Effective childhood cancer treatment: the impact of large scale clinical trials in Germany and Austria.

In Germany and Austria, more than 90% of pediatric cancer patients are enrolled into nationwide disease-specific first-line clinical trials or interim registries. Essential components are a pediatric cancer registry and centralized reference laboratories, imaging review, and tumor board assistance. The five-year overall survival rate in countries where such infrastructures are established has improved from <20% before 1950 to >80% since 1995. Today, treatment intensity is tailored to the individual patient's risk to provide the highest chances of survival while minimizing deleterious late effects. Multicenter clinical trials are internationalized and serve as platforms for further improvements by novel drugs and biologicals.

The ganglioside antigen G(D2) is surface-expressed in Ewing sarcoma and allows for MHC-independent immune targeting.

BACKGROUND: Novel treatment strategies are needed to cure disseminated Ewing sarcoma. Primitive neuroectodermal features and a mesenchymal stem cell origin are both compatible with aberrant expression of the ganglioside antigen G(D2) and led us to explore G(D2) immune targeting in this cancer. METHODS: We investigated G(D2) expression in Ewing sarcoma by immunofluorescence staining. We then assessed the antitumour activity of T cells expressing a chimeric antigen receptor specific for G(D2) against Ewing sarcoma in vitro and in vivo. RESULTS: Surface G(D2) was detected in 10 out of 10 Ewing sarcoma cell lines and 3 out of 3 primary cell cultures. Moreover, diagnostic biopsies from 12 of 14 patients had uniform G(D2) expression. T cells specifically modified to express the G(D2)-specific chimeric receptor 14. G2a-28ζ efficiently interacted with Ewing sarcoma cells, resulting in antigen-specific secretion of cytokines. Moreover, chimeric receptor gene-modified T cells from healthy donors and from a patient exerted potent, G(D2)-specific cytolytic responses to allogeneic and autologous Ewing sarcoma, including tumour cells grown as multicellular, anchorage-independent spheres. G(D2)-specific T cells further had activity against Ewing sarcoma xenografts. CONCLUSION: G(D2) surface expression is a characteristic of Ewing sarcomas and provides a suitable target antigen for immunotherapeutic strategies to eradicate micrometastatic cells and prevent relapse in high-risk disease.

PET surveillance of patients with Ewing sarcomas of the trunk: Must the lower legs be included?

AIM: FDG-PET(/CT) is frequently used in surveillance of Ewing sarcoma (ES) patients. Since ES and PNET (primitive neuroectodermal tumours) may cause peripheral metastases some centers routinely recommend whole body PET acquisition from head to toe what may necessitate repositioning of the patient and thus extending examination time. It is not clear yet whether inclusion of lower leg adds to the diagnostic accuracy of PET scanning, especially in primary tumors of the trunk. PATIENTS, METHOD: 40 patients with ES and PNET of the trunk who were referred for surveillance after primary therapy with complete remission, were evaluated retrospectively: 27 men, 13 women; mean age at diagnosis 16.3 (3-35) years. At the time of diagnosis 28 patients had localized and 12 metastatic disease. Almost all of the patients had undergone a combined chemotherapy with surgery or/and radiotherapy. 156 follow-up PET scans of the legs of these patients were evaluated retrospectively. RESULTS: only in three (1.9%) of 156 scans a pathologic FDG accumulation was attributed to metastatic disease of the lower extremities. In these cases the observation of metastatic disease in the legs did not alter therapy, since in all three cases a multifocal disease progression was observed. CONCLUSION: scanning of the lower legs may be omitted during follow-up in patients in whom the primary tumor was located in the trunk and in whom no clinical signs pointing to metastases in the lower legs are present. This provides a sufficient diagnostic power and a shorter examination time, thus increasing patient comfort and scanner availability.

[Procedure guidelines for whole-body 18F-FDG PET and PET/CT in children with malignant diseases]. / Empfehlungen zur Durchführung der Ganzkörper-18F-FDG-PET und -PET/CT bei Kindern mit onkologischen Erkrankungen. Anpassung der EANM-Guideline an aktuelle Gegebenheiten in Deutschland.

