Inhibition of human lymphocyte transformation as an in vitro parallel line bioassay for anti-human lymphocyte globulin.

Horse anti-human lymphocyte globulin (HALG) is now widely clinically, but the variable immunosuppressive potency of different preparations of HALG has necessitated development of an accurate, reproducible in vitro assay of HALG potency. Currently available tests have several disadvantages, as well as showing little correlation with in vivo activity of the preparations tested. Incorporation of tritiated thymidine into lymphocytes, stimulated with mitogen (PHA) or antigen (PPD) and the inhibition of this process by HALG is described. ID50S and potency ratios have been determined for four HALG preparations. The ID50S obtained with these preparations were reproducible and the potency ratios obtained using 3 + 3 parallel line bioassay were similarly reproducible, a change in rank order being observed only once in ten assays. These in vitro results correlate with in vivo skin graft data. It is suggested that this technique could be used for evaluation of HALG preparations on peripheral blood from potential recipients.