Functional and phenotypic analysis of a T cell prolymphocytic leukemia.

Peripheral blood mononuclear cells obtained from a patient with prolymphocytic leukemia expressed the surface membrane markers characteristic of resting mature T helper lymphocytes. These cells responded to the T cell mitogens PHA and Con A in a blast transformation assay but not the anti-T cell monoclonal antibody Leu 4 and the B cell mitogen, PWM. The concentration of PHA or Con A eliciting maximum blast transformation was less than that required by normal mononuclear cells. The leukemic cells recognised and responded to allogeneic pooled mononuclear cells in a mixed lymphocyte culture. In addition, although they did not express Ia antigens, they served as effective stimulators in the mixed lymphocyte reaction. Consistent with the helper phenotype, the leukemic cells did not produce suppressor factors, but provided help for normal B-enriched lymphocytes to respond to PWM as assessed by both blast transformation and IgG production. T lymphocyte colonies developed when the leukemic cells were treated with PHA during a 20 h liquid culture prior to being seeded into semisolid agar medium containing either PHA or an IL2-containing lymphokine. There was no growth when untreated cells were seeded directly into IL2-containing agar. Analysis of colony formation indicated that, as with normal resting T lymphocytes, proliferation occurred in two distinct steps; activation in response to PHA and replication in response to IL2-like growth factors. These findings demonstrate that in this case the helper T prolymphocytes have the functional capabilities of normal mature T lymphocytes as predicted from their helper phenotype.