Phenotypic Heterogeneity of B Cells
Phenotypic Heterogeneity of B Cells
Although some studies have examined the expression of aberrant markers such as CD2, CD7, CD10, CD13, CD33, and CD34 on B cells in chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), a uniform multiparametric analysis of the frequency of expression of these markers using stringent criteria is lacking. By using 3-color flow cytometry, we analyzed 117 cases (bone marrow, 71; blood, 31; lymph nodes, 15) for coexpression of aberrant markers with CD19. Marker expression was considered positive when present on at least 20% of CD19+ cells. Of 117 cases, 40 (34.2%) showed expression of 1 or more aberrant markers. Expression of 4 aberrant markers was seen in 1 case, 3 in 4 cases, 2 in 15 cases, and 1 in 20 cases. Kaplan-Meier survival curves and the log-rank test revealed that the group with aberrant markers showed significantly shortened overall survival compared with the group without aberrant markers (P < .001). There is considerable phenotypic heterogeneity in CLL/SLL, and expression of aberrant markers indicates aggressiveness.
Chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), although a relatively indolent neoplasm, is known to show considerable heterogeneity with respect to clinical course and life expectancy among patients. For a biologic correlate to this diversity, there has been considerable interest in the phenotypic heterogeneity of B cells in CLL/SLL. Expression of nonlineage markers in acute leukemias, high-grade lymphomas, and multiple myeloma has been associated with an adverse prognosis. This finding encouraged study of the frequency of expression of aberrant markers in CLL/SLL.
As a result, several studies have evaluated the expression of T-cell (CD2 and CD7), myelomonocytic (CD13 and CD33), progenitor cell (CD34), and immature B-cell (CD10) markers in CLL/SLL. However, a good number of these studies were case reports. Among the studies in which a number of cases of CLL were analyzed, there was considerable variation in the frequency of cases with CD2, CD13, and CD33 expression. The wide variation in the frequency of expression of these markers in CLL/SLL may be due to difference in the methods used. In some studies, the marker was considered positive in comparison with negative control samples, and in others, single-color flow cytometry was used. By using these methods, the coexpression of markers in B cells cannot be assessed accurately, and contaminating nonlineage cells in the gate cannot be excluded. Marker coexpression with CD20 was analyzed by some authors; however, CD20 is not a sensitive marker: it can be absent (B.K. and C.S., unpublished data), weak, or expressed heterogeneously in CLL/SLL. In some studies, the marker expression was considered positive when present on at least 10% of CD19+ cells. By using 10% as a cutoff, there can be false-positive cases, especially when marker expression is heterogeneous.
The clinical significance of CD2 expression in CLL/SLL is controversial. Expression of CD2 has been associated with an aggressive clinical course or advanced stage of disease at diagnosis. However, Kaleem et al, found no clinical significance for CD2 expression in CLL at diagnosis. The expression of CD13 and CD33 in B-cell CLL has been associated with unfavorable clinical and prognostic factors. In these studies, the prognostic effect of the expression of aberrant markers was assessed indirectly based on stage of the disease or pattern of bone marrow involvement at diagnosis, but not by a direct measure such as the analysis of long-term survival.
We used 3-color flow cytometry to evaluate coexpression of CD2, CD7, CD10, CD13, CD33, and CD34 with CD19 in 117 cases of CLL/SLL involving bone marrow, peripheral blood, and lymph nodes. We used CD19 to assess coexpression because it is well known to express uniformly and brightly on B cells in CLL/SLL. Marker expression was considered positive when present on at least 20% of CD19+ cells. The percentage of cases positive for each marker was determined. Survival analysis was performed using the Kaplan-Meier survival curve, and survival in patients with expression of aberrant markers was compared with a group without expression of aberrant markers by using the log-rank test.
Although some studies have examined the expression of aberrant markers such as CD2, CD7, CD10, CD13, CD33, and CD34 on B cells in chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), a uniform multiparametric analysis of the frequency of expression of these markers using stringent criteria is lacking. By using 3-color flow cytometry, we analyzed 117 cases (bone marrow, 71; blood, 31; lymph nodes, 15) for coexpression of aberrant markers with CD19. Marker expression was considered positive when present on at least 20% of CD19+ cells. Of 117 cases, 40 (34.2%) showed expression of 1 or more aberrant markers. Expression of 4 aberrant markers was seen in 1 case, 3 in 4 cases, 2 in 15 cases, and 1 in 20 cases. Kaplan-Meier survival curves and the log-rank test revealed that the group with aberrant markers showed significantly shortened overall survival compared with the group without aberrant markers (P < .001). There is considerable phenotypic heterogeneity in CLL/SLL, and expression of aberrant markers indicates aggressiveness.
Chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), although a relatively indolent neoplasm, is known to show considerable heterogeneity with respect to clinical course and life expectancy among patients. For a biologic correlate to this diversity, there has been considerable interest in the phenotypic heterogeneity of B cells in CLL/SLL. Expression of nonlineage markers in acute leukemias, high-grade lymphomas, and multiple myeloma has been associated with an adverse prognosis. This finding encouraged study of the frequency of expression of aberrant markers in CLL/SLL.
As a result, several studies have evaluated the expression of T-cell (CD2 and CD7), myelomonocytic (CD13 and CD33), progenitor cell (CD34), and immature B-cell (CD10) markers in CLL/SLL. However, a good number of these studies were case reports. Among the studies in which a number of cases of CLL were analyzed, there was considerable variation in the frequency of cases with CD2, CD13, and CD33 expression. The wide variation in the frequency of expression of these markers in CLL/SLL may be due to difference in the methods used. In some studies, the marker was considered positive in comparison with negative control samples, and in others, single-color flow cytometry was used. By using these methods, the coexpression of markers in B cells cannot be assessed accurately, and contaminating nonlineage cells in the gate cannot be excluded. Marker coexpression with CD20 was analyzed by some authors; however, CD20 is not a sensitive marker: it can be absent (B.K. and C.S., unpublished data), weak, or expressed heterogeneously in CLL/SLL. In some studies, the marker expression was considered positive when present on at least 10% of CD19+ cells. By using 10% as a cutoff, there can be false-positive cases, especially when marker expression is heterogeneous.
The clinical significance of CD2 expression in CLL/SLL is controversial. Expression of CD2 has been associated with an aggressive clinical course or advanced stage of disease at diagnosis. However, Kaleem et al, found no clinical significance for CD2 expression in CLL at diagnosis. The expression of CD13 and CD33 in B-cell CLL has been associated with unfavorable clinical and prognostic factors. In these studies, the prognostic effect of the expression of aberrant markers was assessed indirectly based on stage of the disease or pattern of bone marrow involvement at diagnosis, but not by a direct measure such as the analysis of long-term survival.
We used 3-color flow cytometry to evaluate coexpression of CD2, CD7, CD10, CD13, CD33, and CD34 with CD19 in 117 cases of CLL/SLL involving bone marrow, peripheral blood, and lymph nodes. We used CD19 to assess coexpression because it is well known to express uniformly and brightly on B cells in CLL/SLL. Marker expression was considered positive when present on at least 20% of CD19+ cells. The percentage of cases positive for each marker was determined. Survival analysis was performed using the Kaplan-Meier survival curve, and survival in patients with expression of aberrant markers was compared with a group without expression of aberrant markers by using the log-rank test.
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