Paper Details

ABSTRACT

Immune surveillance refers to the capacity of the immune system to recognize and control residual malignant cells, and is considered an important mechanism in long-term tumor control. In CML, its potential role in treatment-free remission (TFR) after tyrosine kinase inhibitor (TKI) discontinuation has been mainly investigated after the first discontinuation attempt, whereas its relevance after a second discontinuation remains unclear. In the DASTOP2 study (EudraCT No: 2016-004106-34) a second discontinuation was attempted after dasatinib retreatment for ≥2 years, Dasatinib is known to modulate the T-cell compartment through off-target immunomodulatory effects. We investigated whether dasatinib-associated remodeling of the CD4+ T-cell compartment at second stop is associated with subsequent TFR duration.

We analyzed peripheral-blood immunophenotyping at treatment discontinuation in chronic-phase CML patients undergoing a second TKI discontinuation. The DASTOP2 cohort comprised 67 patients, in whom CD4+ T cells and their naive, central memory, effector memory, and terminally differentiated effector memory re-expressing CD45RA (TEMRA) subsets were quantified as percentages of WBCs at discontinuation by centralized flow cytometry. Patients were classified as relapsed (i.e. loss of MMR, BCR::ABL >0.1% (I.S.)) or non-relapsed by their TFR status one year after dasatinib discontinuation. CD4+ subset distributions were compared between patients and healthy donors (n=19), and between non-relapsed and relapsed patients, using Mann-Whitney U tests with subset frequencies presented as medians. Nominal two-sided p<0.05 was considered significant. For survival analysis, TFR was defined as time from TKI discontinuation until relapse; CD4+ variables were tested as continuous predictors by Cox proportional hazards regression, with hazard ratios (HR) and Wald p-values reported, and data-derived cut-offs were identified using maximally selected log-rank statistics.

 Among 67 patients, 29 relapsed within 1 year (43%). Compared with healthy donor controls, dasatinib-treated patients at discontinuation showed a distinct CD4+ T-cell compartment, characterized by increased terminally differentiated CD4+ TEMRA cells (patient 0.57% vs HD 0.11%; p<0.001), preserved effector memory CD4+ cells (patient 3.01% vs HD 2.80%; p=0.72), and reduced central memory (patient 4.78% vs HD 10.32%; p<0.001) and naive CD4+ T-cell subsets (patient 4.58% vs HD 7.35%; p<0.001). These differences were irrespective of subsequent relapse, consistent with the known immunomodulatory effect of dasatinib and demonstrating that this shift toward terminal CD4+ T-cell differentiation is also present in the second-stop setting. Within this altered landscape, non-relapsing patients only showed higher proportions of total CD4+ T cells (15.1% vs 13.4%; p=0.04), and specifically naive CD4+ T cells (5.2% vs 3.5%; p=0.03) compared with those who relapsed. To assess whether these differences were relevant to the durability of TFR, CD4+ and naive CD4+ T-cell frequencies were then tested as continuous predictors of TFR duration. Higher CD4+ frequency (as continuous variable) at stop was associated with longer TFR by Cox regression (HR 0.93, 95% CI 0.86–0.999, Wald p=0.046), as was naive CD4+ T cell frequency (HR 0.87, 95% CI 0.76–0.997, Wald p=0.044). A data-derived CD4+ cutpoint of 11% identified two groups with markedly different TFR (>11% vs <11% CD4+: HR 0.39, 95% CI 0.18–0.81, Wald p=0.012); the same association was found for naive CD4+ T cell stratification at 5.5% (high vs low: HR 0.35, 95% CI 0.13–0.92, Wald p=0.033).

 These first lab findings from DASTOP2 suggest that patients on second TKI discontinuation after dasatinib show a distinct CD4+ T cell immune landscape, characterized by terminal effector skewing and reduced naive/central memory compartments, consistent with the known immunomodulatory effect of dasatinib. Within this altered landscape, preservation of the naive CD4+ T cells within the WBCs compartment distinguished patients who maintained TFR from those who relapsed, and was associated with longer TFR duration, suggesting clinically relevant association. Naive CD4+ T-cell preservation at discontinuation may therefore represent a candidate correlate of durable TFR after a second dasatinib stop, warranting prospective validation.