A mouse model that is immunologically tolerant to reporter and modifier proteins

Programmability and biomedical utility of intrinsically-disordered protein polymers

Intrinsically disordered proteins (IDPs) exhibit molecular-level conformational dynamics that are functionally harnessed across a wide range of fascinating biological phenomena. The low sequence complexity of IDPs has led to the design and development of intrinsically-disordered protein polymers (IDPPs), a class of engineered repeat IDPs with stimuli-responsive properties. The perfect repetitive architecture of IDPPs allows for repeat-level encoding of tunable protein functionality. Designer IDPPs can be modeled on endogenous IDPs or engineered de novo as protein polymers with dual biophysical and biological functionality. Their properties can be rationally tailored to access enigmatic IDP biology and to create programmable smart biomaterials. With the goal of inspiring the bioengineering of multifunctional IDP-based materials, here we synthesize recent multidisciplinary progress in programming and exploiting the bio-functionality of IDPPs and IDPP-containing proteins. Collectively, expanding beyond the traditional sequence space of extracellular IDPs, emergent sequence-level control of IDPP functionality is fueling the bioengineering of self-assembling biomaterials, advanced drug delivery systems, tissue scaffolds, and biomolecular condensates -genetically encoded organelle-like structures. Looking forward, we emphasize open challenges and emerging opportunities, arguing that the intracellular behaviors of IDPPs represent a rich space for biomedical discovery and innovation. Combined with the intense focus on IDP biology, the growing landscape of IDPPs and their biomedical applications set the stage for the accelerated engineering of high-value biotechnologies and biomaterials.

Overcoming Xenoantigen Immunity to Enable Cellular Tracking and Gene Regulation with Immune-competent "NoGlow" Mice

The ability to temporally regulate gene expression and track labeled cells makes animal models powerful biomedical tools. However, sudden expression of xenobiotic genes [e.g., GFP, luciferase (Luc), or rtTA3] can trigger inadvertent immunity that suppresses foreign protein expression or results in complete rejection of transplanted cells. Germline exposure to foreign antigens somewhat addresses these challenges; however, native fluorescence and bioluminescence abrogates the utility of reporter proteins and highly spatiotemporally restricted expression can lead to suboptimal xenoantigen tolerance. To overcome these unwanted immune responses and enable reliable cell tracking/gene regulation, we developed a novel mouse model that selectively expresses antigen-intact but nonfunctional forms of GFP and Luc, as well as rtTA3, after CRE-mediated recombination. Using tissue-specific CREs, we observed model and sex-based differences in immune tolerance to the encoded xenoantigens, illustrating the obstacles of tolerizing animals to foreign genes and validating the utility of these "NoGlow" mice to dissect mechanisms of central and peripheral tolerance. Critically, tissue unrestricted NoGlow mice possess no detectable background fluorescence or luminescence and exhibit limited adaptive immunity against encoded transgenic xenoantigens after vaccination. Moreover, we demonstrate that NoGlow mice allow tracking and tetracycline-inducible gene regulation of triple-transgenic cells expressing GFP/Luc/rtTA3, in contrast to transgene-negative immune-competent mice that eliminate these cells or prohibit metastatic seeding. Notably, this model enables de novo metastasis from orthotopically implanted, triple-transgenic tumor cells, despite high xenoantigen expression. Altogether, the NoGlow model provides a critical resource for in vivo studies across disciplines, including oncology, developmental biology, infectious disease, autoimmunity, and transplantation.

SIGNIFICANCE

Multitolerant NoGlow mice enable tracking and gene manipulation of transplanted tumor cells without immune-mediated rejection, thus providing a platform to investigate novel mechanisms of adaptive immunity related to metastasis, immunotherapy, and tolerance.

Preclinical Mouse Metastatic Model Established Through Induced Lung Metastases

Metastatic disease is the major cause of cancer death, and the lung is one of the most common sites of cancer metastases. To investigate systemic antitumor effects or protective potential of local therapies, mouse models with induced metastases are indispensable in preclinical cancer research. Here, we describe the protocol for the metastatic mouse model established through induced 4T1 mammary carcinoma metastases. With minor prior optimization, it can be applied to other tumor cell lines of interest.

Lentiviral vector transduction provides nonspecific immunogenicity for syngeneic tumor models

Lentivirus-based transduction systems are widely used in biological science and cancer biology, including cancer immunotherapy. However, in in vivo transplanted tumor model, the immunogenicity of these transduced cells was not appropriately addressed. Here, we used empty vector-transduced mouse melanoma (B16) and carcinoma (lewis lung carcinoma) cells transplanted tumor model to study the immune response due to the transduction processes. We showed that the overall in vivo tumor growth rate gets reduced in transduced cells only in immune-competent mice but not in nude mice. This data indicate the involvement of the immune system in the in vivo tumor growth restriction in the transduced group. Further studies showed that specific activation of CD8⁺ T cells might be responsible for restricted tumor growth. Mechanistically, transduced tumor cells show the higher activity of type I interferon, which might play an essential role in this activation. Overall, our data indicate the modulation of the immune system by lentiviral vector transduced tumor cells, which required further studies to explore the mechanisms and better understand the biological significance. Our data also indicate the importance of considering the immunogenicity of transduced cells when analyzing in vivo results, especially in studies related to immunotherapy.

