Thymic Acute Lymphoblastic Leukemia Research Articles

The Immunologic Detection of Minimal Residual Disease in Acute Leukemia

Certain combinations of differentiation antigens are expressed on leukemia blasts and are absent or extremely rare among normal progenitors in the fetal liver and fetal and regenerating bone marrow. These combinations include cCD3/TdT, a thymic feature retained on thymic-acute lymphoblastic leukemia (T-ALL) blasts outside the thymus, and the coexpression of TdT and myeloid markers (CD13, CD33) on a proportion of ALL and acute myeloid leukemia (AML). Thus, double marker immunofluorescence assays are operationally leukemia-specific and can be applied in 35% of acute leukemias for detecting minimal disease at a less than 10(-4) level; only rare cases, 2 of 35 in our study, switch these relevant features during relapse. The sensitivity and specificity of these assays was tested as follows. First, bone marrow samples taken from patients who had originally presented with blasts expressing the leukemia-associated combinations but were in full morphologic remission were studied, and varying numbers (less than 0.01% to 10% of the mononuclear fraction) of cells with aberrant features were identified in 11.6% of the cases. Second, the outcome of 19 patients with minimal disease identified immunologically while in complete morphologic remission was investigated: all 19 patients have developed systemic relapse within 4 to 25 (median 14.5) weeks. In contrast, 17 of 25 patients also morphologically in complete remission and without residual disease identifiable immunologically after repeated testing are still in morphologic and immunologic remission (follow-up 17 to 114 weeks, median 28 weeks). Only eight patients in this group have relapsed so far: in two patients the relapse was localized in the cerebrospinal fluid, while in six patients a systemic relapse was observed 6 to 51 (median 21.5) weeks after the last negative immunologic bone marrow examination. In conclusion, no false-positive results were detected with these sensitive assays, and the introduction of appropriately planned prospective studies, including the immunologic detection of residual leukemia, is justified on the basis of these observations.

The immunologic detection of minimal residual disease in acute leukemia [published erratum appears in Blood 1990 Nov 1;76(7):1901

Certain combinations of differentiation antigens are expressed on leukemia blasts and are absent or extremely rare among normal progenitors in the fetal liver and fetal and regenerating bone marrow. These combinations include cCD3/TdT, a thymic feature retained on thymic-acute lymphoblastic leukemia (T-ALL) blasts outside the thymus, and the coexpression of TdT and myeloid markers (CD13, CD33) on a proportion of ALL and acute myeloid leukemia (AML). Thus, double marker immunofluorescence assays are operationally leukemia-specific and can be applied in 35% of acute leukemias for detecting minimal disease at a less than 10(-4) level; only rare cases, 2 of 35 in our study, switch these relevant features during relapse. The sensitivity and specificity of these assays was tested as follows. First, bone marrow samples taken from patients who had originally presented with blasts expressing the leukemia-associated combinations but were in full morphologic remission were studied, and varying numbers (less than 0.01% to 10% of the mononuclear fraction) of cells with aberrant features were identified in 11.6% of the cases. Second, the outcome of 19 patients with minimal disease identified immunologically while in complete morphologic remission was investigated: all 19 patients have developed systemic relapse within 4 to 25 (median 14.5) weeks. In contrast, 17 of 25 patients also morphologically in complete remission and without residual disease identifiable immunologically after repeated testing are still in morphologic and immunologic remission (follow-up 17 to 114 weeks, median 28 weeks). Only eight patients in this group have relapsed so far: in two patients the relapse was localized in the cerebrospinal fluid, while in six patients a systemic relapse was observed 6 to 51 (median 21.5) weeks after the last negative immunologic bone marrow examination. In conclusion, no false-positive results were detected with these sensitive assays, and the introduction of appropriately planned prospective studies, including the immunologic detection of residual leukemia, is justified on the basis of these observations.

A Monoclonal Antibody (WT1) for Detecting Leukemias of T-Cell Precursors (T-ALL)

The selectivity of a monoclonal anti-T antibody, designated WT1, has been assessed in a series of 906 leukemias and lymphomas. In acute lymphoblastic leukemias, WT1 reacts comprehensively and selectively with thymic acute lymphoblastic leukemia (ALL) cells in untreated or relapsed patients, thus overriding the extensive antigenic diversity of this cancer and the immaturity of the cell type involved. All 80 cases of thymic ALL examined were WT1-positive. In addition, 18 cases of presumptive prethymic ALL were also WT1-positive, but were unreactive with other maturation-linked T-cell markers. The phenotype WT1+ HLA-DR TdT+ appears to be unique to T-ALL and can therefore be used systematically for the differential diagnosis of this poor prognosis subtype of ALL. Virtually all ALL cases can now be placed into one of two major subgroups representing transformed precursors of either the T- or B-cell lineage. WT1 identifies a single polypeptide of approximately 40,000 mol wt and is similar to two previously described monoclonal antibodies.

