99mTc-labelled rituximab, a new non-Hodgkin's lymphoma imaging agent: first clinical experience.
OBJECTIVE
This study was performed to explore the possibility of using Tc-rituximab as an imaging agent to assess expression of CD20 antigen in patients with B-cell non-Hodgkin's lymphoma (NHL) before (radio) immunotherapy, for staging and subsequent evaluation of remission of NHL.


METHODS
Rituximab was purified from Mabthera and photoactivated by ultraviolet light. The irradiated solution was aliquoted and labelled with pertechnetate. The effectiveness of the labelling method was evaluated by determination of the number of free thiol groups per photoreduced antibody, radiochemical purity determination and in-vitro stability. Immunoreactivity of Tc-rituximab was assessed on Ramos cells using a direct binding assay. Ten patients (age 31-70 years, mean 50 years) were included, nine with CD20 B-cell NHL and one with CD20-NHL. Whole-body and single photon emission computed tomography images were taken 1, 3, 6 and 20 h postinjection of Tc-rituximab. Scintigraphic results were compared with computerized tomography (CT) findings.


RESULTS
In all cases radiochemical purity over 95% was observed with preserved affinity for CD20 antigen. In all patients expected activity was seen in the blood pool, liver, kidneys and spleen. Pathological, moderately to markedly increased Tc-rituximab activity was seen in all but one CT-confirmed NHL involved sites 6 and 20 h postinjection. In one patient, increased activity of Tc-rituximab was additionally seen in one region not seen on CT. In three patients increased accumulation was seen in bone marrow.


CONCLUSIONS
Tc-rituximab is a promising imaging agent suitable for assessing expression of CD20 in patients with NHL before (radio) immunotherapy.
Gmeiner Stopar
Tanja
T
Department for Nuclear Medicine, University Medical Centre Ljubljana, Slovenia. tanja.stopar@kclj.si
Fettich
Jure
J
Zver
Samo
S
Mlinaric-Rascan
Irena
I
Hojker
Sergej
S
Socan
Aljaz
A
Peitl
Petra Kolenc
PK
Mather
Stephen
S
D000328:Adult; D000368:Aged; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000493:pharmacokinetics; D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20 / Q000276:immunology / Q000378:metabolism; D001853:Bone Marrow / Q000000981:diagnostic imaging / Q000473:pathology; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007167:Immunotherapy; D008228:Lymphoma, Non-Hodgkin / Q000000981:diagnostic imaging* / Q000235:genetics / Q000473:pathology / Q000628:therapy; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D015609:Organotechnetium Compounds / Q000276:immunology / Q000493:pharmacokinetics; D016719:Radioimmunodetection; D000069283:Rituximab; D013194:Staining and Labeling; D014018:Tissue Distribution
D000911:Antibodies, Monoclonal; D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20; D015609:Organotechnetium Compounds; C509712:technetium 99m rituximab; D000069283:Rituximab