Detection and characterization of residual disease in breast cancer

Although micrometastatic tumor cell spread largely determines the prognosis of patients with operable breast cancer, it is usually missed by conventional tumor staging. Several groups (including ours) have therefore developed immunocytochemical and molecular assays that allow the specific detection and characterization of individual carcinoma cells disseminated to bone marrow, blood, and lymph nodes. These assays may improve the prognostic precision of the current classification systems and may provide a tool for the early assessment of the therapeutic effects of anticancer drugs on micrometastatic cells in individual patients. Another aspect of such methods is that they enable detection of tumor cell contamination in stem cell grafts and validation of the efficiency of purging techniques. The most extensive experience exists with immunocytochemical methods, some of which have the potential to serve as a benchmark for less validated molecular methods. Still, the specificity and sensitivity of immunocytochemical detection of single cancer cells are affected by several variables, which include the intricacies of antigen expression, the lack of distinct morphological characteristics, the size of the analyzed sample, and the staining techniques for visualization of antibody binding. This article provides a critical review of the opportunities and pitfalls related to new methods for the detection and monitoring of minimal residual disease in breast cancer.

Expression of major histocompatibility class I and class II antigens and intercellular adhesion molecule-1 on operable non-small cell lung carcinomas: frequency and prognostic significance

Major histocompatibility complex (MHC) antigens and adhesion molecules, such as the intercellular adhesion molecule-1 (ICAM-1), appear to play an important role in the immunological recognition and destruction of tumour cells. We, therefore, examined the expression patterns of these proteins on primary tumours of 91 patients with operable non-small cell lung cancer (NSCLC). Applying immunohistochemistry with monoclonal antibody (MAb) W6/32 against a common framework determinant of HLA class I antigens revealed a deficient expression in 33.0% of the cases analysed, while neo-expression of either HLA class II antigens (MAb TAL.1B5) or ICAM-1 (MAb PA3.58-14) was observed in 26.4 or 29.7% of tumours, respectively. Analysis of consecutive tumour specimens indicated that HLA antigens and ICAM-1 were frequently coexpressed. With regard to clinicopathological risk factors, we could demonstrate a preferential expression of those markers in patients with locally restricted and well-differentiated tumours or no lymph node metastases, which was more pronounced in adenocarcinomas than in squamous cell carcinomas. In contrast, the presence versus the absence of HLA antigens and ICAM-1 was not correlated with the rate of tumour recurrence or overall survival in patients with NSCLC. In conclusion, the co-ordinated expression of immunologically relevant cell surface molecules on primary NSCLC is a frequent event that correlates with distinct parameters of favourable prognosis. However, we have no evidence that the immune response facilitated by these molecules can effectively influence the clinical course of the disease.

Methodological analysis of immunocytochemical screening for disseminated epithelial tumor cells in bone marrow

The emerging clinical relevance of bone marrow micrometastasis has prompted several investigations, using a variety of immunocytochemical approaches. The present study was designed to evaluate some of the variables affecting the immunocytochemical detection of individual epithelial tumor cells in bone marrow. Using an alkaline phosphatase-antialkaline phosphatase staining technique, we evaluated bone marrow aspirates from 358 patients with primary carcinomas of the breast (n = 150), lung (n = 66), prostate (n = 42), or colorectum (n = 100). Individual tumor cells in cytological preparations were detected with monoclonal antibody (MAb) CK2 to the epithelial cytokeratin component 18 (CK18), which has been validated in extensive clinical studies. In addition, the utility of the broad-spectrum MAb A45-B/B3 was explored in this study. The high specificity of MAbs CK2 and A45-B/B3 was supported by analysis of bone marrow from 75 noncarcinoma control patients and by double-marker analysis with MAbs to mesenchymal marker proteins (CD45 and vimentin). In contrast, MAbs E29 and HMFG1, directed to mucin-like epithelial membrane proteins, cross-reacted with hematopoietic cells in 26.7-42.7% of all samples tested. The majority of the 154 positive samples (43.0%) from cancer patients displayed less than 10 CK18-positive cells per 8 x 10(5) marrow cells analyzed. The detection rate, however, was affected by blood contamination of the aspirate, the number of aspirates analyzed, and the number of marrow cells screened per aspiration site. Comparative immunostaining of bone marrow specimens with MAbs CK2 and A45-B/B3 indicated that downregulation of CK18 in micrometastatic carcinoma cells occurs in about 50% of the 172 samples analyzed, regardless of the primary tumor origin.(ABSTRACT TRUNCATED AT 250 WORDS)

