Activation of malignant B-lymphocytes: pathophysiologic and clinical importance

Recent advances in clarifying the activation mechanisms of the normal immune system have provided the basis for successful experiments concerning the activation of malignant lymphocytes. Such studies with malignant cells, freshly sampled from patients with lymphoproliferative diseases, can be used for pathophysiological considerations, analysis of tumor evolution, classification of malignant subsets, and karyotyping. Of particular interest is the possibility of abrogating the maturation arrest in some clonally-restricted cells. This might lead to therapeutical implications, since the differentiation blockage plays a fundamental role in the clonal expansion and pathogenesis of tumors. Recently, it has been shown that interferon (IFN) can be a potent inducer of various degrees of transformation, differentiation and even proliferation in different subsets of normal and malignant B cells. This may be important in explaining the divergent results of IFN treatment in various malignant B-cell disorders.

Isolation of a new virus, HBLV, in patients with lymphoproliferative disorders

A novel human B-lymphotropic virus (HBLV) was isolated from the peripheral blood leukocytes of six individuals: two HTLV-III seropositive patients from the United States (one with AIDS-related lymphoma and one with dermatopathic lymphadenopathy), three HTLV-III seronegative patients from the United States (one with angioimmunoblastic lymphadenopathy, one with cutaneous T-cell lymphoma, and one with immunoblastic lymphoma), and one HTLV-III seronegative patient with acute lymphocytic leukemia from Jamaica. All six isolates were closely related by antigenic analysis, and sera from all six virus-positive patients reacted immunologically with each virus isolate. In contrast, only four sera from 220 randomly selected healthy donors and none from 12 AIDS patients without associated lymphoma were seropositive. The virus selectively infected freshly isolated human B cells and converted them into large, refractile mono- or binucleated cells with nuclear and cytoplasmic inclusion bodies. HBLV is morphologically similar to viruses of the herpesvirus family but is readily distinguishable from the known human and nonhuman primate herpesviruses by host range, in vitro biological effects, and antigenic features.

Specificity and diagnostic implications of the reactivity pattern of a panel of monoclonal antibodies against myeloid leukemia cells

The immunological phenotypes of leukemia cell samples from 60 patients, of whom 54 had acute myeloid leukemia (AML), were assessed with a panel of monoclonal antibodies (Mabs) with specificity for the following epitopes: Epitopes associated with myeloid leukemia cells, Epitopes expressed only on immature myeloid cells (or subsets) and on monocytes, Epitopes only expressed on granulocytes or on granulocytes and mature myeloid cells (promyelocytes, myelocytes and monocytes), Epitopes on HLA-class II (DR) and HLA-class I molecules and on insulin receptors. This panel of Mabs proved useful to identify leukemia cells in blood and to assess their myeloid origin. The panel of Mabs was found also to be useful for immunophenotyping of leukemia cells. Furthermore, the analysis revealed considerable variations in the immunological phenotype of AML cells, reflecting antigenic heterogeneity within the individual leukemia cell population as well as abnormal or no expression of histocompatibility antigens and insulin receptors in some samples. Some of the Mabs bound preferentially to subgroups in the French-American-British (FAB) classification.

Cell proliferation and DNA content in non-Hodgkin's lymphoma. Flow cytometry in relation to lymphoma classification

Flow cytofluorometric (FCF) DNA analysis was performed on specimens from 154 patients with non-Hodgkin's lymphoma (NHL) and correlated to histopathology according to the Rappaport classification and the Working Formulation of NHL for clinical usage (WF). NHL associated with unfavorable prognosis (UP) had significantly higher proportions of cells in S-phase as compared to the favorable prognosis (FP) group. The proportion of S-phase cells also differed significantly between the low-, intermediate-, and high-grade malignancy groups of the WF. Aneuploidy was significantly more frequent in the UP (41%) than in the FP (15%) group. By stepwise discriminant analysis, the S-phase frequency was a stronger discriminator between prognostic groups than DNA content. Classification by discriminant analysis showed that over 90% of the low grade/FP lymphomas were allocated to the good prognosis group by their S-phase and DNA values. Due to the variation in the proportion of S-phase cells in the intermediate grade and high grade, as well as the UP lymphomas, only approximately 50% of the UP and 60% of the high-grade lymphomas were identified as such by this discriminant model, while almost one half of the intermediate-grade lymphomas were allocated to the low-grade group. The results suggest that S-phase analysis can be of value in distinguishing intermediate- and high-grade lymphomas with high and low proportions of proliferating cells, which may be prognostic importance.

