Kidney organoids represent a novel platform to study adaptive and innate immunity

ABSTRACT

Background: Human kidney organoids have been utilized as a model to study genetic kidney diseases and kidney development. Innate or adaptive immune responses in organoids are currently poorly defined. Kidney transplant rejection and activation of complement pathways are two common renal immune phenomena. SARS-CoV-2 virus, the pathogen of the recent pandemic, leads to complement pathway activation in human kidneys and can infect kidney organoids. Here, we investigated (i) the alloimmunogenicity of kidney organoids in a humanized mice model, and (ii) the responses to exogenous complement C5a and spike protein (S1) of SARS-CoV-2 in kidney organoids. Methods: Kidney organoids were generated from human embryonic stem cells using protocols developed in our laboratory, and transplanted under the kidney capsule in humanized (BLT) mice. Immunophenotype, mixed lymphocyte reaction, and intracellular cytokine staining were analyzed from grafts and mouse splenocytes collected after 30 days of transplantation. In other experiments organoids were treated with S1 protein and human recombinant C5a for 24 hours or 3 days respectively, followed by qPCR and immunofluorescence analysis. Results: Transplanted organoids were extensively infiltrated by lymphocytes. Graft CD8+ T cells demonstrated a switch from naïve to memory T cells. Splenocytes isolated from transplanted BLT mice showed increased IFN-γ and TNF-α. Splenocytes proliferated after exposure to 2D kidney organoids (MLR) for 72 hours ex vivo, and organoids were markedly injured as reflected by DNA damage (γ-H2AX) and cleaved caspase 3. Reflecting innate responses, robust interstitial fibrosis was found in nontransplanted organoids after direct activation of C5aR by exogenous C5a. We confirmed ACE2 expression on proximal tubules and parietal epithelium of glomeruli, consistent with human autopsy results. Non-transplanted organoids treated with S1 protein showed transcriptionally upregulated C5a1 receptors. Conclusions: Our results indicate the alloimmunogenicity of kidney organoids and the deleterious effects of C5a in kidney organoids. Human kidney organoids represent a novel platform to study renal immunology including adaptive and innate immunity and the inflammatory responses to coronavirus disease (COVID-19).