A monoclonal antibody (WT1) for detecting leukemias of T-cell precursors (T-ALL)

The selectivity of a monoclonal anti-T antibody, designated WT1, has been assessed in a series of 906 leukemias and lymphomas. In acute lymphoblastic leukemias, WT1 reacts comprehensively and selectively with thymic acute lymphoblastic leukemia (ALL) cells in untreated or relapsed patients, thus overriding the extensive antigenic diversity of this cancer and the immaturity of the cell type involved. All 80 cases of thymic ALL examined were WT1-positive. In addition, 18 cases of presumptive prethymic ALL were also WT1-positive, but were unreactive with other maturation-linked T-cell markers. The phenotype WT1+ HLA-DR TdT+ appears to be unique to T-ALL and can therefore be used systematically for the differential diagnosis of this poor prognosis subtype of ALL. Virtually all ALL cases can now be placed into one of two major subgroups representing transformed precursors of either the T- or B-cell lineage. WT1 identifies a single polypeptide of approximately 40,000 mol wt and is similar to two previously described monoclonal antibodies.

Comparison of purine degradative enzymes and terminal deoxynucleotidyl transferase in T cell leukaemias and in normal thymic and post‐thymic T cells

Summary. Adenosine deaminase (ADA), ecto 5’ nucleotidase (5′NT), purine nucleoside phosphorylase (PNP) and terminal deoxynucleotidyl transferase (TdT) were measured in the cells of patients with acute or chronic T cell leukaemia and compared with normal putative prothymocytes (large, blast‐like cortical thymocytes), cortical and medullary thymocytes and peripheral blood T lymphocytes. Distinct patterns of enzyme activities were found in the individual types of T cell leukaemia. Mean ADA, TdT and 5′NT activities in thymic acute lymphoblastic leukaemia (Thy‐ALL) were 41·9 u/108 cells, 31·1 u/108 cells and 4·7 u/106 cells respectively; in chronic T cell leukaemia they were 7·1 u/108 cells, 0·6 u/108 cells and 18·1 u/106 cells respectively. Mean PNP activity was similar between these two groups of leukaemia (68·6 u/106 cells in Thy‐ALL and 77·9 u/106 cells in chronic T cell leukaemia). The activities of these four enzymes in OKT4+ chronic T cell leukaemia did not differ significantly from those in the OKT8+ chronic T cell leukaemia cases. The activities of TdT, ADA, PNP and 5′NT in Thy‐ALL closely resembled those in normal immature thymocytes, and in the chronic T cell leukaemias showed a similar pattern of enzyme activities to that of mature T lymphocytes. These findings are consistent with surface phenotypic studies of T cell malignancies which suggest that different T cell leukaemias represent malignant proliferation of T cell clones arrested at different stages of T cell differentiation. They also demonstrate the value of biochemical markers in defining the different subtypes of acute and chronic leukaemia.

Nucleoside incorporation into DNA and RNA in acute leukaemia: differences between the various leukaemia sub-types.

The incorporation of the labelled deoxyribonucleosides 3H-deoxythymidine (3H-TdR), H3-deoxycytidine (3H-CdR), 3H-deoxyadenosine (3H-AdR), 3H-deoxyguanosine (3G-GdR), 3H-deoxyuridine (3H-UdR) and of labelled uridine (3H-UR) into DNA and RNA was studied in bone marrow (BM) and peripheral blood (PB) cells from 10 normal donors and 11 patients with acute myeloblastic leukaemia, 13 with acute non-T non-B common ALL (c-ALL) and seven with thymic acute lymphoblastic leukaemia. 3H-TdR incorporation was highest into the DNA of normal BM cells, 3H-CdR into DNA in Thy-All and 3H-UdR into DNA of c-ALL cells. Purine deoxynucleoside (3H-AdR and 3H-GdR) incorporation was highest in AML cells and they were incorporated mainly into RNA indicating that before utilization they are partially degraded from the deoxyribose to the corresponding ribose form. In all but three leukaemia samples, the 3H-UdR/3H-TdR incorporation ratio was above the range found in normal bone marrow, suggesting the leukaemic cells are more dependent than a normal mixed marrow cell population on the de novo pathway of thymidylate synthesis. The incorporation of nucleosides by peripheral blood cells was usually much lower than by the corresponding bone marrow cells, irrespective of blast percentage.