Keratin expression reveals mosaic differentiation in vaginal epithelium

OBJECTIVE

Analyzing the expression of keratins has proved to be valuable for identifying of pathways of epithelial differentiation. In stratified epithelia K10 and K13 are representative for either the keratinizing (epidermal-type) or the nonkeratinizing pathway.

STUDY DESIGN

We have investigated keratin expression in "normal" vaginal epithelium from 30 women, applying two-color immunofluorescence with monoclonal antibodies to K10 and K13 on cryostat sections and cell smears.

RESULTS

A differential expression pattern of vaginal cells dependent on their localization within the epithelium was found. In cells of the first suprabasal layers differentiation began and became identifiable by a weak expression of K13. The adjacent layers displayed cells that concurrently expressed K10 and K13. In contrast, cells within the superficial strata expressed exclusively either one of the two keratins.

CONCLUSION

Thus vaginal epithelium appears to be mosaic in differentiation, showing simultaneous expression of keratins K10 and K13, thought to be representative for distinct routes of differentiation.

Differential expression of proliferation-associated molecules in individual micrometastatic carcinoma cells

BACKGROUND

The development of monoclonal antibodies (MAbs) to cytokeratins, which are integral components of the epithelial cytoskeleton, has made possible immunocytochemical detection of epithelial tumor cells. Importantly, this technique allows the detection of epithelial tumor cells that have metastasized from primary adenocarcinomas to secondary sites such as the bone marrow.

PURPOSE

The aim of the study was not only to detect micrometastatic cells in bone marrow, but also to assess the expression of nuclear proliferation markers (Ki-67 and p120) and the erbB2 oncogene (also known as ERBB2) in these cells and, thus, hopefully improve prognostic precision.

METHODS

Bone marrow aspirates were obtained from both sides of the upper iliac crest of 532 patients having definitive diagnoses of either breast or gastrointestinal cancer. The presence of micrometastatic epithelial tumor cells in bone marrow was assayed using the MAb cytokeratin 2 (CK2) to cytokeratin component 18 (CK18), in combination with the alkaline phosphatase-anti-alkaline phosphatase immunostaining technique. After primary screening of all marrow samples with MAb CK2, representative subgroups of CK18+ samples were selected for co-labeling with MAbs either to ErbB (n = 16), ErbB2 (n = 121), Ki-67 (n = 33), or p120 (n = 36) protein. An alternative labeling protocol based on the combination of immunogold and immunoenzymatic techniques was utilized to confirm the results derived from immunoenzymatic double staining.

RESULTS

In total, single CK18-positive tumor cells were detected in 180 (33.8%) of 532 bone marrow aspirates, with few differences among patients with breast or gastrointestinal cancer in TNM stage M0 (i.e., no distant metastasis). In patients with overt metastasis (stage M1), however, the incidence of metastatic cells in marrow increased to 73.7% in breast cancer, 52.5% in gastric cancer, and 39.0% in colon cancer. Whereas expression of Ki-67 or p120 on micrometastatic cells was observed only in 11 (15.9%) of 69 cancer patients analyzed, ErbB2+/CK18+ cells were found in 48 (67.6%) of 71 breast cancer patients and 14 (28.0%) of 50 patients with gastrointestinal cancer (P = .0001). The incidence of ErbB2+/CK18+ cells was positively correlated with the clinical stage of tumor progression.

CONCLUSIONS

The high incidence of ErbB2 expression on micrometastatic breast cancer cells in the bone marrow suggests that these cells might have been positively selected during early stages of metastasis. The majority of these cells appear to be in a dormant state of cell growth.

IMPLICATIONS

Although support from clinical follow-up is still needed, this study demonstrates that, beyond the mere presence of micrometastatic cells in bone marrow, useful prognostic information can be obtained by analysis of additional cell growth markers.

