Naturally Developing Memory T Cell Xenoreactivity to Swine Antigens in Human Peripheral Blood Lymphocytes

Abstract

Naturally developing xenospecific Abs are well-documented barriers to xenograft transplantation in humans, but whether analogous xenoreactive T cell immunity develops is not known. We used an enzyme-linked immunospot assay to determine the frequency and cytokine profiles of xenoreactive PBLs from a panel of human volunteers. Because naive T cells produce only IL-2 in short term culture, IFN-γ production by this approach is a measure of a memory immune response. Stimulation of human PBLs or purified T lymphocytes with stimulator cells from inbred swine revealed a high frequency of IFN-γ producers with 5-fold fewer IL-2 producers. In contrast, lymphocytes obtained from neonatal umbilical cord blood contained swine-specific IL-2 producers but few IFN-γ producers, which is what one would expect to find with a naive phenotype. Moreover, PBLs from adults with a history of abstention from pork consumption responded to swine cells with a significantly lower frequency of IFN-γ producers than PBLs from adults with unrestricted diets did, suggesting that pork consumption may result in priming of swine-specific T cell immunity. Our findings provide the first evidence for naturally occurring xenospecific T cell immunity in humans. The detected strength of this memory response suggests that it will present a formidable barrier to transplantation of swine organs.

Essential Role of Sphingosine-1-Phosphate Receptor 1-Bearing CD8+CD44+CCR7+ T Cells in Acute Skin Allograft Rejection

“…Allo-reactive memory T cells are reported as important mediators in acute rejection, jeopardizing the survival of transplanted allo-grafts (1,2). The questions remain to be answered as to when and how naive T cells develop into effector and specific memory T cells immediate after alloantigen encountering.…”

Direct Antigen Presentation by a Xenograft Induces Immunity Independently of Secondary Lymphoid Organs

“…To investigate whether naive mice possessed anti-porcine effector memory T cells, we used a recall (20-h) ELISPOT assay with IFN-␥ secretion as readout. Such assays have been shown to detect the presence of effector memory T cells in both mice and humans (32). The results show that spleen cells from naive aly/aly mice failed to demonstrate an increase in the frequency of IFN-␥-positive cells when exposed to mitomycin C-treated porcine spleen cells in a one-way MLR vs naive aly/aly responders only (exposed aly/aly spleen cells ϭ 10 spots/1 ϫ 10 6 spleen cells vs aly/aly responders only ϭ 12 spots/1 ϫ 10 6 spleen cells, p ϭ 0.6) (Fig.…”

“…A characteristic of effector memory T cells is their ability to rapidly secrete IFN-␥ in response to their cognate Ag (32). To investigate whether naive mice possessed anti-porcine effector memory T cells, we used a recall (20-h) ELISPOT assay with IFN-␥ secretion as readout.…”

ELISPOT Analysis of Hepatitis C Virus Protein-Specific IFN-γ-Producing Peripheral Blood Lymphocytes in Infected Humans with and without Cirrhosis

“…We previously made use of this approach to characterize human T cell immunity specific for both prototypic protein antigens (i.e., tetanus toxoid and purified protein derivative), for alloantigens, and for xenoantigens (32,33). These published studies have further demonstrated that our approach can have prognostic value in that the frequency of donor antigen-specific T cells, as defined by ELISPOT assay, can predict those renal transplant recipients at highest risk for rejection episodes (33).…”

“…After obtaining consent, 30-cc peripheral blood samples were obtained in green-top vacutainer tubes containing sodium heparin. PBLs were isolated by centrifugation through Isoprep (Robbins Scientific Corp., Sunnyvale, CA) within 4 h of obtaining the sample, as previously described (32,33). A quantity of 20 -40 million PBLs was obtained from a given patient by this method.…”