Development of intestinal intraepithelial lymphocytes, NK cells, and NK 1.1+ T cells in CD45-deficient mice

CD45-Directed CAR-T Cells with CD45 Knockout Efficiently Kill Myeloid Leukemia and Lymphoma Cells In Vitro Even after Extended Culture

BACKGROUND

CAR-T cell therapy has shown impressive results and is now part of standard-of-care treatment of B-lineage malignancies, whereas the treatment of myeloid diseases has been limited by the lack of suitable targets. CD45 is expressed on almost all types of blood cells including myeloid leukemia cells, but not on non-hematopoietic tissue, making it a potential target for CAR-directed therapy. Because of its high expression on T and NK cells, fratricide is expected to hinder CD45CAR-mediated therapy. Due to its important roles in effector cell activation, signal transduction and cytotoxicity, CD45 knockout aimed at preventing fratricide in T and NK cells has been expected to lead to considerable functional impairment.

METHODS

CD45 knockout was established on T and NK cell lines using CRISPR/Cas9-RNPs and electroporation, and the successful protocol was transferred to primary T cells. A combined protocol was developed enabling CD45 knockout and retroviral transduction with a third-generation CAR targeting CD45 or CD19. The functionality of CD45ko effector cells, CD45ko/CD45CAR-T and CD45ko/CD19CAR-T cells was studied using proliferation as well as short- and long-term cytotoxicity assays.

RESULTS

As expected, the introduction of a CD45-CAR into T cells resulted in potent fratricide that can be avoided by CD45 knockout. Unexpectedly, the latter had no negative impact on T- and NK-cell proliferation in vitro. Moreover, CD45ko/CD45CAR-T cells showed potent cytotoxicity against CD45-expressing AML and lymphoma cell lines in short-term and long-term co-culture assays. A pronounced cytotoxicity of CD45ko/CD45CAR-T cells was maintained even after four weeks of culture. In a further setup, we confirmed the conserved functionality of CD45ko cells using a CD19-CAR. Again, the proliferation and cytotoxicity of CD45ko/CD19CAR-T cells showed no differences from those of their CD45-positive counterparts in vitro.

CONCLUSIONS

We report the efficient production of highly and durably active CD45ko/CAR-T cells. CD45 knockout did not impair the functionality of CAR-T cells in vitro, irrespective of the target antigen. If their activity can be confirmed in vivo, CD45ko/CD45CAR-T cells might, for example, be useful as part of conditioning regimens prior to stem cell transplantation.

The Fyn-ADAP Axis: Cytotoxicity Versus Cytokine Production in Killer Cells

Lymphocyte signaling cascades responsible for anti-tumor cytotoxicity and inflammatory cytokine production must be tightly regulated in order to control an immune response. Disruption of these cascades can cause immune suppression as seen in a tumor microenvironment, and loss of signaling integrity can lead to autoimmunity and other forms of host-tissue damage. Therefore, understanding the distinct signaling events that exclusively control specific effector functions of “killer” lymphocytes (T and NK cells) is critical for understanding disease progression and formulating successful immunotherapy. Elucidation of divergent signaling pathways involved in receptor-mediated activation has provided insights into the independent regulation of cytotoxicity and cytokine production in lymphocytes. Specifically, the Fyn signaling axis represents a branch point for killer cell effector functions and provides a model for how cytotoxicity and cytokine production are differentially regulated. While the Fyn–PI(3)K pathway controls multiple functions, including cytotoxicity, cell development, and cytokine production, the Fyn–ADAP pathway preferentially regulates cytokine production in NK and T cells. In this review, we discuss how the structure of Fyn controls its function in lymphocytes and the role this plays in mediating two facets of lymphocyte effector function, cytotoxicity and production of inflammatory cytokines. This offers a model for using mechanistic and structural approaches to understand clinically relevant lymphocyte signaling.