Treatment of patients with metastasizing colo-rectal carcinoma with mouse monoclonal antibodies (Moab 17-1A): a progress report

Eight patients with metastasizing colo-rectal carcinoma have been treated with Moab 17-1A. Before infusion the antibodies were incubated in vitro with isolated autologous blood mononuclear cells (AMC) enriched for monocytes/macrophages. Treatment was given in repeated courses (2-4 times) up to a maximum amount of 1000 mg Moab 17-1A. Two patients had an objective tumor reduction. In further four patients a period of stable disease varying between 3-6 months on was observed. Therapy was well tolerated. Out of 24 treatment courses only on one occasion an anaphylactoid reaction occurred at the third infusion. All patients developed anti-mouse antibodies of IgG and IgM class with increasing levels during the course of therapy. Repeated tumor biopsies and immunohistochemical analyses showed no antigenic modulation, a weak staining for mouse IgG, no deposits of complement components but no obvious increases in the number of cells infiltrating the tumors 24 h after infusion of antibody-armed AMC.

Interferon induces proliferation in leukemic and normal B-cell subsets

3H-thymidine incorporation following stimulation with interferon (IFN) in vitro was investigated in cell cultures from peripheral blood of patients with chronic lymphocytic leukemia (CLL), spleens from necro-kidney transplants and healthy blood donors. It was demonstrated, that IFN can induce a proliferative response in some normal as well as leukemic B lymphocyte subsets. The responses were not T-cell dependent. The results indicate, that B-cell subsets that proliferate in the presence of IFN, are present in higher proportions in spleen than in peripheral blood, and that they constitute a portion of the leukemic blood lymphocyte pool in some patients with CLL. We have previously demonstrated, that IFN induces varying degrees of transformation and differentiation in blood lymphocytes from a majority of CLL patients. The functional characteristics of different B-cell subsets, and their heterogeneous distribution in leukemia, may be important for the results of IFN treatment in various malignant B-cell disorders.

Monoclonal antibodies against carcinoma cells of the human urinary bladder: immunohistochemical staining of tissues

We have previously described the generation of mouse monoclonal antibodies (Mabs) directed to cell surface antigens of human bladder carcinoma. Based on experiments with cultured cells and a limited number of freshly isolated tissues, four distinct antigens were identified as being associated with this disease. In the present investigation, comprising the immunostaining of tissues of normal, malignant, and fetal origin, we have confirmed and extended the close association of these antigens with bladder cancer. Antibodies to all four antigens could clearly discriminate between malignant and normal uroepithelium. Two of the antibodies, SK4H-12 and 4E8, showed no additional reaction when tested with various adult tissues of normal or malignant origin. Antibodies to the remaining two antigens gave a positive staining of a few other tissue types.

Haematological remission of leukaemic polymorphic immunocytoma following splenectomy. Case report with longitudinal immunological and cytogenetic studies

A 56-year old man with a Rai stage IV B-cell chronic lymphocytic leukaemia (polymorphic immunocytoma according to the Kiel classification) of mu kappa-phenotype with a clonal chromosomal abnormality in cells from peripheral blood, bone marrow, and spleen is reported on. Following splenectomy (without further therapy) the blood lymphocytosis gradually decreased to normal and the patient entered a remission, assigned 42 months after splenectomy by immunological and cytogenetic studies that revealed no cells of clonal origin in blood or bone marrow. Utilizing cellular markers of clonality, we thus confirm that haematological remissions may follow splenectomy. A subsequently developed orbital lymphoma (without leukaemia) consisted of tumor cells derived from the initial leukaemia cell clone as indicated by their immune and cytogenetic phenotype. The case report is discussed in relation to previous reports on "spontaneous" remissions of lymphoid leukaemias.

Chronic B-lymphocytic leukemia cells proliferate and differentiate following exposure to interferon in vitro

The ability of interferon (IFN) to induce proliferation and differentiation in malignant B cells from 29 patients with chronic lymphocytic leukemia (CLL) and in lymphoid cells from 11 healthy donors was investigated. IFN induced transformation and plasmacytoid differentiation in B cells from 19 of 29 CLL patients. The transformed cells belonged to the malignant clone as indicated by the immunoglobulin (lg) light chain restriction. Cells exposed to IFN expressed intracellular lg to a varying degree, which was correlated to the level of plasmacytoid differentiation. IFN gave rise to proliferative responses in cells from three patients. Cytogenetic studies on lymphoid cells from one patient showed that proliferation occurred in the malignant B cells. Induction of proliferation and differentiation was observed with various alpha-IFN and gamma-IFN preparations, as well as with a completely pure beta-IFN, showing that IFN and not contaminants in the preparations were responsible for the observed effects. Maximal transformation and proliferation usually occurred after four days of incubation at an IFN concentration of 500 to 5,000 U/mL. The ability of IFN to induce differentiation in CLL cells may be of importance for the reported antitumoral effects observed in some B cell malignancies during IFN therapy.

