High-dose myeloablative radioimmunotherapy of mantle cell non-hodgkin lymphoma with the iodine-131–labeled chimeric anti-CD20 antibody C2B8 and autologous stem cell support. [THIS ARTICLE HAS BEEN RETRACTED]
Results of a pilot study
Article first published online: 12 FEB 2002
Copyright © 2002 American Cancer Society
Supplement: Eighth Conference on Radioimmunodetection and Radioimmunotherapy of Cancer
Volume 94, Issue Supplement 4, pages 1363–1372, 15 February 2002
How to Cite
Behr, T. M., Griesinger, F., Riggert, J., Gratz, S., Béhé, M., Kaufmann, C. C., Wörmann, B., Brittinger, G. and Becker, W. (2002), High-dose myeloablative radioimmunotherapy of mantle cell non-hodgkin lymphoma with the iodine-131–labeled chimeric anti-CD20 antibody C2B8 and autologous stem cell support. [THIS ARTICLE HAS BEEN RETRACTED]. Cancer, 94: 1363–1372. doi: 10.1002/cncr.10307
- Issue published online: 12 FEB 2002
- Article first published online: 12 FEB 2002
- Manuscript Accepted: 14 NOV 2001
- Manuscript Received: 31 OCT 2001
- Deutsche Forschungsgemeinschaft. Grant Number: Be 1689/4-2
- mantle cell non-Hodgkin lymhpoma;
- anti-CD20 antibody;
- high-dose myeloablative therapy;
- stem cell transplantation
CD20 has been used successfully as a target molecule for conventional low-dose, as well as high-dose, myeloablative radioimmunotherapy (RIT) of B-cell non-Hodgkin lymphoma (NHL). Mantle cell lymphoma (MCL) is an especially aggressive, prognostically unfavorable subtype of B-cell NHL, associated with an overall 5-year survival rate of less than 20%. Recent evidence has failed to show convincing therapeutic efficacy of conventional, nonmyeloablative RIT in patients with MCL. The aim of this pilot study was to investigate whether high-dose, myeloablative RIT with the iodine-131 (131I)–labeled chimeric anti-CD20 antibody C2B8 (rituximab, obtained as Mabthera from Roche Pharma, Reinach, Switzerland) is therapeutically effective in MCL patients.
A total of seven patients with chemorefractory or relapsed MCL were studied in this pilot trial. All had relapsed after high-dose chemotherapy with autologous stem cell transplantation (four of them combined with 12 grays (Gy) total-body irradiation). A diagnostic-dosimetric study was performed with approximately 10 mCi of 131I-labeled C2B8 at a protein dose of 2.5 mg per kg body weight, in order to assess its biodistribution and dosimetry. If splenic pooling was observed, as is typically the case in patients with splenomegaly, the protein dose was doubled in additional studies until a “favorable” biodistribution was obtained. Therapy was performed with myeloablative doses of 261–495 mCi of 131I-labeled C2B8 at the previously optimized protein dose, aiming at lung doses ≤ 27 Gy. Homologous stem cell support was provided. Clinical follow-up was obtained at 3-month intervals for up to 38 months (median observation time, 25 months). Overall, in six patients the 2.5 mg/kg protein dose was used, whereas in one patient with splenomegaly, 10 mg/kg was necessary to overcome the splenic antigenic sink.
Blood cell nadirs were reached at 2–3 weeks after therapy infusion, but all patients reengrafted at 7–10 days after stem cell reinfusion. Nonhematologic toxicity was restricted to mild-to-moderate nausea, fever, transient bilirubin, or liver enzyme elevations. One patient with preexisting alcoholic cirrhosis experienced a deterioration of liver function. Despite thyroid blocking, 5 of 7 patients developed hypothyroidism, requiring thyroxine substitution at 6–18 months after RIT. Six patients experienced a complete and one a good partial remission. Five patients were still in CR at the time this article was written, and six are still alive for more than 3 years; one patient relapsed locally at 3 months and one systemically at 26 months after RIT.
High-dose myeloablative radioimmunotherapy with 131I-labeled anti-CD20 antibodies seems to be associated with a high response rate and moderate toxicity in patients with MCL. Further follow-up to monitor the long-term outcome as well as systematic prospective clinical studies are indicated. Cancer 2002;94:1363–72. © 2002 American Cancer Society.