Immune cell inhibition by SLAMF7 is mediated by a mechanism requiring src kinases, CD45, and SHIP-1 that is defective in multiple myeloma cells

Signaling lymphocytic activation molecule F7 (SLAMF7) is a receptor present on immune cells, including natural killer (NK) cells. It is also expressed on multiple myeloma (MM) cells. This led to development of an anti-SLAMF7 antibody, elotuzumab, showing efficacy against MM. SLAMF7 mediates activating or inhibitory effects in NK cells, depending on whether cells express or do not express the adaptor EAT-2. Since MM cells lack EAT-2, we elucidated the inhibitory effectors of SLAMF7 in EAT-2-negative NK cells and tested whether these effectors were triggered in MM cells. SLAMF7-mediated inhibition in NK cells lacking EAT-2 was mediated by SH2 domain-containing inositol phosphatase 1 (SHIP-1), which was recruited via tyrosine 261 of SLAMF7. Coupling of SLAMF7 to SHIP-1 required Src kinases, which phosphorylated SLAMF7. Although MM cells lack EAT-2, elotuzumab did not induce inhibitory signals in these cells. This was at least partly due to a lack of CD45, a phosphatase required for Src kinase activation. A defect in SLAMF7 function was also observed in CD45-deficient NK cells. Hence, SLAMF7-triggered inhibition is mediated by a mechanism involving Src kinases, CD45, and SHIP-1 that is defective in MM cells. This defect might explain why elotuzumab eliminates MM cells by an indirect mechanism involving the activation of NK cells.

Differential requirements for CD45 in NK-cell function reveal distinct roles for Syk-family kinases

The protein tyrosine phosphatase CD45 is an important regulator of Src-family kinase activity. We found that in the absence of CD45, natural killer (NK) cells are defective in protecting the host from mouse cytomegalovirus infection. We show that although CD45 is necessary for all immunoreceptor tyrosine-based activation motif (ITAM)-specific NK-cell functions and processes such as degranulation, cytokine production, and expansion during viral infection, the impact of CD45 deficiency on ITAM signaling differs depending on the downstream function. CD45-deficient NK cells are normal in their response to inflammatory cytokines when administered ex vivo and in the context of viral infection. Syk and ζ chain-associated protein kinase 70 (Zap70) are thought to play redundant roles in transmitting ITAM signals in NK cells. We show that Syk, but not Zap70, controls the remaining CD45-independent, ITAM-specific NK-cell functions, demonstrating a functional difference between these 2 Syk-kinase family members in primary NK cells.

CD45 regulates migration, proliferation, and progression of double negative 1 thymocytes

CD45 is a protein tyrosine phosphatase that is expressed on all nucleated hematopoietic cells, from stem cells to memory cells. Although its function in regulating the threshold of Ag receptor signaling is well established, its role in other leukocytes, particularly progenitor cells, is not well defined. In this study, we find CD45 affects early thymocyte development. Examination of the CD4(-)CD8(-) double negative (DN) populations revealed a significant reduction in the DN1 population, in both the numbers of CD117(+) DN1 cells (the early thymocyte progenitors) and the CD117(-) DN1 cells in the thymus of CD45(-/-) mice. There was also a reduced frequency of CCR9(+) Lin(-)Sca-1(+)c-Kit(+) cells and common lymphoid progenitors in the CD45(-/-) bone marrow. Competitive bone marrow reconstitution showed a reduced contribution of DN1 cells from CD45(-/-) cells, consistent with an intrinsic defect in these cells. CD45(-/-) DN1 cells exhibited reduced proliferation in vivo and reduced CXCL12-mediated migration in vitro. The loss of CD45 led to the accumulation of an intermediate DN1.5 thymocyte population in vivo that was dependent on Notch for progression. In vivo, CD117(-) DN1 cells gave rise to gammadelta T cells. In vitro, CD117(-) DN1 cells progressed to DN4 on OP9-DL1 cells but CD117(-) DN1 cells lacking CD45 did not. CD45(-/-) CD117(-) DN1 cells were also deficient in TCRbeta expression. Thus, CD45 deficiency affects the development and progression of DN1 thymocytes.

