Clinical and cell biological features related to cellular drug resistance of childhood acute lymphoblastic leukemia cells

Several clinical and cell biological features, such as sex, age, leukemic cell burden, morphologic FAB type, and immunophenotype, have prognostic value in childhood acute lymphoblastic leukemia (ALL). The explanation for their prognostic significance is unclear, but might be related to cellular drug resistance. We prospectively studied the relation between the above mentioned features with resistance to 13 drugs in 144 childhood ALL samples obtained at initial diagnosis. The MTT assay was used for drug resistance testing. The interindividual differences in drug resistance were very large and exceeded those between the several subgroups. There was generally no significant relation between sex, leukemic cell burden, and FAB type with drug resistance. However, subgroups with a worse prognosis as defined by age (< 18 months and > 120 months at diagnosis) or immunophenotype (pro-B ALL and T-ALL) did show relatively resistant drug resistance profiles as compared to the subgroups with a better prognosis (age 18-120 months, common and pre-B ALL). Within the group of common and pre-B ALL and compared to the intermediate age-group, samples of the younger children were significantly more resistant to daunorubicin, mitoxantrone and teniposide, and samples of the older children were significantly more resistant to prednisolone and mercaptopurine. Pro-B ALL samples were significantly more resistant to 1-asparaginase and thioguanine, and T-ALL samples were significantly more resistant to prednisolone, dexamethasone, 1-asparaginase, vincristine, vindesine, daunorubicin, doxorubicin, teniposide, and ifosfamide, than the group of common and pre-B ALL cases. We conclude that the prognostic significance of age and immunophenotype in particular may be explained, at least partly, by its relation with resistance to certain drugs. The results of this study may be useful for future rational improvements of chemotherapeutic regimens in childhood ALL.

Topoisomerase II alpha gene expression in childhood acute lymphoblastic leukemia

Previously, we showed that in vitro resistance to daunorubicin (DNR) at initial diagnosis was related to a poor long-term clinical outcome in childhood acute lymphoblastic leukemia (ALL), and that cells of relapsed ALL were in vitro more resistant to DNR than cells of untreated ALL. Topoisomerase II (Topo II) is an intracellular target for anthracyclines and epipodophyllotoxins. Decreased levels and/or activity of Topo II have been associated with multidrug resistance in cell lines. We investigated Topo II alpha gene expression in fresh leukemic samples from 19 children with untreated and 14 children with relapsed ALL using a sensitive RNase protection assay. The in vitro cytotoxicity of the Topo II inhibitors DNA and teniposide (VM26) was measured using the MTT assay, and the cell cycle distribution of leukemic samples was analyzed by DNA flow cytometry. Results showed that (1) relapsed ALL samples were more resistant to DNR, but not to VM26 compared to untreated samples; (2) large interpatient variations existed in both Topo II alpha gene expression and in vitro cytotoxicity results; (3) Topo II alpha gene expression was detectable in 29/33 childhood ALL samples with a median expression of 5% the level of a relatively chemosensitive human small cell lung cancer cell line; (4) Topo II alpha gene expression did not differ between untreated and relapsed ALL; (5) Topo II alpha gene expression was positively correlated with the percentage of ALL cells in S- and G2M-phase, but not with the in vitro cytotoxicity of the drugs tested. In conclusion, resistance to DNR in childhood ALL can not be explained by decreased levels of Topo II alpha gene expression, but additional Topo II activity studies in fresh leukemia samples may need further exploration.

In vitro anthracycline cross-resistance pattern in childhood acute lymphoblastic leukaemia

Daunorubicin (DNR) is a major front-line drug in the treatment of childhood acute lymphoblastic leukaemia (ALL). Previously, we showed that in vitro resistance to DNR at diagnosis is related to a poor long-term clinical outcome in childhood ALL and that relapsed ALL samples are more resistant to DNR than untreated ALL samples. In cell line studies, idarubicin (IDR), aclarubicin (ACR) and mitoxantrone (MIT) showed a (partial) lack of cross-resistance to the conventional anthracyclines DNR and doxorubicin (DOX), but clinical studies in childhood ALL have been inconclusive about the suggested lack of cross-resistance. In the present study we determined the in vitro cross-resistance pattern between DNR, DOX, IDR, ACR and MIT in 48 untreated and 39 relapsed samples from children with ALL using the MTT assay. The relapsed ALL group was about twice as resistant to DNR, DOX, IDR, ACR and MTT as the untreated ALL group. Thus, resistance developed to all five drugs. We found a significant cross-resistance between DNR, DOX, IDR, ACR and MIT, although in some individual cases in vitro anthracycline cross-resistance was less pronounced. We conclude that IDR, ACR and MIT cannot circumvent in vitro resistance to DNR in childhood ALL. Clinical studies may still prove whether IDR, ACR or MIT has a more favourable toxicity profile than DNR.

Drug combination testing in acute lymphoblastic leukemia using the MTT assay

Drug resistance assays may be useful to identify drug interactions. For this purpose, we studied three drug combinations, each at 8-12 concentrations, with the MTT assay in acute lymphoblastic leukemia (ALL) samples from 34 children obtained at initial diagnosis. This resulted in a total of 518 comparisons between expected and observed leukemic cell survivals. The combinations prednisolone (PRD) with vincristine (VCR), PRD with mafosfamide (MAF), and PRD with daunorubicin (DNR) were tested without technical difficulties, and without an increased assay variation as compared to single drugs. We observed a marked heterogeneity in drug interactions between patients, between combinations, and between different concentrations within one specific combination. Between PRD+VCR, synergism was found in 46%, antagonism in 18%, and additivity in 36% of the 228 observations. Between PRD+MAF, synergism was found in 51%, antagonism in 20%, and additivity in 29% of the 140 observations. Between PRD+DNR, synergism was found in 35%, antagonism in 31%, and additivity in 34% of the 150 observations. PRD+VCR and PRD+MAF showed more often synergism than PRD+DNR, while antagonism was observed more frequently between PRD+DNR (p < 0.05). However, the magnitude of antagonism was not much different between the three drug combinations, nor was there a significant antagonistic interaction in any of the drug combinations tested, if all samples were considered together. We conclude that the MTT assay can be used to study drug interactions in vitro in ALL samples. The type of interaction was different between patients, and depends on the drug combination and concentrations. The combinations PRD+VCR and PRD+MAF generally showed additive and even synergistic interactions. The cytotoxicity of PRD+DNR was generally not markedly higher than that of the most active single drug.