Mantle cell non-Hodgkin lymphoma (MCL) shares unfavorable clinical characteristics with both low- and high-grade lymphomas.1–4 It accounts for approximately 5% of all newly diagnosed malignant lymphomas, which means that it occurs about as frequently as chronic lymphocytic leukemia.1 Like other indolent lymphomas, MCL has a pattern of continued relapse. However, its natural history is much more aggressive than that of other low-grade lymphomas.1–4 Overall 5-year survival rates of less than 20% are dramatically (approximately threefold) lower than in other forms of indolent lymphoma.1–4 More aggressive therapy regimens are able to achieve remission rates similar to those for other forms of low- or intermediate-grade lymphoma, but have failed to prevent relapses or to prolong the patients' lives.3 The popular oncologic textbook by DeVita et al. concludes that, “taken together, these data confirm the unique natural history of MCL and suggest that innovative approaches to this disease are needed.”1
Immunotherapy is such a novel concept that has shown impressive therapeutic results when given alone5 and even better results in the form of radioimmunotherapy (RIT). These results were originally seen in low-grade,6–8 but they have been apparent more recently in intermediate- and high-grade NHL as well.9 A variety of B-cell surface antigens have been used for this purpose. CD20 is the most studied target antigen. It is a 33-kD unglycosylated transmembrane phosphoprotein that is expressed on pre-B, resting, activated, or malignant B cells, but absent from mature plasma cells.10 After the highly successful conventional, nonmyeloablative as well as high-dose, myeloablative trials with several murine anti-CD20 antibodies (e.g., B1, MB-1, 1F5),6–9 a chimeric anti-CD20 antibody, IDEC-C2B8 (rituximab), was developed. This antibody has been shown to directly mediate both complement- and cell-mediated cytotoxicity in vitro and in vivo.11 Objective response rates of approximately 50% have been obtained in several multicenter trials with the naked antibody at a protein dose of 375 mg/m2 for each of four weekly cycles.5 However, no convincing results were obtained in MCL patients.12 Furthermore, in contrast to impressive therapeutic results with low-grade NHL, recent evidence failed to show convincing therapeutic efficacy of conventional, nonmyeloablative RIT in patients with MCL.13 Since several groups, including ours, have demonstrated clear increases in both response rates and durations of response by moving toward high-dose, myeloablative RIT,9 we hypothesized that this more aggressive form of treatment may also be beneficial also to MCL patients. The aim of this pilot study, therefore, was to investigate whether high-dose, myeloablative RIT with the iodine-131 (131I)–labeled chimeric anti-CD20 antibody C2B8 (rituximab) may offer therapeutic benefits to MCL patients with advanced stages of disease.
Materials and Methods
Monoclonal Antibodies and Their Radiolabeling
The mouse-human chimeric anti-CD20 antibody IDEC-C2B8 (rituximab, termed C2B8 in this communication) was commercially obtained (as Mabthera) from Roche Pharma (Reinach, Switzerland). Radioiodination of C2B8 with Na131I was performed according to previously described procedures.9, 14 Briefly, Na131I was obtained from Nordion (Fleurus, Belgium). The antibody, in phosphate-buffered saline, was injected into a iodogen-coated glass vial (500 μg iodogen coating the inner surface of a 10-mL vial) with a magnetic stir bar placed inside. Sodium phosphate buffer (0.5 M, pH 7.4) was added in a volume twice as great as the volume of the radioiodine to be used. The specific activity used was 15–20 mCi per mg of antibody protein. The vial was placed on a magnetic stirrer, and the activity was added in 2.5 mL 0.04 M sodium phosphate, pH 7.4. After 15–25 minutes, Dowex 1X8-100 anion exchange resin (Cl− form; Sigma, Deisenhofen, Germany) was added, and the incubation time was prolonged for another 5 minutes. Subsequently, the radioiodinated antibody was filtered through a sterile Millex-GV filter (pore size, 0.22 μm; Millipore, Molsheim, France). The radiolabeled antibody was supplemented with cold antibody protein to give final protein amounts of 2.5 mg per kg body weight, if not indicated otherwise. This was the protein dose that had been shown earlier to give optimal tumor-to-nontumor ratios.15
Patients, Antibody Administration, and Imaging
Patient characteristics, together with abbreviated medical histories, are shown in Table 1. A total of seven patients with chemorefractory or relapsed malignant MCL were included. All had relapsed after high-dose chemotherapy with autologous stem cell transplantation (combined in four cases with 12 Gy total-body irradiation). The patients were at least 4 weeks beyond chemotherapy or external beam radiation, and had a performance status of 60 or greater on the Karnofsky scale.