The localization and migration of natural killer cells in health and disease

Natural killer (NK) cells comprise a finite lymphocyte lineage with distinctive gene expression patterns. Natural killer (NK) cells develop in the bone marrow (BM) and are not static but populate secondary and primary lymphoid organs. A unique feature of NK cells is their expression of activating and inhibitory receptors, which allow them to respond either when ligands for activating receptors are upregulated or when ligands for inhibitory receptors are downregulated. The unique transcriptome of NK cells renders them capable of protecting the host from a vast array of disease states. Their undisputed importance in host protection is conferred by their ability to eliminate unhealthy cells. However, in order for NK cells to exert their effects, they need to be strategically located at the right places. This chapter provides an overview of the current understanding of the localization of NK cell populations and their ability to migrate in response to homeostatic and pathological conditions. NK cells develop in the BM, which they exit using specific molecular interactions. Exit from the BM is followed by localization to a number of tissues, including secondary lymphoid organs. Within each tissue, NK cells often acquire unique function and phenotype that is regulated by the local microenvironment. Their localization is primarily directed by the action of chemokines and therefore is in tight association with the activation status of the organism. Changes in chemokine expression during disease results in further NK cell mobilization and allows them to protect the host from infection and malignancy. Thus, from their time of production until their end, NK cells travel exhaustively over long distances and visit places that influence their already dynamic life.

Key developmental regulators change during hyperoxia-induced injury and recovery in adult mouse lung

Developmentally important genes have recently been linked to tissue regeneration and epithelial cell repair in neonatal and adult animals in several organs, including liver, skin, prostate, and musculature. We hypothesized that developmentally important genes play roles in lung injury repair in adult mice. Although there is considerable information known about these processes, the specific molecular pathways that mediate injury and regulate tissue repair are not fully elucidated. Using a hyperoxic injury model to study these mechanisms of lung injury and tissue repair, we selected the following genes based upon their known or putative roles in lung development and organogenesis: TTF-1, FGF9, FGF10, BMP4, PDGF-A, VEGF, Ptc, Shh, Sca-1, BCRP, CD45, and Cyclin-D2. Our findings demonstrate that several developmentally important genes (Sca-1, Shh, PDGF-A, VEGF, BCRP, CD45, BMP4, and Cyclin-D2) change during hyperoxic injury and normoxic recovery in mice, suggesting that adult lung may reactivate key developmental regulatory pathways for tissue repair. The mRNA for one gene (TTF-1), unchanged during hyperoxia, was upregulated late in recovery phase. These novel findings provide the basis for testing the efficacy of post-injury lung repair in animals genetically modified to inactivate or express individual molecules.

Regulation of Ly49D/DAP12 Signal Transduction by Src-Family Kinases and CD45

Activating, DAP12-coupled members of the Ly-49 family of NK cell receptors help control viral infections in mice. However, the kinases and/or phosphatases mediating tyrosine phosphorylation of Ly-49D-associated DAP12 have not been elucidated. In this study, we show for the first time that Src family tyrosine kinases are physically and functionally associated with Ly-49D/DAP12 signaling in murine NK cells. Specifically, we demonstrate the following: 1) inhibition of Src family kinases suppresses DAP12 phosphorylation and downstream DAP12 signals; 2) both Fyn and Lck are capable of phosphorylating DAP12; and 3) both kinases coimmunoprecipitate with the Ly-49D/DAP12 complex in NK cells. Although we detect enhanced phosphorylation of Fyn upon Ly-49D cross-linking in NK cells, Ly-49D-mediated events in both Fyn-/- and Fyn/Lck-/- mice appear normal, reinforcing the theme of redundancy in the ability of Src family kinases to initiate activation events. In contrast to disruption of specific Src family enzymes, Ly-49D/DAP12-mediated calcium mobilization and cytokine production by CD45 null NK cells are defective. Although others have ascribed the effects of CD45 mutation solely on the suppression of Src family activity, we demonstrate in this study that DAP12 is hyperphosphorylated in CD45 null NK cells, resulting in uncoordinated tyrosine-mediated signaling upon Ly-49D ligation. Therefore, although our data are consistent with a Src kinase activity proximally within DAP12 signaling, DAP12 also appears to be a substrate of CD45, suggesting a more complex role for this phosphatase than has been reported previously.

