Membrane-coated nanoparticles for direct recognition by T cells.

The direct modulation of T cell responses is an emerging therapeutic strategy with the potential to modulate undesired immune responses including, autoimmune disease, and allogeneic cells transplantation. We have previously demonstrated that poly(lactide-co-glycolide) particles were able to modulate T cell responses indirectly through antigen-presenting cells (APCs). In this report, we investigated the design of nanoparticles that can directly interact and modulate T cells by coating the membranes from APCs onto nanoparticles to form membrane-coated nanoparticles (MCNPs). Proteins within the membranes of the APCs, such as Major Histocompatibility Complex class II and co-stimulatory factors, were effectively transferred to the MCNP. Using alloreactive T cell models, MCNP derived from allogeneic dendritic cells were able to stimulate proliferation, which was not observed with membranes from syngeneic dendritic cells and influenced cytokine secretion. Furthermore, we investigated the engineering of the membranes either on the dendritic cells or postfabrication of MCNP. Engineered membranes could be to promote antigen-specific responses, to differentially activate T cells, or to directly induce apoptosis. Collectively, MCNPs represent a tunable platform that can directly interact with and modulate T cell responses.

EWS-FLI1 and Menin Converge to Regulate ATF4 Activity in Ewing Sarcoma.

Ewing sarcomas are driven by EWS-ETS fusions, most commonly EWS-FLI1, which promotes widespread metabolic reprogramming, including activation of serine biosynthesis. We previously reported that serine biosynthesis is also activated in Ewing sarcoma by the scaffolding protein menin through as yet undefined mechanisms. Here, we investigated whether EWS-FLI1 and/or menin orchestrate serine biosynthesis via modulation of ATF4, a stress-response gene that acts as a master transcriptional regulator of serine biosynthesis in other tumors. Our results show that in Ewing sarcoma, ATF4 levels are high and that ATF4 modulates transcription of core serine synthesis pathway (SSP) genes. Inhibition of either EWS-FLI1 or menin leads to loss of ATF4, and this is associated with diminished expression of SSP transcripts and proteins. We identified and validated an EWS-FLI1 binding site at the ATF4 promoter, indicating that the fusion can directly activate ATF4 transcription. In contrast, our results suggest that menin-dependent regulation of ATF4 is mediated by transcriptional and post-transcriptional mechanisms. Importantly, our data also reveal that the downregulation of SSP genes that occurs in the context of EWS-FLI1 or menin loss is indicative of broader inhibition of ATF4-dependent transcription. Moreover, we find that menin inhibition similarly leads to loss of ATF4 and the ATF4-dependent transcriptional signature in MLL-rearranged B-cell acute lymphoblastic leukemia, extending our findings to another cancer in which menin serves an oncogenic role. IMPLICATIONS: These studies provide new insights into metabolic reprogramming in Ewing sarcoma and also uncover a previously undescribed role for menin in the regulation of ATF4.