Page 1405 - Hematology_ Basic Principles and Practice ( PDFDrive )

Chapter 77 Chronic Lymphocytic Leukemia 1251

subsets of CLL: leukemias whose cell of origin has successfully tra- untreated CLL patients. Functional studies in ZAP-70–positive cases
versed the germinal center, resulting in the mutated IGHV phenotype, have shown that BCR ligation leads to increased phosphorylation of
and leukemias that are derived from naive B cells with the unmutated cytosolic proteins (Syk, BLNK, PLCγ), calcium mobilization, degra-
(germline) IGHV sequence. Whereas approximately 60% of CLL dation of IκB, and ultimately NFκB target gene activation. Despite
patients have cells with mutated IGHV genes (<98% identity to clear data showing that ZAP-70 is a prognostic marker, the reproduc-
germline), the remaining patients have cells exhibiting unmutated ibility of this assay across laboratories has been problematic. Incon-
IGHV (≥98% sequence identity with germline), typical of pregermi- sistent measurement of ZAP-70 may be the cause of this lack of
nal B cells. The prognostic significance of the absence of IGHV gene reproducibility because ZAP-70 is a labile protein, and laboratories
mutations is substantial, with studies uniformly noting an inferior have used different methods and reagents. Given the challenges of
survival and high tendency to require early treatment in this patient measuring ZAP-70 protein accurately, others have attempted to
subset. A CLL Research Consortium study examined the impact of identify alternative markers or more stable readouts of ZAP-70
IGHV mutation in 307 untreated CLL patients enrolled in a prospec- expression. For example, methylation of select regions in the proximal
tive tissue collection study. A total of 53% of these patients exhibited 5′ region of the ZAP-70 gene has been shown to correlate closely with
unmutated IGHV genes, and this population had a significantly expression of ZAP-70 and to be correlated with treatment outcome.
shorter median time to initial therapy (3.5 years) than those with Overall, despite the apparent usefulness of ZAP-70 in research labo-
mutated IGHV (9.2 years; p < .001). ratories for discriminating CLL patients at high risk for progression,
Because of the difficulties in determining IGHV gene mutational this test is of limited utility for routine clinical practice.
status, researchers have sought surrogate markers for this parameter.
Correlation between the absence of IGHV gene mutations and ele-
vated expression of the cell surface molecule CD38 on CLL cells has CD49d Expression
been noted. In another report, ZAP-70 expression was shown to
correlate with IGHV gene mutational status. ZAP-70 is a T-cell CD49d is a surface subunit of the integrin heterodimer that is
receptor–associated tyrosine kinase that is aberrantly expressed in involved in promoting survival of the CLL cells through microenvi-
CLL cells, and ZAP-70 expression is generally found in patients with ronment derived growth signals. CD49d can be used as a reliable
unmutated IGHV but not in patients with mutated IGHV. These predictive marker of aggressive disease course and inferior survival is
two associated biomarkers appear to be linked directly to the differ- associated with ≥30% cells expressing CD49d by flow cytometry.
ence in the behavior between these two genetic subtypes of CLL and
are discussed independently. Other surrogate markers for the muta-
tional status of the IGHV gene have been reported, including Other Prognostic Markers
methylation and subsequent silencing of TWIST2, a transcription
factor that negatively regulates p53. TWIST2 methylation and silenc- Various other markers have been used for predicting the disease
ing are preferentially observed in IGHV-mutated CLL cases. Elevated course of CLL patients. Elevated serum LDH levels are associated
levels of lipoprotein lipase and related genes have been noted in with aggressive disease and with the development of Richter syndrome
patients with IGHV-unmutated disease. In addition, it has been and prolymphocytic lymphoma. Similarly, patients with a lympho-
reported that IGHV-mutated CLL cells have long telomeres with low cyte doubling time of 12 months or less have been shown to have a
telomerase activity, but IGHV-unmutated patients have short telo- worse overall and treatment-free survival. Other markers include
meres with high telomerase activity. The extreme shortening of soluble factors including CD23, CD44, VCAM-1, CD27, and
telomeres and elevated telomerase activity are associated with both MMP-9, IL-6 and IL-8, etc. However, none of these biomarkers are
genetic instability and disrupted apoptosis in other diseases, suggest- routinely used in clinical practice.
ing that a similar process occurs in IGHV-unmutated CLL cells. MicroRNAs (miR) are noncoding RNAs that are 19–25 nucleo-
Finally, distinct gene and microRNA (miRNA) expression profiles tides in length and modulate mRNA translation and synthesis of
have also been correlated with IGHV gene mutational status. various proteins. Various microRNAs have been validated as useful
CLL prognostic markers, especially miR-15a and miR-16-1 which
were the first to be identified as being underexpressed in CLL B-cells.
CD38 Expression Deletion of chromosome 13q14 decreases their transcription and
increases the expression of the antiapoptotic BCL2 protein. Similarly,
Retrospective studies have shown that CD38 is an independent miR-34c is affected by del11q23 and regulates the expression of
prognostic marker in CLL, demonstrating that high CD38 expres- ZAP-70 and other proteins involved in the Tp53 pathway. MiR mass
sion is associated with both a shorter time from diagnosis to treatment array profiles have also been found to be predictive of disease progres-
and inferior survival. CD38 functional studies using CD31 and sion, fludarabine resistance and clinical outcomes.
plexin B1 transfected fibroblasts have provided a biologic explanation
for this observation. CD38 interaction with its ligand, CD31, in the
presence of IL-2 results in upregulation of the survival receptor Chromosomal Aberrations
CD100 exclusively on proliferating CLL cells. This occurs with
concomitant downmodulation of CD72, a negative regulator of Conventional metaphase karyotype analysis can identify chromo-
immune response. The interaction between CD38 and CD100 on somal aberrations in only 20% to 50% of CLL cases because of the
CLL cells and CD31 and plexin B1, respectively, on transfected low in vitro mitotic activity of CLL cells. Abnormalities noted in
fibroblasts results in enhanced survival and growth of CLL cells. descending frequency of occurrence include trisomy 12; deletions at
Furthermore, the presence of nurse-like cells in CLL patients express- 13q14; structural aberrations of 14q32; and deletions of 11q, 17p,
ing high levels of CD31 and plexin B1 corroborates the interplay of and 6q. In addition, a complex karyotype (three or more abnormali-
CD38 and CD31 and provides further evidence of activation of ties) occurs in approximately 15% of patients and is predictive of
circulating CD38-positive CLL cells by the microenvironment. This rapid disease progression, Richter transformation, and inferior sur-
finding provides an explanation for the aggressive nature of these CLL vival. The use of CD40L or the combination of IL-2 and CpG for
clones. B-cell stimulation has revealed translocations in 33 of 96 patients
(34%). These translocations were both balanced and unbalanced,
occurring at 13q14, 11(q21q25), 14q32, or regions also seen in
ZAP-70 lymphomas such as 1(p32p36), 1(q21q25), 2(p11p13), 6(p11p12),
6(p21p25), and 18q21. The presence of such translocations defines
ZAP-70 expression was identified as another surrogate marker for a prognostic subgroup of patients with a significantly shorter median
IGHV gene mutational status by a cDNA microarray analysis of time from diagnosis to requiring therapy (24 vs. 106 months) and