Claudio Garavaglia

T cell priming by dendritic cells: thresholds for proliferation, differentiation and death and intraclonal functional diversification.

The variables that influence priming of human naive CD4+ T cells by dendritic cells (DC) were dissected in vitro by analyzing the response to the bacterial superantigen toxicshock syndrome toxin or to alloantigens. We show that under conditions that force DC‐T cell interactions a single DC can prime up to 20 naive T cells. Moreover, the strength of antigenic stimulation, as determined by DC numbers, antigen dose, TCR avidity and duration of DC‐T cell interactions, drives the progressive differentiation of proliferating T cells from a non‐effector CCR7+ stage, to an effector CCR7– stage and, eventually, to cell death. We also show that the proliferating CCR7+ and CCR7– populations share clonotypic sequences, demonstrating that the two cell fates can be generated within a single clone. Taken together these results indicate that the strength of antigenic stimulation regulates T cell progression through thresholds of proliferation, differentiation and death. However, the random nature of DC‐T cell encounters introduces a critical stochastic element in T cell stimulation, which leads to the generation of cells endowed with distinct homing potentials and effector functions within a given T cell clone.

High-frequency and adaptive-like dynamics of human CD1 self-reactive T cells

CD1 molecules present lipid antigens to T cells. An intriguing subset of human T cells recognize CD1‐expressing cells without deliberately added lipids. Frequency, subset distribution, clonal composition, naïve‐to‐memory dynamic transition of these CD1 self‐reactive T cells remain largely unknown. By screening libraries of T‐cell clones, generated from CD4+ or CD4−CD8− double negative (DN) T cells sorted from the same donors, and by limiting dilution analysis, we find that the frequency of CD1 self‐reactive T cells is unexpectedly high in both T‐cell subsets, in the range of 1/10–1/300 circulating T cells. These T cells predominantly recognize CD1a and CD1c and express diverse TCRs. Frequency comparisons of T‐cell clones from sorted naïve and memory compartments of umbilical cord and adult blood show that CD1 self‐reactive T cells are naïve at birth and undergo an age‐dependent increase in the memory compartment, suggesting a naïve/memory adaptive‐like population dynamics. CD1 self‐reactive clones exhibit mostly Th1 and Th0 functional activities, depending on the subset and on the CD1 isotype restriction. These findings unveil the unanticipated relevance of self‐lipid T‐cell response in humans and clarify the basic parameters of the lipid‐specific T‐cell physiology.

A novel self-lipid antigen targets human T cells against CD1c(+) leukemias.

CD1c self-reactive T cells recognize a novel class of self-lipids that are accumulated on leukemia cells.

Human Invariant Vα24-JαQ TCR Supports the Development of CD1d-Dependent NK1.1+ and NK1.1− T Cells in Transgenic Mice

A sizable fraction of T cells expressing the NK cell marker NK1.1 (NKT cells) bear a very conserved TCR, characterized by homologous invariant (inv.) TCR Vα24-JαQ and Vα14-Jα18 rearrangements in humans and mice, respectively, and are thus defined as inv. NKT cells. Because human inv. NKT cells recognize mouse CD1d in vitro, we wondered whether a human inv. Vα24 TCR could be selected in vivo by mouse ligands presented by CD1d, thereby supporting the development of inv. NKT cells in mice. Therefore, we generated transgenic (Tg) mice expressing the human inv. Vα24-JαQ TCR chain in all T cells. The expression of the human inv. Vα24 TCR in TCR Cα−/− mice indeed rescues the development of inv. NKT cells, which home preferentially to the liver and respond to the CD1d-restricted ligand α-galactosylceramide (α-GalCer). However, unlike inv. NKT cells from non-Tg mice, the majority of NKT cells in Vα24 Tg mice display a double-negative phenotype, as well as a significant increase in TCR Vβ7 and a corresponding decrease in TCR Vβ8.2 use. Despite the forced expression of the human CD1d-restricted TCR in Cα−/− mice, staining with mCD1d-α-GalCer tetramers reveals that the absolute numbers of peripheral CD1d-dependent T lymphocytes increase at most by 2-fold. This increase is accounted for mainly by an increased fraction of NK1.1− T cells that bind CD1d-α-GalCer tetramers. These findings indicate that human inv. Vα24 TCR supports the development of CD1d-dependent lymphocytes in mice, and argue for a tight homeostatic control on the total number of inv. NKT cells. Thus, human inv. Vα24 TCR-expressing mice are a valuable model to study different aspects of the inv. NKT cell subset.

