Unmodified, uridine-containing mRNA is known to trigger antiviral immune responses, inflammatory signaling, and apoptosis in transfected cells. To avoid this and enable high expression, modified nucleosides such as N1-methylpseudouridine have become the gold standard for mRNA applications including T cell engineering, albeit at increased cost. Here, immune responses toward mRNA were evaluated across five primary human cell types. Remarkably, T cells, unlike other immune and non-immune cell types tested, exhibited no immune activation by unmodified mRNA. T cell viability and cytokine secretion remained unaffected, regardless of mRNA delivery method via lipid nanoparticles or electroporation. The absence of nucleotide modifications improved expression of chimeric antigen receptor (CAR) in activated T cells and CAR-T cell cytotoxic potency. By eliminating the need for mRNA-nucleoside modification in CAR-T cell engineering, our findings challenge existing paradigms and position mRNA as a non-inflammatory, minimally invasive and highly efficient tool for T cell engineering, while simplifying and reducing manufacturing cost.

Abstract Virus-free genome engineering provides a flexible alternative to viral vectors for generating genetically modified cell models. Here, we establish an integrated biosafety level 1-compatible CRISPR/Cas9 homology-directed repair (HDR) workflow for stable transgene knock-in in neuroblastoma cell lines using non-viral delivery approaches. We systematically evaluated donor cassette architecture and delivery conditions across electroporation-based Cas9 ribonucleoprotein (RNP) delivery and lipid nanoparticle (LNP)-mediated co-delivery of Cas9 mRNA, sgRNA, and donor DNA. Modular AAVS1-targeting donor constructs identified a compact EF1α(s)-Donor-Q8-Tag-sPA cassette that consistently yielded the strongest HDR-associated knock-in readouts, achieving up to 60% stable reporter-positive cells following electroporation without HDR enhancers. While LNP-mediated delivery enabled efficient CRISPR cargo co-delivery and generation of genetically modified tumor cell populations, knock-in efficiencies remained lower than those observed with electroporation. Subsequent enrichment approaches enabled generation of highly pure edited cell populations following both delivery strategies. Functional validation demonstrated stable transgene expression in vitro, including in three-dimensional bioprinted tumor models, and in vivo in xenograft mice without impairing tumor growth or viability. Together, these findings establish a practical non-viral HDR platform for stable engineering of solid tumor models and provide a framework for further optimization of genome editing workflows across distinct delivery modalities. Key findings - We establish a complete, virus-free CRISPR/Cas9 HDR workflow that reliably enables stable knock-in in solid tumor cell lines, demonstrated here in two neuroblastoma models under biosafety level 1 conditions. - We establish and evaluate LNP-mediated co-delivery of Cas9 mRNA, gRNA, and donor DNA for non-viral HDR knock-in in solid tumor models, revealing delivery modality-specific differences in editing efficiency, toxicity, and expression dynamics. - By systematically varying donor architectures, we identify a compact HDR template - combining a shortened custom EF1α promoter, the minimal Q8 surface reporter, and a synthetic polyadenylation signal (sPA) - that markedly improves knock-in efficiency in solid tumor cell lines, outperforming conventional cassettes. - Virus-free edited tumor cells generated using this workflow retain stable transgene expression and functional fitness in 3D bioprinted tumor constructs and xenograft mouse models, directly linking in vitro knock-in optimization to in vivo relevance. - The resulting biosafety level 1 compatible, end-to-end pipeline - integrating donor design, digital PCR-based quantification of precise integration, and enrichment strategies-offers a practical and transferable platform for engineering transgenic solid tumor models without viral vectors.

