Selective response of CD5+ B cell malignancies to activation of the CD72 antigen.

The function of the simultaneous expression of CD5 and its ligand CD72 on B cell malignancies like chronic lymphocytic leukemia and mantle cell lymphoma was assessed. It is unknown if reciprocal interactions between CD72 and CD5 exert an autocrine growth-promoting or -inhibiting effect. CD5+ (n = 13) and CD5- (n = 9) B cell malignancies were cultured with the anti-CD72 mAb WL225. For comparison, five other anti-CD72 mAbs were tested. Only CD5+ B cell malignancies proliferated upon CD72 activation (9 out of 13 cases). A strong suppressive effect of IL-4 on the anti-CD72-induced [3H]thymidine incorporation, partially caused by downmodulation of the CD72 expression, was seen. Stimulation of the CD5 antigen by L cells transfected with human CD72 (LhCD72) and the anti-CD5 mAb 1C12 exerted no (n = 9) or a minor effect (2 out of 8 cases), respectively. Finally, the results of CD72 stimulation were compared with CD40 stimulation, as this "CD40 system" is an effective method for stimulating B cell malignancies. In 4 of the 7 anti-CD72 responsive cases a costimulatory effect was seen.