In vivo labelling of granulocytes with 99mTc anti-NCA monoclonal antibodies for imaging inflammation

The role of nuclear medicine in inflammatory bowel disease. A review with experiences of aspecific bowel activity using immunoscintigraphy with 99mTc anti-granulocyte antibodies

The diagnosis of inflammatory bowel disease (IBD) needs a complex diagnostic work-up. Beside verifying the disease itself, it is fundamental to assess disease extent and activity and to detect associated complications, to find the most effective treatment and for follow up. Scintigraphy with radiolabelled leukocytes is able to provide a complete survey of the whole intestinal tract, both the small and large bowel, and detects septic complications successfully with negligible risk. Radionuclide procedures are useful in establishing or ruling out IBD in patients with intestinal complaints, in assessing disease severity, and in the evaluation of extraintestinal septic complications. Widely available radionuclide procedures are discussed, i.e. scintigraphy by 111Indium oxime or 99mTechnetium HMPAO labelled white blood cells and immunoscintigraphy with 99mTc anti-granulocyte antibodies. Advantages and disadvantages of all three methods are stressed out.

PATIENTS AND METHODS

The immunoscintigraphies with 99mTc anti-granulocyte antibodies (ANTI-GRANULOCYTE(R) BW 250/183) of 27 patients with suspicion of IBD were retrospectively analysed. Planar anterior and posterior images were obtained 4 and 24 h postinjection, respectively. The bowel was divided into six segments and the activity was visually graded with reference to bone marrow in each segments. The scans were compared with the results of radiological and endoscopical investigations. The diagnosis of IBD was proved or ruled out by means of enteroclysis, large bowel enema or endoscopy.

RESULTS

In the 27 patients, 74 bowel segments with increased activity were detected. In the case of 30 segments in 16 patients, bowel inflammation was revealed by the other methods (true positives). In the case of 44 bowel segments, no underlying bowel inflammation could be verified, and these activities were regarded as aspecific activity. We could not differentiate between true positive and aspecific activity based on scan pattern or intensity.

DISCUSSION

These findings of aspecific bowel activity using imuunoscintigraphy are in contrast with the results of former studies, while the existence of non-specific activity decreases the reliability of the method. Based on the literature and our experiences, we conclude that 99mTc HMPAO labelling should be the method of choice for the investigation of IBD patients.

Cold lesion of a vertebral angioma with Tc-99m-labeled monoclonal antibodies against granulocytes

Antigranulocyte immunoscintigraphy is indicated for diagnostic imaging to determine the location and extent of infection. We present a case of a focal cold lesion in a vertebra of a patient thought to have a septic focal lesion. Whole-body scanning and dorsal spine SPECT revealed no focal increased uptake. CT and MR studies revealed the presence of a vertebral angioma. Conditions associated with a defect of uptake in immunoscintigraphy are discussed.

Targeted imaging of infection

The prompt identification, localization and characterization of focal sites of infection in the patients with fever is a critical step in clinical management, particularly, when localizing symptoms are not present. Although the classic signs of inflammation are suitable to localize injury at superficial sites or in the extremities, inflammation of internal structures, such as in the brain, chest and abdomen, can be difficult to localize without additional diagnostic procedures. Tissue injury, regardless of cause or anatomical site, results in a complex series of physiologic changes that we recognize as the inflammatory response. The inflammatory response is characterized by a series of biochemical events in the insulted cells and surrounding structures that results in the three major pathophysiological components: increased tissue perfusion, increased vascular permeability, and leukocytic exudation. Exploitation of the early attributes of the inflammatory process are not sufficient for the routine detection of inflammation. Currently, reagents for targeting infection represent cellular or protein components involved in the inflammatory process. Such approaches have met with some success as these agents comprise integral parts of the complex phenomena known as inflammation. This same fact also limits their utility. Improved agents for targeting infection will likely be based on small molecules whose diffusion into the lesion is not hindered by molecular size constraints and which bind to molecular targets at the site of infection/inflammation. In general, the lower molecular weight should also lead to enhanced blood clearance, avoiding elevated blood pool activity which contributes to background. New agents should also obviate the need to handle blood, as this represents potential hazards to both patient and the medical personnel alike.

