No abstract

In acute myeloid leukemia (AML), SWI/SNF chromatin remodeling complexes sustain leukemic identity by driving high levels of MYC. Previous studies have implicated the hematopoietic transcription factor PU.1 (SPI1) as an important target of SWI/SNF inhibition, but PU.1 is widely regarded to have pioneer-like activity. As a result, many questions have remained regarding the interplay between PU.1 and SWI/SNF in AML as well as normal hematopoiesis. Here we found that PU.1 binds to most of its targets in a SWI/SNF-independent manner and recruits SWI/SNF to promote accessibility for other AML core regulatory factors, including RUNX1, LMO2, and MEIS1. SWI/SNF inhibition in AML cells reduced DNA accessibility and binding of these factors at PU.1 sites and redistributed PU.1 to promoters. Analysis of non-tumor hematopoietic cells revealed that similar effects also impair PU.1-dependent B cell and monocyte populations. Nevertheless, SWI/SNF inhibition induced profound therapeutic response in an immunocompetent AML mouse model as well as in primary human AML samples. In vivo, SWI/SNF inhibition promoted leukemic differentiation and reduced the leukemic stem cell burden in bone marrow but also induced leukopenia. These results reveal a variable therapeutic window for SWI/SNF blockade in AML and highlight important off-tumor effects of such therapies in immunocompetent settings.

Adeno-associated virus (AAV) vector-based gene therapies can be applied to a wide range of diseases. AAV expression can last for months to years, but vector re-administration may be necessary to achieve life-long treatment. Unfortunately, immune system response against these vectors is potentiated after the first administration, which prevents the clinical use of repeated administration of AAVs. Reducing immune response against AAVs while minimizing immunosuppression would improve gene delivery efficiency and long-term safety. In this study, we quantified the contributions of multiple immune system components towards AAV response in mice. We identified B-cell-mediated immunity as a critical component preventing vector readministration. Specifically, we found that IgG depletion was insufficient to enhance readministration, suggesting the key role of B-cell mediated IgM antibodies in the immune response against AAV. Further, we also found that AAV-mediated transduction is improved compared to wild-type mice in µMT mice that lack functional IgM heavy chains and cannot form mature Bcells. Combined, our results suggest that IgM production in B cells is a potential target for therapeutics enabling AAV re-administration. Our results also suggest that the µMT mice are a potentially useful experimental model for gene delivery studies since they allow for up to 15-fold more efficient gene delivery.

Adeno-associated virus (AAV) vector-based gene therapies can be applied to a wide range of diseases. AAV expression can last for months to years, but vector re-administration may be necessary to achieve life-long treatment. Unfortunately, immune system response against these vectors is potentiated after the first administration, which prevents the clinical use of repeated administration of AAVs. Reducing immune response against AAVs while minimizing immunosuppression would improve gene delivery efficiency and long-term safety. In this study, we quantified the contributions of multiple immune system components towards AAV response in mice. We identified B-cell-mediated immunity as a critical component preventing vector re-administration. Specifically, we found that IgG depletion was insufficient to enhance re-administration, suggesting the key role of B-cell mediated IgM antibodies in the immune response against AAV. Further, we also found that AAV-mediated transduction is improved compared to wild-type mice in µMT mice that lack functional IgM heavy chains and cannot form mature B-cells. Combined, our results suggest that IgM production in B cells is a potential target for therapeutics enabling AAV re-administration. Our results also suggest that the µMT mice are a potentially useful experimental model for gene delivery studies since they allow for up to 15-fold more efficient gene delivery.

<p>Supplementary Materials</p>