The role of lymphoid cells in hematopoietic regulation

The present review has summarized evidence supporting the existence of different lymphoid subsets with opposing effects on hematopoietic cell growth (Table 1); specifically; a) growth stimulation resulting from the release of interleukins and granulocyte-macrophage colony-stimulating factor (GM-CSF) by particular subsets of lymphocytes and resting natural killer (NK) cells and b) growth inhibition resulting from the release of interferon (IFN) and tumor necrosis factor (TNF) by stimulated NK, B and lymphokine-activated killer (LAK) cells and inhibitory T lymphoid subsets. The systematic examination of the physiologic relevance of lymphoid subsets would add an important element to a more comprehensive model of hematopoietic regulation that might hold promise in future clinical applications.

Immunocytological detection of bone marrow micrometastasis in operable non-small cell lung cancer

Present diagnostic techniques do not allow the detection of early metastatic spread of tumor cells, although this spread largely determines the clinical course of patients with small primary cancers. By use of monoclonal antibody CK2 to the epithelial cytokeratin component number 18 (CK18), individual disseminated carcinoma cells present in bone marrow of cancer patients can now be identified (G. Schlimok, I. Funke, B. Holzmann, G. Göttlinger, G. Schmidt, H. Häuser, S. Swierkot, H. H. Warnecke, B. Schneider, H. Koprowski, and G. Riethmüller, Proc. Natl. Acad. Sci. USA, 84: 8672-8676, 1987; F. Lindemann, G. Schlimok, P. Dirschedl, J. Witte, and G. Riethmüller, Lancet, 340: 685-689, 1992). In the present study, we applied this approach to patients with operable non-small cell lung cancer. CK18 was expressed on 84 of 88 (95.5%) primary adenocarcinomas and squamous cell carcinomas. Irrespective of primary tumor histology, single aspirates of iliac bone marrow from 18 of 82 (21.9%) lung cancer patients exhibited between 1 and 531 CK18+ cells/4 x 10(5) nucleated marrow cells. The specificity of our assay is underlined by the small rate of "false-positive" cells being observed in only 2 of 117 (1.7%) marrow samples from control patients with no evidence for an epithelial malignancy at the time of aspiration. Comparison with established risk factors demonstrated positive correlations (P < 0.05) between the size and histological grade of the primary carcinoma and cytokeratin positivity in iliac bone marrow. In contrast, the association with the metastatic involvement of regional lymph nodes was only weak (P = 0.09). Following a median observation period of 13 months, patients who displayed cytokeratin-positive cells in iliac bone marrow at the time of primary surgery relapsed more frequently as compared to patients with a negative marrow finding (66.7 versus 36.6%; P < 0.05). This difference was even more pronounced by comparing the rates of manifest skeleton metastasis observed in both groups (26.7 versus 2.4%; P < 0.005). Finally, colabeling of CK18+ cells in marrow with monoclonal antibodies to proliferation-associated markers, such as the nucleolar antigen p120 or the tyrosine kinase receptor erbB2, exemplified the oncogenic capacity of CK18+ micrometastatic cells. In conclusion, CK18+ cells present in the bone marrow of patients with apparently operable non-small cell lung cancer exhibit the potential to form solid metastases. Therefore, the approach presented here may be used to determine the risk of early relapse in operable non-small cell lung cancer with potential consequences for adjuvant therapy.

p53 and K-RAS alterations in pancreatic epithelial cell lesions

We have analysed the expression of p53 at the mRNA level, and extensively at the protein level by immunostaining, Western blotting, and ELISA measurements revealing a p53 increase in 8 out of 14 cell lines established from human pancreatic carcinomas. The mRNA levels closely paralleled the protein levels in most of the cell lines. Overexpression of p53 in tumor cells correlated with mutations in the p53 gene. Immunocytochemistry was also performed with tissue cryosections showing a nuclear p53 staining in 8 out of 12 exocrine, and 2 out of 2 endocrine tumors. In addition, nonmalignant peri-tumoral tissue specimens and cells derived from pancreatic juice of acute pancreatic patients were also positively stained. These findings may suggest functions of p53 in stress situations induced by acute inflammation or tissue regeneration. Genomic mutations in the tumor suppressor gene were associated with point mutations in either codon 12, 13 or 61 in the c-K-RAS oncogene in about two-thirds of cell lines. The frequent activations of a RAS oncogene in combination with mutations of a tumor suppressor gene are likely to contribute to the malignant phenotype of pancreatic adenocarcinomas.