The purpose of these guidelines is to offer the nuclear medicine and the appropriate interdisciplinary team a framework for performing and reporting positron emission tomography (PET) and the combination with computed tomography (PET/CT) in children with malignant diseases mainly using the radiopharmaceutical 18F-fluorodeoxy-glucose (FDG). These guidelines are based on the recent guidelines of the Paediatric Committee of the European Association of Nuclear Medicine (EANM) (57) and have been translated and adapted to the current conditions in Germany. The adaptation of CT-parameters using PET/CT in children is covered in a more detailed way than in the EANM guideline taking into account that in Germany already a good portion of PET examinations is performed using an integrated PET/CT-scanner. Furthermore, a CT-scan without adoption of the CT acquisition parameters would result in a not tolerably high radiation exposition of the child. There are excellent guidelines for FDG PET and PET/CT in oncology published by the German Society of Nuclear Medicine (Deutsche Gesellschaft für Nuklearmedizin, DGN) (42) and EANM (4). These guidelines aim at providing additional information on issues particularly relevant to PET and PET/CT imaging in children. These guidelines should be taken in the context of local and national current standards of quality and rules.

Microsatellite instability in Ewing tumor is not associated with loss of mismatch repair protein expression.

Only few clinical factors predict the prognosis of patients with Ewing tumors. Unfavorable outcome is associated with primary metastatic disease, age > 15 years, tumor volume above 200 ml, and the histological response to chemotherapy. The aim of this study was to elucidate the prevalence and clinical impact of microsatellite instability (MSI) together with the relation between MSI and mismatch repair protein expression in Ewing tumors. DNA from 61 primary Ewing tumors and 11 Ewing tumor cell lines was extracted and microsatellite analysis for the detection of instability or loss of heterozygosity was performed for the five markers of the Bethesda panel BAT25, BAT26, D5S346, D2S123, and D17S250, which represents the established marker panel for the analysis of hereditary non-polyposis colorectal carcinoma (HNPCC) patients. In addition, single nucleotide repeat regions of the two tumor genes BAX and transforming growth factor receptor II (TGFBR2) were also included. All of the 61 samples were suitable for LOH analysis and 55 for the determination of MSI-status. LOH of these microsatellite markers was detected in 9 of the 61 patients (14.8%). Over all, genetic instability, i.e. MSI and/or LOH, was detected in 17 tumors (27.9%). One out of the 11 tumor cell lines (STA ET1) was characterized by instability of all the five Bethesda markers, while from primary tumor samples, only one showed MSI in more than one microsatellite marker (D5S346 and D17S250, MSI-high). Eight of the fifty-five patients (14.5%) showed instability of one microsatellite locus (MSI-low). No instability was detected in BAT26, D2S123, BAX and TGFBR2. There was no significant correlation between MSI and loss of expression of mismatch repair proteins MLH1, MSH2, or MSH6. The impairment of the p53 signaling pathway (expression of TP53 and/or MDM2 by immunohistochemistry) was significantly associated with reduced overall survival (15 of 49 patients (30.6%), P = 0.0410, log-rank test). We conclude that MSI is not prevalent in Ewing tumor and that the nature of instability differs from the form observed in colorectal carcinoma, the model tumor of MSI. This is documented by the different pattern of MSI (no BAT26 instability) in Ewing tumors and the lack of a strict correlation between MSI-high and loss of expression of MSH2, MSH6 and MLH1.

Telomerase activity and telomerase subunits gene expression patterns in neuroblastoma: a molecular and immunohistochemical study establishing prognostic tools for fresh-frozen and paraffin-embedded tissues.

PURPOSE: We have recently demonstrated that telomerase activity (TA) is an independent prognostic factor in neuroblastomas. In the present study, the prognostic impact of TA and gene expression of the three major telomerase subunits is evaluated by molecular and immunohistochemical techniques in fresh-frozen and paraffin-embedded tissues. PATIENTS AND METHODS: One hundred thirty-three neuroblastomas of all stages were analyzed for TA. The TA levels of 75 neuroblastoma cases were correlated with gene expression of telomerase subunits hTRT, human telomerase RNA (hTR), and telomerase protein 1 (TP1) by quantitative reverse transcriptase polymerase chain reaction (RT-PCR), using an innovative approach on the LightCycler instrument (Roche Diagnostics, Mannheim, Germany). For selected cases, the applicability of RT-PCR and immunohistochemistry for hTRT expression analysis was investigated in paraffin-embedded tissues. TA and subunit expression patterns were correlated with traditional prognostic indicators and disease outcome. RESULTS: TA was present in a total of 39 (29.3%) of 133 neuroblastomas and in 31 (29.8%) of 104 initial neuroblastomas without cytotoxic pretreatment. TA was significantly correlated with both event-free and overall survival (P <.0001). Furthermore, we found a significant correlation between expression levels of TA and hTRT (P <.0001) as well as hTR (P <.001). Multivariate analysis revealed only TA and tumor stage but not serum lactate dehydrogenase, MYCN amplification, or age at diagnosis as independent prognostic factors. CONCLUSION: The significant correlation with clinical outcome strongly recommends that analysis of TA be incorporated into the clinical investigation of each individual neuroblastoma at the time of diagnosis. Because the mere presence or absence of TA without further quantification is sufficient basis for predicting disease outcome, the telomeric repeat amplification protocol assay could be complemented with but not replaced by analysis of hTRT or hTR expression.

