[Effect of chronic Chlamydia infection with non-specific inflammation on cardiovascular complications in acute myocardial infarct]

It is known that local and systemic inflammatory processes play an important role in the genesis and development of atheroclerotic lesions and in the pathophysiology of acute coronary syndromes. This hypothesis is supported by findings of elevated parameters of the "inflammatory" reaction in the affected blood vessels but also in the blood of atherosclerotic patients. Known risk factors do not explain quite satisfactorily epidemiological cardiovascular phenomena and different manifestations of coronary heart disease. It is very probable that also Chlamydia pneumoniae is a risk factor. This assumption is based on evaluation of seroepidemiological data, examination of atherosclerotic plaques not only in humans but also in animal models with chlamydial infection. Based on retrospective and prospective evaluation of case-records the authors analyzed the incidence of cardiovascular complications in 83 patients with acute myocardial infarction (AIM), incl. 51 patients (31 men and 20 women, mean age 64.4 +/- 3.4 years who had a non-specific inflammation and chlamydial infection, and 32 patients (24 men and 8 women, mean age 64.7 +/- 3.6 years) who had chlamydial infections but no non-specific inflammation (in the blood). These patients were selected from all patients hospitalized during 1998-2001. When diagnosing acute myocardial infarction we applied WHO criteria, and the presence of at least two of three criteria was necessary: a history of prolonged (more than 20 min). stenocardia, electrocardiographic changes typical for ischaemia and/or necrosis and elevation of myocardial enzymes in serum, Non-specific inflammatory activity was present in patients (i.e. positive) if the following laboratory parameters were recorded: C-reactive protein > 5 mg/l assessed by the radial immunodiffusion method; fibrinogen > 4 mg/l assessed by the coagulation method according to Claus; leukocytes > 9.6 x 10(3)/microliter, leukocytes were counted automatically in a Coulter chamber; lymphocytes > 3.4 x 10(3)/microliter. Red cell sedimentation rate > 20 mm/hour. The activity was evaluated as positive when all parameters were elevated. The presence of chronic infection with Chlamydia pneumoniae was assessed qualitatively by antibody positivity (IgG) in serum using the microimmunoflurescent method (using a set from Labsystems Co.). The incidence of associated risk factors (obesity, smoking, diabetes, hyperlipidaemia and hypertension) is higher in the sub-group of patients with Chlamydia infections without inflammation, however, the difference is not statistically significant. The incidence of cardiovascular attacks was higher in the sub-group of patients with chlamydial infection and concurrent inflammation as compared with the sub-group of patients with chlamydial infection without inflammation. In case of re-infarction of the myocardium, a sudden cerebrovascular attack, death and arrhythmia the difference was statistically significant, while in case of cardiac failure and cardiogenic shock the difference was not significant. Patients with acute myocardial infarction with chlamydial infection and a concurrent non-specific inflammation had to be treated more often by combined (i.e. more intense) treatment, thrombolytic treatment, PTCA and surgery (bypass) of the coronary vessels as compared with patients with Chlamydia infections but without inflammation. The authors assume therefore that not only different risk factors but also the effect of non-specific inflammation and Chlamydia infection contribute towards the increased number of cardiovascular postinfarction complications. Therefore a therapeutic approach involving eradication of infection and suppression of the inflammatory reaction should be considered.

Intraperitoneal adoptive immunotherapy of ovarian carcinoma with tumor-infiltrating lymphocytes and low-dose recombinant interleukin-2: a pilot trial