Interferon induces proliferation and differentiation in primary chronic lymphocytic leukaemia cells

The influence of interferon-alpha (IFN-alpha) on the differentiation of malignant cells from six patients with chronic lymphocytic leukaemia was studied in vitro. IFN induced differentiation in the leukaemic cells from four of the patients. In cells from two of these patients, IFN also induced proliferation. When tested by immunofluorescence, the clonality of the differentiating cells was established by the presence of intracellular light chains of one type only.

Immunohistopathology of lymph nodes in HTLV-III infected homosexuals with persistent adenopathy or AIDS

Lymph node biopsies from 43 male homosexuals with persistent generalized lymphadenopathy and from ten acquired immunodeficiency syndrome patients, all with serum antibodies to human T-cell leukemia virus III, were studied with regard to histopathology, immunohistology, and T-cell subsets in cell suspensions. All acquired immunodeficiency syndrome biopsies except one with Kaposi's sarcoma had the same histopathological pattern of follicular depletion, whereas the persistent generalized lymphadenopathy nodes showed a spectrum of changes characterized as follicular hyperplasia, involution with follicular fragmentation, or involution with follicular atrophy. Immunohistology showed a temporal and structural relation between follicular involution, disappearance of follicular dendritic reticulum cells, and follicular invasion by T-cells. These observations suggest elimination of dendritic reticulum cells as part of a pathogenic mechanism in follicular involution. Angiogenesis measured by staining of endothelial cells with antibodies to Factor VIII was increased in many biopsies in stages of involution and depletion. Our observations indicate the occurrence of marked changes not only in T-cells but also in the B-cell compartment of patients with persistent generalized lymphadenopathy or acquired immunodeficiency syndrome. The possibility of staging lymph nodes of these patients by combined histopathology and immunohistology is indicated. This might improve the evaluation of prognosis in these patients. A possible importance of angiogenesis for the tumorigenesis of Kaposi's sarcoma is suggested.

Maturation asynchrony in leukemic cells. An abnormal combination of normal cell markers

Multiple monoclonal antibodies and enzyme assays were used to study maturity markers (myelo-peroxidase) and immaturity markers (terminal transferase, HLA-2) in acute myeloid leukemia cells from 35 patients. In 8 of the patients, indications were found of an expression of maturity and immaturity markers on the same cells, here in called maturation asynchrony. It is suggested that the orderly appearance and disappearance of markers during the maturation of normal cells is disordered in malignant cells, and that single markers should be used with caution for the maturation classification of tumors. The simultaneous expression of maturity and immaturity marker by tumor cells could explain also why such cells can be recognized as abnormal even in the absence of tumor specific antigens.

B-CLL cell surface markers and mitogen-induced thymidine uptake: a comparison between lymph node cells and peripheral blood lymphocytes in 25 patients

Lymphocytes from peripheral blood and lymph nodes from 25 patients with B-CLL were analysed by immunofluorescent staining of surface membrane immunoglobulin (SmIg), the B-cell marker B1, and the T-cell markers Leu 1/2/3/4. Tritium-thymidine uptake was measured in mitogen-stimulated 4-day cultures. Differences in these parameters between cells from the two sources in each patient were calculated with the paired T-test. All cell samples showed a clonal B-cell population. More blood lymphocytes than lymph node cells expressed the monoclonal SmIg (mu or gamma, p = 0.04; kappa or lambda, p less than 0.01), and T-cells were more frequent in lymph nodes (p = 0.01), where the T helper/suppressor ratio was higher. Furthermore, lymph node cells showed a higher thymidine uptake in response to the mitogens LPS, PWM, and Cowan (p = 0.01, p = 0.01, and p = 0.004, respectively), but there was no difference in the responses to EBV, DxS, TPA and PHA (p greater than 0.5). The higher response in lymph node cells to some mitogens might in part be explained by differences in the numbers of accessory cells, such as T-helper cells, but also by the existence of leukaemic B-cell subsets with different mitogen response patterns and different distributions within the lymphoid compartments. The characterization of subsets within a malignant cell clone might be of clinical importance.