|Patient age, gender||Clinical history of the disease||RIT (mCi, mg protein)||Therapeutic response to RIT||Duration|
|1 58, M||6/91 Dx: MCL Stage IVB 7/91–8/92 CHOP: CR 2/93 local relapse||8/97 495 mCi 131I-C2B8 (2.5 mg/kg, 160 mg)||CR (CT, 67Ga, bone marrow biopsy)||26 mos leukemic relapse|
|3–7/93 mitoxantrone + prednimustine: CR||re-Tx 11/99 (326 mCi, 147 mg):||death of multiorgan failure|
|12/94 systemic recurrence|
|2–8/95 Dexa-BEAM, high-dose BEAM, TBI (12 Gy) with autologous stem cell support: CR|
|5–7/97 CHOP: PR|
|2 61, M||4/93 Dx: MCL Stage IVB||10/97 430 mCi 131I-C2B8 (2.5 mg/kg, 209 mg)||CR (CT, 67Ga, bone marrow biopsy)||38+ mos|
|4–10/93 CHOP: CR|
|5/94 cervical and mediastinal recurrence|
|5–8/94 Dexa-BEAM, high-dose BEAM + TBI (12 Gy) and autologous stem cell support: CR|
|2/95 cervical recurrence|
|4–5/95 local irradition: CR|
|12/96 systemic recurrence|
|1–4/97 fludarabine: CR|
|9/97 mediastinal recurrence|
|3 51, M||8/96 Dx: MCL Stage IVA||9/98 465 mCi 131I-C2B8 (2.5 mg/kg, 190 mg)||CR (CT, 67Ga, bone marrow biopsy)||26+ mos|
|10/96–1/97 chemo (Knospe): PD leukemic spread|
|3–5/97 CHOP: PR|
|7–11/97 Dexa-BEAM, high-dose BEAM and autologous stem cell Tx: PR|
|4–6/98 Dexa-BEAM: PD, leukemic progression, systemic recurrence|
|4 54, M||2/96 Dx: MCL Stage IVA||11/98 261 mCi 131I-C2B8 (2.5 mg/kg, 180 mg)||Good PR (CT, 67Ga, bone marrow biopsy)||3 mos local relapse in the jaw|
|3–7/96 CHOEP: PR|
|9–10/96 involved field irradiation of the abdomen and pelvis (30 Gy)|
|11/97 abdominal recurrence|
|11/97–1/98 Dexa-BEAM: PR|
|4/98 high-dose BEAM with autologous stem cell support: good PR|
|8/98 systemic recurrence with > 90% bone marrow infiltration|
|8–10/98 rituximab (Mabthera): PR|
|5 46, M||8/96 Dx: MCL Stage IVB||12/98 410 mCi 131I-C2B8 (2.5 mg/kg, 205 mg)||CR (CT, PET, bone marrow biopsy)||24+ mos|
|02/97 high-dose chemo (VP16, carmustin, endoxan) with autologous stem cell support|
|2/98 lymph node recurrence|
|2–5/98 rituximab (Mabthera): PD|
|6–10/98 EPOCH + rituximab: PR|
|6 57, F||7/96: Dx MCL Stage IIIB||7/99 401 mCi 131I-C2B8 (2.5 mg/kg, 145 mg)||CR (CT, 67Ga, bone marrow biopsy)||17+ mos|
|8–11/96 CHOEP: PR|
|1–2/97 irradiation of the periaortic lymph nodes (24 Gy), TBI (12 Gy)|
|2/97 high-dose chemo (cyclophosphamide) with autologous stem cell support: good PR|
|12/97 systemic recurrence|
|12/97–07/98 mitoxantrone + dexamethasone: PR|
|11–12/98 rituximab (Mabthera): good PR|
|3/99 retroperitoneal recurrence|
|04–5/99 fludarabine: PD|
|7 63, M||4/98 Dx: MCL Stage IVB 4–8/98 CHOP 10–11/98 Dexa-BEAM 1–2/99 external beam irradiation of the abdomen (24 Gy) high-dose BEAM + TBI (12 Gy) 3/99 CR 9/99 systemic recurrence 10–12/99 CHOP: PR||1/00 485 mCi 131I-C2B8 (10 mg/kg, 720 mg)||CR (CT, 67Ga, bone marrow biopsy)||11+ mos|
All patients underwent thorough staging procedures within 1 week before RIT, including whole-body (i.e., neck to pelvis) computed tomography (CT), chest X-ray, abdominal ultrasonography, a bone and bone marrow scan, gallium-67 citrate scintigraphy, and, optionally, magnetic resonance tomography and 18F-FDG whole-body positron emission tomography. After giving informed consent, therapy patients were premedicated with potassium iodide (200 mg daily, initiated 24 hours before the first antibody administration) in order to decrease thyroid and gastric uptake of metabolically liberated radioiodine, respectively. This medication was continued until patients were removed from radiation restriction.