Immunocytochemical double staining of cytokeratin and prostate specific antigen in individual prostatic tumour cells

Early dissemination of malignant cells is the main cause for metastatic relapse in patients with solid tumours. By use of monoclonal antibodies (mAbs) specific for cytokeratins, disseminated individual epithelial tumour cells can now be identified in mesenchymal organs such as bone marrow. Further to characterize such cells in patients with prostate cancer, an immunocytochemical procedure was developed for simultaneous labelling of cytokeratin component no. 18 (CK18) and prostate specific antigen (PSA). In a first step, cells were incubated with mAb ER-PR8 against PSA and secondary gold-conjugated goat anti-mouse antibodies. In a second step, biotinylated mAb CK2 to CK18 was applied as primary antibody and subsequently incubated with complexes of streptavidin-conjugated alkaline phosphatase, which were developed with the Newfuchsin substrate. The binding of gold-labelled antibodies was visualized by silver enhancement. The sensitivity and specificity of the technique was demonstrated on cryostat sections of hyperplastic prostatic tissue, and cytological preparations of LNCaP prostatic tumour cells. Double staining was restricted to cells derived from the secretory epithelium of the prostate. Cross-reactivity between both detection systems was excluded by several controls, including the use of unrelated antibodies of the same isotype and the staining of CK18+/PSA- HT29 colon carcinoma cells. CK18+ cells co-expressing PSA were found in bone marrow aspirates from 5 out of 13 patients with carcinomas of the prostate, a finding that is consistent with the relative fraction of double-positive LNCaP cells. The specificity of CK18 for epithelial tumour cells in bone marrow was supported by negative staining of 12 control aspirates from patients with benign prostatic hypertrophy.(ABSTRACT TRUNCATED AT 250 WORDS)

Micrometastatic tumour cells in bone marrow of patients with gastric cancer: methodological aspects of detection and prognostic significance

Monoclonal antibodies (Mab) are potent probes to identify individual tumour cells or small tumour cell clusters in bone marrow. In the present study, various antibodies directed against either cell surface or intracytoplasmic antigens of epithelial cells were assessed for their ability to detect such cells in bone marrow of patients with breast, colorectal and gastric cancer. According to the presented data, monoclonal antibodies against intracellular cytokeratin (CK) components are superior in terms of specificity and sensitivity to antibodies reacting with epitopes of the cell membrane. Using a monoclonal antibody against the cytokeratin polypeptide 18 in connection with the alkaline phosphatase anti-alkaline phosphatase detection system (APAAP), we could detect tumour cells in bone marrow of 34 out of 97 patients with gastric cancer examined at the time of primary surgery. The incidence of positive findings was correlated to established risk factors, such as histological classification and locoregional lymph node involvement. Clinical follow-up studies on 38 patients demonstrated a significantly increased relapse rate in patients presenting with CK-positive cells in their bone marrow at the time of primary surgery. Thus the described technique may help to identify patients with gastric cancer carrying a high risk of early relapse.

Identification of the c-kit ligand: end of the road for understanding aplastic anemia in steel mutant mice?

We here report the initiation of hematopoietic recovery in congenitally hypoplastic S1/S1d mice by the cytotoxic ablation of cells bearing the natural killer (NK) phenotype (NK 1.1+). The most striking finding was the early several-fold increase in the cycling fraction of stem and progenitor cells (with the exception of progenitors committed to megakaryocytopoiesis) in the anti-NK 1.1+ antibody-treated group. This increase resulted in an early, complete restoration of total marrow cellularity to the normal (+/+) littermate level. Our data suggest that NK 1.1+ cells exert functions critical to the negative control of hematopoietic cell proliferation in S1/S1d mice.