Specificities and binding properties of 2 monoclonal antibodies against carcinoma cells of the human urinary bladder

Mice were immunized with cultured cells derived from transitional cell carcinoma of the human urinary bladder (TCC). Spleen cells were fused with mouse myeloma cell line Sp2/0-Ag14 and the hybridomas obtained screened for antibody production against a panel of human cells. Two hybridomas were selected for further studies. The antibodies from one of these hybridomas (P7A5-4) could clearly discriminate between malignant and normal cells from the bladder, both when tested with cultured cells and fresh tissue. The P7A5-4 antibodies, however, also reacted with some non-TCC cultured carcinoma and melanoma cells but to a lesser extent. This difference in reactivity was even more pronounced in the fresh tumours tested, thus indicating a quantitative difference in antigen expression between TCC and other cells. From extracts of TCC cells, P7A5-4 bound three polypeptides of mol. wts 92Kd (ConA+), 23 and 17Kd (ConA-). The antibody derived from hybridoma SK4H-12 bound a ConA reactive glycopeptide of 100Kd mol. wt, the expression of which was almost entirely restricted to urothelial cell lines and tissue of TCC origin, as shown by immunocytochemical studies. The finding in this study of new antigens associated with urinary bladder carcinoma, extend the results obtained previously in our laboratory (Koho et al., 1984; Paulie et al., 1984) and further delineate the heterogeneity of tumour-associated antigens in this human tumour system.

Immune phenotype heterogeneity in AML

Blood cells from 46 patients with acute myeloid leukaemia were studied for expression of various surface markers, defined by a panel of 12 monoclonal antibodies and the expression of Fc gamma receptors. Corresponding studies were done on normal bone marrow cells. Antibodies which bound to leukaemic cells in high frequencies were those which most frequently also bound to normal bone marrow cells. Immunophenotypic analysis revealed a marked antigenic heterogeneity in AML, also evident within single FAB subclasses. However, leukaemic cells of FAB subclass M1 significantly more often expressed HLA class I antigen than those of FAB subclass M5a, whereas Fc gamma receptors which were expressed only on a few cells in M5a, were increasingly frequent on leukaemic cells of M1-M2, M4, and M5b leukaemias. The frequency of cells reacting with the monoclonal antibody T50/12,11,2 was related to the complete remission rate of the patients. Patients with high frequencies of cells reacting with this antibody had a better complete remission rate than patients with fewer cells binding to this antibody. The immunophenotypic heterogeneity an AML may reflect a great biological variability of this disease. This variability may be of importance for the classification and treatment of AML.

Transferrin receptors on circulating monocytes in hereditary haemochromatosis

In patients with hereditary haemochromatosis (HH) abnormal functional properties of the macrophage system have been observed. The present study is a preliminary report of increased transferrin receptor expression on monocytes from 12 patients with HH. There was no correlation between the degree of iron overload and the transferrin receptor expression on the monocytes. The results obtained thus indicate that the observed increase in transferrin receptors is not a secondary phenomenon due to systemic iron overload but could be an expression of a primary inborn error of iron metabolism in HH. The functional aspects of the receptors were not evaluated as they were analyzed by means of monoclonal antibody technique.

Antibodies to human T lymphotropic virus type III demonstrated by a dot immunobinding assay

A dot immunobinding (DIB) technique was applied to the demonstration of antibodies to human T-lymphotropic virus type III (HTLV-III). By this technique IgG antibodies to HTLV-III were demonstrated in six of six Swedish patients with acquired immune deficiency syndrome and in 37 of 39 (95%) Swedish homosexual men with persistent generalized lymphadenopathy but in none of 50 Swedish healthy blood donors. Findings obtained by this method showed complete concordance with those obtained by an enzyme-linked immunosorbent assay. All sera positive by DIB were also positive by Western blotting. The DIB assay is simple and well suited for screening of sera for HTLV-III antibodies.

Immunodeficiency and prognosis in patients with non-Hodgkin's lymphomas

Monocyte depleted blood lymphocyte subpopulations, their functions and relation to prognosis were studied in 68 untreated adult patients with non-Hodgkin's lymphomas classified according to the Kiel nomenclature. The median observation time was 48 months (range 41-60). The mean total blood lymphocyte and T (SRBC-rosetting) cell counts were significantly decreased as compared with age-matched controls (n = 57). Twenty-five per cent of the patients had a monoclonal blood B lymphocyte population. The spontaneous lymphocyte DNA synthesis, measured as incorporation of 14C-thymidine, was increased and the response to mitogen and antigen stimulation was decreased. Blood lymphocyte counts and functions before treatment were not related to the rates of remission or survival.