Lung cancer, the leading cause of cancer-related mortality, presents major challenges for both standard therapies and chimeric antigen receptor (CAR) T cell therapy due to tumour heterogeneity and resistance. Preclinical models that capture patient-specific factors are essential for personalizing treatment decisions. Here we show that matched lung tumouroids and healthy lung organoids derived from patients provide a robust platform for studying therapy responses. The tumouroids faithfully retained the molecular and histological identity of the original tumours, as confirmed by genomic, epigenomic and proteomic analyses, and accurately replicated individual patient responses to standard-of-care therapies. Importantly, the platform also revealed patient-specific CAR T cell responses, uncovering a complex interplay between target antigen density and broader, tumour-intrinsic resistance programmes. By capturing these individualized factors, our model supports rational patient selection for CAR T cell therapy in lung cancer and provides a framework for designing CAR T cells tailored to overcome resistance mechanisms in solid tumours. A platform using matched patient-derived lung tumouroids and healthy lung organoids enables accurate examination of patient responses to CAR T therapy and offers a faithful framework for improved CAR T design.

Unwanted alloimmune responses are a central driver of solid organ transplant rejection and currently managed with life-long immunosuppression, which imposes substantial risks and burdens on patients. Adoptive transfer of regulatory T cells (Tregs) offers a strategy to restore immunological balance and reduce long-term adverse effects of generalized immunosuppression. However, although Tregs can potently inhibit incipient immune activation, they struggle to suppress established memory effector T cells, necessitating the continued use of immunosuppression. Calcineurin inhibitors such as Tacrolimus effectively control both, newly activated and pre-existing effector T cells, but unfortunately, they also impair Treg function. Therefore, we hypothesized that gene-editing of Tregs inducing tacrolimus resistance (FKBP12KO) would enable combined therapy that curbs effector T cell responses without compromising Treg efficacy. Here, we developed FKBP12KO-Tregs using a ribonucleoprotein-based CRISPR-Cas9 approach and characterized them extensively in vitro. FKBP12KO-Tregs retained phenotype, high viability, and suppressive function comparable to unedited TregWT, and they remained functionally impervious to Tacrolimus, while preserving sensitivity to alternative CNIs. We additionally established a good-manufacturing practice process for FKBP12KO-Tregs. Comprehensive in vitro phenotypic, functional, and molecular characterization, together with the established manufacturing, provide the rationale for a proof-of-concept clinical trial assessing the feasibility and safety of co-administration of FKBP12KO-Tregs with Tacrolimus in living-donor kidney transplant recipients.

Multiplex genome editing of cellular therapies frequently requires multiple DNA double-strand breaks (DSBs), which can induce genotoxicity through chromosomal rearrangements and large deletions. Base editors enable targeted sequence changes with minimal DSBs and are widely used for gene disruption, but their capacity for transgene insertion has remained unexplored. Here, we have developed base editor-mediated knockin (BEKI), a non-viral platform combining transgene insertion with multiplex gene disruption using a single enzyme. BEKI repurposes the base editor's Cas9 nickase domain to generate paired nicks (inducing a localized DSB) at the knockin locus while achieving multiplex knockouts through base editing. Optimized guide RNA orientation and spacing enabled efficient transgene insertion across multiple T cell-relevant genomic loci. DNA-PK inhibition enhanced knockin efficiency but increased kilobase-scale deletions, which were mitigated by co-inhibition of Polθ. Compared with multiplex Cas9 editing, BEKI markedly reduced chromosomal translocations while preserving cell viability. BEKI supported targeted chimeric antigen receptor (CAR) knockin alongside up to 10 simultaneous gene knockouts, enabling the generation of allogeneic CAR T cells with enhanced cytokine secretion and resistance to immunosuppressants and allo-rejection. Together, BEKI provides a streamlined and scalable strategy for multiplex CAR T cell engineering with improved genomic stability, advancing safer next-generation cell therapies for cancer and autoimmune diseases.