Favorable prognosis of hyperdiploid common acute lymphoblastic leukemia may be explained by sensitivity to antimetabolites and other drugs: results of an in vitro study

DNA hyperdiploidy is a favorable prognostic factor in childhood acute lymphoblastic leukemia (ALL). The explanation for this prognostic significance is largely unknown. We have studied whether DNA ploidy was related to cellular resistance to 12 drugs, assessed with the methyl-thiazol-tetrazolium assay, in samples of 74 children with common (CD10+ precursor B-cell) ALL. Sixteen patients had hyperdiploid ALL cells and 58 patients had nonhyperdiploid ALL cells. Hyperdiploid ALL cells were more sensitive to mercaptopurine (median, 9.0-fold; P = .000003), to thioguanine (1.4-fold; P = .023), to cytarabine (1.8-fold; P = .016), and to I-asparaginase (19.5-fold; P = .022) than were nonhyperdiploid ALL cells. In contrast, these two ploidy groups did not differ significantly in resistance to prednisolone, dexamethasone, vincristine, vindesine, daunorubicin, doxorubicin, mitoxantrone, and teniposide. The percentage of S-phase cells was higher (P = .05) in the hyperdiploid ALL samples (median, 8.5%) than in the nonhyperdiploid ALL samples (median, 5.7%). However, the percentage of cells in S-phase was not significantly related to in vitro drug resistance. We conclude that the favorable prognosis associated with DNA hyperdiploidy in childhood common ALL may be explained by a relative sensitivity of hyperdiploid common ALL cells to antimetabolites, especially to mercaptopurine and to I-asparaginase.

Functional multidrug resistance phenotype associated with combined overexpression of Pgp/MDR1 and MRP together with 1-beta-D-arabinofuranosylcytosine sensitivity may predict clinical response in acute myeloid leukemia

Overexpression of P-glycoprotein (Pgp) or MDR1 mRNA has been shown to be a negative prognostic factor for clinical outcome in acute myeloid leukemia (AML). However, resistance to chemotherapy also occurs in the absence of Pgp overexpression. Therefore, besides Pgp expression, we have assessed the expression of MRP, a novel drug transporter gene, along with the functional multidrug-resistant (MDR) phenotype of leukemic cells. These MDR parameters are correlated with clinical outcome in individual patients. We found functional changes in fresh leukemic cells from de novo or relapsed patients similar to those reported for tumor cell lines with the MDR phenotype. These changes were reduced drug accumulation as assessed with radiolabeled doxorubicin (factor 1.6), daunomycin (factor 1.13), and vincristine (factor 1.6) in patients who were refractory to the combination treatment of 1-beta-D-arabinofuranosylcytosine (ara-C) and daunomycin or mitoxantrone as opposed to patients who had complete responses. Also, the intracellular distribution of doxorubicin fluorescence (nuclear/cytoplasmic ratio), as assessed with laser scan microscopy, was reduced 1.4-fold in blasts from refractory patients. Based on historically known clinical response to single-agent daunomycin or ara-C in the group of responding de novo AML patients, we have set a threshold level such that a defined part of the samples that had the highest drug accumulation or nuclear to cytoplasmic ratios were above this threshold value. This allowed discrimination between patients responding to daunomycin from those who were refractory to this drug. By using this threshold level, in the refractory group clinical resistance corresponded with high sensitivity with a resistant phenotype. A similar threshold was set for the data of the in vitro ara-C sensitivity test. By combining both assays for all individual patients, clinical refractoriness as well as sensitivity could be predicted with high accuracy. There appeared to be no stringent relationship between the functional MDR phenotype with expression of either Pgp (fluorescence-activated cell sorting analysis) or MRP mRNA (RNase protection). However, by combining both parameters the functional MDR phenotype correlated with the overexpression of either one or both of the parameters in 94% of the samples studied. It is concluded that this combined overexpression in conjunction with functional changes for MDR drugs and ara-C reveal a correlation of MDR phenotype with clinical resistance to combination chemotherapy in AML patients and hereby may adequately predict clinical MDR in individual AML patients.

Mononuclear cells contaminating acute lymphoblastic leukaemic samples tested for cellular drug resistance using the methyl-thiazol-tetrazolium assay

The methyl-thiazol-tetrazolium (MTT) assay is a drug resistance assay which cannot discriminate between malignant and non-malignant cells. We previously reported that samples with > or = 80% leukaemic cells at the start of culture give similar results in the MTT assay and the differential staining cytotoxicity assay, in which a discrimination between malignant and non-malignant cells can be made. However, the percentage of leukaemic cells may change during culture, which might affect the results of the MTT assay. We studied 106 untreated childhood acute lymphoblastic leukemia (ALL) samples with > or = 80% leukaemic cells at the start of culture. This percentage decreased below 80% in 28%, and below 70% in 13%, of the samples after 4 days of culture. A decrease below 70% occurred more often in case of 80-89% leukaemic cells (9/29) than in case of > or = 90% leukaemic cells at the start of culture (5/77, P = 0.0009). Samples with < 70% leukaemic cells after culture were significantly more resistant to 6 out of 13 drugs, and showed a trend towards being more resistant to two more drugs, than samples with > or = 80% leukaemic cells. No such differences were seen between samples with 70-79% and samples with > or = 80% leukaemic cells after culture. We next studied in another 30 ALL samples whether contaminating mononuclear cells could be removed by using immunoamagnetic beads. Using a beads to target cell ratio of 10:1, the percentage of leukaemic cells increased from mean 72% (s.d. 9.3%) to mean 87% (s.d. 6.7%), with an absolute increase of 2-35%. The recovery of leukaemic cells was mean 82.1% (range 56-100%, s.d. 14.0%). The procedure itself did not influence the results of the MTT assay in three samples containing only leukaemic cells. We conclude that it is important to determine the percentage of leukaemic cells at the start and at the end of the MTT assay and similar drug resistance assays. Contaminating mononuclear cells can be successfully removed from ALL samples using immunomagnetic beads. This approach may increase the number of leukaemic samples which can be evaluated for cellular drug resistance with the MTT assay or a similar cell culture drug resistance assay.