The radioiodinated antibodies were infused during a 30-minute period in a volume of 35–50 mL of sterile 0.9% NaCl containing 2.5% human serum albumin. A diagnostic-dosimetric study was performed with approximately 10 mCi of 131I-labeled C2B8 at a protein dose of 2.5 mg per kg body weight, in order to assess its biodistribution and dosimetry by external scintigraphy.9 If splenic pooling was observed, as is typically the case in patients with splenomegaly, the protein dose was doubled in additional diagnostic scans, until a more “favorable” biodistribution was obtained. Therapy was performed with myeloablative activities of 131I-labeled C2B8 at the previously optimized protein dose, determined to yield lung doses not exceeding 27 Gy.7–9
Scanning was performed with a Picker Prism 2000 double-headed gamma camera equipped with high-energy collimators (Picker, Cleveland, OH). Anterior and posterior whole-body scans were obtained from 4 hours daily up to 168–240 hours after injection of the diagnostic-dosimetric dose, or after therapy, when the patient's whole-body activity had fallen below 40 mCi. In addition, single photon emission computed tomography of the pelvis, abdomen, and chest was performed on several occasions.
Stem cell or bone marrow (re)infusion was performed when the whole-body activity fell below 15–20 mCi of 131I.9 Clinical follow-up was obtained at 3-month intervals and had lasted up to 38 months at the time this article was written.
For organ and tumor dosimetry, regions of interest of organs and tumors, as well as of the sacrum (as a region representative of red marrow),16 were generated from the anterior and posterior planar views. All calculations were performed with PC software developed for this purpose.17, 18 Time-activity curves were generated and integrated, and cumulated activities as well as residence times were derived. These data were entered into the MIRDOSE3 program,18 which yielded the organ, red marrow, tumor, and whole-body dosimetry according to the Medical Internal Radiation Dose scheme, based on derived residence times.18
All pre- and post-RIT scans (CT, MRI, X-ray, and ultrasonography) were evaluated by a radiologist familiar with the patients' clinical history. Responses were graded as follows, according to standard criteria:
- 1Complete remission—absence of clinically detectable disease for at least 1 month;
- 2Partial remission—at least a 50% reduction in the sum of the diameters of measurable disease, without any appearance of new lesions and without increase in size of any lesion for at least 1 month;
- 3Minor or mixed response, or stabilization of disease—a reduction of less than 50% in the sum of the diameters of measurable lesions without increase in size of any lesion;
- 4Progression of an increase of greater than 25% in measurable disease, or treatment for any new lesion, or both of these criteria.
Patients' Medical History
In this pilot study, seven patients with advanced MCL were included. Six were male and one was female, in the age range of 46–63 years (median age, 57 years). They had had their initial diagnosis of malignant MCL 2–6 years previously. All seven had had cyclophosphamide, hydroxydaunomycin, vincristine, and prednisone (CHOP) or cyclophosphamide, vincristine, doxorubicine, etoposide, prednisolone (CHOEP) as first-line chemotherapy, all had relapsed, and all had undergone high-dose chemotherapy (mostly following the dexamethasone + BCNU, etoposide, arabinoside, and melphalane [Dexa-BEAM/high-dose (BEAM)] regimen) with autologous stem cell transplantation. Four had had total-body irradiation with 12 Gy, and one had had an involved-field irradiation of the abdo- men and pelvis (30 Gy) instead. Two patients had had abdominal irradiation (24 Gy each) in addition to the 12 Gy total-body irradiation. All patients had relapsed despite these high-dose chemotherapy or radiotherapy regimens. Three of these patients had had “cold” anti-CD20 immunotherapy with C2B8 (Mabthera), two of them originally experiencing a PR, but progressed within 4 weeks after the end of Mabthera therapy; one even progressed while receiving this immunotherapy.
