Abstract 2865: CC-3, an IgG-based B7-H3xCD3 bispecific antibody for targeting of gastrointestinal cancers

Despite substantial improvements over the last decades, survival rates in metastatic gastrointestinal cancer are still far from satisfactory, with an accordingly high medical need for new treatment strategies. B7-H3 (CD276) is a member of the B7 immune checkpoint family. Initially thought to act as co-stimulator, recent studies revealed that B7-H3 rather has an inhibitory role for T cells and contributes to tumor immune evasion. Clinically, its overexpression has been linked to invasive and metastatic potential as well as poor prognosis. Due to its expression on both, tumor cells and tumor vasculature, in a variety of cancer entities including colorectal cancer, B7-H3 attracted our interest as therapeutic target for T cell-recruiting bispecific antibodies (bsAbs). We postulate that “dual targeting” of both, the cancer cells and the tumor vasculature may support the influx of T cells into the tumor site, a critical prerequisite for successful immunotherapy of solid tumors allowing for subsequent destruction of antigen-positive malignant cells. We generated a panel of monoclonal antibodies directed to different epitopes of the B7-H3 molecule. After biochemical characterization, we selected two antibodies with distinct binding proprieties and subsequently used them for the construction of Tcell-recruiting B7-H3xCD3 bsAbs in an IgG-based (IgGsc) format. To reduce side effects, constructs were cloned using a UCHT-1 derived low affinity anti-CD3 sequence. In vitro characterization using colorectal and other carcinoma cells allowed for selection of a construct with optimal functional properties (thereafter termed CC-3) as revealed by target cell-restricted induction of T cell activation, proliferation and tumor cell killing. In vivo, potent efficacy of CC-3 was documented in a lung metastasis model and by its ability to eliminate large established flank tumors using immunocompromised NSG mice adoptively transferred with human effector cells. Despite the high therapeutic efficacy of CC-3, no toxicity was observed in the absence of target cells. In summary, CC-3 is a bsAb with promising therapeutic activity against B7-H3 positive tumors. GMP compliant production of CC-3 is presently ongoing to enable evaluation in a clinical “first in human” study in patients with colorectal cancer.

Citation Format: Latifa Zekri, Martina S. Lutz, Ilona Hagelstein, Timo Manz, Monika Engel, Boris Klimovich, Nisha Prakash, Anna Chashchina, Sebastian Hörner, Stefanie Müller, Melanie Märklin, Martin Pflügler, Gundram Jung, Helmut R. Salih. CC-3, an IgG-based B7-H3xCD3 bispecific antibody for targeting of gastrointestinal cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2865.

BCR::ABL1 tyrosine kinase inhibitors hamper the therapeutic efficacy of blinatumomab in vitro

PURPOSE

Acute B-lymphoblastic leukemia (B-ALL) is a malignant disease characterized by accumulation of clonal immature lymphocytes in the bone marrow and peripheral blood. The approval of BCR::ABL1 tyrosine kinase inhibitors (TKI) such as imatinib, dasatinib, nilotinib and ponatinib marked a milestone in targeted therapy only for a subset of patients carrying the translocation t(9;22)(q34;q11). Immunotherapy with the bispecific antibody (bsAb) blinatumomab targeting CD19xCD3 revolutionized treatment of all B-ALL cases. The combination of both TKI and bsAb, so-called "dual targeting", is currently under clinical investigation, although TKI might influence T cell effects.

METHODS

We here investigated the combination of different TKI and blinatumomab in BCR::ABL1⁺ and BCR::ABL1^- B-ALL cell lines and primary samples regarding T cell proliferation, differentiation, cytokine release and killing of tumor cells.

RESULTS

In vitro analysis revealed profound reduction of T cell proliferation, differentiation, cytokine release and killing of tumor cells upon application of BCR::ABL1 TKI with blinatumomab. Inhibition was more pronounced with dasatinib and ponatinib compared to nilotinib and imatinib. T cell signalling after CD3 stimulation was impaired by TKI mirrored by inhibition of LCK phosphorylation. This known off-target effect might influence the efficacy of bsAb therapy when combined with BCR::ABL1 TKI.

CONCLUSION

In conclusion, we propose that nilotinib and imatinib might also be suitable substances for combination with blinatumomab and suggest evaluation in clinical trials.