Radioiodinated (aminostyryl)pyridinium (ASP) dyes: new cell membrane probes for labeling mixed leukocytes and lymphocytes for diagnostic imaging

We prepared [125I/131I]iodo-(aminostyryl)pyridinium dyes from tributylstannyl precursors. ASP 7a and 7b labeled leukocytes ex vivo (70-94%) using saline with or without washing plasma from cells. Viability of peripheral blood lymphocytes (PBLs) (dogs, rats) and splenic lymphocytes (rats) labeled with 7a and 7b (71-82%) was unchanged after labeling (> or = 88%). Canine 7b-leukocytes showed higher uptake in inflammatory lesions than did 111In-oxine leukocytes. At 3 h, aspirates contained more radioiodine than 111In (1.65:1 to 22:1) and radioiodine was cell bound. ROI measurements (3 h) gave abscess to contralateral knee ratios of 12.3 and 10.6 for 131I-7b vs. 4.8 and 2.3 for 111In-oxine.

The contribution of nuclear medicine to the patient with infection

Nuclear medicine imaging of infection has two major indications: (a) the localization of a focus of infection in patients with fever of unknown origin; in this context the radio-pharmaceutical should be highly sensitive whereas specificity is not so important because subsequent biopsy or morphologically based imaging can be performed; (b) the diagnosis of an infection in patients with localized symptoms, for example after surgery, when normal anatomy is absent or when metal implants prevent computed tomography or magnetic resonance imaging. In these latter cases high sensitivity and to an even greater extent high specificity are mandatory to guide further clinical management (conservative or surgical). All radiopharmaceuticals available to date, such as technetium-99m nanocolloids, gallium-67 citrate, indium-111- and 99mTc-labelled white blood cells, 99mTc-antigranulocyte antibodies, and 99mTc-or 111In-labelled unspecific human immunoglobulin, have different biodistributions and different physical characteristics. The absence of physiological uptake in an organ and the radiation exposure of a patient are reasons to use different radiopharmaceuticals in different clinical situations, adapted to the individual circumstances of the patient.

Scintigraphic evaluation of the haemopoietic bone marrow using a 99mTc-anti-granulocyte antibody: a validation study with 52Fe

To specify the validity of bone marrow scanning using a monoclonal anti-granulocyte antibody labelled with 99mTc (BW 250/183) for the functional assessment of haemopoiesis, we compared this method with 52Fe scan in 16 patients with haematological disorders. The examinations were performed using a rectilinear whole-body scanner and the distribution of the two tracers was assessed visually and quantitatively in anatomical bone marrow segments, the spleen and liver. Qualitative comparison showed concordance in the bone marrow distribution of the two tracers in 83% of the segments. Discrepancies were found in six patients with hypoplastic or aplastic marrow. The spleen was visualized in all cases with the 99mTc-Moab, including nine patients without splenic haemopoiesis (i.e. without spleen uptake of 52Fe). The uptake of the two tracers, quantified in bone marrow segments and the spleen, correlated well (P < 0.001), but not in the liver (NS). The correlation between the uptake values for each patient was excellent, except in cases of aplastic bone marrow. In conclusion, bone marrow scanning using a 99mTc labelled anti-granulocyte monoclonal antibody enables functional evaluation of the distribution of haemopoiesis. Limitations include the evaluation of bone marrow aplasia and identification of splenic haemopoiesis, for which 52Fe remains the tracer of choice.

Characterisation of a humanised bispecific monoclonal antibody for cancer therapy

A humanised bispecific monoclonal antibody (bsMAb) with binding specificity for carcinoembryonic antigen (CEA) on one arm and a radiolabelled chelate (DTPA-90Y) on the other arm was generated by consecutively transfecting the humanised genes of an anti-CEA MAb and the chimerised genes of an anti-chelate MAb into eucaryotic BHK cells using the calcium-phosphate coprecipitation technique. The antibodies secreted were of IgG3 isotype with a shortened hinge region (delta gamma 3) and light chains. Double transfectomas were screened for the secretion of bsMAbs using a double determinant enzyme-linked immunosorbent assay (ELISA) based on solid phase attached HSA-benzyl-DTPA and an anti-idiotypic MAb selective for the CEA-specific arm. After purification on two immunoaffinity chromatography columns, the humanised bsMAbs were characterised by SDS-PAGE and a quantitative binding assay in antigen excess. The purification procedure resulted in 95% reactive bispecific MAb. This humanised bsMAb may be employed in two phase radioimmunotherapy, binding to the tumour via the anti-CEA arm and localising a radiolabelled chelate with the other arm, without inducing a strong immune response observed sometimes with murine MAbs.

