We previously developed a
Zr-labeled antibody-based immuno-positron emission tomography (immunoPET) tracer targeting interferon gamma (IFNγ), a cytokine produced predominantly by activated T and ...natural killer (NK) cells during pathogen clearance, anti-tumor immunity, and various inflammatory and autoimmune conditions. The current study investigated
ZrZr-DFO-anti-IFNγ PET as a method to monitor response to immune checkpoint inhibitors (ICIs).
BALB/c mice bearing CT26 colorectal tumors were treated with combined ICI (anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and anti-programmed death 1 (PD-1)). The
ZrZr-DFO-anti-IFNγ PET tracer, generated with antibody clone AN18, was administered on the day of the second ICI treatment, with PET imaging 72 hours later. Tumor mRNA was analyzed by quantitative reverse-transcribed PCR (qRT-PCR).
We detected significantly higher intratumoral localization of
ZrZr-DFO-anti-IFNγ in ICI-treated mice compared to untreated controls, while uptake of an isotype control tracer remained similar between treated and untreated mice. Interestingly,
ZrZr-DFO-anti-IFNγ uptake was also elevated relative to the isotype control in untreated mice, suggesting that the IFNγ-specific tracer might be able to detect underlying immune activity
in this immunogenic model. In an efficacy experiment, a significant inverse correlation between tracer uptake and tumor burden was also observed. Because antibodies to cytokines often exhibit neutralizing effects which might alter cellular communication within the tumor microenvironment, we also evaluated the impact of AN18 on downstream IFNγ signaling and ICI outcomes. Tumor transcript analysis using interferon regulatory factor 1 (IRF1) expression as a readout of IFNγ signaling suggested there may be a marginal disruption of this pathway. However, compared to a 250 µg dose known to neutralize IFNγ, which diminished ICI efficacy, a tracer-equivalent 50 µg dose did not reduce ICI response rates.
These results support the use of IFNγ PET as a method to monitor immune activity
after ICI, which may also extend to additional T cell-activating immunotherapies.
Immune checkpoint inhibitors (ICI) have improved outcomes for a variety of malignancies; however, many patients fail to benefit. While tumor-intrinsic mechanisms are likely involved in therapy ...resistance, it is unclear to what extent host genetic background influences response. To investigate this, we utilized the Diversity Outbred (DO) and Collaborative Cross (CC) mouse models. DO mice are an outbred stock generated by crossbreeding eight inbred founder strains, and CC mice are recombinant inbred mice generated from the same eight founders. We generated 207 DOB6F1 mice representing 48 DO dams and demonstrated that these mice reliably accept the C57BL/6-syngeneic B16F0 tumor and that host genetic background influences response to ICI. Genetic linkage analysis from 142 mice identified multiple regions including one within chromosome 13 that associated with therapeutic response. We utilized 6 CC strains bearing the positive (NZO) or negative (C57BL/6) driver genotype in this locus. We found that 2/3 of predicted responder CCB6F1 crosses show reproducible ICI response. The chromosome 13 locus contains the murine prolactin family, which is a known immunomodulating cytokine associated with various autoimmune disorders. To directly test whether prolactin influences ICI response rates, we implanted inbred C57BL/6 mice with subcutaneous slow-release prolactin pellets to induce mild hyperprolactinemia. Prolactin augmented ICI response against B16F0, with increased CD8 infiltration and 5/8 mice exhibiting slowed tumor growth relative to controls. This study highlights the role of host genetics in ICI response and supports the use of F1 crosses in the DO and CC mouse populations as powerful cancer immunotherapy models.
The immune cytokine interleukin-12 (IL-12) is involved in cancer initiation and progression, autoimmunity, as well as graft versus host disease. The ability to monitor IL-12
imaging may provide ...insight into various immune processes, including levels of antitumor immunity, inflammation, and infection due to its functions in immune signaling. Here, we report the development and preclinical evaluation of an antibody-based IL-12-specific positron emission tomography (PET) tracer. To mimic localized infection and stimulate IL-12 production, BALB/c mice were administered lipopolysaccharide (LPS) intramuscularly.