Immunological monitoring of residual disease in treated thymic acute lymphoblastic leukaemia

Combinations of antisera to human differentiation-linked antigens were used in an indirect immunofluorescence system to identify residual leukaemic blast cells in bone marrow samples from 18 patients treated for the thymic variant of acute lymphoblastic leukaemia (Thy-ALL). In six patients, 0.5 to 5.0% of nucleated cells in marrow samples taken during apparent disease remission were found to have an antigenic phenotype not normally demonstrable on bone marrow cells. These cells contained terminal transferase enzyme, expressed surface human T lymphoid antigens (and in some cases cortical thymocyte antigen) but lacked Ia-like antigens. This phenotype was characteristic of Thy-ALL blasts at the time of diagnosis and at relapse indicating that these minor subpopulations were leukaemic. In the remaining 12 cases, no cells of abnormal phenotype were detected, although some of these patients later relapsed with cells of typical Thy-ALL phenotype. The above findings indicate that Thy-ALL cells may be identified during bone marrow remission by virtue of their expression of a unique combination of differentiation antigens in an anatomically inappropriate site, and that this technique is more sensitive than conventional morphological analysis. The observations also provide information about shifts of membrane marker expression in Thy-ALL.

Subpopulations of Normal and Leukemic Human Thymocytes: An Analysis With the Use of Monoclonal Antibodies<xref ref-type="fn" rid="FN2">2</xref><xref ref-type="fn" rid="FN3">3</xref>

Combinations of antibodies to membrane antigens and to terminal deoxynucleotidyl transferase (TdT) were used to study human thymocyte and bone marrow subpopulations and leukemia cells. Cortical thymocytes were TdT+ and expressed T-cell antigens (HuTLA+), a thymocyte-specific antigen (HTA-1+), and a leukocyte antigen (HLe-l++) but lacked detectable HLA-A,B,C and la (HLA-D) antigens. In contrast, medullary thymocytes were TdT-, HuTLA+, HTA-1-, HLe-l++. A small subpopulation of larger, probably immature, thymocytes were strongly TdT+, HuTLA+, la-, HTA-1-, HLe-l +/-. Many blast cells from cases of thymic acute lymphoblastic leukemia (Thy-ALL) showed the phenotype of this small subset, and only a proportion of Thy-ALL blast cells exhibited HTA-1 and HLe-l antigens as strongly as was observed on normal cortical thymocytes. In contrast, TdT+ cells observed in normal juvenile bone marrow were HuTLA, HTA-1-, HLA+, la+. This phenotype corresponded to the phenotype of the common form of ALL (non-T, non-B) and indicated that further studies are necessary to analyze the differentiation of bone marrow precursors to thymic cells.

Anomalous phenotype in thymic acute lymphoblastic leukaemia.

Malignant blast cells in the various forms of acute leukaemia seem to be ‘frozen’ at early stages of haematopoietic and lymphoid cell maturation. These blasts express relatively stable morphological, enzymatic and antigenic phenotypes which may largely represent the normal gene products of the corresponding precursor cells1–4. A number of findings support these suggestions. The phenotype of the common form of acute lymphoblastic leukaemia (cALL) corresponds to the phenotype of normal small non-T, non-B cells of lymphoid morphology detected in low numbers in the normal and regenerating infant bone marrow4,5. Also, the phenotype of blast cells in Thy-ALL corresponds approximately to that of cortical thymocytes or their immediate precursors6–9. Leukaemia-specific (virus-induced or mutant) changes or aberrant expression of normal gene products may also occur in leukaemia. To describe such phenomena, detailed single cell studies comparing leukaemic cells with their appropriate normal (frequently very rare) counterparts are needed. In this study we have performed such a comparative study and find that the human Thy-ALL blasts express unexpectedly high amounts of HLA-A, -B and -C antigens: the sensitive single cell assays used failed to find normal cells (in infant and fetal thymus, and in bone marrow) which express the exact phenotype of Thy-ALL blasts.