Project 3: Translating Pulmonary Xenotransplantation

Massachusetts General Hospital, Boston MA

Investigators

Abstract

ABSTRACT Translating Pulmonary Xenotransplantation The barriers that prevent use of pig lungs to save human lives remain incompletely understood. Although we have accomplished significant prolongation of in vivo lung xenograft recipient survival over the past decade, the combinations of pig genetics and treatment strategies tested to date have not yet yielded consistent survival beyond 5-7 days. Our extensive prior work in the ex vivo lung perfusion model has identified multiple mechanisms that participate in lung xenograft injury. Specifically, we have shown protective effects are associated with 1) removal of Gal1,3αGal and other carbohydrate targets of preformed human anti- pig antibodies; 2) increased dose of complement pathway regulatory gene and protein expression, underscoring the role of complement; 3) expression of hTBM, particularly in association with hEPCR, demonstrating partial protection from thrombodysregulation; 4) HLA-E/β2µ, implicating NK cells; and 5) humanization of porcine von Willebrands Factor (h*pvWF), which reduces non-physiologic ligation of human platelet GP1B. Important roles for 6) the self-recognition receptor, hCD47, to inhibit macrophage/monocyte- driven lung inflammation, 7) pulmonary intravascular macrophages, 8) and anti-inflammatory agents such as α1 antitrypsin have also been revealed by work and that of others. We have tested lungs in vivo from pigs with a wide variety of combinations of gene modifications and adjuvant anti-inflammatory treatment strategies. Using 10-GE (TKO.GHRKO.hCD46.hCD55.hTBM.hEPCR.hCD47.HO-1), we find that survival is shortened and inflammation is more intense than in association with GalTKO.hCD46.h*pvWF pig lungs, providing additional evidence to data from heart and kidney studies that the TKO gene construct (and specifically the CMAHKO) unveils a ‘4th antigen’ against which baboons (and other NHP) mount strong innate immune responses. Here we propose to test 3 candidate gene modifications to the 10GE pig, each of which is likely to contribute to overcome the current barrier to sustained life-supporting lung xenograft function. 1) By omitting the CMAH KO from the gene construct, we predict that ‘9-GE’ lungs will avoid injury driven by preformed antibody against the as-yet-unidentified ‘4th antigen’ unveiled by that gene modification. 2) HLA-E expression on 9- or 10-GE lungs should reduce NK cell activation and injury. 3) Reduced platelet activation and thrombodysregulation are expected in association with h*pvWF modification to 9- or 10-GE lungs. By testing each of these pig phenotypes in parallel in vivo, with left single lung transplantation into a baboon, and by ex vivo perfusion of the right lung using human blood, and characterizing the innate and adaptive immune responses with robust support from the Pathology/Mechanistic Core, we expect to expand understanding of the residual mechanisms driving lung xenograft injury. Surveillance for opportunistic infections (Microbiology Core) will be conducted as for the other Projects to assess clinically applicable diagnostic tools. Results from this Project, within the Program, are likely to reveal organ-specific barriers and clinically translatable therapeutic opportunities.