To the Editor:

Human AC133 antigen is a 5-transmembrane molecule that belongs to the prominin family.1-4 In the hematopoietic system, AC133 expression is restricted to a subset of CD34+progenitor/stem cells1 and to leukemic blasts from patients with acute myeloid leukemia (AML).2,5-7 Controversy exists whether the AC133 antigen is also expressed on acute lymphoblastic leukemia (ALL) blasts. One group described low levels of AC133 antigen expression on the blasts of some ALL samples,2 whereas 3 other groups reported the exclusive expression of this molecule on AML blasts.5-7 Using multiparameter flow cytometry, we analyzed the correlated expression of AC133 antigen and CD34 in 23 AML and 9 ALL samples from adult patients, as well as on the surface of normal CD34+ bone marrow cells. Table1 shows the distribution of AC133 antigen and CD34 on leukemic blasts in correlation to their morphological classification. In line with previous reports, the majority of CD34+ AML samples (15/18 [83%]) coexpressed the AC133 antigen. Four of the 5 tested CD34 AML samples (80%) were also AC133+. Notably, these samples exclusively displayed the M4/M5 French-American-British (FAB) subtypes. Four of 10 CD34+AC133+ AML samples of the M1/M2 subtypes and 1 of 6 of the M4/M5 subtypes expressed high levels of AC133 antigen (mean log fluorescence intensity between the second and third decade). In addition, 1 of 4 CD34AC133+ AML samples were also AC133bright. Representative plots of a CD34+AC133bright FAB M2 and a CD34AC133dim FAB M4 sample are shown in Fig 1. In contrast to other reports, our data neither confirm that AC133bright cells are exclusively found in M4/M5 AML subtypes2 nor that AC133bright blasts resemble exclusively the most immature FAB types,7 but rather suggest that high levels of AC133 antigen expression is observed on myeloid leukemic blasts of all FAB subtypes.

Table 1.

Expression of AC133 Antigen and CD34 on ALL and AML

Leukemia AC133 CD34
 1. T-ALL  Dim  
 2. T-ALL  —  +  
 3. C-ALL  —  
 4. C-ALL  —  +  
 5. C-ALL  Dim  
 6. C-ALL  Bright  −  
 7. C-ALL  —  − 
 8. C-ALL  Dim  +  
 9. Pro-B ALL  Bright  
10. AML M1/M2  —  −  
11. AML M1/M2  —  
12. AML M1/M2  Dim  +  
13. AML M1/M2  Bright  
14. AML M1/M2  Dim  +  
15. AML M1/M2  Dim  
16. AML M1/M2  Bright  +  
17. AML M1/M2  Dim  
18. AML M1/M2  Bright  +  
19. AML M1/M2  Bright  
20. AML M1/M2  Dim  +  
21. AML M1/M2  Dim  
22. AML M4/M5  Dim  +  
23. AML M4/M5  Dim  
24. AML M4/M5  Dim  +  
25. AML M4/M5  Dim  
26. AML M4/M5  —  +  
27. AML M4/M5  Bright  
28. AML M4/M5  Dim  −  
29. AML M4/M5  Dim  − 
30. AML M4/M5  Dim  +  
31. AML M4/M5  Dim  − 
32. AML M4/M5  Bright  − 
Leukemia AC133 CD34
 1. T-ALL  Dim  
 2. T-ALL  —  +  
 3. C-ALL  —  
 4. C-ALL  —  +  
 5. C-ALL  Dim  
 6. C-ALL  Bright  −  
 7. C-ALL  —  − 
 8. C-ALL  Dim  +  
 9. Pro-B ALL  Bright  
10. AML M1/M2  —  −  
11. AML M1/M2  —  
12. AML M1/M2  Dim  +  
13. AML M1/M2  Bright  
14. AML M1/M2  Dim  +  
15. AML M1/M2  Dim  
16. AML M1/M2  Bright  +  
17. AML M1/M2  Dim  
18. AML M1/M2  Bright  +  
19. AML M1/M2  Bright  
20. AML M1/M2  Dim  +  
21. AML M1/M2  Dim  
22. AML M4/M5  Dim  +  
23. AML M4/M5  Dim  
24. AML M4/M5  Dim  +  
25. AML M4/M5  Dim  
26. AML M4/M5  —  +  
27. AML M4/M5  Bright  
28. AML M4/M5  Dim  −  
29. AML M4/M5  Dim  − 
30. AML M4/M5  Dim  +  
31. AML M4/M5  Dim  − 
32. AML M4/M5  Bright  − 

Bone marrow samples obtained after informed consent from patients with acute leukemia were stained with anti-CD34-FITC and AC133-PE and were analyzed by multiparameter flow cytometry. Leukemic blasts expressing AC133 antigen were subdivided into AC133dim (log fluorescence intensity between the first and the second decade) and AC133bright cells (log fluorescence intensity between the second and the third decade).

Fig. 1.

Coexpression of AC133 antigen and CD34 on leukemic blasts. Representative AML and ALL blasts were stained with anti-CD34-FITC (horizontal axis) and AC133-PE (vertical axis) and analyzed on a FACSCalibur flow cytometer. The mean fluorescence intensity values are derived from the populations gated on AC133+ cells.