ZrZr-DFO-αIL12 tracer was given one hour post LPS administration and PET images were taken after 5, 24, 48, and 72 hours. We observed significantly higher uptake in LPS-treated mice as compared to controls. Biodistribution of the tracer was evaluated in a separate cohort of mice, where tracer uptake was elevated in muscle, spleen, lymph nodes, and intestines after LPS administration. To evaluate the utility of
ZrZr-DFO-αIL12 as an indicator of antigen presenting cell activation after cancer immunotherapy, we compared PET imaging with and without intratumoral delivery of oncolytic adenovirus expressing granulocyte-macrophage colony-stimulating factor (Adv/GM-CSF), which we have shown promotes anti-tumor immunity. BALB/c mice were inoculated orthotopically with the mouse mammary carcinoma line TUBO. Once TUBO tumors reached a volume of ~50 mm
, mice were treated with either three intratumoral injections of 10
PFU Adv/GM-CSF or vehicle control, given every other day. Upon the last dose,
ZrZr-DFO-αIL12 was injected intravenously and 72 hours later all mice were imaged
PET. Tumor-specific uptake of
ZrZr-DFO-αIL12 was higher in Adv/GM-CSF treated mice versus controls. Tissues were harvested after imaging, and elevated levels of macrophages and CD8
T
cells were detected in Adv/GM-CSF treated tumors by immunohistochemistry. We validated that IL-12 expression was induced after Adv/GM-CSF by qRT-PCR. Importantly, expression of genes activated by IL-12 (IFNγ, TNFα, and IL-18) were unaffected after IL-12 imaging relative to mice receiving an IgG control tracer, suggesting the tracer antibody does not significantly disrupt signaling. Our results indicate that targeting soluble cytokines such as IL-12 by PET imaging with antibody tracers may serve as a noninvasive method to evaluate the function of the immune milieu
.
Loss-of-function mutations in ORGANELLE RNA RECOGNITION MOTIF PROTEIN6 (ORRM6) result in the near absence of RNA editing of psbF-C77 and the reduction in accD-C794 editing in Arabidopsis (Arabidopsis ...thaliana). The orrm6 mutants have decreased levels of photosystem II (PSII) proteins, especially PsbF, lower PSII activity, pale green pigmentation, smaller leaf and plant sizes, and retarded growth. Stable expression of ORRM6 rescues the orrm6 editing defects and mutant phenotype. Unlike ORRM1, the other known ORRM plastid editing factor, ORRM6, does not contain RNA editing interacting protein/multiple organellar RNA editing factor (RIP/MORF) boxes, which are required for ORRM1 to interact with site-specific pentatricopeptide repeat protein editing factors. ORRM6 interacts with RIP1/MORF8, RIP2/MORF2, and RIP9/MORF9, known components of RNA editosomes. While some plastid RRM proteins are involved in other forms of RNA processing and translation, the primary function of ORRM6 is evidently to mediate psbF-C77 editing, like the essential site-specific pentatricopeptide repeat protein LOW PSII ACCUMULATION66. Stable expression in the orrm6 mutants of a nucleus-encoded, plastid-targeted PsbF protein from a psbF gene carrying a T at nucleotide 77 significantly increases leaf and plant sizes, chlorophyll content, and PSII activity. These transformants demonstrate that plastid RNA editing can be bypassed through the expression of nucleus-encoded, edited forms of plastid genes.
In land plants, plastid and mitochondrial RNAs are subject to post-transcriptional C-to-U RNA editing. T-DNA insertions in the ORGANELLE RNA RECOGNITION MOTIF PROTEIN6 gene resulted in reduced ...photosystem II (PSII) activity and smaller plant and leaf sizes. Exon coverage analysis of the ORRM6 gene showed that orrm6-1 and orrm6-2 are loss-of-function mutants. Compared to other ORRM proteins, ORRM6 affects a relative small number of RNA editing sites. Sanger sequencing of reverse transcription-PCR products of plastid transcripts revealed 2 plastid RNA editing sites that are substantially affected in the orrm6 mutants: psbF-C77 and accD-C794. The psbF gene encodes the β subunit of cytochrome b
559
, an essential component of PSII. The accD gene encodes the β subunit of acetyl-CoA carboxylase, a protein required in plastid fatty acid biosynthesis. Whole-transcriptome RNA-seq demonstrated that editing at psbF-C77 is nearly absent and the editing extent at accD-C794 was significantly reduced. Gene set enrichment pathway analysis showed that expression of multiple gene sets involved in photosynthesis, especially photosynthetic electron transport, is significantly upregulated in both orrm6 mutants. The upregulation could be a mechanism to compensate for the reduced PSII electron transport rate in the orrm6 mutants. These results further demonstrated that Organelle RNA Recognition Motif protein ORRM6 is required in editing of specific RNAs in the Arabidopsis (Arabidopsis thaliana) plastid.
