Rheumatoid arthritis is characterized by synovial joint infiltration of activated CD4+ T cells and MHC class II+ APC, and is linked to specific HLA-DR alleles. Candidate autoantigens in synovial fluid and cartilage include type II collagen (CII) and cartilage gp39 (HCgp39). Using preparations of native Ag and T cells derived from Ag-immunized DR4-transgenic mice, we determined that human ex vivo differentiated DR4+ dendritic cells (DC) and macrophages (Mφ) can mediate MHC class II presentation of CII or HCgp39 epitopes. The form of the Ag (soluble, partially degraded, or particulate) delivered to the APC influenced its presentation by DC and Mφ. DC efficiently presented partially degraded, but not native CII α-chains, while Mφ presentation was most efficient after phagocytosis of bead-conjugated CII. Both DC and Mφ presented soluble HCgp39, and activated Mφ from some donors presented epitopes derived from endogenously synthesized HCgp39. When synovial fluid from rheumatoid arthritis patients was used as a source of Ag, DC presentation of HCgp39 and CII epitopes was efficient, indicating that synovial fluid contains soluble forms of CII and HCgp39 amenable to internalization, processing, and presentation. These data support the hypothesis that CII and HCgp39 are autoantigens and that their class II-mediated presentation by DC and Mφ to T cells in vivo has a critical role in the pathogenesis of human rheumatoid arthritis.

Successful autologous hematopoietic stem cell (HSC) transplantation in childhood acute lymphoblastic leukemia (ALL) requires the ability to either selectively kill the leukemia cells or separate normal from leukemic HSC. Based on previous studies showing that more than 95% of childhood B-lineage ALL express CD38, this study evaluated whether normal CD34 ؉ CD38 ؊ progenitors from children with B-lineage ALL could be isolated by flow cytometry. CD34 ؉ cells from bone marrow samples from 10 children with B-lineage ALL were isolated at day 28 of treatment, when clinical remission had been attained. The CD34 ؉ progenitor cells were flow cytometrically sorted into CD34 ؉ CD38 ؉ and CD34 ؉ CD38 ؊ populations. The absolute numbers of CD34 ؉ CD38 ؊ cells that could be isolated ranged from 401 to 6245. The cells were then analyzed for the presence of clonotypic rearrangements of the T-cell receptor (TCR) V␦2-D␦3 locus. Only patients whose diagnostic marrow had an informative TCR V␦2-D␦3 rearrangement were included in this study. Detection thresholds were typically 10 ؊4 to 10 ؊5 leukemic cells in normal marrow. In 6 of 10 samples analyzed, the sorted CD34 ؉ CD38 ؊ cells had no detectable V␦2-D␦3 rearrangements. In 4 cases, the clonotypic leukemic V␦2-D␦3 rearrangement was detected in the CD34 ؉ CD38 ؊ population, indicating that the putative normal HSC population also contained leukemic cells. The data indicate that although most childhood ALL cells express CD34 and CD38, leukemic cells are also frequently present in the CD34 ؉ CD38 ؊ population. Therefore, strategies to isolate and transplant normal HSC from children with ALL will require a more stringent definition of the normal HSC than the CD34 ؉ CD38 ؊ phenotype. (Blood. 2001;97:3925-3930)

The beige/nude/xid/human (bnx/hu) model of human hematopoiesis provides a unique opportunity to study extrathymic human T lymphocyte development in an in vivo system. Purified human hematopoietic stem cells develop into mature T lymphocytes and immature progenitors in the bone marrow of athymic bnx mice. The human T cells are all TCRαβ+ and display a restricted TCRVβ repertoire. In the current studies, we examined the effects of systemic human IL-7 (huIL-7) administration on the phenotype and the activation status of the bnx/hu T cells. In the majority of the mice that did not have huIL-7 administration, a higher frequency of human CD3+/CD8+ than CD3+/CD4+ T cells developed in the bone marrow. This phenomenon is also frequently observed in human bone marrow transplant recipients. Extremely low levels of IL-2 were expressed by human CD3+ cells isolated from these mice, in response to PMA plus ionomycin and to CD3 and CD28 cross-linking. IL-4 was not expressed by cells exposed to either stimulus, demonstrating a profound inability of the bnx/hu T cells to produce this cytokine. Systemic production of huIL-7 from engineered stromal cells transplanted into the mice increased the human CD4 to CD8 ratios, and increased the ratio of memory to naive CD4+ and CD8+ T cells. The human CD3+ cells recovered from mice that had systemic huIL-7 and equivalent numbers of CD3+/CD4+ and CD3+/CD8+ cells in the marrow were still unable to produce IL-4 in response to any condition tested, but were capable of normal levels of IL-2 production following stimulation.

We review here the data indicating a role for epidermal growth factor receptor (EGF receptor) signalling in early mouse development. Embryonic development of the metazoan embryo generally begins with the formation of a cystic structure and epithelial layers that subsequently form anlagen of the definitive body parts and organs. For the mammalian embryo, this cystic structure is a blastocyst whose wall consists of trophectoderm, the first epithelium to develop during mammalian embryogenesis. The onset of expression and function of EGF receptors is coincident with the onset of trophectoderm development. Modulating EGF receptor expression and function modulates trophectoderm differentiation, leading to the hypothesis that functional EGF receptors participate in the induction of trophectoderm development and perhaps of other embryonic epithelial derivatives such as nervous tissues.