PubMed Health⌕ Search

Biomedical subjects

R A Maas

Publications and source records attributed to R A Maas.

At least 19 recordsLinked to original sources
PubMed2003

Correlation of haemagglutinin-neuraminidase and fusion protein content with protective antibody response after immunisation with inactivated Newcastle disease vaccines.

The correlation between the antigen content of inactivated Newcastle disease (ND) oil emulsion-vaccines and the serological response after immunisation was studied. The haemagglutinin-neuraminidase (HN) and fusion (F) proteins of Newcastle disease virus (NDV) were quantified in 33 inactivated oil-adjuvanted ND vaccines using isopropylmyristate (IPM)-extraction and antigen ELISAs. These commercial vaccines differed in NDV-vaccine strain, the method applied to inactivate the vaccine virus, the vaccine valence and the composition of the oil emulsions. Large differences, up to 100-fold, in the antigen quantities present in different vaccines were found. The NDV-HN content and the NDV-F content of the vaccines both highly correlated with the haemagglutination-inhibiting (HI) antibody titres after immunisation. These correlation's were found over a 10,000-fold range of applied antigen. The antigen content of the oil emulsion-vaccines also highly correlated with virus neutralising antibody titres. The presence of serum HI antibody titres in individual specific pathogens free (SPF)-chickens after immunisation with inactivated ND vaccines was highly indicative for clinical protection against challenge with the virulent NDV-Herts strain. Our results are the first to demonstrate that the protective serological response after immunisation highly correlates with the antigen content of oil-adjuvanted vaccines.

Adjuvants, Immunologic↗
PubMed2000

Antigen quantification as in vitro alternative for potency testing of inactivated viral poultry vaccines.

Routine batch control of licensed inactivated viral vaccines for poultry usually includes a potency assay as a measure of vaccine efficacy. Potency assays often consist of vaccination-challenge experiments in the target species or in laboratory animals. Instead of measuring the protection of vaccinated animals against virulent pathogens, the serological response after vaccination can be quantified for some vaccines. In vitro antigen quantification assays would be attractive alternatives for the current potency assays because the time and costs involved could be greatly reduced and animal use could be avoided. Such in vitro assays will only be acceptable when the correlation between results and efficacy or potency has been demonstrated convincingly. The results of our studies on antigen quantification assays indicate that, in principle, quantification of viral antigens from inactivated oil-adjuvanted vaccines is feasible and reproducible using specially developed antigen capture ELISAs in combination with specific software for statistical analysis of the ELISA data. We have developed methods to quantify the haemagglutination-neuraminidase (HN) and fusion (F) proteins of Newcastle disease virus (NDV), the viral protein 3 (VP3) of the infectious bursal disease virus (IBDV), and the spike-1 (S1) protein of the infectious bronchitis virus (IBV). Vaccination experiments with inactivated ND vaccines indicate that the in vitro quantified HN- or F-proteins of NDV are reliable indicators of the serological response after vaccination.

Animals↗
PubMed1999

Local low-dose IL-2 therapy.

Interleukin-2 (IL-2) is a powerful drug for treating cancer. However, it is only powerful if it is properly applied. That is, IL-2 should be applied at the tumor site, because at the transition of normal and malignant tissue are the tumor infiltrating cells. These should be activated by IL-2. Local application implies that IL-2 can be used in relatively low doses. It is becoming clear that even a single injection of IL-2 can cure cancer. IL-2 can also enhance the therapeutic effects of irradiation and Cisplatin. Locally applied IL-2 therapy is virtually non-toxic.

Animals↗
PubMed1997

A method to monitor mRNA levels in human breast tumor cells obtained by fine-needle aspiration.