A novel IgG-based FLT3xCD3 bispecific antibody for the treatment of AML and B-ALL

BACKGROUND

In lymphoid malignancies, the introduction of chimeric antigen receptor T (CAR-T) cells and bispecific antibodies (bsAbs) has achieved remarkable clinical success. However, such immunotherapeutic strategies are not yet established for acute myeloid leukemia (AML), the most common form of acute leukemia in adults. Common targets in AML such as CD33, CD123, and CLEC12A are highly expressed on both AML blasts and on normal myeloid cells and hematopoietic stem cells (HSCs), thereby raising toxicity concerns. In B-cell acute lymphoblastic leukemia (B-ALL), bsAbs and CAR-T therapy targeting CD19 and CD22 have demonstrated clinical success, but resistance via antigen loss is common, motivating the development of agents focused on alternative targets. An attractive emerging target is FLT3, a proto-oncogene expressed in both AML and B-ALL, with low and limited expression on myeloid dendritic cells and HSCs.

METHODS

We developed and characterized CLN-049, a T cell-activating bsAb targeting CD3 and FLT3, constructed as an IgG heavy chain/scFv fusion. CLN-049 binds the membrane proximal extracellular domain of the FLT3 protein tyrosine kinase, which facilitates the targeting of leukemic blasts regardless of FLT3 mutational status. CLN-049 was evaluated for preclinical safety and efficacy in vitro and in vivo.

RESULTS

CLN-049 induced target-restricted activation of CD4+ and CD8+ T cells. AML cell lines expressing a broad range of surface levels of FLT3 were efficiently lysed on treatment with subnanomolar concentrations of CLN-049, whereas FLT3-expressing hematopoietic progenitor cells and dendritic cells were not sensitive to CLN-049 killing. Treatment with CLN-049 also induced lysis of AML and B-ALL patient blasts by autologous T cells at the low effector-to-target ratios typically observed in patients with overt disease. Lysis of leukemic cells was not affected by supraphysiological levels of soluble FLT3 or FLT3 ligand. In mouse xenograft models, CLN-049 was highly active against human leukemic cell lines and patient-derived AML and B-ALL blasts.

CONCLUSIONS

CLN-049 has a favorable efficacy and safety profile in preclinical models, warranting evaluation of its antileukemic activity in the clinic.

CD18 Antibody Application Blocks Unwanted Off-Target T Cell Activation Caused by Bispecific Antibodies

Simple Summary

Bispecific antibodies are a very effective immunotherapy against different types of cancer since they activate T cells in the presence of tumor cells. However, they can cause severe side effects, such as a systemic inflammation called cytokine release syndrome. We aimed to clarify an important mechanism that causes cytokine release syndrome. In cocultures of T cells with endothelial cells or lymphoid cells, application of bispecific antibodies can induce T cell activation and cytokine release in the absence of tumor cells. By blocking the adhesion molecule CD18, this interaction is interrupted and the unwanted T cell activation is diminished. CD18 blockade, however, does not interfere with T cell activation when tumor cells are present. Therefore, CD18 blockade could prevent side effects of bispecific antibodies without decreasing the anti-tumor effect.

Abstract

T cell-recruiting bispecific antibodies (bsAbs) are successfully used for the treatment of cancer. However, effective treatment with bsAbs is so far hampered by severe side effects, i.e., potentially life-threatening cytokine release syndrome. Off-target T cell activation due to binding of bispecific CD3 antibodies to T cells in the absence of target cells may contribute to excessive cytokine release. We report here, in an in vitro setting, that off-target T cell activation is induced by bsAbs with high CD3 binding affinity and increased by endothelial- or lymphoid cells that act as stimulating bystander cells. Blocking antibodies directed against the adhesion molecules CD18/CD54 or CD2/CD58 markedly reduced this type of off-target T cell activation. CD18 blockade—in contrast to CD2—did not affect the therapeutic activity of various bsAbs. Since CD18 antibodies have been shown to be safely applicable in patients, blockade of this integrin holds promise as a potential target for the prevention of unwanted off-target T cell activation and allows the application of truly effective bsAb doses.

