The Rho–ROCK pathway as a new pathological mechanism of innate immune subversion in chronic myeloid leukaemia

Abstract

CD1d-restricted invariant natural killer T (iNKT) cells are believed to play a key role in cancer immune surveillance, and are functionally deficient in patients with chronic myeloid leukaemia (CML). Herein, we have hypothesized that this defect might originate from BCR-ABL-dependent dysfunctions in myeloid dendritic cells (mDCs). Indeed, flow cytometry and confocal microscopy revealed that cell surface expression of CD1d was downregulated in CML mDCs, relative to healthy donor (HD) controls. The decreased cell surface display of CD1d could not be ascribed to defective mDC differentiation, as attested by normal expression of HLA-DR and the CD86 maturation marker. On the other hand, reduced membrane expression was not associated with decreased intracytoplasmic levels of CD1d or its mRNA transcripts, consistent with intracellular retention. In vitro treatment of CML mDCs with the Rho-associated protein kinase (ROCK) inhibitor Y-27632 partially restored both cell surface CD1d expression and CD1d-mediated antigen presentation, whereas it had no effect on HD mDCs. An inhibitor of BCR-ABL tyrosine kinase (TK), imatinib mesylate (IM), had no such activity. Similar recovery of CD1d expression occurred with fasudil, another ROCK inhibitor that is commonly used in clinical trials. Our data support the conclusion that BCR-ABL-dependent ROCK, but not TK, is involved in CD1d downregulation. We propose that ROCK, which is most likely activated by the DH/PH domain of BCR-ABL, mediates iNKT-cell immune subversion in CML patients by downregulating CD1d expression on CML mDCs. Our study reveals the ROCK-mDC axis as a new potential target to restore immune surveillance in patients with CML, offering new therapeutic perspectives for CML treatment. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

The Hypothesis of the Human iNKT/Innate CD8(+) T-Cell Axis Applied to Cancer: Evidence for a Deficiency in Chronic Myeloid Leukemia

“…This assumption was earlier based on our demonstration of terminally differentiated effector features of innate CD8(+) T cells in humans, such as rapid production of IFN-γ and induction of cytolytic function upon stimulation in vitro . In the present study, our revelation of the profound impact of CML on these potential antitumoral functions of innate CD8(+) T cells, together with those of NK (see Figure S2 in Supplementary Material) and iNKT cells (22, 27), support a role in cancer immune surveillance of innate CD8(+) T cells analogous to the two other innate cell pools. Even though these findings corroborate the concept that innate CD8(+) T cells, like iNKT cells, may act against tumors in a TCR-independent and NK-like manner, the possibility that these cells recognize leukemia cells cannot be excluded and deserves further investigation.…”

“…These regulatory elements comprise dendritic cells (19), NK cells (20, 21), and invariant natural killer T (iNKT) cells (22), an innate T cell subset co-expressing activated/memory and NK markers, which is well-recognized for its antitumor activity (23–26). In accordance with this notion, we recently reported CML immune subversion of iNKT-cell activities in CML patients at diagnosis (22, 27), including reduced or suppressed expression of perforin, CD95L, and (PLZF), a transcription factor required for maintenance of iNKT cell functions (28, 29). Remarkably, these functional deficiencies were shown to have been partially repaired in patients having achieved complete cytogenetic remission (CCyR) following TKI therapy (22).…”

“…Based on our evidence for CML immune subversion of iNKT-cell activities (22, 27), we first investigated possible dysfunctions of this new innate CD8 T subset (for gating strategy, see Figure 1A) in CML patients at diagnosis (CML-CP). As depicted in Figure 1B, the frequency of KIR/NKG2A(+) Eomes(+) CD8(+) T cells was more than 2.5-fold lower in CML-CP patients (3.1% ± 0.7; n  = 6) than in HDs (8.2% ± 0.9; n  = 15).…”

“…Nonetheless, from our data, it is tempting to speculate that the dysfunctions of innate CD8(+) T cells in CML patients at diagnosis that are remedied by TKI therapy originate from antigen APC-dependent dysfunctions, which in turn might contribute to iNKT cell deficiencies. This hypothesis arises from our recent findings showing that BCR-ABL from CML myeloid DCs mediates iNKT-cell immune subversion by downregulating cell-surface CD1d expression (27). Another non-exclusive mechanism may involve IL-15, which is required for maintenance not only of conventional memory CD8(+) T cells (34, 35) but also innate/memory CD8(+) T cells (32, 36).…”

Phenotype of NK-Like CD8(+) T Cells with Innate Features in Humans and Their Relevance in Cancer Diseases

“…Immune subversion could result from dysfunction of the antigen-presenting cells (APCs), particularly leukemia myeloid dendritic cells (DCs) and their environment; they might be considered as responsible for the loss of function of the innate immune cells, including NK and innate CD8(+) T cells. As regards iNKT cells, their loss of function could be due to a loss of CD1d expression by the leukemic APCs expressing the BCR–ABL oncogene [Figure 5; (65)]. The loss of CD1d expression could reprogram iNKT cells by favoring the loss of PLZF expression and, consequently, of IL-4, thereby decreasing their capacity to orient a differentiation of CD8(+) T cells into innate CD8(+) T cells (Figure 5).…”