In all but one patient, stem cells were available from the initial harvest for the high-dose chemotherapy, whereas in one patient (Patient 5 in Table 1), a fresh stem cell harvest was performed. No purging steps were taken during stem cell preparation.
All patients underwent a diagnostic-dosimetric scan before undergoing high-dose radioimmunotherapy, so that normal organ dosimetry could be assessed. Approximately 10 mCi of 131I-C2B8 were infused at a total protein dose of 2.5 mg/kg (1–2 mg labeled monoclonal antibody substituted with unlabeled C2B8) over approximately 30 minutes. The three patients who had been treated with C2B8 (Mabthera) before did not show any side effects during radioantibody infusion, whereas three of the other four showed mild-to-moderate (common toxicity criteria [CTC] Grade 2–3) signs of cytokine release (chills, fever, itching sensations in the nose and throat, and pain in tumor manifestations). In five patients, plasma half-lives of 24–48 hours were observed, whereas Patient 7 (Table 1), who was a patient with marked splenomegaly, showed a rapid radioantibody clearance from the blood (serum half-life, 5.1 hours) and an intense uptake in the enlarged and involved spleen. In this patient, two additional diagnostic scans were performed by doubling the protein doses (5 and 10 mg/kg) until a more favorable biodistribution was reached at 10 mg/kg (serum half-life, 37.3 hours) (Fig. 1A, B).
Table 2 shows the mean whole-body, red marrow, organ, and tumor dosimetry of 131I-C2B8 in these MCL patients. Therapeutic activities were calculated to yield lung doses of not higher than 27 Gy and restrict the maximum activity to 500 mCi, due to radioactivity handling license restrictions.
|Whole-body||1.9 ± 0.4|
|Red marrow||5.2 ± 1.1|
|Brain/lenses||0.8 ± 0.3|
|Intestines||1.4 ± 0.7|
|Kidneys||6.5 ± 2.8|
|Liver||5.4 ± 3.1|
|Lungs||5.2 ± 2.6|
|Spleen||17.2 ± 6.1|
|Ovaries/Testes||0.8 ± 0.4|
|Thyroid||124 ± 47|
|Urinary bladder||3.3 ± 0.8|
|Tumor||14.3 ± 5.9|
The projected whole-body doses were approximately 10 Gy, the liver and kidney doses up to 35 Gy, the red marrow doses in similar ranges, whereas tumor doses of up to 100 Gy were predicted. Despite cold iodine blocking, predicted thyroid doses ranged up to 600 Gy.
Iodine-131–C2B8 Therapy Injection, Side Effects, and Toxicity
All seven patients included in this study were treated with myeloablative doses of 131I-C2B8 at the activities and protein doses determined by their respective diagnostic-dosimetric studies. Myelotoxicity and its associated problems were the leading side-effects of therapy. Blood cell nadirs were reached at 2–3 weeks after therapy infusion, but all patients reengrafted at 7–10 days after stem cell reinfusion. Figure 2 shows, in an exemplary manner, the blood cell counts in a patient and his hematologic recovery following stem cell transfusion. Typically, the patients went into aplasia within 2 weeks, and the whole-body activity fell below 20 mCi within 3 weeks, the very time of stem cell reinfusion. After 7–10 days, white blood cells began to recover, followed by platelets slightly later. Daily granulocyte-colony stimulating factor and regular platelet transfusions were necessary for about 3 weeks (Fig. 2). All patients developed neutropenic fever, which was overcome in all cases by antibiotic or antimycotic regimens, or both.
Nonhematologic acute toxicity was restricted to transient and self-limiting mild-to-moderate nausea, slight and rapidly transient bilirubin or liver enzyme elevations, and mild-to-moderate dyspepsia. Only one patient (Patient 7, Table 1) with preexisting alcoholic cirrhosis experienced a substantial deterioration of liver function. At 8 weeks after therapy, he presented with severe and increasing ascites (Fig. 1C), and a liver biopsy showed signs of progressive hepatic cirrhosis. His liver had previously been exposed to 24 Gy abdominal external beam plus 12 Gy total-body irradiation. His estimated liver dose by high-dose RIT was another 35 Gy, which may explain this increased hepatic toxicity in this particular case. In one patient, signs of an asymptomatic radiation pneumonitis were detected in the 3-month follow-up chest CT; this rapidly resolved with steroid treatment and further sequelae. Despite thyroid blocking, five of seven patients developed (at least subclinical) hypothyroidism, as indicated by rising thyroid-stimulating hormone levels during follow-up, requiring thyroxine substitution at 6–18 months after RIT.
