Identification of a p69,71 complex expressed on human T cells sharing determinants with B-type chronic lymphatic leukemic cells.

In the course of generating monoclonal antibodies to human thymus-dependent differentiation antigens, we were able to define specificities shared by T cells and by cells from patients with chronic lymphatic leukemia that were not detectable on normal B cells. In particular, one of these antibodies was reactive by indirect immunofluorescence with greater than 95% of the thymocytes and 80--95% of nonadherent sheep erythrocyte-rosetting peripheral blood lymphocytes (PBL), but was unreactive with normal B cells or cell lines derived from PBL by Epstein-Barr virus transformation. However, the leukemic cells from 11 of 14 patients with B-type chronic lymphatic leukemia were found to express detectable concentrations of this surface determinant. The target antigen recognized by this monoclonal antibody was shown by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis to be a p69,71 complex. Our findings suggest a possible relationship between this antigen and the previously described GIX system in the mouse.

Regulated progression of a cultured pre-B-cell line to the B-cell stage.

The variable (V) regions of heavy and light immunoglobulin chains are encoded by multiple germline DNA elements which are assembled into complete variable-region genes in precursor(pre-) B lymphocytes. The heavy-chain V region (VH) is assembled from three separate germline DNA elements, the variable (VH), diversity (D) and joining (JH) segments; whereas light-chain variable regions of either the kappa or lambda type are assembled from two elements, the VL and JL. Analysis of tumour cell lines or sorted cell populations which represent early and late pre-B cells has suggested that heavy-chain assembly and expression generally precedes that of light chains; but, primarily because of the lack of appropriate model systems to study the phenomenon, the mechanism and significance of this apparently orderly differentiation process are much debated. Here we describe for the first time a transformed cell line, 300-19, which sequentially undergoes all of the immunoglobulin gene rearrangement and expression events associated with the differentiation of pre-B cells to surface immunoglobulin-positive B lymphocytes. Analysis of the in vitro differentiation of 300-19 cells provides direct evidence for distinct differentiation phases of first VH and subsequently VL assembly during B-cell differentiation. Furthermore, these analyses suggest that the mu heavy chain, resulting from a productive VHDJH rearrangement, has both a positive and a negative regulatory role in mediating this ordered differentiation process, that is, signalling the cessation of VH gene assembly and simultaneously signalling the onset of VL assembly.

Effect of thymic factor on human lymphoid cells of umbilical cord blood and of children with T cell deficiency.

We report on the in vitro effect of a thymic factor (TF) extracted from pig thymuses, on human lymphoid cells from umbilical cord blood and from peripheral blood of 8 T cell-deficient patients. E rosette formation was not affected by TF when tested on cells from peripheral blood of normal adults. With cells from umbilical cord blood of 13 healthy, full-therm newborn babies, the difference between the percent (mean) of ERFCs before (16.31 +/- 11.13) and after (28.85 +/- 17.10) incubation with TF was statistically significant (p less than 0.05). In most samples, TF transformed about 10-20% of the cells. In the T cell-deficient group the increase in ERFCs of the peripheral blood lymphocytes, though consistent, was variable in degree from case to case. Our data indicate that precursor cells in some individuals with T cell deficiency are very sensitive to TF. Patients with highly responsive precursors appear to be the best candidates for a therapeutic approach with TF when thymus transplant is not possible.

Immunologic and clinical investigation on a bovine thymic extract. Therapeutic applications in primary immunoedificiencies.

Thirteen patients with primary immunodeficiencies (eight with T-cell deficiency, one with Wiskott-Aldrich (W-A) syndrome, two with common variable agammaglobulinemia (CVA), and two with severe combined immunodeficiency (SCID) were treated with a calf thymus extract, called thymostimulin (TS). It has been shown that this extract causes in vitro differentiation of T-cell precursors in patients with T-cell defect. Five of eight patients with pure T-cell defect showed immunologic recovery and clinical remission lasting for several months after interruption of the therapy; one had only transient reconstitution, one had slight increase in T-cells (clinical conditions not yet estimated), and two patients soon died from severe infections after showing a slight increase of T-cells. Immune recovery was assess by an increase of the absolute number of E-rosettes forming cells, of human T-lymphocyte antigen positive cells and of PHA responsiveness in the peripheral blood, and by a positive delayed hypersensitivity reaction to antigens. In five patients, there was also B-cell increase after TS treatment. Clinical remission consisted of disappearance of infections, weight gain, and in improvement in general conditions. No effect was observed in one patient with W-A syndrome, in two with CVA, and in two with SCID. Several hypotheses on the mechanisms involved in immune reconstitution are discussed. It seems likely that TS acts on prethymic cells or on the epithelial cells of hypoplastic thymuses. TS was not effective, either in vitro or in vivo, in patients with SCID probably because of a defect in stem cells.