Adoptive transfer of antigen-specific regulatory T cells (Tregs) is a promising strategy to combat immunopathologies in transplantation and autoimmune diseases. However, their low frequency in peripheral blood poses challenges for both manufacturing and clinical application. Chimeric antigen receptors (CARs) have been used to redirect the specificity of Tregs, employing retroviral vectors. However, retroviral gene transfer is costly, time consuming, and raises safety issues. Here, we explored non-viral CRISPR-Cas12a gene editing to redirect Tregs, using HLA-A2-specific constructs for proof-of-concept studies in transplantation models. Knock-in of an antigen-binding domain into the N terminus of CD3 epsilon (CD3ε) gene generates Tregs expressing a chimeric CD3ε-T cell receptor fusion construct (TRuC) protein which integrates into the endogenous TCR/CD3 complex. These CD3ε-TRuC Tregs exhibit potent antigen-dependent activation while maintaining responsiveness to TCR/CD3 stimulation. This enables preferential enrichment of TRuC-redirected Tregs over CD3ε KO Tregs via repetitive CD3/CD28-stimulation in a GMP-compatible expansion system. CD3ε-TRuC Tregs retained their phenotypic, epigenetic, and functional identity. In a humanized mouse model, HLA-A2-specific CD3ε-TRuC Tregs demonstrate superior protection of allogeneic HLA-A2+ skin grafts from rejection compared to polyclonal Tregs. This approach provides a pathway for developing clinical-grade CD3ε-TRuC-based Treg cell products for transplantation immunotherapy and other immunopathologies.

Regulatory T cells (Tregs) hold promise for treating autoimmune disease and transplant rejection, yet generation of autologous products for adoptive transfer can suffer donor variability and slow turnaround, limiting their use in urgent indications. We therefore examine whether allogeneic, pre-manufactured ('off-the-shelf') Tregs could overcome these barriers. In a human skin-xenograft model, HLA-mismatched Tregs are swiftly eliminated by recipient CD8+ T cells and fail to protect grafts. Stringent matching of HLA class I and II restores efficacy but is clinically impractical. Using non-viral CRISPR editing we disrupt B2M and CIITA while inserting an HLA-E-B2M fusion, generating hypo-immunogenic Tregs that evade both T and NK cell attack. Engineered cells retain FOXP3 stability and potent in vitro suppression, and after a single low-dose infusion, prolong human skin graft survival in a humanized mouse model comparably to autologous Tregs. Histology and spatial transcriptomics reveal minimal cytotoxic infiltration and enrichment of immunoregulatory and tissue-repair programmes. Multiplex HLA engineering thus enables ready-to-use allogeneic Tregs that withstand host immune attack for adoptive transfer.

mRNA-based chimeric antigen receptor (CAR)-T cells offer the promise of enhanced safety and simplified manufacturing. However, in vitro-transcribed (IVT) mRNA is known to trigger antiviral immune responses, inflammatory signaling, and apoptosis in transfected cells. To address these challenges and enable efficient IVT-mRNA expression, modified nucleosides, such as N1-methyl-pseudouridine (m1Ψ), have become the gold standard for CAR-T cell production, albeit at increased cost. In this study, immune responses to IVT-mRNA were evaluated across five primary human cell types, including T-cells. Unexpectedly, T-cells, unlike other immune and non-immune cell types tested, exhibited no immune activation in response to unmodified mRNA. T-cell viability and cytokine secretion patterns remained unaffected, regardless of whether unmodified mRNA was delivered via lipid nanoparticles (LNPs) or electroporation. Furthermore, CAR expression levels in T-cells were not influenced by mRNA modification with m1Ψ or 5-methoxy-uridine (5moU) nucleosides. The absence of nucleoside modifications did not compromise CAR-T cell cytotoxic potency, demonstrating that such modifications are not required for producing functional CAR-T cells. These findings eliminate the need for nucleoside modification in T-cell mRNA, simplifying and reducing the cost of CAR-T cell manufacturing while positioning IVT-mRNA as a highly efficient and minimally invasive tool for CAR-T cell engineering. ### Competing Interest Statement No.Ka. and C.M.D. are employees of Pantherna Therapeutics GmbH, focused on RNA therapeutics. The opinions expressed in this article are those of the authors and not necessarily those of Pantherna. Pantherna was neither financially involved in the creation nor in the publication of this article. H.-D.V. and D.L.W. are co-founders of TCBalance Biopharmaceuticals GmbH focused on regulatory T cell therapy. The opinions expressed in this article are those of the authors and not necessarily those of TCBalance. TCBalance was neither financially involved in the creation nor in the publication of this article. The other authors declare no conflicts of interest.