A method based on the reverse transcriptase-polymerase chain reaction (RT-PCR) was developed that allows the determination of relative mRNA expression levels in fine-needle aspirates from human tumors. The method was developed for the c-erbB-2 gene, using the porphobilinogen deaminase (PBGD) gene as an internal standard. It was validated for mRNA isolated from cell lines and for material obtained by fine-needle aspiration from human breast cancer. Gene expression levels were determined by measuring the activity of radiolabeled RT-PCR-amplified gene-specific bands with a phosphor imager. At least four points are measured on the log-linear part of the amplification cycle versus signal intensity curves, and subsequently the distance between the curves of the gene of interest and that of an internal standard gene is used to calculate the relative expression levels. The method worked equally well with the BRCA1 gene, illustrating that it can be generalized to other genes. The method is suitable to measure or monitor semiquantitively gene expression levels in accessible human tumors in situ.

BRCA1 Protein↗
PubMed1996

Iododeoxyuridine labelling of S-phase fraction in fine needle aspirates from breast carcinomas.

The suitability of measuring the S-phase fraction in human breast cancer by labelling tumour cells from fine needle aspirates (FNAs) in vitro with iododeoxyuridine (IdU) was studied in 11 patients. The S-phase fraction was measured both in preoperative FNAs labelled in vitro with IdU, and in FNAs taken from the same tumour when surgically removed after intravenous administration of IdU. Frozen sections were also immunostained for incorporated IdU. The mean S-phase fraction measured in FNAs after in vitro or in vivo labelling and in sections after in vivo labelling was 4.0, 3.6, and 3.1, respectively. Results of in vitro and in vivo labelling of FNAs with IdU were similar. However, as the S-phase fraction in breast cancer is generally low, the variation between the different measurements is too large; therefore, the S-phase fraction is not a suitable indicator of response to treatment.

Biopsy, Needle↗
PubMed1995

Growth arrest associated changes of mRNA levels in breast cancer cells measured by semi-quantitative RT-PCR: potential early indicators of treatment response.

To find early and sensitive indicators of treatment response in breast cancer, we studied the mRNA levels of proliferation-related genes during growth arrest of the human breast cancer cell lines T47D and MCF7. A sensitive reverse transcriptase-PCR (RT-PCR) technique was used in order to monitor gene expression in small samples of cells. Estrogen-depletion and treatment with tamoxifen effectively induced a G1-arrest in both cell lines, accompanied by a decrease of the mRNA levels of histone H4, cyclin A, cyclin D1, and c-myc. Cyclin A expression decreased most strongly: up to 32-fold within 7 days. The expression of c-fos and WAF1 increased during growth arrest. In conclusion, significant changes of the levels of proliferation-related mRNAs, induced by growth arrest, can be measured in small samples of breast carcinoma cells using RT-PCR. Especially the decrease of the cyclin A mRNA level seems a potential early indicator of clinical response to tamoxifen therapy in breast cancer patients.

Base Sequence↗
PubMed1995

Immunomagnetic purification of human breast carcinoma cells allows tumor-specific detection of multidrug resistance gene 1-mRNA by reverse transcriptase polymerase chain reaction in fine-needle aspirates.

BACKGROUND: The heterogenous composition of tumors is a major obstacle for the measurement of mRNA levels in cancer cells. We report here a combination of immunomagnetic purification of cancer cells and reverse transcriptase polymerase chain reaction (RT-PCR) that enables highly sensitive detection of multidrug resistance gene 1 (MDR1)-mRNA levels in human breast carcinoma cells obtained from fine needle aspirates (FNA). EXPERIMENTAL DESIGN: Murine mAb 115D8 directed against episialin (MUC1/MAM6, epithelial membrane Ag) was used in combination with goat anti-mouse-coated magnetic microbeads to purify human T47D breast carcinoma cells (115D8+, MDR1-) from different mixtures with COLO320 human colon carcinoma cells (115D8-, MDR1+) and to purify carcinoma cells from FNA taken from axillary lymph node metastases in breast cancer patients. The efficacy of the purification was determined by FACS-analysis and by measurement of MDR1-mRNA levels by semiquantitative RT-PCR. RESULTS: FACS-analysis demonstrated that T47D cells could be purified up to 99.8% from mixtures with COLO320 cells ranging from 3:1 to 1:3. The MDR1-mRNA level in these enriched mixtures, as detected by RT-PCR, was reduced 250-fold. It was demonstrated that MDR1 expression present in an FNA from a lymph node metastasis of breast carcinoma could be attributed completely to the leukocytes present in this FNA, because MDR1 expression was no longer detectable after purification of the tumor cells. CONCLUSION: The combination of immunomagnetic purification of breast carcinoma cells and RT-PCR enables the measurement of cancer-specific MDR1 mRNA levels in small cell samples obtained by FNA.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1993

Interleukin-2 in cancer treatment: disappointing or (still) promising? A review.

