The First International Workshop on Soluble HLA antigens focused on the comparison of immunoassay procedures for quantitation of soluble HLA (sHLA) class I antigens and the selection of a sHLA class I antigen international standard. Several sets of serum, plasma, and cell culture supernatant specimens were assayed blindly for levels of sHLA class I antigens by 15 participating laboratories using different immunoassay formats. The sandwich ELISA using (i) for antigen capture: an anti-HLA class I heavy chain monoclonal antibody (mAb) specific for a monomorphic epitope, and (ii) for antigen detection: an anti-beta 2 microglobulin antibody-enzyme conjugate, was the assay format of choice. There was a high inter-laboratory correlation among the majority of laboratories. All serum and plasma specimens from normal donors, and from a single transplant patient, had detectable levels of sHLA class I antigens. Paired serum and plasma specimens had similar levels of sHLA class I antigens, although plasma sHLA antigens seemed more stable than serum sHLA antigens. sHLA-A2 and sHLA-B7 antigens were detected in all specimens from HLA-A2 and HLA-B7 donors, respectively, using allele-specific ELISAs. No difference in reactivity was observed for quantitation of native sHLA class I antigens whether the capture mAb was TP25.99 (alpha 3 domain-specific) or W6/32 (alpha 2 + alpha 3-specific). However, a human-mouse chimeric sHLA class I antigen reacted weakly in assays which used TP25.99 mAb. The wide variation among laboratories in their reporting of micrograms/ml units pointed to the need for an inter-laboratory standardization based on a calibrated sHLA antigen preparation. T.sB7, an sHLA-B7 antigen derived from a cell line transfected within human beta 2 microglobulin and HLA-B7 genes, was accepted as the First sHLA class I Antigen International Standard at the workshop meeting.

To define the junctional diversity of T-cell antigen receptor delta gene rearrangements in fresh T-acute lymphoblastic cells and to correlate cell phenotype with the coding potential of rearrangements, we determined the junctional nucleotide sequences of 13 T-cell antigen receptor delta gene rearrangements involving the preferentially rearranged V (V delta 1) and J (J delta 1) segments using in vitro gene amplification and direct sequencing. We showed that, as in gamma delta+ cell lines, extensive junctional diversity exists in these clones and that this diversity is due both to random nucleotide deletions/additions and to the use of at least two D delta segments. We also showed that a high percentage of these rearrangements are potentially translatable (7:13) and that such functional rearrangements occur in both surface CD3+ and CD3- cells. Comparison of alpha beta versus gamma delta surface expression demonstrates that all CD3+ T acute lymphoblastic leukemias with a functional V delta 1-J delta 1 rearrangement express a surface gamma delta receptor and are recognized by the anti-delta monoclonal antibody delta TCS1, whereas a control CD3+ gamma delta+ leukemic case that had not undergone V delta 1 rearrangement was delta TCS1-. In addition, expression of this monoclonal antibody is not restricted by V gamma or C gamma usage or by the covalent or noncovalent link between gamma and delta chains.

The in vitro sensitivity of peripheral blood myeloblast clonogenic cells (CFU-MLs) to doxorubicin (DOX), aclacinomycin (ACL), and 4'-O-tetrapyranyl-doxorubicin (THP-DOX) was studied to evaluate the individual chemosensitivity of CFU-MLs. CFU-MLs from untreated patients were sensitive to the three tested anthracyclines (in 60% to 69% of the patients). Conversely, CFU-MLs from relapsed patients previously treated with DOX-containing regimens were sensitive to ACL and THP-DOX (in 71% and 75% of the patients, respectively) but resistant to DOX. Six of ten patients who entered complete remission with a combination of DOX, vincristine, and cytosine arabinoside had CFU-MLs in vitro which were sensitive to DOX. Conversely, none of the 13 patients resistant to this chemotherapy regimen displayed CFU-MLs which were sensitive in vitro to DOX. Nine of ten patients who responded to ACL as well as one of three resistant patients had CFU-MLs sensitive to ACL in vitro. No clinical responses were observed with THP-DOX in five of seven patients with CFU-MLs sensitive to this drug. The results indicate that myeloblast clonogenic assays can be used to predict the in vitro sensitivity of CFU-MLs to compounds with established antileukemic activity (ie, DOX, ACL). However, the discrepancy between in vitro and in vivo sensitivity to THP-DOX underlines the importance of knowledge of drug pharmacokinetics and the difficulty of using the CFU-ML test for screening new drugs.

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