Ex Vivo Expansion of Hematopoietic Cells

Summary

Ex vivo expanded progenitor cells have been proposed as a source of cells to support high-dose chemotherapy and to decrease or eliminate the period of neutropenia following transplantation. To date, no clinical studies using ex vivo expanded cells have demonstrated any decrease in the time to neutrophil or platelet recovery, although a number of clinical studies have been performed using a variety of growth factor cocktails and culture conditions. During the past 6 years we have developed a static culture system that results in optimal expansion of myeloid progenitor cells as measured by GMCFC in vitro. We have initiated two clinical studies to evaluate this culture system in cancer patients receiving autologous peripheral blood progenitor cells (PBPC) or allogeneic cord blood cells (CB) to support high-dose chemotherapy. CD34 selected cells were cultured for 10 days in 800 ml of defined media containing 100 ng/ml each of rhSCF, rhG-SCF, and rhMGDF in 1-l teflon bags. After culture the cells were washed with 3 volumes of PBS to remove all media and growth factors and reinfused with doily administration of rhG-CSF. In both studies, unexpanded cells were given in addition to the expanded cells to ensure durability of the graft. Patients transplanted with expanded PBPC cells recovered neutrophil counts on day 5 (3 patients) or day 6 (3 patients) post transplant. The median time to neutrophil engraftment in historical controls was 11 days, with the earliest recovery at day 7. No effect on platelet recovery has been observed in any patients to date. These data demonstrate that PBPC expanded under the conditions defined can significantly shorten the time to engraftment of neutrophils. In the second study adult (weight, 46–116 kg) patients were transplanted with expanded CB cells (40% of product), while 60% of the product was transplanted unmanipulated. The following table summarizes the expansion and engraftment data for these patients:

Patient	Weight (kg)	Infused cells (×107/kg)		Expansion of CFC (fold)	Engraftment
		Day 0	Day 10		ANC	Platelets
1	116	0.35	0.09	26	34	62+
2	74	0.4	0.29	10	21	51
3	86	0.37	0.31	40	26	91
4	59	0.78	0.44	31	21	23+
5	60	0.70	0.40	22	23	102+
6	11	4.9	3.7#	7	15	56+

Reinfusion of the expanded cells was not associated with any adverse events. Neutrophil engraftment (days to an absolute neutrophil count [ANC] >500/μl) occurred between days 21 to 34 in patients 1 to 5 and even earlier in patient 6, who recovered to an ANC >500 on day 15. This rapid engraftment in patient 6 is consistent with the infusion of expanded cells on day 0 compared to day +10 in the other patients. Previous studies by Gluckman and colleagues reported that for patients of more than 45 kg in weight, only 11 of 23 and 5 of 23 achieved neutrophil and platelet engraftment, respectively, by day 60; this suggests that expanded CB cells may provide more rapid engraftment in larger patients, with 5 of 5 achieving neutrophil engraftment by day 34 or earlier. The availability of CB products frozen in aliquots may enable more rapid engraftment, similar to the recovery of patient 6. Other studies are in progress that suggest a role of ex vivo expanded cells in cellular support for high-dose chemotherapy. The optimal use of expanded cells, however, still remains to be defined.