Cellular drug resistance in childhood leukemia

The response to chemotherapy is determined essentially by two factors: first, pharmacokinetic factors, determining which concentration of drug reaches the malignant cells, and second, cellular drug resistance of these cells, determining how many of them will be killed by that concentration of drug. The study of cellular drug resistance has been stimulated by the development of short-term 'total cell kill' assays, such as the MTT assay, for use on patient samples. The drug resistance profiles differed markedly between ALL and ANLL, between immunophenotypic and karyotypic subgroups within ALL, and between initial and relapsed ALL. The results of the MTT assay showed a significant relation between the antileukemic activity of prednisolone in vitro and the clinical response to systemic monotherapy with that drug. At multivariate analysis including several well-known prognostic factors (WBC, age, immunophenotype) only the in vitro resistance to prednisolone, dexamethasone, L-asparaginase, and daunorubicin was significantly related to clinical outcome. At multiple regression analysis, combination of the results for prednisolone, L-asparaginase, and vincristine made it possible to distinguish between three patient groups with increasing levels of drug resistance and markedly different probabilities of 2-year disease-free survival: 100%, 83%, and 60%. These results show that in vitro drug resistance testing can give a correct prediction of prognosis, superior to that of currently used prognostic factors. Stratification of prognostic groups based on the results of drug resistance testing is feasible and should be introduced into new clinical trials. Many questions now remaining could be answered within carefully designed preclinical and clinical studies.

Different cellular drug resistance profiles in childhood lymphoblastic and non-lymphoblastic leukemia: a preliminary report

The better prognosis of acute lymphoblastic leukemia (ALL) than of acute non-lymphoblastic leukemia (ANLL) in children, and the often observed better prognosis of myeloid-antigen (MyAg) negative ALL than of MyAg-positive ALL, may be related to differences in cellular drug resistance. We therefore compared the resistance to 12 drugs of 125 ALL and 28 ANLL samples with the MTT assay. ALL samples were median > 75-fold more sensitive to the glucocorticoids prednisolone and dexamethasone (p < 0.00001), and 2-fold more sensitive to vincristine (p = 0.05) than ANLL samples. Differences for the other drugs were not significant. MyAg-negative ALL samples were more sensitive to glucocorticoids than MyAg-positive ALL-samples (p < or = 0.04). Prednisolone, and dexamethasone if tested, had a stimulatory effect on leukemic cell survival in 36% of ANLL, but in only 2% of ALL samples (p < 0.0001). Vincristine, and vindesine if tested, had a similar effect in 11% of ANLL, and in 4% of ALL samples (p = 0.11). We conclude that the more favorable response of ALL against ANLL to combination chemotherapy in children may be explained by the higher antileukemic activity of glucocorticoids and of vincristine in ALL, while none of the drugs was more active in ANLL. Similarly, the better prognosis of MyAg-negative ALL than of MyAg-positive ALL may be explained by a relative sensitivity to glucocorticoids. Glucocorticoids and vinca-alkaloids induced leukemia cell proliferation in part of the samples, most frequently in ANLL. The findings may be useful in the design of new chemotherapeutic regimens for ALL and ANLL.

Glucocorticoid resistance in childhood leukemia

Glucocorticoids (GC) are being used in the treatment of childhood leukemia for several decades, most successfully in newly diagnosed acute lymphoblastic leukemia (ALL). However, GC resistance is seen in 10-30% of untreated ALL patients, and is much more frequent in relapsed ALL and in acute nonlymphoblastic leukemia (ANLL). Sensitivity or resistance to GC can be measured using a cell culture drug resistance assay. For this purpose, we use the colorimetric methyl-thiazol-tetrazolium (MTT) assay. We have shown that GC resistance in childhood leukemia is related to clinical and cell biological features, and to the clinical outcome after multi-drug chemotherapy. These results are summarized in this review. In addition, we describe the apoptotic 'cell-lysis pathway' by which GC exert their antileukemic activity. This description provides a model to discuss the mechanisms of GC resistance, and to summarize the relevant literature. Possible levels of resistance relate to the diffusion of GC through the cell membrane, binding to the GC receptor (GCR), activation of the GC-GCR complex, translocation of the complex into the nucleus, binding to DNA, endonuclease-mediated DNA fragmentation, and DNA repair. A low number of GCR has been shown to be the cause of resistance in some children with ALL. However, GC resistance is likely to be caused at the post-receptor level in most leukemias. Unfortunately, there is still a lack of knowledge relating to the clinical relevance of mechanisms of GC resistance at the post-receptor level. Studies on the mechanisms of GC resistance other than those directly related to the GCR should be initiated, especially if patient material is used, as the results might indicate ways to circumvent or modulate GC resistance. A further increase in our knowledge regarding the relation between GC resistance and patient and cell biological features, the clinical relevance of GC resistance, and the mechanisms of GC resistance in leukemia patients, may contribute to further improvement in the results of GC therapy in leukemia.

In vitro cytotoxicity of mitoxantrone, daunorubicin and doxorubicin in untreated childhood acute leukemia

Mitoxantrone (MIT) has not been studied as a single agent in children with untreated leukemia. The antileukemic activity of MIT in these patients and its activity in relation to clinical and cell biological features is unknown. We studied the in vitro cytotoxicity of MIT, daunorubicin (DNR) and doxorubicin (DOX) in untreated childhood acute lymphoblastic leukemia (ALL, n = 131) and acute nonlymphoblastic leukemia (ANLL, n = 20) samples, using the MTT assay. There were marked interindividual differences in resistance to all three drugs. A strong, significant cross-resistance was found in ALL between MIT, DNR and DOX. All samples of the T-lineage, a prognostically unfavorable immunophenotype, however, were significantly more resistant to DNR and DOX, but not to MIT, than common or pre-B ALL samples. ALL cells from children with a prognostically unfavorable age at diagnosis, especially those < 2 years, showed a relative resistance to all three drugs compared to the intermediate age-group. This was found within all patients, but also within the common or pre-B ALL cases only. Sex, white blood cell count, or FAB type was not related to in vitro drug resistance. None of the three drugs showed an overall preferential activity in ALL or ANLL. We conclude that the in vitro antileukemic activity of MIT, DNR and DOX is related to certain clinical and cell biological features. There were no major differences between the three drugs in antileukemic activity, except that T-ALL samples were more resistant than common or pre-B ALL samples to DNR and DOX, while MIT was equally active in these two immunophenotypes.