The central question to discuss in this review is whether the results of interleukin-2 (IL-2) treatment are still disappointing or again promising. Although in the (recent) past application of high doses of systemically applied rIL-2 has led to some success, the overall results are not as one had hoped. Considering these poor results it seems clear that the application of high systemic doses rIL-2 was not a good choice. IL-2 has been used more or less as a chemotherapeutic compound in the highest tolerable dose. This has led to a great number of unwanted toxic side-effects. In addition, these doses mainly stimulated nonspecific lymphokine-activated killer activity through low-affinity IL-2 receptors, which does not lead to systemic immunity. On the other hand, several groups have shown that application of intratumoral low doses of IL-2 can be highly effective against cancer and without toxic side-effects. Significant tumor loads constituting up to 6% of the total body weight of a mouse were eradicated after treatment with low-dose rIL-2 given locally. Furthermore local treatment can lead to eradication of a tumor at a distant site. This type of therapy is effective in many systems namely against different tumor types in mice, hepatocellular carcinoma in guinea-pigs and vulval papilloma and carcinoma and ocular carcinoma in cattle. Low-dose IL-2 is very effective in experimental animals if it is given relatively late after inoculation of the tumor cells. In other words, it seems necessary that some sort of immune reaction has started or is developing before low doses of rIL-2 effectively stimulate it. In fact there is strong evidence that T lymphocytes, both CD4+ and CD8+ cells, are directly involved in the process leading to induction of specific immunity. In our opinion rIL-2 therapy should therefore aim at the stimulation of such (originally weak) specific immune reaction. Under these conditions also systemic immunity can be induced. In conclusion, application of rIL-2 as a modality for cancer treatment is still promising. High priority should be given to a further delineation of the mechanisms involved after local application. The method of giving IL-2 systemically in the highest tolerable dose should be abandoned. Specific stimulation of the immune system by low-dose rIL-2 is a much more promising option.

Animals↗
PubMed1993

Histological analysis of IL-2 induced regression of murine solid SL2-tumors.

When DBA/2 mice are inoculated both intraperitoneally (i.p.) and subcutaneously (s.c.) with syngeneic SL2 lymphoma cells and treated i.p. on day 10-14 with 20,000 units IL-2/day, about 50% of the mice reject both the ascitic tumour and the s.c. tumour. During IL-2 therapy large areas of necrosis appear in the solid SL2 tumours between day 12 and 15. Immunohistochemical studies show that only a small number of infiltrating cells is present in the tumours. The percentage of macrophages (MHC-II+) in the tumours is about 1 and the percentage of T-lymphocytes (alpha beta-TCR+) about 0.5. No differences in the numbers of infiltrating cells are seen in untreated and IL-2 treated tumour bearing mice. The tumour surrounding infiltrate consists mainly of mononuclear cells: about 50% macrophages, 20% CD8+ cells, and 15% CD4+ cells. No tumour-infiltrating cells were found that express the IL-2 receptor. We conclude that direct cytotoxic activity of tumour infiltrating cells cannot account for the rapid occurrence of necrosis. When L3T4+ cells were eliminated by treating the mice with alpha-L3T4 monoclonal antibodies before tumor inoculation and treatment with rIL-2, tumor eradication did not occur. So, L3T4+ helper T-cells are essential for IL-2-mediated tumour regression. Exogenous rIL-2 is not directly responsible for the induced tumour regression. A significant stagnation of intratumoural bloodflow is observed after histological analysis; yet it still needs to be determined whether this is the primary cause or consequence of the observed necrosis.

