Increased activation state of the T-PLL cell includes losses of immune regulatory receptors. (A) Significantly increased percentages of T cells (flow cytometry) expressing activation/proliferation markers (CD38, CD40L, CD69, Ki-67) as well as cytokine (IL-2, -4, -7) and chemokine receptors (CCR3, CXCR4) in T-PLL samples (up to 75 cases) and CD3-gated healthy-donor PBMCs (n = 10; unpaired Student t test with Welch’s correction). Cutoffs for percentage of positive cells of the first 6 markers: CD122 (>10%), CD25 (>50%), CD38 (>50%), CD40L (>5%), CD69 (>5%), and Ki-67 (>20%). A sum score entails the counts of individual markers that are expressed above these thresholds (positive) for the 7-tier (0-6) activation score: low (green; 0 or 1 marker) vs high (red; ≥2 markers). (B) Higher number of CD69⁺ T cells at basal (no TCR crosslinking) conditions in leukemic Lck^pr-hTCL1A^tg and no more increase after TCR engagement compared with age-matched C57BL/6J mice (flow cytometry; P = .0036, unpaired Student t test, SEM). T cells of both strains did not show differences in CD69 positivity in young animals and similar responsiveness to anti-CD3/CD28 stimulation. (C-D) Significantly reduced expression of negative TCR-regulatory coreceptors in T-PLL cells over PB-derived normal T cells (unpaired Student t test with SEM). (C) Heatmap on the basis of coreceptor gene transcript abundances (array-based GEP) in the 3 isolated normal T-cell subsets (each from 10 healthy donors) compared with 70 T-PLL. Alignment with TCL1A mRNA expression as well as genomic lesions in ATM and JAK/STAT genes.¹¹  (D) Flow cytometry confirms immune coreceptor downregulation in CD5 gates of healthy-donor naïve and pan-memory T cells (each n = 6) vs 20 T-PLL (unpaired Student t test, SEM). See supplemental Figure 4D for impaired TCR-induced increases of these coreceptors in T-PLL cells.