Background: Unwanted immune responses play a central role in the pathogenesis of solid organ allograft rejection. These are managed by life-long immunosuppression with considerable burden for the patient and society. Adoptive therapy with regulatory T-cells (Treg) is a promising approach to restore sustainable immune balance and avoid long-term adverse effects of immunosuppression. While Treg effectively inhibit activation of unwanted immune responses, they are less effective in controlling pre-existing/activated memory effector T-cells (Teff). Thus, co-administration of Treg with immunosuppressants is required to achieve a sustainable organ acceptance. Calcineurin inhibitors (CNI) are powerful in controlling de novo generated and preformed Teff. However, CNI also dampen Treg immunoregulatory function. Thus, we hypothesize improved results of adoptive Treg therapy in immunosuppressed patients applying tacrolimus-resistant Treg. Methods: While retaining CNI modulation of Teff with tacrolimus, we knocked-out FKBP12 in Treg (FKBP12KO-Treg) by gene-editing using ribonucleoprotein-based CRISPR/Cas9 technology to generate tacrolimus-resistant Treg and characterised them using flow cytometry, functional assays and in-depth phenotyping. Results: This detailed in vitro analysis showed FKBP12KO-Treg were comparable to non-gene edited Treg and impervious to tacrolimus while maintaining immunoregulatory function and sensitivity to alternative CNIs raising no safety concerns. Furthermore, we aligned our methodology to achieve GMP compliance laying the basis for a manufacturing license in preparation of a clinical trial. Conclusion: Based on the presented preclinical dataset implying safety and efficacy of FKBP12KO-Treg, we are now seeking to undertake a proof-of-concept clinical trial to evaluate the co-administration of FKBP12KO-Treg and tacrolimus to enhance the management of living donor kidney transplant recipients. ### Competing Interest Statement The authors declare that the research was conducted as part of a collaboration agreement between Charite-Universitaetsmedizin Berlin and Integrated DNA Technologies (IDT), IDT provided certain reagents and performed experiments. R.T., B.T., M.L.S., G.L.K., and A.M.J. are employees of IDT, which offers reagents for sale similar to some of the compounds described in the manuscript. Products and tools supplied by IDT are for research use only. Purchaser and/or user are solely responsible for all decisions regarding the use of these products and any associated regulatory or legal obligations. PR, HDV, DLW, MSH and LA hold a patent for immunosuppressant-resistant T-cells for adoptive immunotherapy (PCT/EP2021/072651), T.C. is an inventor of CAST-Seq (patent US11319580B2). PR, HDV and DLW founded the startup company TCbalance, which licensed the Treg part of PCT/EP2021/072651 from Charite-Universitaetsmedizin Berlin. European Union, https://ror.org/019w4f821, 825392, 101057438