Tocilizumab, but not dexamethasone, prevents CRS without affecting antitumor activity of bispecific antibodies

Bispecific antibodies (bsAb) and chimeric antigen receptor (CAR) T cells allow for antibody guided recruitment of T cells against tumors. Both are successfully used for treatment of CD19 expressing leukemias, but may cause cytokine release syndrome (CRS) as a major dose-limiting side effect. For CRS prevention, steroids are recommended prior to bsAb treatment, despite their well-known lymphotoxic activity. The IL-6 receptor antibody tocilizumab is established for treatment of CRS induced by CAR T cells, but was not considered for CRS prevention in bsAb therapy. We here compared the influence of dexamethasone and tocilizumab on bsAb-mediated T cell proliferation and tumor lysis in vitro and in vivo and found that dexamethasone profoundly inhibited T cell proliferation and antitumor activity as induced by two different bsAb, particularly at low effector:target ratios, whereas tocilizumab did not affect efficacy. When we applied tocilizumab early during treatment of three patients with a newly developed PSMAxCD3 bsAb, significant CRS attenuation despite high IL-6 serum levels was observed. Thus, early IL-6 blockade may reduce the undesired sequelae of CRS upon bsAb therapy without affecting therapeutic activity, allowing in turn for safe application of effective doses.

Mass spectrometry for quality control of bispecific antibodies after SDS-PAGE in-gel digestion

Recombinant bispecific antibodies (bsAbs) are increasingly included in regimens for cancer therapy. Strict good manufacturing practice (GMP) compliant quality control measures are required to ensure quality and safety of these innovative biologicals. Gel electrophoresis (sodium dodecyl sulfate-polyacrylamide gel electrophoresis [SDS-PAGE]) and size exclusion chromatography (SEC) are the cornerstones of quality control methods. BsAbs are often prone to aggregation or incomplete synthesis due to their artificial nature. In addition, host cell proteins and host cell DNA as well as impurities from the purification process itself constitute potential contaminants. Such impurities may then appear as additional, unexpected bands or peaks on SDS-PAGE gels and SEC, respectively. Here we describe a standardized protocol for rapid analysis of recombinant antibodies by mass spectrometry (MS) after tryptic digestion of bands excised from SDS-PAGE gels. We have used this protocol to characterize unexpected "contaminating bands" that were observed during the clinical development of a novel bsAb with PSMAxCD3 specificity, either during the production of the protein itself or during the development of a surrogate molecule for evaluation in syngeneic mouse models. MS analysis allowed us to precisely determine the origin of these bands, which resulted from artifacts or from incomplete protein synthesis. The combined utilization of SDS-PAGE und MS can therefore substantially support GMP-compliant production of recombinant proteins.

An IgG-based bispecific antibody for improved dual targeting in PSMA-positive cancer

The prostate-specific membrane antigen (PSMA) has been demonstrated in numerous studies to be expressed specifically on prostate carcinoma cells and on the neovasculature of several other cancer entities. However, the simultaneous expression of PSMA on both, tumor cells as well as tumor vessels remains unclear, even if such "dual" expression would constitute an important asset to facilitate sufficient influx of effector cells to a given tumor site. We report here on the generation of a PSMA antibody, termed 10B3, which exerts superior dual reactivity on sections of prostate carcinoma and squamous cell carcinoma of the lung. 10B3 was used for the construction of T-cell recruiting bispecific PSMAxCD3 antibodies in Fab- and IgG-based formats, designated Fabsc and IgGsc, respectively. In vitro, both molecules exhibited comparable activity. In contrast, only the larger IgGsc molecule induced complete and durable elimination of established tumors in humanized mice due to favorable pharmacokinetic properties. Upon treatment of three patients with metastasized prostate carcinoma with the IgGsc reagent, marked activation of T cells and rapid reduction of elevated PSA levels were observed.

Self-Assembled Hybrid Aptamer-Fc Conjugates for Targeted Delivery: A Modular Chemoenzymatic Approach

Over the past decade, DNA and RNA aptamers have attracted keen research interest due to their ability to specifically bind targets of therapeutic relevance. However, their application is often hampered by a short serum half-life and missing effector functions. Conjugation of aptamers to antibody Fc fragments could improve pharmacokinetics, enable immune effector mechanisms, and provide an option for the introduction of desired payloads (e.g., toxins or fluorescent dyes). We developed a modular scaffold-supported system based on human IgG1 Fc fragments, which allows for its dual functionalization with moieties of interest. In our approach, two bioorthogonal, enzyme-mediated reactions were used in combination with oxime ligation and self-assembly based on PNA-DNA base pairing. Thus, an engineered synthetic peptide nucleic acid (PNA) oligomer was coupled to the C-termini of the Fc dimer upon sequence-specific sortase A-mediated transpeptidation. Hybridization of the resulting Fc-PNA conjugate with a tailored DNA aptamer that binds cancer-related hepatocyte growth factor receptor (c-MET) led to a hybrid construct which showed strong and specific binding to c-MET and was readily internalized by c-MET-overexpressing cells. To install an additional orthogonally addressable site, aldehyde tag technology was applied followed by oxime ligation with an aminooxy-bearing fluorescent dye as model cargo. Delivery of fluorescent probe specifically to c-MET-overexpressing cells was confirmed by flow cytometry. Our approach can provide access to engineered aptamer-Fc conjugates with desired target specificity and cytotoxic payloads.

