SCID repopulating cells derived from unmobilised adult human peripheral blood.

Severe combined immunodeficient (SCID)-repopulating cells (termed SRC) with lymphohaematopoietic differentiation potential reside at an extremely low frequency in unmobilised adult human peripheral blood. Recently, an ex vivo method of increasing the relative numbers of at least four distinct human stem cell classes, that include CD34+ haematopoietic progenitor cells, in mononuclear cells (MNC) obtained from unmobilised adult human peripheral blood has been described. This process is triggered by a monoclonal antibody (mAb) against the human monomorphic region of the beta chain of HLA-DP, DQ and DR (clone CR3/43). Herein, we assess the ability of human male donor-derived MNC, following ex vivo culturing for 3 hr in haematopoietic-conducive conditions (HCC) (3-hr MNC/HCC), to form SRC in female non-obese diabetic/severe combined immunodeficient (NOD/SCID) mice. All 3-hr MNC/HCC-recipient animals exhibited significant levels (> 0.5%) of human cell engraftment in the bone marrow, thymus and spleen when compared to animals receiving MNC cultured in the absence of CR3/43. Phenotypic characterisation of the bone marrow cell populations of engrafted mice demonstrated significant levels of human lymphohaematopoietic cell lineages, comprised of T lymphocytes, monocytes, erythrocytes and megakaryocytes, including platelets. In addition, significant levels of clonogenic human CD34+ cells were also detected by in vitro surrogate assay. The thymi of engrafted animals contained maturating human thymocytes, while the spleen consisted mainly of T lymphocytes. Fluorescence in situ hybridisation (FISH) further identified the presence of human male X and Y chromosomes at engrafted sites, whilst the human origin of the cells was confirmed by a specific PCR assay for the human Cart-1 gene. In conclusion, the conversion of MNC to SRC in response to treatment with CR3/43 for 3 hr could have far-reaching clinical implications especially where time and donor-histocompatibility are limiting factors.

Enhanced tumour growth after DNA vaccination against human papilloma virus E7 oncoprotein: evidence for tumour-induced immune deviation.

We have examined the induction of anti-tumour immunity in a murine model using a gene vaccine approach to deliver a well defined tumour antigen. The vaccines expressed the human papilloma virus type 16 (HPV 16) E7 oncoprotein, and protection was measured against HPV 16-expressing C3R tumour cell line in vivo. In control mice injected with saline, C3R cells initially formed tumours but then regressed completely. As expected, animals injected with a peptide that represents the D(b)-presented CTL epitope from E7 (RAHYNIVTF) were completely protected from tumour growth. Contrary to expectation, however, we consistently saw enhanced tumour growth, delayed regression, or tumour outgrowth in mice vaccinated with two different E7-expressing DNA vaccines. We found no evidence for loss of D(b) or K(b) class I MHC molecules from C3R cells recovered from outgrown tumours, and fluorescent MHC/peptide tetramer staining revealed E7 gene vaccination did not delete RAHYNIVTF-specific CD8(+) T cells. However, we did observe an effect on cytokine production. Splenocytes from E7 gene vaccinated animals responded to re-stimulation in vitro with C3R cells by producing IL-4 but background levels of IFN-gamma. We also observed that cytokine production and E7 peptide-specific CTL were only detectable in vaccinated animals after C3R challenge, but not after DNA priming alone. We conclude that 'prime-boosting' is necessary to observe tumour-specific T cell responses with the gene vaccine approach, but that boosting with tumour cells causes skewing of the primed cells in a T2 direction that is incompatible with protective anti-tumour immunity.