High-dose therapy for patients with primary multifocal and early relapsed Ewing's tumors: results of two consecutive regimens assessing the role of total-body irradiation.

PURPOSE: Risk stratification of metastatic and relapsed Ewing's tumors (ETs) has been a matter of debate during the last decade. Patients with bone or bone marrow metastases or early or multiple relapses constitute the worst risk group in ET and have a poorer prognosis than patients with primary lung metastases or late relapses. In this article, the results of the present Meta European Intergroup Cooperative Ewing Sarcoma Study (MetaEICESS) (tandem melphalan/etoposide [TandemME]) were compared with the result of the previous study (hyper melphalan/etoposide [HyperME]), both at 5 years, in a patient population within the same high-risk stratum to determine toxicity. PATIENTS AND METHODS: Among 54 eligible patients, 26 were treated according to the HyperME protocol, and 28 were treated according to TandemME protocol. Patients received six cycles of the Cooperative Ewing Sarcoma Study treatment in HyperME and six cycles of the EICESS treatment in TandemME as induction chemotherapy. Patients also received involved-compartment irradiation for local intensification and myeloablative systemic intensification consolidation with hyperfractionated total-body irradiation (TBI) combined with melphalan/etoposide in HyperME or two times the melphalan/etoposide in TandemME followed by autologous stem-cell transplantation. RESULTS: The event-free survival (EFS) rate +/- SD in HyperME and TandemME was 22% +/- 8% and 29% +/- 9%, respectively. The dead of complication rate was 23% in HyperME and 4% in TandemME. CONCLUSION: TandemME offers a decent, albeit still not satisfactory, rate of long-term remissions in most advanced ETs (AETs), with short-term treatment and acceptable toxicity. TBI was not required to maintain EFS level in this setting but was associated with a high rate of toxic death. Future prospective studies in unselected patients are warranted to evaluate high-dose therapy in an unselected group of patients with AET.

EWS-FLI1 and EWS-ERG gene fusions are associated with similar clinical phenotypes in Ewing's sarcoma.

PURPOSE: There are a variety of solid tumors in which alternative chromosomal translocations generate related fusion products. In alveolar rhabdomyosarcoma and synovial sarcoma, these variant fusions have been found to have major clinical significance. We investigated whether the two alternative gene fusion products, EWS-FLI1 and EWS-ERG, define different clinical subsets within the Ewing's sarcoma family of tumors. PATIENTS AND METHODS: We selected 30 cases of Ewing's sarcoma with the EWS-ERG gene fusion and 106 cases with the EWS-FLI1 fusion. Clinical data were obtained for each case and compared with the molecular diagnostic findings. RESULTS: There were no significant clinical differences observed between the two groups in age of diagnosis, sex, metastasis at diagnosis, primary site, event-free survival, or overall survival. CONCLUSION: Differences in the C-terminal partner in the Ewing's sarcoma family gene fusions are not associated with significant phenotypic differences.

A randomized comparative study of esomeprazole 40 mg versus pantoprazole 40 mg for healing erosive oesophagitis: the EXPO study.