Dysregulation of signaling pathways in CD45-deficient NK cells leads to differentially regulated cytotoxicity and cytokine production

CD45, a protein tyrosine phosphatase that regulates Src family kinases, is important for regulating T cell and B cell receptor signaling; however, little is known about how CD45 regulates immunoreceptor tyrosine-based activation motif (ITAM)-dependent natural killer (NK) cell receptor signaling and the resulting effector functions. NK cells from CD45-deficient mice are relatively competent for ITAM receptor-induced cell-mediated cytotoxicity, yet completely deficient for cytokine secretion after stimulation with ligands to or antibodies against NK1.1, CD16, Ly49H, Ly49D, and NKG2D. This deficiency in cytokine/chemokine production occurs at the level of mRNA expression. After receptor engagement, extracellular signal-regulated kinase and c-Jun N-terminal kinase activation was markedly perturbed, whereas p38 activation was not substantially affected. The pattern and amounts of basal tyrosine phosphorylation were altered in freshly isolated NK cells and were surprisingly and markedly increased in IL-2-expanded NK cells from CD45-/- mice. These findings indicate that CD45-dependent regulation of ITAM-dependent signaling pathways is essential for NK cell-mediated cytokine production but not cytolytic activity.

CD45: all is not yet crystal clear

CD45 has been recognized as an important player in regulating signalling in lymphocytes. However, compared with tyrosine kinases, phosphatases are still poorly understood in terms of the details of their specificity and regulation. Here, the recent progress in understanding the biology of the first recognized receptor tyrosine phosphatase, CD45, is reviewed.

The Helicobacter felis model of adoptive transfer gastritis

The bacterium Helicobacter pylori is a major human pathogen and the principal cause of acute and chronic gastritis, gastric and duodenal ulcer disease, and gastric adenocarcinoma. Infection with gastric Helicobacter results in an early infiltration of neutrophils, monocytes, and natural killer cells, followed by an influx of T cells and plasma cells. Although the critical components of this gastric infiltrate that lead to disease are unclear, the Helicobacter felis-infected mouse and other mouse models of Helicobacter-associated gastritis have demonstrated the critical nature of adaptive immunity in the development of gastric epithelial pathology. To further investigate the role of adaptive immunity in this disease, adoptive transfer models of disease have also been utilized. These models clearly demonstrate that it is the host CD4+ T lymphocyte response that is crucial for the development of Helicobacter-associated gastric epithelial changes.

Developmental program of mouse Valpha14i NKT cells

Natural killer T (NKT) cells are a distinct lymphocyte lineage that regulates immune responses. During their development in the thymus, immature uncommitted double-positive CD4+CD8+ thymocytes that rearrange the semi-invariant T-cell receptor found on mature NKT cells are positively selected by the non-classical MHC class I molecule CD1d, which is expressed at the surface of cortical thymocytes. At this stage, the positively selected cells branch off from the conventional T-cell developmental program and start to acquire activated and/or memory markers and several 'bona fide' NK cell attributes. Recent work has started to reveal the specific developmental requirements for this divergent pathway of differentiation. These include several signal transduction molecules, transcription factors and cytokines, including T-bet, members of the NF-kappaB family, Fyn and IL-15.

Enforced expression of Bcl-2 restores the number of NK cells, but does not rescue the impaired development of NKT cells or intraepithelial lymphocytes, in IL-2/IL-15 receptor beta-chain-deficient mice

IL-2/IL-15Rbeta-deficient mice display impaired development of NK cells, NKT cells, and intraepithelial lymphocytes of the intestine and skin. To determine the role of survival signals mediated by IL-2/IL-15R in the development of these innate lymphocytes, we introduced a bcl-2 transgene into IL-2/IL-15Rbeta-deficient mice. Enforced expression of Bcl-2 restored the number of NK cells in IL-2/IL-15Rbeta-deficient mice, but the rescued NK cells showed no cytotoxic activity. The numbers of NKT cells and intestinal intraepithelial lymphocytes did not increase significantly, and skin intraepithelial lymphocytes remained undetectable in the bcl-2 transgenic IL-2/IL-15Rbeta-deficient mice. These results indicate an essential role of IL-2/IL-15R-mediated survival signals in the development of NK cells, but they also show that additional nonsurvival signals from IL-2/IL-15R are necessary for innate lymphocyte development.