In Situ Immune Profiling Identifies Immune Players Involved in Allograft Rejection

We read with interest about the use of quantitative multiplex immunofluorescence (QmIF) methodology (1), which found significantly increased programmed death-ligand 1 (PD-L1)-positive, forkhead box P3 (FoxP3)-positive, and cluster of differentiation 68 (CD68)-positive cells suppressed in clinically evident rejections, whereas PD-L1-positive, FoxP3-positive, and cluster of differentiation 68-positive cell proportions were significantly higher in “never-rejection” than in “future-rejection.” Peyster et al. (1) suggest that in situ immune players regulate the severity of cardiac allograft rejection (CAR). Conventional study of CAR detection involves the identification and quantification of basophilic immune cells on hematoxylin and eosin-stained slides by using endomyocardial biopsy (EMB), which provides few pathogenic insights into both immune cells and individual mechanisms of rejection. In 2005, expert panels required a more detailed characterization of the inflammatory infiltrate in order to have a clinically relevant framework useful for discovering patients with progressive CAR (2). To date, there has been limited application of tissue-level immune phenotyping in transplanted heart tissues. The authors performed useful in situ identification and quantification of CD3, CD8, CD68, FoxP3, and PD-L1, which were selected from a rejection panel of animal models and renal transplantation due to limited research in transplanted heart tissues. Only 33 EMB samples completed the study analysis: 22 had low International Society for Heart and Lung Transplantation (ISHLT) grades of 1R and 0R, and 11 had high ISHLT grades of 2R and 3R (2). First, data must be considered in the setting of the limited sample size. Second, it is well known that discordantly high ISHLT grade designations are uncertain because it is standard practice for all high ISHLT grade biopsy events to receive some form of altered immunosuppression regardless of the presence of altered clinical data. Third, the most interesting findings support the existence of different “immunobiologies” in comparison to concordantly high ISHLT grade cases. This concept is not entirely new because the presence of distinct phenotypes with distinct fates was proposed in 2003 (3). On the other hand, the relatively high rate of a technical failure of QmIF analysis (26% of EMB) is a real concern in common clinical practice, but as the authors recognized, “it may reflect our dependence on residual material following routine clinical processing and the 6- to 12-year interval between EMB sampling and QmIF analysis” (1). Because of intrinsic limitations of the study and future reorganization of costs for the health care system due to the emergent coronavirus 2019 (COVID-19) pandemic, Peyster et al. (1) performed a valuable study of pathogenesis of clinical interest in the surveillance of CAR. Additionally, it would be interesting to analyze their data also in correlation to human leukocyte antigen-DR isotype (HLA-DR) matching at the time of transplantation, because this index may influence outcomes (4). Nevertheless, cost rationing is an inevitable occurrence where the potential demand for effective high-cost techniques will exceed supply. Despite this rather harmful consideration, the future need is to investigate prospectively whether integration of EMB with tissue (1) and liquid biopsy (5) could act synergistically to form a novel precision medicine paradigm (5) leading to the optimized management of patients undergoing heart transplantation.