Transplantation of Aortic and Pulmonary Allografts, Enhanced Viability of Endothelial Cells by Cryopreservation, Importance of Histocompatibility

Abstract

Fresh heart valve allografts were preserved at 4°C for 14 days, cryopreserved and stored for 63 days, and studied for endothelial viability and antigenicity, in order to obtain some information on the immunobiological status of allografts before transplantation. The surgical technique described by Ross for subcoronary position is preferred and briefly outlined. Four explanted incompatible allografts were studied by light and scanning electron microscopy and immunohistochemistry to assess the immunological reactions and tissue changes that occurred between 9 days and 16 weeks post‐operatively. Valve leaflet motion and opening velocities were studied by echocardiography post‐operatively to establish a baseline with which to distinguish early leaflet degeneration. Distensibility of the aortic annulus was studied postoperatively by supraaortic angiography to justify one of the goals of reconstruction of the aortic root with allografts. Antibiotic preserved allografts at 4°C showed no viable endothelial cells after 8 days while the cryopreserved allografts demonstrated a high rate of viable endothelial cells capable of expressing surface antigens (HLA class I and II). Although the valve explants showed focal mono‐nuclear cell infiltrations with T‐lymphocytes, the allografts healed in place. The “classic” findings of rejection could not therefore be demonstrated. In summary, cryopreserved valve allografts, like the fresh, are antigenic. It is therefore recommended to use compatible valve grafts, when possible, which might be a positive step to improve the functional longevity of valve allografts. Immune response after valve allograft transplantation does not cause acute valvular dysfunction but rather chronic tissue changes which might lead to early degeneration of the allograft. The opening velocities ol preserved aortic and pulmonary allografts were normal at 3–4 years postoperatively irrespective of histocompatibility. Echo‐cardiography might be a useful tool to detect early degenerative changes ofincompatible valve leaflets. The aortic root is distensible after allograft transplantation.

Biological heart valves

“…Integrity and function of the cells within the homograft as well as maintenance of the matrix components have been shown to be important determinants for longterm function of allograft heart valves [70]. On the other hand, endothelial cells express the major histocompatibility complex (MHC) class I and II molecules, representing a potential immunogenic surface and stimulate a donor-specific immune response that can cause the degeneration of the implanted valve [17].…”

Allograft semilunar cardiac valves processing and cryopreservation – morphology in scanning electron microscope

“…Finally, they are stored at least at À140°C for up to 5 years. This type of allograft has been generally accepted (Yankah et al 1987b;Hopkins 1989;Albertucci and Karp 1997;Lund et al 1999). …”

Allograft Aortic Valve Replacement in the Adult: A Review

“…While some authors 44 have advocated ABO matching of aortic allografts based on endothelial cell ABO antigen expression 57 and allograft heart transplantation experience, long-term series have not shown a benefit in valve function related to ABO matching. This may be because cardiac valvular endothelium, unlike micro vascular endothelium, does not express blood group antigens.…”