Two cytotoxic human‐human hybridoma antibodies to HLA: TrAH10 (anti A3.1) and TrAG2 (anti B7,Bw42)

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Abstract
Two cytotoxic human‐human hybridoma IgM antibodies to HLA were generated by EBV transformation of PBMC from multiparous women and fusion of EB V transformed cells with the human fusion partners KR4 or KR12. Both mAbs required the sensitive immunomagnetic cytotoxicity method to display killing of freshly prepared PBMC. One mAb (TrAHIO) was specific for HLA‐A3. Strikingly, TrAHIO reacted much more strongly with lymphoblastoid cell lines of HLA‐A3.1 than of the rare variant HLA‐A3.2, previously detected by cytotoxic T cells. Thus, in the microcytotoxicity test, the titer of conecentrated TrAHIO was approximately 2000 times higher for A3.1 as compared to A3.2, and a clear difference was also observed in radioimmunoassay. Since the two HLA‐A3 variants differ by only two amino acids at positions 152 and 156 of the α2‐domain's α‐helix, the epitopes defined by the mAb TrAHIO and HLA‐A3.1 specific cytotoxic T cells must be closely related. The observations with TrAH10 suggest that the HLA polymorphism detected by human mAbs may turn out to be as extensive as the T‐cell defined HLA polymorphism. The other mAb (TrAG2) bound B7 and Bw42 with equal strength, and in addition bound weakly to some cells that were Bw22 or B39. Magnetic polymerbeads coated with affinity purified human mAbs TrAHIO or TrAG2 formed rosettes with EBV transformed cells carrying relevant HLA antigens; however, rosette formation with freshly isolated PBMC was very weak and unsuitable as a typing assay.