AIM: To assess the efficacy of the 8-week therapy with esomeprazole 40 mg vs. pantoprazole 40 mg for healing erosive oesophagitis (EE) as part of a management study. METHODS: Patients had a history of gastro-oesophageal reflux disease symptoms (> or =6 months) and had suffered heartburn on at least 4 of the 7 days preceding enrollment. Endoscopies were performed to grade EE severity using the Los Angeles (LA) classification system at baseline, 4 and 8 weeks (if unhealed at 4 weeks). Heartburn severity was recorded by patients on diary cards. The primary end point was healing of EE by week 8 of treatment. RESULTS: Of 3170 patients randomized, the intent-to-treat population consisted of 3151 patients (63% male, mean age: 50.6 years, 27% Helicobacter pylori-positive). Esomeprazole 40 mg healed a significantly greater proportion of EE patients than pantoprazole 40 mg at both 4 weeks (life table estimates: esomeprazole 81%, pantoprazole 75%, P < 0.001) and 8 weeks (life table estimates: esomeprazole 96%, pantoprazole 92%, P < 0.001). The median time to reach sustained heartburn resolution was 6 days in patients receiving esomeprazole and 8 days with pantoprazole (P < 0.001). CONCLUSION: Esomeprazole 40 mg is more effective than pantoprazole 40 mg for healing EE and providing resolution of associated heartburn.

Esomeprazole 20 mg vs. pantoprazole 20 mg for maintenance therapy of healed erosive oesophagitis: results from the EXPO study.

BACKGROUND: Following initial healing of erosive oesophagitis, most patients require maintenance therapy to prevent relapse. AIM: To compare endoscopic and symptomatic remission rates over 6 months' maintenance therapy with esomeprazole or pantoprazole (both 20 mg once daily) in patients with healed erosive oesophagitis. METHODS: Patients with symptoms of gastro-oesophageal reflux disease and endoscopically confirmed erosive oesophagitis at baseline were randomized to receive esomeprazole 40 mg or pantoprazole 40 mg for up to 8 weeks. Patients with healed erosive oesophagitis and free of moderate/severe heartburn and acid regurgitation at 4 weeks or, if necessary, 8 weeks entered the 6-month maintenance therapy phase of the study. RESULTS: A total of 2766 patients (63% men; mean age 50 years) received esomeprazole 20 mg (n = 1377) or pantoprazole 20 mg (n = 1389) and comprised the intention-to-treat population. Following 6 months of treatment, the proportion of patients in endoscopic and symptomatic remission was significantly greater for those receiving esomeprazole 20 mg (87.0%) than pantoprazole 20 mg (74.9%, log-rank test P < 0.0001). Esomeprazole 20 mg produced a higher proportion of patients free of moderate to severe gastro-oesophageal reflux disease symptoms and fewer discontinuations because of symptoms than pantoprazole 20 mg (92.2% vs. 88.5%, P < 0.001). CONCLUSIONS: Esomeprazole 20 mg is more effective than pantoprazole 20 mg for maintenance therapy following initial healing of erosive oesophagitis and relief of gastro-oesophageal reflux disease symptoms.

Efficacy and kinetics of bone marrow processing and enrichment of haematopoietic progenitor cells (HPC) by a large-volume apheresis procedure.

We investigated the efficacy of bone marrow (BM) processing by an automated large-volume apheresis procedure (6 x original BM volume) in 10 paediatric and adult patients undergoing BM harvesting before myeloablative therapy. Volume-dependent kinetics during apheresis were analyzed by sequential collection of processed cells into a six-fold collection bag system with consecutive analysis of the single bags. BM processing resulted in an 83.3% (+/- 21) recovery of mononuclear cells (MNC), a 97.9% (+/- 1.1) reduction of erythrocytes (RBC) and a 87.7% (+/- 2.9) volume reduction. To determine volume-dependent kinetics of haematopoietic progenitor cell (HPC) enrichment during apheresis, leukocytes (WBC), mononuclear cells (MNC), CD34 cells and colony-forming cells (CFU-GM) were serially quantitated in subsequent collection bags. Large-volume BM processing significantly enhanced absolute yields of CD34+ cells (mean: 4.01 (+/- 2.81) x 10(6)/kg bw) and CFU-GM (mean: 1.92 (+/- 1.47) x 10(4)/kg bw) compared with the standard procedure (3 x BM volume) by 26.9% (+/- 10.9) and 27.2% (+/- 11.6), respectively. We concluded that large-volume apheresis for BM processing is an efficient technique significantly improving the yields of haematopoietic progenitor cells (HPC) without any relevant changes in the purity of the final product. Moreover, sequential collection and analysis of HPC represents a good model to investigate the volume-dependent kinetics and efficacy of BM processing.