A pilot study was conducted in patients who had advanced epithelial ovarian carcinoma, and who were refractory to platinum-based chemotherapy, to determine the feasibility and clinical effects of a schedule of intraperitoneal (IP) tumor-infiltrating lymphocytes (TIL) expanded in recombinant interleukin-2 (rIL-2), and low-dose rIL-2 IP. TIL were expanded from solid metastases or malignant effusions in serum-free AIM V medium supplemented with low concentrations (600 IU/ml) or rIL-2 using a four-step method of expansion that included a hollow fiber bioreactor (artificial capillary culture system). Patients received IP TIL suspended in dextrose 5% in sodium chloride 0.2% containing 0.1% human albumin and 6 x 10(5) IU rIL-2 on day 1, followed by 6 x 10(5) IU rIL-2/m2 body surface area, administered daily by bolus IP injection, on days 2-4, 8-11, and 15-18. In the absence of disease progression, two additional 4-day cycles of IP rIL-2 were administered. Patients (n = 3) whose TIL failed to grow in vitro received IP IL-2 alone. Eight patients received rIL-2 expanded TIL (10(10)-10(11) range) plus rIL-2 followed by several cycles of rIL-2 alone. One of these patients was treated twice with TIL plus rIL-2. Expanded TIL were primarily CD3+CD4+TCR alpha beta+ (eight TIL-derived T-cell lines). One TIL-derived T-cell line was comprised mostly of CD3+CD8+TCR alpha beta+ cells. Eleven patients (eight treated with TIL plus rIL-2 and three patients treated with rIL-2 alone) received a total of 38 cycles of rIL-2 without TIL. Grade 3 clinical toxicity (peritonitis) occurred in 1 of 9 cycles of TIL plus rIL-2 and 1 of 38 cycles of rIL-2 alone. Each cycle was 4 days long. Grade 3 anemia occurred in 1 of 9 TIL plus rIL-2 cycles and 3 of 38 cycles of rIL-2 alone. There were no measurable responses; however, four of eight patients treated with IP TIL plus rIL-2 had some indication of clinical activity: ascites regression (two patients), tumor and CA-125 reduction (one patient), and surgically confirmed stable tumor and CA-125 values (one patient). The schedule of IP TIL plus low-dose rIL-2 shows manageable toxicity and is worthy of further evaluation in patients with epithelial ovarian cancer who have less tumor burden.

Large-scale expansion in interleukin-2 of tumor-infiltrating lymphocytes from patients with ovarian carcinoma for adoptive immunotherapy

Tumor infiltrating lymphocytes (TIL) from malignant ascites or solid tumor specimens obtained from patients with ovarian carcinoma were expanded to large numbers in vitro (10(10)-10(11)) by a four-step method using AIM V medium and low concentrations of recombinant interleukin-2 (rIL-2). The expansion procedure employed 24-well culture plates, T-flasks, polyolefin gas-permeable bags (PGPB), and an artificial capillary culture system (ACCS). The mean number of mononuclear leukocytes introduced into the 24-well plates was 16.5 +/- 4.2 x 10(6) cells. TIL from a total of 16 patients were expanded only through the first three steps of the process (24-well-plates, T-flasks, and PGPB) with an overall expansion of 255 +/- 99 fold and mean duration of 27.4 +/- 2.2 days. TIL from 9 of 16 patients were expanded further through the fourth step (ACCS) of the expansion method. The cumulative fold-expansion in nine patients was 8044 +/- 4807 (mean +/- SEM), the median was 2876 and the mean expansion time was 47.1 +/- 4.7 days. TIL from seven additional patients did not grow in rIL-2. Six of these 7 patients received chemotherapy at least four weeks before the specimens were collected. Two ACCS were used in parallel to facilitate expansion of TIL. Viable rIL-2-expanded TIL in the range of 1 x 10(10)-1 x 10(11) were recovered from the two ACCS, a number sufficient for adoptive immunotherapy of patients with ovarian carcinoma. The rIL-2-expanded TIL were predominantly CD3+ CD4+ CD8- alpha beta TCR+, although CD3+ CD4- CD8+ alpha beta TCR+ T cell lines were obtained from certain patients. An increase (43 +/- 8 vs 75 +/- 13; P = 0.05) in the proportion of CD4+ cells was observed over the duration of the four expansion steps. However, CD8+ TIL-derived T cells lines were also expanded in the ACCS. The four-step expansion method described here has several significant advantages over existing techniques. It requires substantially less personnel, equipment and space and the risk of contamination during expansion of the cultures is decreased. These results demonstrate that the four-step method described here can be effectively used for the large-scale expansion of ovarian TIL for the treatment of patients with ovarian carcinoma by adoptive immunotherapy.

Induction of interleukin-2 receptor by tumor necrosis factor alpha on cultured ovarian tumor-associated lymphocytes

We have recently reported that autologous tumor-specific cytotoxic T lymphocyte (CTL) lines and clones can be developed from lymphocytes infiltrating ovarian malignant ascites (TAL). In this study, we investigated the biological effects of tumor necrosis factor alpha (TNF alpha) in the induction, expansion, long-term proliferation and lytic function of CD8+ TAL. TNF alpha up-regulated the IL-2 receptor (IL-2R) alpha chain (Tac antigen) on the surface of CD3+ CD8+ CD4- TAL, enhanced the proliferation of autologous tumor-specific CTL, and potentiated their lytic function in long-term cultures. Furthermore, in the induction and expansion phase of CD8+ TAL, the presence of TNF alpha was associated with a selective increase in CD8+ IL-2R+ (Tac+) cells, and subsequent decrease in CD4+ IL-2R+ (Tac+) cells. These results suggest that the observed facilitation of the outgrowth of CD8+ cells in TAL cultures may be due, at least in part, to the up-regulation of IL-2R, and indicate the usefulness of TNF alpha in the analysis of signalling in autologous tumor-reactive CTL.