The CRISPR-Cas system enables precise genome engineering of cell therapies. For allogeneic applications, multiplex editing is frequently required to improve efficacy, persistence, and safety. However, strategies involving multiple DNA double-strand breaks (DSBs) induce genotoxicity by provoking chromosomal aberrations. Base editors, which enable sequence changes without generating DSBs, are widely used for gene disruption, but their capacity for gene insertion remains unexplored. Here, we developed B ase e ditor-mediated k nock- i n ( BEKI ), a non-viral platform that allows targeted transgene insertion in parallel with multiplex gene disruption using a single base editor. Repurposing the Cas9 nickase domain of base editors generates paired nicks, inducing homology-directed repair (HDR). In human T cells, optimized guide RNA orientation and nick distance, together with HDR-enhancing modulators, enabled efficient transgene knock-in at the TRAC , CD3ζ, B2M, and CD3ε loci. Simultaneous base editing of multiple additional genes produced chimeric antigen receptor (CAR) T cells with increased cytokine secretion, drug resistance, and resistance to allo-rejection. Compared to multiplex editing with Cas9, BEKI markedly reduced chromosomal translocations. BEKI therefore provides a streamlined, scalable strategy for multiplex CAR T-cell engineering with a single enzyme, offering a safer route to clinical-grade manufacturing of off-the-shelf therapies for cancer and autoimmune diseases. ![Figure][1] ### Competing Interest Statement V.G., J.K., D.L.W., H.-D.V., P.R. are named as inventors on patent applications filed by Charite - Universitaetsmedizin Berlin, describing parts of this work (EP24222163.8 - BEKI system, D.L.W., V.G., J.K.; CD3-zeta editing: EP4019538A1 - D.L.W., J.K., H.-D.V., P.R.; CD3-epsilon editing: EP4353252A1 - D.L.W., J.K., H.-D.V., P.R.). T.Ca. and G.A. are co-inventors of CAST-Seq (patent US11319580B2). The Wagner Lab at Charite has received reagents related to gene editing from IDT and GenScript Inc. P.R., H.-D.V. and D.L.W. are co-founders of the startup TCBalance Biopharmaceuticals GmbH focused on regulatory T cell therapy, which was not involved in the present study. H.-D.V. is founder and CSO at CheckImmune GmbH. All other authors declare that they do not have no competing interests. European Union, Horizon Europe grant agreement no. 101057438 Berlin Institute of Health at Charité - Universitätsmedizin Berlin, https://ror.org/0493xsw21, SPARK-BIH Program German Federal Ministry of Education and Research (BMBF), Medical Informatics Funding Scheme EkoEstMed–FKZ 01ZZ2015 [1]: pending:yes

Background Chimeric antigen receptor (CAR) T-cell therapy depends on T cells that are genetically modified to recognize and attack cancer cells. Their effectiveness thus hinges on the functionality of a patient’s own T cells. Since CAR T-cell therapy is currently only approved for advanced cancers after at least one line of chemotherapy, we evaluated the potential negative effects of prior exposure to chemotherapy on T-cell functionality.Methods We studied T cells of two B-cell non-Hodgkin’s lymphoma patient cohorts, one collected before treatment (pre-therapy) and the other after one or more (median 3) lines of chemotherapy (post-therapy). Leveraging advanced multiparameter flow cytometry, single-cell RNA sequencing (scRNA-seq), whole-genome DNA methylation arrays and in vitro functionality testing of generated CAR T cells, we compared patient samples in their suitability for effective CAR T-cell therapy.Results We discovered significant modifications in T-cell subsets and their transcriptional profiles secondary to chemotherapy exposure. Our analysis revealed a discernible shift towards phenotypically more differentiated T cells and an upregulation of markers indicative of T-cell exhaustion. Additionally, scRNA-seq and DNA methylation analyses revealed gene expression and epigenetic changes associated with diminished functionality in post-therapy T cells. Cytotoxicity assays demonstrated superior killing efficacy of CAR T cells derived from treatment-naïve patients compared with those with chemotherapy history.Conclusions These findings corroborate that employing T cells collected prior to frontline chemotherapy could enhance the effectiveness of CAR T-cell therapy and improve patient outcomes.