T cell neoepitope discovery in colorectal cancer by high throughput profiling of somatic mutations in expressed genes

Objective Patient-specific (unique) tumour antigens, encoded by somatically mutated cancer genes, generate neoepitopes that are implicated in the induction of tumour-controlling T cell responses. Recent advancements in massive DNA sequencing combined with robust T cell epitope predictions have allowed their systematic identification in several malignancies. Design We undertook the identification of unique neoepitopes in colorectal cancers (CRCs) by using high-throughput sequencing of cDNAs expressed by standard cancer cell cultures, and by related cancer stem/initiating cells (CSCs) cultures, coupled with a reverse immunology approach not requiring human leukocyte antigen (HLA) allele-specific epitope predictions. Results Several unique mutated antigens of CRC, shared by standard cancer and related CSC cultures, were identified by this strategy. CD8+ and CD4+ T cells, either autologous to the patient or derived from HLA-matched healthy donors, were readily expanded in vitro by peptides spanning different cancer mutations and specifically recognised differentiated cancer cells and CSC cultures, expressing the mutations. Neoepitope-specific CD8+ T cell frequency was also increased in a patient, compared with healthy donors, supporting the occurrence of clonal expansion in vivo. Conclusions These results provide a proof-of-concept approach for the identification of unique neoepitopes that are immunogenic in patients with CRC and can also target T cells against the most aggressive CSC component.

CD4+ T cell immunity against the human papillomavirus‐18 E6 transforming protein in healthy donors: identification of promiscuous naturally processed epitopes

Infection by ‘high‐risk’ human papillomaviruses (HPV) is associated with the development of neoplastic lesions. HPV‐18 is responsible for a very aggressive form of cancer and poor survival. As for other HPV types, immune surveillance has probably a role in the control of the infection. However, very little is known on HPV‐18 immunogenicity. CD4+ T cells from 16 healthy donors were tested ex vivo for reactivity to synthetic peptides corresponding to 3 sequences on the HPV‐18 E6 transforming protein predicted by bioinformatics as promiscuous HLA‐DR ligands, and to the recombinant E6 protein. We found 3 donors with CD4+ T cells that specifically proliferated in the presence of HPV‐18 E6 antigens and produced IFN‐γ in the presence of the E6 protein. We then propagated CD4+ T cell lines and clones from the responsive subjects to better characterize the recognized sequences. We show that E652–66 and E697–111 are indeed promiscuous and, most importantly, they contain naturally processed epitopes. Collectively, our data indicate that healthy donors may develop spontaneous CD4 immunity against HPV‐18 E6 epitopes, thus strongly suggesting the potential for this protein to elicit in the host a natural productive immune response.

Peptidome from Renal Cell Carcinoma Contains Antigens Recognized by CD4+ T Cells and Shared among Tumors of Different Histology

Purpose: Renal cell carcinoma (RCC) is considered immunogenic; nonetheless, rare tumor-associated antigens have been identified or are expressed in RCC. Peptidome (i.e., the total content of natural peptides of whole cells) from other tumors, such as melanoma, has proved to be immunogenic. The aims of this study were to determine whether peptidome from RCC is immunogenic and whether it contains tumor peptides shared among allogenic RCCs. Experimental Design: Autologous dendritic cells pulsed with RCC peptidome were used to activate in vitro CD4+ T cells from healthy donors and a metastatic RCC patient. CD4+ T-cell polyclonal lines and clones were characterized for tumor cell recognition by proliferation assay, killing activity, and cytokine secretion. Results: CD4+ T-cell lines and clones recognized HLA-DR-matched allogenic RCC and, for the patient, the autologous tumor. RCC-reactive CD4+ T cells showed a heterogeneous Th1 or Th0/Th2 pattern of cytokine secretion. Moreover, RCC-reactive CD4+ T cells recognized also melanoma, colon carcinoma, cervical carcinoma, pancreas carcinoma, lung carcinoma, gastric carcinoma, and lymphoma cells but not autologous T-cell blasts. Conclusions: Our results show that (a) the RCC peptidome contain antigens recognized by CD4+ T cells and (b) shared among tumors of different histology and (c) it induces both Th1-type and Th2/Th0-type immune responses. These data support the use of the peptidome from allogenic RCC for specific immunotherapy in RCC and possibly in other neoplastic diseases. Moreover, the CD4+ T-cell clones generated here are useful tools for tumor antigen identification.