Development of a cell surface reacting human monoclonal antibody recognizing ovarian and certain other malignancies

A human monoclonal antibody designated AC6C3 was developed by fusing regional lymph node lymphocytes from a patient with epithelial ovarian carcinoma with cells of the hybrid myeloma SPAZ 4. This monoclonal antibody recognized a determinant expressed on the cell surface of ovarian tumor cell lines. The AC6C3 hybridoma has been maintained for more than 24 months by repeated cloning and secretes IgM at concentrations of 2-8 micrograms/10(6) cells/24h. The AC6C3 monoclonal antibody reacted with a cell surface component of ovarian tumor cell lines, as determined by cell surface immunofluorescence staining using the fluorescent activated cell sorter (FACS). In contrast, nylon wool nonadherent peripheral blood lymphocytes or red blood cells from normal donors were negative (less than 5% of the cells were stained). Immunoperoxidase staining with the AC6C3 monoclonal antibody of nonpermeabilized cryostat sections of freshly obtained or cryopreserved ovarian carcinoma specimens and human ovarian tumor xenografts demonstrated strong reactivity of these specimens. Most normal tissues including brain, liver, heart, kidney and peritoneum demonstrated negative or weak reactions with AC6C3. Other carcinomas including breast, colon and some malignancies of neuroectodermal origin were strongly reactive with AC6C3. AC6C3 mediated complement-dependent cytotoxicity and identified a 32 Kd band in Western blotting and immunoprecipitation experiments conducted on surface labelled SKOV3 cells. The association constant for AC6C3 was determined at 2.3 x 10(10) M-1.

Antitumor activity against human tumor samples of cis-diamminedichloroplatinum(II) and analogues at equivalent in vitro myelotoxic concentrations

We compared the antitumor activity of cis-diamminedichloroplatinum(II) (cisplatin; CDDP) with three CDDP analogues: cis-diammine-1,1-cyclobutanedicarboxylateplatinum(II) (CBDCA), N-methyliminodiacetato-1,2-diamino(cyclohexane)platinum(II) (MIDP), and N-(2-hydroxyethyl)-iminodiacetato-1,2-diamino(cyclohexane)platinum (II) (HIDP). Fresh human tumor samples in the adhesive tumor culture system were utilized for this comparison. The equitoxic concentrations of all four drugs were derived based on their inhibitory activity against human bone marrow samples. For these normalized concentrations, CDDP proved to have a higher cytotoxic activity than its analogues. CBDCA's in vitro activity had a significant correlation with CDDP activity (r = 0.67) in vitro. However, the structurally similar substances MIDP and HIDP demonstrated a much greater degree of association (r = 0.90). Our data suggest that CBDCA, HIDP, and MIDP have overall less activity than CDDP when tested at equitoxic in vitro concentrations. Close association between CDDP and CBDCA also reflects known clinical experience with these two drugs, suggesting the method of comparison used here is probably appropriate. These conclusions, however, must be validated by clinical trials.

Involvement of chromosome 7 in primary lung tumor and nonmalignant normal lung tissue

By using the newly developed adhesive tumor cell culture system, we analyzed the chromosomal constitutions of primary lung tumor and nonmalignant normal lung tissue from 10 previously untreated patients with non-small cell lung cancer. Chromosomal analyses were successfully carried out in banded chromosome preparations from 10 tumor and 8 normal lung tissue samples. All analyzed tumor and normal lung tissue samples had a predominantly normal diploid chromosome number. However, there was at least one structural or numerical alteration in every tumor and lung tissue sample analyzed. Chromosomes 1, 3, 4, 6, 7, 8, 9, 12, 15, and 20 were more often involved in rearrangement. The most consistent finding was trisomy 7; 4 patients had trisomy 7 in both tumor and normal lung tissue, and another 2 had this anomaly in tumor tissue only. Of the 4 patients without trisomy 7, 2 had a homogeneously staining region in the short arm of chromosome 7 in tumor tissue. Phytohemagglutinin-stimulated peripheral blood lymphocytes from 7 patients, including 5 patients with trisomy 7 in tumor tissue, did not show trisomy 7. These cytogenetic data suggest that chromosome 7 may be associated with lung cancer development and that trisomy 7 may be the hallmark of premalignant changes, at least in a subgroup of patients with non-small cell lung cancer.

