Cytological examination of bone marrow fom xenografted cynomolgus monkeys (macaca fascicularis)

Introduction: Non-human primates (NHP) are frequently used in preclinical research, including xenotransplantation studies. Cytological examination of bone marrow (BM) is a helpful adjunct for a complete interpretation of hematological data. In this light, the aim of this work is to evaluate the cellular composition of BM in immunosuppressed xenotransplanted NHP. Materials and Methods: Ten NHP recipients of a life-supporting porcine kidney were treated with Cyclosporin A, steroids, Mycophenolate sodium, with Cyclophosphamide (CYP) (N=6) or Rituximab (N=4). Eight animals were euthanized for kidney failure and 2 for life-threatening conditions. A complete pre-euthanasia CBC and 4 femoral BM smears collected at euthanasia were performed. Cytological evaluations and differential counts of erythroid, granulocytic, lymphocytic and plasmacytic series were performed. Megakariocytic series elements were evaluated with regards to number, morphology and maturation. The myeloid to erythroid ratio (M:E) was calculated and the percentage of each cell line was established. Results: No significant interindividual differences in marrow cytology were observed. A severe erythroid hypoplasia and myeloid hyperplasia with marked increase of M:E ratio (from 26,8:1 to 80:1) were observed except in one case (4:1). Increase of plasma cells percentage (8-19%, median 11%) was observed in all recipients except in one case (1,4%). Megakaryocytic lineage was normally represented. Despite of erithropoietin therapy, erythroid hypoplasia was observed, possibly as a consequence of the immunosuppressive therapy or of the suppressive effect of inflammatory cytokines on hematopoietic precursors. The increase in proliferative and maturative neutrophilic lineage was correlated with the inflammatory status. The meaning of plasma cells increase is still unclear. However, this was not correlated with anti-pig antibody levels. Conclusion: The study suggests that BM evaluation in primate recipients of renal porcine xenografts may provide the basis for a complete interpretation of hematological profiles and represent an important tool for a better design of immunosuppressive strategies.