Applying a Clinical Lens to Animal Models of CAR-T Cell Therapies

Chimeric antigen receptor (CAR)-T cells have emerged as a promising treatment modality for various hematologic and solid malignancies over the past decade. Animal models remain the cornerstone of pre-clinical evaluation of human CAR-T cell products and are generally required by regulatory agencies prior to clinical translation. However, pharmacokinetics and pharmacodynamics of adoptively transferred T cells are dependent on various recipient factors, posing challenges for accurately predicting human engineered T cell behavior in non-human animal models. For example, murine xenograft models did not forecast now well-established cytokine-driven systemic toxicities of CAR-T cells seen in humans, highlighting the limitations of animal models that do not perfectly recapitulate complex human immune systems. Understanding the concordance as well as discrepancies between existing pre-clinical animal data and human clinical experiences, along with established advantages and limitations of each model, will facilitate investigators’ ability to appropriately select and design animal models for optimal evaluation of future CAR-T cell products. We summarize the current state of animal models in this field, and the advantages and disadvantages of each approach depending on the pre-clinical questions being asked.

Cyanine Phototruncation Enables Spatiotemporal Cell Labeling

Photoconvertible tracking strategies assess the dynamic migration of cell populations. Here we develop phototruncation-assisted cell tracking (PACT) and apply it to evaluate the migration of immune cells into tumor-draining lymphatics. This method is enabled by a recently discovered cyanine photoconversion reaction that leads to the two-carbon truncation and consequent blue-shift of these commonly used probes. By examining substituent effects on the heptamethine cyanine chromophore, we find that introduction of a single methoxy group increases the yield of the phototruncation reaction in neutral buffer by almost 8-fold. When converted to a membrane-bound cell-tracking variant, this probe can be applied in a series of in vitro and in vivo experiments. These include quantitative, time-dependent measurements of the migration of immune cells from tumors to tumor-draining lymph nodes. Unlike previously reported cellular photoconversion approaches, this method does not require genetic engineering and uses near-infrared (NIR) wavelengths. Overall, PACT provides a straightforward approach to label cell populations with spatiotemporal control.

Autocrine and paracrine IL-2 signals collaborate to regulate distinct phases of CD8 T cell memory

Differential interleukin-2 (IL-2) signaling and production are associated with disparate effector and memory fates. Whether the IL-2 signals perceived by CD8 T cells come from autocrine or paracrine sources, the timing of IL-2 signaling and their differential impact on CD8 T cell responses remain unclear. Using distinct models of germline and conditional IL-2 ablation in post-thymic CD8 T cells, this study shows that paracrine IL-2 is sufficient to drive optimal primary expansion, effector and memory differentiation, and metabolic function. In contrast, autocrine IL-2 is uniquely required during primary expansion to program robust secondary expansion potential in memory-fated cells. This study further shows that IL-2 production by antigen-specific CD8 T cells is largely independent of CD4 licensing of dendritic cells (DCs) in inflammatory infections with robust DC activation. These findings bear implications for immunizations and adoptive T cell immunotherapies, where effector and memory functions may be commandeered through IL-2 programming.

T-independent antigen induces humoral memory through germinal centers

T-dependent humoral responses generate long-lived memory B cells and plasma cells (PCs) predominantly through germinal center (GC) reaction. In human and mouse, memory B cells and long-lived PCs are also generated during immune responses to T-independent antigen, including bacterial polysaccharides, although the underlying mechanism for such T-independent humoral memory is not clear. While T-independent antigen can induce GCs, they are transient and thought to be nonproductive. Unexpectedly, by genetic fate-mapping, we find that these GCs actually output memory B cells and PCs. Using a conditional BCL6 deletion approach, we show memory B cells and PCs fail to last when T-independent GCs are precluded, suggesting that the GC experience per se is important for programming longevity of T-independent memory B cells and PCs. Consistent with the fact that infants cannot mount long-lived humoral memory to T-independent antigen, B cells from young animals intrinsically fail to form T-independent GCs. Our results suggest that T-independent GCs support humoral memory, and GC induction may be key to effective vaccines with T-independent antigen.

Altered Induction of Reactive Oxygen Species by X-rays in Hematopoietic Cells of C57BL/6-Tg (CAG-EGFP) Mice

Previous work pointed to a critical role of excessive production of reactive oxygen species (ROS) in increased radiation hematopoietic death in GFP mice. Meanwhile, enhanced antioxidant capability was not demonstrated in the mouse model of radio-induced adaptive response (RAR) using rescue of radiation hematopoietic death as the endpoint. ROS induction by ex vivo X-irradiation at a dose ranging from 0.1 to 7.5 Gy in the nucleated bone marrow cells was comparatively studied using GFP and wild type (WT) mice. ROS induction was also investigated in the cells collected from mice receiving a priming dose (0.5 Gy) efficient for RAR induction in WT mice. Significantly elevated background and increased induction of ROS in the cells from GFP mice were observed compared to those from WT mice. Markedly lower background and decreased induction of ROS were observed in the cells collected from WT mice but not GFP mice, both receiving the priming dose. GFP overexpression could alter background and induction of ROS by X-irradiation in hematopoietic cells. The results provide a reasonable explanation to the previous study on the fate of cells and mice after X-irradiation and confirm enhanced antioxidant capability in RAR. Investigations involving GFP overexpression should be carefully interpreted.