Precise CRISPR-Cas9 gene repair in autologous memory T cells to treat familial hemophagocytic lymphohistiocytosis.

Familial hemophagocytic lymphohistiocytosis (FHL) is an inherited, often fatal immune deficiency characterized by severe systemic hyperinflammation. Although allogeneic bone marrow transplantation can be curative, more effective therapies are urgently needed. FHL is caused by inactivating mutations in proteins that regulate cellular immunity. Here, we used an adeno-associated virus-based CRISPR-Cas9 system with an inhibitor of nonhomologous end joining to repair such mutations in potentially long-lived T cells ex vivo. Repaired CD8 memory T cells efficiently cured lethal hyperinflammation in a mouse model of Epstein-Barr virus-triggered FHL2, a subtype caused by perforin-1 (Prf1) deficiency. Furthermore, repair of PRF1 and Munc13-4 (UNC13D)-whose deficiency causes the FHL subtype FHL3-in mutant memory T cells from two critically ill patients with FHL restored T cell cytotoxicity. These results provide a starting point for the treatment of genetic T cell immune dysregulation syndromes with repaired autologous T cells.

Concomitant Cytotoxic Effector Differentiation of CD4+ and CD8+ T Cells in Response to EBV-Infected B Cells.

Most people infected by EBV acquire specific immunity, which then controls latent infection throughout their life. Immune surveillance of EBV-infected cells by cytotoxic CD4+ T cells has been recognized; however, the molecular mechanism of generating cytotoxic effector T cells of the CD4+ subset remains poorly understood. Here we compared phenotypic features and the transcriptome of EBV-specific effector-memory CD4+ T cells and CD8+ T cells in mice and found that both T cell types show cytotoxicity and, to our surprise, widely similar gene expression patterns relating to cytotoxicity. Similar to cytotoxic CD8+ T cells, EBV-specific cytotoxic CD4+ T cells from human peripheral blood expressed T-bet, Granzyme B, and Perforin and upregulated the degranulation marker, CD107a, immediately after restimulation. Furthermore, T-bet expression in cytotoxic CD4+ T cells was highly correlated with Granzyme B and Perforin expression at the protein level. Thus, differentiation of EBV-specific cytotoxic CD4+ T cells is possibly controlled by mechanisms shared by cytotoxic CD8+ T cells. T-bet-mediated transcriptional regulation may explain the similarity of cytotoxic effector differentiation between CD4+ T cells and CD8+ T cells, implicating that this differentiation pathway may be directed by environmental input rather than T cell subset.

Functional interplay of Epstein-Barr virus oncoproteins in a mouse model of B cell lymphomagenesis.

Epstein-Barr virus (EBV) is a B cell transforming virus that causes B cell malignancies under conditions of immune suppression. EBV orchestrates B cell transformation through its latent membrane proteins (LMPs) and Epstein-Barr nuclear antigens (EBNAs). We here identify secondary mutations in mouse B cell lymphomas induced by LMP1, to predict and identify key functions of other EBV genes during transformation. We find aberrant activation of early B cell factor 1 (EBF1) to promote transformation of LMP1-expressing B cells by inhibiting their differentiation to plasma cells. EBV EBNA3A phenocopies EBF1 activities in LMP1-expressing B cells, promoting transformation while inhibiting differentiation. In cells expressing LMP1 together with LMP2A, EBNA3A only promotes lymphomagenesis when the EBNA2 target Myc is also overexpressed. Collectively, our data support a model where proproliferative activities of LMP1, LMP2A, and EBNA2 in combination with EBNA3A-mediated inhibition of terminal plasma cell differentiation critically control EBV-mediated B cell lymphomagenesis.

A novel allele for inducible Cre expression in germinal center B cells.

The germinal center reaction is essential for efficient humoral immunity, but it can also give rise to B cell lymphomas. Cre/loxP-mediated conditional gene knock-out or knock-in can be used for the genetic manipulation of germinal center B cells in vivo. Here we present a novel allele, Cγ1-CreERT2, that allows for timed activation of Cre recombinase in a small fraction of germinal center B cells. This allele will be useful to study normal and malignant germinal center B cell development in vivo.