Since the first patient in this cohort (Patient 1, Table 1) experienced a complete lasting for more than 2 years (discussed later in this article), and since stem cells were still available when he systemically relapsed with a chemorefractory leukemic form of his NHL, he was considered for a second high-dose RIT as the only potentially effective treatment option. After having been treated with 495 mCi 131I-C2B8 the first time (estimated lung dose, 23 Gy), his second injection was calculated to limit the cardiopulmonary dose to 14 Gy (corresponding to 326 mCi 131I-C2B8). Although the patient rapidly responded to the therapy injection with a rapid decrease in lymph node sizes and complete disappearance of leukemic blasts, he developed rapidly rising liver enzyme and bilirubin levels as well as rapidly decreasing kidney function parameters. He died of multiorgan failure 5 weeks after this second high-dose therapy injection.
Six of the seven patients experienced complete remission, and the seventh a partial remission. Interestingly, the latter patient (Patient 4, Table 1) received only about half of the therapeutic activity (261 mCi 131I-C2B8) compared with the other patients, due to a more intense lung uptake; thus, a cardiopulmonary dose of 27 Gy was anticipated at this lower activity level. Consequently, his other normal organ and tumor doses were only approximately half as high as in all other patients.
The maximum therapeutic effect was seen during the 3-month follow up, although a substantial tumor shrinkage (corresponding to good partial responses) had already been seen in all cases in the 1-month CT scans (Fig. 1C, Fig. 3). At a median observation time of 25 months, five patients were still in complete remission and six were still alive for up to 3 years or more (Fig. 4); one patient (Patient 4, who had only experienced a partial response before) relapsed locally at 3 months, requiring external radiotherapy; and one patient relapsed systemically (with leukemic relapse) at 26 months after RIT as described above, then died of multiorgan failure after a high-dose RIT retreatment.
Whereas most published radioimmunotherapy trials of hematologic malignancies had low-grade NHL as a major target,6–8, 19, 20 some more recent reports have covered more and less differentiated stages of B-cell maturation and their associated malignancies, including mantle cell lymphoma.9 Although regarded as a form of low-grade NHL, the latter is generally regarded as rather therapy-resistant.1–4
Although the number of patients in this initial report is rather small, there are nevertheless some clearly visible trends. The first and most important is that the preliminary therapeutic results reported here seem very encouraging. In contrast to published results from conventional low-dose radioimmunotherapy trials,13 high response rates seem to be achievable by high-dose myeloablative regimens, and the preliminary relapse-free survival rates are noteworthy, given the fact that all patients in this study had previously experienced failure or relapse with high-dose chemotherapy, approximately half of them even in combination with total-body irradiation. The finding that therapeutic results improve with increasing aggressiveness of the therapeutic regimen, which is well in accord with earlier NHL RIT studies,7–9 is supported by the finding that the patient with the lowest therapy activity administered relapsed after only 3 months, whereas the only other relapse in this study occurred after more than 2 years.
The fatal treatment-related outcome for this retreated patient needs a closer analysis. This patient had very advanced Stage IV MCL at the time of diagnosis. He had relapsed 11/2 years after high-dose chemotherapy that included 12 Gy total-body irradiation. An additional estimated whole-body dose of approximately 10 Gy resulted from his first high-dose RIT. Most likely, the normal organ tolerance was exceeded by the second high-dose RIT. Similarly, the deterioration of a preexisting alcoholic cirrhosis at an estimated total liver dose of approximately 71 Gy (35 Gy from RIT, 36 Gy from previous external beam) is easily explained by the normal organ tolerance being exceeded.