Can pharmacological intervention improve the visualization of the reticuloendothelial system using 99mTc-labeled albumin nanocolloid to that achievable with 111In-labeled granulocytes? Experimental studies in mice

The use of 99mTc-colloids for bone marrow scintigraphy is limited by a high liver uptake, which hampers the evaluation of surrounding skeletal structures. In an experimental mouse system, different measures to increase the bone marrow activity in relation to the liver activity have been tested. A slightly positive, but significant, outcome was achieved by three different measures, namely fasting, pretreatment with a calcium-blocking pharmaceutical (Nimodipine) and pretreatment with large amounts of a gelatine colloid. It is concluded that the possibilities of dramatically improving the bone marrow uptake of a colloid compared to the liver are limited and not comparable to that achievable using radiolabeled granulocytes.

111Indium-F(ab)'2-NCA 102 monoclonal antibody: in vitro study of a specific agent for the detection of inflammatory foci

A new antigranulocyte antibody was evaluated in vitro for the detection of inflammatory foci in man. The specificity for polymorphonuclear cells (PMN) of NCA 102, an anti-NCA 95 monoclonal IgG1, was determined with immunohistochemical and cytofluorometrical tests. Its affinity, assessed by Scatchard analysis, was 1.1 x 10(9) L/mol and the number of epitopes per granulocyte reached about 10(5). The biological properties of PMNs incubated with NCA 102 were not inhibited even when coupled with DTPA. A F(ab)'2 fragment was radiolabelled with 111Indium and incubated in the presence of whole blood. More than 65% radioactivity was selectively taken up by the PMN population. These findings indicated that NCA 102 antibody is suitable for sepsis detection.

Generation of bispecific monoclonal antibodies for two phase radioimmunotherapy

A two phase radioimmunotherapy based on bispecific MAbs in which one arm recognises a tumour antigen and the other a radiolabelled chelate, may prove more effective in the treatment of carcinomas than currently available immunotherapies. To establish this system we first showed that penetration into human carcinoma xenografts as well as long term retention of intact MAb outside the carcinoma cells can be obtained. Epitope saturation was not obtained however, despite the large MAb doses injected i.v. for 10 days. We then generated hybridomas producing high avidity anti-metal chelate MAbs (anti-DTPA-Y). These hybridomas were fused with hybridomas producing MAbs against CEA or GIT-mucin, and stable bispecific MAb producing quadromas were obtained. For the anti-GIT-mucin x anti-chelate MAb a purification procedure based on double anti-idiotype affinity chromatography was shown to result in greater than 95% pure bispecific immunoreactive MAb. Comparative in vivo stability studies profiled DTPA-Y as the chelate of choice for in vivo application.

Recent advances in bone marrow scanning

Interest in bone marrow scanning has been renewed as the result of the development of radiopharmaceuticals for evaluating specific aspects of bone marrow anatomy, physiology and pathology. This article provides a brief review of bone marrow structure, blood flow and function essential to the understanding of basic principles of bone marrow radionuclide imaging. The prospects and limitations of imaging haematopoietic bone marrow in man using indium 111 chloride, technetium-99m (99mTc)-labelled microcolloid or 99mTc-labelled monoclonal antigranulocytic and antimyelocytic antibodies are discussed in more detail. The technical aspects of bone marrow scintigraphy are presented. Results of more recent studies evaluating bone marrow scanning in circulatory, inflammatory and in systemic haematological disorders are summarized. Special attention is paid to the concept of bone marrow micrometastases and its implications for the follow-up of patients with malignant tumours. Recent results suggest that immunoscintigraphy of bone marrow may provide a novel and sensitive approach for establishing the presence and extent of bone marrow infiltration.