ASH: CD55 Blockade Overcomes CD20 Antibody Resistance

[Guest guest]

[2316] CD55 Blockade Overcomes CDC Resistance in Anti-CD20

Antibody Therapy:

Explanation for Bulky Mass Unresponsiveness and Efficacy

for Re-Treatment.

Session Type: Poster Session 487-II

Yasuhito Terui, Takuma Sakurai, Yuko Mishima, Yuji Mishima,

Masahiro

Yokoyama, Eijiro Nagasaki, Hisakazu Nishimori, Shunji

Takahashi, Yoshinori

Ito, Kiyohiko Hatake Clinical Chemotherapy, Japanese

Foundation for Cancer

Research, Toshima-ku, Tokyo, Japan; Biolaboratory Research

Institute,

Morinaga Milk Co., Zama, Kanagawa, Japan

Recently, anti-CD20 antibody is very useful in

therapy for

malignant lymphoma. However, in some cases with malignant

lymphoma after the

treatment of anti-CD20 antibody, lymphoma cells get

resistance to the

treatment of anti-CD20 antibody.

Its mechanism is still not clarified. We have some

regulators in complement

system, and CD55, known as Decay accelerating factor (DAF),

is a major

regulator of the alternative and classical pathways of

complement activation

and is expressed on all serum-exposed cells.

Here, we have found sensitivity to anti-CD20

antibody-mediated CDC was

different during cell growth dependent on expression of

CD55.

[Methods] Human B cell line, Daudi and Rajii cells were

used as sensitive

and insensitive controls in complement-mediated

cytotoxycity (CDC) with

anti-CD20 antibody. CDC assay with anti-CD20 antibody was

performed with

FACscan.

Cells were stained with anti-CD20, anti-CD46, anti-CD55 and

anti-CD59

antibodies and flowcytometry was performed. To see the

effect of CDC

activity on living cells, cells were stained with

a598-labeled anti-CD20

antibody and Mitotracker, and then serum was added to

culture media and

cells were observed at real time under confocal laser

scanning microscopy

system.

[Results] Daudi cells showed 80.5%, 57.1% and 23.3% of dead

cells by

anti-CD20 antibody-mediated CDC after 2, 4 and 6

days-cultivation,

respectively. After 6 days-cultivation, 13% of Daudi cells

got expressed

CD55, but not CD46 and CD59.

These suggest that the increasing of CD55-expressing cells

during cell

culture is related to resistance to anti-CD20

antibody-mediated CDC. Daudi

cells also showed resistance to anti-CD20 antibody-mediated

CDC and increase

of CD55-expressing cells with the supernatant after 6

days-cultivation and

serum-free media. When anti-CD55 antibody was added to the

mixture of CDC

assay, CDC activity after 6 days-cultivation was increased

to 67.6% from

42.1%.

This indicates that anti-CD55 antibody could partially

inhibit CD55 function

as an inhibitor of anti-CD20 antibody-mediated CDC. To

confirm the role of

CD55 on resistance to anti-CD20 antibody-mediated CDC,

Rajii cells, which

express more CD55 and are more resistance to anti-CD20

antibody-mediated CDC

than Daudi cells, were used for the target of CDC.

Anit-CD55 antibody

increased CDC activity against Rajii cells and cells.

[Conclusion] The sensitivity to anti-CD20 antibody-mediated

CDC was changed

under the circumstance surrounding the lymphoma cells, and

that CD55 plays

an important role in resistance to anti-CD20

antibody-mediated CDC.

Lymphoma cells can get resistant characteristics under some

condition such

as bulky mass, poor nutrition and hypoxia. Antibody against

CD55 molecule or

drugs, which inhibit expression of CD55, might be useful

for the treatment

of resistant lymphoma to anti-CD20 antibody therapy.

Abstract #2316 appears in Blood, Volume 102, issue 11,

November 16, 2003

Keywords: anti-CD20 antibody|CD55|CDC

Sunday, December 7, 2003 5:45 PM

Poster Session: Clinicopathologic/Molecular Factors

Impacting Prognosis II

(5:45 PM-7:15 PM)