DIPHTHERIA-TOXIN-A GENE-MEDIATED HIV-1 PROTECTION OF CORD BLOOD-DERIVED T-CELLS IN THE SCID-HU MOUSE MODEL

The reconstitutive potential of CD34+-derived cord blood (CB) cells, t ransduced with a regulated diphtheria toxin A (DT-A) chain gene, was e xamined in SCID-hu mice harboring a conjoint organ composed of human t hymus and liver (thy/liv). The DT-A-transduced cells, injected directl y into the thy/liv organ, showed the same engraftment potential as con trol CB cells transduced with the non-DT-A parental vector. CB cells, distinguishable from the thy/liv cells by the HLA marker B7, were pref erentially maintained in ex vivo culture. In the thy/liv organ, the en grafted CB cells represented >80% of the total cells. A majority of ce lls (>70%) in the thy/liv organ were also CD4+CD8+, as would be expect ed of maturing thymocytes. The incidence of double-positive cells was highest at 44 days (compared with 30 days and 80 days) after injection of CB cells. This suggested that a minimum time was required to achie ve optimal proliferation of cells in the thy/liv organ but that, at la ter times, all of the early cells had matured. Thus, the population us ed for engraftment contained early cells but not self-renewing cells. The double-positive cells matured rapidly into single-positive cells ( either CD4+ or CD8+) when placed in ex vivo culture. Marked cells (neo +) could readily be detected in the thy/liv-derived cells. The cells t ransduced with DT-A showed longterm protection in ex vivo culture agai nst HIV T lymphotropic isolate NL4-3. This study shows that DT-A-trans duced cells had no apparent disadvantage in engraftment of the thy/liv organ and did not have any toxic effects in vivo. Such cells were pro tected against HIV infection evert when challenged more than 2 months after transduction and after a 44-day engraftment period in the thy/li v mice. These data support the feasibility of toxin gene therapy as a strategy for HIV infection.