CADM1/TSLC1 Identifies HTLV-1-Infected Cells and Determines Their Susceptibility to CTL-Mediated Lysis

Abstract

Human T cell lymphotropic virus-1 (HTLV-1) primarily infects CD4+ T cells, causing inflammatory disorders or a T cell malignancy in 5% to 10% of carriers. The cytotoxic T lymphocyte (CTL) response is a key factor that controls the viral load and thus the risk of disease. The ability to detect the viral protein Tax in primary cells has made it possible to estimate the rate at which Tax-expressing infected cells are eliminated by CTLs in persistently infected people. However, most HTLV-1-infected cells are Tax–at a given time, and their immunophenotype is poorly defined. Here, we aimed to identify a cell-surface molecule expressed by both Tax+ and Tax–HTLV-1-infected cells and use it to analyse the CTL response in fresh peripheral blood mononuclear cells. Cell adhesion molecule 1 (CADM1/TSLC1) was the best single marker of HTLV-1 infection, identifying HTLV-1-infected cells with greater sensitivity and specificity than CD25, CCR4 or ICAM-1. CADM1+CD4+ T cells carried a median of 65% of proviral copies in peripheral blood. In a cohort of 23 individuals, we quantified the rate of CTL-mediated killing of Tax+ and Tax−CADM1+ cells. We show that CADM1 expression is associated with enhanced susceptibility of infected cells to CTL lysis: despite the immunodominance of Tax in the CTL response, Tax+CADM1– cells were inefficiently lysed by CTLs. Upregulation of the CADM1 ligand CRTAM on CD8+ T cells correlated with efficient lysis of infected cells. Tax–CADM1+ cells were lysed at a very low rate by autologous CTLs, however, were efficiently killed when loaded with exogenous peptide antigen. High expression of CADM1 on most HTLV-1-infected cells in the face of enhanced CTL counterselection implies that CADM1 confers a strong benefit on the virus.

T Cell Receptor Vβ Staining Identifies the Malignant Clone in Adult T cell Leukemia and Reveals Killing of Leukemia Cells by Autologous CD8+ T cells

“…The frequency distributions of TCRVβ subunits in CADM1 + (which typically carry one proviral copy per cell[36]) and CADM1 − (low proviral load) T cells (both CD4 + and CD8 + ) were ascertained by dividing live CD3 + cells into 50 possible groups on the basis of TCRVβ staining (see Materials and Methods). Linker-mediated PCR (LM-PCR) followed by high-throughput sequencing (HTS) were performed to corroborate the observed frequency distributions (Fig 1A).…”

“…CADM1 expression was significantly higher on ATL clones than on non-malignant infected cells within the same individual, or CADM1 + cells from ACs (Fig 4B and S4 Fig). In polyclonal infected populations (CD4 + CADM1 + cells in ACs, CADM1 + VβX − cells in ATL patients), a median of 11–15% of CADM1 + cells expressed Tax after overnight culture ([36]; Fig 4C and S4 Fig). By contrast, ATL clones fell into two distinct groups: those in which <5% of cells expressed Tax (Tax low ATL) and those in which >5% expressed Tax (Tax high ATL).…”

“…In order to mimic in vivo CD8 + cell:target cell frequencies, we incubated CD4 + PBMCs from ATL patients for 18h with a range of ratios of autologous CD8 + T cells and quantified the absolute number of surviving cells in the following populations: CADM1 − CD4 + cells (which have a low proviral load [36]), malignant HTLV-1 infected CADM1 + VβX + CD4 + cells, and non-malignant CADM1 + VβX − CD4 + cells (Fig 5), which typically carry a single proviral copy per cell. This strategy permitted us to estimate the efficacy by which each subset was targeted by CD8 + cells in vivo, in the presence of other potential CTL targets.…”

“…We recently published that CADM1 expression identifies 60–70% of infected cells in HTLV-1 carriers [36]. ATL patients have high frequencies of CADM1 + [37],CCR4 + [38], CD25 + [1] and CD7 − [39] cells in their peripheral blood.…”

Human T-Lymphotropic Virus Type 1-Induced Overexpression of Activated Leukocyte Cell Adhesion Molecule (ALCAM) Facilitates Trafficking of Infected Lymphocytes through the Blood-Brain Barrier

“…The CD25 ϩϩ population is composed of both T regulatory lymphocytes (Tregs) and HTLV-1-infected cells (27)(28)(29). Thus, the size of the CD25 ϩϩ population was larger for infected individuals (both HACs or HAM/TSP patients) than for HDs (Fig.…”