Comparison between clinical response and in vitro drug sensitivity of primary human tumors in the adhesive tumor cell culture system

The newly described adhesive tumor cell culture system (ATCCS) offers a distinct advantage over other assays in that it has a high plating efficiency requiring low cell inoculum, it affords workable assays in approximately 70% of specimens from the heterogenous tumor types, and it has the ability to assay up to nine drugs at four different concentrations. Clinical correlations based on the ATCCS were obtained in 65 patients undergoing 71 clinical trials. Patients with melanoma, lung cancer, and sarcoma dominated the group. The most active in vitro drug was correlated per clinical trial. Thirteen of 17 (76%) sensitive in vitro predictions and 51 of 54 (94%) resistant in vitro predictions were accurate. The assay in this study had a sensitivity of 81% and specificity of 93%. These preliminary results are encouraging and warrant prospective trials to establish the true value of this assay to patients.

Comparison of antitumor activity of standard and investigational drugs at equivalent granulocyte-macrophage colony-forming cell inhibitory concentrations in the adhesive tumor cell culture system: an in vitro method of screening new drugs

We compared the in vitro growth inhibition of primary human tumor cells in the adhesive tumor cell culture system (ATCCS), exposed to the investigational agents caracemide, spirogermanium and taxol and to standard chemotherapy agents at equitoxic concentrations for granulocyte-macrophage colony-forming cells (GM-CFC) in vitro. Clinically active standard agents tested at up to GM-CFC 90% inhibitory concentrations (IC90) resulted in in vitro activity (greater than or equal to 50% tumor growth inhibition) in at least 30% of tumors tested. In vitro responses for taxol, caracemide and spirogermanium were 78%, 9% and 7%, respectively. This paper proposes a model that incorporates two hypotheses: (1) myelotoxic drugs which inhibit tumor growth at concentrations equal to or less than equitoxic GM-CFC ICs will demonstrate clinical activity; and (2) both myelotoxic and particular nonmyelotoxic drugs inactive in vitro at these doses will not be active clinically. If this drug screening concept is valid, taxol may be clinically more active than caracemide and spirogermanium.

Biological effect of epidermal growth factor on the in vitro growth of human tumors

The effect of epidermal growth factor (EGF) on the in vitro growth of 186 malignant human tumor specimens (45 melanomas, 32 sarcomas, and 56 lung, 16 gynecological, 14 breast, 12 genitourinary, and 11 gastrointestinal carcinomas) was evaluated in the cellular adhesive matrix human tumor culture system supplemented with transferrin, insulin, hydrocortisone, and estradiol. EGF increased tumor growth by at least 50% in 81% of the 186 tumors and by over 100% in 54%. The enhanced growth induced by EGF was related to an accelerated cellular division independent of tumor type and not to an increase in the actual number of clonogenic units. The drug concentrations of cell cycle-independent Adriamycin and cisplatin needed to achieve a 90% tumor cell kill were not altered by the responsiveness of the tumor to EGF.

In vitro cytotoxicity patterns of standard and investigational agents on human bone marrow granulocyte-macrophage progenitor cells

Inhibitory concentrations (ICs) against human bone marrow granulocyte-macrophage colony forming cells (GM-CFC) were established for 26 cancer chemotherapy agents, including seven investigational agents by ten day exposure. Each drug was tested at four or more concentrations to generate reliable survival curves. The analysis of the survival curves produced three patterns according to which drugs were classified: class A drugs had a shouldered curve with terminal exponential kill of GM-CFC, class B drugs produced initial exponential component followed by a plateau, and class C drugs produced linear curves. These categories provide the relationship between drug concentration and cytotoxicity, e.g., the cytotoxicity of class B drugs, after initial kill, did not increase in spite of serial doubling of concentrations whereas the class C drugs had proportional killing with two-fold concentration increment. A number of drugs were active at in vitro concentrations of less than or equal to 0.01 microgram ml-1 and caused log reduction of GM-CFC with an approximate concentration of 0.0001 microgram ml-1. Drugs known to require in vivo bioactivation, namely dacarbazine, procarbazine, and ifosfamide were active at high concentrations (greater than 10.0 micrograms ml-1). We propose that for myelosuppressive agents the GM-CFC provides a useful biologic reference to determine in vitro cut off concentrations to be utilized for drug screening. For nonmyelosuppressive agents, however, it may be suboptimal.

