γδ T cells account for a large fraction of human intestinal intraepithelial lymphocytes (IELs) endowed with potent antitumor activities. However, little is known about their origin, phenotype, and clinical relevance in colorectal cancer (CRC). To determine γδ IEL gut specificity, homing, and functions, γδ T cells were purified from human healthy blood, lymph nodes, liver, skin, and intestine, either disease-free, affected by CRC, or generated from thymic precursors. The constitutive expression of NKp46 specifically identifies a subset of cytotoxic Vδ1 T cells representing the largest fraction of gut-resident IELs. The ontogeny and gut-tropism of NKp46 ⁺ /Vδ1 IELs depends both on distinctive features of Vδ1 thymic precursors and gut-environmental factors. Either the constitutive presence of NKp46 on tissue-resident Vδ1 intestinal IELs or its induced expression on IL-2/IL-15–activated Vδ1 thymocytes are associated with antitumor functions. Higher frequencies of NKp46 ⁺ /Vδ1 IELs in tumor-free specimens from CRC patients correlate with a lower risk of developing metastatic III/IV disease stages. Additionally, our in vitro settings reproducing CRC tumor microenvironment inhibited the expansion of NKp46 ⁺ /Vδ1 cells from activated thymic precursors. These results parallel the very low frequencies of NKp46 ⁺ /Vδ1 IELs able to infiltrate CRC, thus providing insights to either follow-up cancer progression or to develop adoptive cellular therapies.

Acute myeloid leukemia (AML) remains a clinical challenge due to frequent chemotherapy resistance and deadly relapses. We are exploring the immunotherapeutic potential of peripheral blood Vδ1⁺ T cells, which associate with improved long-term survival of stem-cell transplant recipients but have not yet been applied as adoptive cell therapy. Using our clinical-grade protocol for expansion and differentiation of “Delta One T” (DOT) cells, we found DOT cells to be highly cytotoxic against AML primary samples and cell lines, including cells selected for resistance to standard chemotherapy. Unlike chemotherapy, DOT-cell targeting did not select for outgrowth of specific AML lineages, suggesting a broad recognition domain, an outcome that was consistent with the polyclonality of the DOT-cell T-cell receptor (TCR) repertoire. However, AML reactivity was only slightly impaired upon Vδ1⁺ TCR antibody blockade, whereas it was strongly dependent on expression of the NKp30 ligand, B7-H6. In contrast, DOT cells did not show reactivity against normal leukocytes, including CD33⁺ or CD123⁺ myeloid cells. Adoptive transfer of DOT cells in vivo reduced AML load in the blood and target organs of multiple human AML xenograft models and significantly prolonged host survival without detectable toxicity, thus providing proof-of-concept for DOT-cell application in AML treatment.

The unique capabilities of gamma-delta (γδ) T cells to recognize cells under stressed conditions, particularly infected or transformed cells, and killing them or regulating the immune response against them, paved the way to the development of promising therapeutic strategies for cancer and infectious diseases. From a mechanistic standpoint, numerous studies have unveiled a remarkable flexibility of γδ T cells in employing their T cell receptor and/or NK cell receptors for target cell recognition, even if the relevant ligands often remain uncertain. Here, we review the accumulated knowledge on the diverse mechanisms of target cell recognition by γδ T cells, focusing on human γδ T cells, to provide an integrated perspective of their therapeutic potential in cancer and infectious diseases.

γδ T cells are a relatively rare subset of lymphocytes in the human peripheral blood, but they play important roles at the interface between the innate and the adaptive immune systems. The γδ T cell lineage is characterized by a signature γδ T cell receptor (γδTCR) that displays extensive sequence variability originated by DNA rearrangement of the corresponding V(D)J loci. Human γδ T cells comprise Vγ9Vδ2 T cells, the major subset in the peripheral blood; and Vδ1⁺ T cells, the predominant subpopulation in the post-natal thymus and in peripheral tissues. While less studied, Vδ1⁺ T cells recently gathered significant attention due to their anti-cancer and anti-viral activities. In this study we applied next-generation sequencing (NGS) to analyse the γδTCR repertoire of highly (FACS-)purified Vδ1⁺ T cells from human thymic biopsies. Our analysis reveals unsuspected aspects of thymically rearranged and expressed (at the mRNA level) TRG and TRD genes, thus constituting a data resource that qualifies previous conclusions on the TCR repertoire of γδ T cells developing in the human thymus.

This review gives an overview over the most recent progress in the field of lentiviral gene therapy for primary immunodeficiencies (PIDs). The history and state-of-the-art of lentiviral vector development are summarized and the recent advancements for a number of selected diseases are reviewed in detail. Past retroviral vector trials for these diseases, the most recent improvements of lentiviral vector platforms and their application in preclinical development as well as ongoing clinical trials are discussed. Main focus is on the preclinical studies and clinical trials for the treatment of Wiskott-Aldrich syndrome, chronic granulomatous disease, adenosine deaminase deficient severe combined immunodeficiency (ADA-SCID) and X-linked severe combined immunodeficiency with lentiviral gene therapy. Gene therapy for PIDs is an effective treatment, providing potential long-term clinical benefit for affected patients. Substantial progress has been made to make lentiviral gene therapy platforms available for a number of rare genetic diseases. Although many ongoing gene therapy trials are based on ex-vivo approaches with autologous hematopoietic stem cells, other approaches such as in-vivo gene therapy or gene-repair platforms might provide further advancement for certain PIDs.

Common variable immunodeficiency (CVID) is the most frequent primary antibody deficiency whereby follicular helper T (Tfh) cells fail to establish productive responses with B cells in germinal centers. Here, we analyzed the frequency, phenotype, transcriptome, and function of circulating Tfh (cTfh) cells in CVID patients displaying autoimmunity as an additional phenotype. A group of patients showed a high frequency of cTfh1 cells and a prominent expression of PD‐1 and ICOS as well as a cTfh mRNA signature consistent with highly activated, but exhausted, senescent, and apoptotic cells. Plasmatic CXCL13 levels were elevated in this group and positively correlated with cTfh1 cell frequency and PD‐1 levels. Monoallelic variants in RTEL1, a telomere length‐ and DNA repair‐related gene, were identified in four patients belonging to this group. Their blood lymphocytes showed shortened telomeres, while their cTfh were more prone to apoptosis. These data point toward a novel pathogenetic mechanism in CVID, whereby alterations in DNA repair and telomere elongation might predispose to antibody deficiency. A Th1, highly activated but exhausted and apoptotic cTfh phenotype was associated with this form of CVID.