Targeted transfection of the IL-3 gene into primary human hematopoietic progenitor cells through the c-kit receptor.

We recently showed that an antibody-mediated gene transfer procedure termed antifection can be used for targeted gene delivery into lymphoid cells in vitro and in vivo. We here report that antifection also is effective for targeted gene transfer to immature hematopoietic cells. A human IL3-expressing plasmid was chemically linked to an anti-human CD117 antibody. Delivery of the IL3 plasmid into IL-3-dependent myeloid TF-1 cells (bearing the CD117 antigen) was specific and resulted in the transient proliferation of the targeted cells in the absence of exogenous IL-3. Transfection of primary human CD34+ hematopoietic stem/progenitor cells led to transient production of IL-3 and transient proliferation of the target cells. Interestingly, by using a semisolid progenitor cell assay, we found that transfected primary CD34+ cells were able to generate normal numbers of cell colonies in the absence of exogenous IL-3. Polymerase chain reaction analysis confirmed the presence and expression of the IL-3 transgene in the progenitor-derived colonies. In conclusion, our data show that CD117 is a suitable cell surface target to specifically transfer gene by antifection into primary CD34+ cells and that delivery of IL-3 gene in these cells resulted in the expression of a functional IL-3 able to support cell growth in absence of exogenous cytokine. Thus, antifection may provide new therapeutic modality relying on the transient production of appropriate growth factors acting via autocrine and/or paracrine mechanisms.

Gamma-irradiation does not impair ATRA-induced maturation of myeloid leukaemic cells: implication for combined radiation and differentiation therapy.

In the present study we investigated the effects of various doses of gamma-irradiation, followed by induction of granulocytic differentiation with all-trans-retinoic acid (ATRA), on proliferative rate, differentiation capability and oxidative metabolism of leukaemic cells from two different myeloid leukaemia cell lines, HL-60 and PLB-985. Regarding the effects of such combined treatment on the proliferative capabilities of HL-60 and PLB-985 cell lines, we showed that their growth kinetics were similar after 2 Gy gamma-irradiation combined with ATRA. However, with doses >2 Gy, the behaviour of the cell lines differed largely. Indeed, HL-60 appeared to be more radiosensitive than PLB-985 regarding cell viability and proliferation. Besides, whatever dose of irradiation (2, 5 or 10 Gy) was applied, ATRA was still able to induce differentiation of HL-60 and PLB-985 into granulocytes that retained the capacity to produce superoxide anion. The results of these in vitro studies suggest that leukaemia cell lines retain their ability to respond to ATRA, a granulocytic-differentiating inducer following high doses of irradiation. This may have implications for the use of radiation therapy in combination with ATRA for the treatment of extramedullary infiltrations of myeloid leukaemias in humans.

Interleukine-8 acts as a strong peripheral blood granulocyte-recruiting agent rather than as a hematopoietic progenitor cell-mobilizing factor.

Intravenous infusion of Interleukine-8 has been shown to lead to a rapid mobilization of hematopoietic cells in mice and rhesus monkeys. We report in this study that the IL-8-mediated mobilizing effect results in low levels of circulating CD34+ cells, whereas a rapid and strong recruitment of mature granulocytes occurs. This would be of great interest for harvesting large numbers of functional granulocytes to fight infection in immunodepressed patients. We performed a kinetic study of the mobilization in a nonhuman primate model (Papio ursinus), mobilized with a single or double infusion of IL-8 with a dose range of 30-50 microg/kg of body weight. Blood was sampled every 15 min after the IL-8 infusion, and IL-8 plasma levels, complete blood counts, differential WBCC, colony-forming unit assays, and CD34+ cell evaluation assays were performed. At the same time, leukapheresis was performed on the anesthetized animal to collect either hematopoietic stem and progenitor cells (HSPC) or peripheral blood granulocytes (PBG) according to different collection settings. IL-8 induced a rapid increase of PBG (7-12-fold the basal values). The HSPC leukapheresis concentrate showed poor ex vivo expansion abilities. IL-8-mobilized peripheral blood polymorphonuclear cells showed normal oxidative, chemotactic, phagocytic, and adherence abilities. We suggest that IL-8-induced neutrophilia could be used as an allogeneic source of granulocytes for transfusion in neutropenic patients or in granulocyte dysfunction.

Functional studies of maturing myeloid cells during ex vivo expansion for treatment of aplasia: feasibility of ex vivo expansion from cryopreserved bone marrow cell samples.

Ex vivo expanded CD34+ progenitor cells from fresh or cryopreserved primate bone marrow, induced to granulocytic differentiation with growth factors, were investigated to determine whether myeloid cells produced in liquid cultures have the normal biologic functions needed for the treatment of patients with neutropenia following high-dose chemotherapy or therapeutic or accidental radiation exposure. Human and simian (baboons or macaques) CD34+ cells were cultured with granulocyte-colony stimulating factor (G-CSF), stem cell factor (SCF), interleukin-1 (IL-1), IL-3, and IL-6, and assessed at 14 days of culture for their capacity to respond to different functional tests. Immunostaining revealed that human ex vivo expanded cells contained myeloperoxydase (MPO, 82% +/- 8%) and lactoferrin (LF, 30% +/- 6%) in their granules. Maturation of cultured cells was associated with stimulated chemotactic responsiveness and respiratory burst activity (superoxide anion and hydrogen peroxide production) in expansions from human, baboon, and macaque CD34+ progenitor cells. Mature cells obtained from ex vivo expansion of selected cryopreserved human bone marrow CD34+ cells presented reduced but significant functional activities (chemotactic responsiveness and hydrogen peroxide production) when compared with human peripheral blood neutrophils. The validation of nonhuman primate ex vivo expansion systems may permit their use as models of irradiation. The feasibility of ex vivo expansion from cryopreserved bone marrow cell samples may offer considerable opportunity for banking bone marrow for autologous transfusion.