An improved cytogenetic technique for human solid tumors grown in adhesive-tumor-cell culture system

An improved technique for cytogenetic analysis of primary human solid tumors has been developed using an adhesive-tumor-cell culture system. While the previously described in situ harvesting procedure yielded highly condensed chromosome morphology and inadequate metaphase spread, the newly described harvesting procedures have yielded superior quality metaphase morphology and banding patterns. Cytogenetic analysis was successfully carried out on ten primary lung tumors and eight nonmalignant "normal" lung tissues. This procedure is now routinely used in this laboratory for other solid tumor cytogenetic analysis.

Drug and radiation sensitivity measurements of successful primary monolayer culturing of human tumor cells using cell-adhesive matrix and supplemented medium

The limitations of the agar suspension culture method for primary culturing of human tumor cells prompted development of a monolayer system optimized for cell adhesion and growth. This method grew 83% of fresh human tumor cell biopsy specimens, cultured and not contaminated, from a heterogeneous group of 396 tumors including lung cancer (93 of 114, 82%); melanoma (54 of 72, 75%); sarcoma (46 of 59, 78%); breast cancer (35 of 39, 90%); ovarian cancer (16 of 21, 76%); and a miscellaneous group consisting of gastrointestinal, genitourinary, mesothelioma, and unknown primaries (78 of 91, 86%). Cell growth was characterized morphologically with Papanicolaoustained coverslip cultures and cytogenetically with Giemsastained metaphase spreads. Morphological features such as nuclear pleomorphism, chromatin condensation, basophilic cytoplasm, and melanin pigmentation were routinely seen. Aneuploid metaphases were seen in 90% of evaluable cultures, with 15 of 28 showing 70% or more aneuploid metaphases. Colony-forming efficiency ranged between 0.01 and 1% of viable tumor cells, with a median efficiency of 0.2%. This culture system uses a low inoculum of 25,000 viable cells per well which permitted chemosensitivity testing of nine drugs at four doses in duplicate from 2.2 X 10(6) viable tumor cells and radiation sensitivity testing at five doses in quadruplicate from 0.6 X 10(6) cells. Cultures were analyzed for survival by computerized image analysis of crystal violet-stained cells. Drug sensitivity studies showed variability in sensitivity and in survival curve shape with exponential cell killing for cisplatin, Adriamycin, and etoposide, and shouldered survival curves for 5-fluorouracil frequently seen. Radiation sensitivity studies also showed variability in both sensitivity and survival curve shape. Many cultures showed exponential cell killing, although others had shouldered survival curves. This method for growing cells from primary human biopsy specimens is more efficient than the agar culture method, enables easier and better biological analysis of the actual cells grown, and permits improved characterization of drug and radiation survival curves.

Activity of 2-fluoro-Ara AMP against gynecologic tumors in the soft agar assay

To characterize in vitro activity of 2-fluoro-Ara AMP and its relation to the activities of cisplatin and doxorubicin, 28 specimens from patients wit gynecologic tumors (predominantly ovarian) were tested in a soft agar assay. Twenty-six of 28 (93%) grew when the medium was supplemented with four hormones (epidermal growth factor, hydrocortisone, estradiol-17, and insulin). Normal bone marrow cells were utilized as a biologic control to define in vitro concentrations of the three drugs. Tumors were exposed continuously to three different concentrations of each drug. 2-fluoro-Ara AMP was tested against 26 tumors, cisplatin against 24, and doxorubicin against 14. In vitro sensitivity was defined as greater than or equal to 50% colony inhibition at a drug concentration within the bone marrow inhibitory range. Seven of 26 (27%) tumor specimens were sensitive to 2-fluoro-Ara AMP. Among these, four tumors were derived from previously treated patients. However, in the 2-fluoro-Ara AMP concentration range (0.26 micrograms/ml to 0.78 micrograms/ml) tested, five of eight (62.5%) tumors from untreated patients achieved IC50 compared to only seven of 18 (39%) tumors from treated patients. Five of six (83%) specimens demonstrated cross-sensitivity between cisplatin and 2-fluoro-Ara AMP. Seventeen of 18 (94%) specimens demonstrated cross-resistance between cisplatin and 2-fluoro-Ara AMP, and 13 of 13 (100%) specimens demonstrated cross-resistance between 2-fluoro-Ara AMP and doxorubicin. A higher proportion of tumors from previously untreated patients achieved greater than or equal to 50% colony inhibition when exposed to 2-fluoro-Ara-AMP or cisplatin than did those from previously treated patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects and interactions of epidermal growth factor, insulin, hydrocortisone, and estradiol on the cloning of human tumor cells