Thyroid radiation doses showed a high variability in this communication, as was the case in several earlier radioimmunotherapy studies that used radioiodinated immunoconjugates.21 We were able to show that the maximal iodine uptake in the thyroid was less than 1% of the injected activity, indicating that more than 99% of the thyroid was blocked in all cases.21 No correlation had been found between these thyroid doses and conditions leading to an enhanced exposure to free radioiodine, such as unbound I− in the radioantibody preparation, enhanced metabolic breakdown of the labeled antibody due to human anti-MAb antibodies (human antimouse antibodies [HAMA], human antichimeric antibodies [HACA], or human antihuman antibodies [HAHA]), or immune complex formation with circulating antigens.21 However, a relationship between the thyroid doses and the patients' compliance in taking their cold iodide-blocking medications was found.21 Whereas no rising thyroid-stimulating hormone titers or other signs of (latent) hypothyroidism were seen in low-dose therapy patients during a 2-year follow-up period,15, 20, 21 the considerably higher activities in this myeloablative study led to significantly higher thyroid doses, eventually causing hypothyroidism.7–9, 21
At 14.3 ± 5.9 cGy/mCi, the calculated tumor doses were somewhat higher than usually observed with radioiodinated anti-B-cell antigen antibodies. This may be partially due to the finding that several of these patients had tumor manifestations in the spleen, which is the normal organ with the second-highest absorbed radiation dose. This may have led to some overestimation of the actual intrasplenic tumor doses. On the other hand, calculated tumor doses from intra- and extrasplenic sites were not significantly different in this patient cohort. However, dosimetric data from a larger patient population are needed to get a more reliable appreciation of whether achievable tumor doses may be higher for MCL than for other forms of low-grade NHL.
The finding that several patients in this study had had unlabeled antibody treatment previously without enduring clinical response, but responded to the labeled therapy, clearly supports the concept that RIT combines two primarily independent therapeutic principles, namely, the immunologic approach and a form of internal radiotherapy. Both therapeutic principles may have a synergistic therapeutic efficacy. The lack of significant immune responses (HAMA, HACA, and HAHA) to the chimeric or humanized antibodies enables successful RIT even after failure of naked antibody treatment and allows for pretherapeutic dosimetry without jeopardizing the therapeutic infusion of HACA or HAHA.9, 15
Figure 4 compares the failure-free and overall survival curves of the MCL patients treated in this study with high-dose RIT, compared with published courses of disease treated with standard CHOP chemotherapy and compared with published courses of other forms of follicular lymphoma treated with CHOP.1 The curves suggest promising relapse-free and overall survival under this dose-intensified RIT regimen, but much longer follow-up of larger patient cohorts is necessary before final judgments can be made.
In summary, high-dose myeloablative RIT with 131I-labeled anti-CD20 antibodies seems to be associated with a high response rate and moderate toxicity in patients with MCL. Further follow-up to monitor the long-term outcomes, as well as systematic prospective clinical studies, are indicated. Future studies will show whether high-dose RIT with stem cell support, especially when applied earlier in the course of treatment, might be able to induce longer-lasting remissions or even be curative in this hematologic malignancy, which is known to be otherwise somewhat refractory to therapy. Combination approaches with high-dose chemotherapy, myeloablative radioimmunotherapy, and stem cell support may offer new therapeutic opportunities to achieve this goal.
The expert technical assistance of Ms. D. Hempel, Ms. M. Pleuger, Ms. S. Bätzing, Ms. M. Werner, and Ms. M. Ghorbani in the imaging of patients is gratefully acknowledged. The authors also express their gratitude to Ms. E. Weber for her help in dosimetry calculations.
- 1Non-Hodgkin's lymphoma. In: DeVitaJr. VT, H ellmanS, RosenbergSA, editors. Cancer: principles and practice of oncology. 5th ed. Philadelphia: Lippincott-Raven, 1997: 2165–220., , .
- 9Low- versus high-dose radioimmunotherapy with humanized anti-CD22 or chimeric anti-CD20 antibodies in a broad spectrum of B cell-associated malignancies. Clin Cancer Res 1999; 5: 3304–14., , , , , , et al.
- 10The leukocyte antigen facts book. London: Academic Press, 1993., , , , , , et al.
- 15Treatment of Non-Hodgkin's lymphoma with radiolabeled murine, chimeric, or humanized LL2, an anti-CD22 monoclonal antibody. Cancer Res 1995; 55: 5899–907., , , , , , et al.
- 17An automated scheme for internal radiation dosimetry in nuclear therapy: gamma- or bremsstrahlung-based dose calculation in the therapy of differentiated thyroid cancer, radio-synoviorthesis, bone pain palliation and radioimmunotherapy. J Nucl Med 1997; 38: 225P., , , , , .