Background: Despite improved treatment options, myocardial infarction (MI) and its sequelae, e.g. heart failure, remain a major cause of morbidity and mortality. Studies in mice have identified numerous potential therapeutic targets to beneficially influence immunological processes and promote healing after MI. In translational cardiovascular research, the pig is a widely accepted large animal model. However, a lack of knowledge regarding the response of the porcine immune system to experimental MI has hindered immunotherapeutic studies in this species so far. Therefore, we aimed to characterize the transcriptomic landscape of lymphocytes after porcine MI at single-cell resolution, using a closed-chest pig model that resembles the pathophysiology of reperfused MI in humans.
Methods and Results: In two 2.5-month-old Landrace pigs MI was induced by a 90-minute interventional balloon occlusion of the left anterior descending artery, followed by a 7-day reperfusion period. An additional animal underwent a corresponding sham procedure. Eventually, the animals were sacrificed and CD45+ leukocytes isolated from three distinct regions of the myocardium (infarct core (n=2), infarct border zone (n=2), remote myocardium (n=1), sham myocardium (n=1)) and the peripheral blood (MI (n=2), sham (n=1)) were FACS-sorted and analyzed via scRNA-seq (10x Chromium platform).
We identified multiple subtypes of the major lymphatic cell populations (B cells, CD4+ (αβ) T cells, CD8+ (αβ) T cells, γδT cells, unconventional T cells). The proportions of these groups remained relatively stable in the blood comparing sham vs. MI. The T cell compartment comprised naive CD4+ T cells (including a naive subset of FOXP3+ T regulatory cells (Treg)), cytotoxic CD8+ T cells and CD2- γδT cells. The latter represented the largest subpopulation of T cells in the blood (approx. 40%), which is a peculiarity of the porcine immune system.
A different composition is found in the myocardium: The largest proportion of T cells in the sham heart and remote and border zones of the infarcted heart were cytotoxic CD8+ T cells. In the infarct core, this was contrasted by CD4+ T and CD8+ T cells displaying an activated/memory phenotype, which both made up around 20% of T cells each. Treg with an activated phenotype (CTLA4high, BACH2low) were enriched in the border and infarct zones. CD2+ γδT cells were found especially in the sham heart.
Summary and Implications: We present insights into the lymphoid cell landscape at single-cell resolution after experimental MI in the pig. Our analysis can serve as a resource promoting subsequent studies that evaluate the potential of immunotherapeutic approaches post MI in this translationally relevant large animal model.