Animals↗
PubMed1993

Transfer of tumor immunity by both CD4+ and CD8+ tumor infiltrating T lymphocytes activated in vivo by IL-2 therapy of tumor bearing mice.

DBA/2 mice were inoculated i.p. with syngeneic SL2 lymphoma or P815 mastocytoma on day 0 and treated i.p. with 20,000 units IL-2/day on day 10-14. This treatment is curative for 70-90% of the tumor bearing mice. Peritoneal cells and/or spleen cells were isolated from responding mice at the last day of IL-2 therapy. The in vivo antitumor activity of these cells was tested in Winn Assays (i.p.) and by adoptive transfer (i.v.) into mice injected s.c. with tumor previously. Peritoneal exudate cells isolated on day 14 (PEC14) from mice cured of SL2 tumor were highly effective in Winn Assays. Up to 5 x 10(7) SL2 cells could be eliminated in naive mice when injected i.p. together with 2 x 10(7) PEC14. Adoptive transfer (i.v.) of PEC14, without the addition of IL-2, into mice s.c. injected with SL2 tumor cells 1 or 3 days earlier, also prevented outgrowth of the tumor cells. T cells isolated from the spleens were less effective. Only at E:T ratios of 100:1 and 10:1 was tumor outgrowth inhibited. The adoptive transfer of PEC14 resulted in a long lasting immunity of the recipient mice. Furthermore, it was shown that depletion of both the CD8+ and CD4+ T cells from the suspensions used in the transfer studies, resulted in a significant decrease of tumor inhibition. However, the effect was not abrogated completely. PEC14 isolated from IL-2-treated DBA/2 mice cured of P815 tumor, protected naive mice against P815 tumor at E:T ratio 20:1. Adoptive transfer (i.v.) of these PEC14 into mice bearing s.c. P815 did not have an antitumor effect. In conclusion, low dose i.p. IL-2 therapy predominantly induces locally both CD4+ and CD8+ T cells with a strong antitumor activity in vivo. The potency of the IL-2-induced immunity seems related to the type of tumor used.

Animals↗
PubMed1992

Effector cells of low-dose IL-2 immunotherapy in tumor bearing mice: tumor cell killing by CD8+ cytotoxic T lymphocytes and macrophages.

The presence and cytotoxicity of tumor infiltrating cells is described in mice during effective immunotherapy with interleukin 2 (IL-2). DBA/2 mice were inoculated i.p. with 2 x 10(4) tumor cells on day 0 and treated with daily i.p. injections with 20,000 units IL-2 on days 10-14. Mice bearing a large syngeneic i.p. tumor burden (SL2 lymphoma, P815 mastocytoma, L5178Y lymphoma, or L1210 lymphoma) could be cured by i.p. immunotherapy with these low doses of IL-2. In the peritoneal cavity of these mice an infiltrate of mononuclear cells was present. Similar numbers of lymphocytes (10(6)-10(7)) and macrophages (+/- 10(7)) were present in control tumor bearing mice and IL-2 treated tumor bearing mice. The ratio of CD4+/CD8+ T lymphocytes in the peritoneal cavity of mice rejecting the SL2 tumor was smaller than 0.5, whereas this ratio is about 2 in naive mice. In the spleens of IL-2 treated tumor bearing mice only a minor decrease of CD4+/CD8+ ratio was observed from 2.1-2.4 to 0.9-1.9. T cells isolated from the peritoneal cavity of mice inoculated with SL2 tumor cells and treated with IL-2, were highly cytotoxic to SL2 cells: at E:T ratio 2:1 the cytotoxicity index was 37 +/- 3. This cytotoxicity was specific and mediated by CD8+ T lymphocytes. Macrophages that were present in the peritoneal cavity of mice treated with IL-2 were also highly cytotoxic. The C.I. of these cells was 63-76% at E:T ratio 1:1. Cytotoxic macrophages were also present in untreated tumor bearing mice. The i.p. injections of IL-2 (20,000 units/day) caused a four-fold increase in the local NK-activity in the peritoneal cavity in naive mice. These IL-2 injections did not generate LAK-activity in vivo. Specificity of the in vivo tumor rejection was tested by injection SL 2 i.p. on day 0 and P815 i.p. on day 10, or vice versa, followed by IL-2 treatment. Only the tumor cells that were injected on day 0 were rejected. These in vivo experiments point to specific tumor rejection. In conclusion, both cytotoxic macrophages and CTL's are present in a sufficient number and with sufficient cytotoxicity to explain the killing of tumor cells in the peritoneal cavity. The CTL-activity seems of decisive importance for tumor rejection as this is induced by IL-2.