Frequent down-regulation of major histocompatibility class I antigen expression on individual micrometastatic carcinoma cells

An astoundingly high frequency of micrometastatic cells have been found in bone marrow aspirates of patients with colon carcinomas (G. Schlimok et al., J. Clin. Oncol., 8:831-837, 1990), although these tumors very rarely metastasize to the skeleton. This observation has raised questions about the malignant potential of such cells. In a first attempt to characterize this potential, we have assessed the expression of major histocompatibility complex (MHC) class I antigens on bone marrow micrometastases, inasmuch as down-regulation of these molecules is a potential mechanism to escape from MHC class I-restricted lysis by cytotoxic T-cells. The two groups of cancer patients compared were those with tumors known to rarely (stomach and colon cancer) or frequently (breast cancer) manifest skeleton metastases. Bone marrow aspirates taken from these patients were probed for individual disseminated tumor cells using the immunoalkaline phosphatase technique with monoclonal antibody CK2 to the epithelial differentiation antigen cytokeratin 18 (CK-18), as described previously (G. Schlimok et al., Proc. Natl. Acad. Sci. USA, 84:8672-8676, 1987). Specimens containing CK18-positive cells were colabeled with monoclonal antibody W6/32 directed to a framework (or nonpolymorphic) antigenic determinant of MHC class I heavy chains associated with beta 2-microglobulin. W6/32-positive CK-18-positive cells could be detected in 25 of 54 patients (46.3%) with significantly higher incidences in 26 breast cancer patients (61.9%) as compared to 28 patients with carcinomas of the stomach and colon (27.3 and 29.4%). Independent from the origin of the primary carcinoma, the incidence of W6/32-negative CK18-positive cells was positively correlated to both the differentiation grade of the primary tumor (P less than 0.05) and appeared to be linked to the occurrence of regional lymph node metastases (statistically not significant) determined by conventional histological examination. The present results demonstrate for the first time that down-regulation of MHC expression on individual micrometastatic cells correlates to the differential pattern of metastasis obtained by comparing breast and gastrointestinal carcinomas. This finding together with the suggestive link to clinical risk factors supports the significance of reduced MHC class I expression for the survival of residual metastatic cells which is a major determinant of prognosis for patients with solid tumors.

Differential effect of L3T4+ cells on recovery from total-body irradiation

We have examined the importance of L3T4+ (murine equivalent to CD4+) cells for hematopoietic regulation in vivo in unperturbed mice and mice recovering from total-body irradiation (TBI) using a cytotoxic monoclonal antibody (MoAb) raised with the GK 1.5 hybridoma. Ablating L3T4+ cells in "normal" (unperturbed) B6D2F1 mice substantially decreased the S-phase fraction (determined by in vivo hydroxyurea suicide) of erythroid progenitor cells (erythroid colony-forming units, CFU-E) as compared to the pretreatment level (10% +/- 14.1% [day 3 following depletion] vs 79.8% +/- 15.9%, respectively) with a corresponding decrease in the marrow content of CFU-E at this time to approximately 1% of the pretreatment value. Although the S-phase fraction of CFU-GM was decreased to 2.2% +/- 3.1% 3 days after L3T4+ cell ablation from the 21.3% +/- 8.3% pretreatment value, CFU-GM cellularity showed little change over the 3 days following anti-L3T4 treatment. Anti-L3T4 MoAb treatment had little or no effect on either the S-phase fraction or the marrow content of hematopoietic "stem cells" (spleen colony-forming units, CFU-S) committed to myeloerythroid differentiation. Ablating L3T4+ cells prior to a single dose of 2 Gy TBI resulted in significantly reduced marrow contents of CFU-S on day 3 and granulocyte-macrophage colony-forming units (CFU-GM) on day 6 following TBI, with little or no effect on the corresponding recovery of CFU-E. The present findings provide the first in vivo evidence that L3T4+ cells are involved in: 1) maintaining the proliferative activity of CFU-E and CFU-GM in unperturbed mice and 2) supporting the restoration of CFU-S and CFU-GM following TBI-induced myelosuppression.