Correction: Combination of inverse electron-demand Diels–Alder reaction with highly efficient oxime ligation expands the toolbox of site-selective peptide conjugations

Correction for ‘Combination of inverse electron-demand Diels–Alder reaction with highly efficient oxime ligation expands the toolbox of site-selective peptide conjugations’ by S. Hörner, et al., Chem. Commun., 2015, DOI: 10.1039/c5cc03434e.

Combination of inverse electron-demand Diels–Alder reaction with highly efficient oxime ligation expands the toolbox of site-selective peptide conjugations

A modular bioconjugation strategy based on stepwise oxime ligation and inverse electron-demand Diels–Alder reaction.

A chemoenzymatic approach to protein immobilization onto crystalline cellulose nanoscaffolds

The immobilization of bioactive molecules onto nanocellulose leads to constructs that combine the properties of the grafted compounds with the biocompatibility and low cytotoxicity of cellulose carriers and the advantages given by their nanometer dimensions. However, the methods commonly used for protein grafting suffer from lack of selectivity, long reaction times, nonphysiological pH ranges and solvents, and the necessity to develop a tailor-made reaction strategy for each individual case. To overcome these restrictions, a generic two-step procedure was developed that takes advantage of the highly efficient oxime ligation combined with enzyme-mediated protein coupling onto the surface of peptide-modified crystalline nanocellulose. The described method is based on efficient and orthogonal transformations, requires no organic solvents, and takes place under physiological conditions. Being site-directed and regiospecific, it could be applied to a vast number of functional proteins.

Comparative evaluation of standardized ileal amino acid digestibility in protein supplements for piglets

Standardized ileal digestibility (SID) of AA was determined in 6 protein ingredients for piglets. A basal diet based on corn (Zea mays) starch and casein was supplemented with fluid-bed-dried porcine intestinal mucosa hydrolysate, spray-dried porcine intestinal mucosa hydrolysate, soy (Glycine max) protein concentrate, 2 batches of soy protein, or full-fat soybeans. The SID of AA did not differ between the 4 soybean products (P > 0.05). Compared to most SID values in the 4 soybean products, SID of AA were lower in the 2 porcine intestinal mucosa hydrolysates (P ≤ 0.05). In conclusion, although the initial trypsin inhibitor contents in the raw soybeans have not been determined, high SID values in the 4 soybean products indicate that the different processing procedures used to manufacture these products were efficient to inactivate trypsin inhibitors. For most AA in the 2 porcine intestinal mucosa hydrolysates, drying procedure did not affect SID of AA, but SID values were generally lower compared to the 4 soybean products.

From pico to nano: biofunctionalization of cube-octameric silsesquioxanes by peptides and miniproteins

Polyhedral silsesquioxanes are considered valuable conjugation scaffolds. Nevertheless, only a few examples of silsesquioxane-assembled peptide oligomers have been reported to date. We developed a new bioorthogonal cube-octameric silsesquioxane (COSS) scaffold bearing eight aminooxy coupling sites allowing for the conjugation of diverse peptides via oxime ligation. We found that the coupling efficacy depends on the ligand in view of steric hindrance and electrostatic repulsion. For the first time scaffold-based conjugation of cystine-knot miniproteins having a backbone of about thirty amino acids was successfully accomplished without loss of bioactivity. Atomic force microscopy (AFM) provided further knowledge on the size of COSS verifying them as picoscaffolds growing upon bioconjugation to nano-dimension.

Interferon-alpha-treated patients with chronic myelogenous leukemia show BCR/ABL-positive peripheral blood progenitor cells surviving long-term culture