Clinical relevance of in vitro drug resistance testing in childhood acute lymphoblastic leukemia: the state of the art

Nowadays about two-thirds of children with acute lymphoblastic leukemia (ALL) can be cured with chemotherapy, but one-third die from the disease. The clinical response of leukemic cells to chemotherapy is roughly due to two factors: the effective drug levels reaching the cells and the resistance of these cells to the drugs. The clinical value of cellular drug resistance in children with ALL is not known. We developed an in vitro assay to study drug resistance in these children. In this article, the main results obtained with this MTT assay on samples from 137 children with ALL are summarized: (1) patients whose cells are resistant to several drugs at initial diagnosis have a poor prognosis; (2) relapsed leukemias show a considerable drug resistance which might partly explain the poor prognosis. Relapsed cases differ in their type and degree of resistance; (3) the poor outcome of high risk groups as defined by age and immunophenotype can partly be explained by specific patterns of drug resistance; (4) P-glycoprotein-mediated multidrug resistance is not an important cause of resistance in childhood ALL; and (5) no relation exists between the activities of the purine enzymes HGPRT, 5'NT, ADA, and PNP and drug resistance in childhood ALL. The conclusion is that in vitro drug resistance data have clinical relevance and can be used to develop more effective and less toxic treatment strategies in childhood ALL.

Cellular drug resistance profiles that might explain the prognostic value of immunophenotype and age in childhood acute lymphoblastic leukemia

Immunophenotype and age have prognostic value in childhood acute lymphoblastic leukemia (ALL) but how this operates is not understood. In 84 children with ALL at initial diagnosis we studied the correlation between these factors and the in vitro resistance to eight drugs, determined with the 3-(4,5-dimethylthiazol-2-yl-2, 5-diphenyl tetrazolium bromide (MTT) assay. B-lineage ALL samples were classified into four differentiation stages: the CD10- proB ALL; cALL; preB ALL with cytoplasmic mu positive ALL cells; and B-ALL with surface immunoglobulin-positive (Ig+) cells. cALL and preB ALL cases have the best prognosis; proB and T-ALL cases show a worse prognosis and B-ALL the poorest prognosis. Patients aged < 18 months and > 10 years have a poor prognosis compared to patients in the intermediate age group. Our results show that cALL and preB ALL cells were the most drug-sensitive cells compared to the other phenotypes. No differences were found between cALL and preB ALL cases with the exception that preB cells were more sensitive to mustine and mafosfamide (Maf). Compared to cALL and preB ALL cases, T-ALL cases were significantly more resistant to prednisolone (Pred), daunorubicin (DNR), L-asparaginase (L-Asp), cytosine arabinoside (AraC), and Maf; proB ALL cases were more resistant to Pred, DNR, L-Asp, and 6-thioguanine. The three B-ALL cases were resistant to vincristine and DNR. Two out of three B-ALL were resistant to Pred. Compared to cells from patients aged 18 months to 10 years, cells from children < 18 months were more resistant to Pred and DNR; cells from children > 10 years were more resistant to Pred. We conclude that cellular drug-resistance patterns might at least partly explain the prognostic value of immunophenotype and age in childhood ALL.

[The treatment of recurrence in children with acute lymphatic leukemia. Current results and various developments]

The results of current treatment of relapsed childhood acute lymphoblastic leukemia (ALL) are discussed, together with some recent developments which (might) influence such treatment. At present more than 95% of children with ALL will achieve a complete remission (CR), and +/- 70% will remain in CR. Nevertheless, 20-30% of the patients suffer a relapse, which implies a less favorable prognosis. However, after intensive treatment a part of these patients will have a prolonged second complete remission: 30-50% of children with a late relapse and 0-20% of children with an early relapse. It is important to prevent the occurrence of a relapse. The identification at diagnosis of patients at high risk for a relapse, and a subsequent more specific and more intensive treatment of these patients might contribute to that goal. Well-known risk factors are briefly mentioned, factors of which the prognostic significances is therapy-dependent. In addition, the treatment of relapsed ALL needs further improvement. Some alternatives to achieve this goal are discussed, including the role of in vitro cytostatic drug resistance testing.

Relation of 5'-nucleotidase and phosphatase activities with immunophenotype, drug resistance and clinical prognosis in childhood leukemia

Ecto-5'-nucleotidase (ecto-5'NT) catalyzes the extracellular dephosphorylation of nucleotides like IMP. Cytoplasmic 5'NT (cyto-5'NT) and non-specific (e.g. acid- and alkaline) phosphatases (AP) regulate the intracellular degradation of nucleotides. High NT and AP activities might cause a resistance to the thiopurines 6-mercaptopurine (6-MP) and 6-thioguanine (6-TG). We studied the relation between these enzymes and immunophenotype, drug resistance and prognosis in 77 children with acute lymphoblastic leukemia (ALL). Enzyme activities were assessed radiochemically; in vitro drug resistance was measured with the MTT assay. AP activities were higher in T-ALL and B-ALL than in precursor B-ALL. Cyto-5'NT activity was very low in all phenotypes and accounted for a significant proportion of total IMPase activity only in the very immature CD10- c mu- precursor B-ALL. CD10+ ALL cases with high ecto-5'NT activities showed a trend (p = 0.065) for a lower probability of continuous complete remission than those with a low activity. Ecto-5'NT activity was not related to in vitro drug resistance to 6-TG. A weak correlation was found between in vitro 6-TG resistance and cyto-5'NT and AP activities. We conclude that high ecto-5'NT activities do not cause a resistance to 6-thiopurines in childhood ALL. Some patients have high cyto-5'NT and AP activities associated with 6-thiopurine resistance.

Different types of non-P-glycoprotein mediated multiple drug resistance in children with relapsed acute lymphoblastic leukaemia

Although cellular drug resistance is considered to be an important cause of the poor prognosis of children with relapsed acute lymphoblastic leukaemia (ALL), the knowledge of drug resistance in these patients is very limited. Different aspects of drug resistance were studied in 17 children with relapsed ALL. The in vitro sensitivity profile was determined using the MTT assay. Cells from relapsed children were significantly more resistant to 6-thioguanine, prednisolone, cytosine arabinoside, daunorubicin (DNR), mustine-HCl and mafosfamide but not to L-asparaginase and vincristine (VCR) than cells from 41 children with ALL at initial diagnosis. Some relapsed patients showed a general drug resistance while others were resistant to only 1-3 drugs. The relevance of the multidrug resistance (MDR) model was analysed: In all DNR- and VCR resistant cases a co-resistance to drugs not involved in the MDR model was found. P-glycoprotein was not detected in any of 28 untreated and 14 relapsed samples tested. VCR- and DNR accumulation in the most resistant cells were not lower than in sensitive cells. Resistance modifiers did not potentiate the cytotoxicity of VCR and DNR. We conclude that resistance to anthracyclines and vinca alkaloids in childhood relapsed ALL is not due to P-glycoprotein mediated MDR. Different types of drug resistance varying from a resistance to only one drug to a general chemoresistance, can be detected in children with relapsed ALL. VCR and L-asparaginase seemed to be only infrequently involved in drug resistance. Knowledge of drug resistance might lead to more effective and less toxic therapies for children with relapsed ALL.