A mathematical model of erythropoiesis in mice and rats. Part 4: Differences between bone marrow and spleen

In a preceding analysis we hypothesized that the most important parameter controlled by erythropoietic regulation in vivo is the degree of amplification (number of cell divisions) in the CFU-E and erythroblast cell stages. It was concluded that erythropoietic amplification in vivo is controlled according to a sigmoidal dose-response relationship with respect to the control parameter which is the haematocrit (or haemoglobin concentration). Here, this hypothesis is extended to include the differences in murine bone marrow and splenic erythropoiesis that are described and quantified by different dose-response relationships. Comparing several sets of experimental data with mathematical model simulations, this approach leads to the following conclusions: (i) in the unperturbed normal steady state at least one extra erythropoietic cell division takes place in the spleen compared with the bone marrow; (ii) a strong erythropoietic stimulus, such as severe bleeding or hypoxia, can induce five to six additional cell divisions in the spleen but only two to three additional divisions in the bone marrow; this results in a considerable increase in the spleen's contribution to erythropoiesis from about 10% in normal animals to over 40% during strong stimulation; (iii) under erythropoietic suppression, such as red cell transfusion, a similar number of cell divisions is skipped in both organs and the splenic contribution to erythropoiesis remains unchanged. In conclusion, the concept that bone marrow and spleen microenvironments differ in the dose-response relationship for erythropoietic regulation provides an explanation for the changing contribution of splenic murine erythropoiesis following a variety of experimental treatments.

Stem cell recovery from cyclophosphamide-induced myelosuppression requires the presence of CD4+ cells

Recently, we have reviewed studies regarding the growth-stimulating effect of CD4+ cells on haematopoietic cells in culture (Pantel & Nakeff, 1989a). In the present study we have tested the physiologic relevance of this interaction using a drug-perturbed mouse model. The long-term application of cyclophosphamide (CY, 30 mg/kg/d, five i.p. injections per week over 7 weeks) in B6D2F1 mice resulted in initial CY-induced cytotoxicity to CFU-S followed by the reestablishment to pretreatment values of the femoral content of CFU-S within 2-3 weeks of CY-treatment. An examination of CY-metabolism in these treated mice excluded a pharmacological explanation for the compensation of CY-cytotoxicity. However, a three-fold increase in the cycling fraction of CFU-S (determined by in vivo hydroxyurea suicide) was observed concomitant with a two-fold increase in the femoral content of L3T4+ cells (the murine equivalent to human CD4+ cells), as compared to the corresponding values in untreated mice. Ablating these L3T4+ cells in vivo by means of a cytotoxic monoclonal antibody (MoAb) to the L3T4 determinant resulted in a decrease in the cycling fraction of CFU-S from 56 +/- 8% to essentially zero and a decrease in the femoral content of CFU-S when comparing mice receiving either CY alone or CY plus MoAb, respectively. It would appear that the CY-induced increase in the proliferative activity of CFU-S requires the presence of L3T4+ cells. These data constitute the first in situ evidence for the physiologic relevance of immunocompetent L3T4+ cells as regulators involved in the recovery of stem cells from drug-induced myelosuppression.

Inhibition of hematopoietic recovery from radiation-induced myelosuppression by natural killer cells

We have examined the role of natural killer (NK) cells in situ in the recovery of marrow hematopoiesis in B6D2F1 mice receiving various doses of total-body irradiation (TBI) as a well-characterized model for treatment-induced myelosuppression. Applying an in situ cytotoxic approach for ablating NK 1.1 cells, we have demonstrated that NK 1.1 cells differentially inhibit the recovery of hematopoietic stem cells (CFU-S) and their progenitor cells committed to granulocyte-macrophage differentiation from a sublethal dose of TBI (9 Gy) while not affecting the recovery of progenitor cells committed to either erythroid or megakaryocyte differentiation from TBI. However, recoveries of CFU-S and progenitor cells were unaffected by the ablation of NK cells prior to a moderate dose of TBI (2 Gy). These findings provide in situ evidence that NK cells are potential inhibitors of hematopoietic recovery from treatment-induced myelosuppression.

