Homing to secondary lymphoid organs and bone marrow (BM) is a central aspect of leukemic pathophysiology. We investigated the roles of the two major lymphocyte integrins LFA-1 and VLA-4 on B-cell chronic lymphocytic leukemia (CLL) cells in these processes. We found that the majority of CLL cells expressed significantly reduced LFA-1 due to low B2 integrin transcripts. VLA-4 expression was heterogenous but underwent rapid activation by the BM chemokine CXCL12. CLL cells failed to transmigrate across VCAM-1-expressing, ICAM-1-expressing, and CXCL12-expressing endothelium, whereas when LFA-1 expression was regained in subsets of CLL cells, these lymphocytes rapidly transmigrated the endothelium. Furthermore, when injected into tail veins of immunodeficient mice, normal B cells rapidly homed to lymph nodes (LN) in a LFA-1-dependent manner, whereas CLL cells did not. Nevertheless, only residual CLL subsets could reenter BM, whereas both normal and CLL cells homed to the mice spleen in an LFA-1-independent and VLA-4-independent manner. Our results suggest that CLL cells have a reduced capacity to adhere and transmigrate through multiple vascular endothelial beds and poorly home to lymphoid organs other than spleen. Integrin blocking could thus be an efficient strategy to prevent circulating CLL cells from reaching prosurvival niches in LNs and BM but not in spleen.

B-cell chronic lymphocytic leukemia (B-CLL) is a clinically heterogeneous disease in which the clinical course is influenced by the presence or absence of immunoglobulin (Ig) variable heavy chain (VH) gene mutations. The poor clinical outcome of the subgroup with unmutated Ig VH genes has been linked to the persistent ability of the B-cell receptor in tumor cells from these cases to respond to antigen. As B-cell receptor signaling generally relies on T-cell help, we hypothesized that the course of B-CLL might not only be influenced by the Ig VH mutational status but also by the activation/differentiation status of T cells. We assessed the relative distribution of naive and memory T-cell subsets in peripheral blood from patients with mutated (M-CLL, n=71) and unmutated Ig VH genes (UM-CLL, n=42) and correlated it with the course of disease. We also compared the prosurvival potential of naive and memory T cells cocultured with B-CLL cells in vitro. A significant increase in relative numbers of central and effector memory T cells was observed in the CD4 T-cell pool from UM-CLL as compared with M-CLL cases and was associated with high Rai stage, progressive disease and shorter treatment-free survival (TFS). In a multivariate analysis, the relative number of CD4 central and effector memory T cells remained a significant prognostic parameter for TFS after correction for CD38 expression, Ig VH status, genomic aberrations, and Rai stage. The inverse correlation of memory CD4 T cells with TFS might be explained by their potential to support survival of B-CLL cells.

IntroductionB-cell chronic lymphocytic leukemia (B-CLL) is a neoplastic disease of slowly proliferating CD5 ϩ B cells that develops in the older population. Its clinical behavior is variable, with some patients having an indolent course without any therapy and others a rapidly progressing one probably requiring aggressive treatment. As an underlying mechanism of differential disease activity, genomic aberrations 1 and distinct expression levels of signaling molecules influencing survival as well as proliferation of B-CLL cells have been postulated. Besides the B-cell receptor itself 2,3 and Zap-70, a tyrosine kinase involved in B-cell receptor (BCR) signaling, 4 CD38, initially described as a mediator of leukocyte adhesion to endothelium, 5 was identified as a further candidate, since it induces both survival and proliferation signals in B-CLL cells 6 and its expression and signaling capacity correlate with both progression and response to therapy. 7 Its clinical importance as negative prognostic marker was established by analysis of CD38 expression in large patient cohorts. [7][8][9][10] While the study of malignant cells provides many insights into tumor biology, it has also become clear that transformation and progression of tumors is not an independent process but is controlled by their interactions with the tumor microenvironment (for a recent review see Joyce 11 ). Supporting factors in the microenvironment include stromal and vascular cells as well as infiltrating immune cells. Dependency on such supportive signals should also be relevant in B-CLL, in which close cooperation with other immune cells can be expected from normal behavior of B cells. In the present study, we focused on T cells and their expression of CD38 for the following reasons. (1) CD38 has been identified as an important signaling molecule of T cells. 12 (2) The signaling capacity of T cells has been shown to be dysregulated in B-CLL patients (for a review see Scrivener et al 13 ). Such an aberrant immune control might favor a more aggressive outgrowth of the neoplastic B-cell clone and negatively impact on the clinical outcome of patients. (3) T cells might even deliver antiapoptotic and/or proliferative signals to the neoplastic clone when coming into intimate contact with each other in lymphoid compartments like bone marrow or lymph nodes. 14 We therefore raised the question of whether aberrant expression of CD38 in T cells might also be of prognostic relevance in B-CLL. Patients, materials, and methods Patients and samplesThe study was approved by the local ethics committees (those of the Medical University Innsbruck and Provincial Government of Salzburg, Austria) and conducted according to the Declaration of Helsinki. After providing informed patient consent, 204 consecutive, unselected B-CLL For personal use only. on May 11, 2018. by guest www.bloodjournal.org From patients seen at the Department of Hematology and Oncology, University Hospitals Innsbruck and Salzburg, Austria, between March 2000 and November 2005 were included in t...