NK cells are dysfunctional in human chronic myelogenous leukemia before and on imatinib treatment and in BCR-ABL-positive mice.

Although BCR-ABL+ stem cells in chronic myeloid leukemia (CML) resist elimination by targeted pharmacotherapy in most patients, immunological graft-versus-leukemia effects can cure the disease. Besides cytotoxic T cells, natural killer (NK) cells may have a role in immune control of CML. Here, we explored the functionality of NK cells in CML patients and in a transgenic inducible BCR-ABL mouse model. Compared with controls, NK-cell proportions among lymphocytes were decreased at diagnosis of CML and did not recover during imatinib-induced remission for 10-34 months. Functional experiments revealed limited in vitro expansion of NK cells from CML patients and a reduced degranulation response to K562 target cells both at diagnosis and during imatinib therapy. Consistent with the results in human CML, relative numbers of NK1.1+ NK cells were reduced following induction of BCR-ABL expression in mice, and the defects persisted after BCR-ABL reversion. Moreover, target-induced degranulation by expanded BCR-ABL+ NK cells was compromised. We conclude that CML is associated with quantitative and functional defects within the NK-cell compartment, which is reproduced by induced BCR-ABL expression in mice. Further work will aim at identifying the mechanisms of NK-cell deficiency in CML and at developing strategies to exploit NK cells for immunotherapy.

Delay in B-lymphocyte recovery and function following rituximab for EBV-associated lymphoproliferative disease early post-allogeneic hematopoietic SCT.

Treatment with rituximab is highly effective for EBV-associated post transplant lymphoproliferative disease. However, little is known about its immunological sequelae in pediatric allogeneic hematopoietic SCT (HSCT). Time to normal CD19+ B-lymphocyte values in blood and intravenous immunoglobulin (IVIG) substitution needed to maintain an IgG>400 mg per 100 ml in six consecutive pediatric allogeneic HSCT patients treated with rituximab for symptomatic EBV reactivation were compared with a matched cohort of non-rituximab-treated patients. Follow-up of the six patients ranged from 149 to 1546 days; all but one survived. The mean (+/-s.d.) time to recovery of CD19+ B-lymphocytes was 353+/-142 days as compared with 139+/-42 in the controls (P<0.01). Similarly, substitution of IVIG as a measure of functional B-cell recovery was extended from a mean of 122+/-45 to a mean of 647+/-320 days, and the cumulative dose of IVIG increased from a mean of 1.86+/-0.51 to 4.4+/-0.97 g/kg, respectively (P<0.05). One patient had functional B-lymphocyte deficiency for >3 years and ultimately required two stem cell boosts. Rituximab is a live-saving treatment for pediatric HSCT patients but may lead to prolonged and even persistent B-cell deficiency.

CD28 co-stimulation via tumour-specific chimaeric receptors induces an incomplete activation response in Epstein-Barr virus-specific effector memory T cells.

Expression of tumour antigen-specific chimaeric receptors in T lymphocytes can redirect their effector functions towards tumour cells. Integration of the signalling domains of the co-stimulatory molecule CD28 into chRec enhances antigen-specific proliferation of polyclonal human T cell populations. While CD28 plays an essential role in the priming of naive CD4(+) T cells, its contribution to effector memory T cell responses is controversial. We compared the function of the chRec with and without the CD28 co-stimulatory domain, expressing it in peripheral blood T cells or Epstein-Barr virus (EBV)-specific T cell lines. The chimaeric T cell receptors contain an extracellular single-chain antibody domain, to give specificity against the tumour ganglioside antigen G(D2). The transduced cytotoxic T lymphocytes (CTL) maintained their specificity for autologous EBV targets and their capacity to proliferate after stimulation with EBV-infected B cells. Intracellular cytokine staining demonstrated efficient and comparable antigen-specific interferon (IFN)-gamma secretion by CTL following engagement of both the native and the chimaeric receptor, independent of chimaeric CD28 signalling. Furthermore, tumour targets were lysed in an antigen-specific manner by both chRec. However, while antigen engagement by CD28 zeta chRec efficiently induced expansion of polyclonal peripheral blood lymphocytes in an antigen-dependent manner, CD28 signalling did not induce proliferation of EBV-CTL in response to antigen-expressing tumour cells. Thus, the co-stimulatory requirement for the efficient activation response of antigen-specific memory cells cannot be mimicked simply by combining CD28 and zeta signalling. The full potential of this highly cytolytic T cell population for adoptive immunotherapy of cancer requires further exploration of their co-stimulatory requirements.