Current gene transfer methods often lack the precision, versatility, or efficiency when integrating large transgenes, limiting the ability to engineer therapeutic T-cells with more complex payloads. Here, we report ‘one-pot’ PASTA (Programmable and Site-specific Transgene Addition), a non-viral genome engineering strategy for large gene insertion that combines CRISPR-Cas-mediated homology-directed repair (HDR) and site-specific recombination via serine integrases. Using ‘one-pot’ PASTA with the Bxb1 integrase, we demonstrate efficient integration of transgenes at multiple genomic loci relevant for T-cell engineering (e.g., TRAC, B2M, CD3E, CD3Z, GAPDH ). For constructs > 8 kb, ‘one-pot’ PASTA outperforms conventional HDR by 19-fold on average and prime-editing-assisted site-specific integrase gene editing (PASSIGE) by 5-fold. This enables the delivery of multi-cistronic cargo to generate dual-antigen targeting CAR T-cells with a safety-switch that overcome antigen escape in lymphoma models. Finally, ‘one-pot’ PASTA can be further optimized with improved integrase enzymes, such as engineered variants of Pa01 or Bxb1, and plasmids with minimized backbones. In summary, ‘one-pot’ PASTA represents a versatile and scalable platform for precise, non-viral gene insertion in T-cells. ### Competing Interest Statement I.K., J.K., D.M.I., D.L.W. are named as inventors on patent applications filed by Charite - Universitatsmedizin Berlin, describing parts of this work (EP24196550 - efficient integrase-mediated gene transfer in human cells; CD3-zeta editing: EP4019538A1 - D.L.W., J.K.; CD3-epsilon editing: EP4353252A1 - D.L.W., J.K.). The Wagner Lab at Charite has received reagents related to gene editing from IDT and GenScript Inc. D.L.W. is a co-founder of the startup TCBalance Biopharmaceuticals GmbH focused on regulatory T cell therapy, which was not involved in the present study. All other co-authors report no conflict of interest related to this work. European Union, 101057438

The immunosuppressive tumour microenvironment (TME) remains a central barrier to effective immunotherapy in solid tumours. We present a gene-therapeutic strategy that enables localized remodelling of the TME via tumour-intrinsic cytokine expression. Central to this approach is CancerPAM, a multi-omics bioinformatics pipeline that identifies and ranks patient-specific, tumour-exclusive CRISPR-Cas9 knock-in sites with high specificity and integration efficiency. Using neuroblastoma as a model, CancerPAM analysis of tumour sequencing data identifies optimal knock-in sites for pro-inflammatory cytokines (CXCL10, CXCL11, IFNG), and CancerPAM rankings correlate strongly with target-site specificity and knock-in efficiency, validating its predictive performance. CRISPR-mediated CXCL10 knock-in enhances CAR T cell infiltration and antitumour efficacy in vitro and in vivo, including humanized CD34⁺ HuNOG mice, where CXCL10-expressing tumours show stronger immune infiltration and prolonged tumour control within a reconstituted human immune microenvironment. Our findings establish a framework for safe and effective CRISPR-based cytokine delivery, integrating localized TME remodelling with cellular immunotherapies to enhance CAR T cells and other treatments in immune-refractory solid tumours.

BackgroundMultiple genetic modifications may be required to develop potent off-the-shelf chimeric antigen receptor (CAR) T cell therapies. Conventional CRISPR-Cas nucleases install sequence-specific DNA double-strand breaks (DSBs), enabling gene knock-out or targeted transgene knock-in. However, simultaneous DSBs provoke a high rate of genomic rearrangements which may impede the safety of the edited cells.ResultsHere, we combine a non-viral CRISPR-Cas9 nuclease-assisted knock-in and Cas9-derived base editing technology for DSB free knock-outs within a single intervention. We demonstrate efficient insertion of a CAR into the T cell receptor alpha constant (TRAC) gene, along with two knock-outs that silence major histocompatibility complexes (MHC) class I and II expression. This approach reduces translocations to 1.4% of edited cells. Small insertions and deletions at the base editing target sites indicate guide RNA exchange between the editors. This is overcome by using CRISPR enzymes of distinct evolutionary origins. Combining Cas12a Ultra for CAR knock-in and a Cas9-derived base editor enables the efficient generation of triple-edited CAR T cells with a translocation frequency comparable to unedited T cells. Resulting TCR- and MHC-negative CAR T cells resist allogeneic T cell targeting in vitro.ConclusionsWe outline a solution for non-viral CAR gene transfer and efficient gene silencing using different CRISPR enzymes for knock-in and base editing to prevent translocations. This single-step procedure may enable safer multiplex-edited cell products and demonstrates a path towards off-the-shelf CAR therapeutics.