Hypoxanthine-guanine phosphoribosyl-transferase in childhood leukemia: relation with immunophenotype, in vitro drug resistance and clinical prognosis

Decreased activity of hypoxanthine-guanine phosphoribosyl-transferase (HGPRT), responsible for the conversion of 6-mercaptopurine and 6-thioguanine (6-TG) to their cytotoxic nucleotides, may cause resistance to these thiopurines in experimental leukemic systems. The clinical significance of this mechanism is as yet unclear. In 83 children with untreated acute lymphoblastic leukemia (ALL), we determined the prognostic value of HGPRT activity and the relation between HGPRT activity and resistance to thiopurines. HGPRT activity was determined radiochemically; in vitro resistance to 6-TG with the MTT assay. HGPRT level was significantly lower in T-ALL than in B-lineage ALL; no differences were found between sequential differentiation stages of B-lineage ALL. HGPRT activity was inversely related to the white-blood-cell count (WBC). Among patients with cALL and pre-B-ALL with WBC less than 50 x 10(9)/l, cases with a low HGPRT had a significantly poorer prognosis than those with a high HGPRT. WBC, age, sex, organomegaly and differentiation stage were comparable in both patient groups. No correlation was found between HGPRT activity and in vitro 6-TG resistance in cALL and pre-B-ALL patients. T-ALL cases were not more 6-TG-resistant than cALL and pre-B-ALL cases. Cells from 6 relapsed ALL cases did not show decreased HGPRT activity. We conclude that: (a) HGPRT is lower in T- than in B-lineage ALL and is constant in sequential differentiation stages of B-lineage ALL; (b) HGPRT activity is inversely related to tumor load; (c) low HGPRT activities are correlated with a poorer prognosis in precursor B-ALL but this cannot be explained by thiopurine resistance because (d) there is no relation between HGPRT activity and in vitro 6-TG resistance.

Adenosine deaminase and purine nucleoside phosphorylase in childhood lymphoblastic leukemia: relation with differentiation stage, in vitro drug resistance and clinical prognosis

Many reports have described the relationship of adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP) activities with the immunological subclasses of acute lymphoblastic leukemia (ALL). The clinical significance of these enzymes in leukemias is not yet completely understood. We performed a study in 83 children with untreated ALL to establish the relationships of ADA and PNP to clinical outcome, in vitro drug resistance and differentiation stage of B-cell lineage ALL. ADA and PNP activities were determined radiochemically. In vitro resistance to 6-thioguanine (6-TG) was determined with the MTT assay. ADA activity was not different between proB- and cALL cases but decreased in the sequential differentiation stages cALL----preB-ALL----B-ALL. The PNP level was not different between the four stages of B-lineage ALL. Patients with cALL/preB ALL with low ADA activities had a significantly poorer probability of survival (p = 0.005) than patients with high ADA levels. Patients with cALL/preB ALL with low PNP activities showed a non-significant trend for a poorer prognosis (0.05 less than p less than 0.10) than patients with a high PNP level. Low ADA and PNP activities were not related to in vitro resistance to 6-TG. We conclude that ADA decreases and PNP remains constant in sequential differentiation stages of B-lineage ALL. Patients with precursor B-lineage ALL with low activities of ADA have a poorer prognosis than those with high activities of these enzymes. No relationship could be detected between ADA or PNP activity and resistance to 6-TG.

[Growth hormone therapy and leukemia]

In this literature study the possible correlation between GH-therapy and leukemia has been critically evaluated. Two central questions have been studied: 'does leukemia occur more often in GH-deficient children in GH-therapy than in age-related normal individuals' and 'which influences of GH administration upon normal and leukemic leukocytes have been described?'. In some cases leukemia developed in GH-deficient children after GH-therapy. The data have shown a higher incidence of leukemia in the population of children treated with GH (5:100,000) than in the age-related normal population of children (2:100,000). However, hard evidence supporting the hypothesis that GH-therapy could induce leukemia has not yet been found. In vivo studies could not detect enhanced growth of blood cells influenced by GH-therapy. In vitro studies showed that GH either stimulated or did not affect the proliferation of unstimulated lymphocytes of GH-deficient children, normal individuals or leukemia-patients. The same effects occurred in leukemic cell lines. On PHA-stimulated lymphocytes of GH-deficient children and normal individuals both enhancing and inhibiting effects of GH have been found. It is suggested that GH-therapy could improve immunological resistance against tumors by improving Natural-Killer-cell activity. In mice GH seemed to influence lymphocyte-differentiation. In mice also an increase in the frequency of chromosomal aberrations related to GH has been observed. This evaluation suggests that patients, treated with GH-therapy should be carefully followed up. Also, the indication for GH-therapy has to be guarded critically.

Value of routine bone marrow examination for detection of bone marrow relapse in children with standard risk acute lymphoblastic leukemia

The value of routine bone marrow examination (RBME) in children during and after treatment for standard risk acute lymphoblastic leukemia (SR-ALL) was investigated. The clinical symptoms and peripheral blood findings at the time of bone marrow relapse of 28 children were reviewed and compared with those of 28 matched controls in continuous complete remission. Five (45%) children with bone marrow relapse during maintenance therapy and six (35%) after cessation of cytostatic treatment were asymptomatic at the time of relapse. Signs indicative of relapse during treatment were lymphoblast cells in the peripheral blood, thrombocytopenia, hepatomegaly, anemia, or leukopenia in decreasing order of frequency. After cessation of treatment these signs were lymphoblasts in the peripheral blood, hepatomegaly, splenomegaly, thrombocytopenia, or leukocytosis. Except for one case with thrombocytopenia, no signs suspicious for relapse were found in the control groups. When each sign was evaluated separately only the presence of lymphoblasts in peripheral blood and hepatomegaly were significant symptoms for relapse after cessation of treatment. The mean percentage of lymphoblasts in the bone marrow at the time of relapse was significantly lower for patients with an unpredicted relapse (46.8%) than patients with clinical and/or laboratory evidence of relapse (79.5%). When lymphoblasts were present in the peripheral blood the percentage of lymphoblasts in the bone marrow was always more than 40%, both during and after cessation of treatment. These data suggest a relation between clinical and laboratory symptoms and progression of the disease. It is concluded that 46% of relapses are detected by RBME in the absence of clinical or laboratory symptoms. This early detection may have a positive prognostic influence with more effective treatment for relapsed ALL.