Del(3)(p13) in B-prolymphocytic leukemia--a new nonrandom chromosomal aberration possibly related to the c-ras oncogene

Cytogenetic analysis was performed on the leukemic cells from two patients with B-prolymphocytic leukemia. Both patients had del(3)(p13) chromosomal abnormality, as well as other clonal aberrations. Del(3p) was previously reported in one case of B-cell prolymphocytic leukemia, and is known to be a specific aberration in small-cell carcinoma of the lung. In B-cell prolymphocytic leukemia, as in other B-lymphocytic leukemias/lymphomas, the karyotype often involves chromosomes #3, #6, #11, and #12. All of these chromosomes are suggested sites for the c-ras oncogene family.

Leukemic myeloblasts expressing lymphoid markers

Out of 60 patients with acute myeloid leukemia not preceded by chronic myelocytic leukemia or any preleukemic phase, 7 had both lymphoid and myeloid markers. All patients expressed common acute lymphatic leukemia antigen (CALLA) in 20% or more of their leukemic cells, which also showed positive peroxidase reaction. In addition, 4 patients had Auer rods. Two additional patients had morphologically clear acute monocytic leukemia (FAB M5b) and cells expressing CALLA. In 4 of the 7 patients the sum of the percentages of peroxidase or Leu M1 + and CALLA-positive blast cells exceeded 100%, suggesting that at least some of the cells had both myeloid and lymphoid markers. Moreover, out of 3 patients where double staining with the CALLA antibody J5 and the myeloid marker Leu M1 was performed, 2 had both markers on the same cells.

Autoantibodies to the basal cells of squamous epithelium react with thymic epithelial cells

Sera from carriers of hepatitis B surface antigen (17 out of 21), which reacted in immunofluorescence with the basal cell layer (BCL) of squamous epithelium, were also shown to react with a thymic stellate epithelial cell (SEC) characterized by long, dendritic-like cytoplasmic processes. Absorption of the autoantibodies against BCL of squamous epithelium (BCL-Ab) with a thymic homogenate abolished the reactivity with BCL and SEC, demonstrating that the same antigenic determinant was recognized in both cells. In the human thymus, SEC were present both in the cortex and in the medulla. In the outer cortex SEC delineated the septal spaces. SEC were also stained by anti-HLA-DR (Ia) but not by antiactin monoclonal antibodies. The morphology and distribution of SEC were similar to those of the previously described thymic epithelial cells containing alpha-1 thymosin (K. Hirokawa, J. E. McClure, and A. L. Goldstein, Thymus 4, 19, 1982). BCL-Ab were also found to react with five human epithelial thymomas. BCL-Ab seemed to be useful for further characterization of the thymic epithelial cells and for the immunodiagnosis of thymoma.

Cytotoxicity of monoclonal antibodies against individually immunophenotyped human leukemic cells

Peripheral blood and bone marrow mononuclear cells from 12 patients with acute myeloid leukemia (AML), 2 patients with acute lymphatic leukemia, and 1 patient with chronic myeloid leukemia in blastic crisis were taken at diagnosis or in relapse. Cells were immunophenotyped with a panel of monoclonal antibodies (Moab) (OKIa, Leu M1, Leu M2, Leu M3, Leu M4, B1, Okt 11, J5) and the same antibodies were used in an in vitro cytotoxicity test. Of the 14 patients, 10 had antibody-binding cells, and the percentage of lysed cells was almost equal to that of blasts. The other 4 patients had few binding cells and little lysis. Acute leukemia with and without preceding myelodysplastic features did not differ in immunophenotype. Mean spontaneous release of 51Cr was 12.7% and complement alone caused an additional average release of 11.8%. Four single antibodies together with complement showed a mean 51Cr release of 0.7-32.4% above that found with complement alone. Combinations of Moabs resulted in 51Cr release at least 10% above the single most efficient Moab in 8 out of 12 patients. Not all blast cells showed antibody binding, nor were all antibody-binding cells susceptible to cytotoxicity. Normal bone marrow growth in vitro seemed to be stimulated by factors in complement and in the Moab. When this stimulation was compensated for by adding fetal calf serum, cytotoxicity tests prior to CFUc assays resulted in a mean decrease of 46% of colonies and 25% of clusters in normal bone marrow. CFUc are thus sensitive to the cytotoxicity, although CFU may also be resistant.

