Estimates of cytotoxic T-lymphocyte precursor frequencies against HLA class I antigens in responder-stimulator pairs with a negative mixed lymphocyte culture reaction.

Functional studies of helper and cytotoxic T cells in families with recombinant HLA haplotypes have played a crucial role in the early studies of the HLA chromosomal region. It has been shown that for the generation of CTLs directed against HLA-A or -B antigen differences an additional difference in the HLA-D region between responder and stimulator cells was a prerequisite. We have re-examined in a sensitive limiting dilution assay the possibility of generating CTL against HLA class I antigens in responder-stimulator pairs with a negative MLC reaction of two recombinant families (differing in one or two HLA class I antigens but identical in class II antigens) and two pairs of unrelated individuals. In all cases we could detect low but definitely measurable CTL activity (8-15 CTL precursors in 10(6) PBMCs) directed against the mismatched class I HLA antigen(s). We conclude that mismatches in class I HLA antigens in MLC nonreactive responder-stimulator pairs can induce generation of allospecific CTLs. This has implications in allogeneic bone marrow transplantation with HLA-matched unrelated donors; i.e., in the case of an HLA-A,B,DR matched donor a low donor CTLpf against the recipient may be an indication of a serologically not-detected class I HLA "subtype" incompatibility which might cause graft-versus-host disease.

High-resolution histocompatibility testing of a group of sixteen B44-positive, ABDR serologically matched unrelated donor-recipient pairs. Analysis of serologically undisclosed incompatibilities by cellular techniques, isoelectrofocusing, and HLA oligotyping.

We have characterized HLA incompatibilities in a group of 16 B44-positive patients who were serologically ABDR matched with their 23 (unrelated) potential bone marrow donors. After analysis with a combination of cellular techniques, IEF for HLA-A/B and oligotyping for class II and HLA-B44, 44% of the patients revealed one or more HLA incompatibility with at least one of their potential donors. CTL activity was detected in 12 of the 22 combinations tested. CTL incompatibility occurred more frequently in DR subtype-mismatched combinations, but CTL reactivity was always directed against class I. To characterize these incompatibilities between matched unrelated individuals, we analyzed the specificity of T-cell clones from seven primary CTL cultures. In three combinations, CTL reactivity was directed against a subtype of B44. In two combinations, the CTL reactivity was directed against a non-B44 class I subtype. In two of seven combinations, the CTLs recognized an antigen that, though unconditionally associated with B4403, was expressed by 60% of the B4403+ cells only. Because all 12 of these B4403+ targets recognized could be typed for one HLA-C allele only (Cwl-Cw8), we believe that this alloreactivity might be directed against a serologically undefined Cw antigen.