The inability of oral leucovorin to elevate CSF 5-methyl-tetrahydrofolate following high dose intravenous methotrexate therapy.

Osteosarcoma patients free of CNS metastases are at risk for acquiring leukoencephalopathy after receiving multiple courses of high dose intravenous methotrexate followed by oral leucovorin rescue (MTX-LV). A prospective study of the adequacy of CNS rescue of MTX biochemical toxicity by oral leucovorin was undertaken in newly diagnosed neurologically normal osteosarcoma patients. Prior to surgical resection of the primary tumor, ten patients received 4 weekly courses of MTX-LV. During the fourth weekly MTX-LV treatment, 0 and 72 hr serum and CSF determinations of MTX, 5-methyl-tetrahydrofolate (5-MTHF) and LV were made. No CSF MTX was detectable at 0 hr in any patient, but a significant elevation in CSF MTX occurred in 9/9 patients at 72 hr (mean 47.2 +/- 31.8 ng/ml or 1.04 +/- 0.7 X 10(-7) M). There was no significant change in mean CSF 5-MTHF over 72 hr despite a rise in serum 5-MTHF. MTX exceeded 5-MTHF in 6/9 patients in CSF, whereas only 3/8 patients had higher MTX in the serum at 72 hr. No acute systemic or neurotoxicity was seen. The failure of oral leucovorin to consistently elevate CSF 5-MTHF levels at 72 hr in the context of significant levels of CSF MTX may result in intermittent CNS folate deficiency. The clinical and pathological syndrome of leukoencephalopathy may be related to this phenomenon and may evolve after repeated MTX-LV treatments.

Chemical and immunological characteristics of four different L-asparaginase preparations.

We studied the differences in protein composition and immunologic reactivity of two E. coli-derived L-asparaginase (l-Asp) preparations (I and II), Erwinia-Asp (III) and PEG-modified E. coli l-Asp (IV). On gel filtration, each of preparations I-III showed three major peaks at 100, 270 and 460 KD, all with enzyme activity, whereas PEG-Asp showed peaks at 35 and 220 KD. On SDS-PAGE one major subunit could be identified at 32 KD (I and II) or 40 KD (III), whereas PEG-modified l-Asp could only be detected by lowering the polyacrylamide concentration and gave a single band above 200 KD. Using a polyclonal rabbit antibody generated against preparation I, only the E. coli l-Asp preparations (I and II) formed precipitin lines on Ouchterlony double diffusion. After freezing and thawing, preparation IV also reacted with this antibody. In sera from patients treated with preparation I, antibodies (detected by ELISA) reacted with preparations I and II but not with preparations III and IV. These results indicate that Erwinia-Asp (III) and PEG-Asp (IV) are distinct from E. coli preparations (I and II) by molecular weight and immunological behavior. They also provide an experimental rationale for the use of Erwinia-Asp as well as PEG-Asp in E. coli Asp-sensitized patients.

Elimination of l-asparaginase in children treated for acute lymphoblastic leukemia.

The elimination of l-asparaginase (l-Asp) was studied in 8 children treated for acute lymphoblastic leukemia according to the CoALL 82 protocol. The patients received four doses of l-Asp as a single agent during induction chemotherapy. We studied the elimination of l-Asp during the first infusion in 1 child, during the second in 3, during the third in 2 and during the forth in 2 children. Using Western blot technique and an experimental rabbit antibody to l-Asp, we were able to detect a single band at 32 kilodaltons (KD) in the serum of all patients between 4 and 36 h after infusion. The molecular weight remained unchanged and no other bands occurred during the time of observation. The detection limit of this method was calculated to 5 micrograms/ml using radial immunodiffusion. Incubation of l-Asp with pooled normal human serum caused no degradation of the enzyme during 48 h at 37 degrees C. Neither the total enzyme nor fragments were detectable in the urine of the patients collected during 8 h after l-Asp infusion. From these results we conclude that l-Asp is not cleaved by proteases in humans. The enzyme is most probably eliminated by the reticuloendothelial system.