A mathematical model of erythropoiesis suggests an altered plasma volume control as cause for anemia in aged mice

In order to evaluate whether the anemia observed in aged C57B1 and B6D2F1 mice reflects a defect in the control mechanisms regulating erythropoiesis a mathematical model of erythropoietic control is employed, validated previously. In the model it is hypothesized that the most important mechanism for compensating an actual demand of red blood cells is an increase in the mitotic amplification (number of mitoses) of erythroid progenitors (CFU-E, erythroblasts). The same sigmoidal dose-response-relationship between mitotic amplification and hematocrit (Hct) is proposed for young and aged mice. It is mediated by erythropoietin (EPO). Using this relationship one can demonstrate that the expansion of the plasma volume (PV) observed in aged mice is appropriately compensated by an increase in the mitotic amplification of CFU-E and erythroblasts. This implies that aged mice operate in a stimulated state of erythropoietic amplification which is closer to the maximum of the dose-response-relationship than the steady state in young mice. This explains the finding of a reduced proliferative reserve in aged mice following further erythropoietic stimulation. An additional analysis regarding the response of aged mice to bleeding anemia is consistent with the view that young and aged mice share the same dose-response-relationship but start from different steady states. These findings suggest that the control mechanisms regulating erythropoiesis in young and aged mice are similar and that the anemia is due to alterations in the PV control.

Differential effect of natural killer cells on modulating CFU-Meg and BFU-E proliferation in situ

As a result of the striking discrepancy between the substantial amount of information on the role of natural killer (NK) cells derived from in vitro experimentation and the corresponding lack of data demonstrating their physiologic relevance, we have examined the importance of NK cells for the steady state production of hematopoietic stem and progenitor cells in situ. B6D2F1 mice received two 0.2-ml injections of ascites containing anti-NK 1.1 monoclonal antibody (anti-NK) directed to murine NK cells. Another group was treated similarly but received "control" ascites (CA) that was induced solely by injection of a mouse myeloma cell similar to the fusion partner of the NK 1.1 hybridoma. Two days after the last injection, we determined the number and cycling fraction (i.e., percentage of cells in S-phase determined by in vivo hydroxyurea suicide) of femoral stem cells (spleen colony-forming units; CFU-S) and committed granulocyte-macrophage (granulocyte-macrophage colony-forming units; CFU-GM), megakaryocytic (megakaryocyte colony-forming units; CFU-Meg), and erythroid (erythroid burst-forming units; BFU-E and erythroid colony-forming units; CFU-E) progenitor cells. The striking finding was the almost complete abolishment of the proliferation of CFU-Meg in the anti-NK group, resulting in a statistically significant (p less than 0.02) decrease in number to 37% of the CA control. In contrast, the cycling fraction of BFU-E was significantly (p less than 0.05) increased to 205% of the CA control with no increase in number. The number and cycling fraction of CFU-S, CFU-GM, and CFU-E in the anti-NK group were not significantly different from values in the control group. These findings add a novel aspect to the understanding of hematopoietic regulation by providing the first evidence for a differential effect of NK cells on the steady-state proliferation of CFU-Meg and BFU-E in situ.

Cyclophosphamide-induced enhancement of stem cell recovery from whole-body irradiation is radiation dose-dependent

Although the enhancement of CFU-S recovery by CY pretreatment has been described for combinations of TBI greater than 4 Gy, no information exists as to whether such enhancement is operative at lower TBI doses (less than 3 Gy). B6D2F1 mice received intraperitoneal injections of CY (2 and 5 mg/mouse) at various time intervals prior to 2, 5 or 9 Gy TBI. The control group received the same dose of TBI without CY pretreatment. Six days after TBI, we determined the femoral content of CFU-S. Administration of 5 mg CY per mouse 3 days prior to 5 or 9 Gy TBI enhanced recovery of CFU-S with a substantial increase in CFU-S of 3- and 30-fold over control, respectively. In contrast, the administration of CY prior to 2 Gy TBI delayed recovery with CFU-S remaining at only 10 to 40% of control. This prolongation in CFU-S recovery was similar for CY doses of either 2 or 5 mg per mouse at all the time intervals tested (2, 3, 4 and 7 days prior to TBI). Our results demonstrate an enhancement of CFU-S recovery by pretreatment with CY for high doses of TBI that is reversed if the subsequent TBI dose is too low.

