ABSTRACT. Future preventive and/or concurrent therapy of neonatal sepsis may require the use of adjuvant immunohematopoietic therapy. In the present study, using reverse transcription-polymerase chain reaction, we demonstrated a significant increase in IL-11 mRNA extracted from the femurs of group B streptococcus (GBS)-infected rats during acute thrombocytopenia (platelet count: 65.8 +/- 19.3 K/mm3, n=5) compared to that of uninfected neonatal rats (NR) (635.2 +/- 89 K/mm3, n=5) (174 +/- 17% vs. 100%, p<0.001, n=5). We next investigated the prophylactic effect of rhIL-11 on the PLT recovery as well as survival in NR during experimental GBS sepsis. NR received either rhIL-11 (250 microg/kg/d) intraperitoneally for 11 d or sham injections before the induction of experimental GBS sepsis. While experimental GBS sepsis resulted in severe thrombocytopenia in control NR, the rhIL-11 pre-treated group had significantly higher PLT counts (24 hr: 417 +/- 50 vs. 221 +/- 54 K/mm3, p<0.01; 36 hr: 276 +/- 60 vs. 82 +/- 33 K/mm3, p<0.01; 48 hr: 402 +/- 77 vs. 101 +/- 82 K/mm3, p<0.05). Administration of rhIL-11 alone also significantly increased the survival rate at 36 and 48 hrs after GBS inoculation compared to the control group (36 hr: 83% vs. 58%, p<0.05; 48 hr: 50% vs. 18%, p<0.01, n 30), as did the combination of rhIL-11 with ABS treatment at 36 hrs, compared to the control group (90% vs. 69%, p<0.05, n 30). These results suggest that endogenous IL-11 gene expression may be upregulated during acute thrombocytopenia and associated bacterial sepsis in NR. This increase in IL-11 gene expression, however, does not appear to prevent severe thrombocytopenia. Furthermore, prophylactic administration of pharmacological doses of rhIL-11 may be potentially beneficial in the management of neonatal GBS sepsis and its associated thrombocytopenia. Future studies are needed to determine the clinical implications of these findings.

Keywords: IL-11, neonatal rats, thrombocytopenia, mRNA, sepsis.

Reprint requests to: Mitchell S. Cairo, M.D., Director, Hematology/Oncology Research, and Blood and Bone Marrow Transplantation, Children's Hospital of Orange County, 455 S. Main Street, Orange, California 92668 USA, phone: (714) 532-8548, fax: (714) 532-8771, e-mail: chocpsf@aol.com.

ABSTRACT. Mobilized peripheral blood hematopoietic progenitor cells obtained from cancer patients treated with high-dose cyclophosphamide (7g/m2) followed by G-CSF, GM-CSF, IL-3, PIXY321, or combinations of these cytokines have been successfully used for autologous stem cell transplantation. We investigated the ability of hematopoietic progenitor cells (HPC) derived from mobilized peripheral blood (PB) to undergo ex vivo expansion in short term cultures by enumerating numbers of de novo generated CD34+ cells, assayable progenitor cells, and the frequency of long-term hematopoietic culture-initiating cells (LTHC-IC). These parameters were examined in CD34+ cells generated in culture through the use of cell tracking with the membrane dye PKH2. Fresh isolated mobilized CD34+ cells contained 0.49 +/- 0.36% LTHC-IC. However, due to the high number of total CD34+ cells in mobilized PB, the absolute number of LTHC-IC was higher than that contained in a bone marrow (BM) harvest. Mobilized CD34+ cells were stained with PKH2 and incubated with SCF, IL-3, and IL-6. After 5 to 6 days, numbers of total CD34+ cells and clonogenic progenitors increased 1.4- and 2.2-fold, respectively. Numbers of total progenitors continued to increase such that 10 to 12 days after the initiation of cultures a 6.4-fold increase was demonstrable. However, between days 5 and 7 of culture, the frequency of LTHC-IC in CD34+PKH2bright cells (cells which did not divide) was less than 50% of that determined for fresh cells, while the frequency among CD34+PKH2dim cells (cells that had divided) was very low or undetectable. However, moderately higher frequencies of LTHC-IC were detected following expansion for 48 hours only. In similar assays, both BM and cord blood cells were capable of generating LTHC-IC in CD34+PKH2dim cells but not to expand the overall number of these progenitors. These observations suggest that although mobilized PB CD34+ cells contain large numbers of LTHC-IC, these cells might not be capable of further ex vivo expansion and generation of additional LTHC-IC in vitro. Furthermore, these data indicate that mobilized PB CD34+ cells may have undergone maximal "in vivo expansion" such that additional ex vivo expansion of primitive progenitor cells may not be possible.

Keywords: mobilized peripheral blood CD34+ cells, ex vivo expansion.

Reprint requests to: Edward F. Srour, Ph.D. Indiana University School of Medicine, 975 West Walnut Street, IB442, Indianapolis, IN 46202-5121 USA, phone: (317) 274-3589, fax: (317) 274-0396, e-mail: edward_srour@iucc.iupui.edu.