Mechanisms of Cold Preservation and Reperfusion Injury for Solid Organ Transplantation: Implications for Partial Heart Transplantations

Cold preservation is a key component to organ procurement and transplantation. Cold preservation functions by slowing metabolic activity of procured organs and begins the period known as cold ischemic time (CIT). Reducing CIT and warm ischemic time (WIT) are paramount to minimizing donor organ damage from ischemia and the build-up of waste products and signals that drive reperfusion injury prior to transplantation into a matching recipient. Preventing damage from CIT and WIT and extending the amount of time that organs can tolerate has been a major goal of organ transplantation since donors and recipients are frequently not located within the same hospital, region, or state. Meanwhile, the amount of CIT that a transplant center is willing to accept differs based on the organ, the institution receiving the organ offer, and the doctor receiving the offer for that institution. With the introduction of a partial heart transplantation conducted last year at Duke University, it is important to discuss how much CIT transplant centers conducting a partial heart transplantation (pHT) are willing to accept. This article will review the physiology of WIT and CIT, associated organ damage, CIT variation among transplant centers and organ types, and provide a brief discussion of the future of pHT-accepted CIT and the need for research in this field

A single strain of Bacteroides fragilis protects gut integrity and reduces GVHD

Graft-versus-host disease (GVHD) is a pathological process caused by an exaggerated donor lymphocyte response to host antigens after allogeneic hematopoietic cell transplantation (allo-HCT). Donor T cells undergo extensive clonal expansion and differentiation, which culminate in damage to recipient target organs. Damage to the gastrointestinal tract is a main contributor to morbidity and mortality. The loss of diversity among intestinal bacteria caused by pretransplant conditioning regimens leads to an outgrowth of opportunistic pathogens and exacerbated GVHD after allo-HCT. Using murine models of allo-HCT, we found that an increase of Bacteroides in the intestinal microbiota of the recipients was associated with reduced GVHD in mice given fecal microbial transplantation. Administration of Bacteroides fragilis through oral gavage increased gut microbiota diversity and beneficial commensal bacteria and significantly ameliorated acute and chronic GVHD development. Preservation of gut integrity following B. fragilis exposure was likely attributed to increased short chain fatty acids, IL-22, and regulatory T cells, which in turn improved gut tight junction integrity and reduced inflammatory cytokine production of pathogenic T cells. The current study provides a proof of concept that a single strain of commensal bacteria can be a safe and effective means to protect gut integrity and ameliorate GVHD after allo-HCT