A mathematical model of erythropoiesis in mice and rats. Part 2: Stimulated erythropoiesis

A mathematical model of erythropoietic cell production and its regulation process has been proposed in a preceding paper. It is primarily based on the assumption that the number of cell divisions taking place in the CFU-E and erythropoietic precursor stages is regulated depending on the oxygen supply of the tissue. Quantitative dose-response relationships for in vivo erythropoiesis are suggested. Here, we demonstrate that this model adequately reproduces data obtained in situations of stimulated erythropoiesis in mice and rats. In detail, this implies a quantitative description of the following processes: (1) Changes in tissue oxygen tension (Pto2) following removal of red cells (bleeding, haemolytic anaemia) or increase in plasma volume (dilution anaemia) or decrease in atmospheric oxygen pressure (hypoxia). (2) Pto2 dependent erythropoietin (EPO) production. (3) Dose-response of EPO on erythropoietic amplification (up to two to four additional mitoses). (4) The changes of the marrow transit time. Model simulations are compared with experimental data for changes of erythropoiesis during hypoxia, EPO-injection, and different forms of anaemia. A satisfactory agreement suggests that the model adequately describes and correlates different direct and indirect ways to stimulate erythropoiesis. It quantifies the role and relative contribution of the haematocrit, haemoglobin concentration, atmospheric oxygen pressure, tissue oxygen pressure, and plasma volume as triggers in erythropoietic stimulation under various conditions. Furthermore, the model may allow to optimize the scheme of EPO-administration and to find the maximum increase of erythropoiesis for a given amount of erythropoietin.

A mathematical model of erythropoiesis in mice and rats. Part 3: Suppressed erythropoiesis

A mathematical model of erythropoietic cell production and its regulation process has been proposed in a preceding paper. It is primarily based on the assumption that the number of cell divisions taking place in the CFU-E and erythropoietic precursor stages can be regulated depending on the oxygen supply to the tissue. Here we provide evidence that this model adequately describes situations of suppressed erythropoiesis. In detail this implies a quantitative description of the following processes: (1) changes in tissue oxygen tension (Pto2) due to increase in red cell numbers (red cell transfusion, posthypoxia), decrease in plasma volume (dehydration) or increase in atmospheric oxygen pressure (hyperoxia), (2) Pto2 dependent reduction of erythropoietin (EPO) production, (3) dose-response of reduced EPO-levels on erythropoietic amplification (omission of three to five mitoses). Model simulations are compared to experimental data obtained from red cell transfusion, posthypoxia, hyperoxia and dehydration. A satisfactory agreement suggests that the model adequately describes and correlates different ways to suppress erythropoiesis. It quantifies the role and relative contribution of the haematocrit, haemoglobin concentration, atmospheric oxygen pressure, tissue oxygen pressure and plasma volume as triggers in erythropoietic suppression under various conditions. In conjunction with the preceding two papers it could be shown that one unique set of model parameters is sufficient to describe erythropoiesis in steady state, stimulation and suppression. Limitations of the model are discussed and experiments for a more detailed investigation of the feedback mechanisms are proposed.

Lymphoid cell regulation of hematopoiesis

It is clear from extensive in vitro data that different subsets of lymphocytes stimulate and inhibit the growth of hematopoietic stem and progenitor cells. In order to clarify the complexity of the network between regulatory lymphocytes and hematopoietic target cells, we have examined the stimulatory and inhibitory effects derived from different lymphoid subsets. The regulatory influence of lymphocytes is transmitted mainly through the release of cytokines including the interleukins, granulocyte-macrophage colony-stimulating factor, tumor necrosis factor-beta and the interferons, all of which have non-specific effects on a variety of hematopoietic cells. Since these cytokines amplify the effects of other, more lineage-specific cytokines (e.g., erythropoietin, thrombopoietin and granulocyte or macrophage colony-stimulating factor) on the proliferation and differentiation of progenitor cells, the present review supports the conclusion that lymphoid subsets play a critical role in ensuring an optimal hematopoietic response to specific demands.