Animals↗
PubMed1991

Intratumoral low-dose interleukin-2 induces rejection of distant solid tumour.

This study shows that local tumor treatment with low-dose recombinant interleukin-2 (IL-2) can mediate rejection of a large distant solid tumour. When SL2 lymphoma cells were injected intraperitoneally (i.p.) in syngeneic DBA/2 mice on day 0.70% of these mice were cured by daily i.p. injections with 20,000 units IL-2 on days 10-14. After injecting mice with SL2 both i.p. and subcutaneously (s.c.) on the flank. 50% of the mice treated i.p. with low-dose IL-2 rejected both the i.p. tumour and the large distant s.c. tumour. In contrast, i.p. IL-2 treatment on days 10-14 cured fewer than 10% of the mice bearing only a s.c. SL2 tumour. The described IL-2 immunotherapy also caused systemic tumour rejection in mice bearing both ascitic and solid P815 mastocytoma. Thus it was shown that low-dose IL-2 can induce systemic tumour rejection, when injected at a site of tumour growth. Interleukin-2-induced rejection of s.c. SL2 tumour was highly specific, as mice that were rejecting i.p. and solid s.c. SL2 lymphoma did not reject solid P815 mastocytoma, which was injected s.c. simultaneously on the other flank. Furthermore, solid s.c. tumours consisting of mixtures of SL2 and P815 were not rejected in mice that rejected i.p. SL2 or P815. We conclude that intratumoral injections of low-dose IL-2 can enhance an ongoing weak immune reaction against the tumour resulting in systemic tumour rejection.

Animals↗
PubMed1991

Lymphokine-activated killer-cell-mediated killing of WiDr colon carcinoma cells is inhibited by K562 erythroleukemia cells.

Lymphokine activated killer (LAK) activity was induced in human peripheral mononuclear blood cells by human recombinant interleukin-2. Monocytes were required for optimal rapid proliferation of cells with LAK activity. They had no influence on the expression of tumoricidal activity by the LAK cells. The effector cells killed K562 erythroleukemia cells and WiDr colon cells differently, i.e. contact areas with WiDr cells were limited, whereas the contact areas between effector cells and K562 cells were much longer. Using mixtures of hot and cold target cells it was shown that effector cells preferably bind with K562 cells, impeding the binding of WiDr cells. Differences in expression of cytotoxicity of LAK cells against WiDr and K562 cells respectively was also observed after culturing the LAK cells for a relatively longer period. Cytotoxicity against WiDr was maximal at 3-16 days after starting LAK cell generation, whereas cytotoxicity against K562 was kept constantly high for at least 21 days. The addition of biological response modifiers [PHA and anti-CD3 antibody (OKT3)] during the LAK cell induction also had different effects on the expression of LAK activity against WiDr and K562 cells. Whereas PHA, in combination with rIL-2 had no significant influence on the cytotoxicity against WiDr cells, the cytotoxicity against K562 was significantly inhibited. Addition of anti-CD3 antibody diminished the cytotoxicity against WiDr target cells and had no influence on the cytotoxicity against K562 cells.

Carcinoma↗
PubMed1989

Immunotherapy of mice with a large burden of disseminated lymphoma with low-dose interleukin 2.

