Linda Warmuth

The chromatin organizer SATB1 is indispensable for thymic regulatory T cell (Treg cell) development and T helper cell induction. Several gene loci have been described to be SATB1-controlled, including the transcription factor GATA3 and the cytokine loci IL-4 and IL-17. However, the global effects of SATB1 on fully differentiated human CD4 conventional T cells (Tconv cells) and Treg cells, and thus the potential of SATB1 as a target for T-cell engineering, are poorly understood. Here, we describe SATB1-regulated gene signatures as largely subset-specific, with broader effects on Treg cells. Despite distinct gene-regulatory patterns, we observe overarching dysregulated cytokine and JAK-STAT signaling after SATB1 ablation. Functionally, SATB1 KO reduces suppressive capacities of human Treg cells but boosts tumor clearance via CD4 CAR T cells in a preclinical, humanized mouse model. Taken together, Treg destabilization and simultaneous increased activation of CD4 CAR T cells by SATB1 modulation may be a strategy to boost the efficiency of CAR T cell therapies.

Recent studies suggest that Chimeric Antigen Receptor (CAR) binding affinity to its ligand affects CAR-T-cell functionality. Affinity engineering towards lower binding strengths might mitigate therapeutic side effects arising from intense CAR-T-cell activation as well as tumor relapse due to antigen-escape or limited persistence of CAR-T cells during sustained activation via high-affinity receptors. Here we characterize a broad range of CARs with varying affinities to the same target epitope and leverage the insights we gain to design a combined high- and low-affinity CAR product. While CAR affinity impacts in vitro functionality minimally, it strongly correlates with tumor control in vivo. Low-affinity binders cause only mild cytokine release syndrome (CRS) in humanized mouse models at the expense of anti-tumour efficiency. In mixtures with low-affinity CARs, high-affinity CARs maintain strong functionality while showing reduced signs of exhaustion and monocyte-induced cytokine production, compared to high-affinity CAR-T cells alone. In long term in vitro and in vivo settings, low-affinity CAR-T cells dominate over time, proving more resilience to chronic antigen exposure. Overall, our findings demonstrate that affinity combination represents a promising strategy to generate more effective CAR-T-cell products with an improved therapeutic index, beyond affinity engineering alone.

Synthetic biology has fundamentally advanced cell engineering and helped to develop effective therapeutics such as chimeric antigen receptor (CAR)-T cells. For these applications, the detection, localization, and quantification of heterologous fusion proteins assembled from interchangeable building blocks is of high importance. The V5 tag, a 14-residue epitope tag, offers promising characteristics for these applications but has only rarely been used in this context. Thus, we have systematically evaluated the murine anti-V5 tag antibody mu_SV5-Pk1 as well as its humanized version, hu_SV5-Pk1, to analyze cells expressing V5-tagged receptors in samples from various in vitro and in vivo experiments. We found that the V5 tag signal on cells is affected by certain fixation and detachment reagents. Immunohistochemistry (IHC) on formalin-fixed paraffin-embedded (FFPE) mouse tissue samples was performed to sensitively detect cells in tissue. We improved IHC by applying the hu_SV5-Pk1 monoclonal antibody (mAb) to avoid cross-reactivity within and unspecific background signals arising on fixed mouse tissue. Conversely, the absence of unspecific binding by the mu_SV5-Pk1 mAb was evaluated on 46 human normal or cancer tissues. Our findings present a robust toolbox for utilizing the V5 tag and cognate antibodies in synthetic biology applications.

Humanized mice are a powerful tool in preclinical assessment of novel therapeutics. However, generation of large homogenous cohorts is believed to be hampered by the limited number of human stem cells retrievable from individual donors, like from umbilical cord blood specimens. Here, we present a streamlined CD34+ cell isolation method that improves yield and purity compared to standard isolation protocols, enabling more efficient use of umbilical cord blood donations. Enriched CD34+ stem cell preparations yield robust humanization of NSG-SGM3 mice, even with very low input doses, down to a few thousand cells. Using our findings to effectively humanize large cohorts of mice (in this study up to 30 mice from a single stem cell donor), we resolve differences in cytokine release syndrome for two different CAR-T cell products within single-donor settings. These optimizations facilitate larger or smaller humanization experiments, with reduced economical and logistical burden for critical translational research.

Adoptive cellular therapies have shown enormous potential but are complicated by personalization. Because of HLA mismatch, rejection of transferred T cells frequently occurs, compromising the T-cell graft's functionality. This obstacle has led to the development of HLA knock-out (KO) T cells as universal donor cells. Whether such editing directly affects T-cell functionality remains poorly understood. In addition, HLA KO T cells are susceptible to missing self-recognition through natural killer (NK) cells and lack of canonical HLA class I expression may represent a safety hazard. Engineering of noncanonical HLA molecules could counteract NK-cell recognition, but further complicates the generation of cell products. Here, we show that HLA KO does not alter T-cell functionality in vitro and in vivo. Although HLA KO abrogates allogeneic T-cell responses, it elicits NK-cell recognition. To circumvent this problem, we demonstrate that selective editing of individual HLA class I molecules in primary human T cells is possible. Such HLA reduction not only inhibits T-cell alloreactivity and NK-cell recognition simultaneously, but also preserves the T-cell graft's canonical HLA class I expression. In the presence of allogeneic T cells and NK cells, T cells with remaining expression of a single, matched HLA class I allele show improved functionality in vivo in comparison with conventional allogeneic T cells. Since reduction to only a few, most frequent HLA haplotypes would already be compatible with large shares of patient populations, this approach significantly extends the toolbox to generate broadly applicable cellular products.

Engagement of the inhibitory T cell receptor programmed cell death protein 1 (PD-1) associates with dysfunctional states of pathogen- or tumor-specific T cells. Accordingly, systemic antibody-mediated blockade of PD-1 has become a central target for immunotherapies but is also associated with severe toxicities due to loss of peripheral tolerance. Therefore, selective ablation of PD-1 expression on adoptively transferred T cells through direct genetic knockout (KO) is currently being explored as an alternative therapeutic approach. However, since PD-1 might also be required for the regulation of physiological T cell function and differentiation, the suitability of PD-1 as an engineering target is controversial. In this study, we systematically investigated the maintenance of T cell functionality after CRISPR/Cas9-mediated PD-1 KO in vivo during and after acute and chronic antigen encounter. Under all tested conditions, PD-1 ablation preserved the persistence, differentiation, and memory formation of adoptively transferred receptor transgenic T cells. Functional PD-1 KO T cells expressing chimeric antigen receptors (CARs) targeting CD19 could be robustly detected for over 390 d in a syngeneic immunocompetent mouse model, in which constant antigen exposure was provided by continuous B cell renewal, representing the longest in vivo follow-up of CAR-T cells described to date. PD-1 KO CAR-T cells showed no evidence for malignant transformation during the entire observation period. Our data demonstrate that genetic ablation of PD-1 does not impair functionality and longevity of adoptively transferred T cells per se and therefore may be pursued more generally in engineered T cell-based immunotherapy to overcome a central immunosuppressive axis.