Several groups have shown that Ph-progenitors reappear in LTC of CML bone marrow or PBMNC when the cell preparations were derived from newly diagnosed Ph-positive patients or after induction chemotherapy. We have tested the hypothesis whether LTC may further decrease CML progenitors if the cells to be cultured were from IFN-treated patients. In our experiments, PBMNC were cultured from 7 IFN- and 5 HU-treated patients in stable chronic phase of the disease, and from 9 patients at diagnosis. Progenitor cells in PBMNC were quantitatively analyzed before and after 35 days of LTC by combining the clonogenic assay in semisolid medium with dual-color interphase FISH for identification of the BCR/ABL status of colony-forming progenitor cells. A median of 22 colonies (range 7-88) before and 30 colonies (5-71) after LTC were analyzed per patient. Our results show that the number of BCR/ABL-positive CFC before and after LTC was approximately the same. This was independent of IFN or HU therapy. In the IFN group there were 58% (median) BCR/ABL-positive CFC before and 54% (median) after LTC of PBMNC. In the HU group, 80% of CFC were BCR/ABL-positive before and 85% after LTC. A complete elimination of BCR/ABL-positive cells was not achieved. We conclude that CML early progenitors in PBMNC of IFN-treated CML patients may survive LTC.

Predominantly BCR-ABL negative myeloid precursors in interferon-alpha treated chronic myelogenous leukemia: a follow-up study of peripheral blood colony-forming cells with fluorescence in situ hybridization

The mechanism and target cell of the life-prolonging effect of interferon-alpha (IFN-alpha) in chronic myelogenous leukemia (CML) are controversial. We studied the influence of IFN-alpha treatment on the frequency of malignant hematopoietic precursor cells in the peripheral blood (PB) of CML patients during the course of the disease. PB 10-day colony-forming cells (PB-CFCs) were assessed with regard to their quantity, lineage distribution, and BCR-ABL status, as determined by fluorescence in situ hybridization (FISH). PB-CFC numbers were determined in 39 patients (29 in the chronic phase, 6 in an advanced stage, and 4 with progression to an advanced stage during follow-up). Thirty-one patients were evaluated either once or several times to determine the BCR-ABL status of the colonies. BCR-ABL negative PB-CFCs were detectable at diagnosis in 5 of 11 patients. A major reduction of BCR-ABL positive colonies to <25% of PB-CFCs was observed in 10/13 determinable IFN-alpha treated patients in early and late chronic phases, indicating a high proportion of BCR-ABL negativity at the clonogenic cell level. In contrast, only 3 of these patients had a cytogenetic response of <25% Philadelphia chromosome (Ph1)-positive metaphases in bone marrow cytogenetics. Treatment with IFN-alpha and/or hydroxyurea (HU) during chronic phase was accompanied by a reduction of PB-CFCs to subnormal levels (median 24 CFCs/ml) compared to controls (median 207 CFCs/ml), untreated patients in chronic phase (median 25,979 CFCs/ml), and patients with advanced disease (median 6,047 CFCs/ml). In blast crisis (6 patients), all colonies tested were BCR-ABL positive. Our results show that IFN-alpha treatment leads to a marked reduction of malignant myeloid precursor cells in the PB of CML patients, which exceeds the degree of cytogenetic remission. This offers an explanation for the good therapeutic efficacy and even life-prolonging effect of IFN-alpha, which is also observed in cytogenetic non-responders.

CD14+ peripheral blood mononuclear cells from chronic myeloid leukemia and normal donors are inhibitory to short- and long-term cultured colony-forming cells

Monocyte-induced cell-cytotoxicity has been implicated in the mechanism of suppression of normal haematopoietic progenitors in chronic myeloid leukemia (CML). We examined here the in vitro effect of CML-derived and normal peripheral blood (PB) monocytes on short- and long-term cultured haematopoietic progenitor cells. Short-term coculture (5 days) of CML or normal monocytes with CML or normal peripheral blood mononuclear cells (PBMNC)/CD34+ cells as targets resulted in a significant inhibition of colony-forming cell (CFC) growth. Coculture conditioned medium (CCM) from 5-days cocultures of normal or CML CD14+ monocytes with CD34+ cells were likewise inhibitory to CFC. In 5-week long-term cocultures of monocytes in direct contact with normal bone marrow (BM) progenitors, CML monocytes reduced the proportion of long-term cultured CFC (LTC-CFC) significantly to 52% of the controls, while normal monocytes had a less pronounced inhibitory effect (89% of the controls) on LTC-CFC. Reduction of LTC-CFC was great when CML monocytes and target cells were separated by a transwell membrane as compared to control cultures in the absence of CD14+ cells (53.5 vs. 9%). CCM from 5-week cocultures of normal or CML CD14+ monocytes with CD34+ progenitors from bone marrow (BM) cells were also inhibitory to CFC. No difference in cytokine levels for TNF-alpha, IFN-gamma, G-CSF, IL-10, IL-6 was detectable between CML CD14+ CCM and control CCM derived from short- and long-term cocultures. Our results suggest that CML monocytes may play a role in the inhibition of normal haematopoiesis through a yet not defined soluble factor supporting the expansion of the malignant clone in CML.