Abstract
Immune checkpoint inhibitors (ICI) for cancer therapy have improved outcomes for a variety of malignancies, however many patients fail to benefit. To date, most pre-clinical studies ...investigating the tumor microenvironment (TME) have utilized different spontaneous or implanted tumor lines to separately investigate immunologically cold or hot TMEs. These models are often in different mouse strains, leading to confounding variables and a disconnect as to whether the tumor or the host is contributing to the observed immunological phenotype. To account for host diversity and reduce variation on the part of the tumor, we have developed immunotherapy models using genetically heterogeneous Diversity Outbred (DO) and recombinant inbred Collaborative Cross (CC) mice. We crossed DO mice with C57BL/6 (B6) to generate DOB6F1 mice that reliably accept B6-syngeneic B16F0 tumors after subcutaneous inoculation. DOB6F1 mice (n=142) treated with combined anti-PD1/anti-CTLA-4 ICI on days 3, 6, and 10 after inoculation exhibited a wide variation in tumor latency, up to a maximum of 65 days, with 19 mice never developing tumor. Quantitative Trait Locus analysis revealed multiple loci influencing response to ICI. We utilized this data to challenge 12 CCB6F1 strains selected based on predicted response where ICI outcomes range from non-responsive to near complete response. In addition, we show evidence that the DOB6F1 model recreates acquired resistance to ICI, with 9 mice having an extremely delayed tumor latency (>40 days). Melanin-free regions were observed in 3/9 of these tumors, suggesting tumor editing. Acquired resistance was also noted 3/10 ICI-treated CC051B6F1 mice. Whole transcriptomic analysis compared tumors from non-responder versus delayed latency DOB6F1 mice. Despite implantation within genetically heterogeneous mice, transcriptomic profiles from late-onset tumors cluster together. Gene Set Enrichment Analysis identified immune processes, with antigen processing and presentation as the most significantly dysregulated gene set. Many of the upregulated genes in late-onset tumors are driven by IFNγ, suggesting IFNγ signaling may contribute to immune escape. We tested this directly by culturing B16 cells with IFNγ prior to inoculation. Short exposure of B16 to IFNγ results in aggressive growth regardless of treatment, but long exposure increases tumor immunogenicity and responsiveness to ICI in inbred B6 mice. Experiments in ICI-responsive CT26-bearing BALB/c mice indicate IFNγ signaling contributes to ICI response, as demonstrated by increased tumor burden after a single 250 µg dose of neutralizing anti-IFNγ antibody concurrent with ICI treatment. Collectively, our DO and CC F1 models allow for reduced tumor variation with a focus on the host and associated TME, and we show differential roles of IFNγ in response to ICI based on the timing of IFNγ exposure.
Citation Format: Justin B. Hackett, James Glassbrook, Nasrin Movahhedin, Madeline Bross, Alicia Kevelin, Maria Múniz, Heather Gibson. Genetically heterogeneous mouse models identify IFNg signaling as a shared signature of acquired resistance to immune checkpoint inhibitors abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB065.
An organelle RNA recognition motif protein is required for psbF transcript editing and the production of efficient PSII in Arabidopsis.
Loss-of-function mutations in ORGANELLE RNA RECOGNITION MOTIF ...PROTEIN6 (ORRM6) result in the near absence of RNA editing of
psbF
-C77 and the reduction in
accD
-C794 editing in Arabidopsis (
Arabidopsis thaliana
). The
orrm6
mutants have decreased levels of photosystem II (PSII) proteins, especially PsbF, lower PSII activity, pale green pigmentation, smaller leaf and plant sizes, and retarded growth. Stable expression of
ORRM6
rescues the
orrm6
editing defects and mutant phenotype. Unlike ORRM1, the other known ORRM plastid editing factor, ORRM6, does not contain RNA editing interacting protein/multiple organellar RNA editing factor (RIP/MORF) boxes, which are required for ORRM1 to interact with site-specific pentatricopeptide repeat protein editing factors. ORRM6 interacts with RIP1/MORF8, RIP2/MORF2, and RIP9/MORF9, known components of RNA editosomes. While some plastid RRM proteins are involved in other forms of RNA processing and translation, the primary function of ORRM6 is evidently to mediate
psbF
-C77 editing, like the essential site-specific pentatricopeptide repeat protein LOW PSII ACCUMULATION66. Stable expression in the
orrm6
mutants of a nucleus-encoded, plastid-targeted PsbF protein from a
psbF
gene carrying a T at nucleotide 77 significantly increases leaf and plant sizes, chlorophyll content, and PSII activity. These transformants demonstrate that plastid RNA editing can be bypassed through the expression of nucleus-encoded, edited forms of plastid genes.
PDF
