Highly oncolytic adherent lymphocytes: Therapeutic relevance for leukemia

We have generated and characterized a highly oncolytic adherent lymphocyte subset (A-LAK) from eight leukemic patients with non-lymphocytic leukemia (NLL) in remission and one NLL patient in relapse. Our studies demonstrated that A-LAK was superior in its oncolytic activity (tested in a 3-h ⁵¹Cr release assay) to conventionally prepared (LAK) and non-adherent (NA) IL-2 cultures. No activity was observed by this highly oncolytic subset against normal bone marrow (BM). A-LAK also displayed highest proliferative activity in 7-11 day cultures (5- to 58-fold expansion) in comparison to LAK (0.7- to 2.7-fold) or NA (1.0- to 2.6-fold) cultures. Analysis of phenotype of unseparated, NA and adherent (A-LAK) lymphocytes 24 h after IL-2 activation showed that the A-LAK was composed predominantly of high intensity (bright) CD11a⁺ (LFA-1) lymphocytes (75 ± 4.8%) when compared to the other two populations (12 ± 2.1%). Similarly, A-LAK contained higher proportion of CD11b (CR3 receptor)-positive lymphocytes (39 ± 2.1%) than unseparated and NA lymphocytes (11 ± 1.4%). Double marker phenotypic studies showed that A-LAK cultures were heterogeneous and distribution of individual lymphocyte subsets differed among NLL patients. While in A-LAK culture of some patients the CD56⁺, CD3^- natural killer (NK) cell subset was predominant, CD3⁺, CD56^- lymphocyte subset was prevalent in others. Highest A-LAK lytic activity was always correlated with highest NK cell content. Characterization studies (using the complement-depletion technique) showed that independently of the distribution of lymphocytes in A-LAK cultures, CD16⁺, CD56⁺, CD3^- NK cell subset displayed highest oncolytic effect. CD5⁺ subset also participated in cytotoxic function. These observations indicated that A-LAK may represent a new therapeutic approach to treatment of leukemia.