear; (3) the critical PBMC components include both human T cells and human macrophages; (4) the required T cell component is CD4+ and not CD8+ and (5) transvivo DTH responses are antigen specific and require prior antigen sensitization, since PBMC from individuals who are TT sensitized, and CMV seronegative, respond to DTH challenge with TT but not CMV antigens, whereas PBMC from CMV seropositive individuals make strong DTH responses to CMV antigens. Conclusion: This transvivo DTH assay system should allow the assessment of donor-reactive DTH status in pre- and post-transplant patients without the risk of allosensitization due to subcutaneous deposition of alloantigens during DTH challenge.