Targeting The T Cell Component Of The Tumour Microenvironment In Chronic Lymphocytic Leukaemia; A Potential Therapeutic Strategy

It has recently become clear that B cell receptor (BCR) activation plays an important role in the pathogenesis of chronic lymphocytic leukaemia (CLL); a fact that is underlined by the marked efficacy of drugs that inhibit components of this pathway. Although the underlying mechanisms remain unclear, CLL BCRs have been shown to recognize a variety of autoantigens and there is evidence of ongoing activation of a number of downstream signaling molecules including Syk, Erk, Akt and the NFkB and NFAT family of transcription factors. In addition to BCR activation, it is thought that signals from other cells in the tumour microenvironment such as T cells, the vascular endothelium and other stromal cells may also play a role in promoting the growth of the disease.

In the present study we chose to revisit the effects of ciclosporin (CsA), a calcineurin antagonist with effects on antigen receptor signaling, in CLL. When this agent is used to treat the autoimmune complications of CLL, concurrent responses in the underlying disease have been noted in about 20% of patients, although the underlying mechanism has not been thoroughly investigated. Since CsA primarily inhibits T cell activation we hypothesized that its effects in CLL might be due to a reduction in T cell mediated co-stimulation in the lymph nodes. We therefore investigated the effect of CsA on the activation of CLL B and T cells using conventional and multispectral imaging flow cytometry to measure the expression of activation markers and the nuclear translocation of NFAT and NFKB family transcription factors. Cells were collected from eight unselected patients with a confirmed diagnosis of CLL for each study. T and B cells were purified by negative immunomagnetic selection and activated by incubation with phorbol ester and ionomycin (PMA/I) or CD40L transfected fibroblasts in the presence of absence of CsA. The activation of CD4+ T cells and CD19+ CLL cells was assessed by staining for CD69/interferon gamma (IFNΥ) and CD69/CD25 respectively. Nuclear translocation of NFATc2 and NFKB p65 was measured by image flow cytometry (Amnis Imagestream). Leukaemia and Lymphoma Research provided the funding for this study.

NFkB(p65) translocation at 30 minutes was inhibited by a mean of 22.5% (p=0.0003) in activated CLL CD4+ T cells treated with CsA compared to those treated with vehicle control (VC). Similarly, in the presence of CsA, NFAT-c2 translocation was inhibited by a mean of 24.3% (p=0.008) at 10 minutes in CLL CD4+ T cells compared to those treated with VC. NFkB(p65) translocation was not inhibited (mean of differences=0.63%, p=0.645) and NFAT-c2 translocation was minimally inhibited (mean of differences = -4%, p = 0.007) in activated CLL B Cells treated with CsA.

The proportion of activated CLL CD4+ T cells expressing both CD69 and IFNΥ was reduced by 13.2% (p=0.003) in the presence of CsA whereas there was no inhibition of CD25(-1.5, p=0.16) and CD69(-1.4, p=0.5) expression in activated CLL B cells treated with CsA.

In summary, CsA had a profound effect on CD4+ T cell activation in patients with CLL, as demonstrated by the reduction in NFkB (p65), NFAT-c2 nuclear translocation and CD69/IFNΥ expressing cells. In contrast, there was a minimal effect on NFAT-c2 translocation in activated CLL B cells and no impact on NFkB (p65) translocation or the expression of CD25 and CD69. These findings suggest that the previously documented activity of CsA in CLL is not due to a direct effect on the tumour but is instead indirect and mediated through inhibition of other microenvironment derived signals such as those provided by activated CD4+ T cells. Since it is likely that these co-stimulatory effects act in concert other signals, such as those induced by BCR activation, reexamination of CsA and similar agents in CLL would thus seem warranted.