Background: Ischemic heart disease is a leading cause of heart failure and despite advanced therapeutic options, morbidity and mortality rates remain high. Although acute inflammation in response to myocardial cell death has been extensively studied, subsequent adaptive immune activity and anti-heart autoimmunity may also contribute to the development of HF. After ischemic injury to the myocardium, dendritic cells (DC) respond to cardiomyocyte necrosis, present cardiac antigen to T cells and potentially initiate a persistent autoimmune response against the heart. Cross-priming DC have the ability to activate both CD4+ helper and CD8 + cytotoxic T cells in response to necrotic cells and may thus be crucial players in exacerbating autoimmunity targeting the heart. This study investigates a role for cross-priming DC in post-MI myocardial impairment through presentation of self-antigen from necrotic cardiomyocytes to cytotoxic CD8 + T cells. Methods: We induced type-2 myocardial infarction (MI)-like ischemic injury in the heart by treatment with a single high dose of the beta-adrenergic agonist isoproterenol. We characterized the DC population in the heart and mediastinal lymph nodes and analyzed long-term cardiac immunopathology and functional decline in wild type and Clec9a -depleted mice lacking DC cross-priming function. Results: A diverse DC population, including cross-priming DC, is present in the heart and activated after ischemic injury. Clec9a -/- mice deficient in DC cross-priming are protected from long-term immune-mediated myocardial damage and decline of cardiac function, likely due to dampened activation of cytotoxic CD8 + T cells. Conclusions: Activation of cytotoxic CD8 + T cells by cross-priming DC contributes to exacerbation of post-ischemic inflammatory damage of the myocardium and corresponding decline in cardiac function. Importantly, this provides novel therapeutic targets to prevent immune-mediated worsening of post-ischemic HF.

Systemic autoimmune diseases such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) show significant heart involvement and cardiovascular morbidity, which can be due to systemically increased levels of inflammation or direct autoreactivity targeting cardiac tissue. Despite high clinical relevance, cardiac damage secondary to systemic autoimmunity lacks inducible rodent models. Here, we characterise immune-mediated cardiac tissue damage in a new model of SLE induced by topical application of the Toll-like receptor 7/8 (TLR7/8) agonist Resiquimod. We observe a cardiac phenotype reminiscent of autoimmune-mediated dilated cardiomyopathy, and identify auto-antibodies as major contributors to cardiac tissue damage. Resiquimod-induced heart disease is a highly relevant mouse model for mechanistic and therapeutic studies aiming to protect the heart during autoimmunity.

Inhibition of the RAD51 homologous recombination factor prevents the repair of AID-initiated DNA breaks and induces apoptosis preferentially in AID-expressing human CLL.

B-lymphocytes play a key role in type 1 diabetes (T1D) development by serving as a subset of APC preferentially supporting expansion of autoreactive pathogenic T-cells. As a result of their pathogenic importance, B-lymphocyte-targeted therapies have received considerable interest as potential T1D interventions. Unfortunately, B-lymphocyte-directed T1D interventions tested to date failed to halt β-cell demise. IgG autoantibodies marking humans at future T1D risk indicate B-lymphocytes producing them have undergone the affinity maturation processes of class switch recombination (CSR) and possibly somatic hypermutation (SHM). This study found that CRISPR/Cas9-mediated ablation of the Aicda gene required for CSR/SHM induction, inhibits T1D development in the NOD mouse model. The Aicda encoded AID molecule induces genome-wide DNA breaks that, if not repaired through RAD51-mediated homologous recombination (HR), result in B-lymphocyte death. Treatment with the RAD51 inhibitor 4,4′-diisothiocyanatostilbene-2, 2′-disulfonic acid (DIDS) also strongly inhibited T1D development in NOD mice. Both the genetic and small molecule-targeting approaches expanded CD73+ B-lymphocytes exerting regulatory activity suppressing diabetogenic T-cell responses. Hence, an initial CRISPR/Cas9 mediated genetic modification approach has identified the AID/RAD51 axis as a target for a potentially clinically translatable pharmacological approach that can block T1D development by converting B-lymphocytes to a disease inhibitory CD73+ regulatory state.

Activation-induced cytidine deaminase (AID) initiates DNA double strand breaks (DSBs) in the immunoglobulin heavy chain gene (Igh) to stimulate isotype class switch recombination (CSR), and widespread breaks in non-Igh (off-target) loci throughout the genome. Because the DSBs that initiate class switching occur during the G1 phase of the cell cycle, and are repaired via end joining, CSR is considered a predominantly G1 reaction. By contrast, AID-induced non-Igh DSBs are repaired by homologous recombination. Although little is known about the connection between the cell cycle and either induction or resolution of AID-mediated non-Igh DSBs, their repair by homologous recombination implicates post-G1 phases. Coordination of DNA breakage and repair during the cell cycle is critical to promote normal class switching and prevent genomic instability. To understand how AID-mediated events are regulated through the cell cycle, we have investigated G1-to-S control in AID-dependent genome-wide DSBs. We find that AID-mediated off-target DSBs, like those induced in the Igh locus, are generated during G1. These data suggest that AID-mediated DSBs can evade G1/S checkpoint activation and persist beyond G1, becoming resolved during S-phase. Interestingly, DSB resolution during S-phase can promote not only non-Igh break repair, but also immunoglobulin CSR. Our results reveal novel cell cycle dynamics in response to AID-initiated DSBs, and suggest that the regulation of the repair of these DSBs through the cell cycle may ensure proper class switching while preventing AID-induced genomic instability.