Mouse model for acute Epstein-Barr virus infection.

Epstein-Barr Virus (EBV) infects human B cells and drives them into continuous proliferation. Two key viral factors in this process are the latent membrane proteins LMP1 and LMP2A, which mimic constitutively activated CD40 receptor and B-cell receptor signaling, respectively. EBV-infected B cells elicit a powerful T-cell response that clears the infected B cells and leads to life-long immunity. Insufficient immune surveillance of EBV-infected B cells causes life-threatening lymphoproliferative disorders, including mostly germinal center (GC)-derived B-cell lymphomas. We have modeled acute EBV infection of naive and GC B cells in mice through timed expression of LMP1 and LMP2A. Although lethal when induced in all B cells, induction of LMP1 and LMP2A in just a small fraction of naive B cells initiated a phase of rapid B-cell expansion followed by a proliferative T-cell response, clearing the LMP-expressing B cells. Interfering with T-cell activity prevented clearance of LMP-expressing B cells. This was also true for perforin deficiency, which in the human causes a life-threatening EBV-related immunoproliferative syndrome. LMP expression in GC B cells impeded the GC reaction but, upon loss of T-cell surveillance, led to fatal B-cell expansion. Thus, timed expression of LMP1 together with LMP2A in subsets of mouse B cells allows one to study major clinically relevant features of human EBV infection in vivo, opening the way to new therapeutic approaches.

Efficient CRISPR-mediated mutagenesis in primary immune cells using CrispRGold and a C57BL/6 Cas9 transgenic mouse line.

Applying clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR associated protein 9 (Cas9)-mediated mutagenesis to primary mouse immune cells, we used high-fidelity single guide RNAs (sgRNAs) designed with an sgRNA design tool (CrispRGold) to target genes in primary B cells, T cells, and macrophages isolated from a Cas9 transgenic mouse line. Using this system, we achieved an average knockout efficiency of 80% in B cells. On this basis, we established a robust small-scale CRISPR-mediated screen in these cells and identified genes essential for B-cell activation and plasma cell differentiation. This screening system does not require deep sequencing and may serve as a precedent for the application of CRISPR/Cas9 to primary mouse cells.

Efficient genome engineering by targeted homologous recombination in mouse embryos using transcription activator-like effector nucleases.

Generation of mouse models by introducing transgenes using homologous recombination is critical for understanding fundamental biology and pathology of human diseases. Here we investigate whether artificial transcription activator-like effector nucleases (TALENs)-powerful tools that induce DNA double-strand breaks at specific genomic locations-can be combined with a targeting vector to induce homologous recombination for the introduction of a transgene in embryonic stem cells and fertilized murine oocytes. We describe the generation of a conditional mouse model using TALENs, which introduce double-strand breaks at the genomic locus of the special AT-rich sequence-binding protein-1 in combination with a large 14.4 kb targeting template vector. We report successful germline transmission of this allele and demonstrate its recombination in primary cells in the presence of Cre-recombinase. These results suggest that TALEN-assisted induction of DNA double-strand breaks can facilitate homologous recombination of complex targeting constructs directly in oocytes.

Studying Epstein-Barr virus pathologies and immune surveillance by reconstructing EBV infection in mice.

Epstein-Barr virus (EBV) is a γ herpes virus endemic in humans and transforming human B lymphocytes. It causes a variety of human pathologies ranging from infectious mononucleosis upon acute infection to EBV-driven B-cell lymphomas. In humans, EBV-infected cells are under powerful immune surveillance by T and NK cells. If this immune surveillance is compromised as in immunosuppressed (AIDS- or posttransplantation) patients, the virus can spread from rare, EBV-containing cells and cause life-threatening pathologies. We have found that EBV immune surveillance and lymphomagenesis can be modeled in mice by targeted expression of key EBV proteins in the B-cell lineage. As EBV does not infect mouse B cells and mice have thus not coevolved with the virus, EBV exploits basic modes of the host immune response to optimize its coexistence with the host.