Advanced human T-cell leukemia virus type 1 carriers and early-stage indolent adult T-cell leukemia-lymphoma are indistinguishable based on CADM1 positivity in flow cytometry

Abstract

We previously reported that the cell adhesion molecule 1 (CADM1) versus CD7 plot in flow cytometry reflects disease progression in human T-cell leukemia virus type 1 (HTLV-1) infection. In CD4(+) cells from peripheral blood, CADM1(-) CD7(+) (P), CADM1(+) CD7(dim) (D) and CADM1(+) CD7(-) (N) subpopulations are observed. The D and N subpopulations increase as asymptomatic HTLV-1 carriers (AC) progress to indolent adult T-cell leukemia-lymphoma (ATL) and the N subpopulation then expands in aggressive ATL. In the present study we examined whether the analysis can estimate the risk of developing ATL in advanced AC. Peripheral blood samples from AC (N = 41) and indolent ATL patients (N = 19) were analyzed by flow cytometry using the CADM1 versus CD7 plot for CD4(+) cells and inverse long PCR (clonality analysis) of FACS-sorted subpopulations. Almost all AC with a high HTLV-1 proviral load (>4 copies/100 cells) had a CADM1(+) (D + N) frequency of >10%. AC with 25% < CADM1(+) ≤ 50% contained expanded clones similar to smoldering-type ATL. In many patients in the 25% < CADM1(+) ≤ 50% group, the proportion of abnormal lymphocytes was distributed around the 5% line, which divides AC and smoldering-type ATL in Shimoyama's classification. In conclusion, the CADM1 versus CD7 plot is useful for selection of putative high-risk AC. The characteristics of some AC and smoldering ATL are said to be similar; however, long-term follow up is required and the clinical outcome (e.g. rate of transformation) of these cases should be used to determine whether to include them in the same clinical category.

Keywords: Adult T-cell leukemia-lymphoma; CADM1 protein; CD7 antigen; HTLV-1; flow cytometry.

Fig 1

The cell adhesion molecule 1 (CADM1) versus CD7 profile in asymptomatic HTLV-1 carriers (AC) correlates with proviral load (PVL). (a) A representative CADM1 versus CD7 profile for CD4⁺ cells. P (CADM1⁻CD7⁺), D (CADM1⁺CD7^dim) and N (CADM1⁺CD7⁻) subpopulations were gated according to our previous report. (b) Almost all AC with PVL >4 copies/100 peripheral blood mononuclear cells (PBMC) had CADM1⁺ (D + N) values of more than 10% in the CADM1 versus CD7 plot, and almost all AC with PVL <4 copies/100 PBMC had CADM1⁺ values of <10%.

Fig 2

Clonality analysis of the FACS-sorted subpopulations in the cell adhesion molecule 1 (CADM1) versus CD7 plot. (a) Three representative cases are shown. The three subpopulations (P, D and N) in the CADM1 versus CD7 plot were FACS-sorted and subjected to inverse long PCR. The observed band patterns were classified into “polyclonal” (left), “oligoclonal” (left middle) and “major clone” (right middle and right) states according to the number and density of the clonal bands. (b) Summary of all analyzed asymptomatic HTLV-1 carriers (AC) (left), cases of smoldering-type ATL (left) and chronic-type ATL (right). The two-dimensional plot shows the D and N subpopulation proportions for each case. The diagonal lines indicate CADM1⁺ (D + N) = 10%, 25% and 50%.

Fig 3

Percentages of abnormal lymphocytes in groups classified by CADM1⁺ (%) in the CADM1 versus CD7 plot. All cases were classified into four groups according to CADM1⁺ (%): CADM1⁺ ≤ 10%, 10% < CADM1⁺ ≤ 25%, 25% < CADM1⁺ ≤ 50% and 50% < CADM1⁺ (see also Fig.2b). The dotted line (5% abnormal lymphocytes) indicates the borderline between asymptomatic HTLV-1 carriers (AC) and smoldering-type ATL according to Shimoyama's classification. The 25% < CADM1⁺ ≤ 50% group includes smoldering-type ATL and AC with high PVL and major clones (see also Figs1 and 2). *P < 0.05. CADM1, cell adhesion molecule 1.

Fig 4

Serial changes in abnormal lymphocytes (%) in groups classified by CADM1⁺ (%) in the CADM1 versus CD7 plot. (a) Data for the CADM1⁺ ≤ 10% group. The red line (5% abnormal lymphocytes) indicates the borderline between asymptomatic HTLV-1 carriers (AC) and smoldering-type ATL according to Shimoyama's classification. (b) Data for the 10% < CADM1⁺ ≤ 25% group. (c) Data for the 25% < CADM1⁺ ≤ 50% group. In many cases, the proportion of abnormal lymphocytes fluctuated around the 5% line (the AC/smoldering ATL borderline) during the observation period. (d) Data for the 50% < CADM1⁺ group. CADM1, cell adhesion molecule 1.