GROWTH-INHIBITORY EFFECT OF 2-CDA ON MYELOID CFU-GM PROGENITORS IN NORMAL HUMAN LONG-TERM BONE-MARROW CULTURES AND ITS COMPENSATION BY G-CSF OR IL-3

As neutropenia is a common side effect of treatment with 2-chlorodeoxy adenosine (2-CdA), we investigated the myelosuppressive action of 2-Cd A in Dexter-type human long-term bone marrow cultures (LTBMCs). LTBMCs were incubated with varying doses of 2-CdA (5 to 20 nM/L) during the first week. At 20 and 10 nM/L 2-CdA, we found a marked reduction in co lony-forming unit-granulocyte/macrophage (CFU-GM) production throughou t the culture period of 7 weeks (maximum reduction to 3.5% of untreate d control cultures with 20 nM/L and to 27.2% with 10 nM/L, respectivel y). Even the lowest 2-CdA dose tested (5 nM/L) strongly reduced the nu mber of CFU-GM progenitors during the first 3 weeks (maximum reduction to 52.4% of untreated controls), but this effect was transient, and v alues had recovered to normal within 5 weeks. 2-CdA was also shown to cause a dose-dependent decrease in long-term culture-initiating cell ( LTCIC) detections after 5 weeks in culture (49.6% of control cultures with 10 nM/L 2-CdA and 14% with 20 nM/L 2-CdA, respectively). When 2-C dA was added to LTBMCs initiated on preformed irradiated stromal feede r layers, similar results on CFU-GM production were obtained, indicati ng that the effects observed were not secondary to effects on the form ation of a supportive layer. In addition, IL-6-concentrations in the s upernatant of LTBMCs measured at various intervals after the addition of fresh medium with or without 2-CdA showed no significant decrease i n cultures treated with 2-CdA. As neutropenia has been shown to be ass ociated with a small but significant risk of fatal infection, we subse quently investigated the reversal potential of the 2-CdA effect by add ition of recombinant human granulocyte colony-stimulating factor (rhG- CSF) or rh interleukin-3 (rhIL-3). The weekly addition of 100 ng/mL rh G-CSF counteracted the 2-CdA-mediated decrease in CFU-GM numbers durin g the entire period of 7 weeks, reaching statistical significance from weeks 3 to 7 (p<0.05). Addition of rhIL-3 (100 ng/mL) showed an enhan cement of CFU-GM output in 2-CdA-treated cultures that resulted in the ir numbers exceeding those in control cultures (without 2-CdA) from we eks 1 to 5 (p<0.05) with a maximum increase of 5.1-fold over the paral lel control value at week 3. The number of nonadherent cells also incr eased in cultures treated with rhG-CSF or rhIL-3, although this did no t become statistically significant (p<0.05) until after 3 weeks in the case of the rhIL-3 additions. These findings indicate that rhG-CSF an d rhIL-3 are able to abrogate the growth-inhibitory effect of 2-CdA on CFU-GM progenitors in LTBMCs and might suggest a potential role for t he use of these growth factors in reversing 2-CdA-mediated myelotoxici ty.