Prognostic information from cytogenetic analysis in chronic B-lymphocytic leukemia and leukemic immunocytoma

Fifty-five patients with a clonal expansion of B lymphocytes in the peripheral blood were studied. According to the Kiel classification, 22 patients had chronic lymphocytic leukemia (CLL), 29 had immunocytoma (IC), two had prolymphocytic leukemia, and one had centrocytic lymphoma; one was not subclassified. Cytogenetic studies after B cell mitogen stimulation showed that six patients had an extra chromosome 12 as the sole abnormality. Another ten patients had an extra chromosome 12 together with other abnormalities. One patient had dup(12). Fifteen patients showed clonal aberrations without +12. Eleven patients showed only normal metaphases, and 12 patients were not evaluated cytogenetically. The cytogenetic subgroup pattern did not distinguish between CLL and IC patients. There was no significant difference between the CLL and IC groups as regards clinical findings and prognosis. However, the cytogenetic typing proved to be of prognostic significance. Increasing numbers of chromosomal aberrations within the cell clone were significantly associated with a poorer prognosis, ie, with impairment of survival (P = .04) and therapy-free survival (P less than 10(-4]. Patients with complex karyotypes (at least clonal aberrations) showed the poorest survival (P = .007). Patients with +12 required treatment earlier than patients with a normal karyotype (P = .01) and patients with karyotypic changes other than +12 (P = .006). These latter differences were even more pronounced when only IC patients were considered (P = .005 and P = .002, respectively). A multivariate analysis revealed that +12 was as strong an indicator of poor survival as advanced Rai or Binet stages and a stronger predictor of therapy-demanding disease.

Subpopulations of mononuclear cells in microscopic lesions of psoriatic patients. Selective accumulation of suppressor/cytotoxic T cells in epidermis during the evolution of the lesion

The age of microscopic lesions in psoriatic subjects was assessed from the stacking characteristics in the horny layer and related to type and density (cells/tissue volume) of mononuclear cells in the epidermis and the dermis determined by immunoperoxidase methods using monoclonal antibodies. Pan T cells (Lyt-2+, Lyt-3+, Leu-4+, OKT3+), T helper cells (Leu-3a+, OKT4+), T suppressor/cytotoxic cells (Leu-2a+, OKT8+), Ia+ cells and monocytes (OKM2+, BRL alpha mono+) were determined in epidermis and dermis. The psoriatic lesion was divided into regions underneath a parakeratotic and an orthohyperkeratotic/hypergranular portion of the horny layer and contrasted with perilesional and uninvolved psoriatic skin as well as with healthy skin. In the various regions and skin layers, the cell density was highest in parakeratosis and decreased toward normality with decreasing histologic abnormality. The relation between epidermal and dermal cell densities of the T-cell subsets was modified in the involved psoriatic skin with a selective preponderance of T suppressor/cytotoxic cells in the epidermis. The accumulation was present in the youngest lesion found (3 days) and cell densities were unchanged in older lesions. The findings suggests that the altered relationship in the subsets of T cells has an important role during the induction and progress of the psoriatic process in the skin.

Anchorage and lymphocyte function: pattern of spreading distinguishes T- and B-cell chronic lymphocytic leukaemia

T and B lymphocytes from normal individuals and patients with T and B chronic lymphocytic leukaemia (TCLL and BCLL) were induced to spread on a solid surface in the presence of Con A. The proportion of cell circumference exhibiting lamellar activity was considerably greater in T than in B cells. This difference also applied to T and B cells with a single leading lamellipodium. The different pattern of formation of active cell edges implied that the degree of polarity measured as the ratio between the largest and the shortest diameter (over the nucleus) was significantly greater in B than in T cells. This was also obvious when T and B cells, both with a single leading lamellipodium, were compared. The formation of active cell edges in T lymphocytes was generally accompanied by nuclear flattening, even in polar cells with a single leading lamellipodium. B cells, with the exception of one BCLL case, did not exhibit nuclear flattening. Thus, during the entire course of a contact-induced morphogenetic response, T- and B-cell leukaemias were easily distinguishable on the basis of the following criteria: (i) the proportion of the lymphocyte perimeter showing active cell edges, (ii) the degree of polarity and (iii) nuclear flattening.