Does long-term culture favor normal clonogenic cells from interferon-treated patients with chronic myelogenous leukemia?

We have tested whether peripheral blood mononuclear cells (PBMNCs) from interferon (IFN)-treated patients may lose residual BCR-ABL sequence-positive progenitor cells when long-term cultured for 35 days on allogeneic stromal cells. IFN-treated patients have low white blood cell counts and a fair number of BCR-ABL-negative colony-forming cells in the peripheral blood. Particularly, IFN responders show increased numbers of normal hematopoietic cells. We have quantitatively analyzed progenitor cells in PBMNCs of IFN-treated patients by combining the clonogenic assay in semisolid medium with interphase fluorescent in situ hybridization (FISH). Thus, the identification is possible of the BCR-ABL status of colony-forming progenitor cells. In IFN-treated patients, the number of BCR-ABL-positive CFCs is considerably decreased and BCR-ABL-negative CFCs appear in the peripheral blood. We could show that after LTC for 35 days of the same PBMNCs on irradiated allogeneic normal stromal cells residual BCR-ABL sequence-positive CFCs were still present. In some cases the relative number of BCR-ABL sequence-positive CFCs was found to be increased after LTC. A minor proportion of blood samples from IFN-treated patients did not give rise to CFCs after LTC on allogeneic stromal cells (three of 10 patients). Inter- and intraindividual variations can be found with regard to loss or gain of BCR-ABL sequence-positive colonies after LTC. We conclude that early CML progenitor cells persist in the peripheral blood of IFN-treated patients and that a certain proportion may survive long-term culture.

Adhesion to fibronectin stimulates proliferation of wild-type and bcr/abl-transfected murine hematopoietic cells

Cells of most tissues require adhesion to a surface to grow. However, for hematopoietic cells, both stimulation and inhibition of proliferation by adhesion to extracellular matrix components have been described. Furthermore, it has been suggested that progenitor cells from chronic myelogenous leukemia show decreased beta1 integrin-mediated adhesion to fibronectin, resulting in increased proliferation and abnormal trafficking. However, we show here that the chronic myelogenous leukemia-specific fusion protein p210bcr/abl stimulates the expression of alpha5beta1 integrins and induces adhesion to fibronectin when expressed in the myeloid cell line 32D. Moreover, proliferation of both p210bcr/abl-transfected 32D (32Dp210) cells and untransfected 32D cells is stimulated by immobilized fibronectin. Cell cycle analysis revealed that nonadherent 32D and 32Dp210 cells are arrested in late G1 or early S phase, whereas the adherent fractions continue cycling. Although both adherent and nonadherent p210bcr/abl-transfected and parental 32D cells express equal amounts of cyclin A, a protein necessary for cell cycle progression at the G1/S boundary, cyclin A complexes immunoprecipitated from 32D cells cultured on immobilized fibronectin were found to be catalytically inactive in nonadherent but not in adherent cells. In addition, as compared with untransfected 32D cells, cyclin A immunoprecipitates from 32Dp210 cells exhibited a greatly elevated kinase activity and remained partially active irrespective of the adhesion status. The lack of cyclin A/cyclin-dependent kinase (CDK) 2 activity in nonadherent 32D cells appeared to result from increased expression and cyclin A complex formation of the CDK inhibitor p27(Kip1). Taken together, our results indicate that adhesion stimulates cell cycle progression of hematopoietic cells by down-regulation of p27(Kip1), resulting in activation of cyclin A/CDK2 complexes and subsequent transition through the G1/S adhesion checkpoint.

A statistically significant sex difference in the number of colony-forming cells from human peripheral blood

The number of colony-forming cells (CFC) in the peripheral blood (PB) of 43 volunteers was examined using a semisolid clonogenic culture assay. In all, 22 male (age 21-39 years) and 21 female individuals (age 21-39 years) were tested, ten of each group twice to examine the intraindividual variability of colony-forming cells in PB. A statistically significant sex difference in the number of CFC, erythroblastic colonies (BFU-E), and granulocyte/macrophage colonies (CFU-GM) in PB was detected in favor of male individuals. No significant difference between female and male PB was found for the number of CFU-GEMM. The intraindividual variability of CFC and BFU-E was significantly higher in female donors. These results support previous reports by others on a potential influence of sex steroids on hematopoiesis.