Myelomonocytic Leukemia in an Orangutan

We report a ca se of spo n ta neous myelom on ocytic leukemi a in a n ora ngu ta n ( Pongo pygma eus). We believe thi s is th e fir st rec orded hematogen ou s mali gn ancy in thi s spec ies . A B­ ly m p ho id cell line producin g an E BV-like herpes virus [l Z] was derived from the o ra ng u ta n. The ora ngu tan , a wild-born 13-y ear-old fem al e, had been at the Los Angeles Z oo since 1965. III health was fir st noted in F ebruary 1976 a nd she was kill ed 8 months la ter a fter a clin ica l co u rse characterized by slo w deterioration . Sh e rece ived neither c he mo the rapy, radiotherapy, nor blood transfu sion s. The hem oglobin was co ns isten tly ab out 6.0 gm /dl, plat elets were increased in number and the white blood cell co u n t ran ged between 7,000 a nd 26,000 with primitive mon onuclear cells rep eatedly found in th e peripheral blood a nd bone marrow . Cy to ch em ica l stud ies on peripheral blood buffy coa t and bon e marrow indicated th e diagn osis o f myel omon ocyti c leukemia by sho wing th at ma ny o f th e a bno rm a l mon onuclear cell s stained stro ng ly for histi ocytic-m on ocytic ma rkers (ac id ph osphat ase and non spe cifi c es te ras e) and for gr anulocyti c markers (Sudan black B, per oxid ase and chlo roaceta te es teras e). The persisten ce of adequate megakaryoc yte s de sp ite de creased er ythro- a nd granulop oie sis in th e bone marrow, together with the mi ld clinical signs a nd lack o f detectable orga no mega ly o r ade no pa thy , sugges ted a su ba cute form o f thi s di sease . G ross findings a t a u to psy we re unremark ab le a part from two incidental hyd at id cysts in th e liver, o ne active and o ne inactive . Spleen, liver a nd lymph nodes wer e not e n la rged , unduly so ft, o r di scol ored nor we re leukem ic infiltrate s visible in a ny tis sue . T he bon e marrow from multiple sites wa s gen erally pale and sclero tic . T issue sec tions, sta ine d with hemat oxylin and eos in aft e r fo rmalin fixati on a nd par affin embedding, sho wed unequivocal mic ro scopi c ev ide nce o f myeloproliferative di sea se. In vir­ tu all y every o rgan, including the brain, perivascular mon onuclear leukemi c infiltrates wer e not ed (fig . I, 2). Leukemic cell s infiltrated the bon e marrow, lymph nodes, and splee n to a major extent, de spite th e lack of o rga n en largement. In th e bone marrow the leukemic infiltrates were spotty and the intervening marrow sho wed di ffu se sligh t fibrosis a nd an ove ra ll paucity o f normal hematop oietic ce lls . In th e lymph nodes a nd sp lee n th e infiltrates oc cur red p rimarily in the medullary co rds and red pulp, resp ectiv el y, wi t h so me spa ring o f residual lymphoid nodules. T he only in filtra tes in the live r a nd kidney were perivas cular in the port al tra cts and medulla, respe ctively. C h lo ro ac etate esterase stai ni ng of sp leen a nd lymph node sec tio ns confirmed the gr anulocytic nature o f the leu kem ic infiltrate. Extra med u llary hema­ topoiesis wa s not noted at any site . Sec tion s of th e in active hyd atid cyst sho wed a typ ica l degenerating brood ca ps u le. A n hem at opoietic cell line (C P-8 1), de scribed elsewhere [ 12] and now in more th an its hundredth passage wa s derived from the orangu ta n 's peripheral bl ood 6 months before death. The cu lt ure co nsisted mainly, if not ex cl us ively, o f B lyrnphobl asts , ba sed up on d etect ion in 90% o f the cell s of F e receptor s a n d human kappa light ch ains. Although marker ch ro mosoma l abnormali tie s were noted, th ey were different from the Phil adelphia chromosome in human gr anulocyti c leukemia . The ce ll lin e she d a n endogeno us herpes virus relat ed to but di stin ct fr om the Epste in- Ba rr viru s (E BV) of man . Whereas ab out 90% of the cell nuclei sta ined for