Expression of the leucocyte integrin LFA-1 (CD11a/CD18) and its ligand ICAM-1 (CD54) in lymphoid malignancies is related to lineage derivation and stage of differentiation but not to tumor grade

The leucocyte adhesion molecule LFA-1 (CD11a/CD18) and its counter structure ICAM-1 (CD54) play a pivotal role in cell-cell interactions in the immune system and hence their expression on malignant cells might play an important role in determining the biological behavior of lymphoid malignancies. This study examined the LFA-1 (CD11a/CD18) and ICAM-1 (CD54) expression profiles of a large series of non-Hodgkin's lymphomas (NHL, n = 220) and lymphoid leukemias (LL, n = 48), which, by their differentiation-antigen phenotype represented essentially all stages of lymphoid development from stem cell to mature activated T- and B-lymphocyte. It was found that NHL and LL differentially express LFA-1 and ICAM-1 molecules according to their lineage derivation, stage of differentiation, and growth pattern. Specifically: (a) T-cell neoplasms nearly always express LFA-1 whereas B-cell tumors are often LFA-1 low/negative; (b) ICAM-1 expression is largely confined to tumors with a mature or activated T- or B-cell phenotype; (c) neoplasms with a leukemic dissemination pattern are either ICAM-1 low or negative. Importantly, neither LFA-1 nor ICAM-1 expression was related to tumor grade.

In vitro drug sensitivity of normal peripheral blood lymphocytes and childhood leukaemic cells from bone marrow and peripheral blood

In vitro drug sensitivity of leukaemic cells might be influenced by the contamination of such a sample with non-malignant cells and the sample source. To study this, sensitivity of normal peripheral blood (PB) lymphocytes to a number of cytostatic drugs was assessed with the MTT assay. We compared this sensitivity with the drug sensitivity of leukaemic cells of 38 children with acute lymphoblastic leukaemia. We also studied a possible differential sensitivity of leukaemic cells from bone marrow (BM) and PB. The following drugs were used: Prednisolone, dexamethasone, 6-mercaptopurine, 6-thioguanine, cytosine arabinoside, vincristine, vindesine, daunorubicin, doxorubicin, mafosfamide (Maf), 4-hydroperoxy-ifosfamide, teniposide, mitoxantrone, L-asparaginase, methotrexate and mustine. Normal PB lymphocytes were significantly more resistant to all drugs tested, except to Maf. Leukaemic BM and PB cells from 38 patients (unpaired samples) showed no significant differences in sensitivity to any of the drugs. Moreover, in 11 of 12 children with acute leukaemia of whom we investigated simultaneously obtained BM and PB (paired samples), their leukaemic BM and PB cells showed comparable drug sensitivity profiles. In one patient the BM cells were more sensitive to most drugs than those from the PB, but the actual differences in sensitivity were small. We conclude that the contamination of a leukaemic sample with normal PB lymphocytes will influence the results of the MTT assay. The source of the leukaemic sample, BM or PB, does not significantly influence the assay results.

Cytotoxic effects of vitamin A in combination with vincristine, daunorubicin and 6-thioguanine upon cells from lymphoblastic leukemic patients

We studied whether isotretinoin potentiated the effects of vincristine (VCR), daunorubicin (DNR), and 6-thioguanine (6-TG) against cells obtained from 24 patients with acute lymphoblastic leukemia (ALL). Treatment with 5 micrograms/ml isotretinoin alone resulted in a leukemic cell survival of 82% +/- 28.1%. So isotretinoin is toxic to ALL cells. Dose-response curves were obtained for VCR, DNR and 6-TG in the presence and absence of isotretinoin Isotretinoin showed additive leukemic cell kills in combination with VCR and DNR. When corrected for cell kill by isotretinoin alone, it appeared that isotretinoin did not significantly enhance leukemic cell kills by VCR, DNR and 6-TG. No differences were found between samples from patients at initial diagnosis and at relapse with respect to cell kill by isotretinoin alone and with respect to a possible synergistic effect of isotretinoin and the cytostatic drugs. It is concluded that isotretinoin has additive antileukemic effects in combination with VCR or DNR. However, isotretinoin does not potentiate the antileukemic effects of VCR, DNR and 6-TG against leukemic cells obtained from patients with ALL.

Relation of cellular drug resistance to long-term clinical outcome in childhood acute lymphoblastic leukaemia

The clinical relevance of cellular drug resistance in children with acute lymphoblastic leukaemia (ALL) is unknown. The relation between in-vitro sensitivity to chemotherapeutic drugs at initial diagnosis and long-term clinical outcome was investigated in 44 children with ALL. The short-term MTT assay was used to assess sensitivity to prednisolone, vincristine, colaspase (asparaginase), daunorubicin, and thioguanine (instead of mercaptopurine which is unstable in vitro). For vincristine and colaspase there was no difference in outcome (probability of continuous complete remission) between sensitive and resistant patients. However, the probability of continuous complete remission was significantly lower in patients with resistant cells than in those with sensitive cells for thioguanine (p less than 0.01), daunorubicin (p less than 0.02), and prednisolone (p less than 0.05). For prednisolone there was a significant worsening of the prognosis (p less than 0.05) from the extremely sensitive patients through an intermediate group to the most resistant group. The prognostic significance of cellular drug resistance was independent of white-blood-cell count, age, sex, and hepatosplenomegaly. Leukaemic cells from boys were more resistant to thioguanine than those from girls. Thus, the short-term highly efficient MTT assay can help to predict long-term response to chemotherapy in childhood ALL.

Differentiation dependent expression of P-glycoprotein in the normal and neoplastic human kidney

Adult renal cell carcinoma (RCC) is clinically resistant to chemotherapy. However, in nephroblastoma (NBL) chemotherapy has increased survival dramatically. We studied the P-glycoprotein (P-gp) expression of 18 RCC and 9 NBL as well as 1 benign renal adenoma and fetal renal tissue using three different monoclonal antibodies (MRK-16, C-219, JSB-1). P-gp was found positive with all three antibodies in 12/18 RCC, while only 2 tumors were completely negative. Staining varied with respect to intensity and number of positive cells [5%-90%]. Intense staining was seen at the apical side of malignant tubules in well differentiated parts of RCC and in tubular structures of the benign renal adenoma. Poorly differentiated parts of the tumors showed less staining. In NBL blastemal parts were negative. In 4/8 specimens showing focal epithelial differentiation, however, the luminal side of more differentiated tubular structures did stain, strongly resembling P-gp staining in the developing fetal human kidney. These results indicate that P-gp expression in normal (fetal) human kidney as well as in benign and malignant tumors derived from this organ depends on the degree of differentiation of tubules, which may have implications for chemotherapy sensitivity in both malignant tumors.

