Similar myeloid recovery despite superior overall engraftment in NOD/SCID mice after transplantation of human CD34(+) cells from umbilical cord blood as compared to adult sources.

Umbilical cord blood (UCB), bone marrow (BM) and mobilized peripheral blood (mPB) are used as sources of hematopoietic stem cells for transplantation. The NOD/SCID mouse model was used to compare the lineage-specific repopulating potential of CD34(+) cells derived from these sources. Six to 8 weeks after transplantation, blood, BM, spleen, liver and thymus, were harvested, and analyzed by flow cytometry using CD34, CD45, myeloid, and lymphoid lineage-specific antibodies. Fifty percent engraftment of human cells in bone marrow of mice was estimated to be reached with 0.55 x 10(6) CD34(+) UCB cells or with 7.9 x 10(6) CD34(+) cells from adult sources, illustrating a 10-fold superiority of UCB CD34(+) cells to engraft NOD/SCID mice. Lineage-specific characterization of engrafted human cells showed that the high engraftment potential of CD34(+) cells from UCB was due to a preferential B cell development (2-81%). In contrast, comparable percentages of myeloid cells were found following transplantation of CD34(+) cells from UCB, BM and mPB (1-38%), and occurred at significant levels only at relatively high doses. Since the CD34 content of UCB transplants is usually at least one log lower than of transplant from adult sources, these results correspond to the clinical findings with UCB transplantation showing a relatively high overall engraftment, but delayed myeloid recovery.

Dual HLA class I and class II restricted recognition of alloreactive T lymphocytes mediated by a single T cell receptor complex.

The alloreactive human T cell clone MBM15 was found to exhibit dual specificity recognizing both an antigen in the context of the HLA class I A2 molecule and an antigen in the context of the HLA class II DR1. We demonstrated that the dual reactivity that was mediated via a single clonal T cell population depended on specific peptide binding. For complete recognition of the HLA-A2-restricted specificity the interaction of CD8 with HLA class I is essential. Interestingly, interaction of the CD8 molecule with HLA class I contributed to the HLA-DR1-restricted specificity. T cell clone MBM15 expressed two in-frame T cell receptor (TCR) Valpha transcripts (Valpha1 and Valpha2) and one TCR Vbeta transcript (Vbeta13). To elucidate whether two TCR complexes were responsible for the dual recognition or one complex, cytotoxic T cells were transduced with retroviral vectors encoding the different TCR chains. Only T cells transduced with the TCR Valpha1Vbeta13 combination specifically recognized both the HLA-A2(+) and HLA-DR1(+) target cells, whereas the Valpha2Vbeta13 combination did not result in a TCR on the cell surface. Thus a single TCRalphabeta complex can have dual specificity, recognizing both a peptide in the context of HLA class I as well as a peptide in the context of HLA class II. Transactivation of T cells by an unrelated antigen in the context of HLA class II may evoke an HLA class I-specific T cell response. We propose that this finding may have major implications for immunotherapeutic interventions and insight into the development of autoimmune diseases.