Successful immunotherapy with recombinant interleukin 2 (rIL-2) of mice bearing a large burden of lymphokine-activated killer-resistant disseminated SL2 lymphoma is described. When mice were challenged i.p. with 2 x 10(4) SL2 cells on day 0 and treated with daily i.p. injections of 5,000 units rIL-2 on days 3-7, no therapeutic effect was observed. However after treatment with daily IL-2 injections on day 10-14, 25% of the mice survived. Ten days after this tumor challenge more than 10(8) SL2 cells were present growing as ascitic tumor. On day 10, SL2 cells were also present as solid tumor in the greater omentum and as metastases in lungs and liver. Surviving mice were able to reject a second challenge with SL2 cells given on day 60. A second challenge with P815, another DBA/2 tumor, resulted in death of the mice due to tumor development. This finding is of particular importance as the SL2 cells are resistant to lymphokine-activated killer activity. Thus local (i.p.) injection of low dose rIL-2 can cause the systemic rejection of advanced and metastasized cancer. Our data indicate that IL-2 can strongly enhance a specific immune reaction against tumor cells.

Animals↗
PubMedDate not supplied

Dose-response effects of inactivated Newcastle disease vaccines: influence of serologic assay, time after vaccination, and type of chickens.

Knowledge of the dose-response relation of inactivated vaccines and of the factors that influence this relation is essential for the evaluation of existing vaccine potency assays and the development of new potency assays that are based on the antigen content of the inactivated vaccines. We quantified the relation between vaccine dose, serologic response, and clinical protection after vaccination for three different inactivated Newcastle disease (ND) vaccines. Qualitatively, similar dose-response curves were obtained for the three vaccines when either the serologic response or the clinical protection of specific-pathogen-free (SPF) chickens was plotted against the different vaccine doses applied. However, the vaccines differed quantitatively: doses of vaccines that induced similar antibody titers or clinical protection differed 2-8-fold. In contrast with the narrow range of antibody titers induced by a full vaccine dose, a very broad range of titers was obtained after dilution of the vaccines. At least 95% of the SPF chickens with detectable antibody in the serum were protected against a challenge with virulent Herts ND virus. The relation between the dosage of two different ND vaccines and the serum antibody titers remained markedly constant between 3 and 18 wk after vaccination. Vaccination of broilers instead of layers with a dilution series of inactivated ND vaccine resulted in significantly lower antibody levels and less clinical protection against virulent challenge. In conclusion, despite quantitative differences, we found comparable dose-response relations for the three inactivated ND vaccines studied.

Animals↗
PubMedDate not supplied

Effective immunotherapy with local low doses of interleukin-2.

IL-2 treatment for metastatic tumors in man is usually given systemically with high doses, often in conjunction with large numbers of LAK-cells. Complete tumor regression is obtained in less than 10%, this treatment causes severe toxicity, and culturing of LAK-cells is laborious and expensive. In this paper we demonstrate that small amounts of locally applied rIL-2 alone, if given at the right time, can cure about 70% of DBA/2 mice with large metastasized syngeneic SL2 lymphoma comprising 4-10% of the total body weight, a tumor load hitherto considered fatal. Moreover, 3 out of 5 cows with ocular squamous cell carcinoma (BOSCC) of 1 x 1 up to 3 x 4 cm were cured with low doses of rIL-2 only. Taken together, we have now tested 11 tumors in animals. No antitumor effect was observed in EL4 lymphoma in C57BL mice. Partial antitumor effects were detected in RBL5 lymphoma in C57BL mice, stomach carcinoma in BALB/c mice, MOT-carcinoma in C3H mice, liver carcinoma in guinea pigs and bovine vulval papilloma/carcinoma. Complete tumor regression was obtained in SL2 lymphoma, L5178Y lymphoma, L1210 lymphoma, and P815 mastocytoma in DBA/2 mice and in bovine ocular squamous cell carcinoma. Low doses of locally injected IL-2 induce systemic immunity, as shown in DBA/2 mice bearing syngeneic SL2 lymphoma cells. We conclude that local low dose treatment can be effective and results in a high cure rate in several tumor models. In the DBA/2-SL2 lymphoma model this treatment is 100-1000 times more effective than any form of immunotherapy we have tested during 20 years in this model.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