In vitro drug sensitivity of cells from children with leukemia using the MTT assay with improved culture conditions

The knowledge about drug resistance in childhood leukemias and acute lymphoblastic leukemia (ALL) in general is limited. This is because of the lack of a suitable in vitro drug sensitivity assay, which is in part due to low in vitro ALL cell survival. We recently adapted the highly efficient 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay to test cells from ALL patients and showed that its results were comparable with those of the DiSC assay, up to now the most valid but laborious assay. In this study, in vitro drug sensitivity was assessed in cells from 82 children with leukemia, 79 of whom had ALL, with the MTT assay. Dose response curves were obtained for 6-mercaptopurine, 6-thioguanine (6-TG), prednisolone (Pred), daunorubicin (DNR), vincristine (VCR), cytosine arabinoside (Ara-C), L-asparaginase (L-Asp), mafosfamide, and mustine. A cytotoxic effect of methotrexate could be detected in only a few cases. Large interindividual differences in drug sensitivity were detected. Compared with leukemia cells from newly diagnosed patients, leukemia cells from relapsed patients were significantly more in vitro resistant to 6-TG, Pred, Ara-C, mafosfamide and mustine but not to DNR, VCR, and L-Asp. Improvements of culture medium and methods to increase MTT reduction were studied. From 10 components tested, addition of insulin and bovine serum albumin to serum-containing medium improved ALL cell survival. Addition of succinate did not increase the amount of MTT reduction. We conclude that the in vitro MTT assay highly facilitates large-scale studies on drug resistance of ALL patients that can lead to rational improvements in existing treatment protocols.

Expression of a human homing receptor (CD44) in lymphoid malignancies and related stages of lymphoid development

Lymphocyte adhesion to high endothelial venules, a central step during extravasation into lymphoid tissues, involves an 85 to 95-kD class of lymphocyte surface glycoproteins, which fall in the cluster of CD44 antigens. In this paper we describe the expression of this homing receptor glycoprotein during lymphoid development. CD44 expression was examined on a large panel of non-Hodgkin's lymphomas (n = 234) and lymphoid leukemias (n = 44). These tumors, which are the malignant counterparts of normal lymphoid cells "frozen" at a certain stage of maturation/activation, are thought to represent a complete spectrum of lymphoid development from stem cell to mature, activated T and B lymphocyte. It was found that CD44 exhibits a trimodal distribution on developing lymphocytes of both the T and B lineage: the CD44 antigen is expressed at relatively high levels during early stages of lymphoid differentiation, i.e., on prothymocytes and immature precursor B cells (null acute lymphoblastic leukemia (ALL) and common ALL). Subsequently, at the stage of the immature/common thymocyte, the pre-B cell and early B cell (pre-B-ALL and B-ALL), the CD44 antigen is temporarily lost from the cell surface to be reacquired during further T and B cell maturation. At the activated (germinal center) B cell stage. CD44 is heterogeneously expressed. This distribution pattern of the CD44 molecule closely matches the recirculatory versus sessile nature of lymphoid cells at consecutive phases of their development, and thus apparently reflects its homing receptor function. In addition, the relatively high expression of the CD44 antigen in the earliest phases of T and B cell development suggests that the molecule may also be involved in the migration of bone marrow derived lymphoid precursors to their site of maturation.

The role of 5'nucleotidase in therapy-resistance of childhood leukemia

Purine nucleotides become available for a cell by two routes, namely purine de novo synthesis and the purine salvage pathway. 5'Nucleotidase is a purine pathway enzyme and is present in two forms. Cytoplasmic 5'nucleotidase (cyto 5'NT) catalyzes the intracellular degradation of purine nucleotides into their corresponding nucleosides. The plasma membrane bound form (ecto 5'NT) has its active site facing the external medium. Its function is the extracellular dephosphorylation of nucleotides, to which cells are generally impermeable, into nucleosides and the transport of these nucleosides through the cell membrane. Lymphoblastic 5'NT activity varies between different children with common-ALL. 5'NT positive cases have a higher relapse rate and thus a poorer prognosis than 5'NT negative cases. This can be explained by two hypotheses which are not mutually exclusive: 1. Rescue hypothesis. When purine de novo synthesis is blocked by methotrexate (MTX) and/or 6-mercaptopurine (6-MP), the malignant cell has to rely on the purine salvage pathway. This pathway depends on the ecto-5'NT activity. So, leukemic cells might be resistant to MTX and/or 6-MP because of ecto-5'NT activity. 2. Breakdown hypothesis. Leukemic cells are resistant to 6-MP because of the breakdown of the toxic nucleotide form of 6-MP into the nucleoside form by cyto-5'NT.

Adaptation of the rapid automated tetrazolium dye based (MTT) assay for chemosensitivity testing in childhood leukemia

The reduction of the tetrazolium salt MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) to a blue-black formazan product by living but not by dead cells can be used to measure chemosensitivity of tumor cells. The main advantages of the MTT assay are its simplicity, rapidity, and the fact that the results are read automatically with a microplate spectrophotometer. Several reports on the use of the MTT assay in chemosensitivity testing have been published, but all these studies dealt with established cell lines and not with specimens obtained directly from patients. Here we present a study in which the MTT assay has been adapted to assess the effect of antineoplastic drugs on lymphoblasts of children with leukemia.

Immunological phenotype of lymphoid cells in regenerating bone marrow of children after treatment for acute lymphoblastic leukemia

Bone marrow samples from 8 children treated for acute lymphoblastic leukemia (ALL) were investigated at cessation of cytostatic treatment and during 18 months thereafter. The course of the percentage of lymphoid cells and characterization of these cells by means of monoclonal antibodies, peanut agglutinin (PNA) binding and S-phase determination are shown. The percentage of lymphocytes rises in the first 1.5 months, followed by a non-significant decline. The percentage of cells in S-phase is higher at 0 months than at 6, 15 and 18 months. The percentage of T-cells does not change significantly. In the first 1.5 months a sudden rise in the percentage of common-ALL-antigen (cALLA)-positive lymphocytes occurs. The number of B-cells rises to a peak at 6 months. PNA positively increases to a maximum at 3 months and is correlated with positivity for markers of the B-cell lineage. The percentages of B-cells, cALLA-positive, and PNA-positive lymphocytes do not change significantly after they reach their maximum values and are still high at 18 months. Our results show that after cessation of chemotherapy for ALL a lymphoid cell regeneration occurs in the bone marrow consisting of cells of the B-cell lineage; many of these are cALLA-positive, but are discernible from their malignant counterparts by PNA-positivity.