Fig. 1.

Coexpression of AC133 antigen and CD34 on leukemic blasts. Representative AML and ALL blasts were stained with anti-CD34-FITC (horizontal axis) and AC133-PE (vertical axis) and analyzed on a FACSCalibur flow cytometer. The mean fluorescence intensity values are derived from the populations gated on AC133+ cells.

Table 1 also demonstrates that 3 of 6 C-ALL, 1 of 1 pro-B ALL, and 1 of 2 T-ALL samples were AC133+. These data are in line with the observations of Miraglia et al,2 who found AC133 antigen expression on 4 of 6 ALL samples, but do not support the findings of Snell et al,7 who could not detect AC133 antigen expression on any of the 17 tested ALL samples. In contrast to Miraglia et al,2 we found high levels of AC133 expression in some B-lymphoid ALL samples (2/7). Figure 1 shows that 1 AC133bright sample was of the C-ALL and 1 was of the pro-B ALL phenotype. Notably, the AC133bright blasts of the pro-B ALL sample were heterogeneous with regard to CD34 expression. However, whether the CD34+AC133bright and the CD34AC133bright represent populations of different maturational stages has yet to be determined.

To analyze whether AC133+ B-lymphoid cells exist also among nonleukemic hematopoietic precursor cells, normal bone marrow cells enriched for CD34+ cells by MACS technology were stained with anti-CD34-peridine chlorophyll protein (PerCP), AC133-phycoerythrin (PE), and anti-CD10-fluorescein isothiocyanate (FITC) or anti-CD19-FITC, respectively, and analyzed on a FACSCalibur flow cytometer. Figure 2 shows that the majority of the CD34+CD10+ and CD34+CD19+ cells (34.8% v 29.4%) are AC133. However, a minor CD34+CD10+ and CD34+CD19+ B-cell precursor population exists (15.1% v 5.9%) that is also AC133+ and may represent the normal counterpart of AC133+ ALL cells. Our data suggest that AC133 antigen is not only expressed on stem cells and myeloid progenitor cells and their leukemic counterparts,1,2 but also on ALL blasts and normal CD34+ B-lymphoid precursor cells.

Fig. 2.

Coexpression of AC133 and CD10 or CD19 on CD34+ bone marrow cells. Mononuclear bone marrow cells were enriched for CD34+ cells by MACS and stained with anti-CD34-PECY5, AC133-PE, and anti-CD10-FITC or anti-CD19-FITC, respectively. The plots show expression of AC133 antigen versus CD10 or CD19 on cells gated on CD34+ cells.

Fig. 2.

Coexpression of AC133 and CD10 or CD19 on CD34+ bone marrow cells. Mononuclear bone marrow cells were enriched for CD34+ cells by MACS and stained with anti-CD34-PECY5, AC133-PE, and anti-CD10-FITC or anti-CD19-FITC, respectively. The plots show expression of AC133 antigen versus CD10 or CD19 on cells gated on CD34+ cells.

ACKNOWLEDGMENT

These studies were supported by the Deutsche Forschungsgemeinschaft (SFB 510, project A1), by a grant from the Federal Ministry of Education and Research and the Interdisciplinary Clinical Research Center (project II A1), and by a grant from the Deutsche Krebshilfe (W16/94 Br1).

REFERENCES

REFERENCES
1
Yin
AH
Miraglia
S
Zanjani
ED
Almeida-Porada
G
Ogawa
M
Leary
AG
Olweus
J
Kearny
J
Buck
DW
AC133, a novel marker for human hematopoietic stem and progenitor cells.
Blood
90
1997
5002
2
Miraglia
S
Godfrey
W
Yin
AH
Atkins
K
Warnke
R
Holden
JT
Bray
RA
Waller
EK
Buck
DW
A novel five-transmembrane hematopoietic stem cell antigen: Isolation, characterization, and molecular cloning.
Blood
90
1997
5013
3
Corbeil
D
Röper
K
Weigmann
A
Huttner
WB
AC133 hematopoietic stem cell antigen: Human homologue of mouse kidney prominin or distinct member of a novel protein family?
Blood
91
1998
2625
(letter)
4
Miraglia
S
Godfrey
W
Buck
DW
A response to AC133 hematopoietic stem cell antigen: Human homologue of mouse kidney prominin or distinct member of a novel protein family?
Blood
91
1998
4390
(letter)
5
Horn
PA
Tesch
H
Staib
P
Kube
D
Diel
V
Voliotis
D
Expression of AC133, a novel hematopoietic precursor antigen, on acute myeloid leukemia cells.
Blood
93
1999
1435
(letter)
6
Kratz-Albers
K
Zühlsdorf
M
Leo
R
Berdel
WE
Büchner
T
Serve
H
Expression of AC133, a novel stem cell marker, on human leukemic blasts lacking CD34 antigen and on a human CD34+ leukemic cell line: MUTZ-2.
Blood
92
1998
4485
(letter)
7
Snell
V
Jackson
E
Buck
D
Andreeff
M
Expression of the AC133 antigen in leukemic and normal progenitors.
Blood
92
1998
119a
(abstr, suppl 1)