Persistent antigen stimulation and inflammatory environments drive exhaustion, senescence, and activation-induced cell death, impairing both endogenous and therapeutic T cells. Understanding the mechanisms underlying T cell dysfunction is critical for improving immunotherapies. While the transcription factor forkhead box protein P3 (FOXP3) is primarily known for its role in regulatory T cell development and maintenance, recent studies suggest it may also influence effector T cell function. However, its impact on therapeutic T cells, including CAR T cells, remains poorly defined. Here, we used non-viral CRISPR-Cas9 editing to knockout FOXP3 in CD19-directed CAR T cell products (TCPs) generated via lentiviral transduction. FOXP3 expression was upregulated at both the protein and RNA level following CAR stimulation. Compared to unmodified CAR TCPs, FOXP3-KO CAR TCPs showed comparable exhaustion profiles but enhanced cytokine production and prolonged cytotoxic function across repeated antigen challenges. These findings identify FOXP3 as a context-dependent modulator of CAR T cell function and suggest that its disruption may enhance therapeutic potency without exacerbating exhaustion. FOXP3 targeting may represent a complementary strategy to improve the functional resilience of CAR T cell therapies in cancer or autoimmune disease.

CRISPR-Cas12a gene editing offers an alternative to Cas9-based methods, providing better targeting of AT-rich regions, simplified guide RNA manufacturing, and high specificity. However, the efficacy of donor-based editing is subject to various factors, with template format playing a crucial role. Currently, the predominant non-viral template format for homology-directed repair (HDR) after nuclease-induced DNA breaks is double-stranded DNA, which is toxic when transfected at high doses. Others have demonstrated that using single-stranded DNA (ssDNA) with flanking double-stranded Cas-target-sequences (CTS) as a template for Cas9-mediated gene editing can mitigate this toxicity and increase knock-in efficiency. Here, we investigate CTS design for AsCas12a Ultra by exploring PAM orientation and binding requirements. Additionally, we rule out ssDNase activity of AsCas12a under cell-physiological Mg2+ conditions. Finally, we showcase the advantage of ssDNA donors with CTS (ssCTS) at high doses for delivering clinically relevant transgenes of varying sizes into three TCR-CD3 complex genes (TRAC, CD3ζ, CD3ε), achieving up to 90% knock-in rates for a 0.8kb-insert at the CD3ε locus. Long-read sequencing confirmed higher HDR rates and revealed that CTS reduced partial integration events compared to unmodified ssDNA. Overall, AsCas12a and ssCTS represent a platform for highly efficient knock-in in primary human T cells with minimal toxicity.

Plasma cells (PCs) in bone marrow (BM) play an important role in both protective and pathogenic humoral immune responses, e.g. in various malignant and non-malignant diseases such as multiple myeloma, primary and secondary immunodeficiencies and autoimmune diseases. Dedicated microenvironmental niches in the BM provide PCs with biomechanical and soluble factors that support their long-term survival. There is a high need for appropriate and robust model systems to better understand PCs biology, to develop new therapeutic strategies for PCs-related diseases and perform targeted preclinical studies with high predictive value. Most preclinical data have been derived from in vivo studies in mice, as in vitro studies of human PCs are limited due to restricted survival and functionality in conventional 2D cultures that do not reflect the unique niche architecture of the BM. We have developed a microphysiological, dynamic 3D BM culture system (BM-MPS) based on human primary tissue (femoral biopsies), mechanically supported by a hydrogel scaffold casing. While a bioinert agarose casing did not support PCs survival, a photo-crosslinked collagen-hyaluronic acid (Col-HA) hydrogel preserved the native BM niche architecture and allowed PCs survival in vitro for up to 2 weeks. Further, the Col-HA hydrogel was permissive to lymphocyte migration into the microphysiological system´s circulation. Long-term PCs survival was related to the stable presence in the culture of soluble factors, as APRIL, BAFF, and IL-6. Increasing immunoglobulins concentrations in the medium confirm their functionality over culture time. To the best of our knowledge, this study is the first report of successful long-term maintenance of primary-derived non-malignant PCs in vitro . Our innovative model system is suitable for in-depth in vitro studies of human PCs regulation and exploration of targeted therapeutic approaches such as CAR-T cell therapy or biologics.