Consultation among peers in general practice; from no consultation to peer review

The present study concerned several aspects of peer consultation by general practitioners, investigated in a group of 184 doctors (response rate: 83%) who had their vocational training in the department of general practice of the University of Utrecht and practised for at least three years at the time of the study. Questionnaire responses indicated that consultation during and outside surgery hours and participation in case-discussion groups generally extended over more than two years, occurred frequently, and usually pertained to diverse problems associated with diagnosis and treatment. Participation in study and peer review groups extended usually over a shorter time (1 to 1 1/2 years) and the problems dealt with were predominantly the same as for individual consultation. One-third of the general practitioners consulted colleagues frequently and continued to do so for long periods, dealing systematically with a variety of problems; one-third did so infrequently or unsystematically, and one-third did little or not at all. A relationship was found between the setting of the practice and consulting behaviour: 20% of those who practised alone never consulted peers, whereas those in group practices and health centres were accustomed to do so regularly.

Nuclear magnetic resonance imaging of bone marrow in childhood leukaemia

Bone marrow infarction is known to occur in childhood leukaemia. Although it may be suspected on clinical grounds, radiographic evidence is infrequent. We present three cases in which magnetic resonance imaging demonstrated unexpectedly extensive bone marrow lesions and discuss the evidence that these lesions were due to bone marrow infarction.

Bone marrow magnetic resonance studies in childhood leukemia. Evaluation of osteonecrosis

In 25 patients under treatment or during follow-up for acute lymphoblastic leukemia magnetic resonance imaging (MRI) of both knees was compared to history and physical examination to detect osteonecrosis. Results of MRI were classified as: O, normal bone marrow (BM); 1, diffuse decrease in signal intensity; 2, circumscript lesions. Patients clinically suspected of osteonecrosis had a statistically significant increased incidence of Type 2 lesions. Three patients with a BM relapse also showed Type 2 lesions. Circumscript lesions of the epiphyses were seen exclusively in the four patients with clinical suspicion of osteonecrosis during BM remission and this may be a MR finding strongly indicative of osteonecrosis. Patients with Type 2 lesions during BM remission had received systemic chemotherapy for a statistically significant longer period than the other patients. Using MRI findings we suspect that at least four patients suffered osteonecrosis due to chemotherapy. MRI is a promising means of detecting this disorder.

Prognostic significance of acid alpha-naphthyl acetate esterase and acid phosphatase in childhood acute lymphoblastic leukemia

We studied the prognostic value of the enzymes acid alpha-naphthyl acetate esterase (ANAE) and acid phosphatase (AP) in 89 children with acute lymphoblastic leukemia (ALL). Follow-up data were available for 61 out of 67 cases of non T- non B-ALL, which were treated in different hospitals according to the same protocols. Sex, age, initial white blood cell count (WBC) and number of high risk patients (WBC above 25 X 10(9)/l) were comparable between enzyme-positive and -negative cases. The probabilities of complete continuous remission (CCR) were virtually identical in the AP+ and AP- group. For the ANAE+ group the probability of CCR was lower than for the ANAE- group, but this difference was not statistically significant (0.10 greater than p greater than 0.05). Within the common-ALL group (n = 32), no difference was found in probability of CCR between the AP+ and AP- group but ANAE+ cases had a significantly lower probability of CCR than ANAE- cases. This study is a contribution to the view that the cytochemical profile of ALL cells may have prognostic value.

Rheumatoid arthritis associated with bronchiolitis obliterans and immunoblastic sarcoma

A case is reported of a 72 year old man suffering from classical seropositive RA for 10 years. Two months before admission he experienced general illness, fever and itching. Lymph nodes enlargement and hepatosplenomegaly were found. Histologic features of lymph node biopsy were compatible with angioimmunoblastic lymphadenopathy and Lennert lymphoma. Rapidly progressive pulmonary deterioration followed with hilar invasion and honeycombing. Sternal punction, bone biopsy, bronchus biopsy and blind lung biopsy however, did not reveal lymphomatous invasion. On the contrary, lung biopsy, showed bronchiolitis obliterans, an often fatal, small airway disease whose connection with RA is discussed. Plasmapheresis induced a correction of leucopenia and thrombocytopenia. A fatal evolution evolved within six months. Autopsy revealed diffuse invasion by immunoblastic sarcoma. The clinicopathological entities angioimmunoblastic lymphadenopathy and Lennert lymphoma are referred to. The relationship with autoimmune disorders is stressed.

Arteritis associated with hyperviscosity-like syndrome in rheumatoid arthritis, treated by intermittent plasma-exchange for 2.5 years

A case is reported of a hyperviscosity-like syndrome in a 53-year-old male suffering from rheumatoid arthritis. The clinical presentation was an acute abdomen, peripheral neuritis, otovestibular areflexy, and central retinal vein thrombosis (papilloedema and retinopathy with venous engorgement, haemorrhages and exudates). Plasma viscosity was normal and whole blood viscosity, measured with an Oswald viscometer, was slightly elevated. The patient had markedly elevated rheumatoid factor tire and fibrinogen level. Histologically, there were no signs of arteritis in the mesentery. Intermittent plasma-exchange resulted in general improvement and no new vascular accidents after 2.5 years.

The effect of plasma exchange on synovitis in rheumatoid arthritis

Eight patients with a severe exacerbation of rheumatoid arthritis were treated by twice weekly plasma-exchange for 3 weeks in order to evaluate the effect of plasma-exchange on synovitis. During the plasma-exchange period, patients remained on the drug regimen they were on at admission to the hospital. Plasma was replaced isovolemically with human, purified plasma protein fraction. Improvement in clinical parameters of synovitis and serological parameters of inflammation occurred in almost all patients. After 6 months the clinical remissions were sustained. Three patients experienced a rebound synovitis and one patient a rebound vasculitis at the end of or just after the plasma-exchange period. The rebound phenomena were moderate and of short duration. Plasma-exchange may exert its beneficial effects by depleting important mediators of injury such a complement fibrinogen and circulating immune complexes, by improving reticuloendothelial function, and by increasing the drug response of the inflammatory target tissue. The role of depletion of circulating immune complexes was not so clear in this study. It is concluded that limited plasma-exchange is an effective means to induce a symptomatic improvement in an acute exacerbation of polyarthritis, without changing the basic therapy and thus avoiding corticosteroid dependency.