Impact of Mixed Xenogeneic Porcine Hematopoietic Chimerism on Human NK Cell Recognition in a Humanized Mouse Model

Abstract

Mixed chimerism is a promising approach to inducing allograft and xenograft tolerance. Mixed allogeneic and xenogeneic chimerism in mouse models induced specific tolerance and global hyporesponsiveness, respectively, of host mouse NK cells. In this study, we investigated whether pig/human mixed chimerism could tolerize human NK cells in a humanized mouse model. Our results showed no impact of induced human NK cell reconstitution on porcine chimerism. NK cells from most pig/human mixed chimeric mice showed either specifically decreased cytotoxicity to pig cells or global hyporesponsiveness in an vitro cytotoxicity assay. Mixed xenogeneic chimerism did not hamper the maturation of human NK cells, but was associated with an alteration in NK cell subset distribution and IFN-γ production in the bone marrow. In summary, we demonstrate that mixed xenogeneic chimerism induces human NK cell hyporesponsiveness to pig cells. Our results support the use of this approach to inducing xenogeneic tolerance in the clinical setting. However, additional approaches are required to improve the efficacy of tolerance induction while assuring adequate NK cell functions.

IXA Honorary Member Lecture, 2017: The long and winding road to tolerance

“…In such animals, we observed that, while human NK cells developing in non‐chimeric mice were able to kill and produce cytokines in response to porcine lymphoblasts, those developing in mixed xenogeneic chimeras lacked cytolytic activity against porcine lymphoblasts. In some such animals, the lack of pig‐specific killing was associated with a failure to kill the human class I MHC‐deficient target K562 (ie, global hyporesponsiveness), whereas in others the tolerance was donor‐specific and associated with significant ability to lyse K562 targets . These results are consistent with the observation that many human killer inhibitory receptors (KIRs) do not interact with porcine MHC molecules, whereas a few receptors do .…”

“…Importantly, recent studies in the pig‐to‐humanized mouse (H. W. Li and M. Sykes, unpublished data) and pig‐to‐baboon model (H. Watanabe, T. Tanabe, K. Yamada, unpublished data) are consistent with the prediction that mixed chimerism can tolerize anti‐pig xenoantibodies, suggesting that the immmunobiology of Nab production and tolerization will be translatable from the rat→mouse model to the large animal and human transplant settings.…”

Reduced positive selection of a human TCR in a swine thymus using a humanized mouse model for xenotolerance induction

“…Appropriate TCR expression and in vitro MART1 TCR responses were assessed using stably transfected JRT3‐T3.5 cells, a variant Jurkat cell line that does not express TCRβ . Cells were cultured in complete RPMI 1640 medium (Thermo Fisher Scientific) supplemented with 10% heat‐inactivated fetal bovine serum (Gemini Bio‐Products), 10 mmol/L HEPES buffer (Gibco), 20 mmol/L l ‐glutamine (ACROS Organics), 1 mmol/L sodium pyruvate (Fisher BioReagents), and 0.2% 2‐Mercaptoethanol (MP Biomedicals, LLC).…”

Tolerance in xenotransplantation

“…Mixed chimerism also has the capacity to tolerize natural killer (NK) cells (54). In the case of allogeneic chimerism, the tolerance is specific for the donor, with otherwise preserved NK cell function.…”

“…However, in the rat-to-mouse xenogeneic chimerism model, mouse NK cells were rendered globally unresponsive by the presence of even low levels of rat chimerism (55). In the pig-human mixed chimerism model in humanized mice, we recently showed that human NK cells are rendered tolerant by porcine mixed chimerism, as reflected in some cases by specific unresponsiveness with otherwise preserved NK cell function and, in others, global hyporesponsiveness (54). Collectively, our data argue for a mechanism of NK cell tolerance involving anergy induced by repeated, unopposed activating signals, as opposed to a requirement for licensing by the presence of inhibitory ligands, as we have discussed previously (56).…”