mRNAs encoding self-DNA reactive cGAS enhance the immunogenicity of lipid nanoparticle vaccines.

Lipid nanoparticle (LNP)-encapsulated mRNAs have emerged as effective vaccination tools to stimulate immunity. The most common application of this technology is to deliver mRNAs that encode antigenic proteins to dendritic cells (DCs), which then stimulate antigen-specific lymphocyte responses. It is unclear whether other immunostimulatory DC activities necessary for vaccine efficacy, beyond antigen presentation, can be induced via mRNA-encoded proteins. Herein, we report an mRNA encoding a self-DNA reactive variant of the enzyme cyclic GMP-AMP synthase (cGAS), known as cGAS∆N. cGAS∆N produces the cyclic dinucleotide cGAMP upon binding intra-mitochondrial DNA. cGAMP binds the protein STING, which activates innate immune responses that stimulate T cells. We found that when delivered to DCs via LNPs, mRNA-encoded cGAS∆N induced the upregulation of chemokine receptors, T cell costimulatory molecules, major histocompatibility complex proteins, pro-inflammatory cytokines and type I interferons from murine and human DCs. These activities exceeded the immunostimulatory activities of mRNA-encoded antigens delivered via LNPs. Co-immunization of mice with antigen-LNPs and cGAS∆N-LNPs led to the robust production of antigen-specific IFNγ-producing T cells. These T cell responses were durable and circulated through the lymphatics, blood, and lungs. Immunizations with antigen-LNPs alone, akin to what are used in the clinic, stimulated weak and transient T cell responses. Antibody responses to antigen-LNPs were biased towards type I isotypes when co-injected with cGAS∆N-LNPs, as compared to immunizations with antigen-LNPs alone. These findings establish the enzyme cGAS∆N as a catalytic adjuvant, which may prove useful in enhancing the immunogenicity of nucleic acid-based vaccines. IMPORTANCE Nucleic acid-based vaccines hold promise in preventing infections and treating cancer. The most common use of this technology is to encode antigenic proteins on mRNAs that are delivered to cells via lipid nanoparticle (LNP) formulations. In this study, we discovered that immunostimulatory proteins can also be encoded on mRNAs in LNPs. We found that an active mutant of the enzyme cGAS, referred to as cGAS∆N, acts as a catalytic adjuvant in LNP-encapsulated mRNA vaccines. The delivery of cGAS∆N mRNA via LNPs in combination with antigen mRNA-LNPs led to durable antigen-specific IFNγ-producing T cells that exceeded the efficiency of antigen-LNPs similar to those currently used in the clinic. This strategy did not compromise B cell responses; rather it induced Th1-biased antibody isotypes. This work unveils new vaccine design strategies using mRNA-encoded catalytic adjuvants that could be ideal for generating CD8+ T cell and B cell responses for immunotherapies.

Adult Gamma Camera Myocardial Perfusion Imaging: Diagnostic Reference Levels and Achievable Administered Activities Derived From ACR Accreditation Data.

PURPOSE: The aim of this study was to glean from accreditation surveys of US nuclear medicine facilities the in-practice radiopharmaceutical diagnostic reference levels (DRLs) and achievable administered activities (AAAs) for adult gamma camera myocardial perfusion imaging (MPI). METHODS: Data were collected from the ACR Nuclear Medicine Accreditation Program during one three-year accreditation cycle from May 1, 2012, to April 30, 2015. Data elements included radiopharmaceutical, administered activity, examination protocol, interpreting physician specialty, practice type, and facility annual examination volume. Facility demographics, DRLs, and AAAs were tabulated for analysis. RESULTS: The calculated DRLs and AAAs are consistent with previously published surveys, and they adhere to national societal guidelines. Facilities seeking ACR accreditation are nearly evenly split between hospital based with multiple gamma cameras and office based with single gamma cameras. The majority of facilities use single-day, low-dosage/high-dosage (99m)Tc-based protocols; a small minority use (201)TlCl protocols. Administered activities show a consistency across facilities, likely reflecting adoption of standard MPI protocols. CONCLUSIONS: This practice-based analysis provides DRL and AAA benchmarks that nuclear medicine facilities may use to refine gamma camera MPI protocols. In general, the protocols submitted for ACR accreditation are consistent with national societal guidelines. The results suggest that there may be opportunities to further reduce patient radiation exposure by using modified examination protocols and newer gamma camera software and hardware technologies.

ACR accreditation of nuclear medicine and PET imaging departments.

The accreditation programs of the American College of Radiology (ACR) are the most established and widely proven for all imaging modalities. For facilities committed to quality imaging, the ACR Nuclear Medicine and PET Accreditation Program provides a solid foundation for a continuous quality improvement program through a peer review and educational process. This article provides general information describing the goals and development of the ACR accreditation programs. The ACR Nuclear Medicine and PET Accreditation Program evaluates the qualifications of personnel, equipment, image quality, and quality control measures. It is believed that these are the primary factors that have an impact on the quality of patient imaging. This article describes the application process, including the clinical examinations that are required and the quality control and performance tests that are expected from each facility. Outcomes and pass/fail statistics are discussed, as are common pitfalls that may cause deficiencies. Upon completion of this article, the reader should be able to describe the application process, the components of the ACR accreditation program, the most common causes for failure, and the site survey process.