We investigated the effects and interactions of epidermal growth factor (EGF), insulin, hydrocortisone, and estradiol on the growth of 18 freshly obtained human tumors in our human tumor stem cell assay (HTSCA) cultured at a reduced serum concentration (8.5% ml). All possible combinations of these four supplement factors were added to the assay to determine the ability of each component to enhance colony formation. We found that hydrocortisone was the most effective single supplement in stimulating colony growth in the HTSCA. Supplementation with insulin, estradiol, or both had some growth-promoting effect but not as great as hydrocortisone. Moreover, the addition of insulin, estradiol, or both often demonstrated a negative interaction with hydrocortisone. EGF supplementation alone; in dual combination with insulin, estradiol, or hydrocortisone; or in combination with estradiol and insulin in the assay did not significantly increase colony formation. However, EGF added to the cultures containing hydrocortisone with insulin and/or estradiol significantly increased colony formation and reversed the negative effect of insulin and estradiol on hydrocortisone activity. Thus, under conditions of our assay, the most effective combination in promoting colony growth contained all four factors.

Survival of human bone marrow cells after in vitro treatment with 12 anticancer drugs and implications for tumor drug sensitivity assays

We investigated the responsiveness of human normal granulocyte-macrophage colony-forming units in culture (GM-CFUC) continuously exposed in vitro to 1 of 12 anticancer drugs. All drugs except bleomycin showed a simple negative exponential dose-survival curve. The in vitro toxicity of drugs in GM-CFUC did not always correlate with the relative myelosuppressive potency observed in vivo. In addition, tumor specimens from 38 patients mainly with ovarian cancer were cultured in a human tumor colony-forming assay and continuously exposed to drugs at low, intermediate, and high concentrations capable of killing 40%, 78%, and 99% of GM-CFUC, respectively. The most active drugs were cis-platinum, velban, 5-fluorouracil, and 5-fluoro-ara-AMP. Dose-survival curves of bone marrow progenitor cells may serve as an in vitro reference system for selecting appropriate drug concentrations of myelosuppressive drugs in drug-sensitivity assays of human tumors.

The human tumor stem cell assay revisited

The human tumor stem cell assay (HTSCA) is a bilayer soft agar system for growing fresh human tumor specimens in vitro to determine drug sensitivity and improve our understanding of tumor biology. Recent clinical correlations of 60% accuracy for predicting a positive clinical response and a 90% accuracy for predicting a lack of response to therapeutic agents suggest promising clinical usefulness. However, the clinician should be aware of the assay's inherent pitfalls, such as heterogeneity of the tumor specimen, inability to obtain pure single-cell suspensions, low cloning efficiency, unusual drug dose-dependent survival curves, uncertain validity of in vitro pharmacology, non-standardized criteria for in vitro sensitivity, and the variability of in vitro results. A brief summary of the concepts, potential, and limitations of this assay are discussed.

Dose-survival curves of cis-platinum, melphalan, and velban in human granulocyte/macrophage progenitor cells

To optimize the in vitro concentrations of anticancer agents with clinical dose-limiting myelosuppression in the human tumor stem cell assay, we established dose-survival curves for cis-platinum, melphalan, and velban in normal human granulocyte/macrophage colony-forming units (CFU-gm) in a bilayer agar system. The LD50 (drug concentration capable of killing 50% of CFU-gm) of cis-platinum, melphalan, and velban for one-hour exposure was (a) greater than 10 micrograms/ml, (b) 0.9 microgram/ml, and 1.2 micrograms/ml, respectively. The respective values for continuous exposure were 0.3 microgram/ml, 0.12 microgram/ml, and 0.001 microgram/ml. The use of dose ranges based on bone marrow tolerance may influence the clinical value of in vitro tumor sensitivity studies of drugs with hematologic toxicity.