Hematologic recovery in mice transplanted with bone marrow stem cells expressing anti-human immunodeficiency virus genes

We have used a mouse bone marrow transplantation (BMT) model to study the s afety of retrovirus-mediated transfer of anti-HIV genes (RevM10 and HIV-1 p ol antisense) into hematopoietic stem/progenitor cells (HSPCs). In particul ar, we have monitored the hematologic recovery post-BMT and transgene expre ssion in myeloid and lymphoid lineages, and analyzed tissue sections for ev idence of any transgene-related pathological condition. Expression of anti- HIV genes had no effect on kinetics of hematologic recovery post-BMT. The a verage time to reach 20% of normal cell counts was 15-17 days for white blo od cells and 12-14 days for platelets, and the average time to reach comple te recovery was 42-56 days for leukocytes and 104-161 days for platelets. H ematocrit levels were not significantly affected by irradiation and transpl antation procedures. Donor chimerism was uniformly greater than or equal to 90% in all transplanted animals. At 4-5 weeks post-BMT transgene expressio n was detected in peripheral blood leukocytes in 100% of the animals and ra nged from 4.5 to 44.7%. In a majority of the animals the percentage of tran sgene-expressing cells in circulation decreased over time but remained dete ctable for the length of the study (>6 months). Expression was detected in all analyzed cell lineages (RBCs, platelets, monocytes, granulocytes, and T and B cells). Relative counts of various leukocytes (Mac1(+) monocytes, Gr 1(+) granulocytes, CD3(+) T cells, and B220(+) B cells) were normal. There were no treatment-related histopathological changes in it wide range of tis sues examined. In addition, there were no treatment effects on differential leukocyte counts, and morphology of peripheral blood and bone marrow brush smears. In summary, transfer and expression of the RevM10 and the HIV-1 an tisense genes into hematopoietic stem/progenitor cells ia vivo appears safe . We propose that the mouse bone marrow transplantation model could be used to evaluate some safety aspects of HSPC-based gene therapies.